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Q-talk 142 - Burt Rutan Strength Demo

You tube has become a great videos.  Every once in a while you'll run across a gem like the video below.  It shows a much younger Burt Rutan and future Civilian Astronaut Mike Meville preaching the gospel of composite structures.  I archived the video here on this site for you (In case it ever gets taken down on YouTube) but the original link is here foranyone interested.


The full transcription of the audio appears below: 

BURT RUTAN: What we have here is a sample of two small wings, actual aircraft construction, similar metal construction and fiberglass construction. They’re both the same weight, the same size, and provide the same aerodynamic function. Notice the aluminum one has a myriad of stress concentrations. Very low stress in this area and then high concentrations where rib loads doved into the spar, and where rivets are.

The composite full core moldless construction, like we use in the homebuilts, is very uniformly loaded. It doesn’t have any ribs, or indeed it has one rib that runs from here to here. It’s a full solid core of rigid foam.

It’s very very stiff, it doesn’t deform under loads, and more importantly it’s very uniformly loaded. The core does not have traps for water to get into. It doesn’t corrode as easily as this. It holds it’s shape better. And it is stronger. . . We’re just going to put it down here and leap up on top of it, and show you what happens when it is overloaded. OK?. . . Ready. . . {BAM!}

The metal one not only failed the spar, but it failed the skin, under loads it’s very weak and it’s very susceptible to fatigue. The glass one on the other hand can take extreme overload, and they are both the same weight.

Notice the aluminum where the spar ended at this point, and went to a lighter spar is where we had a spar failure. Notice also that we have skin failures, wrinkles, buckles, ribs rivets popped out, and in general, a lot of deformation going on that’s permanent.

In general the composite takes much higher loads even though it’s the same weight, takes much higher loads without any permanent deformation, and without any loss of its aerodynamic qualities. The composite is extremely, extremely strong. For the same weight it is considerably more durable and considerably stronger structure.

In general the composite allows the builder to make a spar that smoothly decreases its thickness, instead of more abruptly like you have when you’re stuck with various material sizes that have to be riveted together.

The composites are also considerably better for corrosion, if you take and dip this whole assembly in salt water for example. You would totally destroy the structural integrity of the aluminum within just a few hours actually.

In a salt water environment, both of these structures exposed similarly, you would ruin the metal and not damage the fiberglass at all. Fiberglass does have to be protected from ultraviolet radiation, with appropriate paints, and ultraviolet barriers.

Hopefully, our airplanes won't encounter any stomping feet when they're in the air, but the point is well taken.  wink Stay safe out there!