View Full Version : Need Help AUW

05-01-2006, 02:40 AM
Need a rough steer for a 30 inch Waco , weightwise my friends maybe way over , ballpark type stuff
Thanks so much

Dick Adams
10-04-2006, 01:06 PM
If you are scaling up or scaling down from a known airplane to arrive at your 30" WS, take the old WS and divide it by the new WS (30") and then square that result to get your scaling factor and then mulitply the old known weight of airframe by the scaling factor to get an estimated airframe weight for your 30" WS airplane. (Then add in motor, battery, electronics to obtain the all up weight).

For example, if you know that the airframe for a 48" WS version weighed 2 pounds and carried 1 pound of motor/battery/RC gear, divide 30 by 48, which gives you .625. Square that to arrive at a scaling factor of .3906. Multiply the old airframe weight of 2 pounds, or 32 ounces, by .3906 and you arrive at the new airframe weight of 12.5 ounces. Now add the estimated weight of new motor/battery/RC gear and you will get an approximate AUW for your project airplane.

This won't give an exact result because building materials come in standardized thicknesses, so scaling down won't save as much as the scaling factor dictates it should.

If you want to project performance of your new bird go to one of the online calculators that can do just that. For the small airplanes I build, I find the Flight Calculator at this site to be quite useful:


Click on "Tech Resources" to find the flight calculator.

Credit goes to my friends Larry Markey, of Northville, MI, and Paul Bradley, of Houston, TX, for guiding me through this scaling process!

Hope that helps more than it confuses!