The Aeroplane Speaks. Fifth Edition

FLUTTER.--Propeller "flutter," or vibration, may be due to faulty pitch angle, balance, camber, surface area, or to bad mounting. It causes a condition sometimes mistaken for engine trouble, and one which may easily lead to the collapse of the propeller. CARE OF PROPELLERS.--The care of propellers is of the greatest importance, as they become distorted very easily. 1. Do not store them in a very damp or a very dry place. 2. Do not store them where the sun will shine upon them. 3. Never leave them long in a horizontal position or leaning up against a wall. 4. They should be hung on horizontal pegs, and the position of the propellers should be vertical. If the points I have impressed upon you in these notes are not attended to, you may be sure of the following results: 1. Lack of efficiency, resulting in less aeroplane speed and climb than would otherwise be the case. 2. Propeller "flutter" and possible collapse. 3. A bad stress upon the propeller shaft and its bearings. TRACTOR.--A propeller mounted in front of the main surface. PUSHER.--A propeller mounted behind the main surface. FOUR-BLADED PROPELLERS.--Four-bladed propellers are suitable only when the pitch is comparatively large. For a given pitch, and having regard to "interference," they are not so efficient as two-bladed propellers. The smaller the pitch, the less the "gap," i.e., the distance, measured in the direction of the thrust, between the spiral courses of the blades (see illustration on preceding page). If the gap is too small, then the following blade will engage air which the preceding blade has put into motion, with the result that the following blade will not secure as good a reaction as would otherwise be the case. It is very much the same as in the case of the aeroplane gap.