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  • Re: gel coat

    From David Carus@21:1/5 to [email protected] on Tue Feb 7 09:24:05 2023
    On Sunday, October 20, 2019 at 1:09:37 AM UTC+1, [email protected] wrote:
    On Friday, September 27, 2019 at 4:16:17 PM UTC-7, Papa3 wrote:
    On Thursday, September 26, 2019 at 8:40:34 PM UTC-4, Charles Longley wrote:
    How many wing failures have composite gliders had over the years?

    A fair number, but I can't think of any that were due to normal flight. For example, at least 1 or 2 Slingsby Vegas came apart, but I believe both of those were due to exceeding design limits. Same for a Zuni. A fair number of others came apart due
    to flutter.

    P3
    P3 - I was the owner of one of the Vegas that crashed (N4312B, in 1987 in Hemet) - the root cause was elevator flutter resulting in failure of the elevator linkage. No overspeed, no structural failure, just flutter followed by loss of pitch control
    causing the pilot to bail out (unfortunately at low altitude, with serious injuries).

    Cheers,

    Barry

    Barry
    Could we correspond privately about the Vega bailout? My email is [email protected]
    Thanks
    David

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  • From Turkey Vulture@21:1/5 to All on Wed Feb 8 04:29:38 2023
    I believe Sara Arnold won a club class race in a badly crazed/cracking ASW-15 if anyone wonders where they should spend their money between refinish and tows.
    Years ago I owned a badly crazed glider. You could pull pieces of the gelcoat off with your fingers. It was literally flaking even along the leading edge. It flew beautifully and seemed to achieve book numbers with regards to L/D.
    My A&P finally said he would no longer sign it off so I had to sell it. I contacted just about everyone I could regarding the safety of the glider. I couldn't find any refinisher that had seen a wing failure or structural issue because of gel coat
    crazing. $25k-35k for the full refinish in Poly.
    If your A&P is OK with it, I think its safe to say crazing/cracking gelcoat is 95% cosmetic and 5% performance 0% safety.

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  • From Hank Nixon@21:1/5 to Turkey Vulture on Wed Feb 8 07:36:52 2023
    On Wednesday, February 8, 2023 at 7:29:41 AM UTC-5, Turkey Vulture wrote:
    I believe Sara Arnold won a club class race in a badly crazed/cracking ASW-15 if anyone wonders where they should spend their money between refinish and tows.
    Years ago I owned a badly crazed glider. You could pull pieces of the gelcoat off with your fingers. It was literally flaking even along the leading edge. It flew beautifully and seemed to achieve book numbers with regards to L/D.
    My A&P finally said he would no longer sign it off so I had to sell it. I contacted just about everyone I could regarding the safety of the glider. I couldn't find any refinisher that had seen a wing failure or structural issue because of gel coat
    crazing. $25k-35k for the full refinish in Poly.
    If your A&P is OK with it, I think its safe to say crazing/cracking gelcoat is 95% cosmetic and 5% performance 0% safety.

    Turkey,
    Your example is not a great one. Sarah could win flying a barn door.
    Your message seems mostly about denial.
    My experience is that most A&P's don't have enough knowledge to make a really good judgement.
    They all need a refinish sooner or later. Wait too long and it is worse. I have seen ships with control surfaces that in my experience were too far gone to be saved.
    UH

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  • From mark grubb@21:1/5 to All on Wed Feb 8 23:45:35 2023
    Some relevant observation across 30 years of working working with and observing glider composites:

    My AS-W12 had crazing that extended through the resin of the first glass layer but the glass fibers were generally intact. The storage conditions prior to me buying it were horrendous: A very leaky metal trailer in VT. There was a 2 inch oak seedling
    growing on top of the wooden tail "dog house" of the trailer.

    I have observed several gliders tied out for years in the desert SW USA that have shown signs of the resin being "baked" (vaporized?) out of the fiberglass matrix. The fibers were still intact but the areas in between and above the fibers were voids
    where there should have been resin. I know of a piece of a wrecked wing that is almost completely devoid of resin. The structure has been exposed to the the SW USA elements for 25+ years, however.

    Prestec had a USA milspec number and its current iteration, SImtec is probably the best polyester coating available today. I used both as topcoats for the canopy refit, tailwheel fairing modification, and minor repairs on my AS-W20c in 1989. It has
    aged beautifully; still bright white, shiny, and exhibits zero crazing. It is noticeably whiter compared to the adjacent factory gelcoat which is yellowed and lightly crazed along the seam.

    AS UH said, gelcoat noticeably stiffens structure. I saw a customer pick up a stripped AS-W20a flap in the middle, way too quickly and roughly. The g's and single support point caused it to crack structure.

    I also have seen control surfaces that were destroyed due to lack of care and exposure to the elements.

    I believe Richard's process and materials are essntiaLLY what I would do today, especially the vinyl ester primer and PU topcoat.

    Nice discussion. I appreciate the education.

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