wrote in message
oups.com...
Thanks for the ideas. The student in question only compared total
travel time between the two wings. I suggested that he try out
throttling the motor to check performance in different flight regimes.
My hypothesis is that the increased length of the leading edge
increases parasitic drag and that at the airspeed he was using this
rather than induced drag was the limiting factor.

Parasitic drag should be related to wing surface area, not solely to frontal
cross-section (ie increased length of the leading edge). Of all the
possible explanations, that seems the least compelling to me.

I agree that throttling the motor is important. If the student did not
control for the motor's power output, then the two trials are not
comparable.

I still agree with the issues raised by Geoff, the CG in particular. A
stable airplane configuration results from CG forward of the center of lift,
and a down-force aft of the center of lift (usually from some sort of
horizontal stabilizer and/or elevator). It's not clear from the information
provided how this test aircraft was designed, but unless the airplane was
100% unstable (CG and center of lift at the same position), the CG needs to
be taken into account (I would do so simply by ensuring that the CG and
center of lift are the same distance apart in both trials, resulting in the
same total lift and stabilizing downforce for both trials).

It should go without saying that unless both flights have perfectly level
flight paths, then any climb or descent must be accounted for as well (and
preferably eliminated so that a true comparison can be made).

As far as wing flex goes, again without knowing the actual design of the
airplane, it's not possible to comment specifically. But I would think that
on an airplane of that scale, it should be possible to construct wings that
have effectively no flex at all, eliminating that source of error for all
practical purposes.

The Reynolds number issue sounds like a red herring to me, but I suppose a
drastic enough difference in the wings could affect the trial.

Pete