

Nov 06, 2005, 02:34 PM  

Beep, just to add to what Aio1 said  you really only need to know the wing area and models weight to get a quite decent estimate of how slowly it can fly and still make enough lift to stay in the air (i.e., the stall speed). Or turn that around, decide how slowly you want it to land, and that will tell you how much wing area you need for a given model weight.
Astonishingly, you can completely ignore details like the actual airfoil, and still get very usable results for our purposes. Once you know the stall speed, you know the pitch speed should be two to three times the stall speed. Once you know the pitch speed, you can estimate the thrust from the prop: a magical 100% efficient prop would produce a thrust (at speed) in ounces given by: Thrust (oz) = 8.2 x power (watts)/pitch speed(mph) Actual thrust might be 70% or 80% of that number. So now you know how much power you need to get enough thrust to fly, and you know how much wing area you need, and you know what your model should weigh. All that remains is to find a prop, gear ratio, motor, and battery that provides that power at that pitch speed, and you're in business. This method won't make a contestwinning sailplane design, but it will result in something that will fly. You can use WebOCalc to do the mathematical lifting for you: get it from my RC Groups website, http://flbeagle.rchomepage.com . (Click Software, WebOCalc). Flieslikeabeagle 
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