Ron McKinnon wrote:
From: "Matt Whiting"

Ron McKinnon wrote:


"Matt Whiting" wrote in message

...Why? It is acceptable to "polish the frost smooth" per FAR 91.527.

Interesting. It seems a rather dubious practice to me. It would indeed
appear to be legal in the US - but, FWIW, it isn't legal in Canada.

Why? Smooth frost is less of an aerodynamic issue that a thick layer of
dirt, bugs and dust...


Be that as it may, arguing that its not as bad as something else (that you
shouldn't fly with either), isn't any argument at all for the acceptability
of flying with smooth frost.

Frost, smooth or otherwise, or other contaminants arguably affect the
aerodynamic behaviour. How much does it change with a given
level of contamination?, what level of contamination is significant?
or how significant is such a change? how much is too much? how
smooth is smooth enough? in what way will such change affect the
aerodynamic behaviour of the plane? (does it change the critical
angle of attack for the wings? the control surfaces?, what are
the new critical angles (what's the new stall behaviour? is a
tailplane stall more likely? will it spin easier? how does it change
rudder effectiveness?) for instance) are critical questions. But
these are not questions that a typical pilot is in a position to answer
operationally. This a job for computer simulations, and lab analysis
in controlled test conditions, and for test pilots in controlled test
situations.

They only affect the aerodynamic behavior if they significantly affectt
he flow in the boundary layer. On some airfoils this a concern with
fairly small disturbances, but on others it isn't much of a concern at
all. Saying that you should not fly an airplane that has any frost on
it is just as silly as saying you should never take off with less than
full fuel. You have to know your airplane, nobody is arguing that.
Most light airplanes will fly just fine with polished frost on the wings
and even the control surfaces, I know my 182 did.


Critical surfaces should be clean.

Only if being clean is critical. :-) It often isn't.

Do you really wipe your entire airplane completely clean of bugs and
dirt after every flight? If you fly through bugs do you land
immediately to clean them off?


Matt