plywood seat truss reinforcement

[akflyer 1427]

OK guys, I know this has been posted and talked about, but I can't find it.  What was the suggested thickness of ply for the seat truss beef up.  I want to say it was 1/4 or 3/8" but I could be all messed up.  This is for a bird that is already covered so he does not want to be doing any welding.

 

 

[dholly 718]

I used Baltic birch 1/4" x 90° marine 3-ply. Dunno if the new owner ever tested it though, ha!

[wypaul 448]

I also use 1/4 plywood that is used for underlayer when putting down a new floor,  it is 5 ply and available for free as scrap from flooring contractors.  I had the scraps on hand from my kitchen remodel.

[akflyer 1427]

Thanks guys.  I was pretty sure it was 1/4" that had been used.

 

[Turbo 162]

Just my gut feel recommendation, but I wouldn't go below 1/2" if you want any compression resistance.  Also, high-quality multi-layer plywood, perhaps with the face layers in the direction of the expected crushing force, and tightly fitted into the triangle.  Mine are held in place with both the bungees and some zip-ties.  No test data, though!  Does anyone have any crush test data on this subject?  If not, it's a matter of educated guesswork, with no real answer, other than the obvious "Not so thick that it rubs on and chews up the bungees.".

Edited 28 Sep 2019 by Turbo

[1avidflyer 1983]

I think Avid said to epoxy the plywood in place, so that makes even a sloppy fit work.  To lazy to see if this was already covered in this thread.... JImChuk

[FredStork 453]

Reinforcement of the seat truss is good, cutting the damn guillotine, sorry "safety", wire is better...

Been there, done that, broke that...

Replace it with an horizontal chock cord:

 

 

 

[109jb 181]

I like the horizontal shock cord idea.  I just got a Kitfox IV with the stock gear and the shock cords are good, but there is no safety cable or anything.  Can I ask the size of the cord you used and if you tested to see if it will hold a tip off of the ground?

[FredStork 453]

I like the horizontal shock cord idea.  I just got a Kitfox IV with the stock gear and the shock cords are good, but there is no safety cable or anything.  Can I ask the size of the cord you used and if you tested to see if it will hold a tip off of the ground?

The  »horizontal » chock cord will not, and is not intended to, replace a broken normal bungee. IT WILL NOT ALONE HOLD YOU OFF THE GROUND. But it will very efficiently add deflection resistance, almost noting at normal « soft » landing but exponentially the more deflection there is. I have never heard about broken bungees - but, according to a friend, hard landing do occur.... and I, I mean my friend, has not had a pro strike even at hard  landing that with the “safety wire “ would have broken the seat truss of my, I mean his, plane.

The stiffer chock cord the better.

Edited 29 Sep 2019 by FredStork

[1avidflyer 1983]

Fred,  sounds like we have the same kind of friends.   JmChuk