Re: carbon


Mike Perry
 

Bob:

Someone is crazy here. I don't think it's Lynn French. Your recent posts contains some interesting insights mixed with some half truths and some gross errors. Let's start with your comments about Burt Rutan.

1) The Q2 is NOT a Rutan design and he objects vigorously to being associated with it. You seem to mix comments on the Q1 with the Q2 without realizing that.
2) The wing spar takes the main load but what prevents torsion (twisting)? Some part of the structure has to prevent twisting, what is it? I do not know the context of Burt's remarks about the skins not carrying the loads but I do not think the foam alone is enough to resist twisting in any Q wing. BTW, just what is the "spar" in the Q wing? 3) "[Burt's] spars were designed with ultimate loads double the service loads as opposed to 1.5X in a metal structure." That is an FAA standard for composite structures and a generally accepted criteria in engineering work with composites. This is based on the failure mode of composites and on variability in materials and construction. There are whole books written on this, I'm not reproducing them here.
4) "[Burt's] design process was always minimal while his testing was rigorous." Great. Just who tested the Q-2 wing? Or the Q-1 wing for that matter? If QAC tested them there is no record I know of.

This seems to be the right point to inject that I tested a Q2 wing. The results will be in the next Q-talk. There were several problems with the test, so I don't think we can say much about the safety of the Q2 wing; however, the wing broke at 7.5 Gs (design limit 12 Gs) with a failure that appeared torsional. It started just outside of an area that was repaired and reinforced for testing purposes -- it certainly seemed like a minor change that would make the overall wing stronger, but instead the wing broke early. That experience makes me very skeptical of people who say these wings are over-designed, or who say the skins aren't important for torsion resistance, or who substitute materials without engineering and testing.

Returning to your posts, you wrote, "The only real structural change was adding carbon spars to the canard and that was in an attempt to keep bad pilots from breaking their planes during Pilot-Induced-Oscillation (PIO) on landing." Really? I'm glad to hear it wasn't needed to increase the gross weight of the airplane or to change to a thinner airfoil that was less susceptible to surface contamination, esp. rain.

You also wrote, "So on wings of this type (where the spars carry the majority of loads) a single layer of cloth on the 45-degree bias offers enough strength to carry any torsion loads and keep the insides of the wing on the inside." Which cloth? Surely not UNI. Has a single layer of BID been tested in this application? Based on the wing test I did I would strongly disagree with this advice.

You also wrote, "What is the history of structural failures on Quickies? Zero." If you mean only the single seat Quickie I am not aware of any structural failures, but there have been main wing failures in the Q2. Two Q-2 wings failed due to non-standard construction (building a core from smaller blocks) or a non standard repair (using expanding foam). This makes me suspicious when people propose "minor" changes or substitutions because the airplane is "so over-built that you can make lots of changes with relative impunity."

You also wrote, "I'm not cutting any foam for my Q. I'm making female molds for all the parts and will vacuum bag and cure them at 250 degrees in my home-made oven. I expect to finish the plane by September." Great. Please stop calling this airplane a Q, Q1 or Quickie. You are talking about a totally redesigned airplane.

THIS DISCUSSION BELONGS ON Q-PERFORMANCE. You are talking about an entirely new design. This is not about building testing and flying a standard Quickie or Q2xx.

I am not an engineer. From what I read neither are you. For your safety I recommend you get one involved, or do a lot of testing, or both.
Mike Perry

bob@... wrote:


I don't know how to put this politely, but are you CRAZY?

I fly 300+ hours per year entirely in experimental aircraft. Next year I will go to California (I live in South Carolina) 18 times -- all at 16-18K. So I have quite a bit of experience doing just the sort of flying you describe. In my youth (I am 56) I went as high as 22K without oxygen -- ONCE. Today I use O2 fulltime at night (no matter what altitude) and above 8000 during the day. What you propose to do is insane.

Bob


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