The Measurement of the Pressure Distribution over the Wing of an Aircraft in Flight Matthew McCarty A thesis submitted in fulfilment of the requirements for the Degree of Masters of Aerospace Engineering School of Aerospace, Civil and Mechanical Engineering University of New South Wales Australian Defence Force Academy August 2008 Statements Originality Statement ‘I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institute, except where due acknowledgement is made in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that the assistance from others in the project’s design and conception or in style, presentation and linguistic expression is acknowledged.’ Signed ………………………………………………… Date ………………………………………………… Copyright Statement ‘I hereby grant to The University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the Universities libraries, in all forms of media, now or hereafter known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I have either used no substantial portions of copyright material in my thesis, or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation.’ Signed ………………………………………………… Date ………………………………………………… Authenticity Statement ‘I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are minor variations in formatting, they are the result of conversion to digital format.’ Signed ………………………………………………… Date ………………………………………………… ii Abstract A measurement system has been developed for use on a light aircraft to measure the pressure distribution over the wing surfaces. The measurement system was developed as a low-cost alternative to existing advanced measurement systems. The system consisted of low profile, low cost pressure sensors that interfaced digitally with microcontrollers for data acquisition. The pressure sensors and microcontrollers were developed into self-contained sensor modules with all electronic components mounted on flexible circuit board that formed the base of the modules. Two types of module were developed; a module with a single pressure sensor and a module with a row of seven pressure sensors at fifteen millimetre spacing. The total cost of the sensor modules was approximately ninety dollars for a single sensor module and one hundred and forty dollars for the seven sensor module. Studies were carried out using numerical methods to predict the pressure distribution over a NACA2412 airfoil. The numerical studies were used to evaluate the effect of adding the sensor modules to the wing, and the effect of the sensor distribution on measured force coefficients. Numerical predictions were made using the XFOIL software package. This software was validated using the Hess-Smith inviscid panel method. Flight testing was carried out with the pressure distribution measurement system to confirm the operation of the system and to make preliminary measurements. The flight testing focused on the measurement of steady state pressure distributions for comparison with the numerical predictions. Good agreement was found between the measured pressure distributions and the XFOIL predictions. Integration of the pressure distributions enabled comparison of normal force, lift force and quarter chord moment coefficients. The measured force coefficients showed the expected trends with angle of attack although it was found that the limited number of sensor modules used caused large error in the quarter chord moment coefficient compared to the numerical predictions. iii Acknowledgments First and foremost I would like to thank my supervisor Dr Michael Harrap. The chance to undertake postgraduate research that involved flying was a rare one and I am extremely grateful for the opportunity. I would like to thank those from the ‘aviation research group’ at UNSW@ADFA; Sue Burdekin, Raymond Lewis, and Martin Copeland for their support. For the tremendous help and time devoted to teaching a mechanical engineer the intricacies of electrical and electronic engineering I would like to thank Andrew Roberts, Evan Hawke, Tony Peebles, and Geno Ewyk. Thanks needs to go to the other academic staff from the University, whose expertise in various areas was invaluable to bounce ideas off, especially John Milthorpe, Alan Fien, John Young, Krishna Shankar, and Andrew Neely. A big thanks needs to go to the workshop staff that helped with the project, especially Marcus DeAlmeida, Bob Bleakley, Dave Sharp, Jim Baxter and Wayne Jealous. I would like to acknowledge the support of the office staff at the School of ACME; Carol Obrien, Cheri Khalil, Gill Taylor, and Vira Berra. I would like to thank the postgrads from ACME; Chris Hang, Orio Kieboom, Laxmikant Kannapan, Vishwas Puttige, Arif Ashraff, Kartik ‘Ram’ Ramakrishnan, Steve Choi, Abhi Kallapur, Kamal Singh, and Sebastian Oberst. Thanks to my housemates; Ra, Beth, Dave and Sam. Finally thanks must go to my family, Mum, Dad, Jennifer and Thomas whose support from abroad for my endeavours ‘across the ditch’ was invaluable. iv Table of Contents Statements.........................................................................................................................i Statements........................................................................................................................ii Abstract...........................................................................................................................iii Acknowledgments ..........................................................................................................iv Table of Contents ............................................................................................................v List of Figures................................................................................................................vii List of Tables .................................................................................................................xii List of Tables .................................................................................................................xii 1 Introduction.............................................................................................................1 1.1 Why measure pressure distribution? .................................................................1 1.2 Air Pressure Distribution ..................................................................................1 1.3 Measuring the pressure distribution in flight ....................................................6 1.4 Objective ...........................................................................................................6 1.5 Flight Labs........................................................................................................6 1.6 Project Origin....................................................................................................6 1.7 Thesis structure.................................................................................................7 2 A Review of In-Flight Pressure Measurement Techniques.................................9 2.1 Why measure aircraft pressure distributions?...................................................9 2.2 Methods for measuring pressure distributions ................................................11 2.2.1 Tubed Pressure Belts ............................................................................................................11 2.2.2 Flush surface orifices............................................................................................................ 16 2.2.3 Pressure sensitive paint......................................................................................................... 17 2.2.4 Modern advancements .......................................................................................................... 19 2.3 Aerodynamic properties measured using pressure belts .................................23 2.4 Comparisons between pressure distribution measurement methods...............26 2.4.1 Comparison with wind tunnel testing................................................................................... 26 2.4.2 Comparison between flush orifice and pressure belt methods ............................................ 28 2.5 Conclusions.....................................................................................................30 3 Development of the pressure measurement system ...........................................31 3.1 Description of the system................................................................................31 3.2 Pressure Sensor...............................................................................................33 3.2.1 SCP1000 pressure sensor.....................................................................................................