[net.aviation] Slow Speed Snap Rolls

peterb@pbear.UUCP (02/06/85)

	If your airplane was GROSSLY overpowered, I presume that you
had to put a large or high pitch propeller on that beast in order to keep
engine load up and revs down.

	If this is so, then that monster prop is going to alter the airflow
characteristics near the wing root. If the engine is rotating counter
clockwise (looking at the front) then the airflow moving over the right
wing is being deflected down by the prop descending on that side,
and on the left the airflow is being deflected up. This usually has no
effect on the stal/roll charecteristics, but with a wing that is loaded
critically, this slight change can really mess the works.

	In this configuration, the right wing will stall later than the left
since the right wingroot will be flying on "ground effect" as the air is
pushed under the wing and down whereas the left wing will stall earlier
since the upward moving air is 'increasing' the angle of attack.

	Also if the slow flight you are describing is near stall speed
(which is increased along with wing loading due to the monster engine)
then these charecteristics can greatly effect the stall response of
the aircraft.

	As a test you can slow the aircraft in level flight (adjust
elevator to keep on level course) and keep increasing angle of attack
and reducing speed until the aircraft stalls. If counter aileron has
NO effect in preventing the snap then you know it can not be a torque
induced roll since the engine power is down close to idle.

	If this is so, then the judicious placement of wing root canards
can make all the difference in the world. They have been used in STOL
experiments on Cessna 404 and 402's and have reduced the stall speed by
about 10-15 knots by deflectin the airflow down over the wing in
high angle of attack attitudes.

						Peter Barada
						ima!pbear!peterb