"Q-tip props are thought to be another route for noise reduction. The curled-up tips of the prop blades reduce the airflow off the end of the tip, much like winglets reduce wake vortex at wingtips. The manufacturer does not claim that the Q-tip prop reduces noise, but its diameter is two inches less than the props it replaces. At the same RPM as a non-Q-tip prop it produces more thrust at a less tip speed and thus less noise."

"75 hp Revmaster", Q-tip prop. Note~ This might mean that Q-tip props are manufactured for the power output of the UniCopter.

Winglets use the forward component of the helical flow at the
tip (the resultant of the chrodwise and spanwise flows) to produce
"thrust" and this reduce net drag. The overall effect is in some ways
similar to the effect of increasing the aspect ratio, but is isn't the
same.

Increasing the aspect ratio simply reduces the induced drag [the
Cl^2/2Pi*Ar term] at the cost of increased form drag, skin friction,
structure weight etc and the benefit is enjoyed whenever Cl is reasobably
high. A decently designed winglet can actually yeild a much bigger net
reduction in drag for a given increase in weight & frontal area, but the
effect only works at specific speed/weight/Cl combinations becuase the
required winglet geometry is linked to the helix angle of the wingtip
flow.

Now a cross country glider has to fly at a wide range of speeds to cover
the max-climb-in-lift and best-glide-angle-for-dash cases, so the winglets
would have to be configured for one or the other and whichever case wasn't
selected would actually see a drag *increase*, so it possibly is
influenced by the span limits for the class. For an airliner this isn't an
issue, because airliners cruise at a specific point in terms of Cl, mach
number etc and so the winglet solution usually offers greater benefit than
the increased Ar would.

Peter D Rieden