§ 7. The most suitable propeller for this form of model. § 8. Professor Kress' method of launching. § 9. How to launch a twin screw model. § 10. A prior revolution of the propellers. § 11. The best angle at which to launch a model

109 CHAPTER XI. HELICOPTER MODELS. § 1. Models quite easy to make. § 2. Sir George Cayley's helicopter model. § 3. Phillips' successful power-driven model. § 4. Toy helicopters. § 5. Incorrect and correct way of arranging the propellers. § 6. Fabric covered screws. § 7. A design to obviate weight. § 8. The question of a fin or keel. 113 CHAPTER XII. EXPERIMENTAL RECORDS 116 CHAPTER XIII. MODEL FLYING COMPETITIONS. § 1. A few general details concerning such. § 2. Aero Models Association's classification, etc. § 3. Various points to be kept in mind when competing. 119 CHAPTER XIV. USEFUL NOTES, TABLES, FORMULÆ, ETC. § 1. Comparative velocities. § 2. Conversions. § 3. Areas of various shaped surfaces. § 4. French and English measures. § 5. Useful data. § 6. Table of equivalent inclinations. § 7. Table of skin friction. § 8. Table I. (metals). § 9. Table II. (wind pressures). § 10. Wind pressure on various shaped bodies. § 11. Table III. (lift and drift) on a cambered surface. § 12. Table IV. (lift and drift)—On a plane aerofoil—Deductions. § 13. Table V. (timber). § 14. Formula connecting weight lifted and velocity. § 15. Formula connecting models of similar design but different weights. § 16. Formula connecting power and speed. § 17. Propeller thrust. § 18. To determine experimentally the static thrust of a propeller. § 19. Horse-power and the number of revolutions. § 20. To compare one model with another. § 21. Work done by a clockwork spring motor. § 22. To ascertain the horse-power of a rubber motor. § 23. Foot-pounds of energy in a given weight of rubber—Experimental determination of. § 24. Theoretical length of flight. § 25. To test different motors. § 26. Efficiency of a model. § 27. Efficiency of design. § 28. Naphtha engines. § 29. Horse-power and weight of model petrol motors. § 30. Formula for rating the same. § 30A. Relation between static thrust of propeller and total weight of model. § 31. How to find the height of an inaccessible object (kite, balloon, etc.). § 32. Formula for I.H.P. of model steam engines. 125 APPENDIX A. Some models which have won medals at open competitions 143

---

GLOSSARY OF TERMS USED IN
MODEL AEROPLANING.

Aeroplane. A motor-driven flying machine which relies upon surfaces for its support in the air.

Monoplane (single). An aeroplane with one pair of outstretched wings.

Aerofoil. These outstretched wings are often called aerofoil surfaces. One pair of wings forming one aerofoil surface.

Monoplane (double). An aeroplane with two aerofoils, one behind the other or two main planes, tandem-wise.

Biplane. An aeroplane with two aerofoils, one below the other, or having two main planes superposed.

Triplane. An aeroplane having three such aerofoils or three such main planes.

Multiplane. Any such machine having more than three of the above.

Glider. A motorless aeroplane.

Helicopter. A flying machine in which propellers are employed to raise the machine in the air by their own unaided efforts.

Dihedral Angle. A dihedral angle is an angle made by two surfaces that do not lie in the same plane, i.e. when the aerofoils are arranged V-shaped. It is better, however, to somewhat extend this definition, and not to consider it as necessary that the two surfaces do actually meet, but would do so if produced thus in figure. BA and CD are still dihedrals, sometimes termed "upturned tips."

Span is the distance from tip to tip of the main supporting surface measured transversely (across) the line of flight.

Camber (a slight arching or convexity upwards). This term denotes that the aerofoil has such a curved transverse section.

Chord is the distance between the entering (or leading) edge of the main supporting surface (aerofoil) and the trailing edge of the same; also defined as the fore and aft dimension of the main planes measured in a straight line between the leading and trailing edges.

Aspect Ratio is ^span/_chord

Gap is the vertical distance between one aerofoil and the one which is immediately above it.

(The gap is usually made equal to the chord).

Angle of Incidence. The angle of incidence is the angle made by the chord with the line of flight.

Width. The width of an aerofoil is the distance from the front to the rear edge, allowing for camber.

Length. This term is usually applied to the machine as a whole, from the front leading edge of elevator (or supports) to tip of tail.

Arched. This term is usually applied to aerofoil surfaces which dip downwards like the wings of a bird. The curve in this case being at right angles to "camber." A surface can, of course, be both cambered and arched.

Propeller. A device for propelling or pushing an aeroplane forward or for raising it vertically (lifting screw).

Tractor Screw. A device for pulling the machine (used when the propeller is placed in the front of the machine).

Keel. A vertical plane or planes (usually termed "fins") arranged longitudinally for the purposes of stability and steering.

Tail. The plane, or group of planes, at the rear end of an aeroplane for the purpose chiefly of giving