To take out dirt or oily patches,
try acetone. If that will not remedy matters, then try
petrol, but use it sparingly, as otherwise it will take off an
unnecessary amount of dope. If that will not remove the
dirt, then hot water and soap will do so, but, in that case,
be sure to use soap having no alkali in it, as otherwise it may
injure the fabric. Use the water sparingly, or it may get
inside the planes and rust the internal bracing wires, or cause
some of the wooden framework to swell.
The wheels of the undercarriage have a way of throwing
up mud on to the lower surface. This should, if possible, be
taken off while wet. It should never be scraped off when
dry, as that may injure the fabric. If dry, then it should
be moistened before being removed.
Measures should be taken to prevent dirt from collecting
upon any part of the aeroplane, as, otherwise, excessive skin-
friction will be produced with resultant loss of flight speed.
The wires, being greasy, collect dirt very easily.
CONTROL CABLES.--After every flight the rigger should
pass his hand over the control cables and carefully examine
them near pulleys. Removal of grease may be necessary
to make a close inspection possible. If only one strand is
broken the wire should be replaced. Do not forget the aileron
balance wire on the top surface.
Once a day try the tension of the control cables by smartly
moving the control levers about as explained elsewhere.
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