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Thread: Series-5 Seat Pan Cracking

  1. #21
    Senior Member jiott's Avatar
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    Default Re: Series-5 Seat Pan Cracking

    Don't forget to put supports under the seat; they may possibly be more effective than reinforcing the seat.
    077.jpg076.jpg
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  2. #22
    Senior Member jmodguy's Avatar
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    Default Re: Series-5 Seat Pan Cracking

    Ok hereís what I have picked up during my cowl redesign/layups.
    Epoxy and polyester resins are VERY different.
    The tensile strength of epoxy resins are much stronger than polyester and much less brittle.
    Gel coat is a polyester product and will not adhere to epoxy well and vice versa.
    Gelcoat weighs about 10lb/gal!
    Parts made with polyester resin are typically heavier due to the Gelcoat, added resin and matting added for strength.
    Epoxy resin is waterproof. Polyester not so much
    Epoxy will not shrink when curing. Polyester typically will, especially in larger quantities.
    carbon fiber requires special fasteners (titanium). Aerospace cf layups typically have barriers between the cf and what it is contact with.
    There are 3 basic types of fiberglass cloth.
    E glass - this is the every day cheap stuff
    S glass - this glass is stronger than E glass and costs a bit more
    S2 glass - this is an aerospace grade glass and has tensile strength close to cf but is not as stiff. This is nearly as expensive as cf. This is what I used for my cowl.
    carbon fiber is strong, but brittle.
    some cf fabrics are interwoven with Kevlar to mitigate the brittle properties of the cf. I do not know how well these fabrics wear. With epoxy they should wear very well.
    I will be making a seat pan using epoxy resin and either S2 glass, or the cf/Kevlar cloth I the near future. It will be less brittle, and stronger/lighter than the polyester seat pan. Iíll let everyone know what I learn!
    I am NOT an expert in composites. I have learned a bit about composites over the last year or so...
    So take this for about what you paid for it...!
    Jeff
    KF 5
    340KF

  3. #23

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    Default Re: Series-5 Seat Pan Cracking

    what a piece of kit is what I kept saying to myself as the weeks passed while trying to come up with something better than little blocks of wood placed over little horizontal tubes that were not intended to take vertical loading ..
    to get clearance for the control rods under the pilot, and more shoulder room at the same time, the seat pan has been cut in two and supported by two bands of 2inch velcro, fully lapped, and the pilot seat being raised higher is taken up on the top mounting of the seat pan, thereby creating some additional shoulder room ...
    forget about the little curved lip of the original seat pan, what kind of structural fastening can happen with that, sikaflex glue an aluminum strip and bolt onto some adel clamps ..
    it takes a bit of trial and error to set some tension / load bearing on the velcro, but IMHO far better than trying to bond some additional strength onto a gel coat polyester glass fractured piece of kit
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  4. #24

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    Default Re: Series-5 Seat Pan Cracking

    Quote Originally Posted by jmodguy View Post
    Ok hereís what I have picked up during my cowl redesign/layups.
    Epoxy and polyester resins are VERY different.
    The tensile strength of epoxy resins are much stronger than polyester and much less brittle.
    Gel coat is a polyester product and will not adhere to epoxy well and vice versa.
    Gelcoat weighs about 10lb/gal!
    Parts made with polyester resin are typically heavier due to the Gelcoat, added resin and matting added for strength.
    Epoxy resin is waterproof. Polyester not so much
    Epoxy will not shrink when curing. Polyester typically will, especially in larger quantities.
    carbon fiber requires special fasteners (titanium). Aerospace cf layups typically have barriers between the cf and what it is contact with.
    There are 3 basic types of fiberglass cloth.
    E glass - this is the every day cheap stuff
    S glass - this glass is stronger than E glass and costs a bit more
    S2 glass - this is an aerospace grade glass and has tensile strength close to cf but is not as stiff. This is nearly as expensive as cf. This is what I used for my cowl.
    carbon fiber is strong, but brittle.
    some cf fabrics are interwoven with Kevlar to mitigate the brittle properties of the cf. I do not know how well these fabrics wear. With epoxy they should wear very well.
    I will be making a seat pan using epoxy resin and either S2 glass, or the cf/Kevlar cloth I the near future. It will be less brittle, and stronger/lighter than the polyester seat pan. Iíll let everyone know what I learn!
    I am NOT an expert in composites. I have learned a bit about composites over the last year or so...
    So take this for about what you paid for it...!

    Good info. Only thing I'd add is that you do not have to use gelcoat with any of the fiberglass's nor CF. It's purely cosmetic.

    CF is not always the best thing for the job. It's greatest strength is it's stiffness when properly paired with the correct resin, but a lot of other materials are close with the same resin.

    Being parts crack, a material such as Kevlar might be a better choice as it's more resilient and therefore does not crack as easily. In boats we layer CF and Kevlar to gain stiffness and some flexibility without failure. Meaning a pure CF product will break whereas a combination will flex and not break at the same loads.

    Epoxy resins and chop fiber glass do not mix as the binder in the chop fiber is not compatible with epoxy.

    As you touched on, polyester resins and gelcoat will not cure (kick off) when applied over epoxy, therefore a boundary layer must be put down first. Can be as simple as a layer of primer.

    Finally, CF is no lighter than anything else out there. It's the biggest joke of a statement I read all the time. A 16 oz cloth of CF has the same weight as a 16 oz cloth of E Glass. I't just a matter of can you use less of one over the other and that's the key as sometimes the answer is no so the weight is the SAME.

    S2 is damn amazing just not as attractive as CF but is definitely a swapable choice.

  5. #25
    Senior Member jmodguy's Avatar
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    Default Re: Series-5 Seat Pan Cracking

    Hey Rik
    I agree with you on the gelcoat. I won't use it if the part is to be painted. I guesstimated the weight on an average kitfox cowl and came up with about 5 or 6 lbs. I could be way off...
    I used kevlar in some of my parts. I think it is best to get it in between the laminates. The kevlar I put on the edges of my boot cowl peeled off like peel ply.
    My boot cowl and upper cowl were a layup of 5 layers of 8.6 oz S2 glass. After the epoxy resin was cured they became very stiff! I made a test layup (8x12) of 3 layers and the results were amazing! My lower cowl has a lot of compound curves so I stopped at 3 layers and added a 4th to the frontal areas. I shaved about 6 lbs off the weight of a factory cowl.
    THanks for the other info. I was aware of some but it is good to get the info out.

    Cheers
    Jeff
    KF 5
    340KF

  6. #26

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    Default Re: Series-5 Seat Pan Cracking

    Without the Gelcoat you will have some pin holes that need to be filled. You can primer the mold prior to laying up the first layer and it will help with the pin holes.

    Structurally speaking, the only areas that are prone to cracking are the mounting and any area where there's a hole. You can beef just those area's up and leave a single or fewer layers everywhere else in order to save weight.

    With boats, we use a peel ply and then use bubble wrap to squeeze the resin under vacuum in order to get the resin out as it's the majority of the weight.

  7. #27

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    Default Re: Series-5 Seat Pan Cracking

    jmodguy, you wrote, "Gel coat is a polyester product and will not adhere to epoxy well and vice versa."

    My question is regarding the adherence of the epoxy to the polyester resin. The Gel Coat is on the top surface of the seat pan. On the bottom there is no Gel Coat so, will adding strips of Kevlar/Carbon Fiber weave added to the bottom of the seat pan with epoxy adhere or am I just spitting in the wind?

  8. #28
    Senior Member jrevens's Avatar
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    Default Re: Series-5 Seat Pan Cracking

    If any release agents, wax, etc. are removed and the surface is roughed up, epoxy will bond to it just fine.
    Polyester over epoxy, no.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE

  9. #29
    Senior Member jmodguy's Avatar
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    Default Re: Series-5 Seat Pan Cracking

    Quote Originally Posted by Maverick View Post
    jmodguy, you wrote, "Gel coat is a polyester product and will not adhere to epoxy well and vice versa."

    My question is regarding the adherence of the epoxy to the polyester resin. The Gel Coat is on the top surface of the seat pan. On the bottom there is no Gel Coat so, will adding strips of Kevlar/Carbon Fiber weave added to the bottom of the seat pan with epoxy adhere or am I just spitting in the wind?
    Like John said, if you rough it up well with 80 grit paper you should get an acceptable bond. I re-inforced the edges of my seat pan with cf and west system epoxy resin after it sagged and got stuck under the door frame 😤
    Jeff
    KF 5
    340KF

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