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Thread: Series-5 Seat Pan Cracking

  1. #1
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    Default Series-5 Seat Pan Cracking

    Just thought I'd post a comment about my seat pans, after my recent
    re-upholstery project. When I stripped the seat pan I found significant cracking
    along the front lip, and the lip at the top of the seat back. I have since
    significantly reinforced the seat, but it's something people should look at
    carefully at annual.

    I added about 6 layers of glass in the cracked areas, and .025 aluminum
    doublers which are riveted and bonded in place. I also upgraded to 3/8 wide
    cable ties.

    Just for what it's worth I weigh 170 and typically fly solo, so the seat is not
    overloaded. I do have under the pilot seat a safety tunnel to keep the seat
    off the controls as well if the seat should somehow bust loose.

    Here's a pic with the upholstery installed, and even with the very big cable
    ties in place they are hidden beneath the carpet which is velcro backed
    under the seat cushions.

    Jeff Hays
    Attached Images Attached Images

  2. #2
    Administrator DesertFox4's Avatar
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    Default Re: Series-5 Seat Pan Cracking

    Good info. Jeff. Thanks.


    DesertFox4
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    Building 7 Super Sport
    912 ULS Tri-gear

  3. #3
    Senior Member PapuaPilot's Avatar
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    Default Re: Series-5 Seat Pan Cracking

    Hey Jeff do you have any pictures of your repair. It might be prudent for me to beef mine up before I start flying mine.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5, Continental IO-240
    Flying

  4. #4
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    Default Re: Series-5 Seat Pan Cracking

    No pics, but if you can visualize a bit, here is what I did:

    where the seat lip goes over the lower front tube, and behind your back
    the upper tube, I scuff sanded, and cleaned the top and bottom of the
    pan with MEK and layed up about 6 layers of additional glass cloth. I used
    polyester Resin, as I think the seats are polysester resin based. In any case
    it sticks well.

    With the seat pan in the plane I marked with pencil where the frame tubes
    were located. I then removed the pan, and cutout 3" wide strips of .025
    aluminum (6061) the full width of the flat area of the pan (under your thighs,
    and behind your shoulders). I did an inside and outside piece for the four
    flat sections of the pan (8 pieces of aluminum). These were located right
    behind the pencil marks. I painted them with polyester resin, and thru
    riveted them in place sandwiching the seat pan between them. The rivets
    I used are 5/32 Avex every 40mm around the periphery of the aluminum.
    (I'm also a Zenith builder so I have a ton of these rivets on hand)

    Next through all this mess I figured out the best places for my cable ties to
    go and drilled holes all the way through. So the ties are going through the
    upper aluminum, seat pan, and lower aluminum and around the frame tube.

    So imagine under your thighs there is a strip of aluminum left to right directly
    behind the frame tube, both above and below the seat pan, through which there are six
    3/8 cable ties. Same behind your back, and copied on the CP
    side.

    This might be an enormous amount of overkill, but I do NOT want my seat
    to break loose.

    I will also say that I even notice that the seat feels firmer .... Something I
    previously thought was the foam in the seats.

    My seat install originally was exactly per Skystar's version of the instructions
    with no deviation, which like a lot of things I now think (after ten years
    flying it) was inadequate. Like I said I'm about 170, and have only ever had
    1-2 passengers over 200 so the seat has never had a heavy load. It just was
    not strong enough by design over the frame rails.

    Regards,
    Jeff

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

    Thanks, I can understand what you did. Sounds like a good idea, I weigh around 210 pounds.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5, Continental IO-240
    Flying

  6. #6
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    Default Re: Series-5 Seat Pan Cracking

    Thanks for the details and ideas Jeff. I think this issue has been mentioned a few times with some people installing timber supports under the seats to stop the seats falling onto the control rods under them in the event of cracking. I wonder if anyone knows if the design ( shape/strength etc) has been changed for the model 7 or is it the same as the 5???

    thanks again for the really practical post.
    cheers

    ross

  7. #7
    Administrator DesertFox4's Avatar
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    Default Re: Series-5 Seat Pan Cracking

    Ross- the seat has been changed since the model 5. One obvious example, the seat tool boxes have been incorporated into the seat. No cutting of the seat is needed. Just make a lid and hinge. This retains, in my mind anyway, lots of initial strength. Cable ties are no longer used to retain the seat although I'm not quite far enough along to tell you exactly what the final retaining system is but I know there are welded attach points now. Likely changed not because of weakness but knowing John, more to make building and service easier.
    I've seen many earlier models with too much fiberglass material removed from the top and bottom seat lips by builders. It makes you wonder how the seat stays on the tubing even during a normal landing or minor turbulence.
    Zip ties lose their strength over time so relying completely on those keeping the seat off the controls with 2 big guys in the seat seems optimistic to me, although at least once a year those ties should be replaced with new if following the conditional inspection check list.

    I've seen many creative ways to prevent seats from slipping off the support tubing to prevent control binding. Early model owners should be using at least one of those methods to prevent this problem.


    DesertFox4
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  8. #8
    Senior Member Dave S's Avatar
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    Default Re: Series-5 Seat Pan Cracking

    DF 4 is totally up on the current configuration - but then I guess he has one of the new kits!.

    I had one of the early S-7 kits prior to John's ownership of the company and I can confirm that the new seat strucure which I have seen on newer kitfoxes is great.

    Although I had the old seats with our kit, I did get the aftermarket under seat buckets from John to make the storage and provide support to the seat (and keep my tochous off the control rods if the seat didn't hold). There were some weak spots on the original seat and I also did some minor fiberglass work to fix that.

    Although our kit did not have the welded attach points that the new kits have (great improvement), I never liked the zip tie thing and got some clamps so the seat is clamped firmly in place....a little putzy to work with the nuts/washers on back to take the seat out, but I like that better than the zip ties. To keep the cushion thickness at a minimum I used plain clamps with a strip of hockey stick tape around the steel tubes to prevent contact between the clamp and steel tube.

    I am not that heavy either but I understand I might stress the seat a bit more in a steep bank

    Sincerely,

    Dave S
    KF7 Trigear - Flying
    912ULS Warp Drive
    St Paul MN

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

    I made some clamps out of stainless steel, then secured them to the tubing with Hysol. I also secured them in the "clamped" position with a couple of flush s.s. pop rivets. I then installed 10-32 steel nutserts (TricNuts) in lieu of nutplates. On the seat, I epoxied AN970 large area washers at the 8 locations where the clamps & screws will secure the seat.
    Attached Images Attached Images
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE

  10. #10
    Dave Holl's Avatar
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    Default Re: Series-5 Seat Pan Cracking

    I have reinforced my seat with a couple of layers of carbon. I also have fitted the underseat stages but only the p2 has the lid the pilot one helps keep the seat stiff. I have also fitted carbon and fibrelam bum blocks to protect the control push rods.
    Dave Holl
    Building Kitfox MK7
    Rotax 912ULS

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