Propeller Aerodynamics , livre ebook

Andrews UK - Frank Hitchens

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203 pages

English

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Description

Classical aerodynamics is a compulsory study subject for pilots at all levels of experience. Propeller Aerodynamics is a subset of this fascinating subject. Propellers have their unique aerodynamic terminology, forces and handling requirements, knowledge of which all pilots must be aware of to safely handle the aircraft they are flying. Incorrect propeller handling can cause damage to the aircraft and reduce performance efficiency. Most aerodynamic text books only give a brief view of propeller aerodynamics; however this book Propeller Aerodynamics delves more deeply into this subject. The book covers the history and operation of aircraft propellers, prop pitch, thrust, efficiency, aircraft stability, prop forces, constant-speed units and more. This is all essential reading for the pilot progressing to more advanced high-performance aircraft.

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Sciences et techniques

Informations

Publié par	Andrews UK
Date de parution	11 mai 2015
Nombre de lectures	0
EAN13	9781785381256
Langue	English
Poids de l'ouvrage	5 Mo

Informations légales : prix de location à la page 0,0750€. Cette information est donnée uniquement à titre indicatif conformément à la législation en vigueur.

Extrait

Contents

Introduction                              iii

1 – The History of Aircraft Propellers              1 Airscrews              1Lockheed C-130 Hercules 18  The First Airborne Props     De-ice for Props         0 The Wright Brothers       Propeller Manufacturers   0 Aerodynamic Theories      4The First Turboprops      Variable-pitch Propellers    6Supersonic Propellers     5 Constant-speed Propellers   7 Record Breakers         7 Spitires and Hurricanes   10Propulsors            9 Five-blades or Six?       1 Propfans              0 Counter &Conclusion             Contra-rotating Props    14

2 – Propeller Pitch                         34 The Working Fluid               45       4 Slip  Propeller Terminology     6 Brief Review           46 Propeller Pitch          9 Advance/Diameter Ratio   47 Helix Angle    49Fixed-pitch Propellers           40  Blade Angle & Twist      41Variable Pitch & ConstantExperimental Pitch       41 Speed Propellers       51 Geometric Pitch         4

3 – Thrust & Eficiency                      61 Propulsive Eficiency    6            78Aspect Ratio Power to the Prop        65 Prop Blade Loading       78 Power Absorption        71 Prop Disc Loading        80 Activity Factor          71Propwash Thrust      8  Solidity               71 Prop Blade Drag         88 Prop Diameter          7 Propeller Icing          9 Number of Blades      7 

4 – Effect on the Aircraft’s Stability              97 Prop Torque Force       97Centreline Thrust108       Prop Location          98Minimum Control Speed (VMC)109 Helical Propwash      10  Counter-rotating Propellers 109 ‘P’ Factor              10 Contra-rotating Propellers  11 Gyroscopic Effect        105

5 – Prop Tip Speed & Noise                  115 The Cause of Noise       115Tips, Blade Shape & Materials11 High-speed Aerodynamics  116 Synchronizing          14 Tip Speed             119How Noisy are They?17     6 – Propeller Forces & Stress                 129 Windmilling Prop Forces   10 Prop Stress            14 Reverse Thrust Forces140      Balanced Prop 1 The     7 – Turboprops, Propulsors & Propfans          143 Propulsors             148146 Propfans             8 – Constant-speed Units                    153 The Oil/Counterweight Type 156 Air/Oil Type           158 The Beech & McCauley Types157The Hydromatic CSU158     The Hamilton Standard Type157The Curtiss Electric Propeller159 9 – Propeller Operation                     162 Governor Check         16Ground Feathering       171 Running Square164        Negative Torque System17   Reducing power       164  Autofeathering17         Lock-on              166Simulated Zero Thrust    174 Overspeed Condition      166Reverse Thrust         175 Windmilling            168Safety Around the Prop    176 The Feathering Prop      168Conclusion181           

Glossary                               183 Bibliography                            192 Other Titles Available                      194

Propellor Aerodynamics

The History, Aerodynamics & Operation of Aircraft Propellers

Frank E. Hitchens

Published in 2015 by Andrews UK Limited www.andrewsuk.com

The right of Frank E. Hitchens to be identiied as the Author of this Work has been asserted in accordance with the Copyright, Designs and Patents Act 1998

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means without the prior written permission of the publisher, nor be otherwise circulated in any form of binding or cover other than that in which it is published and without a similar condition being imposed on the subsequent purchaser. Any person who does so may be liable to criminal prosecution and civil claims for damages.

Introduction

Imagine you are the pilot of a light aircraft on a cross-country VFR light. As you tick-off each landmark along your route, you watch as it disappears below the leading edge of the wing to reappear a few seconds later behind the trailing edge Your thoughts turn to your ground studies and knowledge of basic classical aerodynamics. You understand how the airlow separates at the wing’s leading edge and lows over and under the wing to rejoin at the trailing edge. You also understand the forces of lift and drag produced by the aerodynamic reaction of the aircraft’s wing. Now, as you look ahead for the next approaching landmark, your view is through the almost invisible blur of the propeller disc. Because the prop is an almost continuous blur, we tend to ignore its presence and take it for granted Therefore, what about the propeller’s forces of thrust and torque, or the prop’s stress, tip speed, power absorption and it’s eficiency of operation, etc? Do you ever think about them? Where did propellers originate? They have been around a great deal longer than you may realise! How do you operate a constant speed or feathering propeller? How do props do their job of producing thrust? That is what this book is all about – propeller aerodynamics, covering the history of the propeller’s development, its operation and of course, the aerodynamics associated to the propeller Most text books on general aerodynamics give only a brief mention to propeller aerodynamics. It has been this author’s intent to present this material in an easy to understand manner, suitable for study by the low time private pilot. Nevertheless, that’s not to say the more knowledgeable reader won’t beneit from this book. It has been assumed the reader has an understanding of basic aerodynamics to at least the private pilot’s level The text on propeller aerodynamics will

therefore, compliment his/her knowledge on this fascinating subject. We start with a look at the propeller’s history of development and followed by the different aerodynamic theories put forward by William Rankine, Robert and William Froude and Stefan Drzeweicke, which in this book, concentrates mainly on the blade element theory and briely, on the axial momentum theory. The text continues with different aspects of propeller pitch and the factors that affect the propeller’s eficiency. This is followed by the forces acting on the propeller during different operating conditions and is followed by a brief look at turboprops, Propulsor and Propfans. The book concludes with a chapter on propeller operation. A few simple formulas have been included along with several diagrams to help clarify the text Note, all diagrams have been drawn free hand by this author and then computer scanned and do not represent any on particular propeller or airplane. In writing this book, a choice had to be made on the use of either Imperial or Metric units. With my home country of New Zealand and many other overseas countries turning to the Metric system more and more, this was at irst deemed to be the most appropriate system to use. However, in the aviation industry, Imperial units are still commonly used. For example propeller size and manifold pressure are still measured in inches, and piston-engine power mostly in brake horsepower, true air speed in Knots, prop thrust in pounds, and prop disc area in square feet. One notable exception being temperature measured in the Metric system of degrees Celsius. Young pilots may well be familiar with the Metric system while older generation pilots (myself included) will be more familiar with Imperial units, which I have chosen to use in this work with Metric equivalents in brackets. A total of sixty-one photographs are included from this author’s collection with the exception of the MD-80 Propfan test plane photograph, which was freely donated by Hamilton

Standard of Connecticut, USA, to whom I am truly thankful. My thanks also go out to those pilots and ground engineers who were most helpful in supplying useful information and answering my numerous questions on aircraft propellers and arranging access to aircraft parked in the restricted operational areas of the airport I visited

Frank Hitchens, Wellington, New Zealand.

Front cover photo:Lockheed P-C Orion propeller

1 – The History of Aircraft Propellers

In the Beginning… Before the advent of jet propulsion, a piston-engine driving a propeller to provide the necessary thrust or forward motion powered all aircraft To this end, the propeller has always been an accepted part of an airplane. However, how many people realize that propellers were around long before the irst airplane lew? So, where did propellers originate? Some authorities claim the propeller originated in China several centuries ago as a descendant from the windmill. In Europe, the windmill can be traced as far back as the 1 century AD, but windmills built in China before this time were of a different type, their axles being vertical It is believed the windmills of China have no apparent relationship with European windmills, however, from the principle of the windmill the idea of the propeller was born

Airscrews The word ‘airscrew’ was introduced to aviation to distinguish between the aeronautical and marine type propellers (which were usually referred to as ‘screws’). The word airscrew was more commonly used in Europe than in the USA. Between the 1920s and 1950s, the name airscrew usually referred to a ‘tractor’ propeller (a propeller in front of the engine as opposed to pusher propeller behind the engine). It is now a virtually redundant term and has been replaced by the word propeller or prop for short, although the word airscrew is quite often used by writers of early aeronautical history when writing about propellers of that era. The term propeller was irst used to describe any mechanical device used to propel

The erm ‘aîrscrew’ îs synonymous wîh eary aîrcrat such as this example of a Sopwith F.1. Camel Scout.

a vehicle and it came into aviation terminology circa 1850 to have the same meaning as the word airscrew

The First Airborne Props At the end of the 15 century, circa 1490, the artist and inventor Leonardo Da Vinci (1452–1519) designed a crude form of airscrew (or prop) for his helicopter design. The design never left the drawing board but the word helicopter has been with us ever since. The French mathematician, J.P. Paucton introduced the idea of using two propellers on airships, one to propel the craft forwards and the other to lift it upwards; it was not successful! It was to be nearly three hundred years until 16 October 1784, when Jeanne-Pierre Blanchard (1753– 1809) used the irst airborne propeller on his hot air balloon. The propeller consisted of three metal plates attached to the