EXPLORATORY FLIGHT LOADS INVESTIGATION OF THE P-2V AIRCRAFT IN
AERIAL FIREFIGHTING OPERATIONS
A Thesis by
Richard B. Bramlette
M.S. Aerospace Engineering, Wichita State University, 2008
B.S. Aerospace Engineering, Auburn University, 2006
Submitted to the Department of Aerospace Engineering
and the faculty of the Graduate School of
Wichita State University
in partial fulfillment of
the requirements for the degree of
Master of Science
December 2008
© Copyright 2008 by Richard B. Bramlette
All Rights Reserved
EXPLORATORY FLIGHT LOADS INVESTIGATION OF THE P-2V AIRCRAFT IN
AERIAL FIREFIGHTING OPERATIONS
The following Faculty have examined the final copy of this thesis for form and content, and
recommend that it be accepted in partial fulfillment of the requirement for the degree of Master
of Science in Aerospace Engineering.
Kamran Rokhsaz, Committee Chair
James Steck, Committee Member
John Watkins, Committee Member
iii
DEDICATION
For my family and their hard work.
iv
ABSTRACT
An exploratory analysis has been performed on a small number of flights of the P-2V
aircraft operating in the firefighting mode as opposed to the anti-submarine and search-andrescue operations for which it was designed. The data consists of 38 flights from the 2005 and
2007 fire seasons, for the same aircraft, totaling approximately 35 flight hours. Each flight has
been divided into two ground and five flight phases and analyzed separately, with emphasis on
the loads and atmospheric turbulence experienced by the aircraft. Some aircraft usage data has
also been extracted and shown.
Aircraft usage information in terms of operating altitudes and airspeeds, as well as
maximum loads and V-n diagrams, have been examined for each flight phase. Flight loads for
each phase have been separated into gusts and maneuvers using the “Two-Second Rule” and
have been normalized per 1000 hours and per nautical mile. Atmospheric gust velocities for
each phase have also been extracted and presented in both forms. Finally, the resultant gust and
maneuver flight loads have been compared with standard design gust loads and Mil-8866
maneuver loads.
A number of general trends have been observed by comparing the phases before and after
the release of retardant.
It has been shown that the release of retardant weight would
significantly decrease wing loading and thus both the cruise speed and response to atmospheric
turbulence. This has been demonstrated as being caused by weight by showing the levels of
atmospheric turbulence to be the same before and after the drop.
The effect of the changing weight on loads has also been examined in detail. The
decrease in the weight of the aircraft during the taxi after the drop has been shown to increase the
frequency of all loads as well as their severity compared to taxi loads prior to the drop. A similar
v
effect has been highlighted for the cruise phases before and after the drop. Maneuver loads
while delivering the retardant have been shown to be the highest in both sets of data. However, a
significant part of the increased vertical acceleration is believed to be due to the change of mass
while releasing the retardant and not due to maneuvering of the aircraft as is commonly believed
to be.
The derived and continuous gust velocities are shown not to be remarkably different
before and after the release of retardant. The results suggest that the atmospheric turbulence is
largely the same before and after the drop with a trend of lower severity at higher altitudes.
Comparisons of the results with the military standards for design gust and maneuver
loads are provided and show that lower-magnitude accelerations can be as much as 10 times
more frequent than design conditions predicted. This is not deemed to pose a threat to exceeding
the limit load factor for the airframe, but it can lead to a lower than expected fatigue life for the
aircraft. These results indicate that these aircraft are operated in environments different from
those for which they were designed. Therefore, maintenance schedules developed for their naval
missions may not be applicable for their operation as firefighters.
vi
TABLE OF CONTENTS
Chapter
Page
I. INTRODUCTION ....................................................................................................................... 1
A. Background ............................................................................................................................ 1
B. Literature Review................................................................................................................... 2
C. Thesis Structure...................................................................................................................... 4
II. METHOD OF ANALYSIS........................................................................................................ 5
A. Aircraft Analyzed................................................................................................................... 5
B. Recorded Flight Data ............................................................................................................. 6
C. Categories of Data.................................................................................................................. 9
D. Flight Data Files................................................................................................................... 10
E. Mission Profile ..................................................................................................................... 11
F. Phase Separation................................................................................................................... 12
G. Peak/Valley Counting of Flight Loads ................................................................................ 14
G. Gusts and Maneuvers ........................................................................................................... 15
H. Atmospheric Turbulence...................................................................................................... 15
I. Overall Usage Statistics......................................................................................................... 18
III. RESULTS AND DISCUSSION ............................................................................................. 20
A. Available Data...................................................................................................................... 20
B. Method Validation................................................................................................................ 21
C. Ground-Air-Ground Usage Results...................................................................................... 25
D. Taxi Phases .......................................................................................................................... 38
E. Cruise Phases........................................................................................................................ 41
vii
TABLE OF CONTENTS (Continued)
Chapter
Page
F. Entry, Drop, and Exit Phases................................................................................................ 69
G. Comparison with Gust and Maneuver Load Standards ..................................................... 103
IV. SUMMARY.......................................................................................................................... 107
V. CONCLUSIONS.................................................................................................................... 108
VI. RECOMMENDATIONS...................................................................................................... 110
REFERENCES ........................................................................................................................... 112
APPENDICES ............................................................................................................................ 115
viii
LIST OF TABLES
Table 1: P-2V Aircraft Specifications............................................................................................. 5
Table 2: Densities and Maximum Weights of Various Retardant Chemicals ................................ 6
Table 3: P-2V Data Channel Specifications ................................................................................... 8
Table 4: P-2V Strain Gauge Locations ........................................................................................... 9
Table 5: Flight Phase Separation Logic Reference....................................................................... 13
Table 6: Assumed Weight of Each Phase ..................................................................................... 16
Table 7: Gust Velocity Altitude Bands......................................................................................... 18
Table 8: Overall Extracted Usage Data Summary........................................................................ 19
Table 9: Ground-Air-Ground Overall Statistics ........................................................................... 26
Table 10: Taxi Phase Statistics ..................................................................................................... 38
Table 11: Cruise Phase Statistics .................................................................................................. 42
Table 12: Entry, Drop, Exit Phase Statistics................................................................................. 69
Table 13: Taxi-1 Strain Ranges (με)........................................................................................... 116
Table 14: Taxi-2 Strain Ranges (με)........................................................................................... 116
Table 15: Cruise-1 Strain Ranges (με)........................................................................................ 117
Table 16: Cruise-2 Strain Ranges (με)........................................................................................ 117
Table 17: Entry Strain Ranges (με)............................................................................................. 118
Table 18: Drop Strain Ranges (με) ............................................................................................. 118
Table 19: Exit Strain Ranges (με)............................................................................................... 119
ix
LIST OF FIGURES
Figure 1: P-2V Aircraft Planform ................................................................................................... 5
Figure 2: Excerpt from a Typical CSV Flight File ....................................................................... 10
Figure 3: Excerpt from a Typical Fixed-Width Flight File........................................................... 11
Figure 4: Aerial Firefighting Mission Profile ............................................................................... 12
Figure 5: Peak Between Means Logic .......................................................................................... 14
Figure 6: Cruise-1 Avenger/WSU Vertical Load Comparison..................................................... 23
Figure 7: Entry Avenger/WSU Vertical Load Comparison.......................................................... 23
Figure 8: Drop Avenger/WSU Vertical Load Comparison .......................................................... 24
Figure 9: Exit Avenger/WSU Vertical Load Comparison............................................................ 24
Figure 10: Cruise-2 Avenger/WSU Vertical Load Comparison................................................... 25
Figure 11: Overall Maximum Altitude vs. Coincident Airspeed.................................................. 28
Figure 12: Overall Coincident Altitude vs. Maximum Airspeed.................................................. 28
Figure 13: Overall Maximum Altitude vs. Flight Duration.......................................................... 29
Figure 14: Overall Maximum Altitude vs. Flight Distance .......................................................... 29
Figure 15: Overall V-n Diagram – 2005 Data .............................................................................. 30
Figure 16: Overall V-n Diagram – 2007 Data .............................................................................. 30
Figure 17: Overall Load Factor vs. Coincident Flap Setting ........................................................ 32
Figure 18: First Door-Open Vertical Load Factor vs. Flap Setting .............................................. 32
Figure 19: First Door-Open Vertical Load Factor vs. Airspeed ................................................... 33
Figure 20: Overall Flap Range Percent of Flight Duration........................................................... 33
Figure 21: Overall Normal Distribution of Flight Duration ......................................................... 35
Figure 22: Overall Normal Distribution of Flight Distance.......................................................... 35
x
LIST OF FIGURES (Continued)
Figure 23: Overall Normal Distribution of Maximum Vertical Load Factor – 2005 Data........... 36
Figure 24: Overall Normal Distribution of Minimum Vertical Load Factor – 2005 Data ........... 36
Figure 25: Overall Normal Distribution of Maximum Vertical Load Factor – 2007 Data........... 37
Figure 26: Overall Normal Distribution of Minimum Vertical Load Factor – 2007 Data ........... 37
Figure 27: Taxi Δnz Occurrences per 1000 Hours – 2005 Data.................................................... 40
Figure 28: Taxi Δnz Occurrences per 1000 Hours – 2007 Data.................................................... 40
Figure 29: Taxi Roll Acceleration Occurrences per 1000 Hours – 2005 Data............................. 41
Figure 30: Cruise Maximum Altitude vs. Coincident Airspeed – 2005 Data............................... 43
Figure 31: Cruise Maximum Airspeed vs. Coincident Altitude – 2005 Data............................... 43
Figure 32: Cruise Maximum Altitude vs. Coincident Airspeed – 2007 Data............................... 44
Figure 33: Cruise Maximum Airspeed vs. Coincident Altitude– 2007 Data................................ 44
Figure 34: Cruise Maximum Altitude vs. Flight Duration – 2005 Data....................................... 45
Figure 35: Cruise Maximum Altitude vs. Flight Distance – 2005 Data ....................................... 45
Figure 36: Cruise Maximum Altitude vs. Flight Duration – 2007 Data....................................... 46
Figure 37: Cruise Maximum Altitude vs. Flight Distance – 2007 Data ....................................... 46
Figure 38: Cruise Δnz Gust Occurrences per Nautical Mile – 2005 Data..................................... 48
Figure 39: Cruise Δnz Maneuver Occurrences per Nautical Mile – 2005 Data............................ 48
Figure 40: Cruise Δnz Gust Occurrences per 1000 Hours – 2005 Data........................................ 49
Figure 41: Cruise Δnz Maneuver Occurrences per 1000 Hours – 2005 Data ............................... 49
Figure 42: Cruise Δnz Gust Occurrences per Nautical Mile – 2007 Data..................................... 50
Figure 43: Cruise Δnz Maneuver Occurrences per Nautical Mile – 2007 Data............................ 50
Figure 44: Cruise Δnz Gust Occurrences per 1000 Hours – 2007 Data........................................ 51
xi
LIST OF FIGURES (Continued)
Figure 45: Cruise Δnz Maneuver Occurrences per 1000 Hours – 2007 Data ............................... 51
Figure 46: Cruise Roll Acceleration Gust Occurrences per Nautical Mile – 2005 Data.............. 52
Figure 47: Cruise Roll Acceleration Maneuver Occurrences per Nautical Mile – 2005 Data ..... 52
Figure 48: Cruise Roll Acceleration Gust Occurrences per 1000 Hours – 2005 Data ................. 53
Figure 49: Cruise Roll Acceleration Maneuver Occurrences per 1000 Hours– 2005 Data.......... 53
Figure 50: Cruise V-n Diagram Comparing Phases – 2005 Data................................................. 55
Figure 51: Cruise V-n Diagram Comparing Flap Ranges– 2005 Data......................................... 55
Figure 52: Cruise V-n Diagram Comparing Phases– 2007 Data.................................................. 56
Figure 53: Cruise V-n Diagram Comparing Flap Ranges – 2007 Data........................................ 56
Figure 54: Cruise-1 Derived Gust Velocity Occurrences per Nautical Mile – 2005 Data ........... 58
Figure 55: Cruise-1 Derived Gust Velocity Occurrences per 1000 Hours – 2005 Data............... 58
Figure 56: Cruise-1 Derived Gust Velocity Occurrences per Nautical Mile – 2007 Data ........... 59
Figure 57: Cruise-1 Derived Gust Velocity Occurrences per 1000 Hours – 2007 Data............... 59
Figure 58: Cruise-2 Derived Gust Velocity Occurrences per Nautical Mile – 2005 Data ........... 61
Figure 59: Cruise-2 Derived Gust Velocity Occurrences per 1000 Hours – 2005 Data............... 61
Figure 60: Cruise-2 Derived Gust Velocity Occurrences per Nautical Mile – 2007 Data ........... 62
Figure 61: Cruise-2 Derived Gust Velocity Occurrences per 1000 Hours – 2007 Data............... 62
Figure 62: Cruise-1 Continuous Gust Velocity Occurrences per Nautical Mile – 2005 Data...... 64
Figure 63: Cruise-1 Continuous Gust Velocity Occurrences per 1000 Hours – 2005 Data ......... 64
Figure 64: Cruise-1 Continuous Gust Velocity Occurrences per Nautical Mile – 2007 Data...... 65
Figure 65: Cruise-1 Continuous Gust Velocity Occurrences per 1000 Hours – 2007 Data ......... 65
Figure 66: Cruise-2 Continuous Gust Velocity Occurrences per Nautical Mile – 2005 Data...... 67
xii
LIST OF FIGURES (Continued)
Figure 67: Cruise-2 Continuous Gust Velocity Occurrences per 1000 Hours – 2005 Data ......... 67
Figure 68: Cruise-2 Continuous Gust Velocity Occurrences per Nautical Mile – 2007 Data...... 68
Figure 69: Cruise-2 Continuous Gust Velocity Occurrences per 1000 Hours – 2007 Data ......... 68
Figure 70: Entry, Drop, Exit Maximum Altitude vs. Coincident Airspeed – 2005 Data ............. 70
Figure 71: Entry, Drop, Exit Coincident Altitude vs. Maximum Airspeed – 2005 Data ............. 70
Figure 72: Entry, Drop, Exit Maximum Altitude vs. Coincident Airspeed – 2007 Data ............. 71
Figure 73: Entry, Drop, Exit Coincident Altitude vs. Maximum Airspeed – 2007 Data ............. 71
Figure 74: Entry, Drop, Exit Maximum Altitude vs. Duration – 2005 Data ................................ 73
Figure 75: Entry, Drop, Exit Maximum Altitude and Distance – 2005 Data ............................... 73
Figure 76: Entry, Drop, Exit Maximum Altitude vs. Duration – 2007 Data ................................ 74
Figure 77: Entry, Drop, Exit Maximum Altitude vs. Distance – 2007 Data ................................ 74
Figure 78: Entry, Drop, Exit Δnz Gust Occurrences per Nautical Mile – 2005 Data ................... 76
Figure 79: Entry, Drop, Exit Δnz Maneuver Occurrences per Nautical Mile – 2005 Data........... 76
Figure 80: Entry, Drop, Exit Δnz Gust Occurrences per 1000 Hours – 2005 Data....................... 77
Figure 81: Entry, Drop, Exit Δnz Maneuver Occurrences per 1000 Hours – 2005 Data .............. 77
Figure 82: Entry, Drop, Exit Δnz Gust Occurrences per Nautical Mile – 2007 Data ................... 78
Figure 83: Entry, Drop, Exit Δnz Maneuver Occurrences per Nautical Mile – 2007 Data........... 78
Figure 84: Entry, Drop, Exit Δnz Gust Occurrences per 1000 Hours – 2007 Data....................... 79
Figure 85: Entry, Drop, Exit Δnz Maneuver Occurrences per 1000 Hours – 2007 Data .............. 79
Figure 86: Entry, Drop, Exit Roll Acceleration Gust Occurrences per Nautical Mile – 2005 Data
............................................................................................................................................... 80
xiii
LIST OF FIGURES (Continued)
Figure 87: Entry, Drop, Exit Roll Acceleration Maneuver Occurrences per Nautical Mile – 2005
Data ....................................................................................................................................... 80
Figure 88: Entry, Drop, Exit Roll Acceleration Gust Occurrences per 1000 Hours – 2005 Data 81
Figure 89: Entry, Drop, Exit Roll Acceleration Maneuver Occurrences per 1000 Hours – 2005
Data ....................................................................................................................................... 81
Figure 90: Entry, Drop, Exit V-n Diagram Comparing Phases – 2005 Data................................ 83
Figure 91: Entry, Drop, Exit V-n Diagram Comparing Flap Ranges – 2005 Data....................... 83
Figure 92: Entry, Drop, Exit V-n Diagram Comparing Phases – 2007 Data................................ 84
Figure 93: Entry, Drop, Exit V-n Diagram Comparing Flap Ranges – 2007 Data....................... 84
Figure 94: Entry Derived Gust Velocity Occurrences per Nautical Mile – 2005 Data ................ 86
Figure 95: Entry Derived Gust Velocity Occurrences per 1000 Hours – 2005 Data ................... 86
Figure 96: Entry Derived Gust Velocity Occurrences per Nautical Mile – 2007 Data ................ 87
Figure 97: Entry Derived Gust Velocity Occurrences per 1000 Hours – 2007 Data ................... 87
Figure 98: Drop Derived Gust Velocity Occurrences per Nautical Mile – 2005 Data................. 89
Figure 99: Drop Derived Gust Velocity Occurrences per 1000 Hours – 2005 Data .................... 89
Figure 100: Drop Derived Gust Velocity Occurrences per Nautical Mile – 2007 Data............... 90
Figure 101: Drop Derived Gust Velocity Occurrences per 1000 Hours – 2007 Data .................. 90
Figure 102: Exit Derived Gust Velocity Occurrences per Nautical Mile – 2005 Data ................ 92
Figure 103: Exit Derived Gust Velocity Occurrences per 1000 Hours – 2005 Data.................... 92
Figure 104: Exit Derived Gust Velocity Occurrences per Nautical Mile – 2007 Data ................ 93
Figure 105: Exit Derived Gust Velocity Occurrences per 1000 Hours – 2007 Data.................... 93
Figure 106: Entry Continuous Gust Velocity Occurrences per Nautical Mile – 2005 Data......... 95
xiv
LIST OF FIGURES (Continued)
Figure 107: Entry Continuous Gust Velocity Occurrences per 1000 Hours – 2005 Data............ 95
Figure 108: Entry Continuous Gust Velocity Occurrences per Nautical Mile – 2007 Data......... 96
Figure 109: Entry Continuous Gust Velocity Occurrences per 1000 Hours – 2007 Data............ 96
Figure 110: Drop Continuous Gust Velocity Occurrences per Nautical Mile – 2005 Data ......... 98
Figure 111: Drop Continuous Gust Velocity Occurrences per 1000 Hours – 2005 Data............. 98
Figure 112: Drop Continuous Gust Velocity Occurrences per Nautical Mile – 2007 Data ......... 99
Figure 113: Drop Continuous Gust Velocity Occurrences per 1000 Hours – 2007 Data............. 99
Figure 114: Exit Continuous Gust Velocity Occurrences per Nautical Mile – 2005 Data......... 101
Figure 115: Exit Continuous Gust Velocity Occurrences per 1000 Hours – 2005 Data ............ 101
Figure 116: Exit Continuous Gust Velocity Occurrences per Nautical Mile – 2007 Data......... 102
Figure 117: Exit Continuous Gust Velocity Occurrences per 1000 Hours – 2007 Data ............ 102
Figure 118: Design Gust Loads Comparison – 2005 Data ......................................................... 105
Figure 119: Mil-8866 Maneuver Loads Comparison – 2005 Data............................................. 105
Figure 120: Design Gust Loads Comparison – 2007 Data ......................................................... 106
Figure 121: Mil-8866 Maneuver Loads Comparison – 2007 Data............................................. 106
xv
NOMENCLATURE
A
aircraft PSD gust response factor
Ar
aspect ratio b2/S
c
wing mean geometric chord (ft)
C
aircraft derived gust response factor
Cl
wing lift curve slope per radian
CL
airplane lift curve slope per radian
c.g.
center of gravity
D
distance
F(PSD) continuous gust alleviation factor
g
gravity constant, 32.17 ft/sec2
Hp
pressure altitude (ft)
K
gust alleviation constant
Kg
derived gust alleviation factor, 0.88 µg/(5.3 + µg)
L
turbulence scale length (ft)
N
number of occurrences for U(PSD gust procedure)
nm
nautical mile
nz
vertical load factor (g)
N0
number of zero crossings per nautical mile (PSD gust procedure)
q
dynamic pressure (lbs/ft2)
S
wing area (ft2)
t
time (sec)
t1
phase start time (sec)
xvi
NOMENCLATURE (Continued)
t2
phase stop time (sec)
Ude
derived gust velocity (ft/sec)
U
continuous turbulence gust intensity (ft/sec)
Vi
indicated airspeed
VT
true airspeed
W
weight (lbs)
Greek Symbols
Λ
wing sweep angle (radians)
β
mach number correction 1  M 2
Δnz
incremental vertical load factor (g)
ρ
air density, slugs/ft3 (at altitude)
ρ0
standard sea level air density, 0.0023769 slugs/ft3
μg
aircraft mass parameter (non-dimensional)
με
microstrain
Acronyms
AGL
Above Ground Level (altitude)
BRP
Blue Ribbon Panel
CAFE Consortium for Aerial Firefighting Evolution
CSV
Comma-Separated Variable (file type)
FAA
Federal Aviation Administration
xvii
NOMENCLATURE (Continued)
FR
Flight Record (line type)
GAG Ground-Air-Ground (cycle)
GPS
Global Positioning System
HSS
Horizontal Stabilizer Station
KIAS Knots, Indicated Airspeed
KTAS Knots, True Airspeed
LE
Leading Edge
MSL
Mean Sea-Level (altitude)
NACA National Advisory Committee on Aeronautics
NASA National Aeronautics and Space Administration
PSD
Power Spectral Density
PD
Parameter Definition (line type)
PE
Periodic (line type)
PO
Power On (line type)
RPM Revolutions Per Minute
TR
Triggered (line type)
USFS United States Forest Service
VSS
Vertical Stabilizer Station
WS
Wing Station
WSU Wichita State University
xviii
I. INTRODUCTION
A. Background
Aircraft have a long history of combating forest fires by dropping water or fire-retardant
chemicals. Because modifying existing, retired military and cargo aircraft is less costly than
designing new configurations for the role, these vehicles have been stripped bare to minimize
weight and fitted with a variety of mechanisms for aerial firefighting. Over the following
decades the mechanisms for releasing water and fire-retardant chemicals evolved but the fatigue
and loads research did not. During that time, the flight loads inherent to the firefighting missions
were known to be more severe [1] than those included in the design of the refitted aircraft, but no
significant structural health-monitoring programs were enacted. Although several crashes due to
“mechanical failure” were recorded, nearly 75% of all accidents between 1976 and 1998 were
due to “human error.” [2] So the crashes due to fatigue of two airtankers within a month came as
a shock to the U.S. Forest Service (USFS).
A “Blue-Ribbon Panel” (BRP) provided
recommendations for the aerial firefighting industry and the Consortium for Aerial Firefighting
Evolution (CAFE) was formed to implement them. [3]
Meanwhile, NACA/NASA and the Federal Aviation Administration (FAA) had extensive
experience in flight loads, fatigue analysis, and health monitoring for a variety of aircraft
beginning as early as 1933. [4][5] In the late-1990s, the FAA began developing the maneuver
and gust loads environments for a wider range of aircraft roles and operating altitudes. [6][7][8]
More recent work by the FAA and combining years of health monitoring programs showed that
aircraft operating at a low altitude were subject to more severe fatigue loads than at higher
altitudes. The aerial firefighting environment was clearly more complex than the civil aviation
flight loads standards could explain.
1
In implementing the findings of the BRP, the USFS realized that a better understanding
of the firefighting environment was necessary to continue operating tanker aircraft safely. The
FAA was sought to provide expertise in certification as well as in developing the gust and
maneuver loads environment.
The FAA previously worked with Wichita State University
(WSU) to characterize the loads environment of the Beech BE-1900D commuter aircraft [9].
Therefore the FAA expanded its scope to include a new set of data taken from four tanker
aircraft – a Douglas DC-7, a Lockheed P-3, and two Lockheed P-2Vs and to develop the same
analysis of this data for the aerial firefighting environment as was performed on the Beech BE1900D. This thesis presents the exploratory analysis of the loads environment developed from
flight data recorded on one of the P-2V Aircraft in the aerial firefighting role.
B. Literature Review
NASA performed the first detailed study on the statistical loads environment of
firefighting aircraft in 1974 using VGH (airspeed, loads, and altitude) data from two Douglas
DC-6B Aircraft. It marked the first complete characterization of the aerial firefighting role
containing statistical data for airspeed, vertical load, altitude, duration, and some other
parameters separated by flight phase. The study found that maneuver load factors between 2.0
and 2.4 were experienced 1000 times more often than on commercial transports. Accordingly,
the authors noted, “shortening of the structural life of the aircraft should be expected.” [1]
The research into firefighting aircraft was a specialized application of much older
techniques of separating flight data into gust and maneuver loads. Gust loads had been studied
as early as 1931 when Rhode and Lundquist [10] used Boeing B-247 flight data to develop a
“sharp-edged” gust model. Their model uses a set of discrete gust lengths throughout the time
2
domain to determine the loads response of the aircraft. Rhode later showed [11] that this model
was not conservative enough for large aircraft and overly conservative for small aircraft. So, in
1950 Donely [12] reevaluated the B-247 data with a “smooth-edged” gust model which added a
“Gust Alleviation Factor,” Kg. While the discrete gust model has been used extensively since,
the more accurate power spectral density (PSD) continuous gust model has been employed in
recent years. PSD relies on modeling a field of randomized gust lengths in the frequency
domain. [1] In 1990 NASA evaluated both gust models for a range of different aircraft to study
observed overlap between them. The authors found the response for each aircraft to be within
10% of a constant ratio between both methods. [14] In the last decade, the FAA began using the
continuous gust model to supplement the discrete model in its study of commercial aircraft. [15]
Between the 1974 NASA study and the formation of the BRP, most research pertaining
to firefighting aircraft dealt with understanding the drop phase of the mission. Supported by the
NASA study, the consensus in the industry was that the highest loads occurred during this phase.
In fact, the NASA study cited low weight following the drop as the reason no damage was found
after one DC-6 aircraft exceeded its ultimate load factor. So in subsequent years, more research
was done to understand the behavior of the retardant during the drop phase [16] rather than
studying the fatigue and loads environment further.
Since 2002, however, that gap has closed. In 2005, Hall [17] developed the most
comprehensive loads spectrum by combining all the firefighting data to date and separating the
aircraft into four types: Large, Standard, and Small Air Tankers, and Lead Aircraft. Hall noted
the current practice of using “severity factors” and loads-based flight stresses ignored the effects
of changing weight during the drop phase. He also found that the same aircraft operating a
shorter mission statistically experienced a more severe environment. In 2006, James Burd [18]
3
came to the same conclusion through investigation of the structure of the Lockheed P-2V for
fatigue and damage tolerance. The stresses measured in flight showed a minimum of three
obvious peaks: one on take-off, one during the drop phase, and one on landing. With respect to
fatigue loads, Burd termed this the “Ground-Air-Ground” (GAG) Cycle. Because fatigue life
was measured in hours as opposed to flights, aircraft flying shorter flights thus flew more flights
and fatigued more quickly. He performed a further study on the P-2V structure to evaluate other
structural problems such as crack propagation. Burd’s work, however, does not fully evaluate
the mission profile as Hall did for the historical data.
Instead, he emphasized a clear
understanding of how the P-2V was aging, not the environment in which it aged.
The set of new data gathered by the USFS between 2005 and 2007, some of which has
been analyzed in this thesis, clarifies of the flight environment. Flight data was used to generate
the frequency of encountered flight loads, atmospheric turbulence in the form of gust velocities,
and usage statistics. The recorded gust and maneuver loads were compared to the design gust
loads and Mil-8866 maneuver loads to determine if the aircraft was used outside the scope of its
original design and for comparison to earlier analysis on the P-2V.
C. Thesis Structure
The methods used to analyze the flight data and the treatments of special cases inherent
in the aerial firefighting role are presented in Chapter 2. The results for each mission segment
and the usage of the aircraft are then discussed in Chapter 3. The lengthy results and discussion
were summarized in Chapter 4. The relevant conclusions based on the results are given in
Chapter 5, with recommendations for future efforts summarized in Chapter 6. The Appendices
contain additional strain data describing the mission’s effect on the aircraft structure.
4
II. METHOD OF ANALYSIS
A. Aircraft Analyzed
A Lockheed P-2V “Neptune” designated “Tanker-44” with 30-channels of flight data was
analyzed. The aircraft planform and specifications are given in Figure 1 and Table 1.
Figure 1: P-2V Aircraft Planform
Table 1: P-2V Aircraft Specifications
P-2V [19]
Wingspan (ft)
100.00
Length (ft)
86.00
Cruise Speed (kts)
187
Max Take-Off Weight (lb)
80,000
Max Landing Weight (lb)
67,000
Contract Operating Weight (lb)
73,000
Max Retardant Load (gal)
2450
The Lockheed P-2V is representative of the low end of the heavy air tankers. However, it
is not outside the range of heavy air tankers used by the Consortium for Aerial Firefighting
Evolution (CAFE). While the tankers can carry a finite volume of retardant, the actual weights
of retardant lifted vary depending on the mixture of water and chemicals used. Retardant density
is a variable factor chosen by the operator, typically about 9 lb/gal. A list of some common
5
retardant materials and their densities are given in Table 2 [20] as well as the maximum weight
which may be lifted by the P-2V aircraft (based on the available volume).
Table 2: Densities and Maximum Weights of Various Retardant Chemicals
Water
Avg. Density
lb/gal
8.345
P-2V
lb
17358
Avenger Aircraft [24]
9.230
19198
Liquid Concentrates (Unthickened)
9.127
18984
Liquid Concentrates (Gum-Thickened)
8.930
18574
Gum-Thickened High Viscosity
8.990
18699
Gum-Thickened Low Viscosity
8.875
18460
Retardant
The P-2V uses six independently armed and pneumatically-operated doors to release the
retardant in a pre-determined sequence. Often, tankers must make multiple drops in which only
a few doors are opened for each drop. Only cases in which the full retardant load was released in
a single drop, however, are evaluated in this document. The aircraft retardant system does not
use a constant flow mechanism, nor does it have a “float” measurement to provide retardant
levels.
B. Recorded Flight Data
The flight data recorder stores 30 data channels (listed in Table 3 [21]) at uneven time
intervals as they are triggered as well as a periodic recording every 15 seconds. When the slope
of any one of the first 14 parameters changes sign and exceeds a threshold, recording is
triggered, and all parameters are saved. The parameter that triggered the output is identified by
its channel number and a peak or valley indication. If two channels are triggered at the same
time, two lines for the same time are written with different trigger numbers.
6
A total of twelve strain gauges are installed throughout the aircraft (their locations are
in
described
7
Table 4 [23]) as well as accelerometers measuring roll and vertical acceleration. No lateral
acceleration is recorded. Both the indicated airspeed and pressure altitude are recorded based on
pitot tube measurements. The control deflections (flaps, aileron, and elevator) are recorded, but
no rates of rotation (pitch, roll, or yaw) are recorded. The P-2V aircraft considered here features
both prop-driven engines and smaller outboard jet engines, for which the “Jet Tachometer” RPM
is recorded.
Table 3: P-2V Data Channel Specifications
#
Parameter
Units
1
…
12
13
14
15
16
17
18
19
Time
Strain 1
…
Strain 12
Roll Accel.
Vertical Accel.
Flap Setting
Varicam
Ind. Airspeed
Press. Altitude
Jet Tachometer
H:M:S
με
με
με
rad/s2
g
deg
deg
kts
ft
rpm
Sample
Rate
0.02 sec
32 Hz
32 Hz
32 Hz
32 Hz
32 Hz
8 Hz
NI
8 Hz
NI
NI
8
#
Parameter
Units
20
21
22
23
24
25
26
27
28
29
30
Left Aileron
Elevator
Spoiler
AV Record
Door 6
Door 5
Door 4
Door 3
Door 2
Door 1
Gear Up
deg
deg
Discrete
Discrete
Discrete
Discrete
Discrete
Discrete
Discrete
Discrete
Discrete
Sample
Rate
NI
8 Hz
NI
NI
NI
NI
NI
NI
NI
NI
NI
Table 4: P-2V Strain Gauge Locations
Strain #
Location
1
WS 61 – Left Wing, Lower LE
2
WS 61 – Right Wing, Lower LE
3
HSS 34
4
VSS 39
5
WS 61 – Left Wing, Upper LE
6
WS 46 – Right Stringer 17
7
WS 180 – Right Stringer 18
8
WS 180 – Right Front Spar
9
WS 197 – Aft Spar
10
Rosette Z – WS 220 – Right Rear Spar Web
11
Rosette Y – WS 220 – Right Rear Spar Web
12
Rosette X – WS 220 – Right Rear Spar Web
C. Categories of Data
The data available overlapped a change in the recording methods used by the US Forest
Service. Data from the 2005 fire season (referred to as the “2005 Data”) exhibits a few notable
differences than data from the 2007 fire season (referred to as the “2007 Data”). The 2005 Data
was provided directly to Wichita State University where it is hosted on a secure server in the
WSU Flight Dynamics Laboratory. The 2007 Data, however, is stored on a secure server by
nCode, a company which provides support for the data analysis software GlyphWorks for which
the FAA obtained a set of licenses. A set of 20 files from the 2005 Data were analyzed with 20
files from the 2007 Data (which were copied from nCode’s server and formatted to fit the 2005
Data’s structure). Two of the 2007 Data files were subsequently omitted for they appeared to
contain data on more than one drop. However, the analysis codes treat both sets of data
similarly.
9
D. Flight Data Files
The data files resident at Wichita State University and those in the nCode library are in a
comma-separated-variable (CSV) format. These are rewritten and analyzed in a more userreadable format with fixed-width columns in which each line of flight data pertains to a provided
point in time. Preceding the flight data is a block of text first describing the software format (the
“FR” line) and secondly identifying each recorded channel referred to as “Parameter Definition”
or “PD” lines. Though this information is useful for programming, it is removed prior to the
analysis.
A “Power-On” or “PO” line provides the reading of each channel when the flight data
recorder is activated. The strain channels automatically record zero on the PO line whereas all
others show an initial value specific to each flight. It is not known if the strain gauges zero
themselves prior to the PO line. The PO line data are used as offset values to normalize the
accelerations prior to any analysis. Time is referenced to that given in the PO line such that the
flight data is given in elapsed time from the power-on event. For clarity, an excerpt from a
typical CSV file is shown in Figure 2 and an excerpt from a typical fixed-width flight file is
shown in Figure 3.
Figure 2: Excerpt from a Typical CSV Flight File
10
Figure 3: Excerpt from a Typical Fixed-Width Flight File
The actual flight data in each file is either in a “PE” (Periodic) or “TR” (Triggered) line.
The PE lines are recorded every 15 seconds regardless of the values of any channel. The TR lines
are recorded when any channel triggers an output. If more than one channel triggers output at
the same time, multiple TR lines for the same time are recorded. The useful consequence of this
is that the flight files can be screened for any given trigger or channel number. Thus, a separate
history for each trigger can be extracted from the main flight data. During analysis, it is thus
more useful to evaluate each trigger individually (for peak counting and usage data) than to
evaluate the file strictly line-by-line.
E. Mission Profile
As this is an exploratory study, the present document concerns single-drop missions only.
In these cases the cruise altitudes are low and ground operations are not of primary interest.
Therefore the basic profile includes “Taxi 1,” “Cruise 1,” “Entry” (the maneuver just before the
drop), “Drop” (during which the weight of the retardant is quickly lost), “Exit” (the maneuver
immediately following the drop), “Cruise 2” and “Taxi 2.” The two cruise segments and the two
taxi segments cannot be combined due to the large weight difference between them – the
retardant weight can account for 25% of the operating weight. Maintaining separation between
11
the phases before and after such a large change in the wing loading allows a much cleaner
separation of effects on the aircraft. The resulting mission profile is shown schematically in
Figure 4.
Figure 4: Aerial Firefighting Mission Profile
F. Phase Separation
Rather than separating the flight phases strictly in the order of their occurrence in the
flight file (and thus in time), it was simpler to identify the phases somewhat out of order.
Presently, in the codes, the first phase identified is “Taxi 1” immediately followed by “Taxi 2” as
both rely on essentially the same logic. Because none of the considered files have multiple
flights or incomplete flights, the start of Taxi 1 and the end of Taxi 2 are identified by the
beginning and end of the flight data, respectively. The end of Taxi 1 is found by comparing the
current altitude to the runway altitude found using the average altitude of the first 20 seconds. If
the current altitude is above the runway altitude, the code steps forward checking that the altitude
remains above the runway for 30 seconds. If this is the case, the initial point is defined as the
end of Taxi 1. The Taxi 2 phase is found using identical logic though stepping backward
12
through time. This logic worked for both the 2005 and the 2007 Data despite the 2005 pressurebased altitude exhibiting much more noise than the 2007 GPS-based altitude.
The Drop phase is then identified using the discrete door signal. Because the arming and
disarming signals are also recorded in the 2005 Data, both signal change and direction are coded
into the analysis as opposed to identifying “1” as doors closed and “0” as doors open. The doors
are counted as they open and once the sixth door opens, the end of drop is marked at 2 seconds
later. The 2007 Data does not show the arm and disarm signals, so the code uses the same logic
for the 2007 Data, albeit without the arm and disarm logic.
The start of the Entry phase is identified next by stepping backward in time, from the
start of the Drop phase until the flap deflection is below 5 degrees (essentially identifying a
cruise flap setting). The end of the Exit phase is then identified by stepping forward in time from
the end of the Drop phase exploiting the use of jets to accelerate out of the drop zone. The jet
tachometer is referenced at the end of the Drop and once the current reading varies by more than
2000 RPM (as the pilots deactivate the jets), the end of the Exit phase is defined. The cruise
phases are then identified as the remaining time between the taxi and the entry or exit phases.
The complete logic as it was coded is detailed in Table 5.
Table 5: Flight Phase Separation Logic Reference
Flight Phase
Start Time (t1) Identification
Stop Time (t2) Identification
Taxi-1
Start of Data
Alt(t)>Runway Alt for 30 s
Cruise-1
t2 of Taxi-Out
t1 of Entry
Entry
Flap(t)<5° (backward from t2)
t1 of Drop
Drop
First Door Opens
2s After 6th Door Opens
Exit
t2 of Drop
(JetTach(t)-JetTach(t1))>2000 rpm
Cruise-2
t2 of Exit
t1 of Taxi-In
Taxi-2
Alt(t)>Runway Alt for 30 s
End of Data
13
G. Peak/Valley Counting of Flight Loads
Peaks and valleys for vertical and roll acceleration were counted using a standard “PeakBetween-Means” method in which a single peak is counted between crossings of a predefined
mean. This method was employed to allow analysis of the flight loads on the basis of load
cycles across a known mean as opposed to strictly counting all experienced loads. Only one
absolute maximum value between mean-crossings is counted as a peak, and similarly, only one
absolute minimum value between crossings is labeled as a valley. The mean for incremental
vertical acceleration and roll acceleration is simply zero. Using incremental vertical acceleration
allowed the same peak-counting logic to be used on both accelerations.
A graphical
representation of the logic used to count peaks and valleys is given in Figure 5.
No dead band around the mean is defined for counting the acceleration data. The
smallest increment of acceleration recorded was 0.01 making this an artificial dead band. A dead
band of 2 ft/sec was chosen for counting the gust velocities.
Figure 5: Peak Between Means Logic
14
G. Gusts and Maneuvers
The “Peak-Between-Means” method of counting accelerations allows for a “duration
between means” to be recorded for each peak or valley. Separation of loads into gusts and
maneuvers allows comparison of the loads due to atmospheric turbulence and due to pilot
control. The “Two-Second Rule” is used to categorize the vertical load factors into gusts or
maneuvers. A peak or valley from less than two seconds outside the mean is counted as a gust.
More recent research from the FAA shows that the “Two-Second Rule” is not the most accurate
method for separation of gusts and maneuvers from flight data. However, because the alternative
methods [22] require heading and bank data (which are unavailable), the “Two-Second Rule”
was implemented.
H. Atmospheric Turbulence
The calculation of gust velocities poses a problem specific to aerial firefighting
operations. Aircraft weight, which enters these calculations, is typically assumed to be constant
with fuel burn contributing a known error. However in the case of a heavy air tanker, as much as
25% of the take-off weight is in the form of retardant which can be released over a few seconds
during the Drop phase. Therefore it is critical to track the change of the mass of the aircraft
during this phase. A collection of the assumed weights during each flight phase is given in Table
6. The weight during the Drop phase is assumed to vary linearly with time between the assumed
Entry phase weight and the assumed Exit phase weight. As a result, each line of data during the
drop phase has a corresponding weight and a set of weight-dependent gust velocity parameters
such that the continuous and discrete gust velocities are calculated with a valid aircraft weight.
15
Table 6: Assumed Weight of Each Phase
Flight Phase
Taxi-1
Assumed Weight (lbf)
77,550
Cruise-1
76,630
Entry
76,370
Drop
Linearly time-variant
Exit
56,950
Cruise-2
56,930
Taxi-2
56,670
The assumed weight data is based on characterizations of the P-2V’s usage and load
history [23] which were based on pilots’ supplemental data detailing a total fuel weight of 11,700
pounds (1,800 gallons at 6.5 pounds per gallon) and an average retardant weight of 19,200
pounds (2,080 gallons at 9.23 pounds per gallon). So with the exception of the drop phase, the
aircraft weight was assumed to remain constant and equal to the average weight of each flight
phase.
Both the continuous and discrete gust models were implemented based on calculation
methods used in prior FAA documents. [8][9] First, the P-2V aircraft lift-curve slope (estimated
as 10% greater than the wing lift-curve slope) was calculated:
CL







2Ar
2Ar


 1.10  C l  1.10
1
.
10

1 
2

 2  4  Ar 2

tan 2   
2 2
 
 2  4  Ar  1 
 2  






, for   0
1 
2


(1)
The aircraft lift curve slope was calculated to be 5.15 per radian. The aircraft lift curve slope
was then used to calculate the P-2V’s non-dimensional mass parameter, μg:
g 
2 W S
 g c C L
(2)
16
which was used to calculate the discrete gust model’s gust alleviation factor, Kg:
Kg 
0.88   g
(3)
5.3   g
Using these parameters, the derived gust velocity, Ude, for the discrete gust could be related to
the incremental load factor by:
U de  n
2W S
V C L K g
(4)
The continuous gust model was similarly implemented with a power spectral density
function, F(PSD):
1
g
11.8  c  3
F PSD  
  2 L  110   g
(5)
which was then used to calculate the continuous gust velocity corresponding to a change in
vertical acceleration:
U   n
2W S
 V C L F PSD 
(6)
The number of occurrences, N, for Uσ was then calculated from:

c  
N
 g 
203   0

0.46
(7)
In this manner, each peak/valley in Uσ was counted as N counts. [15] This number of counts was
then used to determine the number of counts per nautical mile or:

counts 
N


nm
 Dist. flown during counting time 
(8)
Counts per nautical mile and per 1000 hours were used to allow comparison with earlier flight
loads research in Ref. [8] and [9] as well as gust and maneuver load standards in Ref. [23] and
reflect maintenance practices in part fatigue and replacement schedules.
17
So for each time step of flight data a discrete and a continuous gust velocity was
calculated. The two gust velocities were individually peak counted in the same manner as the
vertical and roll accelerations. Unlike the accelerations, however, the gust velocities were further
grouped according to altitudes above the terrain (AGL) at which they occurred. This allowed
comparison of the results with the existing atmospheric turbulence models. The data files,
however, did not include AGL altitudes. Therefore the AGL altitude was calculated assuming a
constant ground level equal to the take-off runway altitude. The altitude bands used for this
purpose are shown in Table 7.
Table 7: Gust Velocity Altitude Bands
Band #
1
2
3
4
Range
0 – 1000 ft
1001 – 2000 ft
2001 – 5000 ft
> 5000 ft
So for each altitude band, two plots (one for discrete gusts and the other for continuous
gusts) of the peak-counted gust speed occurrences were constructed. Because the continuous
gust model accounts for variation of severity by altitude (by Equation 7) and the discrete gust
model does not, the full effect of altitude (based on the flight accelerations) should be evident in
these plots.
I. Overall Usage Statistics
To examine the general usage of the aircraft, a separate code was written to analyze each
flight file on a “Ground-Air-Ground” basis rather than by flight phases. This code recorded a
number of usage factors listed in Table 8.
18
Table 8: Overall Extracted Usage Data Summary
Condition
During All Flight
Time
Flaps < 10°
10° < Flaps < 25°
Flaps > 25°
Extracted Data
Max Altitude
Max Airspeed
Max & Min nz
Max & Min Roll Accel.
Lift-Off ±5 sec
Touchdown ±5 sec
1st Door Opens
Max & Min nz
Max & Min Roll Accel.
Max & Min nz
Max & Min Roll Accel.
Max & Min nz
Max & Min Roll Accel.
Airspeed
Altitude
Altitude
Altitude
Max NZ
Max NZ
NZ
Airspeed
Airspeed
Airspeed
Airspeed
Airspeed
Airspeed
Coincident Data
Airspeed
Flap
Airspeed
Flap
Roll Accel. Airspeed
-
Flap
-
Further usage data was gathered concerning the distances and durations of each flight. The
distance was calculated by integrating the true airspeed which was corrected from the indicated
airspeed using:
VT  Vi
0

(9)
where ρ is calculated using:
   0 1  6.876 x10 6 H p  4.256
(10)
In addition to the flight distance, the duration for both ground phases and the duration in flight
were recorded. The length of time the aircraft was in flight with the flaps in each of the three
ranges was also recorded.
19
III. RESULTS AND DISCUSSION
A. Available Data
A total of 177 files from the 2005 fire season with inerrant flight data were available.
The flight files analyzed were chosen to provide a representation of all the important phases of
the firefighting role while also being consistent (allowing for easier separation of flight phases).
The files were limited to complete single-flight, single-drop cases. A total of 73 files did not
conform to these limitations and were separated. From the remaining 104 files, a set of 20 files
from throughout the 2005 season were chosen for exploratory analysis. An additional set of 20
flight files from the 2007 season were extracted from nCode’s library. Later, two of these files
showed multiple drops which reduced the number of analyzed files from 2007 to 18. All flight
files pertain to the same P-2V aircraft designated tanker 44. A list of the analyzed flight files is
given in the Appendix.
Most of the extracted data is based on the recorded vertical accelerations. The vertical
accelerations combined with airspeed and altitude data allowed calculation of derived and
continuous gust velocities. Various other data such as relevant altitudes, airspeeds, flap settings,
door settings, etc… were also extracted for use in analyzing the usage of the aircraft. The
altitude was used to calculate a density based on a standard atmosphere. The density was then
used with the indicated airspeed to calculate a true airspeed.
The true airspeed allowed
calculation of a flight distance.
However, there were a few differences associated with the 2005 and 2007 data sets.
First, the altitude in the 2005 Data was based on pitot tube data and exhibited more noise than
the 2007 altitude which was based on GPS recordings. The 2007 Data also showed a pressure
altitude but it appeared to be incorrectly normalized and although a few methods to correct the
20
data were attempted, none satisfactorily matched the GPS altitude. The airspeed measurements
for between 2005 and 2007 also show considerable difference from each other. The airspeeds
from the 2007 Data were considered to be correct which implies the recorded 2005 airspeeds
were lower than the actual indicated airspeed. Avenger Aircraft confirmed this by checking the
2005 recorded airspeeds with flight following data. Also, during the take-off roll (possibly
during the rotation) the 2007 airspeed data exhibited a tendency to jump erratically until a
consistent airspeed was reached. The roll acceleration data from 2005 was recorded in rad/s2 but
the instrumentation in 2007 measured it in different units despite the data acquisition expecting
rad/s2. As a result, the roll accelerations from 2007 peaked at much lower values and were rarely
triggered for recording. As a result, the roll acceleration peak counts from 2007 did not exhibit
enough data to plot.
B. Method Validation
The 2005 and the 2007 Data files were first analyzed and the results were compared with
each other as well as with earlier analysis of all the flights in Reference [23]. Comparing the
2005 Data results with those of Reference [23] validated the method of analysis while
comparison of the data from the two different years could point to any significant differences
between the two. The results for each flight phase are given in Figure 6 through Figure 10. The
data shown includes the combined gust and maneuver vertical load occurrences. It is noteworthy
that the results presented in Reference [23] were for all the flight phases combined.
Comparison of the results with those of Reference [23] showed similarity in occurrences
and severity which suggested the analysis methods were implemented correctly. There were
small deviations, however, which were likely due to the comparably small number of flights
21
analyzed in the present case. The effect of the small sample size was most apparent in the form
of some scatter, specifically in the drop phase, which was by a wide margin the shortest phase.
Nonetheless, certain differences between the results was obvious and could be attributed to the
fact that the results of Reference [23] were for the combination of all flight phases, and therefore,
were dominated by those of the cruise legs. For example, the Entry and Exit phases showed
slightly higher vertical load factors, which was expected due to flying at lower altitudes and
closer to the fire zones. The same results were skewed slightly toward the positive side of the
scale, highlighting the significance of maneuver loads during these flight segments.
When comparing the 2005 Data with the 2007 Data, no significant difference could be
discerned, as obvious from these figures. The two set of results followed each other very
closely, which highlighted the similarity in instrumentation and recording of data during these
two seasons. Again, the difference shown in Figure 8 for the Drop phase can be attributed to the
short duration of this phase and the scarcity of the data, resulting in large scatter as described
earlier. Consequently, it was concluded that either set of data would represent the vertical load
factors accurately.
22
1.E+07
Avenger Ref 23
WSU 2005
WSU 2007
Occurrences per 1000 hours
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
1.E+00
-2
-1
0
Incremental nz (g)
1
2
Figure 6: Cruise-1 Avenger/WSU Vertical Load Comparison
1.E+07
Avenger Ref 23
WSU 2005
WSU 2007
Occurrences per 1000 hours
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
1.E+00
-2
-1
0
Incremental nz (g)
1
2
Figure 7: Entry Avenger/WSU Vertical Load Comparison
23
1.E+07
Avenger Ref 23
WSU 2005
WSU 2007
Occurrences per 1000 hours
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
1.E+00
-2
-1
0
Incremental nz (g)
1
2
Figure 8: Drop Avenger/WSU Vertical Load Comparison
1.E+07
Avenger Ref 23
WSU 2005
WSU 2007
Occurrences per 1000 hours
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
1.E+00
-2
-1
0
Incremental nz (g)
1
2
Figure 9: Exit Avenger/WSU Vertical Load Comparison
24
1.E+07
Avenger Ref 23
WSU 2005
WSU 2007
Occurrences per 1000 hours
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
1.E+00
-2
-1
0
Incremental nz (g)
1
2
Figure 10: Cruise-2 Avenger/WSU Vertical Load Comparison
C. Ground-Air-Ground Usage Results
The overall Ground-Air-Ground (GAG) statistics for are given in Table 9. The usage
statistics for the ground segments such as maximum vertical load factor are presented in the Taxi
phase analyses. The same logic to separate Taxi from Cruise is used to separate “Ground” from
“Air”. The “Air” segment is composed of all time between the ground segments. Evident in
Table 9 are the large differences in maximum indicated airspeed (29% difference) and the roll
acceleration (84% difference) between the 2005 and 2007 Data. A consequence of the former is
lower average distance (based on integrating the airspeed) despite a small difference in the
average flight duration. This difference in airspeeds was attributed to erroneous values recorded
in the 2005 Data. This fact, which was also substantiated in Reference [23], will become
apparent in the subsequent discussions as well.
25
Table 9: Ground-Air-Ground Overall Statistics
Phase
Taxi 1
Air
Taxi 2
Data
2005
2007
2005
2007
2005
2007
Avg.
Duration
(sec)
282.8
646.5
3067.7
3779.6
289.6
271.8
Avg.
Distance
(nm)
117.2
236.7
-
Max.
Altitude
(ft MSL)
6722.8
4872.0
18588.6
14783.3
6407.8
4875.3
Max.
Airspeed
(KIAS)
138.39
229.77
198.85
283.14
117.66
177.95
Max. Δnz
(g)
0.29
0.27
1.00
1.43
0.75
0.71
Max. Roll
Accel.
(rad/s2)
12.64
0.03
10.23
0.03
16.27
0.05
The reader is reminded that the ground phases included all phases that were typically
separated between taxi, take-off roll, rotation, etc… so incremental vertical loads above 0.0
correspond to some acceleration of the aircraft in one of these roles. Without more data to
separate ground operation in this way, the loads could not be definitively assigned to a specific
operation of the aircraft.
The relations between altitude and airspeed are given in Figure 11 and Figure 12. They
show the maximum altitude found in the flight data and the coincident airspeed, as well as the
maximum airspeed with the coincident altitudes. The difference between the airspeeds of both
data sets is most apparent comparing the maximum airspeeds. The 2005 Data appears similar to
the 2007 Data albeit shifted roughly 80 KIAS lower. Both sets of results show the operating
altitudes.
The duration and distance relations with maximum altitude are given in Figure 13 and
Figure 14. The 2005 flights tended to fall into three categories that could be described as short,
medium, and long-range flights. In general, the longer a flight the aircraft had to make, the
higher the maximum altitude at which it cruised. The reader is cautioned again that distances
were calculated from integration of the airspeed. Since the 2005 Data had lower recorded
airspeeds, the distances associated with it also appeared shorter than those of the 2007 Data.
26
The overall GAG V-n Diagrams are shown in Figure 15 and Figure 16. The diagrams are
composed of the maximum and minimum (i.e. maximum negative) incremental vertical load
factors for each flight. The 2007 Data shows three clear regions, each corresponding to a flap
setting. The 2005 Data, however, seems equally dispersed among the full airspeed range. The
peak incremental vertical load of 1g in the 2005 Data occurred at a flap setting greater than 25
degrees. While the 2007 Data had a peak of 1.02g in the same flap range, the overall maximum
of 1.43g occurred at a flap setting between 10 and 25 degrees. In fact, the three largest load
factors from the 2007 data (1.43g, 1.28g and 1.08g) occurred in this flap range. High vertical
load factors in the higher flap settings imply either strong maneuvers or strong gusts occurring
either during take-off, approach, or during the drop.
Again, the disparity in the recorded
airspeeds is quite obvious from comparison of these two figures.
27
Maximum Altitude (ft MSL)
20000
2005 Data
2007 Data
16000
12000
8000
4000
0
0
50
100
150
200
250
300
Coincident Airspeed (KIAS)
Figure 11: Overall Maximum Altitude vs. Coincident Airspeed
Coincident Altitude (ft MSL)
20000
2005 Data
2007 Data
16000
12000
8000
4000
0
0
50
100
150
200
250
300
Maximum Airspeed (KIAS)
Figure 12: Overall Coincident Altitude vs. Maximum Airspeed
28
Maximum Altitude (ft MSL)
20000
2005 Data
2007 Data
16000
12000
8000
4000
0
0
2000
4000
6000
8000
10000
Flight Duration (sec)
Figure 13: Overall Maximum Altitude vs. Flight Duration
Maximum Altitude (ft MSL)
20000
2005 Data
2007 Data
16000
12000
8000
4000
0
0
100
200
300
400
500
600
Flight Distance (nm)
Figure 14: Overall Maximum Altitude vs. Flight Distance
29
Max and Min Incremental nz (g)
1.2
0.8
0.4
0
-0.4
Flap<10
-0.8
10<Flap<25
Flap>25
-1.2
70
90
110
130
150
170
Coincident Airspeed (KIAS)
Figure 15: Overall V-n Diagram – 2005 Data
Max and Min Incremental nz (g)
1.5
1
0.5
0
-0.5
Flap<10
-1
10<Flap<25
Flap>25
-1.5
100
140
180
220
260
Coincident Airspeed (KIAS)
Figure 16: Overall V-n Diagram – 2007 Data
30
300
A comparison of the load factors and the coincident flap setting is given in Figure 17.
This relation illustrates the high vertical loads which may be outside the allowable range for the
given flap settings. The collection of maximum load factors around the maximum flap setting is
expected during the Drop Phase (which is evident in the 2005 Data). The 2007 Data does not
show this trend. The maximum loads are still found during the Drop, but at a lower flap setting
in 2007. This is best illustrated in Figure 18 which relates the incremental vertical load factor
and flap setting when the first retardant door is opened. While the flights from 2005 remained
within a small flap range (between 32.75 and 34.4 degrees) the flights from 2007 displayed a
much wider yet lower range of flap settings (between 6.29 and 23.9 degrees). It is clear from
Figure 18 that the maximum vertical accelerations did not necessarily occur at the instant the
retardant is first released.
Both sets of data were processed using the same logic for separation of the flight phases,
so it is logical to assume that the data reflected a difference in the actual usage of the aircraft.
Thus, Figure 18 indicates that in 2007, drops were performed at lower flap settings, which would
also indicate higher airspeeds. Figure 19 may illustrate this effect though the 2005 airspeeds
were known to be abnormally low. If the 2005 airspeeds are shifted toward the 2007 airspeeds, a
small decrease in vertical loads is evident which could be related to the smaller flap settings.
The decrease in use of the maximum flap setting is also evident in Figure 20 showing the percent
of total flight duration spent in each flap range. The lowest flap range is most common due to
the long duration of the cruise-condition and in the 2007 Data, the lower flap setting during
release.
31
Max and Min Incremental nz (g)
1.5
1
0.5
0
-0.5
-1
2005 Data
2007 Data
-1.5
-20
-10
0
10
20
30
40
Coincident Flap Setting (deg)
Figure 17: Overall Load Factor vs. Coincident Flap Setting
Door Incremental nz (g)
0.6
0.4
0.2
0
-0.2
-0.4
2005 Data
2007 Data
-0.6
0
10
20
30
40
Coincident Flap Setting (deg)
Figure 18: First Door-Open Vertical Load Factor vs. Flap Setting
32
0.6
2005 Data
2007 Data
Door Incremental nz (g)
0.4
0.2
0
-0.2
-0.4
-0.6
80
100
120
140
160
180
200
220
240
Coincident Airspeed (KIAS)
Figure 19: First Door-Open Vertical Load Factor vs. Airspeed
100%
2005
Percent of Flight Duration
90%
2007
80%
70%
60%
50%
40%
30%
20%
10%
0%
Flap<10
10>Flap<25
Flap>25
Figure 20: Overall Flap Range Percent of Flight Duration
33
Normal probability distributions of flight duration and flight distance are shown in Figure
21 and Figure 22. It is obvious from these figures that the flight durations in the 2005 Data were
not very different from those of the 2007 Data. The 2005 Flights were somewhat shorter, but
both data sets had almost the same scatter (i.e. standard deviation). However, this was not the
case for the flight distance. The average distance for the 2005 Data was considerably shorter
than that of the 2007 Data (roughly 110 nm versus 240 nm). This behavior could only be
attributed to the erroneously recorded airspeeds of the 2005 Data.
Normal distributions of the maximum and minimum (i.e. maximum negative) values of
vertical incremental load factor for the two sets of data are shown in Figure 23 through Figure
26. The data in these figures is divided into three groups, according to the magnitude of the flap
deflection. It is interesting that in the 2005 Data, the average of the maximum load factors
corresponded to flights where the flaps were fully extended. At this writing, this anomaly cannot
be explained. It could only be speculated that these results may be different for a larger sample
population.
34
0.018
2005
Normal Distribution
0.016
2007
0.014
0.012
0.01
0.008
0.006
0.004
0.002
0
0
30
60
90
120
150
Flight Duration (min)
Figure 21: Overall Normal Distribution of Flight Duration
0.008
2005
2007
Normal Distribution
0.007
0.006
0.005
0.004
0.003
0.002
0.001
0
0
100
200
300
400
500
600
Flight Distance (nm)
Figure 22: Overall Normal Distribution of Flight Distance
35
4.5
Flap<10
Normal Distribution
4.0
10<Flap<25
Flap>25
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
0.2
0.4
0.6
0.8
1
1.2
Maximum Incremental nz (g)
Figure 23: Overall Normal Distribution of Maximum Vertical Load Factor – 2005 Data
4.0
Flap<10
10<Flap<25
3.5
Normal Distribution
Flap>25
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.8
-0.6
-0.4
-0.2
0
Minimum Incremental nz (g)
Figure 24: Overall Normal Distribution of Minimum Vertical Load Factor – 2005 Data
36
3
Flap<10
10<Flap<25
Normal Distribution
2.5
Flap>25
2
1.5
1
0.5
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
Maximum Incremental nz (g)
Figure 25: Overall Normal Distribution of Maximum Vertical Load Factor – 2007 Data
4.5
Flap<10
Normal Distribution
4
10<Flap<25
Flap>25
3.5
3
2.5
2
1.5
1
0.5
0
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
Minimum Incremental nz (g)
Figure 26: Overall Normal Distribution of Minimum Vertical Load Factor – 2007 Data
37
D. Taxi Phases
The Taxi-1 (pre-drop) and Taxi-2 (post-drop) phases were compared to each other to
determine what effect, if any, the change in weight had on the aircraft’s response to ground
operations. However, limitations on the minimum airspeed and the lack of angular position
(such as heading or pitch) limited the amount of analysis that could be performed on the taxi
phases. The statistics for both Taxi Phases are given in Table 10. The lowest airspeeds did not
record below around 30 knots for the 2005 Data and 15 knots for the 2007 Data. Therefore, the
average distance for the Taxi Phases could not be calculated using this method. The data shown
in Table 10 agreed well with expectations. Maximum roll accelerations and the maximum
incremental load factors were quite reasonable. At this point, the reader is reminded that this
phase included the takeoff roll, which explains rather high values of the maximum indicated
airspeed in this table.
Table 10: Taxi Phase Statistics
Phase
Taxi-1
Taxi-2
Data
2005
2007
2005
2007
Avg.
Duration
(sec)
282.8
646.5
287.1
264.3
Avg.
Distance
(nm)
-
Max.
Altitude
(ft MSL)
6722.8
4872.0
6407.8
4875.3
Max.
Airspeed
(KIAS)
138.39
229.77
117.66
177.95
Max. Δnz
(g)
0.29
0.27
0.75
0.71
Max. Roll
Accel.
(rad/s2)
12.64
0.03
16.27
0.05
The maximum altitude during taxi was typically near the calculated runway altitude
although the noise in the 2005 altitude data could vary by as much as 200 ft. The noise was
especially pronounced during the takeoff roll in which the altitude could jump as much as 900 ft
despite both the airspeed and a visual check of the altitude confirming the aircraft was not in a
climbing state.
38
The occurrences of incremental vertical loads per 1000 hours for both Taxi phases are
given in Figure 27 and Figure 28. Plots of the loads per nautical mile could not be formed due to
the lack of a reliable airspeed (and thus integrated distance) during the Taxi phases. Gust and
maneuver loads were not separated so the occurrence plots depict the total loads during Taxi.
The Taxi-2 phase consistently showed higher occurrences of the same loads (a shift in height on
the occurrence plots) but roughly the same range of loads or “severity” (little increase in width).
This was a result of the lower aircraft weight during Taxi-2. While rolling on the ground, a
disturbance would impart a larger vertical acceleration than an equal disturbance during Taxi-1
(with the added inertia of the retardant and unspent fuel).
The extended flat line in the 2007 loads was due to a single valley of -2.97g during the
Taxi-1 phase. This was believed to be a statistical outlier and, assuming it reflected a true
occurrence of nearly -3g, was a result of the ground conditions as opposed to reflecting the
aircraft’s typical handling properties. There was not enough data to compare with and determine
what caused this vertical acceleration as it occurred one the ground at an off-scale low airspeed.
The roll acceleration occurrences per 1000 hours are given in Figure 29. Only data from
2005 is presented because there was insufficient data from 2007 to establish frequencies of
occurrence.
The Taxi-1 Phase showed consistently higher roll accelerations with higher
frequencies.
39
1.E+07
Taxi 1
Cumulative Occurrences
Taxi 2
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-1.5
-1
-0.5
0
0.5
Incremental nz (g)
1
1.5
Figure 27: Taxi Δnz Occurrences per 1000 Hours – 2005 Data
1.E+07
Taxi 1
Cumulative Occurrences
Taxi 2
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 28: Taxi Δnz Occurrences per 1000 Hours – 2007 Data
40
1.E+08
Taxi 1
Taxi 2
Cumulative Occurrences
1.E+07
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-20
-10
0
2
10
20
Roll Accel. (rad/s )
Figure 29: Taxi Roll Acceleration Occurrences per 1000 Hours – 2005 Data
E. Cruise Phases
The Cruise-1 and Cruise-2 phases were compared to determine what effect, if any, the
change in weight had on the aircraft’s response to the flight environment. These phases also
included what is normally considered climb and descent. Consequently, the results discussed
below were somewhat affected by the off-cruise data.
The statistics for the Cruise Phases are given in Table 11. Because a typical flight
involved takeoff and landing at the same airport, both cruise segments were expected to have
similar distances. Some deviation was expected if the aircraft loitered before entry into the drop
zone. This explains why the return trips had a shorter duration and distance in both data sets.
The differences between the 2005 and 2007 recorded airspeeds are also evident in this table.
41
Table 11: Cruise Phase Statistics
Phase
Cruise-1
Cruise-2
Data
2005
2007
2005
2007
Avg.
Duration
(sec)
1582.3
1690.9
1089.9
1512.3
Avg.
Distance
(nm)
61.2
106.7
41.3
96.1
Max.
Altitude
(ft MSL)
18588.6
14392.9
18457.3
14783.3
Max.
Airspeed
(KIAS)
198.9
283.1
187.5
247.7
Max. Δnz
(g)
0.52
0.96
0.58
0.75
Max. Roll
Accel.
(rad/s2)
10.17
0.02
10.23
0.03
The altitude and airspeed relations are given in Figure 30 through Figure 33. The
airspeeds appeared slightly higher in Cruise-1 which was expected due to the higher wing
loading and stall speed prior to release. Cruise maximum altitudes were roughly equal and
typically between 6,000 and 12,000 ft MSL (roughly 5,000 and 7,000 ft AGL). Maximum
altitudes, correlated with cruise duration and distance are given in Figure 34 through Figure 37.
Both data sets showed a trend toward higher altitude for longer durations and distances. The
distances traveled in the 2005 Data appeared shorter than reality due to the lower recorded
airspeeds.
42
20000
Cruise 1
Maximum Altitude (ft MSL)
18000
Cruis e 2
16000
14000
12000
10000
8000
6000
4000
2000
0
80
100
120
140
160
180
200
Coincident Airspeed (KIAS)
Figure 30: Cruise Maximum Altitude vs. Coincident Airspeed – 2005 Data
12000
Cruise 1
Coincident Altitude (ft MSL)
Cruise 2
10000
8000
6000
4000
2000
0
80
100
120
140
160
180
200
Maximum Airspeed (KIAS)
Figure 31: Cruise Maximum Airspeed vs. Coincident Altitude – 2005 Data
43
16000
Cruise 1
Cruise 2
Maximum Altitude (ft MSL)
14000
12000
10000
8000
6000
4000
2000
0
140
160
180
200
220
240
260
280
300
Coincident Airspeed (KIAS)
Figure 32: Cruise Maximum Altitude vs. Coincident Airspeed – 2007 Data
16000
Cruise 1
Cruise 2
Coincident Altitude (ft MSL)
14000
12000
10000
8000
6000
4000
2000
0
140
160
180
200
220
240
260
280
300
Maximum Airspeed (KIAS)
Figure 33: Cruise Maximum Airspeed vs. Coincident Altitude– 2007 Data
44
20000
Cruise 1
Maximum Altitude (ft MSL)
18000
Cruise 2
16000
14000
12000
10000
8000
6000
4000
2000
0
0
1000
2000
3000
4000
5000
6000
Cruise Duration (sec)
Figure 34: Cruise Maximum Altitude vs. Flight Duration – 2005 Data
20000
Cruise 1
Maximum Altitude (ft MSL)
18000
Cruise 2
16000
14000
12000
10000
8000
6000
4000
2000
0
0
40
80
120
160
200
Cruise Distance (nm)
Figure 35: Cruise Maximum Altitude vs. Flight Distance – 2005 Data
45
16000
Maximum Altitude (ft MSL)
14000
12000
10000
8000
6000
4000
2000
Cruise 1
Cruise 2
0
0
1000
2000
3000
4000
5000
6000
Cruise Duration (sec)
Figure 36: Cruise Maximum Altitude vs. Flight Duration – 2007 Data
16000
Maximum Altitude (ft MSL)
14000
12000
10000
8000
6000
4000
2000
Cruise 1
Cruise 2
0
0
100
200
300
400
500
Cruise Distance (nm)
Figure 37: Cruise Maximum Altitude vs. Flight Distance – 2007 Data
46
The occurrences of incremental vertical load factor per nautical mile and per 1000 hours
separated into gusts and maneuvers for both cruise phases are given in Figure 38 through Figure
45. It is obvious from these figures that during the Cruise-2 phase the vertical loads were of
higher magnitude and occurred with increased frequency relative to the Cruise-1 phase. This
effect was caused by the lower weight and thus lower wing loading after the drop which resulted
in a higher vertical acceleration for the same gust intensity. This reasoning was supported by the
fact that the maneuver loads, which are independent of the wing loading, in both data sets, were
nearly equal.
The occurrences of roll acceleration for the 2005 Data were also separated into gusts and
maneuvers and are shown in Figure 46 through Figure 49. The two-second rule that was
primarily developed for vertical acceleration was also used in this case. It is understood that this
method may not be applicable to roll accelerations. However, in the absence of an alternative, it
was used for separating the two types of loads. These figures show that during the cruise toward
a fire, roll accelerations as high as 5 rad/s2 are as common as once per nautical mile. However,
during the flight back they were as rare as once every ten nautical miles.
47
1.E+02
Cruise 1
Cruise 2
Cumulative Occurrences
1.E+01
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 38: Cruise Δnz Gust Occurrences per Nautical Mile – 2005 Data
1.E+02
Cruise 1
Cruise 2
Cumulative Occurrences
1.E+01
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-1.5
-1
-0.5
0
0.5
Incremental nz (g)
1
1.5
Figure 39: Cruise Δnz Maneuver Occurrences per Nautical Mile – 2005 Data
48
1.E+07
Cruise 1
Cruise 2
Cumulative Occurrences
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
-1.5
-1
-0.5
0
0.5
Incremental nz (g)
1
1.5
Figure 40: Cruise Δnz Gust Occurrences per 1000 Hours – 2005 Data
1.E+07
Cruise 1
Cruise 2
Cumulative Occurrences
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
-1.5
-1
-0.5
0
0.5
Incremental nz (g)
1
1.5
Figure 41: Cruise Δnz Maneuver Occurrences per 1000 Hours – 2005 Data
49
1.E+01
Cruise 1
Cumulative Occurrences
Cruise 2
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 42: Cruise Δnz Gust Occurrences per Nautical Mile – 2007 Data
1.E+01
Cruise 1
Cumulative Occurrences
Cruise 2
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 43: Cruise Δnz Maneuver Occurrences per Nautical Mile – 2007 Data
50
1.E+07
Cruise 1
Cumulative Occurrences
Cruise 2
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 44: Cruise Δnz Gust Occurrences per 1000 Hours – 2007 Data
1.E+07
Cruise 1
Cumulative Occurrences
Cruise 2
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 45: Cruise Δnz Maneuver Occurrences per 1000 Hours – 2007 Data
51
1.E+02
Cruise 1
Cruise 2
Cumulative Occurrences
1.E+01
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-20
-10
0
10
20
2
Roll Accel. (rad/s )
Figure 46: Cruise Roll Acceleration Gust Occurrences per Nautical Mile – 2005 Data
1.E+00
Cruise 1
Cumulative Occurrences
Cruise 2
1.E-01
1.E-02
1.E-03
1.E-04
-20
-10
0
2
10
20
Roll Accel. (rad/s )
Figure 47: Cruise Roll Acceleration Maneuver Occurrences per Nautical Mile – 2005 Data
52
1.E+07
Cruise 1
Cumulative Occurrences
Cruise 2
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-20
-10
0
2
10
20
Roll Accel. (rad/s )
Figure 48: Cruise Roll Acceleration Gust Occurrences per 1000 Hours – 2005 Data
1.E+05
Cruise 1
Cumulative Occurrences
Cruise 2
1.E+04
1.E+03
1.E+02
1.E+01
-20
-10
0
2
10
20
Roll Accel. (rad/s )
Figure 49: Cruise Roll Acceleration Maneuver Occurrences per 1000 Hours– 2005 Data
53
The V-n diagrams for the cruise phase are given in Figure 50 through Figure 53. These
plots contain a combination of maximum and minimum vertical load factors (and coincident
airspeeds) from all three flap deflection ranges. The 2005 Data showed rather equal distribution
of airspeeds across both cruise phases as well as among different flap deflection ranges. The
2007 flights, however, showed three distinct groupings of airspeeds depending on flap
deflection. It is clear from Figure 53 that the lowest airspeeds correlated with the largest flap
deflections, as would be expected. The middle flap range (between 10 and 25 degrees) seemed
to show consistently lower vertical loads than either of the other two.
54
Max and Min Incremental nz (g)
1
Cruise 1
0.8
Cruise 2
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
60
80
100
120
140
160
180
Coincident Airspeed (KIAS)
Figure 50: Cruise V-n Diagram Comparing Phases – 2005 Data
Max and Min Incremental nz (g)
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
Flap<10
-0.8
10<Flap<25
Flap>25
-1
60
80
100
120
140
160
180
Coincident Airspeed (KIAS)
Figure 51: Cruise V-n Diagram Comparing Flap Ranges– 2005 Data
55
Max and Min Incremental nz (g)
1.2
Cruise 1
Cruise 2
0.8
0.4
0
-0.4
-0.8
-1.2
0
50
100
150
200
250
300
Coincident Airspeed (KIAS)
Figure 52: Cruise V-n Diagram Comparing Phases– 2007 Data
Max and Min Incremental nz (g)
1.2
0.8
0.4
0
-0.4
Flap<10
-0.8
10<Flap<25
Flap>25
-1.2
0
50
100
150
200
250
300
Coincident Airspeed (KIAS)
Figure 53: Cruise V-n Diagram Comparing Flap Ranges – 2007 Data
56
The occurrences of the derived gust velocities for Cruise-1 per nautical mile and per 1000
hours are given in Figure 54 through Figure 57. The 2005 Data showed all gust velocities in the
lowest altitude band as slightly more frequent with roughly the same severity. Higher altitudes
tended to show fewer occurrences but the same severity. The top altitude band, however,
exhibited nearly the same occurrences and slightly higher derived gust speeds than the second
altitude band. Positive gust velocities appeared to be more frequent than the negative ones.
The 2007 Data did not show this same trend. Instead, all four altitude bands showed
nearly the same frequency and magnitude except that the highest altitude band showed an
increase in the negative derived gust velocities which extended outside the range of the other
three bands. In general, the 2007 Data also showed significantly lower gust velocities than the
2005 Data. This is a result of the consistently lower airspeed in the 2005 Data. Since, the
derived gust velocity is inversely related to the airspeed, a lower airspeed for the same vertical
acceleration would appear to have been caused by a higher derived gust velocity. It is further
possible that the pronounced difference between the loads at different altitude bands evident in
the 2005 Data was a result of lower actual airspeeds than the 2007 Data at lower altitudes.
Without a method to correct the 2005 airspeeds, however, this remains speculative in nature.
57
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
1.E+01
2001-5000ft
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 54: Cruise-1 Derived Gust Velocity Occurrences per Nautical Mile – 2005 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 55: Cruise-1 Derived Gust Velocity Occurrences per 1000 Hours – 2005 Data
58
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
1.E+01
2001-5000ft
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 56: Cruise-1 Derived Gust Velocity Occurrences per Nautical Mile – 2007 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 57: Cruise-1 Derived Gust Velocity Occurrences per 1000 Hours – 2007 Data
59
The occurrences of the derived gust velocities for Cruise-2 per nautical mile and per 1000
hours are given in Figure 58 through Figure 61. Both data showed all gust velocities in the
lowest altitude band as slightly more frequent with roughly the same severity. The higher gust
velocities in the lowest altitude band were particularly more frequent. The other three altitude
bands, however, showed roughly equal severity and frequency. Furthermore, for derived gust
velocities below 20 ft/s, all data appeared to collapse onto a single curve. Also, the 2007 derived
gust velocities were lower than the 2005 derived gust velocities as a result of the disparity
between their respective airspeeds.
The derived gust velocities between both cruise phases did not show much difference.
Cruise-1 showed roughly the same severity and frequency as Cruise-2 for both data sets. This
similarity in gust velocities was to be expected and to a certain extent validated the method of
calculating the derived gust velocities as a function of the vehicle weight, airspeed, and vertical
load factor. From Cruise-1 to Cruise-2, the weight and the airspeed decreased while the vertical
gust loads slightly increased (see earlier Figure 38 and Figure 42) roughly balancing each other
resulting in the very similar atmospheric turbulence before and after the drop.
60
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
1.E+01
2001-5000ft
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 58: Cruise-2 Derived Gust Velocity Occurrences per Nautical Mile – 2005 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 59: Cruise-2 Derived Gust Velocity Occurrences per 1000 Hours – 2005 Data
61
Cumulative Occurrences
1.E+02
0-1000ft
1001-2000ft
1.E+01
2001-5000ft
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 60: Cruise-2 Derived Gust Velocity Occurrences per Nautical Mile – 2007 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 61: Cruise-2 Derived Gust Velocity Occurrences per 1000 Hours – 2007 Data
62
The occurrences of the continuous gust velocities for Cruise-1 per nautical mile and per
1000 hours are given in Figure 62 through Figure 65. The 2005 Data showed all gust velocities
in the lowest altitude band as slightly more frequent with roughly the same severity. Increasing
altitude tended to result in fewer occurrences for the same severity. The top altitude band,
however like the discrete gust velocities, exhibited nearly the same occurrences and higher gust
speeds than the second altitude band. There was a slight increase in severity toward positive
derived gust velocities in comparison to negative ones.
The 2007 Data did not show the altitude trend. Instead, all four altitude bands showed
nearly the same frequency and magnitude.
In general, the 2007 Data showed lower gust
velocities than the 2005 Data as a result of the consistently lower airspeeds in the latter data set.
63
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
1.E+01
2001-5000ft
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 62: Cruise-1 Continuous Gust Velocity Occurrences per Nautical Mile – 2005 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 63: Cruise-1 Continuous Gust Velocity Occurrences per 1000 Hours – 2005 Data
64
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
1.E+01
2001-5000ft
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 64: Cruise-1 Continuous Gust Velocity Occurrences per Nautical Mile – 2007 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 65: Cruise-1 Continuous Gust Velocity Occurrences per 1000 Hours – 2007 Data
65
The occurrences of the continuous gust velocities for Cruise-2 per nautical mile and per
1000 hours are given in Figure 66 through Figure 69. Again, the 2005 data showed all gust
velocities in the lowest altitude band as slightly more frequent with roughly the same severity.
The higher gust velocities in the lowest altitude band were particularly more frequent. The other
three altitude bands, however, showed roughly equal severity and frequency. Furthermore, the
data appeared to collapse onto a single curve for continuous gust velocities in excess of 20 ft/s.
In the 2007 Data continuous gust velocities were much more frequent and slightly more
severe in the lowest altitude band only. Again, the values for the 2007 Data were lower than
those of the 2005 Data as a result of the disparity between their respective airspeeds.
The continuous gust velocities between both cruise phases, much like the derived gust
velocities, did not show much difference. Cruise-1 showed roughly the same severity and
frequency as Cruise-2 in both data sets. This similarity was expected as the weight, airspeed,
and vertical gust loads roughly balanced each other which resulted in the very similar
atmospheric turbulence before and after the drop.
66
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
1.E+01
2001-5000ft
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 66: Cruise-2 Continuous Gust Velocity Occurrences per Nautical Mile – 2005 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 67: Cruise-2 Continuous Gust Velocity Occurrences per 1000 Hours – 2005 Data
67
Cumulative Occurrences
1.E+02
0-1000ft
1001-2000ft
1.E+01
2001-5000ft
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 68: Cruise-2 Continuous Gust Velocity Occurrences per Nautical Mile – 2007 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 69: Cruise-2 Continuous Gust Velocity Occurrences per 1000 Hours – 2007 Data
68
F. Entry, Drop, and Exit Phases
The statistics for the Entry, Drop, and Exit Phases are given in Table 12. The Entry
phase is initiated by configuring the aircraft for the drop and may include flying in a holding
pattern. This includes lowering the flaps to the first “notch.” During the entry phase, the aircraft
is typically engaged in a maneuvering dive toward the release point while extending the flaps.
During the drop phase, the aircraft is flown with the flaps extended while the retardant is
released. Once the retardant is released, the flaps are quickly retracted, and the exit phase (a full
power climb maneuver) is initiated.
Table 12: Entry, Drop, Exit Phase Statistics
Phase
Entry
Drop
Exit
Data
2005
2007
2005
2007
2005
2007
Avg.
Duration
(sec)
310.1
429.9
6.3
5.6
79.5
140.9
Avg.
Distance
(nm)
11.6
24.9
0.2
0.3
2.9
8.6
Max.
Altitude
(ft)
10476.8
11473.0
9663.0
7463.8
10188.0
14333.8
Max.
Airspeed
(KIAS)
173.97
272.26
170.35
233.57
183.65
277.79
Max. Δnz
(g)
0.86
1.01
1.00
1.43
0.71
0.89
Max. Roll
Accel.
(rad/s2)
4.36
0.02
5.16
0.01
4.30
0.02
The relations between altitude and airspeed are given in Figure 70 through Figure 73.
The lowest altitudes and airspeeds in both data sets were during the Drop phase while the Entry
and Exit phases fell in the same range of altitudes. The Exit phase, however, was typically at a
higher airspeed than the Entry phase which was a combined result of fully retracted flaps and use
of the jet engines to boost the aircraft out of the drop zone. Again, the two sets of data differed
in recorded airspeed.
69
12000
Entry
Maximum Altitude (ft MSL)
Drop
10000
Exit
8000
6000
4000
2000
0
60
80
100
120
140
160
180
Coincident Airspe ed (KIAS)
Figure 70: Entry, Drop, Exit Maximum Altitude vs. Coincident Airspeed – 2005 Data
Coincident Altitude (ft MSL)
12000
10000
8000
6000
4000
Entry
2000
Drop
Exit
0
60
80
100
120
140
160
180
200
Maximum Airspeed (KIAS)
Figure 71: Entry, Drop, Exit Coincident Altitude vs. Maximum Airspeed – 2005 Data
70
16000
Entry
Drop
Maximum Altitude (ft MSL)
14000
Exit
12000
10000
8000
6000
4000
2000
0
140
160
180
200
220
240
260
280
Coincident Airspeed (KIAS)
Figure 72: Entry, Drop, Exit Maximum Altitude vs. Coincident Airspeed – 2007 Data
16000
Entry
Drop
Coincident Altitude (ft MSL)
14000
Exit
12000
10000
8000
6000
4000
2000
0
140
160
180
200
220
240
260
280
300
Maximum Airspeed (KIAS)
Figure 73: Entry, Drop, Exit Coincident Altitude vs. Maximum Airspeed – 2007 Data
71
The correlations of altitude with distance and duration are given in Figure 74 through
Figure 77. The Drop phase was much shorter than the Entry and Exit phases so both the
distances and durations are nearly zero. The Entry phase was consistently longer in duration and
distance than the exit phase despite their altitudes typically being equal. This was evident in
both the 2005 and the 2007 data sets although in the latter the Entry phases were more consistent
with the Exit phases.
72
Maximum Altitude (ft MSL)
12000
10000
8000
6000
4000
Entry
2000
Drop
Exit
0
0
100
200
300
400
500
Phase Duration (sec)
Figure 74: Entry, Drop, Exit Maximum Altitude vs. Duration – 2005 Data
Maximum Altitude (ft MSL)
12000
10000
8000
6000
4000
Entry
2000
Drop
Exit
0
0
5
10
15
20
Phase Distance (nm)
Figure 75: Entry, Drop, Exit Maximum Altitude and Distance – 2005 Data
73
16000
Entry
Drop
Maximum Altitude (ft MSL)
14000
Exit
12000
10000
8000
6000
4000
2000
0
0
100
200
300
400
500
Phase Duration (sec)
Figure 76: Entry, Drop, Exit Maximum Altitude vs. Duration – 2007 Data
16000
Entry
Drop
Maximum Altitude (ft MSL)
14000
Exit
12000
10000
8000
6000
4000
2000
0
0
5
10
15
20
Phase Distance (nm)
Figure 77: Entry, Drop, Exit Maximum Altitude vs. Distance – 2007 Data
74
The occurrences of incremental vertical load factor separated into gusts and maneuvers
for the Entry, Drop, and Exit phases are given in Figure 78 through Figure 85. The Exit and the
Drop phases showed increased frequency and severity of gust loads, with the latter leading the
way. The 2005 Drop phases showed the same occurrences at low loads as the Exit phases but it
did show significantly higher occurrences of the higher loads. The positive loads were both
more common and more severe than the negative vertical loads which implied possible inclusion
of some maneuver loads among the gust loads stemming from the use of the two-second rule.
The 2007 Drop phases, however showed slightly fewer occurrences than the Exit phase and
roughly the same trends as the Entry and Exit phases in negative loads. The 2007 Drop phase
positive vertical loads were still more common than the Exit and Entry phases.
The occurrences of the roll accelerations separated into gusts and maneuvers are given in
Figure 86 through Figure 89. Again, the two second rule was used for this parameter as well,
even though there was no evidence that it would be applicable. There were an insufficient
number of peaks and valleys in the roll acceleration to allow plotting them for the 2007 Data.
The Entry and Exit phases exhibited the same gust occurrences and severity at comparatively
low accelerations which implied the Entry, Drop, and Exit phases were less severe in roll than in
the cruise segments.
The Drop phase, however, showed as much as 10 times the gust
occurrences as Entry and Exit, which reflects the higher level of atmospheric turbulence in the
drop zone. The maneuver plots indicated an increase in occurrences but not severity for the Exit
phase over the Entry phase.
The reader is reminded that these phases were so short that in many cases there was not
an abundance of data available. Therefore, these results could be slightly distorted. More
reliable results would require many more than 20 flights to establish.
75
1.E+02
Entry
Cumulative Occurrences
Drop
Exit
1.E+01
1.E+00
1.E-01
1.E-02
1.E-03
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 78: Entry, Drop, Exit Δnz Gust Occurrences per Nautical Mile – 2005 Data
1.E+02
Entry
Cumulative Occurrences
Drop
Exit
1.E+01
1.E+00
1.E-01
1.E-02
1.E-03
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 79: Entry, Drop, Exit Δnz Maneuver Occurrences per Nautical Mile – 2005 Data
76
1.E+07
Entry
Cumulative Occurrences
Drop
Exit
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 80: Entry, Drop, Exit Δnz Gust Occurrences per 1000 Hours – 2005 Data
1.E+07
Entry
Cumulative Occurrences
Drop
Exit
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 81: Entry, Drop, Exit Δnz Maneuver Occurrences per 1000 Hours – 2005 Data
77
1.E+01
Entry
Cumulative Occurrences
Drop
Exit
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 82: Entry, Drop, Exit Δnz Gust Occurrences per Nautical Mile – 2007 Data
1.E+01
Entry
Cumulative Occurrences
Drop
Exit
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental Nz (g)
Figure 83: Entry, Drop, Exit Δnz Maneuver Occurrences per Nautical Mile – 2007 Data
78
1.E+07
Entry
Cumulative Occurrences
Drop
Exit
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 84: Entry, Drop, Exit Δnz Gust Occurrences per 1000 Hours – 2007 Data
1.E+07
Entry
Cumulative Occurrences
Drop
Exit
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-1.5
-1
-0.5
0
0.5
1
1.5
Incremental nz (g)
Figure 85: Entry, Drop, Exit Δnz Maneuver Occurrences per 1000 Hours – 2007 Data
79
1.E+02
Entry
Cumulative Occurrences
Drop
Exit
1.E+01
1.E+00
1.E-01
1.E-02
1.E-03
-20
-10
0
10
20
2
Roll Accel. (rad/s )
Figure 86: Entry, Drop, Exit Roll Acceleration Gust Occurrences per Nautical Mile – 2005
Data
1.E+02
Entry
Cumulative Occurrences
Drop
Exit
1.E+01
1.E+00
1.E-01
1.E-02
1.E-03
-20
-10
0
10
20
2
Roll Accel. (rad/s )
Figure 87: Entry, Drop, Exit Roll Acceleration Maneuver Occurrences per Nautical Mile –
2005 Data
80
1.E+07
Entry
Cumulative Occurrences
Drop
Exit
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-20
-10
0
10
20
2
Roll Accel. (rad/s )
Figure 88: Entry, Drop, Exit Roll Acceleration Gust Occurrences per 1000 Hours – 2005
Data
1.E+07
Entry
Cumulative Occurrences
Drop
Exit
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
-20
-10
0
10
20
2
Roll Accel. (rad/s )
Figure 89: Entry, Drop, Exit Roll Acceleration Maneuver Occurrences per 1000 Hours –
2005 Data
81
The V-n diagrams for the Entry, Drop, and Exit phases are given in Figure 90 through
Figure 93. There did not appear to be any obvious trends other than a tendency toward higher
positive vertical loads than negative vertical loads. The Drop phase showed the highest vertical
loads in both the 2005 and 2007 Data. However, in 2005 these loads occurred at the maximum
flap range while in 2007, they occurred in the middle flap range. The reader is cautioned that the
higher vertical accelerations during the Drop phase were not necessarily as the result of the
maneuvering or atmospheric turbulence. It is relatively easy to discern that these accelerations
could be caused by the change in the aircraft mass over a short time as the result of releasing
load, which could be as large as 25% of the gross weight.
82
Max and Min Incremental nz (g)
1.2
0.8
0.4
0
-0.4
Entry
-0.8
Drop
Exit
-1.2
60
80
100
120
140
160
180
Coincident Airspeed (KIAS)
Figure 90: Entry, Drop, Exit V-n Diagram Comparing Phases – 2005 Data
Max and Min Incremental nz (g)
1.2
0.8
0.4
0
-0.4
Flap<10
-0.8
10>Flap<25
Flap>25
-1.2
60
80
100
120
140
160
180
Coincident Airspeed (KIAS)
Figure 91: Entry, Drop, Exit V-n Diagram Comparing Flap Ranges – 2005 Data
83
Max and Min Incremental nz (g)
1.5
Entry
Drop
1
Exit
0.5
0
-0.5
-1
-1.5
120
140
160
180
200
220
240
260
280
Coincident Airspeed (KIAS)
Figure 92: Entry, Drop, Exit V-n Diagram Comparing Phases – 2007 Data
Max and Min Incremental nz (g)
1.5
Flap<10
10>Flap<25
1
Flap>25
0.5
0
-0.5
-1
-1.5
120
140
160
180
200
220
240
260
280
Coincident Airspeed (KIAS)
Figure 93: Entry, Drop, Exit V-n Diagram Comparing Flap Ranges – 2007 Data
84
The occurrences of the derived gust velocities for the Entry phase per nautical mile and
per 1000 hours are given in Figure 94 through Figure 97. The 2005 Data showed all gust
velocities in the lowest altitude band as slightly more frequent and severe. Increasing altitude
tended to show fewer occurrences but roughly the same severity. The highest altitude band
exhibited the fewest occurrences particularly at higher gust velocities. There was also a slight
increase in severity toward positive derived gust velocities in comparison to negative ones.
The 2007 Data again did not show this same trend. There were very few occurrences in
the lowest altitude band and the remaining three altitude bands exhibited roughly the same
frequency and magnitude. As was found with the Cruise phases, the 2007 Entry phase also
showed significantly lower gust velocities and lower occurrences per nautical mile than the 2005
Data as a result of the consistently lower airspeed in the 2005 Data.
It is worth noting that the Entry phase was one of the shortest flight phases separated so
some trends may be due to the small sample size of analyzed flights as opposed to a reflection of
the aerial firefighting environment.
85
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 94: Entry Derived Gust Velocity Occurrences per Nautical Mile – 2005 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 95: Entry Derived Gust Velocity Occurrences per 1000 Hours – 2005 Data
86
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 96: Entry Derived Gust Velocity Occurrences per Nautical Mile – 2007 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 97: Entry Derived Gust Velocity Occurrences per 1000 Hours – 2007 Data
87
The occurrences of the derived gust velocities for the Drop phase per nautical mile and
per 1000 hours are given in Figure 98 through Figure 101. The 2005 Data showed the gust
velocities in the lowest altitude band were much more frequent and severe. There was a clear
trend which showed that increasing altitude tended to exhibit fewer occurrences but similar
severity.
The 2007 Data again did not show this trend. There were very few occurrences in the
lowest altitude band and the remaining three altitude bands exhibited the same frequency and
magnitude. In the 2007 Data there were simply too few occurrences of the loads in the 18 data
files used for this analysis to establish any meaningful trends
It is worth noting that the Drop phase was the shortest flight phase separated so some
trends may be due to the small sample size of analyzed flights as opposed to a reflection of the
aerial firefighting environment. This is particularly evident in the highest altitude band of the
2005 Data in which a single high negative gust velocity recording has pressed the entire
distribution higher in occurrences than it may actually be.
88
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 98: Drop Derived Gust Velocity Occurrences per Nautical Mile – 2005 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 99: Drop Derived Gust Velocity Occurrences per 1000 Hours – 2005 Data
89
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 100: Drop Derived Gust Velocity Occurrences per Nautical Mile – 2007 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 101: Drop Derived Gust Velocity Occurrences per 1000 Hours – 2007 Data
90
The derived gust velocity occurrences for the Exit phase are included in Figure 102
through Figure 105. The 2005 gust velocities in the lowest altitude band were much more
frequent and severe than similar gusts at higher altitudes. Increasing altitude tended to exhibit
fewer occurrences and slightly less severity. The lowest altitude band also showed a slight
increase in severity toward positive derived gust velocities in comparison to negative ones.
The 2007 Data included no occurrences in the lowest altitude band and the remaining
three bands exhibited the same frequency and magnitude. As was found with the Entry and Drop
phases, the 2007 Exit phase also showed significantly lower gust velocities and lower
occurrences per nautical mile than the 2005 Data as a result of the consistently lower airspeed
recorded in the 2005 Data.
It is again worth noting that the Exit phase was one of the shorter flight phases so some
trends may reflect the small sample size as opposed to a result of the aerial firefighting
environment. The derived gust velocities during the Drop, and Exit phases were slightly higher
than those during the Entry phase. This trend was evident in both the 2005 and the 2007 Data.
The maximum magnitudes of each phase varied by a small amount but the differences were not
enough to identify a clear trend of severity between the Entry, Drop, or Exit phases. The Drop
derived gust velocities appeared more severe in the lowest altitude band, but this could be an
artifact of small sample size which seems apparent above +20ft/s in Figure 98.
91
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 102: Exit Derived Gust Velocity Occurrences per Nautical Mile – 2005 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 103: Exit Derived Gust Velocity Occurrences per 1000 Hours – 2005 Data
92
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 104: Exit Derived Gust Velocity Occurrences per Nautical Mile – 2007 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-60
-40
-20
0
20
40
60
Derived Gust Velocity (ft/s)
Figure 105: Exit Derived Gust Velocity Occurrences per 1000 Hours – 2007 Data
93
The occurrences of the continuous gust velocities for the Entry phase per nautical mile
and per 1000 hours are given in Figure 106 through Figure 109. The 2005 Data showed all gust
velocities in the lowest altitude band as slightly more frequent and severe. Increasing altitude
tended to show fewer occurrences but the same severity. The highest altitude band exhibited the
fewest occurrences particularly at higher gust velocities. There was also a slight increase in
severity toward positive continuous gust velocities for the lowest altitude band, but the other
three bands were balanced nearly equally.
The 2007 Data again did not show this same trend. There were very few occurrences in
the lowest altitude band which were counted roughly equally with the other three bands. The
remaining three altitude bands exhibited roughly the same frequency and magnitude. Again, the
2007 Entry phase showed significantly lower gust velocities and lower occurrences per nautical
mile than the 2005 Data as a result of the consistently lower airspeed in the 2005 Data.
The reader is reminded that the Entry phase was one of the shortest flight phases
separated. Consequently, some trends may be due to the small sample size of analyzed flights as
opposed to a reflection of the aerial firefighting environment.
94
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 106: Entry Continuous Gust Velocity Occurrences per Nautical Mile – 2005 Data
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 107: Entry Continuous Gust Velocity Occurrences per 1000 Hours – 2005 Data
95
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 108: Entry Continuous Gust Velocity Occurrences per Nautical Mile – 2007 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 109: Entry Continuous Gust Velocity Occurrences per 1000 Hours – 2007 Data
96
The occurrences of the continuous gust velocities for the Drop phase per nautical mile
and per 1000 hours are given in Figure 110 through Figure 113. The 2005 Data showed the gust
velocities in the lowest altitude band were much more frequent and severe. This trend was more
pronounced in the continuous gust velocities than in the derived gusts. There was a trend which
showed that increasing altitude tended to exhibit a lower frequency of gusts and slightly less
severity.
The 2007 Data again showed a different trend. There were very few occurrences in the
lowest altitude band and the remaining three altitude bands exhibited the same frequency and
magnitude. As was found with the Entry phases, the 2007 Drop phase also showed significantly
lower gust velocities and lower occurrences per nautical mile than the 2005 Data as a result of
the consistently lower airspeed in the 2005 Data.
The reader should be reminded that the Drop phase was the shortest flight phase
separated so some trends may be due to the small sample size of analyzed flights as opposed to a
reflection of the aerial firefighting environment. This is particularly evident in the highest and
lowest altitude bands of the 2005 Data in which a single high gust velocity recording has pressed
the entire distribution higher in occurrences than it may actually be.
97
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 110: Drop Continuous Gust Velocity Occurrences per Nautical Mile – 2005 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 111: Drop Continuous Gust Velocity Occurrences per 1000 Hours – 2005 Data
98
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 112: Drop Continuous Gust Velocity Occurrences per Nautical Mile – 2007 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 113: Drop Continuous Gust Velocity Occurrences per 1000 Hours – 2007 Data
99
The continuous gust velocity occurrences for the Exit phase per nautical mile and per
1000 hours are given in Figure 114 through Figure 117. The 2005 gust velocities in the lowest
altitude band were much more frequent and severe. Higher altitudes exhibited lower gust
frequency and slightly less severity. Positive gusts in the lowest altitude band were also slightly
more severe than negative gusts.
The 2007 Data again showed no occurrences in the lowest altitude band and the
remaining three bands exhibited the same frequency and magnitude. As was found with the
Entry and Drop phases, the 2007 Exit phase showed significantly lower gust velocities and lower
occurrences per nautical mile than the 2005 Data as a result of the consistently lower airspeed
recorded in the 2005 Data.
It is again worth noting that the Exit phases were very short, so some trends may be due
to the small sample size of analyzed flights as opposed to a reflection of the aerial firefighting
environment. The continuous gust velocities during the Drop, and Exit phases were slightly
higher than those during the Entry phase. This trend was evident in both the 2005 and the 2007
Data. The maximum magnitudes of each phase varied by a small amount but the differences
were not enough to identify a clear trend of severity between the Entry, Drop, or Exit phases.
100
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 114: Exit Continuous Gust Velocity Occurrences per Nautical Mile – 2005 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 115: Exit Continuous Gust Velocity Occurrences per 1000 Hours – 2005 Data
101
1.E+02
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+01
Above 5000ft
1.E+00
1.E-01
1.E-02
1.E-03
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 116: Exit Continuous Gust Velocity Occurrences per Nautical Mile – 2007 Data
1.E+07
0-1000ft
Cumulative Occurrences
1001-2000ft
2001-5000ft
1.E+06
Above 5000ft
1.E+05
1.E+04
1.E+03
1.E+02
-120
-80
-40
0
40
80
120
Continuous Gust Velocity (ft/s)
Figure 117: Exit Continuous Gust Velocity Occurrences per 1000 Hours – 2007 Data
102
G. Comparison with Gust and Maneuver Load Standards
Lastly, the flight data was compared to the appropriate standards for gusts and maneuvers
used in Ref. [23] to determine what part of the loads environment may be outside the original
design or standard ranges. The plots of the gust and maneuver comparisons are given in Figure
118 through Figure 121. Two design gust ranges are included: “Gust 5k” which describes the
expected gust loads for design ranging between 0 and 5,000 ft AGL and Gust 10k which
similarly provides design gust loads between 5,000 and 10,000 ft AGL. [23] The Mil-8866 Navy
Maneuver specification [23] depicting expected usage of a P-2V aircraft in conventional military
flight is also included.
Both the gust and maneuver comparisons showed higher frequency of the lower strength
accelerations than were expected from design standards or from the military maneuver
specification. This result was very similar to those found in Reference [23] where the authors
pointed out, however, that in fatigue analysis loads below a known damage threshold are
typically removed and they cautioned that the lower amplitude loads, “may turn out to be
inconsequential.”
The Cruise and Entry gust loads above approximately ±0.33g were within the expected
design gust loads. The Entry maneuver loads below approximately ±0.70g, however, were
outside the expected Mil-8866 maneuver loads while Cruise maneuver loads were less severe
(within the expected frequency at ±0.33g). The Drop and Exit loads were consistently more
common and more severe than both the design gust loads and the Mil-8866 loads. Again, this
could be a result of the low sample size as the occurrences are particularly erratic for these
shorter phases. There were no significant differences between the 2005 and 2007 Data with
respect to the design gust loads or the Mil-8866 loads.
103
Most loads which were within the design gust data were very near the predicted limit. If
the high cycle (low magnitude) loads are within the no-damage threshold for fatigue analysis, the
higher magnitude loads are approaching the limits of expected frequency. Furthermore, the
motivation behind this study being the early fatigue of firefighting aircraft, it is expected that the
higher cycle loads exceed the no-damage threshold. These results support the initial assertion
that these aircraft are operated in environments different from those for which they were
designed.
Therefore, maintenance schedules developed for their naval role may not be
applicable for their operation as firefighters.
Again, the reader is cautioned that these results were based on examination of a very
limited number of flights. However, they indicate the need for a far more comprehensive
investigation of their operations and flight environment.
104
1.E+07
Gust 5k
Gust 10k
Cruise-1
Entry
Drop
Exit
Cruise-2
Occurrences per 1000 hours
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
1.E+00
-3
-2
-1
0
1
Incremental nz
2
3
Figure 118: Design Gust Loads Comparison – 2005 Data
1.E+07
Mil 8866
Cruise-1
Occurrences per 1000 hours
1.E+06
Entry
Drop
1.E+05
Exit
Cruise-2
1.E+04
1.E+03
1.E+02
1.E+01
1.E+00
-3
-2
-1
0
1
Incremental nz
2
3
Figure 119: Mil-8866 Maneuver Loads Comparison – 2005 Data
105
1.E+07
Gust 5k
Gust 10k
Cruise-1
Entry
Drop
Exit
Cruise-2
Occurrences per 1000 hours
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
1.E+01
1.E+00
-3
-2
-1
0
1
Incremental nz
2
3
Figure 120: Design Gust Loads Comparison – 2007 Data
1.E+07
Mil 8866
Cruise-1
Occurrences per 1000 hours
1.E+06
Entry
Drop
1.E+05
Exit
Cruise-2
1.E+04
1.E+03
1.E+02
1.E+01
1.E+00
-3
-2
-1
0
1
Incremental nz
2
3
Figure 121: Mil-8866 Maneuver Loads Comparison – 2007 Data
106
IV. SUMMARY
An exploratory analysis was performed on 38 flights of the P-2V aircraft operating in the
firefighting role. The flights considered consisted of 20 from the 2005 and 18 from the 2007 fire
seasons. They contained 17.04 and 18.90 hours of flight data respectively. Each flight was
divided into seven phases which were analyzed separately. Emphasis was placed on the loads
and the atmospheric turbulence experienced by these aircraft, while some aircraft usage data was
also examined.
Aircraft loads, in terms of coincident altitudes and airspeeds, as well as maximum loads
and V-n diagrams were examined for each phase. Flight loads for each phase were separated
into gusts and maneuvers using the “Two-Second Rule” and were presented on a per 1000 hours
basis as well as per nautical mile. Atmospheric gust velocities (less than two seconds in length)
for each phase were also presented per 1000 hours and per nautical mile. The 2005 distances,
however, were inaccurate as they were based on integrating a lower-than-normal true airspeed.
Lastly, the resultant gust and maneuver flight loads were compared with standard design
gust loads and Mil-8866 maneuver loads to determine what parts of the flight regime, if any,
were outside the expected range.
107
V. CONCLUSIONS
A number of general trends were observed when comparing the phases before and after
the release of retardant. It was shown that the release of retardant weight had a noticeable effect
on the flight characteristics of the aircraft and its response to atmospheric turbulence in the form
of normal accelerations. This was proven to be the case by showing the levels of atmospheric
turbulence to be the same before and after the drop, as would be expected.
The first noticeable effect of the weight loss was found in the vertical load factors. The
decrease in weight between Taxi-1 and Taxi-2 increased the frequency of all loads as well as
their severity. A similar effect was noticed between Cruise-1 and Cruise-2. The Entry, Drop,
and Exit phases had significant scatter due to their short durations so the effect of weight loss
could not be clearly separated. Maneuver loads during the Drop phase remained the highest in
both sets of data. However, a significant part of the increased load is believed to be due to the
change of mass during the Drop phase and not due to maneuvering of the aircraft as is commonly
believed to be.
The roll accelerations also exhibited a general trend before and after the Drop. Roll
accelerations during Cruise-1 (with retardant) were as much as 100 times more frequent and
twice as severe as those in Cruise-2 (without retardant). Roll accelerations during the Taxi
phases showed a similar trend with weight. This trend, however, defied expectations of higher
roll accelerations at lower weight much the same way the same gust velocity at a lower wing
loading causes a higher vertical load. This investigation did not lead to any obvious explanation
for this behavior. The lower roll accelerations of the Entry and Exit phases were very similar
which suggested the weight loss during the Drop phase had little effect on low-magnitude roll
accelerations immediately before and after the release of retardant. The Entry phase did not
108
exhibit the same frequency of higher roll accelerations as Cruise-1 which suggested that the
phenomenon was specifically connected to the cruise condition as opposed to being strictly a
result of weight.
The derived and continuous gust velocities did not show any remarkable difference
before and after the release of retardant with the exception of Cruise-2 in the 2007 Data. There,
the derived and continuous gust velocities showed increases in frequency and severity beyond
about ±10 ft/s. The results suggested that the atmospheric turbulence was largely the same
before and after the drop with a trend of lower severity at higher altitudes (subtly present in the
2007 Data but more exaggerated in the 2005 Data).
The Drop phase showed the most
pronounced altitude effect, but also suffered the most scatter from the short duration of this
phase.
Comparisons with the military standards for gust and maneuver loads showed that lowermagnitude accelerations were as much as 10 times more frequent. These excessively frequent
loads were well below an incremental vertical load factor of 1g and so do not appear to pose a
threat to exceeding the limit load factor for the airframe, but it could lead to a lower than
expected fatigue life for the aircraft.
109
VI. RECOMMENDATIONS
A number of limitations prevented further analysis of the data which was left for future
research. Given additional recorded parameters such as bank angle and pitch angle, more
sophisticated gust and maneuver separation methods could be used to better understand whether
flight loads are due to either piloted maneuvers, atmospheric turbulence, or mass change during
the Drop Phase. Perhaps the greatest room for improvement is in the calculation and analysis of
gust velocities. The AGL altitude was based on the runway altitude as opposed to an in-flight
measurement which could refine both the calculation of gust velocities and their separation into
altitude bands. The gust velocities were also approximated based on a simplified weight. A
more sophisticated weight estimate is expected in future data sets.
Many flights showed multiple Drop phases while others showed a phase similar to a
drop, but without releasing retardant which is referred to as a “dry run.” It is possible that higher
loads than those encountered in a single-drop case are experienced during a “dry run.” Also,
initially the P-2V data was part of a library containing data from DC-7 and P-3 tanker aircraft,
but only the P-2V data was without significant errors. Analyzing multiple aircraft should result
in a more comprehensive description of the flight loads and operational environment.
A further refinement of the results shown here could be obtained from examination of
many more flights. For aircraft in civil operation, the number of flight hours resulting in reliable
statistical characterization of their operation is believed to be around 10,000 hours. The present
results and conclusions are based no fewer than 50 hours of flight time.
It is also important to recall why the flight loads analysis of heavy air tankers is needed.
The tanker aircraft operated by USFS contractors are subjected to severe fatigue which is a result
of the similarly unique aircraft usage. The combination of higher gust velocities at low altitudes
110
through which these aircraft spend roughly 70-75% of their time in cruise and the high vertical
accelerations while maneuvering around the drop uniquely fatigues the airframe. Although the
analysis of the strains and resulting stresses was not included as part of this thesis, tables of basic
strain statistics for the aircraft are given in the Appendix. Because the flight loads alone do not
fully characterize the aircraft’s mission, future analysis on the firefighting environment should
compare the strain on the aircraft during different phases to more accurately locate the most
damaging flight conditions. Identifying such conditions will make it possible for the US Forest
Service and the aerial firefighting industry to continue safely operating tanker aircraft in
preventing the spread of forest fires.
111
REFERENCES
112
LIST OF REFERENCES
[1]
Jewel Jr., Joseph W., Morris, Garland J., Avery, Donald E. “Operating Experiences of
Retardant Bombers During Firefighting Operations,” NASA, NASA TM X-72622, Nov.
1974
[2]
Veillette, Patrick R., “Crew Error Cited as Major Cause of U.S. Aerial Firefighting
Accidents,” Flight Safety Digest, Vol. 18 No. 4, Apr. 1999, pp. 1-19
[3]
Consortium For Aerial Firefighting Evolution, “Strategic Aerial Firefighting Excellence,”
Mar. 2004, http://www.avweb.com/other/STRATEGIC_AERIAL_FIREFIGHTI.pdf
[4]
Flomenhoft, Hubert I., “Brief History of Gust Models for Aircraft Design,” AIAA Journal
of Aircraft, Vol. 31 No. 5, Nov. 1993, pp. 1225-1227
[5]
Taylor, Paul F., Hanson, Laurence C., Barnes, Terence J., “A Brief History of Aircraft
Loads Analysis Methods,” AIAA 44th Structures, Structural Dynamics, and Materials
Conference, AIAA-2003-1892, Apr. 2003
[6]
Rustenburg, John W., Skinn, Donald A., Tipps, Daniel O., “Statistical Loads Data for
Boeing 737-400 Aircraft in Commercial Operations,” Federal Aviation Administration,
DOT/FAA/AR-98/28, Aug. 1998
[7]
Rustenburg, John W., Skinn, Donald A., Tipps, Daniel O., “Statistical Loads Data for
MD-82/83 Aircraft in Commercial Operations,” Federal Aviation Administration,
DOT/FAA/AR-98/65, Feb. 1999
[8]
Rustenburg, John W., Skinn, Donald A., Tipps, Daniel O., Zeiler, Thomas A., “Statistical
Loads Data for BE-1900D Aircraft in Commuter Operations,” Federal Aviation
Administration, DOT/FAA/AR-00/11, Apr. 2000
[9]
Rokhsaz, K., Kliment, L. K., Bramlette, R. B., and DeFiroe, T., “Statistical Loads
Analysis of BE-1900D in Commuter Operation,” Federal Aviation Administration, Draft
Report DOT/FAA/AR-TBD, 2008
[10]
Rhode, R. V., and Lundquist, E. E., “Preliminary Study of Applied Load Factors in
Bumpy Air,” NACA TN-374, Apr. 1931
[11]
Rhode, R. V., “Gust Loads on Airplanes,” Journal of the Society of Automotive
Engineers, Vol. 40, No. 3, 1937, pp. 81-88
[12]
Donely, P., “Summary of Information Relating to Gust Loads on Airplanes,” NACA TR997, 1950
113
LIST OF REFERENCES (Continued)
[13]
Hoblit, Frederic M., Gust Loads on Aircraft: Concepts and Applications, AIAA
Education Series, AIAA, © 1988
[14]
Perry III, Boyd, Pototzky, Anthony S., Woods, Jessica A., “NASA Investigation of a
Claimed ‘Overlap’ Between Two Gust Response Analysis Methods,” AIAA Journal of
Aircraft, Vol. 27 No. 7, Jul. 1990, pp.605-611
[15]
DeFiore, Thomas, Jones, Todd, Rustenburg, John W., Skinn, Donald A., Tipps, Daniel
O., “Statistical Data for the Boeing 747-400 Aircraft in Commerical Operations,” Federal
Aviation Administration, DOT/FAA/AR-04/44, Jan. 2005
[16]
Suter, Ann, “Drop Testing Airtankers: A Discussion of the Cup and Grid Method,”
USDA Forest Service Technology & Development Program, 0057-2868-MTDC, Dec.
2000
[17]
Hall, Stephen R., “Consolidation and Analysis of Loading Data in Firefighting
Operations. Analysis of Existing Data and Definition of Preliminary Air Tanker and Lead
Aircraft Spectra,” Federal Aviation Administration, DOT/FAA/AR-05/35, Oct. 2005
[18]
Burd, James, “Lockheed P2V: P2V-5/-7 Aerial Dispersion With 2005-2006 Tanker Data
Fatigue and Damage Tolerance Report,” Avenger Aircraft and Services, LLC., AASSSR-06-071, Dec. 2006
[19]
Martin, Michael, Kern, Tony, “Interagency Airtanker Base Operations Guide,” Aviation
Management Council, PMS 444-3, May 2003, pp. 165 & 167
[20]
Raybould, S., Johnson, C.W., Alter, D.L., Palm, Sig, George, Charles W., “Lot
Acceptance, Quality Assurance, and Field Quality Control for Fire Retardant Chemicals,”
USDA Forest Service, National Interagency Fire Center, PMS 444-1, Apr. 1995
[21]
Miner, J., “ADAPT Phase 1 System Specification,” Celeris Aerospace Canada Inc.,
CAC/TR/04-010, Sep. 2003
[22]
DeFiore, Thomas, Rustenburg, John W., Skinn, Donald A., Tipps, Daniel O., “An
Evaluation of Methods to Separate Maneuver and Gust Load Factors From Measured
Acceleration Time Histories,” Federal Aviation Administration, DOT/FAA/AR-099/14,
Apr. 1999
[23]
Burd, James, Pritchard, Michelle, Riccio, Ted, “Lockheed P2V: P2V-5/-7 Aerial
Dispersion Mission Configuration, Usage and Load History for Fatigue Loads,” Avenger
Aircraft and Services, LLC., AAS-SSR-05-023, Dec. 2006
114
APPENDICES
115
APPENDIX A. Taxi Strain Statistics
Table 13: Taxi-1 Strain Ranges (με)
Strain #
1
2
3
4
5
6
7
8
9
10
11
12
2005 Data
Maximum
Minimum
197.06
-615.07
638.95
-176.16
77.63
-143.32
68.67
-206.02
113.46
-767.34
895.73
-77.63
561.32
-77.63
1131.60
-128.39
279.55
-110.66
1991.80
-262.08
320.32
-273.73
247.82
-1197.29
2007 Data
Maximum
Minimum
185.12
-2194.53
689.71
-206.02
74.64
-140.33
83.6
-226.92
128.39
-776.30
534.45
-59.72
501.61
-77.63
1107.72
152.27
1112.38
203.84
564.92
-949.31
139.78
-372.73
259.76
-1110.70
Table 14: Taxi-2 Strain Ranges (με)
Strain #
1
2
3
4
5
6
7
8
9
10
11
12
2005 Data
Maximum
Minimum
322.46
-337.39
361.28
-349.33
104.50
-247.82
155.26
-101.52
280.66
-403.08
585.21
-214.97
331.42
-188.10
952.46
-74.64
343.61
-93.18
2265.52
-390.21
227.13
-221.31
161.23
-1068.9
116
2007 Data
Maximum
Minimum
301.56
-432.94
504.59
-376.21
38.81
-325.45
188.10
-80.62
223.93
-418.01
370.23
-498.62
298.58
-188.10
952.46
-65.69
1059.96
-186.37
623.16
-69.89
139.78
-285.37
149.29
-1027.1
APPENDIX B. Cruise Strain Statistics
Table 15: Cruise-1 Strain Ranges (με)
Strain #
1
2
3
4
5
6
7
8
9
10
11
12
2005 Data
Maximum
Minimum
-149.29
-904.69
1015.16
220.95
125.40
-188.10
253.79
-307.53
-385.16
-1140.56
1322.69
355.31
797.20
211.99
1746.67
507.58
326.14
110.66
2218.93
669.76
390.21
-40.77
-564.31
-1758.61
2007 Data
Maximum
Minimum
20.90
-1442.12
1239.09
-50.76
38.81
-295.59
286.63
-334.41
-98.53
-1286.86
898.71
29.86
821.08
14.93
2030.32
62.70
931.83
-366.91
751.29
157.25
221.31
-384.38
-77.63
-2006.43
Table 16: Cruise-2 Strain Ranges (με)
Strain #
1
2
3
4
5
6
7
8
9
10
11
12
2005 Data
Maximum
Minimum
232.89
-647.91
603.12
-140.33
62.17
-328.43
209.00
-316.49
59.72
-671.80
874.83
-65.69
525.49
5.97
1361.51
83.60
396.03
-69.89
2486.83
553.28
267.9
-81.54
-110.47
-1406.29
117
2007 Data
Maximum
Minimum
170.19
-859.90
856.91
-203.03
2.99
-394.12
313.50
-226.92
167.20
-767.34
644.92
-262.75
731.51
-86.59
1528.71
11.94
1100.73
-267.90
658.11
139.78
180.54
-512.51
-104.5
-1540.65
APPENDIX C. Entry, Drop, and Exit Strain Statistics
Table 17: Entry Strain Ranges (με)
Strain #
1
2
3
4
5
6
7
8
9
10
11
12
2005 Data
Maximum
Minimum
-119.43
-952.46
1077.86
134.36
47.77
-373.32
271.70
-262.75
-179.15
-1125.63
1394.35
304.55
773.31
50.76
1716.81
495.64
465.92
151.42
2830.45
902.71
500.86
-58.24
-582.22
-1680.98
2007 Data
Maximum
Minimum
-107.49
-1048.00
1206.25
107.49
-17.91
-295.59
307.53
-283.65
-131.37
-1125.63
818.10
5.97
755.40
17.91
1824.30
513.55
931.83
-337.79
1077.43
366.91
168.89
-396.03
-576.25
-1818.33
Table 18: Drop Strain Ranges (με)
Strain #
1
2
3
4
5
6
7
8
9
10
11
12
2005 Data
Maximum
Minimum
83.60
-689.71
752.41
-80.62
-50.76
-468.76
167.20
-238.86
59.72
-737.48
1134.59
128.39
549.38
38.81
1376.44
358.29
430.97
180.54
2824.62
693.05
454.27
-64.06
-423.98
-1370.46
118
2007 Data
Maximum
Minimum
23.89
-791.23
907.67
-26.87
-56.73
-313.50
226.92
-295.59
-68.67
-749.43
698.67
-14.93
609.09
74.64
1633.21
379.19
926.01
-244.61
757.12
343.61
116.48
-273.73
-465.78
-1489.89
APPENDIX C. Entry, Drop, and Exit Strain Statistics (Continued)
Table 19: Exit Strain Ranges (με)
Strain #
1
2
3
4
5
6
7
8
9
10
11
12
2005 Data
Maximum
Minimum
83.60
-546.39
525.49
-32.84
5.97
-492.65
200.05
-214.97
35.83
-653.88
833.03
134.36
504.59
29.86
1239.09
364.26
425.15
110.66
2230.58
762.94
372.73
-58.24
-465.78
-1298.81
119
2007 Data
Maximum
Minimum
53.74
-782.27
847.96
2.99
-20.90
-313.50
238.86
-352.32
-134.36
-716.58
585.21
-53.74
627.01
89.57
1573.50
176.16
960.95
-238.78
599.87
139.78
209.66
-326.14
-364.26
-1522.74
APPENDIX D. Analyzed Flight Files
Data Set
2005
2007
#
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
File Name
ADAPT_000107_20050711_1226_Flt_0005.txt
ADAPT_000107_20050711_1226_Flt_0006.txt
ADAPT_000107_20050711_1235_Flt_0004.txt
ADAPT_000107_20050711_1235_Flt_0013.txt
ADAPT_000107_20050712_1444_Flt_0005.txt
ADAPT_000107_20050712_1444_Flt_0006.txt
ADAPT_000107_20050726_1415_Flt_0004.txt
ADAPT_000107_20050726_1415_Flt_0007.txt
ADAPT_000107_20050728_0836_Flt_0002.txt
ADAPT_000107_20050728_0836_Flt_0003.txt
ADAPT_000107_20050728_0839_Flt_0001.txt
ADAPT_000107_20050728_0839_Flt_0007.txt
ADAPT_000107_20050728_0839_Flt_0011.txt
ADAPT_000107_20050801_1429_Flt_0005.txt
ADAPT_000107_20050804_1353_Flt_0002.txt
ADAPT_000107_20050811_1211_Flt_0005.txt
ADAPT_000107_20050816_1331_Flt_0002.txt
ADAPT_000107_20050907_1401_Flt_0003.txt
ADAPT_000107_20051219_1220_Flt_0006.txt
ADAPT_000107_20051219_1222_Flt_0001.txt
0001_20070903_1913.txt
0003_20070809_0109.txt
0003_20071023_1936.txt
0005_20071023_2141.txt
0006_20070625_2207.txt
0006_20071023_2239.txt
0011_20070811_2135.txt
0014_20070629_1649.txt
0014_20070813_1919.txt
0016_20070629_1919.txt
0016_20070714_1912.txt
0016_20070813_2235.txt
0018_20070714_2108.txt
0019_20070914_2242.txt
0020_20070630_2030.txt
0021_20070915_1711.txt
0025_20070717_1957.txt
0026_20070718_2032.txt
0028_20070622_2321.txt
0038_20071001_1837.txt
120
Comments
Removed
Removed