What's holding this thing together, anyway? Part II   When I was building my aircraft, I was always wondering if the work I was doing was strong enough.  Several years later I was searching for a suitable thesis topic and thought perhaps I could answer the question "Is this part I'm making safe"?    I decided to take a bunch of fledgling A&P students at Southern Illinois University's Aviation Technology program and see what kind of work they could turn out.  None of them had any previous composite experience.  I basically locked them in a room with The Quickie Aircraft Company basic composite instructions, composite materials, and a balance.

AN ABSTRACT OF THE THESIS OF

Samuel R. Hoskins, for the Master of Science in Manufacturing Systems, presented on April 6, 1995 at Southern Illinois University at Carbondale.

Title:    Characterization of Bi-directional Composite Fiberglass Construction Fabricated by Untrained Personnel - An Application to Amateur Constructed Aircraft.

    This work examines the variations in composite fabrication that may be expected when a random sample of people make a part.  The properties evaluated are overall quality, weight, fiber orientation, and tensile strength.

    A group of subjects were directed to a work station and given instructions to perform a face lay-up similar to techniques used in constructing amateur built aircraft.  The task was completed in two sessions; the first to fabricate a three ply lay-up on a foam core with bi-directional fabric orientated 45 degrees, and the second to splice (join) two pieces together.

    The resulting work piece was analyzed for variations from sample to sample.  Of the 23 samples produced in the experiment, 10 (43.4% of all) were considered to nominally meet the design criteria.

    The range of the best rated sample's average weight was plus 12.33% to minus 8.22% of the mean.

    The population range of the best rated samples for proper fiber orientation was between 29 degrees to 44 degrees, with a mean of 37.7 degrees, using a 45 degree design specification.

The whole thing is about 180 pages long and if you really want to see it, a copy is on the shelf at SIU Morris Library and I gave one to the Boeing Library at EAA headquarters.  Oh, and my mom has a copy.

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Summary and conclusions In non-academic terms;  I had a bunch of pure rookies do a one sided layup. After cure, I cut the layup in half and had them do a two BID splice. I then cut the samples into two inch wide coupons and pull tested them on some excellent equipment in the engineering lab at Southern Illinois University.

The resuts showed that if you do even halfway decent work, the part will be strong. I confirmed that extra weight from additional epoxy does not add strength.