Fig. 49d.—A very Light Weight Model.
Constructed by the author. Provided with twin propellers of a modified Fleming-Williams type. This machine flew well when provided with an abnormal amount of rubber, owing to the poor dynamic thrust given by the propellers.
§ 13. In the Clarke models with the small front plane, the centre of pressure is slightly in front of the main plane.
The balancing point of most models is generally slightly in front, or just within the front edge of the main aerofoil. The best plan is to adjust the rod carrying the rubber motor and propeller until the best balance is obtained, then hang up the machine to ascertain the centre of gravity, and you will have (approximately) the centre of pressure.
Fig. 49e.—Useful Fittings for Models.
1. Rubber tyred wheels. 2. Ball-bearing steel axle shafts. 3. Brass wire strainers with steel screws; breaking strain 200 lb. 4. Magnalium tubing. 5. Steel eyebolt. 6. Aluminium "T" joint. 7. Aluminium "L" piece. 8. Brass brazed fittings. 9. Ball-bearing thrust. 10. Flat aluminium "L" piece.
[The above illustrations taken (by permission) from Messrs. Gamage's catalogue on Model Aviation]
§ 14. The elevator (or tail) should be of the non-lifting type—in other words, the entire weight should be carried by the main aerofoil or aerofoils; the elevator being used simply as a balancer.[39] If the machine be so constructed that part of the weight be carried by the elevator, then either it must be large (in proportion) or set up at a large angle to carry it. Both mean considerably more resistance—which is to be avoided. In practice this means the propeller being some little distance in rear of the main supporting surface.
Fig. 49f.—Useful Fittings for Models.
11. Aluminium ball thrust and racket. 12. Ball-bearing propeller, thrust, and stay.
[The above illustrations taken (by permission) from Messrs. Gamage's catalogue on Model Aviation.]
§ 15. In actual flying models "skids" should be used and not "wheels"; the latter to be of any real use must be of large diameter, and the weight is prohibitive. Skids can be constructed of cane, imitation whalebone, steel watch or clock-spring, steel pianoforte wire. Steel mainsprings are better than imitation whalebone, but steel pianoforte wire best of all. For larger sized models bamboo is also suitable, as also ash or strong cane.