Fig. 9.—Clark's Model Flyer.
Main aerofoil set at a slight negative angle. Dihedral angles on both aerofoils.
The theoretical conditions stated in F and N are fully borne out in practice.
And since a curved aerofoil even when set at a slight negative angle has still considerable powers of sustentation, it is possible to give the main aerofoil a slight negative angle and the elevator a slight positive one. This fact is of the greatest importance, since it enables us to counteract the effect of the travel of the "centre of pressure."[11]
Fig. 10.—Large Model Monoplane.
Designed and constructed by the author, with vertical fin (no dihedral angle). With a larger and more efficient propeller than the one here shown some excellent flights were obtained. Constructed of bamboo and nainsook. Stayed with steel wire.
§ 8. Referring to I. This, again, is of primary importance in longitudinal stability. The Farman machine has three such planes—elevator, main aerofoil, tail the Wright originally had not, but is now being fitted with a tail, and experiments on the Short-Wright biplane have quite proved its stabilising efficiency.
The three plane (triple monoplane) in the case of models has been tried, but possesses no advantage so far over the double monoplane type. The writer has made many experiments with vertical fins, and has found the machine very stable, even when the fin or vertical keel is placed some distance above the centre of gravity.
§ 9. The question of transverse (side to side) stability at once brings us to the question of the dihedral angle, practically similar in its action to a flat plane with vertical fins.
Fig. 11.—Sir George Cayley's Flying Machine.
Eight feathers, two corks, a thin rod, a piece of whalebone, and a piece of thread.