Re: Airplanes

["John S. Denker" <jsd@MONMOUTH.COM>]

Clarence Bennett wrote:
> Yesterday midday, as I was approaching DFW in the rear of a Boing Super 80,
> I saw a vapor trail starting between the outer end of the flap and the aeleron.
>
> But there was no trace of a trail on the port side, so I wondered what the
> difference might be.
>
> I don't suppose there is any chirality of water condensation?

Not that you would notice.

More-likely hypotheses include:
 -- The engine on one side might be producing slightly more thrust
than the engine on the other side, resulting in the airplane flying
in a slight slip.  For details see
http://www.monmouth.com/~jsd/how/htm/multi.html#sec-1out-coordination
 -- Since both engines rotate the same way, they dump a nonzero
amount of angular momentum into the air.  (This phenomenon is quite
conspicuous on propeller aircraft;  on jets it is less conspicuous
but still present to some degree.)  To compensate, you need to hold
a steady aileron deflection, especially during high-power low-airspeed
flight.
http://www.monmouth.com/~jsd/how/htm/roll.html#sec-propeller-drag
 -- The flaps might not be rigged perfectly.  On one side, (a) the flap
extends less, and (b) you need extra aileron deflection to maintain zero
roll ... each of which makes a contribution to reducing the difference
in circulation at the flap/aileron joint, and therefore the amount of
trailing vortex that must be shed at this point.
http://www.monmouth.com/~jsd/how/htm/airfoils.html#sec-circulation
 -- There may be other hypotheses that didn't immediately occur to me.