EASA MODULE 8 PDF - Basic Aerodynamics

Module FOR B1 & B2 CERTIFICATION 08 BASIC AERODYNAMICS Aviation Maintenance Technician Certification Series - Physics of the Atmosphere - Aerodynamics - Theory of Flig...

Module FOR B1 & B2 CERTIFICATION 08 BASIC AERODYNAMICS Aviation Maintenance Technician Certification Series - Physics of the Atmosphere - Aerodynamics - Theory of Flight - Flight Stability and Dynamics www.amequestionpaper.in  EASA Part-66 Aviation Maintenance Technician Certification Series NO COST REVISION/UPDATE SUBSCRIPTION PROGRAM Complete EASA Part-66 Aviation Maintenance Technician Certification Series NO COST REVISION/UPDATE PROGRAM Aircraft Technical Book Company is offering a revision/update program to our customers who purchase an EASA Module from the EASA Aviation Maintenance Technician Certification Series. The update is good for two (2) years from time of registration of any EASA Module or EASA bundled kits. If a revision occurs within two (2) years from date of registration, we will send you the revised pages FREE of cost to the registered email. Go to the link provided at the bottom of this page and fill out the form to be included in the EASA Revision/Update Subscription Program. In an effort to provide quality customer service please let us know if your email you register with changes so we can update our records. If you have any questions about this process please send an email to: [email protected] HERE’S HOW IT WORKS 1. All EASA Module Series textbooks contain an EASA subscription page explaining the subscription update process and provide a web site link to register for the EASA Revision/Update Subscription Program. 2. Go to the link provided below and fill out the web based form with your first and last name, current email address, and school if applicable. 3. From the time of purchase, if a revision occurs to the Module you have registered for, a revised PDF file containing the pages with edits will be sent to the registered email provided. 4. Please note that we try to keep our records as current as possible. If your email address provided at time of registration changes please let us know as soon as possible so we can update your account. 5. This service is FREE of charge for two (2) years from date of registration. LINK TO REGISTER FOR REVISION/UPDATE PROGRAM http://www.actechbooks.com/easasub/m08  www.amequestionpaper.in > Visit our website to download all latest EASA / DGCA CAR 66 Module examination Question papers and study material  MODULE 08 FOR B1 & B2 CERTIFICATION BASIC AERODYNAMICS Aviation Maintenance Technician Certification Series 72413 U.S. Hwy 40 Tabernash, CO 80478-0270 USA www.actechbooks.com +1 970 726-5111  AVAILABLE IN Printed Edition and Electronic (eBook) Format AVIATION MAINTENANCE TECHNICIAN CERTIFICATION SERIES Author Thomas Forenz Contributor Nerijus Baublys Layout/Design Michael Amrine Version 3 - Effective Date 07.01.2018 Copyright © 2015, 2018 — Aircraft Technical Book Company. All Rights Reserved. No part of this publication may be reproduced, stored in a retrieval system, transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher. To order books or for Customer Service, please call +1 970 726-5111. www.actechbooks.com Printed in the United States of America For comments or suggestions about this book, please call or write to: 1.970.726.5111 | [email protected]  WELCOME The publishers of this Aviation Maintenance Technician Certification Series welcome you to the world of aviation maintenance. As you move towards EASA certification, you are required to gain suitable knowledge and experience in your chosen area. Qualification on basic subjects for each aircraft maintenance license category or subcategory is accomplished in accordance with the following matrix. Where applicable, subjects are indicated by an "X" in the column below the license heading. For other educational tools created to prepare candidates for licensure, contact Aircraft Technical Book Company. We wish you good luck and success in your studies and in your aviation career! REVISION LOG VERSION EFFECTIVE DATE DESCRIPTION OF CHANGE 001 2015 01 Module Creation and Release 002 2016 07 Format Update and Minor Content Revisions Adjusted sequence for Appendix 1; Added content to Sub-Module 02: Free Stream Air Flow, 003 2018 07 Wash-In/Wash-Out. Sub-Module 03: Steady State Flight; High Speed Aerodynamics; Helicopter Aerodynamics. Sub-Module 04: Passive and Active Stability. Module 08 - Basic Aerodynamics iii  FORWARD PART-66 and the Acceptable Means of Compliance (AMC) and Guidance Material (GM) of the European Aviation Safety Agency (EASA), Appendix 1 establishes the Basic Knowledge Requirements for those seeking an aircraft maintenance license. The information in this Module of the Aviation Maintenance Technical Certification Series published by the Aircraft Technical Book Company meets or exceeds the breadth and depth of knowledge subject matter referenced in Appendix 1 of the Implementing Rules. However, the order of the material presented is at the discretion of the editor in an effort to convey the required knowledge in the most sequential and comprehensible manner. Knowledge levels required for Category A1, B1, B2, and B3 aircraft maintenance licenses remain unchanged from those listed in Appendix 1 Basic Knowledge Requirements. Tables from Appendix 1 Basic Knowledge Requirements are reproduced at the beginning of each module in the series and again at the beginning of each Sub-Module. How numbers are written in this book: This book uses the International Civil Aviation Organization (ICAO) standard of writing numbers. This method displays large numbers by adding a space between each group of 3 digits. This is opposed to the American method which uses commas and the European method which uses periods. For example, the number one million is expressed as so: ICAO Standard 1 000 000 European Standard 1.000.000 American Standard 1,000,000 SI Units: The International System of Units (SI) developed and maintained by the General Conference of Weights and Measures (CGPM) shall be used as the standard system of units of measurement for all aspects of international civil aviation air and ground operations. Prefixes: The prefixes and symbols listed in the table below shall be used to form names and symbols of the decimal multiples and submultiples of International System of Units (SI) units. MULTIPLICATION FACTOR PReFIx SyMbOL 1 000 000 000 000 000 000 = 101⁸ exa E 1 000 000 000 000 000 = 101⁵ peta P 1 000 000 000 000 = 1012 tera T 1 000 000 000 = 10⁹ giga G 1 000 000 = 10⁶ mega M 1 000 = 103 kilo k 100 = 102 hecto h 10 = 101 deca da 0.1 =10-1 deci d 0.01 = 10-2 centi c 0.001 = 10-3 milli m 0.000 001 = 10-⁶ micro µ 0.000 000 001 = 10-⁹ nano n 0.000 000 000 001 = 10-12 pico p 0.000 000 000 000 001 = 10-1⁵ femto f 0.000 000 000 000 000 001 = 10-1⁸ atto a International System of Units (SI) Prefixes iv Module 08 - Basic Aerodynamics  EASA LICENSE CATEGORY CHART A1 B1.1 B1.2 B1.3 B2 Module Number and Title Airplane Airplane Airplane Helicopter Avionics Turbine Turbine Piston Turbine 1 Mathematics X X X X X 2 Physics X X X X X 3 Electrical Fundamentals X X X X X 4 Electronic Fundamentals X X X X 5 Digital Techniques / Electronic Instrument Systems X X X X X 6 Materials and Hardware X X X X X 7A Maintenance Practices X X X X X 8 Basic Aerodynamics X X X X X 9A Human Factors X X X X X 10 Aviation Legislation X X X X X 11A Turbine Aeroplane Aerodynamics, Structures and Systems X X 11B Piston Aeroplane Aerodynamics, Structures and Systems X 12 Helicopter Aerodynamics, Structures and Systems X 13 Aircraft Aerodynamics, Structures and Systems X 14 Propulsion X 15 Gas Turbine Engine X X X 16 Piston Engine X 17A Propeller X X X GENERAL KNOWLEDGE REQUIREMENTS MODULE 08 SYLLABUS AS OUTLINED IN PART-66, APPENDIX 1 Level 1 Level 2 Level 3 A familiarization with the principal elements of A general knowledge of the theoretical and practical A detailed knowledge of the theoretical and practical the subject. aspects of the subject and an ability to apply aspects of the subject and a capacity to combine and Objectives: that knowledge. apply the separate elements of knowledge in a logical a. The applicant should be familiar with the basic Objectives: and comprehensive manner. elements of the subject. a. The applicant should be able to understand the Objectives: b. The applicant should be able to give a simple theoretical fundamentals of the subject. a. The applicant should know the theory of the description of the whole subject, using common b. The applicant should be able to give a general subject and interrelationships with other subjects. words and examples. description of the subject using, as appropriate, b. The applicant should be able to give a detailed c. The applicant should be able to use typical terms. typical examples. description of the subject using theoretical c. The applicant should be able to use mathematical fundamentals and specific examples. formula in conjunction with physical laws c. The applicant should understand and be able to describing the subject. use mathematical formula related to the subject. d. The applicant should be able to read and d. The applicant should be able to read, understand understand sketches, drawings and schematics and prepare sketches, simple drawings and describing the subject. schematics describing the subject. e. The applicant should be able to apply his e. The applicant should be able to apply his knowledge in a practical manner using knowledge in a practical manner using detailed procedures. manufacturer’s instructions. f. The applicant should be able to interpret results from various sources and measurements and apply corrective action where appropriate. Module 08 - Basic Aerodynamics v  LEVELS PART-66 - APPENDIX I BASIC KNOWLEDGE REQUIREMENTS B1 B2 Sub-Module 01 - Physics of the Atmosphere International Standard Atmosphere (ISA), application to aerodynamics. 20 20 Sub-Module 02 - Aerodynamics Airflow around a body; 2 2 Boundary layer, laminar and turbulent flow, free stream flow, relative airflow, upwash and downwash, vortices, stagnation; The terms: camber, chord, mean aerodynamic chord, profile (parasite) drag, induced drag, center of pressure, angle of attack, wash in and wash out, fineness ratio, wing shape and aspect ratio; Thrust, Weight, Aerodynamic Resultant; Generation of Lift and Drag: Angle of Attack, Lift coefficient, Drag coefficient, polar curve, stall; Aerofoil contamination including ice, snow, frost. Sub-Module 03 - Theory of Flight Relationship between lift, weight, thrust and drag; 2 2 Glide ratio; Steady state flights, performance; Theory of the turn; Influence of load factor: stall, flight envelope and structural limitations; Lift augmentation. Sub-Module 04 - Flight Stability and Dynamics Longitudinal, lateral and directional stability (active and passive). 2 2 vi Module 08 - Basic Aerodynamics  CONTENTS BASIC AERODYNAMICS Parasitic Drag‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.13 Welcome‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ iii Form Drag‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.13 Revision Log‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ iii Friction Drag‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.13 Forward‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ iv Interference Drag‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.14 EASA License Category Chart‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ v Induced Drag‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.15 General Knowledge Requirements‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ v Wave Drag‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.16 Contents‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ vii Drag and Airspeed‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.16 Aerodynamic Contamination‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.16 SUB-MODULE 01 Questions‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.17 PHYSICS OF THE ATMOSPHERE Answers‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.18 Knowledge Requirements‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 1.1 8.1 - Physics Of The Atmosphere‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 1.2 SUB-MODULE 03 Basic Aerodynamics‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 1.2 THEORY OF FLIGHT Physics of the Atmosphere‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 1.2 Knowledge Requirements‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.1 Pressure‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 1.2 8.3 - Theory of Flight‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.2 Density‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 1.4 Relationship Between Lift, Weight, Thrust and Drag Humidity‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 1.4 3.2 Temperature and Altitude‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 1.4 Weight‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.2 International Standard Atmosphere‥‥‥‥‥‥‥‥‥‥‥‥‥ 1.5 Lift‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.2 Questions‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 1.7 Thrust and Drag‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.3 Answers‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 1.8 Steady State Flight‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.3 Glide Ratio‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.3 SUB-MODULE 02 Polar Curve‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.4 AERODYNAMICS Aerodynamic Forces in Turns‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.5 Knowledge Requirements‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.1 Influence of Load‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.7 8.2 - Aerodynamics‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.2 Stalls‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.7 Velocity and Acceleration‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.2 Flight Envelope‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.9 Newton's Laws of Motion‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.2 Structural Limitations‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.9 Airflow Around a Body‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.3 Load Factors‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.9 Bernoulli's Principle and Subsonic Flow‥‥‥‥‥‥‥ 2.3 Load Factors in Aircraft Design‥‥‥‥‥‥‥‥‥‥‥ 3.9 Upwash and Downwash‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.4 High Speed Flight‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.10 Free Stream Flow ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.4 Subsonic vs Supersonic Flow‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.10 Boundary Layer and Friction Effects‥‥‥‥‥‥‥‥‥‥ 2.4 Speed Ranges‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.11 Laminar and Turbulent Flow‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.5 Mach Number vs Airspeed‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.12 Planform and Vortices‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.6 Shock Waves‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.12 Aerodynamic Terms‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.7 Sweepback‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.14 Chord AND Chamber‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.7 Lift Augmentation‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.15 Airfoils‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.8 Flaps‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.15 Shape of the Airfoil‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.9 Leading Edge Devices‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.16 Wash-out/Wash-in‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.9 Fixed Airflow Devices‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.17 Forces in Flight‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.10 High-Speed Aerodynamics‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.18 Aerodynamic Resultant‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.10 The Speed of Sound‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.18 Generation of Lift and Drag‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.10 Subsonic, Transonic, and Supersonic Flight‥‥‥‥ 3.18 Lift and Drag Coefficients‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.11 Shock Waves‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.19 Lift/Drag Ratio‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.11 Normal Shock Wave‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.20 Angle of Attack (AOA)‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.12 Oblique Shock Wave‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.20 Drag‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2.13 Expansion Wave‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.20 Module 08 - Basic Aerodynamics vii  CONTENTS High-Speed Airfoils‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.20 Aerodynamic Heating‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.21 Helicopter Aerodynamics‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.21 Helicopter Structures and Airfoils‥‥‥‥‥‥‥‥‥‥‥‥ 3.21 Main Rotor Systems‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.22 Anti-Torque Systems‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.23 Helicopter Axes of Flight‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.25 Control Around the Vertical Axis‥‥‥‥‥‥‥‥‥‥ 3.25 Control Around the Longitudinal and Lateral Axes ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.26 Helicopters in Flight‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.26 Hovering‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.26 Forward Flight‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.27 Blade Flapping‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.27 Advancing Blade and Retreating Blade Problems 3.28 Autorotation‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.28 Questions‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.29 Answers‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3.30 SUB-MODULE 04 FLIGHT STABILITY AND DYNAMICS Knowledge Requirements‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.1 8.4 - Flight Stability and Dynamics‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.2 The Axes of an Aircraft‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.2 Stability and Control‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.3 Static Stability‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.3 Dynamic Stability‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.3 Longitudinal Stability (Pitching)‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.4 Lateral Stability (Rolling)‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.6 Dihedral‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.7 Sweepback‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.7 Keel Effect/Weight Distribution‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.7 Directional Stability (Yawing)‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.8 Free Directional Oscillations (Dutch Roll)‥‥‥‥‥ 4.9 Passive and Active Stability‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.9 Questions‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.11 Answers‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 4.12 Acronym Index‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ A.1 Glossary‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ G.1 Index‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ I.1 viii Module 08 - Basic Aerodynamics  PHYSICS OF THE ATMOSPHERE PART-66 SYLLABUS LEVELS CERTIFICATION CATEGORY ¦ B1 B2 Sub-Module 01 PHYSICS OF THE ATMOSPHERE Knowledge Requirements 8.1 - Physics of the Atmosphere International Standard Atmosphere (ISA), application to aerodynamics. 2 2 www.amequestionpaper.in > Visit our website to download all latest EASA / DGCA CAR 66 Module examination Question papers and study material Module 08 - Basic Aerodynamics 1.1 8.1 - PHYSICS OF THE ATMOSPHERE BASIC AERODYNAMICS Aerodynamically, an aircraft can be def ined as an Three topics that are directly related to the manufacture, object traveling through space that is affected by the operation, and repair of aircraft are: aerodynamics, changes in atmospheric conditions. To state it another aircraft assembly, and rigging. Each of these subject way, aerodynamics covers the relationships between the areas, though studied separately, eventually connect to aircraft, relative wind, and atmosphere. provide a scientific and physical understanding of how an aircraft is prepared for flight. A logical place to start PHYSICS OF THE ATMOSPHERE with these three topics is the study of basic aerodynamics. Before examining the fundamental laws of f light, By studying aerodynamics, a person becomes familiar several basic facts must be considered. An aircraft with the fundamentals of aircraft flight. operates in the air. Therefore, those properties of air that affect the control and performance of an aircraft must Aerodynamics is the study of the dynamics of gases. The be understood. interaction between a moving object and the atmosphere is the primary interest in this module. The movement of The air in the earth's atmosphere is composed mostly of an object and its reaction to the air flow around it can nitrogen and oxygen. Air is considered a fluid because it be seen when watching water passing the bow of a ship. fits the definition of a substance that has the ability to The major difference between water and air is that air flow or assume the shape of the container in which it is is compressible and water is incompressible. The action enclosed. If the container is heated, pressure increases; of the airflow over a body is a large part of the study of if cooled, the pressure decreases. The weight of air is aerodynamics. Some common aircraft terms, such as heaviest at sea level where it has been compressed by rudder, hull, water line, and keel beam, were borrowed all of the air above. This compression of air is called from nautical terms. atmospheric pressure. M a ny te x t b o ok s h av e b e en w r it ten a b out t he PRESSURE aerodynamics of aircraft f light. It is not necessary Atmospheric pressure is usually def ined as the force for an airframe and powerplant technician to be as exerted against the earth's surface by the weight of the knowledgeable as an aeronautical design engineer air above that surface. Weight is force applied to an area about aerodynamics. The technician must be able to that results in pressure. Force (F) equals area (A) times understand the relationships between how an aircraft pressure (P), or F = AP. Therefore, to find the amount of performs in flight and its reaction to the forces acting pressure, divide area into force (P = F/A). A column of on its structural parts. Understanding why aircraft air (one square inch) extending from sea level to the top are designed with particular types of primary and of the atmosphere weighs approximately 14.7 pounds; secondary control systems and why the surfaces must therefore, atmospheric pressure is stated in pounds per be aerodynamically smooth becomes essential when square inch (psi). Thus, atmospheric pressure at sea level maintaining today's complex aircraft. is 14.7 psi. (Figure 1-1) The theory of f light should be described in terms of Atmospheric pressure is measured with an instrument the laws of flight because what happens to an aircraft called a barometer, composed of mercury in a tube that when it flies is not based upon assumptions, but upon records atmospheric pressure in inches of mercury (Hg). a series of facts. Aerodynamics is a study of laws which (Figure 1-2) have been proven to be the physical reasons why an airplane flies. The term aerodynamics is derived from The standard measurement in aviation altimeters and the combination of two Greek words: "aero," meaning U.S. weather reports has been "Hg". However, worldwide air, and "dyne," meaning force of power. Thus, when weather maps and some non-U.S., manufactured "aero" joins "dynamics" the result is "aerodynamics"; the aircraft instruments indicate pressure in millibars (mb), study of objects in motion through the air and the forces an SI metric unit. that produce or change such motion. 1.2 Module 08 - Basic Aerodynamics  PHYSICS OF THE Height of Earth’s Thermosphere ATMOSPHERE atmosphere (about 50 miles) 350 km 1 inch 1 inch Mesosphere Entire air column weight 14.7lb 90 km Ozone layer 50 km Stratosphere Tropopause Troposphere 18 km 14 km Sea level Earth Figure 1-1. The weight exerted by a 1 square inch column of air stretching from sea level to the top of the atmosphere is what is measured when it is said that atmospheric pressure is equal to 14.7 pounds per square inch. Aviators often interchange references to atmospheric Vacuum Inches of Millibars Standard Sea Level Mercury Standard Sea Level pressure between linear displacement (e.g., inches of Pressure 30 1016 Pressure mercury) and units of force (e.g., psi). Over the years, 29.92" Hg 25 847 1013 meteorology has shifted its use of linear displacement mb 20 677 representation of atmospheric pressure to units of 15 508 force. The unit of force nearly universally used today 10 339 to represent atmospheric pressure in meteorology is 5 170 the hectopascal (hPa). A pascal is a SI metric unit 0 0 that expresses force in Newtons per square meter. A hectoPascal is 100 Pascals. 1 013.2 hPa is equal to 14.7 1" psi which is equal to 29.92 Hg. (Figure 1-3) 1" Atmospheric pressure decreases with increasing altitude. The simplest explanation for this is that the column of 1" air that is weighed is shorter. How the pressure changes 0.491 lb Mercury for a given altitude is shown in Figure 1-4. The decrease Figure 1-2. Barometer used to measure atmospheric pressure. Atmospheric Pressure Standard atmospheric pressure at sea level is also known as 1 atmosphere, or 1 atm. The following measurements of standard atmospheric pressure are all equal to each other. 1 atm = 14.7 psi = 29.92 in Hg = 1013.2 hPa = 1013.2 mb = 760 mm Hg (or 101325 (prounds per (inches of (millimeters (atmosphere) newtons per (millibars) square inch) mercury) of mercury) square meters) Figure 1-3. Various equivalent representations of atmospheric pressure at sea level. Module 08 - Basic Aerodynamics 1.3 in pressure is a rapid one and, at 50 000 feet, the is greater. This is because air offers less resistance to atmospheric pressure has dropped to almost one-tenth the aircraft when it contains a smaller number of air of the sea level value. particles per unit of volume. As an aircraft ascends, atmospheric pressure drops, the HUMIDITY quantity of oxygen decreases, and temperature drops. Humidity is the amount of water vapor in the air. The These changes in altitude affect an aircraft's performance maximum amount of water vapor that air can hold varies in such areas as lift and engine horsepower. The effects with the temperature. The higher the temperature of the of temperature, altitude, and density of air on aircraft air, the more water vapor it can absorb. performance are covered in the following paragraphs. 1. Absolute humidity is the weight of water vapor in a unit volume of air. DENSITY 2. Relative humidity is the ratio, in percent, of the Density is weight per unit of volume. Since air is a moisture actually in the air to the moisture it would mixture of gases, it can be compressed. If the air in one hold if it were saturated at the same temperature container is under half as much pressure as an equal and pressure. amount of air in an identical container, the air under greater pressure is twice as dense as that in the other Assuming that the temperature and pressure remain container. For the equal weight of air, that which is the same, the density of the air varies inversely with under the greater pressure occupies only half the volume the humidity. On damp days, the air density is less of that under half the pressure. than on dry days. For this reason, an aircraft requires a longer runway for takeoff on damp days than it does on The density of gases is governed by the following rules: dry days. 1. Density varies in direct proportion with the pressure. By itself, water vapor weighs approximately five-eighths 2. Density varies inversely with the temperature. as much as an equal amount of perfectly dr y air. Therefore, when air contains water vapor, it is not as Thus, air at high altitudes is less dense than air at low heavy as dry air containing no moisture. altitudes, and a mass of hot air is less dense than a mass of cool air. Changes in density affect the aerodynamic TEMPERATURE AND ALTITUDE performance of aircraft with the same horsepower. An Temperature variations in the atmosphere are of concern aircraft can fly faster at a high altitude where the air to aviators. Weather systems produce changes in density is low than at a low altitude where the density temperature near the earth's surface. Temperature also changes as altitude is increased. The troposphere is the lowest layer of the atmosphere. On average, it ranges 100 000 from the earth's surface to about 38 000 feet above it. Over the poles, the troposphere extends to only 25 000 - 80 000 30 000 feet and, at the equator, it may extend to around 60 000 feet. This oblong nature of the troposphere is Altitude (feet) 60 000 illustrated in Figure 1-5. 40 000 Most civilian aviation takes place in the troposphere in which temperature decreases as altitude increases. The 20 000 rate of change is somewhat constant at about –2°C or Sea level –3.5°F for every 1 000 feet of increase in altitude. The 0 2 4 6 8 10 12 14 upper boundary of the troposphere is the tropopause. Pressure (pounds per square inch) It is characterized as a zone of relatively constant Figure 1-4. Atmospheric pressure decreasing with altitude. temperature of –57°C or –69°F. At sea level the pressure is 14.7 psi, while at 40 000 feet, as the dotted lines show, the pressure is only 2.72 psi. 1.4 Module 08 - Basic Aerodynamics  90 100 000–116 000 feet PHYSICS OF THE ATMOSPHERE 80 137 000–153 000 feet Thermosphere 25 000–30 000 feet 70 N Equator 60 S 55 000–65 000 feet Troposphere 160 000 ft Mesopause 50 Height (km) Stratosphere Tem Mesosphere per 40 Mesosphere atu re Thermosphere 160 000 ft Stratopause 30 Figure 1-5. The troposphere extends higher above the earth's surface at the equator than it does at the poles. Stratosphere 20 Ozone layer Above the tropopause lies the stratosphere. Temperature 10 increases with altitude in the stratosphere to near 0°C 38 000 ft Tropopause before decreasing again in the mesosphere, which lies Mt. Everest Troposphere above it. The stratosphere contains the ozone layer –100 –80 –60 –40 –20 0 20 40 50 °C that protects the earth's inhabitants from harmful UV (Ultraviolet) rays. Some civilian flights and numerous –140 –100 –60 –20 0 20 60 100 120 °F military f lights occur in the stratosphere. Figure 1-6 Temperature diagrams the temperature variations in different layers Figure 1-6. The atmospheric layers with temperature of the atmosphere. changes depicted by the red line. As stated, density varies inversely with temperature or, as temperature increases, air density decreases. This phenomenon explains why on very warm days, aircraft takeoff performance decreases. The air available for combustion is less dense. Air with low density contains less total oxygen to combine with the fuel. INTERNATIONAL STANDARD ATMOSPHERE The atmosphere is never at rest. Pressure, temperature, humidity, and density of the air are continuously changing. To provide a basis for theoretical calculations, performance comparisons and instrumentation parity, standard values for these and other characteristic of the atmosphere have been developed. International Civil Aviation Organization (ICAO), International Organization for Standardization (ISO), and various governments establish and publish the values known as the International Standard Atmosphere. (Figure 1-7) Module 08 - Basic Aerodynamics 1.5  ALTITUDE TEMPERATURE PRESSURE DENSITY Feet °F °C psi hPa slug/ft³ kg/m³ Sea Level 59 15 14.67 1013.53 0.002378 1.23 1000 55.4 13 14.17 977.16 0.002309 1.19 2000 51.9 11 13.66 941.82 0.002242 1.15 3000 48.3 9.1 13.17 908.11 0.002176 1.12 4000 44.7 7.1 12.69 874.94 0.002112 1.09 5000 41.2 5.1 12.05 843.07 0.002049 1.06 6000 37.6 3.1 11.78 812.2 0.001988 1.02 7000 34 1.1 11.34 781.85 0.001928 0.99 8000 30.5 -0.9 10.92 752.91 0.001869 0.96 9000 26.9 -2.8 10.5 724.28 0.001812 0.93 10 000 23.3 -4.8 10.11 697.06 0.001756 0.9 15 000 5.5 -14.7 8.3 571.82 0.001496 0.77 20 000 -12.3 -24.6 6.75 465.4 0.001267 0.65 25 000 -30.2 -34.5 5.46 376.01 0.001066 0.55 30 000 -48 -44.4 4.37 301.3 0.000891 0.46 35 000 -65.8 -54.3 3.47 238.42 0.000738 0.38 40 000 -69.7 -56.5 2.72 187.54 0.000587 0.3 45 000 -69.7 -56.5 2.15 147.48 0.000462 0.24 50 000 -69.7 -56.5 1.68 115.83 0.000362 0.19 Figure 1-7. The International Standard Atmosphere. 1.6 Module 08 - Basic Aerodynamics  QUESTIONS Question: 1-1 Question: 1-4 Atmospheric pressure is measured with an instrument If air temperature is 20°C at sea level; what will be its called a __________________. approximate temperature at 30 000 feet altitude? Question: 1-2 Question: 1-5 In which layer of the atmosphere does most civilian What are the 4 primary factors which effect aviation take place? the atmosphere? Question: 1-3 Question: 1-6 In what atmospheric conditions will an aircraft perform What rule making body determines standards for the best? studying the atmosphere? Module 08 - Basic Aerodynamics 1.7  ANSWERS Answer: 1-1 Answer: 1-4 barometer. -40°C (Air temperature drops on average 2°C each 1 000 feet of altitude) Answer: 1-2 Answer: 1-5 Troposphere. Pressure, density, temperature, humidity. Answer: 1-3 Answer: 1-6 Cold dry days at low altitude. ICAO – International Civil Aviation Organization. 1.8 Module 08 - Basic Aerodynamics  AERODYNAMICS PART-66 SYLLABUS LEVELS CERTIFICATION CATEGORY ¦ B1 B2 Sub-Module 02 AERODYNAMICS Knowledge Requirements 8.2 - Aerodynamics Airflow around a body; 2 2 Boundary layer, laminar and turbulent flow, free stream flow, relative airflow, upwash and downwash, vortices, stagnation; The terms: camber, chord, mean aerodynamic chord, profile (parasite) drag, induced drag, center of pressure, angle of attack, wash in and wash out, fineness ratio, wing shape and aspect ratio; Thrust, Weight, Aerodynamic Resultant; Generation of Lift and Drag: Angle of Attack, Lift coefficient, Drag coefficient, stall; Aerofoil contamination including ice, snow, frost. www.amequestionpaper.in > Visit our website to download all latest EASA / DGCA CAR 66 Module examination Question papers and study material Module 08 - Basic Aerodynamics 2.1 8.2 - AERODYNAMICS The law of conservation of energy states that energy may NEWTON'S LAWS OF MOTION neither be created nor destroyed. Motion is the act or The fundamental laws governing the action of air about process of changing place or position. An object may a wing are known as Newton's laws of motion. be in motion with respect to one object and motionless with respect to another. For example, a person sitting Newton's first law is normally referred to as the law quietly in an aircraft f lying at 200 knots is at rest or of inertia. It simply states that a body at rest does not motionless with respect to the aircraft; however, the move unless force is applied to it. If a body is moving at person and the aircraft are in motion with respect to the uniform speed in a straight line, force must be applied to air and to the earth. increase or decrease the speed. Air has no force or power, except pressure, unless it is in According to Newton's law, since air has mass, it motion. When it is moving, however, its force becomes is a body. When an aircraft is on the ground with apparent. A moving object in motionless air has a force its engines off, inertia keeps the aircraft at rest. An exerted on it as a result of its own motion. It makes no aircraft is moved from its state of rest by the thrust force difference in the effect then, whether an object is moving created by a propeller, or by the expanding exhaust, or with respect to the air or the air is moving with respect both. When an aircraft is flying at uniform speed in a to the object. The flow of air around an object caused by straight line, inertia tends to keep the aircraft moving. the movement of either the air or the object, or both, is Some external force is required to change the aircraft called the relative wind. from its path of flight. VELOCITY AND ACCELERATION Newton's second law states that if a body moving The terms speed and velocity are often used interchangeably with uniform speed is acted upon by an external but they do not have the same meaning. Speed is the rate force, the change of motion is proportional to the of motion in relation to time, and velocity is the rate of amount of the force, and motion takes place in the motion in a particular direction in relation to time. direction in which the force acts. This law may be stated mathematically as follows: An aircraft starts from New York City and flies 10 hours at an average speed of 260 kilometers per hour (kph). Force = mass × acceleration (F = ma) At the end of this time, the aircraft may be over the Atlantic Ocean, Canada the Gulf of Mexico, or, if its If an aircraft is flying against a headwind, it is slowed flight were in a circular path, it may even be back over down. If the wind is coming from either side of the New York City. If this same aircraft flew at a velocity of aircraft's heading, the aircraft is pushed off course unless 260 kph in a southwestward direction, it would arrive in the pilot takes corrective action against the wind direction. Dallas, TX in about 10 hours. Only the rate of motion is indicated in the first example and denotes the speed of Newton's third law is the law of action and reaction. the aircraft. In the last example, the particular direction This law states that for every action (force) there is an is included with the rate of motion, thus, denoting the equal and opposite reaction (force). This law can be velocity of the aircraft. illustrated by the example of firing a gun. The action is the forward movement of the bullet while the reaction is Acceleration is defined as the rate of change of velocity. An the backward recoil of the gun. The three laws of motion aircraft increasing in velocity is an example of positive that have been discussed apply to the theory of flight. In acceleration, while another aircraft reducing its velocity many cases, all three laws may be operating on an aircraft is an example of negative acceleration, or deceleration. at the same time. 2.2 Module 08 - Basic Aerodynamics  A Mass of Air S a m e M as s o f A ir AERODYNAMICS Velocity Increased Normal Pressure Pressure Decreased Normal Pressure (Compared to Original) B Normal Flow Increased Flow Normal Flow Figure 2-1. Bernoulli's Principle. AIRFLOW AROUND A BODY Point of Stagnation BERNOULLI'S PRINCIPLE AND SUBSONIC FLOW Bernoulli's principle states that when a fluid (air) flowing through a tube reaches a constriction, or narrowing, of Peak Suction the tube, the speed of the fluid flowing through that Pressure constriction increases and its pressure decreases. The Forward cambered (curved) surface of an airfoil (wing) affects the Stagnation - Point airflow exactly as a constriction in a tube affects airflow. Aft + Stagnation (Figure 2-2) Diagram A of Figure 2-1 illustrates the + Point effect of air passing through a constriction in a tube. - In B, air is flowing past a cambered surface, such as an airfoil, and the effect is similar to that of air passing Figure 2-2. Velocity distribution of airflow over a symmetrical through a restriction. airfoil (top); and the resulting pressure (bottom). An airfoil is a surface designed to obtain lift from the air through which it moves. As the air flows over the curved Note that in order to f it the model of Bernoulli's upper surface of an airfoil, its velocity increases and its Principle, the airflow over the wing surfaces must be pressure decreases; an area of low pressure is formed. laminar. Laminar air flow refers to airflow that is flowing There is an area of greater pressure on the lower surface in a consistent smooth stream. Turbulent flow is also of the airfoil, and this greater pressure tends to move possible. This is where the air flowing over the surface the wing upward. The difference in pressure between no longer so closely adheres to it. The flow is thicker and the upper and lower surfaces of the wing is called lift. faster, however, some lift is produced. When the airflow Three-fourths of the total lift of an airfoil is the result actually separates from the surface of a wing, a different of the decrease in pressure over the upper surface. The type of turbulence occurs. This type of turbulence does impact of air on the lower surface of an airfoil produces not produce lift and Bernoulli's Principle does not apply. the other one-fourth of the total lift. More discussion of these phenomena occur below in the section entitled Boundary Layer and Friction Effects. Module 08 - Basic Aerodynamics 2.3 Free stream airflow is air flowing without obstruction is generated ahead of the airfoil, the forward stagnation before it engages the aircraft structure. The velocity of point moves under the leading edge, and a downwash the free stream flow is equal to the speed aircraft. The is evident aft of the airfoil. (Upwash and downwash are pressure of the free stream airflow is static pressure. the deflection directions of the air as it negotiates its When the free stream f low arrives at the aircraft path around the airfoil.) The pressure distribution on structure, such as the wing, it must flow around the the airfoil now provides a net force perpendicular to the surface areas. As it does so, the pressure and velocity airstream in the upward direct. This is lift. (Figure 2-3) of the air change depending on the shape of the wing. The creation of lift is discussed in greater detail below. There is a point in front of the structure, however, where the velocity of the air is zero. This is known as Free Stream Flow the point of stagnation. Free Stream Flow, which is also known as Relative Airf low, is the air which is far enough upstream or Typical airflow patterns show the relationship between away from the oncoming aircraft that its pressure, static pressure and velocity defined by Bernoulli. In temperature, or relative velocity has not yet been, or will aerodynamics, when positive pressure is mentioned, it not be affected by the aircraft's passage through it. refers to pressures above atmospheric pressure. Negative pressure or suction pressure is lower than atmospheric BOUNDARY LAYER AND pressure. Any object placed in an airstream will have FRICTION EFFECTS the air impact or stagnate at some point near the leading In the study of physics and fluid mechanics, a boundary edge. The pressure at this point of stagnation will be layer is that layer of f luid in the immediate vicinity an absolute static pressure equal to the total pressure of of a bounding surface. In relation to an aircraft, the the airstream. In other words, the static pressure at the boundary layer is the part of the airflow closest to the stagnation point will be greater than the atmospheric surface of the aircraft. In designing high-performance pressure by the amount of the dynamic pressure of the aircraft, considerable attention is paid to controlling the airstream. As the f low divides and proceeds around behavior of the boundary layer to minimize pressure the object, the increases in local velocity produce drag and skin friction drag. decreases in static pressure. This procedure of f low is best illustrated by the f low patterns and pressure Because air has viscosity (internal resistance to flow), distributions of Figure 2-2. air encounters resistance to f low over a surface. The viscous nature of airflow reduces the local velocities on Note that the "streamlines" in the diagram show the a surface and accounts for the drag of skin friction. The velocity of the airflow. When they are close together, high retardation of air particles due to viscosity is greatest velocity exists at that point and when they are far apart, immediately adjacent to the surface. At the very surface low velocity exists at that point. The vector arrows in the of an object, the air particles are slowed to a relative diagram show the magnitude and direction of the low velocity of near zero. Above this area other particles pressure caused by the increased velocity of the airflow. Positive Lift Upwash and Downwash Because the object in Figure 2-2 is a symmetrical airfoil, the relative airflow striking it flows above and below the airfoil in the same manner. The pressures are the same and no lift is produced. By reshaping the airfoil or by Upwash Increased Local Velocity tilting it in relation to the relative airflow, uneven flow Downwash over the upper and lower surfaces occurs. This causes uneven pressure above and below the airfoil which results in the creation of lift. Simply by tilting the same Decreased Local symmetrical airfoil, an increase in upper surface suction Velocity occurs and the decreased in velocity on the lower surface Figure 2-3. Uneven airflow, uneven pressure, upwash and downwash causes a decrease in lower surface suction. Also, upwash are all caused by tilting the airfoil in relation to the free stream airflow. 2.4 Module 08 - Basic Aerodynamics experience successively smaller retardation until finally, the leading edge, the laminar boundary layer begins an at some distance above surface, the local velocity reaches oscillatory disturbance which is unstable. A waviness the full value of the airstream above the surface. occurs in the laminar boundary layer which ultimately grows larger and more severe and destroys the smooth This layer of air over the surface which shows local laminar flow. Thus, a transition takes place in which retardation of airflow from viscosity is the boundary the laminar boundary layer decays into a "turbulent" layer. The characteristics of this boundary layer are boundary layer. The same sort of transition can be AERODYNAMICS illustrated in Figure 2-4 with the f low of air over a noticed in the smoke from a cigarette in still air. At, smooth flat plate. first, the smoke ribbon is smooth and laminar, then it develops a definite waviness and decays into a random LAMINAR AND TURBULENT FLOW turbulent smoke pattern. The beginning flow on a smooth surface gives evidence of a very thin boundary layer with the flow occurring As soon as the transition to the turbulent boundary in smooth laminations. The boundary layer flow near layer takes place, the boundary layer thickens and the leading edge is similar to layers or laminations of grows at a more rapid rate. (The small scale, turbulent air sliding smoothly over one another. The term for flow within the boundary layer should not be confused this type of f low is the "laminar" boundary layer as with the large scale turbulence associated with airflow mentioned previously. This smooth laminar flow exists separation.) The flow in the turbulent boundary layer without the air particles moving from a given elevation allows the air particles to travel from one layer to above the surface. another producing an energy exchange. However, some small laminar flow continues to exist in the very lower As the f low continues back from the leading edge, levels of the turbulent boundary layer and is referred to friction forces in the boundar y layer continue to as the "laminar sub-layer." dissipate energy of the airstream and the laminar boundary layer increases in thickness with distance from the leading edge. After some distance back from Turbulent Boundary Layer Transition region Laminar Boundary Layer Laminar Sub Layer Comparison of Velocity Profiles for Laminar and Turbulent Boundary Layers Turbulant Profile Laminar Profile - Low Thickness - GreaterThickness - Low Velocities Next to Surface - Higher Velocities Next to Surface - Gradual Velocity Change - SharpVelocity Change - Low Skin Friction - Higher Skin Friction Figure 2-4. Boundary Layer Characteristics. Module 08 - Basic Aerodynamics 2.5  Tapered Leading Edge, Tapered Leading and Delta Wing Straight Trailing Edge Trailing Edges Sweptback Wings Rectangular Wing Straight Leading Edge, Tapered Trailing Edge Figure 2-5. Various wing planforms. The turbulence which exists in the turbulent boundary As a result of these differences, a comparison shows: layer allows determination of the point of transition 1. The turbulent boundary layer has a fuller velocity by several means. Since the turbulent boundary layer profile and has higher local velocities immediately transfers heat more easily than the laminar layer, frost, adjacent to the surface. The turbulent boundary water, and oil films will be removed more rapidly from layer has higher kinetic energy in the airflow next to the area aft of the transition point. Also, a small probe may the surface. be attached to a stethoscope and positioned at various 2. At the surface, the laminar boundary layer has the points along a surface. When the probe is in the laminar less rapid change of velocity with distance above the area, a low "hiss" will be heard. When the probe is in surface. Since the shearing stress is proportional to the turbulent area, a sharp "crackling" will be audible. the velocity gradient, the lower velocity gradient of In order to compare the characteristics of the laminar the laminar boundary layer is evidence of a lower and turbulent boundary layers, the velocity profiles (the friction drag on the surface. In conditions of flow variation of boundary layer velocity with height above where a turbulent and a laminar boundary layer can the surface) should be compared under conditions which exist, the laminar skin friction is about one-third could produce either laminar or turbulent flow. that for turbulent flow. And while the low friction drag of the laminar boundary layer is desirable, the The typical laminar and turbulent profiles are shown transition to turbulent boundary layer flow is natural in Figure 2-4. The velocity profile of the turbulent and largely inevitable. boundary layer shows a much sharper initial change of velocity but a greater height (or boundary layer thickness) PLANFORM AND VORTICES required to reach the free stream velocity. The previous discussion of aerodynamic forces concerned the properties of airfoil sections in two-dimensional f low with no consideration given to the inf luence of the planform. The planform is the shape or outline of an aircraft wing as projected onto a horizontal plane. 2.6 Module 08 - Basic Aerodynamics (Figure 2-5) When the effects of wing planform are This air current forms a similar vortex to a wingtip vortex introduced, attention must be directed to the existence but at the inner portion of the trailing edge of the wing. of flow components in the span-wise direction. In other All vortices increase drag because of the turbulence words, the airfoil section properties considered thus far produced, and constitute induced drag. Vortices increase deal with flow in two dimensions. Planform properties as lift (and drag) increase. Drag will be discussed in consider flow in three dimensions. further detail later in this module. AERODYNAMICS The pressure above the wing is less than atmospheric Just as lift increases by increasing of the angle of the pressure, and the pressure below the wing is equal airfoil into the wind, drag also increases as the angle to or greater than atmospheric pressure. Since fluids becomes greater. This occurs because, within limits, as always move from high pressure toward low pressure, the angle is increased, the pressure difference between in addition to the movement of air over the wing from the top and bottom of the wing becomes greater. This front to rear, there is also a spanwise movement of causes more violent vortices to be set up, resulting in air from the bottom of the wing outward from the more turbulence and more induced drag. fuselage and upward around the wing tip. This flow of air results in spillage over the wing tip, thereby setting AERODYNAMIC TERMS up a whirlpool of air called a "vortex." (Figure 2-6) The plural of vortex is vortices. CHORD AND CHAMBER Before continuing the discussion on aerodynamics, As the difference in the pressure between the air on some terms are defined and illustrations considered. the bottom and top of the wing increases, more lift The chord of a wing is the width of the wing from the is generated. This increased pressure differential also leading edge apex to the trailing edge. A chord line is causes more violent vortices. Small aircraft pilots must be a line depicting the chord which extends forward of especially vigilant when flying behind large aircraft. The the leading edge. It is used for angular reference to the vortices coming off the wingtips of a transport category chord. (Figure 2-9) The average chord is the area of the aircraft could cause loss of control if encountered before wing divided by the wing span. The mean aerodynamic they have had time to dissipate into the atmosphere. chord is the average distance from the leading edge to the trailing edge of the wing. Due to the many wing Note that the air on the upper surface of the wing planform designs, the mean aerodynamic chord is not planform has a tendency to move in toward the fuselage necessarily half way from the fuselage to the wing tip and off the trailing edge as shown by the blue arrows in as it is on a perfectly rectangular wing. However, the Figure 2-6. mean aerodynamic chord has half of the surface area of the wing on each side of it. (Figure 2-7) The mean aerodynamic chord is used by aerodynamicists when calculating stability and other design factors. MAC ex Vort Figure 2-6. Wingtip vortices. Figure 2-7. Mean aerodynamic chord (MAC). Module 08 - Basic Aerodynamics 2.7 The acute angle the wing chord makes with the AIRFOILS longitudinal axis of the aircraft is called the angle of Since an airfoil is a surface designed to obtain lift from incidence, or the angle of wing setting. (Figure 2-8) the air through which it moves, it can be stated that any part of the aircraft that converts air resistance into lift The angle of incidence in most cases is a fixed, built-in is an airfoil. The profile of a conventional wing is an angle. When the leading edge of the wing is higher excellent example of an airfoil. (Figure 2-10) than the trailing edge, the angle of incidence is said to be positive. The angle of incidence is negative when the Notice that the top surface of the wing profile has leading edge is lower than the trailing edge of the wing. greater curvature than the lower surface. Other unique features of wings include wash in and The difference in curvature of the upper and lower wash out. A wing does not have to be constructed flat in surfaces of the wing creates the lifting force. Air flowing a single plain. A wing may be twisted from root to tip over the top surface of the wing must reach the trailing in order to provide better aerodynamic characteristics edge of the wing in the same amount of time as the air especially stall characteristics. When a wing is twisted flowing under the wing. To do this, the air passing over down at the tip so that the angle of incidence is less the top surface moves at a greater velocity than the air at the wingtip than it is at the wing root, it is called passing below the wing because of the greater distance washout. If the wing is twisted in the opposite direction it must travel along the top surface. This increased so that the wing tip angle of incidence is greater than at velocity, according to Bernoulli's Principle, means a the wing root, it's called wash in. corresponding decrease in pressure on the upper surface. Thus, a pressure differential is created between the upper Refer to Figure 2-9 to clarify the following terms. The and lower surfaces of the wing, forcing the wing upward camber of a wing is the curve of the upper wing surface. in the direction of the lower pressure. The lower surface of the wing also has camber. The mean camber line lies within the wing half way between the upper camber and the lower camber. Maximum camber is located where the mean camber line is the greatest distance from the chord line. 115 mph 14.54 lb/in² Angle of Incidence Longitudinal Axis Chord Line of Wing 100 mph 14.7 lb/in² 105 mph 14.67 lb/in² Figure 2-8. Angle of incidence. Figure 2-10. Airflow over a wing section. Maximum Thickness Location of Max. Thickness Upper Surface Mean Camber Leading Maximum Line Edge Camber Radius Chord Line Chord Line Chord Line Lower Surface Leading Edge Trailing Edge Chord Location of Maximum Camber Figure 2-9. Chord and camber of a wing. 2.8 Module 08 - Basic Aerodynamics Shape of the Airfoil mean camber to the mean line of the section. Camber is Individual airfoil section properties differ from those positive when departure from the chord line is outward properties of the entire wing or aircraft as a whole and negative when it is inward. Thus, high-lift wings have because of the effect of the wing planform. A wing a large positive camber on the upper surface and a slightly may have various airfoil sections from root to tip, with negative camber on the lower surface. taper, twist, and sweepback. The resulting aerodynamic properties of the wing are determined by the action of Wing flaps cause an ordinary wing to approximate this AERODYNAMICS each section along the span. same condition by increasing the upper camber and by creating a negative lower camber. It is also known that The shape of the airfoil determines the amount of the larger the wingspan, as compared to the chord, turbulence or skin friction that it produces, consequently the greater the lift obtained. This comparison is called affecting the efficiency of the wing. Turbulence and skin aspect ratio. The higher the aspect ratio, the greater friction are controlled mainly by the fineness ratio, which the lift. In spite of the benefits from an increase in is defined as the ratio of the chord of the airfoil to its aspect ratio, there are definite limitations defined by maximum thickness. If the wing has a high fineness structural and drag considerations. On the other hand, ratio, it is a very thin wing. A thick wing has a low an airfoil that is perfectly streamlined and offers little fineness ratio. A wing with a high fineness ratio produces wind resistance sometimes does not have enough lifting a large amount of skin friction. A wing with a low power to take the aircraft off the ground. Thus, modern fineness ratio produces a large amount of turbulence. The aircraft have airfoils which strike a medium between best wing is a compromise between these two extremes extremes, the shape depending on the purposes of the to hold both turbulence and skin friction to a minimum. aircraft for which it is designed. Figure 2-11 illustrates a wide variety of airfoil shapes. Wash-out/Wash-in Wash-out is the decreasing angle of attack (or twist) High-lift wings and high-lift devices for wings have built into wings from the root to the tips. The purpose been developed by shaping the airfoils to produce the of washout is so root of the wing has a higher angle of desired effect. The amount of lift produced by an airfoil attack than the tip which then causes the root to stall increases with an increase in wing camber. As stated, first before the tip. (Figure 2-12) This allows the pilot camber refers to the curvature of an airfoil surface above to maintain greater control of the aircraft during a stall. and below the chord line. Upper camber refers to the upper surface, lower camber to the lower surface, and Wash-out is particularly important if the airplane has swept wings. When swept wings stall, the center of pressure of the wing moves forward and inwards towards the root due to the spanwise airflow. This makes Early Airfoil the nose of the aircraft pitch up more pushing it further Later Airfoil Clark 'Y' Airfoil (Subsonic) Laminar Flow Airfoil High Angle of Incidence at Tip (Subsonic) Average Angle of Incidence Mid-wing Circular Arc Airfoil (Supersonic) Double Wedge Airfoil Low Angle of Incidence at Tip (Supersonic) Figure 2-12. Wash-out on a wing shows how the root of Figure 2-11. Airfoil designs. the wing's angle of attack is greater than the tips. Module 08 - Basic Aerodynamics 2.9 into the stall. This can be very dangerous and can make AERODYNAMIC RESULTANT the aircraft go fully out of control. Adding wash-out to An aircraft in flight is continuously affected by thrust, a wing prevents the tips from stalling and also keeps the weight, lift and drag. The directions in which the ailerons effective during a stall. forces act is known. The magnitude of the forces can be calculated. When the forces are not in balance, Wash-in would be the opposite of wash-out giving a a resultant or resulting force will exist. This is the higher angle of attack to the tips than to the root of combined force of all of the forces acting on the aircraft. the wing. This would not be desirable and is not used In all types of flying, flight calculations are based on the on aircraft.