"It also seems as if variations in temperature and humidity could affect
lift and drag in some complex, difficult-to-quantify ways."
Both of those will affect the air density, as will pressure and therefore
altitude, which will require a different speed to support the same weight.
That will also affect the speed required of the propeller to develop the same
thrust. The same thrust implies the same torque, but temperature differences
may require a different cross section to get that torque. Lower density means
the forces are the same, in proportion to weight which is not affected by
weather, but speeds are greater, so the duration may be less. Higher humidity
means lower density. Water vapor is less dense than dry air.
Higher temperature by itself means lower density, higher required speed,
higher prop RPMs. This suggests a shorter duration, but if the motor cross
section is adjusted down and turns go up to get the same starting torque, the
torque curve loses some of the spike and fills more of the energy rectangle.
It's hard to say on general principles what the outcome would be, hard to know
the tradeoff.
"Do these sound like good approaches?"
Yes. Might want to use the backup model for site familiarization flights.
And precondition the rubber the same as at home so you know what it is going
to do.
Gary Hinze
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Received on Mon Feb 26 2007 - 17:07:27 CET