Model Airplane Design Preview

WHAT OTHERS ARE SAYING …

“is book is a joy to read! e writing style and wit adddimension in a way that is rarely found in today’s referencematerials. If someone has considered designing their ownairplane and been put off because of complicated formulas,vocabulary and reference style that would bore even anengineer, this will convince them to go ahead and try it.Wrien with real people in mind and not engineers—and Imean that in a good way. is is a book that will reside alongthe other favorites on my bookshelf. Carlos really managed toproduce a book that will last a long time and become one ofthe standards for modelers.”

Greg GimliElectrics columnist

Model Aviation magazine

“is book is definitely needed by anyone geing into R/C or isa veteran flight fanatic! Tons of good info that ras my brainand gets me thinking.”

Jamie BurkeHost

AllThingsThatFly.com

“A comprehensive look at what you need to know to designand build your own RC model aircra. Carlos has distilledhis many years of aerodynamic study and model airplaneexperience into one easy to read book.”

Ri WitterEngineer and Private Pilot

“RCAdvisor’s Model Airplane Design Made Easy is theultimate model airplane design book for both beginning andexperienced modelers. Everything you need to know is righthere with clear, easy-to-understand content that you will referto again and again. Your understanding of what it takes todesign a model airplane will be greatly enhanced by readingthis book.”

Riard KlineInventor

KFm airfoils

“RCadvisor’s Model Airplane Design Made Easy is a real contribution to the world’s literature on the subject. It providesan excellent bridge between full scale aviation and aeromodeling, showing the relationship between the two, for beer understanding of the differences and similarities whi should beapplied for good model performance.

While thorough in detail, the book is also easily readable sothat the information is simple to understand. It is a verygood combination of theory and practical application. Nicelyillustrated, the book is also full of common sense explanationsand references to other sources of information.”

John Worthformer President and Executive Director of the

Academy of Model Aeronautics and currently ExecutiveEditor of RC Micro World, an online monthly magazine about the smallest and lightest of model aircra:

www.cloud9rc.com

“If you’ve ever thought about designing your own models …

If you’ve ever thought it would be nice to have alternatives toexpensive model building materials …

If you’ve ever tried kit-bashing …

If you’ve ever looked for a source that could explain the basicprinciples of aerodynamics clearly and concisely without resorting to complex mathematical formulas …

en RCadvisor’s Model Airplane Design Made Easy is thebook for you.

It’s a great common-sense guide to the rules-of-thumb ofaerodynamics and aircra design.”

Roy S. Stone years of modeling experience

“Carlos Reyes personably leads the reader through some basicaerodynamics, materials considerations, electric power systemplanning and a practical application of theory as it is appliedto a finished flying model. e baground history of varioustypes of aircra shows the development of aviation and howit relates to the models that we build and fly today, as wellas how models have influenced general aviation. It is alwaysexciting to find some “new to me” concepts and theories, andthere were several in this well-wrien narrative.”

Ken MyersEditor

Ampeer electric flight newsleer

“No maer how long you’ve been aeromodelling, or what yourinterests are in our great hobby, the greatest thrill of all is standing behind a unique model that you’ve designed and built yourself, from a blank sheet of paper—or even a blank CADfile—andpreparing to make that first take off.

So sit yourself down in a comfy air, read RCadvisor’s ModelAirplane Design Made Easy and set off on aeromodelling’sgreatest adventure.

Let Carlos Reyes—an aeromodeller of long standing and greattalent—take you through the mysteries of how to arrive at thepoint that every lover of model aircra should experience.”

Dere Woodwardaeromodeller, designer and

magazine writer for the past fiy years

RC’M A D

M EThe Simple Guide to

Designing R/C Model Aircraftor

Build Your OwnRadio Control Flying Model Plane

Carlos Reyeswww.RCadvisor.com founder

RCadvisor.comAlbuquerque, New Mexico

Copyright © by Carlos Reyes. All rights reserved.

No part of this book may be reproduced in any form or by any electronic or meanical means including information storage and retrievalsystems, without permission in writing from the author. e only exceptionis by a reviewer, who may quote short excerpts in a review.

Published by:RCadvisor.com Elizabeth St NEAlbuquerque, NM [email protected]

ISBN ----

Library of Congress Control Number: Library of Congress subject headings:Airplanes—Models—Design and construction.Airplanes—Models—Aerodynamics.Airplanes—Models—Radio control.

Cover design by Tammy Crespin. Book design by Carlos Reyes.Typeset using the amazing LATEX system.

is paper meets the requirements of ANSI/NISO Z.-(Permanence of Paper).

Version .

To Tammy and Autumn,the ladies in my life.

Summary Table of Contents

Preface

1 Fluid Dynamics Boot Camp

2 Airfoils

3 Propellers

4 Structures

5 Wings

6 Airplanes

7 Power Systems

8 Design Process

A Inexpensive Design Tools

B Free On-line Resources

C Where to Buy Stuff

Glossary

Annotated Bibliography

RCadvisor’s Model Airplane Design Made Easy

Index

Colophon

Contents

Preface

1 Fluid Dynamics Boot Camp . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . Viscosity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Viscous and Inviscid Flows . . . . . . . . . . . . . . . . . . . Li . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.. Skin Friction Drag . . . . . . . . . . . . . . . . . . . .. Separation Drag . . . . . . . . . . . . . . . . . . . . .. Induced Drag . . . . . . . . . . . . . . . . . . . . .

. Laminar Flow . . . . . . . . . . . . . . . . . . . . . . . . . . Separation Bubbles . . . . . . . . . . . . . . . . . . . . . . . . Chaos eory . . . . . . . . . . . . . . . . . . . . . . . . . . . Turbulent Flow . . . . . . . . . . . . . . . . . . . . . . . . . . Dimensionless Numbers . . . . . . . . . . . . . . . . . . . .

.. Reynolds Number . . . . . . . . . . . . . . . . . . . .. Ma Number . . . . . . . . . . . . . . . . . . . . .

. Boundary Layer . . . . . . . . . . . . . . . . . . . . . . . . . Micro Vortex Generators . . . . . . . . . . . . . . . . . . . . . Low Reynolds Numbers . . . . . . . . . . . . . . . . . . . . . Golf Balls . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 Airfoils


. Key Performance Characteristics . . . . . . . . . . . . . . . .. Minimum Drag Coefficient . . . . . . . . . . . . . . .. Maximum Li Coefficient . . . . . . . . . . . . . . .. Maximum Li to Drag Ratio . . . . . . . . . . . . .

. Recommendations . . . . . . . . . . . . . . . . . . . . . . . .. Low Reynolds Numbers . . . . . . . . . . . . . . . .

. XFoil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary Table . . . . . . . . . . . . . . . . . . . . . . . . . . Kline-Fogleman . . . . . . . . . . . . . . . . . . . . . . . .

.. History . . . . . . . . . . . . . . . . . . . . . . . . . .. Variations . . . . . . . . . . . . . . . . . . . . . . . .. Published Resear . . . . . . . . . . . . . . . . . . .. eory . . . . . . . . . . . . . . . . . . . . . . . . . .. Applications . . . . . . . . . . . . . . . . . . . . . .

3 Propellers . History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Baground . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diameter and Pit . . . . . . . . . . . . . . . . . . . . . . . . Problems Analyzing . . . . . . . . . . . . . . . . . . . . . . . Spinners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ma Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Zero Airspeed . . . . . . . . . . . . . . . . . . . . . . . . . . Advance Ratio . . . . . . . . . . . . . . . . . . . . . . . . .

4 Structures . Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.. Material Properties . . . . . . . . . . . . . . . . . . .. Polystyrene Foam . . . . . . . . . . . . . . . . . . . .. Polypropylene Foam . . . . . . . . . . . . . . . . . .. Wood . . . . . . . . . . . . . . . . . . . . . . . . . . .. Fiberglass . . . . . . . . . . . . . . . . . . . . . . .

Contents

.. Aramid . . . . . . . . . . . . . . . . . . . . . . . . . .. Carbon Fiber . . . . . . . . . . . . . . . . . . . . . . .. Metals . . . . . . . . . . . . . . . . . . . . . . . . .

. Adhesives . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Cyanoacrylates . . . . . . . . . . . . . . . . . . . . .. Polyurethanes . . . . . . . . . . . . . . . . . . . . . .. Epoxies . . . . . . . . . . . . . . . . . . . . . . . . .

. Wing Structures . . . . . . . . . . . . . . . . . . . . . . . . .. Bending Moment . . . . . . . . . . . . . . . . . . . .. Main Spar . . . . . . . . . . . . . . . . . . . . . . .

5 Wings . Aspect Ratio . . . . . . . . . . . . . . . . . . . . . . . . . .

.. Inverse Zimmerman . . . . . . . . . . . . . . . . . . . Wing area . . . . . . . . . . . . . . . . . . . . . . . . . . . . Taper Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sweep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.. Wing Fences . . . . . . . . . . . . . . . . . . . . . . . Washout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wingtips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multiple Wings . . . . . . . . . . . . . . . . . . . . . . . . .

.. History . . . . . . . . . . . . . . . . . . . . . . . . . .. Disadvantages . . . . . . . . . . . . . . . . . . . . . .. Advantages . . . . . . . . . . . . . . . . . . . . . .

. Tailless . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. History . . . . . . . . . . . . . . . . . . . . . . . . . .. Twist . . . . . . . . . . . . . . . . . . . . . . . . . . .. Disadvantages . . . . . . . . . . . . . . . . . . . . . .. Advantages . . . . . . . . . . . . . . . . . . . . . . .. Airfoil Recommendations . . . . . . . . . . . . . . .

6 Airplanes . Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


.. Up and Down . . . . . . . . . . . . . . . . . . . . . .. Turning . . . . . . . . . . . . . . . . . . . . . . . . .. Side to Side . . . . . . . . . . . . . . . . . . . . . .

. Control Surfaces . . . . . . . . . . . . . . . . . . . . . . . . .. Horizontal Stabilizers . . . . . . . . . . . . . . . . . .. Flaps . . . . . . . . . . . . . . . . . . . . . . . . . .

. Trailing Edges . . . . . . . . . . . . . . . . . . . . . . . . . . Fluer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wing incidence . . . . . . . . . . . . . . . . . . . . . . . . . . Scale Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . Visibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.. Minimize Zero Li Drag . . . . . . . . . . . . . . . .. Lower the Span Loading . . . . . . . . . . . . . . . .. Increase the Oswald Efficiency Factor . . . . . . . .

7 Power Systems . Gas Engines . . . . . . . . . . . . . . . . . . . . . . . . . . . Baeries . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.. A Cells . . . . . . . . . . . . . . . . . . . . . . . . Electronic Speed Controllers . . . . . . . . . . . . . . . . . . . Electric Motors . . . . . . . . . . . . . . . . . . . . . . . . .

.. Types . . . . . . . . . . . . . . . . . . . . . . . . . . .. Motor Constants . . . . . . . . . . . . . . . . . . . . .. ermal Capacity . . . . . . . . . . . . . . . . . . . .. Windings . . . . . . . . . . . . . . . . . . . . . . . .. Efficiency . . . . . . . . . . . . . . . . . . . . . . .

. e Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . Carlos’ Power Rule . . . . . . . . . . . . . . . . . . . . . . . . Tradeoffs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brushless Motors and LiPo Cells . . . . . . . . . . . . . . . . Connectors and Wiring . . . . . . . . . . . . . . . . . . . . . Power System Calculators . . . . . . . . . . . . . . . . . . .

Contents

8 Design Process . e Dangers of Uncertainty . . . . . . . . . . . . . . . . . . . A Practical Approa . . . . . . . . . . . . . . . . . . . . . . Define Goals . . . . . . . . . . . . . . . . . . . . . . . . . .

.. Ungoals . . . . . . . . . . . . . . . . . . . . . . . . .. Airplane Size . . . . . . . . . . . . . . . . . . . . . .. Materials . . . . . . . . . . . . . . . . . . . . . . . . .. Construction Difficulty . . . . . . . . . . . . . . . . .. Performance . . . . . . . . . . . . . . . . . . . . . .

. Flight Testing . . . . . . . . . . . . . . . . . . . . . . . . . . .. Flight Test Plan . . . . . . . . . . . . . . . . . . . . .. Robustness . . . . . . . . . . . . . . . . . . . . . . .

. Design Best Practices . . . . . . . . . . . . . . . . . . . . . . Final oughts . . . . . . . . . . . . . . . . . . . . . . . . .

A Inexpensive Design Tools

B Free On-line Resources

C Where to Buy Stuff

Glossary

Annotated Bibliography Highly Recommended . . . . . . . . . . . . . . . . . . . . . . . . Aircra Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aerodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aerodynamics History . . . . . . . . . . . . . . . . . . . . . . . . Propellers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sailplanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tailless . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Power Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . .


Index

Colophon About the Author . . . . . . . . . . . . . . . . . . . . . . . . . . . RCadvisor’s Calculator . . . . . . . . . . . . . . . . . . . . . . . . Website . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . is Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

List of Figures

. Model helicopter . . . . . . . . . . . . . . . . . . . . . . . .

. Bristol Boxkite . . . . . . . . . . . . . . . . . . . . . . . . . . Transition to turbulent flow . . . . . . . . . . . . . . . . . . . Micro vortex generator . . . . . . . . . . . . . . . . . . . .

. Sopwith Camel . . . . . . . . . . . . . . . . . . . . . . . . . . Fokker D-VII . . . . . . . . . . . . . . . . . . . . . . . . . . . Airfoil geometry . . . . . . . . . . . . . . . . . . . . . . . . . NASA LS()- airfoil . . . . . . . . . . . . . . . . . . . . . Göingen airfoil . . . . . . . . . . . . . . . . . . . . . . . Eppler E airfoil . . . . . . . . . . . . . . . . . . . . . . . . . North American P-D Mustang . . . . . . . . . . . . . . . . Kline-Fogleman paper airplane . . . . . . . . . . . . . . . . . KFm airfoils . . . . . . . . . . . . . . . . . . . . . . . . . . . Clark Y airfoil with KFm step . . . . . . . . . . . . . . . . . Propeller with KFm tip . . . . . . . . . . . . . . . . . . . .

. Jodel Dauphin . . . . . . . . . . . . . . . . . . . . . . . . .

. Inv Zimmerman wing planform . . . . . . . . . . . . . . . . . Zimmerman dihedral . . . . . . . . . . . . . . . . . . . . . . Supermarine Spitfire . . . . . . . . . . . . . . . . . . . . . . . Raked wing . . . . . . . . . . . . . . . . . . . . . . . . . . . . Crescent-shaped moon . . . . . . . . . . . . . . . . . . . . .


. Flying bird . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hörner wing tip . . . . . . . . . . . . . . . . . . . . . . . . . Rutan VariEze . . . . . . . . . . . . . . . . . . . . . . . . . . Eurofighter Typhoon . . . . . . . . . . . . . . . . . . . . . . . Fokker Triplane . . . . . . . . . . . . . . . . . . . . . . . . . . Mignet Flying Flea (Pou-du-Ciel) . . . . . . . . . . . . . . . . Rutan iie . . . . . . . . . . . . . . . . . . . . . . . . . . Dunne Tailless Biplane . . . . . . . . . . . . . . . . . . . . . . Messersmi Me Komet . . . . . . . . . . . . . . . . . . EMX- airfoil . . . . . . . . . . . . . . . . . . . . . . . . . . MH airfoil . . . . . . . . . . . . . . . . . . . . . . . . . .

. NACA airfoil . . . . . . . . . . . . . . . . . . . . . . . . Piper Super Cub . . . . . . . . . . . . . . . . . . . . . . . . . Model warplane . . . . . . . . . . . . . . . . . . . . . . . . . Wiman Tailwind . . . . . . . . . . . . . . . . . . . . . . .

. Two-stroke glow engine . . . . . . . . . . . . . . . . . . . . . Diesel engine . . . . . . . . . . . . . . . . . . . . . . . . . . . Four-stroke engine . . . . . . . . . . . . . . . . . . . . . . . . Transmier . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electric motor windings . . . . . . . . . . . . . . . . . . . . . Brushed can motor . . . . . . . . . . . . . . . . . . . . . . .

. Handling qualities scale . . . . . . . . . . . . . . . . . . . . . Launing a new model . . . . . . . . . . . . . . . . . . . .

C. Carlos Reyes . . . . . . . . . . . . . . . . . . . . . . . . . . C. RCadvisor’s calculator . . . . . . . . . . . . . . . . . . . . .

List of Tables

. Air drag on exposed wire . . . . . . . . . . . . . . . . . . .

. Airfoil properties . . . . . . . . . . . . . . . . . . . . . . . .

. Change in wood moisture . . . . . . . . . . . . . . . . . . . . Material property ratios . . . . . . . . . . . . . . . . . . . . . Wing loads . . . . . . . . . . . . . . . . . . . . . . . . . . .

. CLₐₓ loss due to wing sweep . . . . . . . . . . . . . . . . .

. Scale factors . . . . . . . . . . . . . . . . . . . . . . . . . .

. Engine/Motor tradeoffs . . . . . . . . . . . . . . . . . . . . . Baery types . . . . . . . . . . . . . . . . . . . . . . . . . . . Baery tradeoffs . . . . . . . . . . . . . . . . . . . . . . . . . Speed control tradeoffs . . . . . . . . . . . . . . . . . . . . . . Motor tradeoffs . . . . . . . . . . . . . . . . . . . . . . . . . . Gearbox tradeoffs . . . . . . . . . . . . . . . . . . . . . . . . Propeller diameter tradeoffs . . . . . . . . . . . . . . . . . . . Propeller pit tradeoffs . . . . . . . . . . . . . . . . . . . . . Connectors and wiring . . . . . . . . . . . . . . . . . . . . .

. Airplane log . . . . . . . . . . . . . . . . . . . . . . . . . . . Flight log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flight testing elist . . . . . . . . . . . . . . . . . . . . .

List of Equations

. Reynolds number . . . . . . . . . . . . . . . . . . . . . . . . . . Laminar boundary layer thiness . . . . . . . . . . . . . . . . . Turbulent boundary layer thiness . . . . . . . . . . . . . . .

. Required li coefficient . . . . . . . . . . . . . . . . . . . . . .

. Propeller advance ratio . . . . . . . . . . . . . . . . . . . . . .

. Wing bending moment . . . . . . . . . . . . . . . . . . . . . .

. Wing aspect ratio . . . . . . . . . . . . . . . . . . . . . . . . . . Zimmerman planform . . . . . . . . . . . . . . . . . . . . . . . . Zimmerman dihedral . . . . . . . . . . . . . . . . . . . . . . . . Taper effect on stall start . . . . . . . . . . . . . . . . . . . . . . Panknin-Senk tailless twist . . . . . . . . . . . . . . . . . . .

. MAC size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dihedral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Airplane scaling . . . . . . . . . . . . . . . . . . . . . . . . . . . Airplane span loading . . . . . . . . . . . . . . . . . . . . . . .

. Motor resistance from voltage and current . . . . . . . . . . . . . Motor resistance from power curve . . . . . . . . . . . . . . . . . Motor voltage constant . . . . . . . . . . . . . . . . . . . . . . . Motor current for maximum power . . . . . . . . . . . . . . . .

List of Equations

. Motor stall current . . . . . . . . . . . . . . . . . . . . . . . . . . Motor power loss due to current . . . . . . . . . . . . . . . . . . Motor power loss due to voltage . . . . . . . . . . . . . . . . . . Motor maximum efficiency . . . . . . . . . . . . . . . . . . . . . Motor current at maximum efficiency . . . . . . . . . . . . . . . Motor RPM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Motor efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . Motor target current . . . . . . . . . . . . . . . . . . . . . . . . . Motor symbols summary . . . . . . . . . . . . . . . . . . . . .

Preface

“If we are what we eat, then some pilots need to eat moreien.”

Anonymous

I’m a licensed full-size glider pilot with hundreds of hours of experience.I enjoyed flying these majestic birds immensely, but I haven’t done so forabout four years now and I don’t regret leaving the sport. How come? I’mhaving a ton of fun with what I’m doing now.

I used to belong to a large soaring club that has been around for over fiyyears. One of my fellow club members had actually built his own fiberglassglider. As I recall, it had taken him about five years of full-time work. Halfway through he developed an epoxy allergy, so his retired wife had to finishthe fiberglass work for him. e finished glider looked and flew beautifully,but puing it together was an ordeal that he did not wish to repeat.

Designing model airplanes is fun. ey provide an incredible creativeoutlet, unmated in full-size aviation. A very dedicated individual couldperhaps design, build and test fly one full-size airplane per decade and itwould cost many thousands of dollars. On the other hand, a model airplanecan be designed and built in one day for very lile money.

I founded RCadvisor¹ out of my love for aviation in general and modelairplanes in particular. With thousands of registered website members, I seefirst hand the allenges faced by modelers every day. Puing together anefficient power system for a model airplane is not easy. Designing your ownoriginal model airplane is not easy to do well. Today, RCadvisor’s on-line

¹www.RCadvisor.com


calculator helps you with the first task. is book helps you with the secondone.

Overview of the book

is book consists of a broad overview of a series of topics important tomodel airplane design. A lot of theory is covered, but always with an eyestrictly on its practical application.

Appendices contain various resources that I’ve found useful.I also enjoy flyingmodel helicopters (see Figure . on the facing page), but

they, unfortunately, do not lend themselves easily to homegrown designs.ey will not be discussed directly, though mu of the book is relevant tounderstanding how they fly.

e apters in the book follow a logical progression. You may have difficulty understanding the material in a later apter if you are unfamiliarwith the subjects covered earlier on.

A lot of ground is covered very quily. Don’t let the short length ofsome sections tri you into believing that they are not important and can beskipped. Everything in the book is here for a reason, and it is oen becausethe information is important and it is difficult to find elsewhere.

At the same time, I gloss over information readers may already be familiarwith or that a qui Internet sear will yield dozens of explanations. Afavorite resource of mine isWikipedia², usually providing just the right levelof detail.

ink of the book as a set of recipes. Regardless of the specific goals foryour design, you will find mu information that can be leveraged and applied successfully. At the very least, my hope is to get the reader to considerall of these dimensions of their design.

e dual goals of targeing a global audience and staying away from thecluer of units of measure proved to be a allenge. Where no units arespecified, it is imperative to use a consistent set of units. If you decide to mix

²www.wikipedia.org

Preface

Figure .. Model helicopterMu of the book applies directly to model helicopters.

together centimeters and ines, you are on your own. Angles are alwaysin degrees unless specified otherwise.

Dimensionless quantities by definition have no units associated withthem. Sometimes all the units of the values they are derived from do notentirely cancel out. at is fine as long as the units were consistent withea other to begin with.

Disclaimers

is book is designed to provide information on designing, building andflying model aircra. It is sold with the understanding that the publisherand author are not involved in rendering professional services. If expertassistance is required, the services of a competent professional should besought.

It is not the purpose of this book to reprint all the information that isotherwise available, but instead to complement, amplify and supplementother information sources.

Trademarked names are used throughout this book. We are using thenames only in an editorial fashion. e usage is to the benefit of the trademark owners and there is no intention to infringe on their legal rights.


Every effort has been made to make this book as complete and accurateas possible. However, I am not perfect. is book may contain both typographical and content errors.

e purpose of this book is to educate and entertain. e author andRCadvisor.com shall have neither liability nor responsibility to any personor entity with respect to any loss or damage caused, or alleged to have beencaused, directly or indirectly, by the information contained in this book.

Acknowledgments

I have not aempted to cite in the text all the authorities and sources consulted in the preparation of this book. To do so would require more spacethan is available.

When I decided to write this book, I figured I would be the only personthat would read it all before it’s release. Imagine my delight and dismaywhen most of the recipients of early rough dras proceeded to read it coverto cover! In no particular order, the reviewers were Roy Stone, DereWoodward, Greg Gimli, Jamie Burke, John Worth, Ken Myers, RiardKline, Ri Wier, Edgar Reyes, and Tammy Crespin. e book is muimproved because of their many thoughtful comments. ank you.

1. Fluid Dynamics Boot Camp

1.1. Introduction

A flight instructor named Al Santilli used to live near me, here in Albuquerque, New Mexico. He died in at the age of . Why am I tellingyou about him? He was the ʳ private pilot licensed in the United States.His flight instructor was Orville Wright, the co-inventor of the first successful powered airplane.

e history of manned flight is barely a hundred years old. Aerodynamicsis a fairly new science. ere is mu that we understand, but there are alsomany mysteries waiting to be solved. I have a shelf full of aerodynamicsbooks whi I’m constantly consulting. Several of these books contain over, pages. e purpose of this apter is not to try and summarize everything that I’ve learned about this important subject. Instead, I want to giveyou a flavor of the aerodynamic allenges faced by flying model airplanes.Along the way I’ll share some rules of thumb that I’ve found useful and youmight want to apply to your own designs.

e concepts explained in this apter are critical to understanding howairfoils, propellers, and wings work. It is impossible to make rational design decisions without at least a basic understanding of the aerodynamicsinvolved. Model airplanes face unique aerodynamic allenges because oftheir small sizes and slow speeds, making this basic knowledge doubly important.

Index

A cells, adhesives, adverse pressure gradient, , Aerospace Web, AIAA, airfoils, ,

design, differences, Kline-Fogleman, laminar, low Reynolds numbers, maximum li coefficient, maximum li to drag ratio, minimum drag coefficient, moment coefficient, piting moment, stall,

airplanes, control surfaces, efficiency, longitudinal stability, roll stability, scale effects, stability, yaw stability,

Alibre, All ings at Fly,

AMA Insider, Ampeer, aramid, Audubon, James, Autodesk,

balsa, bamboo, baeries, , bir, Blenderm tape, boundary layer, brushed motors, brushless motors,

CA, canards, carbon fiber, cells, center of lateral area, Century of Flight, aos theory, CLA, Collins, Miael, control surfaces, Crasman, critical Ma number, cyanoacrylates,


design process, airplane size, best practices, difficulty, flight testing, goals, materials, performance, practical approa, risks, robustness, test plan, uncertainty, ungoals,

design tools, dimensionless numbers, directional stability, dogs, Dollar Tree, Douglas-fir, drag,

induced, separation, skin friction,

Dunne, John William, Dut roll, Dyneema,

EBay, Einstein, Albert, electric motors, electronic speed controllers, energy density, epoxies, , , EPP, EPS, ESCs,

Euler number,

Fiberglass, flight testing, fluid dynamics, Froude number,

gas engines, Gimli, Greg, golf balls, Google SketUp, Gorilla glue, graphite,

Hörner wing tip, , hand launed gliders, Harbor Freight, heat, HLG, Hobby City, Hobby King, Hobby Lobby, Home Depot, Horten brothers,

inrunners, Inventor LT, inviscid flows,

Kevlar, KFm, Kline, Riard, Kline-Fogleman, Krazy glue, KRC,

laminar flow, Langley, Samuel Pierpont,

Index

lateral stability, le and right stability, li, liing stabilizer, Lilienthal, Oo, LiPo cells, Lippis, Alexander, Lile, Harold, low Reynolds numbers, Lowe’s,

M cells, MAC, MAC location, Ma number, magazines, Magnus effect, MAN, materials,

properties, MAV, mean aerodynamic ord, Messersmi, metals, methanol, Miael’s, micro air vehicle, micro vortex generators, Mignet, Henri, Model Airplane News, Model Aviation, ModelCAD, Molicel, motors, , multiple wings,

advantages, disadvantages,

history, problems,

MVGs, Mylar,

NASA, Newton, Isaac, NiCad, , niel cadmium cells, , NiMH, nitro, Nomex, Nurflügel Page, e,

Oswald efficiency, outrunners, ,

Panknin, Walter, Peyret, Louis, pine, pit stability, polypropylene foam, polystyrene foam, polyurethane glues, power density, power rule, power systems,

A cells, oosing, problems, tradeoffs,

Prandtl, Ludwig, propellers, ,

advance ratio, analyzing, baground, diameter, efficiency,


history, Ma effects, pit, spinners, zero airspeed,

PUR,

Qcad,

R/C Flight Cast, RC Modeler, RC Soaring Digest, RCadvisor, , , ,

calculator, RCGroups, RCHangOut, RCSD, RCTalk, RCUniverse, , receivers, retailers, Reynolds number,

critical, , Rutan,

scale effects, Senk, Helmut, Sears, separation, separation bubbles, Shaw, Keith, , side to side stability, SloFly, sources, Spectra, speed controllers, spiral instability, spruce,

structures, Sumo glue, sweep,

tailless, advantages, airfoils, disadvantages, history, wing twist,

tandem wings, advantages, disadvantages, history, problems,

taper ratio, thermal capacity, ird Law of Motion, orp, John, Toyota Prius, trailing edges, transmiers, TurboCAD, turbulators, turbulent flow, turning stability, Twaron, TWITT,

up and down stability,

vertical tail moment arm, viscosity, viscous flows, visibility, vortex generators, VTMA,

Index

Walmart, washout, , WaFlyer, weight, Wikipedia, Wing is the ing, e, wings, ,

aspect ratio, , , bending moment, design li coefficient, flaps, fluer, incidence, inverse Zimmerman, Oswald efficiency, span loading, structures, sweep, taper ratio, tips, washout, wing area, zero li drag,

wingtips, Wiman Tailwind, wood, Wright brothers, , , ,

XFoil, XPS,

Zimmerman,

Colophon

About the Author

I founded RCadvisor.com in . Born in Puerto Rico, I grew up in NewYork City.

I’ve had life-long love affairs with airplanes and computers. As a ild, Ibuilt and flew many rubber-powered model airplanes. I then moved on tosmall gas control-line models. In the mid-s I helped pioneer the electricrevolution by flying a . size electric model. I hold a Private Pilot-Gliderlicense and once owned a full-size AS-W high performance sailplane. I’mcurrently very active in my local model airplane clubs, recently acceptingthe position of Vice President at one of them.

I bought my first personal computer in and got my first paying job asa computer programmer in . I received a degree in Computer Sciencefrom Columbia University and have extensive experience in the field.

RCadvisor’s Calculator

Some of the website visitors are very curious about the story behind thecalculator. Here is a summary of that story.

I’ve been a computer programmer all my life. I got my first personalcomputer in and got my first paid job as a computer programmer acouple of years later while still in high sool. I’ve also been a fan of aviationfor as long as I can recall. While growing up, I always dreamed of becomingan airline pilot. I’ve been straddling these two fields my entire life.

During the summer of I was puing together an electric power system for a new model airplane I had just purased. I was very disappointed


Figure C.. Carlos Reyes

with the power system calculators available. It looked like the timewas rightfor a shake-up in the model airplane calculator market. I’ve been workingon it full-time since then. I don’t have mu time to go flying right now!

I wrote the first version of the calculator using Dojo¹, a web browser AJAXtoolkit whi uses JavaScript. I liked how it was coming together, but raninto a problem when it came time to do the arts. You see, there are nogood solutions for doing interactive graphics from JavaScript today. ebest solution I found was a Flash art control. It worked fine, but then Istarted thinking. Why not do the whole application using Flash?

I finally seled on Adobe Flex², a very powerful application framework.Flex is compiled and runs inside Flash. It looks great (see Figure C. onthe next page)! I’m only using the open source core of Flex. Ironically, Iended up writing my own arting module. e calculator was at about, lines of source code the last time I eed. Flex is a very high-levelcomputer programming language, so that actually is a lot of source code.

¹www.dojotoolkit.org²www.adobe.com/flex

Colophon

Figure C.. RCadvisor’s calculator


Website

It sounds funny to me now, but my original plan was to keep the websitearound the calculator as minimal as possible. Similar to Google’s³ landingpage, it was going to consist of not mu more than the calculator. About aweek before the official laun on January , , I decided that the calculator merited a full-blown website.

e web server runs Drupal⁴, a great open source content managementsystem. I’ve customized it with about fiy add-on modules and mu elbowgrease.

This Book

is is my first published book. I decided to do all the work myself. I wroteit using LATEX, an incredibly powerful open source document processing system with an equally massive learning curve. e entire book is just onelarge plain text file of about , lines with the contents and all the LATEXcommands all mixed in together.

As you can probably guess, I’m a big fan of open source soware. I’vebeen running Linux⁵ as the primary operating system on my desktop forseveral years now.

Regrets? Never.

³www.google.com⁴www.drupal.org⁵www.linux.org

Crafts & Hobbies/Models

You Can Do It!uild and fly your very own model airplane design. Using clear explanations, you will learn important design trade-offs and how to choose among them. The latest research and techniques are discussed using easy to understand language.B

You will discover:• The special challenges faced by the smaller models and how to overcome them.• How to choose the right material for each part of the airplane.• Easy rules for selecting the right power system, gas or electric.• When it makes sense to use one of the innovative KFm airfoils.• Pros and cons of canard and multi-wing configurations.• A step-by-step design process that includes goal setting and flight testing.• In-depth discussions of important topics like airfoils and wing design.• The sources of air drag and how to minimize their impact.

A perfect complement to RCadvisor's online model airplane calculator, this book stands completely on its own. All of the formulas included can be easily used with a hand-held calculator.

RCadvisor's easy to use calculator is the leading online tool for model airplane building and design. Numerous ToolTips, interactive tutorials, and real-time graphs make understanding easy.

Carlos Reyes founded www.rcadvisor.com in 2007. He's had a life-long love affair with aviation, building and flying model airplanes since childhood. He holds a Private Pilot-Glider license and is the Vice President of his local model airplane club.

“This book is a joy to read! The writing style and wit add dimension in a way that is rarely found in today's reference materials. If someone has considered designing their own airplane and been put off because of complicated formulas, vocabulary and reference style that would bore even an engineer, this will convince them to go ahead and try it. Written with real people in mind and not engineers—and I mean that in a good way. This is a book that will reside along the other favorites on my bookshelf. Carlos really managed to produce a book that will last a long time and become one of the standards for modelers.”

⁓Greg Gimlick, Electrics columnist, Model Aviation magazine

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