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Model Aircraft Aerodynamics Fourth Edition by Martin Simons Soft Cover 1999
Model Aircraft Aerodynamics Fourth Edition by Martin Simons Soft Cover 1999 344 Pages
fourth edition
The purpose of this book is to present in a practically useful form some standard aerodynamic theory as it applies to model aeroplanes, helicopters and gliders.
Anyone whose interest in model flying is more than casual will benefit from understanding the behaviour of the aircraft better - there will be fewer serious mistakes in trimming or control. Those who build or design models will be able to improve them. Apart from these considerations, aerodynamics is an interesting study in its own right and adds a further fascination to the sport.
Successful models may be designed and flown by rule of thumb. A sort of evolutionary survival of the fittest has produced a great many successful aircraft and it is not claimed that this book will bring about any revolution. It is, however, likely that some new ideas for future development will be extracted by those who read with an open mind. Some of the material contained will be familiar to experienced modellers but in other cases they will find their old notions under criticism. This is particularly likely in discussions of the basic description and selection of aerofoil sections. Model fliers and many books and articles written for them frequently adopt a very misleading aerofoil nomenclature: undercambered, flat bottomed, semi-symmetrical and symmetrical, even Phillips entry. (This harks back a century to Horatio Phillips' patent of 1891.) Such terms can lead the beginner into serious trouble. At least the camber of the centre line of the profile should be known and taken together with the profile thickness.
The basic layout and trim of nearly all 'free flight' models also seems to be dominated by fashion to the exclusion of elementary principles. This is not to say that these models do not fly well; clearly they do. But trimming them for consistent performance and safety is made unnecessarily difficult when the centre of gravity is in the wrong position relative to the mainplane, as it almost invariably is. No gain in performance results -indeed, there is some small performance penalty for slow-flying models if the centre of gravity is located where, on current contest-winning models, it usually is. The fact that such models do win is because they are flown very skilfully despite their inherent faults. Arguments in favour of this kind of trim, sometimes loaded with mathematical equations, prove on examination to be mistaken.
Other common misunderstandings arise through the confusion between trimming and stability. This is examined in some detail in Chapter 12.
It is assumed throughout that the reader is a practising model flier and knows, or is prepared to learn, at least the essentials of how model aircraft are constructed, trimmed and flown. The underly- ing principles are emphasised throughout. The mathematics has been kept to a bare minimum. Where numerical examples have been thought important or interesting enough to merit inclusion, they have been placed in Appendix 1 and may be ignored by those who do not wish to become involved in figuring. It is rarely necessary or worthwhile in aeromodelling to carry out elabo- rate calculations. When a little arithmetic is essen- tial it is usually confined to the four basic rules. If a reader is prepared to do a little more work, many of the problems arising can be solved to a sufficient degree of precision by the use of simple graphical methods or with an ordinary pocket calculator. It helps to have a few additional functions such as square roots and trigonometrical ratios (cosines, sines, tangents etc.), but these are not essential.
On the commercial market now there are various kinds of computer software packages with model aircraft applications. These range from glider performance programs to flight simulators and elementary aerofoil section plotting and design. (These last should be distinguished from the highly sophisticated programs used for aerofoil design by professional aerodynamicists such as Eppler, Somers, Williams, Selig etc. in university and other research institutions.) Modellers using any such packages should remember that they are all based on fundamental assumptions which may be wrong. If garbage goes into the computer, it emerges in the output. It is necessary to compre- hend the underlying theory if the computer is to produce meaningful results. This book should provide the necessary background enabling the model flier to discriminate between sense and nonsense.
The theories discussed are in general use by aerodynamicists but are not to be regarded as final truths. There is always room, and in some cases great need, for new discoveries. On the other hand, model aerodynamics, like any other branch of engineering science, must be firmly based on fundamental natural principles as these have been found by test and experiment. Some of the most basic principles are examined in the first chapter. Readers already familiar with the laws of motion may wish to skip this early section, though it is important that these passages be understood before the later ones are tackled.
Problems associated with flight and airflow speeds approaching the speed of sound are not considered in this book.
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