OPERATIONAL USAGE AND FLIGHT LOADS STUDY OF GLOBAL EXPRESS XRS BUSINESS JET. A Thesis by. Alhambra L. Yee

Transcription

1 OPERATIONAL USAGE AND FLIGHT LOADS STUDY OF GLOBAL EXPRESS BUSINESS JET A Thesis by Alhambra L. Yee Bachelor of Science, Boston University, 2006 Submitted to the Department of Aerospace Engineering and the faculty of the Graduate School of Wichita State University in the partial fulfillment of the requirements for the degree of Master of Science May 2012

2 Copyright 2012 by Alhambra L. Yee All Rights Reserved

3 OPERATIONAL USAGE AND FLIGHT LOADS STUDY OF GLOBAL EXPRESS BUSINESS JET The following faculty members 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 Linda Kliment, Committee Member Alan Elcrat, Committee Member iii

4 DEDICATION To my family and friends, especially my mother. If not for the premium she placed on education and commitment to sacrifice and deferment, none of my academic endeavors would have been ensured To those seeking knowledge hopefully for the betterment of something iv

5 ACKNOWLEDGEMENTS A frank teaching fellow once told me acknowledgements were not necessary, that the development and progression of the individual was the primary goal. I have to disagree. I would like to thank my committee members, Dr. Rokhsaz, Dr. Kliment, and Dr. Elcrat for their time and advice. Dr. Rokhsaz and Dr. Kliment s weekly meetings, drop in open door policy, and non belief in hesitating to help has been invaluable in my completion of this project. To say that Dr. Rokhsaz has been with me every step of the way would be an understatement; he has always been a couple steps ahead. In my frank opinion the figurative pedestal has always been well placed. I would like to thank Jim D Ottavi from the FAA for preparing the data for download. I would also like to thank the FAA for funding this research. v

6 ABSTRACT Operational usage analysis and flight loads analysis is performed on one Global Express business jet. A total of 388 useful flights with 1053 hours and 454,254 nm are analyzed. Usage analysis performed during airborne is separated into seven flight phases with information presented for maximum altitude, flight duration, flight distance, indicated airspeed, pitch, bank, and rate of climb. For a majority of the time the is flown within operational limits. The rare occurrence of exceeding operational limits is shown to occur during initial approach, one of the shortest flight segments. Loads analysis is performed for both ground and air operations. Ground operations are separated into five phases with longitudinal, lateral, and incremental vertical load analysis normalized per 1000 flights for these segments. Landing roll is shown to have the most frequent and severe loads for ground phases. Airborne operations are separated into seven flight phases and incremental vertical accelerations are separated into maneuver and gusts using the two second rule. Incremental vertical acceleration is further categorized into discrete and continuous gust velocities normalized per 1000 hours and per nautical mile. Gust velocities are altitude dependent and shown to be more severe and occur more frequently at low altitudes. Continuous turbulence field parameters are derived from continuous gust velocities from cruise and compared to FAR 25 results in the form of generalized exceedance plots. Most of the exceedance curves are shown to lie significantly below those from FAR 25. Data collected from this study can help establish operational and design standards for larger business jets. The statistical data created will help enable the FAA, the manufacturer, and the operator to better understand those factors that influence the structural integrity of these aircraft. vi

7 TABLE OF CONTENTS Chapter Page I. INTRODUCTION...1 A. Background... 1 B. Thesis Structure... 3 II. METHOD OF ANALYSIS...4 A. Aircraft Analyzed... 4 B. Recorded Flight Data... 4 C. Reduction of Raw Data... 6 D. Data Processing Pressure Altitude Averaging Normalizing Acceleration Identification of Liftoff and Touchdown Standard Atmosphere Calculation of True Airspeed, V t Flight Distance Atmospheric Turbulence Discrete Gust Continuous Gust Data Reduction Flight Phase Separation Flight Loads Counting Determination of Atmospheric Turbulence Parameters, P s and b s III. RESULTS AND DISCUSSION AIRCRAFT USAGE...23 A. Available Data B. Overall Usage C. Phase-Specific Usage Departure Climb Cruise Descent Approach Phases Liftoff and Touchdown V-n Diagrams IV. RESULTS AND DISCUSSION AIRCRAFT LOADS...62 A. Ground Loads Taxi In and Taxi Out Takeoff and Landing Rolls Runway Turnoff B. Airborne Loads vii

8 TABLE OF CONTENTS (continued) Chapter Page 1. Departure Climb Cruise Descent Approach Phases C. Atmospheric Turbulence Parameters V. CONCLUSION 106 REFERENCES APPENDICES.111 A. Ground Phase Loads Investigation with Emphasis on Lateral Acceleration 112 B. Extrapolation of 2N 0 From Continuous Gust Velocity. 139 viii

9 LIST OF TABLES Table Page 1. Global Express Aircraft Specifications Parameters Extracted from 128-Channel Flight Data Derived Parameters from Raw Data Local Atmosphere Values Pressure Altitude Bands Flight Phase Separation Criteria Dead Band Limit Breakdown of Files Summary of Available Information and Some Results Minimum and Maximum Values for Pitch and Bank Angles and Rate of Climb Departure Minimum and Maximum Values for Pitch and Bank Angles and Rate of Climb Climb Minimum and Maximum Values for Pitch and Bank Cruise Minimum and Maximum Values for Pitch, Bank, Rate of Climb Descent Minimum and Maximum Values for Pitch, Bank, Rate of Climb Initial Approach Minimum and Maximum Values for Pitch, Bank, Rate of Climb Middle Approach Minimum and Maximum Values for Pitch, Bank, Rate of Climb Final Approach Derived Continuous Turbulence Parameters Distances from Cruise Continuous Gust Velocities ix

10 LIST OF FIGURES Figure Page 1. Excerpt from CSV File Excerpt from Fixed-Width Flight File Diagram of Flight Phases Sample Flight Time History Peaks-Between-Means Loads Counting Sample of Generalized Exceedance Graph Zero Intercept Extrapolation Correlation of Maximum Altitude and Flight Distance All Phases Correlation of Maximum Altitude and Flight Duration All Phases Coincident Altitude and Maximum Indicated Airspeed All Phases Maximum Altitude at Coincident Indicated Airspeed All Phases Coincident Altitude at Maximum Indicated Airspeed Departure Maximum Altitude at Coincident Indicated Airspeed Departure Cumulative Probability of Maximum and Minimum Pitch Angle Departure Cumulative Probability of Maximum and Minimum Bank Angle Departure Cumulative Probability of Average Rate of Climb Departure Coincident Altitude at Maximum Indicated Airspeed Climb Maximum Altitude at Coincident Indicated Airspeed Climb Cumulative Probability of Maximum and Minimum Pitch Angle Climb Cumulative Probability of Maximum and Minimum Bank Angle Climb Cumulative Probability of Average Rate of Climb Climb x

11 LIST OF FIGURES (continued) Figure Page 22. Coincident Altitude at Maximum Indicated Airspeed Cruise Maximum Altitude at Coincident Indicated Airspeed Cruise Cumulative Probability of Maximum and Minimum Pitch Angle Cruise Cumulative Probability of Maximum and Minimum Bank Angle Cruise Coincident Altitude at Maximum Indicated Airspeed Descent Starting Altitude at Coincident Indicated Airspeed Descent Cumulative Probability of Maximum and Minimum Pitch Angle Descent Cumulative Probability of Maximum and Minimum Bank Angle Descent Cumulative Probability of Average Rate of Descent Descent Coincident Altitude at Maximum Indicated Airspeed Initial Approach Maximum Altitude at Coincident Indicated Airspeed Initial Approach Cumulative Probability of Maximum and Minimum Pitch Angle Initial Approach Cumulative Probability of Maximum and Minimum Bank Angle Initial Approach Cumulative Probability of Average Rate of Descent Initial Approach Coincident Altitude at Maximum Indicated Airspeed Middle Approach Maximum Altitude at Coincident Indicated Airspeed Middle Approach Cumulative Probability of Maximum and Minimum Pitch Angle Middle Approach Cumulative Probability of Maximum and Minimum Bank Angle Middle Approach Cumulative Probability of Average Rate of Descent Middle Approach Coincident Altitude at Maximum Indicated Airspeed Final Approach Starting Altitude at Coincident Indicated Airspeed Final Approach xi

12 LIST OF FIGURES (continued) Figure Page 43. Cumulative Probability of Maximum and Minimum Pitch Angle Final Approach Cumulative Probability of Maximum and Minimum Bank Angle Final Approach Cumulative Probability of Average Rate of Descent Final Approach Probability Distribution of Airspeed at Liftoff and Touchdown Cumulative Probability of Airspeed at Liftoff and Touchdown Probability Distribution of Pitch Angle at Liftoff and Touchdown Cumulative Probability of Pitch Angle at Liftoff and Touchdown V-n Diagram for Flaps Retracted V-n Diagram for the First Flap Detent V-n Diagram for the Second Flap Detent V-n Diagram for the Third Flap Detent Cumulative Occurrences of Lateral Load Factor per 1000 Flights Taxi Out and Taxi In Cumulative Occurrences of Longitudinal Load Factor per 1000 Flights Taxi Out and Taxi In Cumulative Occurrences of Incremental Vertical Load Factor per 1000 Flights Taxi Out and Taxi In Cumulative Occurrences of Lateral Load Factor per 1000 Flights Takeoff Roll and Landing Roll Cumulative Occurrences of Longitudinal Load Factor per 1000 Flights Takeoff Roll and Landing Roll Cumulative Occurrences of Incremental Vertical Load Factor per 1000 Flights Takeoff Roll and Landing Roll Cumulative Occurrences of Lateral Load Factor per 1000 Flights Runway Turnoff xii

13 LIST OF FIGURES (continued) Figure Page 61. Cumulative Occurrences of Longitudinal Load Factor per 1000 Flights Runway Turnoff Cumulative Occurrences of Incremental Vertical Load Factor per 1000 Flights Runway Turnoff Cumulative Occurrences of Incremental Vertical Gust Load Factor per 1000 Hours Departure Cumulative Occurrences of Incremental Vertical Gust Load Factor per Nautical Mile Departure Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per 1000 Hours Departure Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per Nautical Mile Departure Cumulative Occurrences of Incremental Vertical Gust Load Factor per 1000 Hours Climb Cumulative Occurrences of Incremental Vertical Gust Load Factor per Nautical Mile Climb Cumulative Occurrences of Incremental Maneuver Load Factor per 1000 Hours Climb Cumulative Occurrences of Incremental Maneuver Load Factor per Nautical Mile Climb Cumulative Occurrences of Derived Gust Velocity per 1000 Hours Climb Cumulative Occurrences of Derived Gust Velocity per Nautical Mile Climb Cumulative Occurrences of Continuous Gust Velocity per 1000 Hours Climb Cumulative Occurrences of Continuous Gust Velocity per Nautical Mile Climb Cumulative Occurrences of Incremental Vertical Gust Load Factor per 1000 Hours before Omission Cruise xiii

14 LIST OF FIGURES (continued) Figure Page 76. Cumulative Occurrences of Incremental Vertical Gust Load Factor per 1000 Hours after Omission Cruise Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per 1000 Hours before Omission Cruise Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per 1000 Hours after Omission Cruise Cumulative Occurrences of Incremental Vertical Gust Load Factor per 1000 Hours Cruise Cumulative Occurrences of Incremental Vertical Gust Load Factor per Nautical Mile Cruise Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per 1000 Hours Cruise Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per Nautical Mile Cruise Cumulative Occurrences of Derived Gust Velocity per 1000 Hours Cruise Cumulative Occurrences of Derived Gust Velocity per Nautical Mile Cruise Cumulative Occurrences of Continuous Gust Velocity per 1000 Hours Cruise Cumulative Occurrences of Continuous Gust Velocity per Nautical Mile Cruise Cumulative Occurrences of Incremental Vertical Gust Load Factor per 1000 Hours Descent Cumulative Occurrences of Incremental Vertical Gust Load Factor per Nautical Mile Descent Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per 1000 Hours Descent Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per Nautical Mile Descent xiv

15 LIST OF FIGURES (continued) Figure Page 91. Cumulative Occurrences of Derived Gust Velocity per 1000 Hours Descent Cumulative Occurrences of Derived Gust Velocity per Nautical Mile Descent Cumulative Occurrences of Continuous Gust Velocity per 1000 Hours Descent Cumulative Occurrences of Continuous Gust Intensity per Nautical Mile Descent Cumulative Occurrences of Incremental Vertical Gust Load Factor per 1000 Hours Initial Approach Cumulative Occurrences of Incremental Vertical Gust Load Factor per Nautical Mile Initial Approach Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per 1000 Hours Initial Approach Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per Nautical Mile Initial Approach Cumulative Occurrences of Incremental Vertical Gust Load Factor per 1000 Hours Middle Approach Cumulative Occurrences of Incremental Vertical Gust Load Factor per Nautical Mile Middle Approach Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per 1000 Hours Middle Approach Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per Nautical Mile Middle Approach Cumulative Occurrences of Incremental Vertical Gust Load Factor per 1000 Hours Final Approach Cumulative Occurrences of Incremental Vertical Gust Load Factor per Nautical Mile Final Approach Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per 1000 Hours Final Approach xv

16 LIST OF FIGURES (continued) Figure Page 106. Cumulative Occurrences of Incremental Vertical Maneuver Load Factor per Nautical Mile Final Approach Comparison of P s Derived and FAR Comparison of b s Derived and FAR Generalized Exceedance Graph for Altitude at 3000 ft Generalized Exceedance Graph for Altitude at 7000 ft Generalized Exceedance Graph for Altitude at ft Generalized Exceedance Graph for Altitude at ft Generalized Exceedance Graph for Altitude at ft Generalized Exceedance Graph for Altitude at ft Generalized Exceedance Graph for Altitude at ft Generalized Exceedance Graph for Altitude at ft Generalized Exceedance Graph for Altitude at ft Generalized Exceedance Graph for Altitude at ft Vertical Acceleration during Takeoff Roll 2_9_ Vertical Acceleration during Landing Roll 2_9_ Lateral Acceleration during Takeoff Roll 2_9_ Lateral Acceleration during Landing Roll 2_9_ Longitudinal Acceleration during Takeoff Roll 2_9_ Longitudinal Acceleration during Landing Roll 2_9_ Vertical Acceleration from Start of Landing Roll to End of Taxi In 2_9_ xvi

17 LIST OF FIGURES (continued) Figure Page 126. Lateral Acceleration from Start of Landing Roll to End of Taxi In 2_9_ Longitudinal Acceleration from Start of Landing Roll to End of Taxi In 2_9_ Vertical Acceleration during Takeoff Roll 7_7_ Vertical Acceleration during Landing Roll 7_7_ Lateral Acceleration during Takeoff Roll 7_7_ Lateral Acceleration during Landing Roll 7_7_ Longitudinal Acceleration during Takeoff Roll 7_7_ Longitudinal Acceleration during Landing Roll 7_7_ Vertical Acceleration from Start of Landing Roll to End of Taxi In 7_7_ Lateral Acceleration from Start of Landing Roll to End of Taxi In 7_7_ Longitudinal Acceleration from Start of Landing Roll to End of Taxi In - 7_7_ Vertical Acceleration during Takeoff Roll 2_9_ Vertical Acceleration during Landing Roll 2_9_ Lateral Acceleration during Takeoff Roll 2_9_ Lateral Acceleration during Landing Roll 2_9_ Longitudinal Acceleration during Takeoff Roll 2_9_ Longitudinal Acceleration during Landing Roll 2_9_ Vertical Acceleration from Start of Landing Roll to End of Taxi In 2_9_ Lateral Acceleration from Start of Landing Roll to End of Taxi In 2_9_ Longitudinal Acceleration from Start of Landing Roll to End of Taxi In 2_9_ Vertical Acceleration during Takeoff Roll 2_9_ xvii

18 LIST OF FIGURES (continued) Figure Page 147. Vertical Acceleration during Landing Roll 2_9_ Lateral Acceleration during Takeoff Roll 2_9_ Lateral Acceleration during Landing Roll 2_9_ Longitudinal Acceleration during Takeoff Roll 2_9_ Longitudinal Acceleration during Landing Roll 2_9_ Vertical Acceleration from Start of Landing Roll to End of Taxi In 2_9_ Lateral Acceleration from Start of Landing Roll to End of Taxi In 2_9_ Longitudinal Acceleration from Start of Landing Roll to End of Taxi In 2_9_ Vertical Acceleration during Takeoff Roll 2_9_ Vertical Acceleration during Landing Roll 2_9_ Lateral Acceleration during Takeoff Roll 2_9_ Lateral Acceleration during Landing Roll 2_9_ Longitudinal Acceleration during Takeoff Roll 2_9_ Longitudinal Acceleration during Landing Roll 2_9_ Vertical Acceleration from Start of Landing Roll to End of Taxi In 2_9_ Lateral Acceleration from Start of Landing Roll to End of Taxi In 2_9_ Longitudinal Acceleration from Start of Landing Roll to End of Taxi In 2_9_ N 0 Extrapolation for Altitude at 3000 ft N 0 Extrapolation for Altitude at 7000 ft N 0 Extrapolation for Altitude at ft N 0 Extrapolation for Altitude at ft xviii

19 LIST OF FIGURES (continued) Figure Page 168. N 0 Extrapolation for Altitude at ft N 0 Extrapolation for Altitude at ft N 0 Extrapolation for Altitude at ft N 0 Extrapolation for Altitude at ft N 0 Extrapolation for Altitude at ft N 0 Extrapolation for Altitude at ft xix

20 NOMENCLATURE A r A a a a w a wb a t b b 1,2 C c CL aspect ratio aircraft PSD gust response factor temperature lapse rate ( R/ft) local speed of sound (ft/s) wing lift-curve slope (per radian) wing-body lift-curve slope (per radian) tail lift-curve slope (per radian) wing span (ft) gust intensity parameters aircraft gust response factor wing mean geometric chord (ft) aircraft lift curve slope (per radian) D D total D turbulence F(PSD) distance (ft) total distance flown in altitude band (nm) distance flown while in turbulence (nm) continuous gust alleviation factor g gravity constant, ft/s 2 h h base h H K g L mean sea level (MSL) altitude (ft) reference altitude in standard atmosphere (ft) vertical distance from mac of tail to root chord of wing (ft) gust alleviation factor turbulence scale length, 2500 ft xx

21 l H M N N y N 0 longitudinal distance from mac of the tail to mac of the wing (ft) Mach number number of occurrences average number of peaks per distance or time exceeding a given level y average number of zero crossing per distance or time with positive slope N 0,1 contribution of non storm turbulence to N 0 N 0,2 contribution of storm turbulence to N 0 n z vertical load factor (g) P pressure (lb f /ft 2 ) P 0 total pressure (lb f /ft 2 ) P 1,2 proportion of total time or distance in turbulence P base reference pressure in standard atmosphere (lb f /ft 2 ) S wing planform area (ft 2 ) S t tail planform area (ft 2 ) t T T base U de U σ W V e V i V t time (seconds) temperature ( R) reference temperature in standard atmosphere ( R) derived gust velocity (ft/s) continuous turbulence gust velocity (ft/s) aircraft weight, lbs equivalent airspeed (ft/s) indicated airspeed (ft/s) true airspeed (ft/s) xxi

22 Greek Symbols β 2 Goethert similarity parameter = γ ratio of specific heats, 1.4 downwash gradient κ ratio of airfoil lift curve slope to 2π sweep angle where n is fraction of chord length μ g taper ratio, tip chord/root chord reduced mass parameter ρ air density (slugs/ft 3 ) ρ base reference air density in standard atmosphere (slugs/ft 3 ) ρ 0 sea level air density (slugs/ft 3 ), slugs/ft 3 Acronyms AGL AOA CSV FAA FDR MAC MSL QAR Above Ground Level Angle of Attack Comma-Separated Values Federal Aviation Administration Flight Data Recording Mean Aerodynamic Chord Mean Sea Level Quick Access Recorder Bombardier Global Express xxii

23 CHAPTER I I. INTRODUCTION A. Background An aircraft flying in steady level flight experiences a 1-g load factor, that is, the lift is equal to the weight of the aircraft. Increase in load factor, which leads to increased stress in structural components, can be attributed to controlled maneuvers or an aircraft s dynamic response to random gusts within the atmosphere. Chaotic random motion of wind in the atmosphere, or more formally known as atmospheric turbulence, arises mainly from wind shear and convection. Turbulence due to wind shear can be simply thought of as the interaction of wind with ground terrain, such as mountains, hills, trees, or buildings, and severe examples of turbulence due to convection are thunderstorms and cold fronts [1]. Aircraft structural design is required to take into account the natural random encounter of atmospheric turbulence [2]. Also, the fatigue life of the airframe depends on the frequency of occurrence of the loading and unloading of such cyclic loads. Of course the problem and concern for gust encounter did not elude the aerospace community, for after its inception NACA s first report was titled Report on Behavior of Aeroplane in Gusts followed by the publication of Theory of an Aeroplane Encountering Gusts, II in the subsequent year [3][4]. During the early 1930s, NACA started to equip testing aircraft with probes to measure gusts and these planes were also equipped with accelerometers and inertial platforms. These measurements allowed the calculation of true gust velocities once data from the probes were corrected for airplane motion. At the same time a larger fleet of routine transport aircraft equipped with just V-G recorders, which measured aircraft speed and 1

24 acceleration, were also used in the collection of data. Accelerations measured on routine transport missions were much easier and plentiful to attain. The discrete gust velocities derived from the measurement of accelerations are known as derived gust velocities. The discrete gust is modeled as a single occurrence of gust and the concept of a sharp edged gust was reported by Rhode [5]. The final (1-cos) gust representation with incorporation of the gust alleviation factor, Kg, which took into account the plunge degree of freedom and unsteady aerodynamics, was reported by Pratt and Walker [6]. The final discrete gust structure was incorporated into the Civil Air Regulations in 1956, the predecessor of the Federal Air Regulations [7]. Around the same time, the study of the power spectral methods on aircraft flight loads was performed [8]. Power spectral techniques utilize mathematics from generalized harmonic analysis to model the continuous random nature of atmospheric turbulence. Currently FAR 25 requires design loads based on derived gusts accompanied with an obligatory complement from power spectral techniques [9]. The University of Dayton Research Institute since 1995 has assisted the FAA in analyzing and presenting statistical loads data for various transport aircraft for airlines [10-12]. These aircraft are certified under FAR 25 and have a maximum takeoff-weight in excess of 100,000 lbs. However business jets span a spectrum of different aircraft and depending on design are certified under either FAR 23 [13] or FAR 25. A Cessna Citation Mustang with a maximum takeoff weight of around 8500 lbs is certified under FAR 23, while the Bombardier Global Express (), which is analyzed in this thesis, has a maximum takeoff weight of 92,500 lbs, is certified under FAR 25. Some business jets also fly shorter flights so the airframe is subjected to larger numbers of ground-air-ground cycles. In contrast, some are used for longrange mission flying with cruise legs as long as 6,000 miles at flight levels of little turbulence. 2

25 Another operational factor separating business jets and airlines is the common operating altitudes. Most airline operations are at flight levels below 30,000 ft, whereas many business jets can fly at slightly higher altitudes. The is certified to fly at up to 51,000 ft. Recorded normal accelerations at these flight levels can shed additional light on the nature and magnitude of atmospheric turbulence. Some of the data from airliners can be applied to establish operational and design standards for larger business jets. However, the large variations in type and nature of airline operations call for a separate analysis of business jets. Development of loads exceedance spectra, used for fail safe and safe life design and evaluations, from actual flight operations is critical. Furthermore, presenting the processed data in statistical formats will enable the FAA, the manufacturer, and the operator to better understand and control those factors that influence the structural integrity of these aircraft. B. Thesis Structure A summary of the flight recorder data files, analytical methods, and detailed data processing procedures are presented in Chapter 2. Statistical data related to flight usage information and the discussion of these results are presented in Chapter 3. Aircraft flight loads and continuous atmospheric turbulence parameters is presented and discussed in Chapter 4. Chapter 5 offers the conclusion of this work. 3

26 CHAPTER II II. METHOD OF ANALYSIS A. Aircraft Analyzed Flight data provided by the FAA for the was analyzed. General aircraft specifications are listed in Table 1. Table 1: Global Express Aircraft Specifications [14] Parameter 4 Magnitude and Unit Normal Cruising Speed 488 kts Maximum Take-Off Weight 98,000 lbs Maximum Landing Weight 78,600 lbs Zero-fuel Weight 56,000 lbs Length 99 ft 5 in Wingspan 94.0 ft Wing Aspect Ratio 8.6 Wing Area 1022 ft 2 Wing MAC* ft Derived quantity Bombardier produces three families of business aircraft. Listed from smallest to largest in terms of both size and passenger capacity they are the Learjet family, Challenger family, and Global family. The is a long-range business jet that can accommodate between 8-19 passengers. An important design feature was maximum range (6000 nm) at high speed (M = 0.85). B. Recorded Flight Data A Quick Access Recorder (QAR) was installed on one. Periodically, the operator would send the raw data to the FAA Technical Center, which would reduce it into Comma- Separated Values (CSV) file format and provide it to WSU. The QAR is an independent recording system that records the same data as the Flight Data Recording (FDR) system. A QAR

27 device at 128 channels can record 1500 hours of flight data as compared to 25 hours of flight data on an FDR device; thus reducing the frequency of downloads [15]. The QAR stored 128 channels of flight data. Vertical acceleration was recorded at a constant data rate of 8 Hz, but the rest of the channels sampled data at a lower rate, as indicated in Table 2. The parameters shown in this table are limited to those used for the present investigation. Table 2: Parameters Extracted from 128-Channel Flight Data Parameter Units Sample Rate (Hz) Time Seconds 8 Indicated Airspeed Knots 0.5 Pressure Altitude Feet 1 Total Temperature Celsius 0.5 Vertical Acceleration g 8 Longitudinal Acceleration g 4 Lateral Acceleration g 4 Heading degrees 1 Pitch degrees 4 Roll degrees 2 GPS Latitude degrees 1 GPS Longitude degrees 1 Left Angle of Attack degrees 1 Right Angle of Attack degrees 1 Flap Integer 1 Slat Integer 1 Weight on Wheel left Ground/Air 4 Weight on Wheel middle Ground/Air 4 Weight on Wheel right Ground/Air 4 Right Engine Fan Speed Percentage 1 Right Engine Core Speed Percentage 1 Left Engine Fan Speed Percentage 1 Left Engine Core Speed Percentage 1 5

28 C. Reduction of Raw Data Raw data in CSV format was stored on an FAA site from which large data sets could be downloaded. Within a data set, each flight file was separated by a blank line. Further examination revealed two problems; 1) between successive blank lines occasionally more than one flight file was found, and 2) in some cases a separated file contained no flight data (i.e. the aircraft never took-off). To deal with the case of multiple files within successive blank lines another separation criterion was implemented. When engine core and fan for both right and left sides all read 0 followed by an indicated airspeed greater than 30 knots, then those conditions would mark the start of a new flight file. Minimum reading for indicated airspeed was 30 knots, so a reading larger than 30 would indicate a take-off. Data downloaded on July 2010 resulted in 184 flight files. Additional data downloaded on February 2011 resulted in another 206 flight files for a total of 390 flight files. After the individual flight files were separated, the raw CSV file was generated. Each line of the CSV file was read then the extracted parameters were output to a fixed width file. Figure 1 shows an excerpt from the CSV file and Figure 2 shows an excerpt for a flight file. Parameters that were derived from raw data are shown in Table 3. Figure 1: Excerpt from CSV File 6

29 Figure 2: Excerpt from Fixed-Width Flight File Table 3: Derived Parameters from Raw Data Parameter Raw Format Processed Format Angle of Attack (AOA) (deg) Integer Flap Position Deflection (deg) Integer [0] 0 (0,6] 1 (6,16] 2 (16,30] 3 Slat Deflection (deg) Integer [0] Up (0,20] Down D. Data Processing 1. Pressure Altitude Averaging The inherent noise in the recorded pressure altitude did not allow a derivation for an instantaneous rate of climb for each line of data. Therefore a pressure altitude for each line of data was calculated using a 2 second running average. 2. Normalizing Acceleration Since the accelerometers registered a small reading while the aircraft was on the ground, lines 101 through 200 were averaged and used to determine the offset values for normalizing the acceleration readings. Vertical acceleration was normalized to 1.0 and longitudinal and lateral accelerations were normalized to

30 3. Identification of Liftoff and Touchdown Liftoff was identified when all three squat switches recorded an Air reading. Touchdown was identified when any squat switch recorded a Ground reading. 4. Standard Atmosphere The cruises at high altitudes, generally around ft. The aircraft is certified for flight at ft. Local atmospheric conditions of temperature, pressure and density were calculated using pressure altitude. Since there was no information on local pressure and temperature, standard atmospheric values corresponding to pressure altitude were assumed. The aircraft operates in both gradient and isothermal layers of the atmosphere. Table 4 shows the values for the variables used in Equations (1 6) to determine local pressure, temperature, and air density. Layer Geopotential Height ft Table 4: Local Atmosphere Values Lapse Rate, a R/ft T base R P base lb f /ft 2 ρ base slugs/ft 3 Gradient 0 h x x 10-3 Isothermal h N.A x 10-4 In the gradient layer, temperature varies linearly with altitude. Therefore the following relations hold: base base T T a h h (1) P T Pbase Tbase T base Tbase g ar g ar1 (2) (3) 8

31 In the isothermal layer, temperature does not vary with altitude. Therefore: T T base (4) g RT h h base (5) P P e base g RT h h base (6) base e 5. Calculation of True Airspeed, V t Indicated airspeed is given by the equation 1 P P V i 2 From the energy equation and isentropic relationship (7) P P M 2 1 (8) Solving Equation (8) for P 0 with the substitution M V a results in the equation below t 2 1V 1 0 P 1 t 2 P 2 a (9) Inserting Equation (9) into Equation (7) and factoring produces 2 1V 1 t 1 P V 2 a 2 2 i (10) True airspeed results from solving Equation (10) V 1 2a 1 V P i t (11) 9

32 6. Flight Distance Flight distance was determined by integrating true airspeed between takeoff and landing. t end t (12) D V t t start 7. Atmospheric Turbulence Two methods to model atmospheric turbulence were of interest; 1) discrete, and 2) continuous. Both discrete gust and continuous gust require aircraft lift-curve slope. Aircraft liftcurve-slope was calculated by [16] C L at St awb 1 1 awb S (13) where wing lift-curve-slope, a w, and tail lift-curve-slope, a t, were calculated with [17] a w, a t 2 A Ar tan 0.5c r (14) Lift-curve-slope for the wing-body combination was assumed to equal the lift-curve-slope for the wing. Downwash gradient was calculated with [16] hh b 4.44 cos 1.7 2l h Ar 1 Ar 7 b 0.25c 1.19 (15) where h H is the vertical distance from the mean aerodynamic quarter chord of the aft surface to the root chord of the main surface measured along the aircraft plane of symmetry. Also, l h is the longitudinal distance from the mean aerodynamic quarter chord of the aft surface to that of the main surface [16]. 10

33 Reference 17 contains an equation to correct for the effects of compressibility for the downwash gradient. However there is inadequate test data to validate this correction. Nevertheless the correction for compressibility, shown in Equation (16), was used. C C L M M low speed L low speed (16) where was calculated using Equation (15) and L low speed C low speed was calculated using Equation (14) with M = 0. Rustenburg et al. [18] compared wing lift-curve slope determined by Equation (14) with aircraft lift-curve slope and found that the wing lift-curve slope was about 14 percent below aircraft lift-curve slope. They subsequently determined aircraft lift-curve slope by multiplying Equation (14), calculated for the wing, by a factor of By comparison, accounting for downwash resulted in an aircraft lift-curve slope that varied between percent higher than wing lift-curve slope. 8. Discrete Gust Developed before continuous turbulence, discrete gust is a method to model gust velocities. A discrete gust is a one-time event. When an aircraft encounters a gust, the response in plunge and pitch (i.e. motion constrained to the vertical plane) results in an increase in vertical acceleration. Gust velocities can be derived from measured acceleration data. With vertical acceleration data, derived gust velocity was calculated with U de n C z (17) where nz is the incremental vertical acceleration which equals vertical acceleration minus 1g. The aircraft response factor, C, is given by 11

34 C 0VC e L Kg (18) 2W Aircraft weight was not a recorded parameter; therefore, a constant weight of lbs was used. Gust alleviation factor, aerodynamic forces, is approximated by K, which accounts for the airplane motion and the lag in the change of g K g 0.88g 5.3 g (19) where non-dimensional reduced mass, g, is 9. Continuous Gust g 2W gcc S (20) In a field of varying gust profiles, the discrete model provides a description of each individual gust; whereas the continuous model provides a statistical description of the gust velocity for the whole field. The continuous gust model uses power-spectral techniques to derive the root-mean squared, RMS, of the gust velocity, also called continuous gust intensity. This method provides a more realistic account of gust shape, intensity, and distance [19]. Continuous gust intensity was calculated with U n z A L (21) Aircraft PSD gust response factor, A, is given by 0VC e L A F PSD (22) 2W where the power spectral density function equals 12

35 F PSD c g 2L 110 g (23) The number of occurrences corresponding to each was calculated using c N g (24) Each peak/valley was counted as N counts at that value. These were used to determine the number of counts per nautical mile counts nm N distance flown in counting interval (25) Both discrete and continuous gust results were then further grouped into pressure altitude bands which are referenced to mean sea level (MSL). The different bands and the corresponding altitudes are shown in Table 5. Departure and approach phases were grouped into above ground level (AGL) altitude bands determined by the difference between pressure altitude and that of the departure airport and pressure altitude and landing airport, respectively. Altitude bands for these phases were also grouped according to Table 5. 13

36 Table 5: Pressure Altitude Bands 10. Data Reduction Band Altitude (ft) 1 < > Each flight was divided into seven airborne phases and six ground phases. These were: Taxi-out Takeoff roll Rotation Departure Climb Cruise Descent Initial Approach Mid-approach Final approach Landing Roll Runway turn-off Taxi-in 14

37 These phases are depicted schematically in Figure 3, with one example shown in Figure 4. The criteria used for flight phase separation are outlined in Table 6 and are discussed in detail below. The reader is reminded that each flight could contain more than one of each phase. Taxi Out Takeoff Roll Departure Climb Cruise Descent Initial Approach Mid Approach Final Approach Landing Roll Runway Turnoff Taxi In Rotation Figure 3: Diagram of Flight Phases _ Altitude (ft) :00:00 0:28:48 0:57:36 1:26:24 1:55:12 2:24:00 2:52:48 Time (hr:min:sec) Figure 4: Sample Flight Time History 15

38 Table 6: Flight Phase Separation Criteria Flight Phase Start Time (t 1 ) Identification Stop Time (t 2 ) Identification Taxi-Out Roll Rotation Heading(I+5) - Heading(I) > 20 deg. (dhdg(i) < 270 deg.; On ground) ACCELX > 0.15g (On Ground, Airspeed is increasing) t 2 of Roll (t 1 of Roll) minus 5 sec. PITCH(I) - PITCH_ref > 3 deg. PITCH(I) > 15 deg OR PITCH(I) - PITCH_ref > 10 deg Departure t 2 of Rotation Flaps are up (not on ground) Climb Cruise Descent 20 sec. mark if RC > 750 fpm for 40 sec. AND Flaps are up (Not on ground) RC < 200 fpm for 20 sec. (Not on ground; flaps up) 20 sec. mark if RC < -750 fpm for 40 sec. (Not on ground; flaps are up) RC < 750 fpm for 20 sec. (Not on ground; flaps up) h > 250 ft (from avg of ISTARTCRUISE+20 sec.) (Not on ground; flaps up) Flaps are In Transit or set to Approach (Not on ground) OR RC > -750 fpm for 20 sec. (Not on ground) Initial Approach Flaps at 1 Time reading before flaps at 2 Mid Approach Flaps at 2 Time reading before flaps at 3 Final Approach Flaps at 3 (On Ground) minus 3 sec. Landing Roll t 2 of Final Approach ΔHDG (from t 1 ) > 5.0 minus 5 sec. Runway Turn-Off t 2 of Landing Roll dhdg < 2 deg for 5 sec. Taxi-In t 2 of Runway Turn-Off Engine core < 11% minus 38 sec. OR End of File 11. Flight Phase Separation The taxi-out phase started when the heading angle changed by more than 20 degrees in five seconds. This indicated the aircraft started moving. The end of the taxi-out phase was marked at five seconds before the longitudinal acceleration reached greater than 0.15g. This 16

39 resulted in the inclusion of all the times when the aircraft was stationary between the initial motion and the start of the takeoff roll. For future efforts, changes in the aircraft latitude and longitude over time can be used to eliminate the periods when the aircraft is stationary. The takeoff roll phase was assumed to start when the longitudinal acceleration exceeded 0.15g and ended when the change in pitch angle became greater than 3 degrees relative to the reference pitch angle. The latter parameter was defined as the average value of the pitch angle during the taxi-out phase. The start of the rotation phase coincided with the end of the takeoff roll phase. The end of the rotation phase was assumed when the pitch angle either surpassed 15 degrees or exceeded the reference pitch angle by more than 10 degrees. The rotation phase was followed immediately by the departure phase, with the aircraft climbing out with some flap deflection. This phase ended when the flaps were fully retracted. The climb phase was defined as flight at the 20 second midpoint when rate of climb was greater than 750 fpm for at least 40 consecutive seconds. The midpoint of the 40 second interval was used to prevent overlap between the start of a cruise phase and the end of a climb phase. When the rate of climb decreased to below 750 fpm for 20 seconds, the climb phase was terminated. The start of the cruise phase was marked as the point when the absolute value of rate of climb remained less than 200 fpm for 20 seconds. The end of the cruise phase was assumed when the absolute value of the change in height was greater than 250 ft, relative to the first 20 seconds of this phase. It is noteworthy that one cruise phase could be followed immediately by another, for example if the aircraft gradually climbed or descended from one altitude band into another. 17

40 Similar to the cruise phase, the descent phase was assumed to start at the 20 second midpoint when the rate of climb became less than -750 fpm (i.e. descent rate of 750 fpm) for 40 seconds with the flaps retracted. The end of this phase was when either the rate of climb became larger than negative 750 fpm for 20 seconds or the flap deflection was detected. Three approach phases were defined according to the flap settings. A positive average rate of descent for the entire phase was not necessary for classification as an approach. Flaps at the first detent would indicate the start of the initial approach. The end of the initial approach was assumed when the flaps were deflected to the second detent. The second detent indicated the start of the middle approach. The start of the final approach was marked with the flaps moving into the third detent. The end of this phase was assumed 3 seconds before touchdown. Touchdown was marked when any squat switch registered a ground reading. Landing roll started at the end of the final approach. Based on this aircraft, landing roll was assumed to end five seconds before from when the change in the heading after landing became greater than 5 degrees. This was followed by runway turn-off that started at the end of the landing roll and ended when the change in heading remained less than 2 degrees for 5 seconds. The mission was assumed to culminate with taxi-in following the runway turn-off. The end of the mission was marked 38 seconds before either engine core was below 11 percent or the end of file was reached. It was noticed while analyzing the data that engine core idle speed was around 64 percent and when the engines were shut down there would be a spike in the vertical acceleration data from the moment idle speed was decreasing. This may have been the result of shutting down electrical equipment. Thirty-eight seconds was more than adequate to circumvent this problem. 18

41 12. Flight Loads Counting Occurrences of the loads were counted using the method of peaks-between-means. Figure 5 shows a schematic of the peaks and valleys counted using this method. Within each successive crossing of the mean one peak was counted if the absolute maximum fell outside of a pre-defined dead band. Valleys were counted in a similar manner. A dead band was established to eliminate excessive counts due to inherent noise in the data. The dead bands associated with various parameters are shown in Table 7. Mean Crossing Peak Valley Dead Band Figure 5: Peaks-Between-Means Loads Counting Table 7: Dead Band Limit Parameter Incremental Normal Acceleration Lateral Acceleration Longitudinal Acceleration Derived/Continuous Gust Velocity Dead Band Width ± 0.05 g ± g ±0.005 g ±2.00 ft/s For normal loads, after identifying the maximum and minimum loads a further classification into gusts and maneuvers was necessary. The two-second rule was used for separation of gusts and maneuvers [20]. A peak or valley that remained outside of the dead band 19

42 for longer than two seconds was classified as a maneuver load, while one lasting less than two seconds was classified as a gust load. Again this pertained only to vertical accelerations. 13. Determination of Atmospheric Turbulence Parameters, P s and b s A detailed description for the determination of P s and b s can be found in Reference 18. With cumulative occurrences of continuous gust velocities gathered from flight loads measurements, generalized exceedance curves can be generated and turbulence field parameters can be derived. A generalized exceedance curve is shown schematically in Figure 6 and represented by Equation (26) [21]. U U N y b b 1 2 N0 1 2 Pe P e (26) 1 Ny / N 0 log 10 2 Figure 6: Sample of Generalized Exceedance Graph Section 1 represents non-storm turbulence while section 2 represents storm turbulence. The vertical intercepts, P 1 and P 2, represent the proportion of total flight spent in turbulence. The U slope is equal to the b values and represents the intensity of each type of turbulence. The N 0 value is the aircraft s characteristic frequency and requires detailed aircraft information to 20

43 calculate which is not available. However N 0 can be found from the number of positive crossings of continuous gust velocities from cumulative occurrence data. To derive turbulence parameters one starts with a cumulative occurrence graph. An example of a graph of cumulative occurrences per nautical mile versus continuous gust intensity is shown in Figure 7. Cumulative occurrences represented in Figure 7 were determined from the summation of negative and positive counts. A curve fitting software from MATLAB using the Levenberg-Marquardt method modeled with the expression of Equation (26) was used to determine the value of 2N 0. The Levenberg-Marquardt method is a numerical iterative technique used for curve fitting nonlinear equations by minimizing least squares of the error. The N 0,1 value is the contribution from non-storm turbulence, the N 0,2 value is the contribution from storm turbulence, and the sum of these values is equal to the 2N 0 value. Cumulative Occurrences Per Nautical Mile, 2N y 1.E+03 1.E+02 1.E+01 1.E+00 1.E-01 1.E-02 1.E-03 1.E-04 1.E-05 2N 0 1.E Continuous Gust Velocity, U σ (ft/s) Figure 7: Zero Intercept Extrapolation 2N 0,1 = 0.77 b 1 = N 0,2 = 2.70x10-3 b 2 = N 0 = 0.77 R 2 = Band 12 curve fit 21

44 The values of P s and b s can be determined from the curve fit. The values for b 1 and b 2 were taken directly from the curve fit. The P values were determined using Equations (27) and (28). P 1 D N turbulence 0,1 D N N total 0,1 0,2 (27) P 2 D N turbulence 0,2 D N N total 0,1 0,2 (28) Not all flight distance is spent in turbulence, therefore to take into account the percentage of flight while in turbulence Equations (27) and (28) have the terms Dturbulence Dtotal where Dturbulence is the distance flown in turbulence and Dtotal is the total distance flown in a band. In Chapter II the techniques used in processing the data were explained. The following chapter shows the results of implementation of these techniques and their discussions. General usage results for airborne phases are examined first. This is followed by examination of the vertical loads during airborne segments. This part includes the comparison of the turbulence field parameters derived from the present data with those from FAR 25. Finally, the results for the ground phases are presented and discussed. 22

45 CHAPTER III III. RESULTS AND DISCUSSION AIRCRAFT USAGE A. Available Data Using the separation criteria described in the method of analysis resulted in 212 files from the first set of data (July 2010) and 242 files from the second set (February 2011). A breakdown of the various types of erroneous files is shown in Table 8. Data downloaded on February 2011 resulted in 331 files, but 89 files were duplicates from July 2010 and were omitted. Erroneous files fell under three types. A Type 1 error resulted when the aircraft did not take off; a Type 2 error developed when lines , which were used to normalize the acceleration, registered large values, usually for lateral and longitudinal acceleration; a Type 3 error occurred when the numbers in the file suddenly showed a reset in data as if the instruments had just been turned on. In these cases, a line of data showed the aircraft as being in the air followed immediately by another line of data that showed the aircraft was on the ground. Examination of the seven Type 3 files revealed a strange characteristic for these files: the sudden reset always occurred above 40,000 ft, therefore, it could not be due to the flight separation algorithm. An interesting note is that no data from February fell under a Type 2 error and no data from July was characterized as a Type 3 error. In addition to the erroneous files, two flight files recorded a large amount of loads and relative to other cruise phases represented a large percentage (greater than fifty percent in some cases) of the loads. These two files were omitted from the analysis. Discussion of these two files is presented in the flight loads section under the cruise phase. 23