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Low Cost Accurate Angle of Attack System

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Low Cost Accurate Angle of Attack System DOT/FAA/TC-18/7 Low-Cost Accurate Angle of Federal Aviation Administration William J. Hughes Technical Center Attack System Aviation Research Division Atlantic City International Airport New Jersey 08405 January 2018 Final Report This document is available to the U.S. public through the National Technical Information Services (NTIS), Springfield, Virginia 22161. This document is also available from the Federal Aviation Administration William J. Hughes Technical Center at actlibrary.tc.faa.gov. U.S. Department of Transportation Federal Aviation Administration NOTICE This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the contents or use thereof. The U.S. Government does not endorse products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the objective of this report. The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the funding agency. This document does not constitute FAA policy. Consult the FAA sponsoring organization listed on the Technical Documentation page as to its use. This report is available at the Federal Aviation Administration William J. Hughes Technical Center’s Full-Text Technical Reports page: actlibrary.tc.faa.gov in Adobe Acrobat portable document format (PDF). Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. DOT/FAA/TC-18/7 4. Title and Subtitle 5. Report Date LOW-COST ACCURATE ANGLE OF ATTACK SYSTEM January 2018 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. David F. Rogers, Borja Martos1, and Francisco Rodrigues1 10. Work Unit No. (TRAIS) 1 Embry-Riddle Aeronautical University Eagle Flight Research Center/College of Engineering 1585 Aviation Parkway, Suite 606 Daytona Beach, FL 32114 11. Contract or Grant No. 2014-G-013 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered U.S. Department of Transportation Final Report Federal Aviation Administration Central Regional Office 901 Locust St Kansas City, MO 64106 14. Sponsoring Agency Code AIR-690 15. Supplementary Notes The FAA William J. Hughes Technical Center Aviation Research Division COR was Robert J. McGuire. 16. Abstract A low-cost ($100/see table A-1 of appendix A) differential pressure-based commercial off-the-shelf (COTS) angle of attack (AoA) data acquisition system was designed, successfully reduced to practice, wind tunnel tested, and flight tested. The accuracy of the differential pressure AoA system was determined to be ¼ to ½ of a degree. The repeatability of the data from the COTS system was excellent. Using un-normalized differential pressure (Pfwd-P45) does not provide adequate accuracy throughout the aircraft’s AoA range. This technique is dynamic pressure-dependent. For a limited range of high angles of attack near stall, a linear fit to the data provides adequate accuracy. However, the accuracy at low AoA, such as those required by cruise, is poor. Therefore, systems similar to that tested using a linear calibration are basically stall warning devices. A physics-based determination of AoA was successful, provided that a reasonably accurate aircraft lift curve was determined. The calculation of the lift curve slope was within 0.01 degrees of the value determined by the flight test using an alpha/beta probe. A calibration curve based on the ratio of Pfwd/P45 was studied and determined to be linear throughout the aircraft’s AoA when the probe was located on the wing’s lower surface between an estimated 25% and 60% of the local wing chord. 17. Key Words 18. Distribution Statement This document is available to the U.S. public through the Angle of attack, General aviation, Sensors, Instrumentation National Technical Information Service (NTIS), Springfield, Virginia 22161. This document is also available from the FAA William J. Hughes Technical Center at actlibrary.tc.faa.gov. 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 117 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized ACKNOWLEDGEMENTS Dave Rogers gratefully acknowledges the critical contributions of Francisco Rodriguez, specifically his conversion of concepts into electronic and computer code. He also acknowledges the professional support of Borja Martos, of Eagle Flight Research Center, for the exceptional conduct of the flight test program. Martos is an outstanding flight test engineer and a superb pilot whose skills facilitated excellent datasets. Rogers also acknowledges the support of Peter Osterc, Alfonso Noriega, and Yosvanny Alonso, students of the Eagle Flight Research Center, for their efforts as computer flight test engineers on the various test flights. Additionally, Rogers wishes to thank Dave Sizoo of the FAA Small Airplane Directorate and Bob McGuire of the FAA William J. Hughes Technical Center for their willingness to support the flight test program. iii TABLE OF CONTENTS Page EXECUTIVE SUMMARY ix 1. INTRODUCTION 1 2. THE AIRCRAFT FUNDAMENTAL ANGLE OF ATTACK 1 2.1 Nondimensionalization 2 2.2 Relation Between Angle of Attack and Velocity 3 2.3 Fundamental Angle of Attack — αL/Dmax 4 2.4 Power Required and Angle of Attack 5 2.5 Why is Flying Angle of Attack Important? 6 3. WIND TUNNEL TESTS 6 3.1 The Calibration Effect 8 3.2 Calibration Techniques 9 3.3 Alternate Normalization Techniques 9 4. DESIGN OF THE DATA ACQUISITION SYSTEM 11 4.1 Accuracy 11 4.2 Pressure Range 12 4.3 Reference Pressure 12 4.4 Pressure Sensors 12 4.5 Development System 13 4.6 Basic Design of the DFRDAS 14 4.7 Software Description 14 4.8 Wind Tunnel Testing Of The DFRDAS Breadboard 15 4.9 Noload Altitude Test 16 5. ROAD TESTS 16 6. PROOF OF CONCEPT FLIGHT TEST 18 7. THE AIRCRAFT 18 8. THE JANUARY 21 AND 22, 2015 FLIGHTS 18 8.1 Physics-Based Determination of Absolute AoA 19 8.2 The Results of the January 21 and 22, 2015 Flight Tests 19 9. AIR DATA PROBE AND ALPHA/BETA BOOM 20 10. THE RESULTS OF THE 22 APRIL 2015 FLIGHT TEST 22 iv 10.1 Left Wing DFRDAS-1 Results 23 10.2 Right wing DFRDAS-2 Results 24 11. THE RESULTS OF THE MAY 26 AND 27, 2015 FLIGHT TESTS 27 11.1 Left Wing DFRDAS-1 Results 28 11.2 Right Wing DFRDAS-2 Results 29 11.3 Right Wing Flaps 40º Results 30 12. AERODYNAMICS OF WHY A LINEAR CALIBRATION CURVE? AERODYNAMICS OF WHY A LINEAR CALIBRATION CURVE? 31 13. THE RESULTS OF THE AUGUST 18 AND 19, 2015 FLIGHT TESTS 33 13.1 Right Wing DFRDAS-2 Results 33 13.2 Stall Results 33 14. WHAT WORKS AND WHAT DOES NOT WORK 37 15. CONCLUSIONS 39 16. SUGGESTED FUTURE WORK 40 17. REFERENCES 41 APPENDICES A—DETAILS FOR THE ARDUINO-BASED COMMERCIAL OFF-THE- SHELF SYSTEM B—MECHANICAL DRAWINGS, GENERAL ASSEMBLY, GROUND AND FLIGHT TESTING C—AERODYNAMICS OF WHY A LINEAR CALIBRATION WORKS D—THE EFFECT OF THE AVERAGE OF AN AVERAGE E—THE RESPONSE OF THE DFRDAS TO VARIOUS STALL CONFIGURATIONS F—HAZARDS, TEST CARDS, AND FLIGHT LOG v LIST OF FIGURES Figure Page 1 Altitude effect on power required 2 2 Nondimensional power required—multiple effects 3 3 Relationship between nondimensional velocity and nondimensional angle of attack 4 4 Relationship between nondimensional power required and nondimensional AoA 6 5 Probe mounted in the wind tunnel 7 6 Probe pressure port locations 7 7 Pfwd-P45 as a function of AoA 8 8 Pfwd-P45 normalized with dynamic pressure 8 9 Flight line and the e ect of two-point and four-point linear calibration 9 10 An alternate method of normalizing the pressure 11 ff 11 AoA as a function of Pfwd/P45 11 12 MS4525 di erential pressure sensor 13 13 Bosch BMP085 altitude/pressure absolute pressure sensor 13 ff 14 Arduino UNO R3 development microcontroller system 14 15 DFRDAS breadboard as used for wind tunnel verification tests 15 16 Comparison of wind tunnel result for the breadboard DAS and the results read from the inclined manometer 16 17 Combined results for the January 21 and 22, 2015 flight tests 20 18 Alpha/beta probe mounted on the aircraft 20 19 Alpha/beta probe head 21 20 Spanwise location of the right wing probe DFRDAS-2 23 21 Alpha vs. Pfwd/P45 results for the left wing DFRDAS-1 probe for the April 22, 2015 flight test 24 22 Alpha vs. Pfwd/P45 results for the right wing DFRDAS-2 probe for the April 22, 2015 flight test 25 23 Pfwd/P45 vs. Alpha results for the right wing DFRDAS-2 probe for the April 22, 2015 flight test 25 24 Alpha vs. Pfwd/P45 results for the right wing DFRDAS-2 for the April 22, 2015 flight test 26 25 Lift coe cient vs. AoA with respect to the fuselage reference line for two stall flight tests 27 ffi vi 26 Absolute angle of attack vs. time for stall 1. Pfwd/P45 data is from DFRDAS-2. The absolute angle of attack is calculated using the calibration curve for the DFRDAS-2 shown in figure 23 28 27 Absolute AoA vs. Pfwd/P45 for the DFRDAS-1 from the May 26, 2015 flight test: the probe is mounted approximately at the leading edge of the left wing of the aircraft 29 28 Absolute AoA vs. Pfwd/P45 for the DFRDAS-2 from the May 26, 2015 flight test: the probe is mounted at 38.9% of the local chord on the right wing of the aircraft 30 29 Absolute AoA vs.
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