Introduction to Flight Testing E-Book

James W. Gregory

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: Aerospace Series (PEP)
• Sprache: Englisch

Seitenzahl: 695

Veröffentlichungsjahr: 2021

Beschreibung

Introduction to Flight Testing

Introduction to Flight Testing

Provides an introduction to the basic flight testing methods employed on general aviation aircraft and unmanned aerial vehicles

Introduction to Flight Testing provides a concise introduction to the basic flight testing methods employed on general aviation aircraft and unmanned aerial vehicles for courses in aeronautical engineering. There is particular emphasis on the use of modern on-board instruments and inexpensive, off-the-shelf portable devices that make flight testing accessible to nearly any student.

This text presents a clear articulation of standard methods for measuring aircraft performance characteristics. Topics covered include aircraft and instruments, digital data acquisition techniques, flight test planning, the standard atmosphere, uncertainty analysis, level flight performance, airspeed calibration, stall, climb and glide, take-off and landing, level turn, static and dynamic longitudinal stability, lateral-directional stability, and flight testing of unmanned aircraft systems.

Unique to this book is a detailed discussion of digital data acquisition (DAQ) techniques, which are an integral part of modern flight test programs. This treatment includes discussion of the analog-to-digital conversion, sample rate, aliasing, and filtering. These critical details provide the flight test engineer with the insight needed to understand the capabilities and limitations of digital DAQ.

Key features:

• Provides an introduction to the basic flight testing methods and instrumentation employed on general aviation aircraft and unmanned aerial vehicles.
• Includes examples of flight testing on general aviation aircraft such as Cirrus, Diamond, and Cessna aircraft, along with unmanned aircraft vehicles.
• Suitable for courses on Aircraft Flight Test Engineering.

Introduction to Flight Testing provides resources and guidance for practitioners in the rapidly-developing field of drone performance flight test and the general aviation flight test community.

Leseprobe

Table of Contents

Cover

Series Page

Title Page

Copyright

dedication

About the Authors

Series Preface

Preface

Acknowledgements

About the Companion Website

1 Introduction

1.1 Case Study: Supersonic Flight in the Bell XS‐1

1.2 Types of Flight Testing

1.3 Objectives and Organization of this Book

References

2 The Flight Environment: Standard Atmosphere

2.1 Earth's Atmosphere

2.2 Standard Atmosphere Model

2.3 Altitudes Used in Aviation

References

Notes

3 Aircraft and Flight Test Instrumentation

3.1 Traditional Cockpit Instruments

3.2 Glass Cockpit Instruments

3.3 Flight Test Instrumentation

3.4 Summary

References

Note

4 Data Acquisition and Analysis

4.1 Temporal and Spectral Analysis

4.2 Filtering

4.3 Digital Sampling: Bit Depth Resolution and Sample Rate

4.4 Aliasing

4.5 Flight Testing Example

4.6 Summary

References

5 Uncertainty Analysis

5.1 Error Theory

5.2 Basic Error Sources in Flight Testing

References

6 Flight Test Planning

6.1 Flight Test Process

6.2 Risk Management

6.3 Case Study: Accept No Unnecessary Risk

6.4 Individual Flight Planning

6.5 Conclusion

References

7 Drag Polar Measurement in Level Flight

7.1 Theory

7.2 Flight Testing Procedures

7.3 Flight Test Example: Cirrus SR20

References

Note

8 Airspeed Calibration

8.1 Theory

8.2 Measurement Errors

8.3 Airspeed Calibration Methods

8.4 Flight Testing Procedures

8.5 Flight Test Example: Cirrus SR20

References

Note

9 Climb Performance and Level Acceleration to Measure Excess Power

9.1 Theory

9.2 Flight Testing Procedures

9.3 Data Analysis

9.4 Flight Test Example: Cirrus SR20

References

10 Glide Speed and Distance

10.1 Theory

10.2 Flight Testing Procedures

10.3 Data Analysis

10.4 Flight Test Example: Cirrus SR20

References

11 Takeoff and Landing

11.1 Theory

11.2 Measurement Methods

11.3 Flight Testing Procedures

11.4 Flight Test Example: Cessna R182

References

Notes

12 Stall Speed

12.1 Theory

12.2 Flight Testing Procedures

12.3 Data Analysis

12.4 Flight Test Example: Cirrus SR20

References

13 Turning Flight

13.1 Theory

13.2 Flight Testing Procedures

13.3 Flight Test Example: Diamond DA40

References

14 Longitudinal Stability

14.1 Static Longitudinal Stability

14.2 Dynamic Longitudinal Stability

References

15 Lateral‐Directional Stability

15.1 Static Lateral‐Directional Stability

15.2 Dynamic Lateral‐Directional Stability

Nomenclature

Acronyms and Abbreviations

References

16 UAV Flight Testing

1

16.1 Overview of Unmanned Aircraft

16.2 UAV Design Principles and Features

16.3 Flight Regulations

16.4 Flight Testing Principles

16.5 Flight Testing Examples with the Peregrine UAS

16.6 Flight Testing Examples with the Avanti UAS

16.7 Conclusion

References

Notes

Appendix A: Appendix AStandard Atmosphere Tables

Appendix B: Appendix BUseful Constants and Unit Conversion Factors

Reference

Appendix C: Appendix CStability and Control Derivatives for a Notional GA Aircraft

Reference

Index

End User License Agreement

List of Tables

Chapter 1

Table 1.1  Airworthiness certification levels defined by part 23.

Chapter 2

Table 2.1 Definition of temperature lapse rates in various regions of the atm...

Table 2.2  Constants used in Sutherland's Law.

Chapter 3

Table 3.1  DAQ sensor utility matrix.

Chapter 5

Table 5.1  Typical uncertainty values for an airspeed indicator.

Table 5.2  Maximum scale error permitted by 14 CFR 43 Appendix E.

Table 5.3  Maximum friction error permitted by 14 CFR 43 Appendix E.

Table 5.4  Maximum barometric scale error permitted by 14 CFR 43 Appendix E.

Chapter 6

Table 6.1 Taxonomy for assigning likelihood and severity levels in risk asses...

Table 6.2 Sample weight and balance calculations for a typical general aviati...

Chapter 7

Table 7.1  Overall skin friction coefficients for various aircraft.

Table 7.2  Basic flight test data.

Table 7.3  Flight data from Cirrus SR20 level flight.

Table 7.4  Derived quantities from flight test data.

Chapter 8

Table 8.1  Speed definitions.

Table 8.2  Flight data obtained at a pressure altitude of 3000 ft.

Table 8.3 Airspeeds and wind speeds for airspeed calibration at a pressure al...

Chapter 9

Table 9.1 Flight data from a Cirrus SR20 in climb at a pressure altitude of 3...

Table 9.2 Flight data from a Cirrus SR20 in climb at a pressure altitude of 6...

Table 9.3 Derived quantities from flight test data at a pressure altitude of ...

Table 9.4 Derived quantities from flight test data at a pressure altitude of ...

Chapter 10

Table 10.1 Flight data from a Cirrus SR20 in glide at a pressure altitude of ...

Table 10.2 Derived quantities from flight test data at a pressure altitude of...

Chapter 11

Table 11.1  Values of runway surface friction coefficient.

Table 11.2  Basic parameters of the Cessna R182.

Chapter 14

Table 14.1  Summary of long‐period dynamic longitudinal stability results.

Chapter 16

Table 16.1  U.S. Department of Defense UAS classifications.

Table 16.2  Key characteristics of the Peregrine UAS.

Table 16.3  Predicted and measured drag polar for the Peregrine UAS.

Table 16.4  Key characteristics of the Avanti UAS.

Appendix A

Table A.1  Standard sea‐level properties in English units.

Table A.2  Standard Atmosphere in English units.

Table A.3  Standard sea‐level properties in SI units.

Table A.4  Standard Atmosphere in SI units.

Appendix B

Table B.1  Standard, consistent units for the English and SI unit systems.

Table B.2  Useful conversion factors.

Table B.3  Useful constants in standard, consistent units.

Table B.4  SI prefix definitions.

Appendix C

Table C.1  Stability derivatives for a notional GA aircraft.

List of Illustrations

Chapter 1

Figure 1.1 The caricature view of flight test is of an individualistic, cowb...

Figure 1.2 A more realistic view of the people behind flight testing – a tea...

Figure 1.3  Three‐view drawing of the Bell XS‐1.

Figure 1.4 The Air Materiel Command XS‐1 flight test team, composed of (from...

Figure 1.5 Yeager accelerates in the Bell XS‐1 on his way to breaking the “s...

Figure 1.6 Plot of the total and static pressure for the first supersonic fl...

Figure 1.7 Inspection of pressure‐sensitive paint on Purdue University's Bee...

Figure 1.8  Notre Dame's Dassault Falcon 10.

Figure 1.9 Smoke and tuft flow visualization on the NASA F‐18 High Alpha Res...

Figure 1.10 Early X‐planes, including the Douglas X‐3 Stiletto (center) and ...

Figure 1.11  Sikorsky S‐72 X‐wing testbed aircraft.

Figure 1.12 The Ohio State University's Avanti jet unmanned aircraft system....

Figure 1.13 Maj Rachael Winiecki, a developmental test pilot with the 461st ...

Figure 1.14 Ohio State University students Greg Rhodes and Jennifer Haines f...

Chapter 2

Figure 2.1  The layers of Earth's atmosphere.

Figure 2.2  Forces acting on a hydrostatic control volume.

Figure 2.3  Standard temperature profile.

Figure 2.4 The normalized temperature, pressure, and density distributions i...

Figure 2.5 Launch of a high‐altitude weather balloon from the oval of The Oh...

Figure 2.6 Comparison of the standard atmosphere with temperature data measu...

Figure 2.7 Comparison of the standard atmosphere with pressure data measured...

Figure 2.8  Illustration of different altitudes used in aviation.

Chapter 3

Figure 3.1 Overview of aircraft cockpit instrumentation for traditional “ste...

Figure 3.2 Detailed view of the six pack of key instruments in a traditional...

Figure 3.3 Examples of the pitot tube (a) and static pressure port (b) on an...

Figure 3.4  Schematic of the pitot‐static system.

Figure 3.5 Diagram of an aircraft altimeter. The reference pressure is set b...

Figure 3.6 Overview of aircraft cockpit instrumentation for a glass panel av...

Figure 3.7 Detailed view of the primary flight display (PFD) on a Cirrus SR2...

Figure 3.8 Detailed view of the multifunction display (MFD) on a Cirrus SR20...

Figure 3.9 Modern flight testing board with built‐in GPS, accelerometers, gy...

Figure 3.10  Typical differential GPS architecture.

Chapter 4

Figure 4.1  Sample signal in the time domain.

Figure 4.2  Sample signal in the frequency domain.

Figure 4.3  Fourier series approximation of a triangle waveform.

Figure 4.4 Fourier components of the sine series approximation to a triangle...

Figure 4.5  Power spectrum based on the FFT of the triangle waveform.

Figure 4.6 Examples of various filtering schemes applied to signals in the t...

Figure 4.7 Digital representation of an analog waveform with input range of ...

Figure 4.8 Digital representation of the analog waveform with input range of...

Figure 4.9 Digital representation of the analog waveform with a sample rate ...

Figure 4.10 Digital representation of the analog waveform with a sample rate...

Figure 4.11 Digital representation of the analog waveform with a sample rate...

Figure 4.12 Illustration of aliasing due to insufficiently high sample rate....

Chapter 5

Figure 5.1 Illustration of the importance of uncertainty analysis in guiding...

Figure 5.2  Illustration of bias error and precision error.

Figure 5.3 Illustration of (a) high bias error with low precision error; (b)...

Figure 5.4 Linear relationship between the measured and true values, which i...

Figure 5.5 The Gaussian distribution and histogram of a series of measuremen...

Figure 5.6 Histograms of the input variables: (a) indicated airspeed, (b) ou...

Figure 5.7  Histogram of the calculated true airspeed.

Chapter 6

Figure 6.1  Sample flight test card for an airspeed calibration test.

Figure 6.2  Risk assessment matrix.

Figure 6.3 XB‐70 (large aircraft, center), flying with four other GE‐powered...

Figure 6.4 Sample portion of an FAA chart for navigation under visual flight...

Figure 6.5  Aircraft center of gravity limits.

Figure 6.6 Example of a CG envelope, showing the forward and aft limits of t...

Chapter 7

Figure 7.1  Force diagram for level flight.

Figure 7.2 Induced drag factor for varying aspect ratio and taper ratio wing...

Figure 7.3 Power–velocity curve for level flight of a typical general aviati...

Figure 7.4 Altitude effects on the power–velocity curve for light aircraft....

Figure 7.5  Weight effects on the power–velocity curve for light aircraft.

Figure 7.6  Continental IO‐360 engine.

Figure 7.7  Side view of the 210‐hp Continental Motors IO‐360‐ES.

Figure 7.8  Four‐stroke spark ignition cycle.

Figure 7.9  Engine performance charts for the Continental IO‐360‐ES.

Figure 7.10  Propeller velocity triangles.

Figure 7.11 Side view of Hartzell propeller, illustrating blade twist along ...

Figure 7.12 Propeller efficiency for a Hartzell 3‐bladed, 74-in. diameter pr...

Figure 7.13 Flight test PIW–VIW data for determining the drag polar of the C...

Chapter 8

Figure 8.1  The compressibility factor for airspeed correction.

Figure 8.2 Correction (in kts) between EAS and CAS for a range of airspeeds ...

Figure 8.3 Cutaway diagram of the airspeed indicator, illustrating how the d...

Figure 8.4 The pitot‐static probe mounted on an airplane and the surface pre...

Figure 8.5 Relationship between altitude error and velocity error as a resul...

Figure 8.6 Effect of a wing/body on measurement of the static pressure in th...

Figure 8.7 Air data boom (a) diagram and (b) installation on the nose of an ...

Figure 8.8 Illustration of airspeed calibration methods of trailing bomb, tr...

Figure 8.9 Sample ground track (a “cloverleaf”) for GPS‐based determination ...

Figure 8.10 Vector diagram for the GPS ground velocity, true airspeed, and w...

Figure 8.11 Airspeed calibration flight test results for the SR20G6, compare...

Chapter 9

Figure 9.1  Forces acting on an aircraft in climb.

Figure 9.2  Velocity triangle for an aircraft in a steady climb.

Figure 9.3  Drag characteristics of a typical light aircraft.

Figure 9.4 Power characteristics of a typical light aircraft. The “back side...

Figure 9.5 Power required and power available characteristics for a typical ...

Figure 9.6 Rate of climb variation with airspeed and altitude for a typical ...

Figure 9.7 Extrapolation of maximum rates of climb to define service and abs...

Figure 9.8 Instantaneous time to climb, which asymptotes to infinity at the ...

Figure 9.9 Climb hodograph, illustrating the difference between best climb a...

Figure 9.10  Airspeeds for best climb angle and best rate of climb.

Figure 9.11  Contours of constant energy height.

Figure 9.12 Energy diagram for a notional fighter aircraft, with contours of...

Figure 9.13 Rate of climb flight test data compared to theoretical predictio...

Figure 9.14 Rate of climb flight test data compared with level acceleration ...

Figure 9.15 Comparison of maximum rate of climb flight test data with POH da...

Chapter 10

Figure 10.1 US Airways flight 1549, moments after gliding to a water landing...

Figure 10.2  Smoke visualization of wing tip vortices on a Boeing 727.

Figure 10.3 Variation of induced, parasitic, and total drag with airspeed fo...

Figure 10.4 Forces acting on an aircraft in glide, assuming no thrust or dra...

Figure 10.5  Velocity and distance triangles for aircraft motion in glide.

Figure 10.6  Sample glide hodograph for a typical light aircraft.

Figure 10.7 Dependency of the lift‐to‐drag characteristics on (a) aircraft w...

Figure 10.8 Glide hodograph of flight test data and theoretical data based o...

Chapter 11

Figure 11.1  Takeoff diagram.

Figure 11.2  Force diagram for takeoff ground roll.

Figure 11.3  Transition distance geometry.

Figure 11.4  Standard airport traffic pattern for takeoff and landing.

Figure 11.5 The altitude, speed, and distance of the Cessna R182 aircraft du...

Chapter 12

Figure 12.1  Flow separation associated with stall.

Figure 12.2 Lift coefficient data for a typical airfoil (SM701, calculated i...

Figure 12.3 Examples of laminar and turbulent boundary layer velocity profil...

Figure 12.4  Boundary layer profiles illustrating flow separation.

Figure 12.5 Stall characteristics of several canonical airfoil sections, ill...

Figure 12.6  Effects of Reynolds number on airfoil stall characteristics.

Figure 12.7 Stall progression for various wing planforms. (a) Elliptical win...

Figure 12.8 Three examples of stall control devices on the wing of a Cessna ...

Figure 12.9 Sample airspeed time history during a stall event and definition...

Figure 12.10 Diagram of forces acting in equilibrium on the wing and tail in...

Figure 12.11 Identification of the stall event by cross‐plotting acceleratio...

Figure 12.12 Tufts on a Cirrus SR20 showing (a) attached flow, (b) trailing ...

Chapter 13

Figure 13.1 Forces acting on an aircraft in a steady turn (inertial frame of...

Figure 13.2 Forces acting on an aircraft in a steady turn (aircraft frame of...

Figure 13.3  Simplified

V

–

n

diagram for a typical, normal category general av...

Figure 13.4  

V

–

n

diagrams for the same aircraft at maximum takeoff weight and...

Figure 13.5  

V

–

n

diagram with overlaid contours of specific excess power (ft/...

Figure 13.6 (a) GPS flight test data from a DA40 in turning flight. Symbols ...

Chapter 14

Figure 14.1  Forces and moments acting on an aircraft.

Figure 14.2 Illustration of pitch moment coefficient versus angle of attack ...

Figure 14.3 Forces and moments acting about the aircraft center of gravity....

Figure 14.4  Depiction of the neutral point.

Figure 14.5 Notional data of required elevator position (trim angle) as a fu...

Figure 14.6 Measured stick deflection at various airspeed and CG test points...

Figure 14.7 Illustration of the neutral point identification by extrapolatio...

Figure 14.8 Aircraft coordinate axes, angles, and forces for dynamic longitu...

Figure 14.9 Analytical predictions of the long‐period mode based on estimate...

Figure 14.10  

Z

‐Axis acceleration time record of the Cirrus SR20 phugoid mode...

Figure 14.11 Spectral analysis of the time record shown in Figure 14.10 indi...

Chapter 15

Figure 15.1 Definition of forces and moments for lateral‐directional stabili...

Figure 15.2 Definition of forces and moments for lateral‐directional stabili...

Figure 15.3 Calibration of the rudder and aileron control surface deflection...

Figure 15.4 Static directional stability characteristics from steady heading...

Figure 15.5 Static lateral stability characteristics from steady heading sid...

Figure 15.6  Side force characteristics from steady heading sideslip data.

Figure 15.7 Doublet rudder input to excite lateral‐directional dynamic respo...

Figure 15.8 3‐2‐1‐1 rudder input to excite lateral‐directional dynamic respo...

Figure 15.9  

Y

‐axis acceleration (low‐pass filtered at 4 Hz) for a SR20 in Du...

Chapter 16

Figure 16.1  Example of a palm‐sized quad‐rotor drone.

Figure 16.2  An RQ‐4 Global Hawk drone.

Figure 16.3 The MQ‐8B Fire Scout, an example of an unmanned aircraft with a ...

Figure 16.4 A typical quadrotor drone, the most common configuration of a UA...

Figure 16.5 The OSU Octavian, an eight‐rotor VTOL drone carrying a mast‐moun...

Figure 16.6 The NASA “Greased Lightning” GL‐10 prototype UAV, an example of ...

Figure 16.7  Typical data display for a UAS ground control station.

Figure 16.8  Typical avionics system architecture for an unmanned aircraft.

Figure 16.9 The Peregrine UAS, a fixed‐wing electric propulsion aircraft for...

Figure 16.10 Performance data for the APC 10×7E propeller. Note the dependen...

Figure 16.11  Excess power of the Peregrine UAS.

Figure 16.12 Lift‐to‐drag ratio of the Peregrine from flight testing, compar...

Figure 16.13  Glide flight test results for gusting wind conditions.

Figure 16.14 Comparison of glide flight test results obtained from the air d...

Figure 16.15 The Avanti turbojet‐powered UAS, depicted in the flare to landi...

Figure 16.16 Testing of the Avanti communications antenna radiation patterns...

Figure 16.17 The Avanti UAS during the world record‐setting flight (as seen ...

Figure 16.18 Measured deceleration as a function of airspeed during coast‐do...

Figure 16.19 Lift‐to‐drag ratio data from coast‐down testing, along with a m...

Figure 16.20  Radio range flight testing results.

Figure 16.21 Example of an emergent property of an autonomous system, where ...

Guide

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Civil Avionics Systems, 2nd EditionIan Moir, Allan Seabridge, Malcolm Jukes

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Modelling and Managing Airport PerformanceKonstantinos Zografos, Giovanni Andreatta, Amedeo Odoni

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Aircraft Systems: Mechanical, Electrical, and Avionics Subsystems Integration, 3rd EditionIan Moir, Allan Seabridge

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System Health Management: with Aerospace ApplicationsStephen B. Johnson, Thomas Gormley, Seth Kessler, Charles Mott, Ann Patterson-Hine, Karl Reichard, Philip Scandura Jr.

Advanced Control of Aircraft, Spacecraft and RocketsAshish Tewari

Air Travel and Health: A Systems PerspectiveAllan Seabridge, Shirley Morgan

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Handbook of Space TechnologyWilfried Ley, Klaus Wittmann, Willi Hallmann

Cooperative Path Planning of Unmanned Aerial VehiclesAntonios Tsourdos, Brian White, Madhavan Shanmugavel

Design and Analysis of Composite Structures: With Applications to Aerospace StructuresChristos Kassapoglou

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Aircraft Conceptual Design SynthesisDenis Howe

Introduction to Flight Testing

James W. Gregory

The Ohio State University

Tianshu Liu

Western Michigan University

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Library of Congress Cataloging‐in‐Publication Data

Names: Gregory, James W., author. | Liu, T. (Tianshu), author.

Title: Introduction to flight testing / James W. Gregory, The Ohio State University; Tianshu Liu, Western Michigan University.

Description: First edition. | Hoboken, NJ : Wiley, 2021. | Includes bibliographical references and index.

Identifiers: LCCN 2020048350 (print) | LCCN 2020048351 (ebook) | ISBN 9781118949825 (hardback) | ISBN 9781118949795 (adobe pdf) | ISBN 9781118949801 (epub)

Subjects: LCSH: Airplanes--Flight testing--Textbooks.

Classification: LCC TL671.7 .G74 2021 (print) | LCC TL671.7 (ebook) | DDC 629.134/53--dc23

LC record available at https://lccn.loc.gov/2020048350

LC ebook record available at https://lccn.loc.gov/2020048351

Cover Design: WileyCover Image: © NNehring/Getty Images

Dedicated to

Deb, Alina, and Maggie – J. W. G.

Ruomei and Ranya – T. L.

About the Authors

James W. Gregory is professor and chair of the Department of Mechanical and Aerospace Engineering at The Ohio State University (OSU). He received his Bachelor of Aerospace Engineering from Georgia Tech in 1999 and his PhD in Aeronautics and Astronautics from Purdue University in 2005. He has been a faculty member at OSU since 2008 and served as Director of OSU's Aerospace Research Center from 2017 to 2020. In 2017, he led a team of research staff and students to set FAI/NAA‐sanctioned world records for speed and distance for an autonomous drone. He teaches classes at OSU on Flight Test Engineering and Introduction to Aerospace Engineering. Prof. Gregory also recorded a series of video lectures on the Science of Flight, produced by the Great Courses. He is an instrument‐rated commercial pilot and holds a remote pilot certificate.

Tianshu Liu is a professor in Department of Mechanical and Aerospace Engineering at Western Michigan University (WMU). He received a PhD in Aeronautics and Astronautics from Purdue University in 1996. He was a research scientist at NASA Langley Research Center from 1999 to 2004. His research focuses on experimental aerodynamics and fluid mechanics, particularly on global measurement techniques for various physical quantities such as pressure, temperature, heat flux, skin friction, velocity, aeroelastic deformation, and aerodynamic force. He teaches classes in aerodynamics and flight testing at WMU.

Series Preface

The field of aerospace is multidisciplinary and wide‐ranging, covering a large variety of platforms, disciplines, and domains, not merely in engineering but in many related supporting activities. These combine to enable the aerospace industry to produce innovative and technologically advanced vehicles. The wealth of knowledge and experience that has been gained by expert practitioners in the various aerospace fields needs to be passed onto others working in the industry and also researchers, teachers, and the student body in universities.

The Aerospace Series aims to be a practical, topical, and relevant series of books aimed at people working in the aerospace industry, including engineering professionals and operators, engineers in academia, and allied professions such as commercial and legal executives. The range of topics is intended to be wide‐ranging, covering design and development, manufacture, operation and support of aircraft, as well as topics such as infrastructure operations and current advances in research and technology.

Flight testing is a vital part of the certification and validation phase of all new aircraft and is performed to determine or verify the performance and handling qualities. Although the flight characteristics are predicted in the design and development stages of new aircraft programs, the real‐world capabilities are not known until the aircraft is flown and tested. Most aircraft flight testing programs are focused on meeting airworthiness certification requirements and demonstrate all aspects of the flight vehicle's performance and handling characteristics to ensure flight safety.

This book, Introduction to Flight Testing, is aimed at advanced‐level undergraduate students, graduate students, and practicing engineers who are looking for an introduction to the field of flight testing. With a focus on light aircraft and UAVs, the book covers the engineering fundamentals of flight, including the flight environment, aircraft performance and stability and control, combined with the piloting, sensors, and digital data acquisition and analysis required to perform flight tests. This book is a very welcome addition to the Wiley Aerospace Series.

October 2020 Peter Belobaba, Jonathan Cooper and Allan Seabridge

Preface

The goal of this book is to provide an accessible introduction to the fascinating and intriguing world of aircraft flight testing. This unique discipline directly straddles the domains of engineering and piloting, requiring knowledge of both the theory and practice of flight. Our target audience is advanced‐level undergraduate students, beginning graduate students, and practicing engineers who are looking for an introduction to the field of flight testing. Flight testing professionals (engineers, pilots, managers, etc.) may also find this to be a helpful resource if they wish to solidify their understanding of the fundamentals beyond what is provided in most other flight testing resources. We have attempted to write this book in an engaging, conversational style that invites the reader into understanding the fundamental principles.

Both authors teach a senior‐year technical elective course at our home universities on the topic of flight test engineering. Within this context, we have found that students best learn the material when they actively engage with flight testing practice. Experiencing flight in an aircraft is the best way to develop a tacit understanding of the principles of flight, to augment and deepen the intellectual knowledge of engineering practice that students receive in the classroom. In working with our senior‐year engineering students, we have developed the following learning objectives for our courses, as well as for this book. Our aim is that readers of this book will:

Have an appreciation for the purpose, scope, and magnitude of historical and modern flight test programs in the commercial and military aircraft sectors.

Understand the theoretical foundations of the flight environment, aircraft performance, and stability and control as it applies to flight testing.

Be familiar with aircraft cockpit instrumentation, supplemental sensors for flight testing, and digital data acquisition techniques.

Be able to plan a flight test to evaluate the performance or handling qualities of a general aviation or unmanned aircraft.

Have the ability to coordinate with an experienced pilot to successfully conduct the flight test.

Have the knowledge and background needed to perform postflight analysis and data reduction.

Be able to professionally and succinctly communicate the findings of a flight test program via oral and written communication.

Have a general familiarity with piloting, aviation weather, and flight planning.

Thus, this book is best approached in conjunction with flight in an actual aircraft. No specially instrumented aircraft are needed in order to do most of the flight tests in this book. No exceptional training is needed in order to fly the basic maneuvers described in this book. In fact, all of the procedures described herein are routine maneuvers that are encountered often in piloting practice. An interested reader can simply head to their nearest airport and work with a qualified, professional pilot (e.g., a certified flight instructor) to conduct the flights described here. In our educational contexts, we collaborate with flight instructors in the aviation programs at The Ohio State University and Western Michigan University to conduct flight tests for our students, but any flight instructor would be capable of performing these basic maneuvers.

We must be sure to emphasize that flying an aircraft involves elevated risk compared to other routine activities in daily life. It is critical for the pilot in command to always maintain positive control of the aircraft and to maintain flight within the performance envelope of the aircraft. All operating limitations of the Pilot's Operating Handbook, as well as all regulatory limitations and best practices for safety of flight, must be observed. Flights should be conducted with a minimum crew of two, where the pilot is solely focused on safe operation of the aircraft. Since precise flying is important for acquiring quality data, the pilot should be experienced – a pilot with a commercial license is likely a safe minimum standard for piloting credentials. The second crew member – the flight test engineer – should be dedicated to acquiring flight data and not have any responsibilities related to ensuring safe operation of flight. The flight test engineer is essentially a passenger for these flights, and all piloting authority and responsibility for the flight rest with the pilot in command. Chapter 6 of this book describes the principles of flight test safety and risk management, which form an essential foundation for the flight test profession. Fly safely!

While there are several other resources on flight testing already available, we saw a specific need for this textbook. Some of the existing resources are targeted toward flight testing professionals and may not be as accessible to the general student. Other resources have become dated, with the relatively recent rewrite of airworthiness certification standards for normal category airplanes (Title 14 of the U.S. Code of Federal Regulations, Part 23). In writing this book, we have sought to provide a modern and accessible resource for flight test educators and students, with several unique features that we hope will set it apart as a helpful and leading resource. Our primary audience is engineering students, with the goal of drawing connections between engineering practice and flight testing experience. We have provided guidelines on how to conduct each flight test, which will guide the reader in the flight test planning process. We have also included unique chapters on digital data acquisition and analysis techniques, uncertainty analysis, and unmanned aircraft flight testing. These are all modern topics that are not covered in the flight testing literature, but are now critical topics. And, with the proliferation of smartphones (repurposed as digital data acquisition devices in manned flight testing) and drones, the modern principles of flight testing are more accessible than ever.

The focus of our book is predominantly on light aircraft (small general aviation airplanes) and small unmanned aircraft. We have homed in on this subset of aviation since these aircraft are generally accessible to the public. While our focus is on light aircraft, the principles described here are equally applicable to all regimes of flight testing. This book provides an introduction, while other resources can be consulted for more advanced topics. The discussion here has been tailored to academic classroom instruction to convey the main principles of flight testing, rather than as a “field manual” for definitive best practices in all situations for flight testing. Having said that, we have made a reasonable effort to align the guidance provided here with accepted best practices. Also, we have decided to omit discussions of spin flight testing and flutter flight testing. These are significant and important topics in flight testing practice, but these are hazardous flight tests. We wish to encourage the reader to engage only with the safer dimensions of flight testing as an entry point.

Throughout this book, we'll predominantly use English units. This is primarily because aviation practice in North America has mostly converged on English units. For example, most air traffic control organizations around the world assign altitude in units of feet and airspeed in units of knots. While SI units are generally preferable in science and engineering environments, we'll generally work with the aviation standard. We view this choice as an educational opportunity for the reader to become acquainted with and proficient in multiple unit systems. There is clear pedagogical value in learning how to quickly convert between and track various units – we hope that students and professional engineers alike will become comfortable with all units and how to convert between them. Appendix B includes a range of unit conversion factors and discussion on best practices for handling units in aviation and engineering practice.

Furthermore, we have avoided embedding implied units into equations. This practice can be convenient for some cases when input and output units for a formula are well established and clearly documented – this can facilitate situations where rapid computations are needed without encumbering the analysis with unit conversions. However, in many cases this practice leads to confusion or ambiguity since the input and output units are seldom clearly documented or agreed upon. Another disadvantage of embedded units is that constants must be embedded in the formula, which have no basis on the physics. This can be confusing to a student who is exposed to theory for the first time. Finally, embedded units force the reader into one specific unit system. Our approach with equations that are unit‐agnostic will allow the reader to use either English or SI consistent units as desired. Thus, the assumption throughout this text (unless otherwise specified) is that equations are based on standard, consistent units.

To the reader – thank you for picking up this book. We are passionate about flight testing and are eager to share our deep interest in this domain with you. We hope that this book will be rewarding, enriching, and fascinating.

James W. GregoryColumbus, OhioTianshu LiuKalamazoo, Michigan

September 6, 2020

Acknowledgements

The authors are grateful for a wide array of colleagues, collaborators, and students who have shaped our thinking and provided input and feedback on this book.

JG would like to thank Profs. Stacy Weislogel and Gerald M. Gregorek, who as pioneers of educational flight testing in the 1970s were inspirations for this work. Prof. Hubert C. “Skip” Smith was also generous with ideas and resources along the way. The flight education department and colleagues in Aviation at The Ohio State University have been extremely helpful in providing tactical support over the years – D. Gelter, D. Hammon, B. Mann, S. Morgan, S. Pruchnicki, C. Roby, B. Strzempkowski, and S. Young. Special thanks go to Profs. Jeffrey Bons and Cliff Whitfield, who helped review significant portions of a near‐final version of the manuscript. (Any remaining errors or inaccuracies are solely the responsibility of the authors). Portions of this book were written in 2014–15 while JG was on sabbatical at the Technion in Israel; the support of Ohio State University and the Fulbright foundation is gratefully acknowledged.

JG also wishes to extend special thanks to Dr. Matt McCrink, who assisted with many of the flight tests presented in this book and coauthored the final chapter on UAV flight testing. He has been an instrumental sounding board and key partner throughout this project.

TL would like to thank M. Schulte, M. Mandziuk, S. Yurk, M. Grashik, S. Woodiga, P. Wewengkang, D. M. Salazar, and WMU's College of Aviation.

Numerous colleagues, including M. Abdulrahim, J. Baughn, K. Colvin, C. Cotting, K. Garman, B. Gray, C. Hall, J. Jacob, J. Kidd, K. Kolsti, J. Langelaan, B. Martos, N. Sarigul‐Klijn, R. Smith, J.P. Stewart, A. Suplisson, A. Tucker, J. Valasek, C. Walker, O. Yakimenko, and M. Yukish, helped influence the presentation of ideas in this book. The Flight Test Education Workshop, hosted by the USAF Test Pilot School, was a particularly helpful resource for materials and connections. A. Bertagnolli of Continental Aerospace Technologies (Continental Motors) and J. J. Frigge of Hartzell Propeller generously provided data and resources for the text. C. Daniloff, K. King, R. Heidersbach, H. Henley, K. King, N. Lachendro, H. Rice, H. Sakaue, B. Stirm, and R. Winiecki gracefully allowed their images or likenesses to be published in this book.

JG and TL also wish to thank their doctoral advisor, Prof. J. P. Sullivan of Purdue University, for his encouragement for us to pursue and finish this project.

Finally, JG and TL especially thank their families for their patience and support over the many years it took to complete this project.

About the Companion Website

The companion website for this book is at

https://www.wiley.com/go/flighttesting

Scan this QR code to visit the companion website.

1Introduction

Flight testing is seemingly the stuff of legends, with tales of derring‐do and bravery, spearheaded by great pilots such as Yeager, Armstrong, Glenn, and others. But what exactly is flight testing all about? What is being tested, and why? What's the difference between a test pilot and a flight test engineer? Is flight testing an inherently dangerous or risky activity?

With this book, we hope to show that flight testing is both exciting and accessible – we hope to make flight testing understandable and achievable by the typical undergraduate aerospace engineering student. The basic principles of flight testing can be explored in any aircraft, all the while remaining safely well within the standard operating envelope of an aircraft. This book will introduce students to the principles that experienced flight test engineers work with as they evaluate new aircraft systems.

Flight testing is all about determining or verifying the performance and handling qualities of an aircraft. These flight characteristics may be predicted in the design and development stages of a new aircraft program, but we never really know the exact capabilities until the full system is flown and tested. Most aircraft flight testing programs are focused on airworthiness certification, which is the rigorous demonstration of all facets of the flight vehicle's performance and handling characteristics in order to ensure safety of flight.

We also wish to highlight that most flight testing should not incur the levels of risk and danger that we associate with the great test pilots of the 20th century. Their bravery was indeed laudable, since they ventured into flight that no human had done before, such as breaking the “sound barrier” or being the first person to walk on the Moon. But, if done correctly, flight testing should be a methodical process where risks are managed at an acceptable level, where human life and property are not exposed to undue risk. Even more hazardous flight testing such as flutter boundary determination or spin recovery should be done in a methodical, well‐controlled manner that mitigates risk. In fact, most flight testing, at least to an experienced professional, can be almost mundane (Corda 2017).

Nor is flight testing an individualistic activity where an intrepid pilot relies solely on their superlative piloting skills to push the aircraft to its limits, as suggested by the caricature in Figure 1.1. Quite the contrary, flight testing is a team effort with many individuals carefully contributing to the overall success of a flight testing program (see Figure 1.2). There is, of course, a pilot involved whose job it is to fly the aircraft as precisely and accurately as possible to put the aircraft through the necessary maneuvers to extract the needed performance or handling data. If an aircraft can carry more than just the pilot, then there is almost always a flight test engineer on board. The flight test engineer is responsible for preparing the plan for the flight test and for acquiring the data in flight while the pilot puts the aircraft through the required maneuvers. Beyond the role of the flight test engineer, there are many others involved – including those who monitor systems and downlinked data on the ground, data analysts who post‐process and interpret the data after the test is complete, and program managers who set the strategic direction for the program and make budgetary decisions.

Figure 1.1 The caricature view of flight test is of an individualistic, cowboy‐like, rugged test pilot who single‐handedly defies danger. Here, Joe Walker playfully boards the Bell X‐1A in a moment of levity.

Source: NASA.

Figure 1.2 A more realistic view of the people behind flight testing – a team effort is required to promote safety and professionalism of flight. Depicted here is the team of NACA scientists and engineers who supported the XS‐1 flight test program.

Source: NASA.

Flight testing is a critical endeavor in the overall design cycle of a new aircraft system. The main objective is to prove out the assumptions that are inherent to every design process and to discover any hidden anomalies in the performance of the aircraft system. Aircraft design typically proceeds by drawing upon historical data to estimate the performance of a new aircraft concept, but there is always uncertainty in those design estimates. The initial stages of design have very crude estimates made for a wide range of parameters and theories applied to the design. Over time, the design team reduces the uncertainty in the design by refining the analysis with improved design tools and higher‐fidelity (more expensive!) analysis, wind tunnel testing, and ground testing of functional systems and even the entire aircraft. But, then the moment of truth always comes, where it is time for first flight of the aircraft. It is at this point that the flight test team documents the true performance of the airplane. If differences arise between actual and predicted performance, minor tweaks to the design may be needed (e.g., the addition of vortex generators on the wings). Also, the insight gleaned from flight testing is documented and fed back into the design process for future aircraft.

This chapter will provide a brief overview of the flight testing endeavor through a historical anecdote that illustrates the key outcomes of flight testing, how flight testing is actually done, and the roles of all involved. Following this, we'll take a look at the various kinds of flight testing that are done, with a particular emphasis on airworthiness certification of an aircraft, which is the main objective of many flight testing programs. We'll then conclude this chapter with an overview of the rest of the book, including our objectives in writing this book and what we hope the reader will glean from this text.

1.1 Case Study: Supersonic Flight in the Bell XS‐1

A great way to learn about the essential elements of a successful flight test program is to look at a historical case study. We'll consider the push by the Army Air Forces (AAF) in 1947 to fly an aircraft faster than the speed of sound. Along the way, we'll pick up some insight into how flight testing is done and some of the values and principles of the flight test community.

At the time, many scientists and engineers did not think that supersonic flight could be achieved. They observed significant increases in drag as the flight speed increased. On top of that, there were significant loss‐of‐control incidents where pilots found that their aircraft could not be pulled out of a high‐speed dive. These highly publicized incidents led some to conclude that the so‐called “sound barrier” could not be broken. We now know, however, that this barrier only amounted to a lack of insight into the physics of shock–boundary layer interaction, shock‐induced separation, and the transonic drag rise, along with a lack of high‐thrust propulsion sources to power through the high drag. Scientific advancements in theoretical analysis, experimental testing, and flight testing, along with engineering advancements in propulsion and airframe design, ultimately opened the door to supersonic flight.

In a program kept out of public sight, the U.S. Army Air Forces, the National Advisory Committee for Aeronautics (NACA, the predecessor to NASA), and the Bell aircraft company collaborated on a program to develop the Bell XS‐1 with the specific intent of “breaking the sound barrier” to supersonic flight. (Note that the “S” in XS‐1 stands for “supersonic”; this letter was dropped early in the flight testing program, leaving us with the commonly known X‐1 notation.) The XS‐1 (see Figure 1.3) was a fixed‐wing aircraft with a gross weight of 12,250 lb, measured 30‐ft 11‐in. long, had a straight (unswept) wing with an aspect ratio of 6.0 and a span of 28 ft, and an all‐moving horizontal tail (a detail that we'll soon see was important!). The XS‐1 was powered by a four‐chamber liquid‐fueled rocket engine producing 6000 lb of thrust. The overarching narrative of the program is well documented in numerous historical and popular sources (e.g., see Young 1997; Gorn 2001; Peebles 2014; Hallion 1972; Hallion and Gorn 2003; or Wolfe 1979), but we'll pick up the story in the latter stages of the flight test program at Muroc Army Airfield, positioned on the expansive Rogers Dry Lake bed that is today the home of Edwards Air Force Base and NASA Armstrong Flight Research Center.

Figure 1.3 Three‐view drawing of the Bell XS‐1.

Source: NASA, X‐1/XS‐1 3‐View line art. Available at http://www.dfrc.nasa.gov/Gallery/Graphics/X‐1/index.html.

The XS‐1 had an aggressive flight test schedule, with not too many check‐out flights before going for the performance goal of supersonic flight. The extent of the test program was actually a matter of contentious debate between the AAF, the NACA, and Bell. In the end, Bell dropped out of the mix for contractual and financial reasons, and the NACA and AAF proceeded to collaborate on the flight test program. But the continued collaboration was not without tension. The AAF leaders and pilots continually pushed for an aggressive flight test program, making significant steps with each flight. The NACA, on the other hand, advocated for a much slower, methodical pace where substantial data would be recorded with each flight and carefully analyzed before proceeding on to the next boundary. In the end, the AAF vision predominantly prevailed, although there was a reasonable suite of instrumentation on board the aircraft. The XS‐1 was outfitted with a six‐channel telemeter, where NACA downlinked data on airspeed, altitude, elevator position, normal acceleration, stabilizer position, aileron position, and elevator stick force, along with strain gauges to record airloads and vibrations (Gorn 2001, p. 195). On the ground, the NACA crew had five trucks to support the data acquisition system – one to supply power, one for telemetry data, and three for radar. The radar system was manually directed through an optical sight, but if visual of the aircraft was lost, the radar system could be switched to automatic direction finding (Gorn 2001, pp. 187–188).

To lead the flying of the aircraft toward the perceived “sound barrier,” the AAF needed a pilot with precision flying capabilities, someone who was unflappable under pressure, and someone with scientific understanding of the principles involved. The Army turned to Captain Charles E. “Chuck” Yeager – a young, 24‐year‐old P‐51 ace from World War II – for the honor and responsibility of being primary pilot. According to Colonel Albert Boyd who selected him, Yeager had impeccable instinctive piloting skills and could work through the nuance of the aircraft's response to figure out exactly how it was performing (Young 1997, p. 41). Not only could he fly with amazing skill, but the engineering team on the ground loved him for his postflight debriefs. Yeager was able to return from a flight and relate in uncanny detail exactly how the aircraft responded to his precise control inputs, all in a vernacular that the engineering staff could immediately appreciate (Peebles 2014, p. 29). But it wasn't just Yeager doing all of the work – he had a team around him. Backing him up and flying an FP‐80 chase plane was First Lieutenant Robert A. “Bob” Hoover, who was also well known as an exceptional pilot. Captain Jackie L. “Jack” Ridley, an AAF test pilot and engineer with an MS degree from Caltech, was the engineer in charge of the project. Others involved included Major Robert L. “Bob” Cardenas, pilot of the B‐29 Superfortress carrier aircraft and officer in charge, and Lieutenant Edward L. “Ed” Swindell, flight engineer for the B‐29. Backing up these AAF officers was Richard “Dick” Frost, a Bell engineer and test pilot who already had flight experience in the XS‐1 and got Yeager up to speed on the intricacies of the aircraft. This cast of characters is depicted in Figure 1.4.

Beyond this core group of military professionals was a team of NACA scientists and engineers led by Walt Williams (see Figure 1.2). This team was focused predominantly on understanding the flight physics in this exploratory program, providing deep technical insight and support to the Air Force crew. Yet, this objective was inherently at odds with the AAF's stated desire to push to supersonic flight as quickly and safely as possible. This tension was aptly described by Williams: “We were enthusiastic, there is little question. The Air Force group – Yeager, Ridley – were very, very enthusiastic. We were just beginning to know each other, just beginning to work together. There had to be a balance between complete enthusiasm and the hard, cold facts. We knew that if this program should fail, the whole research airplane program would be set back. So, our problem became one of maintaining the necessary balance between enthusiasm and eagerness to get the job completed with a scientific approach that would assure success of the program. That was accomplished” (Gorn 2001, pp. 194–195).

Figure 1.4 The Air Materiel Command XS‐1 flight test team, composed of (from left to right): Ed Swindell (B‐29 Flight Engineer), Bob Hoover (XS‐1 Backup and Chase Pilot), Bob Cardenas (Officer‐in‐charge and B‐29 Pilot), Chuck Yeager (XS‐1 Pilot), Dick Frost (Bell Engineer), and Jack Ridley (Project Engineer).

Source: U.S. Air Force.

In the run‐up to the first supersonic flight, the team carefully pushed forward. On Yeager's first powered flight on August 29, 1947, he accelerated up to Mach 0.85, exceeding the planned test point of Mach 0.8. This negated NACA's need to acquire telemetered data in the Mach 0.8–0.85 range, leading to further tension between Yeager and Williams. In Yeager's words, “They [the NACA engineers and technicians] were there as advisers, with high‐speed wind tunnel experience, and were performing the data reduction collected on the X[S]‐1 flights, so they tried to dictate the speed in our flight plans. Ridley, Frost, and I always wanted to go faster than they did. They would recommend a Mach number, then the three of us would sit down and decide whether or not we wanted to stick with their recommendation. They were so conservative that it would've taken me six months to get to the [sound] barrier” (Young 1997, p. 51 – quoted from Yeager and Janos (1985), p. 122).

Yeager was admonished by Colonel Boyd to cooperate more carefully with the NACA technical specialists and to follow the test plan. This led to careful preflight briefings that, while Yeager considered to be tedious, were essential to flight safety and accomplishment of the test objectives. At each briefing, Williams would review the lessons learned from the previous flight and detail the objectives of the upcoming mission (Gorn 2001, pp. 195–196).