Some
propeller tips have a speed of over 30,000 feet a minute,
and any roughness will produce a bad drift or resistance
and lower the efficiency.
9. MOUNTING.--Great care should be taken to see that
the propeller is mounted quite straight on its shaft. Test in
the same way as for straightness. If it is not straight, it
is possibly due to some of the propeller bolts being too slack
or to others having been pulled up too tightly.
FLUTTER.--Propeller ``flutter,'' or vibration, may be due
to faulty pitch angle, balance, camber, or surface area. 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.
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