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A Tale of Two Model Airplanes

May 05, 2015

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Airfield Models ( Tale of Two Airplanes

Mike Phillips, a good friend of mine, owns a locally kitted R/C aircraft called the A Model.  It is a typical .40 size Stik model.  I have Rustik.

Each plane is powered by an O.S. .52 four-stroke engine.  Both models have a wing area of approximately 600 in2.  Those are the only similarities.

Rustik's wing is built up, fully sheeted and has approximately twice the number of ribs as the A Model.  The A Model wing is D-tube construction with cap strips.

Mike's A Model has 1/8" thick solid balsa wood sheet tail surfaces.  Rustik has a 3/4" thick built up and sheeted airfoiled stabilizer.  The fin and rudder are approximately 1/2" thick and are also built up and sheeted.

Mike's model is covered with Monokote.  My model is completely fiberglassed and top-coated with several sprayed coats of clear polyurethane.  Additionally, my model has 8 inlaid Maltese crosses made from 1/64" plywood.  The four crosses on the wing are 8" square.

Mike's plane has a pair of 1" wide x 1/8" thick strip ailerons powered by a single servo mounted in the center of the wing. Rustik has separate flaps and ailerons (4 surfaces in total) that are 2" wide.  Each of the four surfaces has its own servo, hatch, mount and servo extension.  Each surface is built up, sheeted and approximately 3/4" thick.

Mike's model has a carbon fiber landing gear.  Mine has a laminated plywood landing gear.

I don't know the exact measurements of Mike's fuselage, but it is shorter and smaller around than Rustik's.

Correction - 12/2004

Apparently I mis-disremembered Rustik's overall weight.

Mike and I weighed Rustik again to double-check.  The airframe weighs 4 lbs 9 oz less fuel 2 ounces less than what I originally reported.

We are going to weigh Mike's plane again as well.

I also plan to take a photo of the planes side by side which should help put all of this in context.

Mike's airplane weighs 4 lbs 10 oz. ready-to-fly.  Rustik weighs 4 lbs 11 oz.  The sheeting, painted finish, extra servos, built up tail surfaces and other embellishments only cost 1 oz over the weight of the A Model.  So did Mike build a heavy model or did I build a light model?  Yes is the correct answer to both questions.

My model is very light for what it is.  Most builders would have had trouble building Rustik to a ready-to-fly weight of under 6 lbs.  Mike's model is very heavy for what it is.  It should have weighed about one pound less.  Mike says the wood that came in the kit could have been used to make hockey sticks and he used it anyway.  To get the weight down, he would have had to use the kit parts as patterns and replace them all with lighter wood.

Both models have reasonable wing loadings and they both fly well.  But the A Model could have had a substantially lower wing loading (20% less) and been a stellar performer (except for its bizarre airfoil which is a completely different topic).



How to Design and Build Lightweight Model Airplanes
Engineering for Light Weight, Strength and Rigidity

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Copyright 2004 Paul K. Johnson