Short Final: Structural Integrity

7

My first job in aviation back in 1978 was as an admissions counselor at East Coast Aero Tech, an A&P school in Lexington, Massachusetts (a town you may have heard of). As a freshly certificated private pilot, I discovered the magical world of homebuilt airplanes and quickly joined the Experimental Aircraft Association. At the time, there were a few very basic homebuilt designs that used plywood airframes with Styrofoam formers wrapped in fabric to shape the airfoil, control surfaces and various fillets and a fuselage smoother-outer here and there. I even ordered a set of plans for one of the designs. I think it cost me $25.

One day, I was standing around in the airframe shop area and I asked a few of the old-school instructors what they thought of the wood-and-foam construction technique I had “invested” in. After an awkward pause, one of them took his empty Styrofoam coffee cup, bent his wooden stirrer double and stuck it inside, then dropped it on the floor and crushed it under his shop boot.

He said, “That’s what they look like when they crash,” and walked away.

Mark Phelps
Mark Phelps is a senior editor at AVweb. He is an instrument rated private pilot and former owner of a Grumman American AA1B and a V-tail Bonanza.

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7 COMMENTS

  1. Actually, radio-controlled model airplanes made from Styrofoam survive crashes much better than those made from balsa and plywood. Welded steel tubing would be a bit heavy and take much longer to build.. 😉

    • That’s due to the scale effect. You can’t scale up from your model aircraft and expect the same strength to weight relationships to hold true.

    • Have you ever aggressively swept a bug off your arm and watched it hit the ground, then it just rights itself and either walks or flies away? That is an even greater example of scale effect.

  2. All depends upon the structure and the direction of the applied forces. An aluminum can will withstand a lot of vertical force, but very little horizontal force. Styrofoam plastic is a cellular plastic which is different than the aligned fibers in wood. Determining the strength of various materials isn’t necessarily a snap judgment thing. Adding wise cracks doesn’t change the physics.

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