The Aeroplane Speaks. Fifth Edition

It is due to the combination of (1) a very steep spiral descent of small radius, and (2) insufficiency of keel-surface behind the vertical axis, or the jamming of the rudder and/or elevator into a position by which the aeroplane is forced into an increasingly steep and small spiral. Owing to the small radius of such a spiral, the mass of the aeroplane may gain a rotary momentum greater, in effect, than the air pressure of the keel-surface or controlling surfaces opposed to it; and, when once such a condition occurs, it is difficult to see what can be done by the pilot to remedy it. The sensible pilot will not go beyond reasonable limits of steepness and radius when executing spiral descents. In this connection every pilot of an aeroplane fitted with a rotary engine should bear in mind the gyroscopic effect of such engine. In the case of such an engine fitted to a "pusher" aeroplane, its effect when a left-hand turn is made is to depress the nose of the machine. If fitted to a "tractor" it is reversed, so the effect is to depress the nose if a right-hand turn is made. The sharper the turn, the greater such effect--an effect which may render the aeroplane unmanageable if the spiral is one of very small radius and the engine is revolving with sufficient speed to produce a material gyroscopic effect. Such gyroscopic effect should, however, slightly assist the pilot to navigate a small spiral if he will remember to (1) make right-hand spirals in the case of a "pusher," (2) make left-hand spirals in the case of a "tractor." The effect will then be to keep the nose up and prevent a nose-dive. I say "slightly" assist because the engine is, of course, throttled down for a spiral descent, and its lesser revolutions will produce a lesser gyroscopic effect.