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Seat mod help please

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Dominic Eller

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Hi all, I would like to put a new curved and lowered seat pan in place of the 1/4” ply flat plate.
I’m thinking either Ali or fiberglass and Kevlar.
Ideally I would like to save weight not add it of course.
As per the pics I will need to chop out the middle of the seat, leaving a small lip where the longerons, seat back and front support are.
I’m thinking of mounting a carbon tube I have as a second front support and use the existing front seat support too.
My concern is the rear mounting shear loads the new pan, be it composite or Ali will see.
What sort of fasteners and how many should I use to carry the shear loads the vertical rear part of the seat pan will see?
I hope the pics make my rambling a bit more clear 🙂
My crude sketch gives and idea of what I’m aiming for.
Thanks for taking the time to read this 👍63BFAEE8-D100-4E91-9888-9D686013E1FD.jpeg5E3E3F60-56DF-44DB-ABE4-3D494C37F30A.jpeg8FD9CC46-E687-485C-AAAC-F07943E45533.jpegCF741721-8811-4AF7-B25F-E06D4D488163.jpeg1CC4FFEB-BE7D-4412-A725-2E61CC4FE90F.jpeg
 

Riggerrob

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A simple fabric sling seat (ala. Chilton) will do the job.
If you want a fancier, fiberglass seat, may I suggest that you do like the Formula One car racers and fill a plastic bag with fresh foam, sit on it until it solidifies. Trim and wrap with fiberglass.
If you used the correct density of foam, leaving some foam in will help cushion your spine during a hard landing.
 

Dominic Eller

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Cheers for ideas, do you have some idea on the shear loads and what fasteners to use?
 

Riggerrob

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Design your seat for a 40G impact. Many years ago, the US Navy concluded that a properly-belted pilot could withstand a 40G impact without long term injury.
In a light plane, most of that decelleration is going to be straight ahead.
 

Rockiedog2

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This is a confortable seat and typically weighs 1.5-2#. 016 6061T6 strips 1"-1.25" wide, machine screws holding the wrap around in the bottom, pop rivets in the seat back wrap around. One hardware store pop rivet in each intersection. Use a thin seat cushion to avoid a bad case of waffle ass. Those plywood seats are awful.
 

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Dominic Eller

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Cheers all for input 👍

Rockiedog2, that’s some good info, thanks. I think I will go for a sheet instead of strips perhaps with lighting holes.
Because removing the original seat is not an option I will need to work out a method of mounting the rear of the seat through the existing 1/4 ply bulkhead.
As per my sketch I’m thinking some washer head bolts should do the trick, the question is how many and what size will be enough? I’m thinking around 6 x AN3 should do the job. The idea for the seat is to allow a more forward and deeper position for the butt to allow the foam padding and the wedge parachute to provide some slope and lumber support.
Would 6061 or 2024 be the preferred material? DDFDE1BB-C15F-4121-8843-DAF8A8AF714D.jpeg
 

Rockiedog2

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Don't think you said what type airplane?
That seat design came from Legal Eagle plans but mine is beefed up since it's in a higher performance heavier plane with potentially higher crash forces and G loads. The material is same as the LEU; 016 6061T6 but if you notice I have 28 #8 machine screws holding the wrap around the tubes. The LE uses one fastener per strap end and IIRC they're pop rivets. My simple stuff doesn't need 2024T3 I use T6 most everywhere. Your drawing looks to put the entire rear support load on 3 fasteners til they fail and then the several above those 3 take over. Not knowing any details, I would probably prefer to take the seat pan straight up rather than turn that corner. You have the fasteners going thru the pan twice on the upper support so more load bearing and the load will mostly be taken by the channel section going over the support rather than the fasteners. According to my Redneck Engineering. I defer to those more qualified who may speak up.

Edit: Seems like I may have used 020 for the bottom and 016 for the back.
 

Dominic Eller

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It’s a Jungster 1 bi plane, aerobatic so it needs to have a strong seat.
The structure under the seat means the little joggle has to be there. The 3 fastners on my top sketch was just a bit of over doodling, not really a good idea most likely. I agree that the channel section going through the seat back should take a fair amount of load.
 

Riggerrob

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"
Cheers all for input 👍

Rockiedog2, that’s some good info, thanks. I think I will go for a sheet instead of strips perhaps with lighting holes. ..."


Maybe you can copy Mr. Davis who built some simple sheet aluminum seats with lightening holes. No, he did not press flanges around the edges of lightening holes.
Which model of wedge type pilot emergency parachute are you planning to install?

Rob Warner, FAA Master Parachute Rigger
 

Riggerrob

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My pilot emergency parachute recommendation depends upon the finer points of matching your butt to any remaining free space in your cockpit. When you chose an emergency parachute, it may be your last chance to tailor the cockpit to fit your physique.

How tall are you?
Do you have long legs or a long torso/spine?
Are you slender enough to fit comfortably in a narrow Jungster 1 cockpit?

It has been a long time since I stared deep into a Jungman or Jungmeister cockpit, so my memory is rusty. Jungmann and Jungmeister cockpits are narrow, so narrow that they need Spitfire/Tiger Moth style flop-down side panels that allow the pilot to enter or exit. They are also so short - between instrument panel and seat back - that any parachute must be thin across the shoulders. Finally, the original German cockpits are quite tall, with infinite headroom. I think they were originally designed for military seat-packs.

I have never looked closely at a Jungster 1 homebuilt.

From your seat mod, I get the impression that your spine is a bit too tall for your Jungster 1 biplane. The other limitation is that control rod under the seat. You definitely want to give the control rod 2 or 3 inches of clearance. Those two factors may eliminate a seat-pack from your options. At best, you might be able to cram in a 2 inch thick seat pack.

With the original flat plywood seat, where are your eyes relative to the windshield? ... and how well can you see to taxi?

The next question is; how much free space remains under your knees when you are seated?
If you have some spare room between your thighs and the front of the seat, you may be able to wear a seat pack that is thin at the rear, but 3 inches thick at the front, like the specialized Softie seat container intended for Citabria.
When you sit in the cockpit how much spare travel do you feel in your rudder pedals?

Ideally, you can post a few photos of yourself sitting in the partially-completed Jungster 1 cockpit. Even better if you can take the photos before wrapping fabric around the outside.

How long and tall is that step where your seat back meets the new, flexible seat bottom?

Yes, the Softie line of pilot emergency parachutes will work well in most aerobatic airplanes.
Frankly, a parachute from any of the top half-dozen manufacturers (Butler, National, Para-Phernalia "Softie", Rigging Innovations or Strong). will save your butt, but it comes down to which container is the best fit for your airplane. The Softie factory recommends a seat type parachute for Jungman. A seat type parachute requires a much deeper seat pan (2 to 4 inches deeper). Aerobatic pilots usually opt for thin, hard seat cushions to prevent their sight picture from changing too much when transitioning from pulling positive Gs to pushing negative Gs.

Today I am mailing an article to KITPLANES Magazine entitled "Where can you stuff a parachute?"
 
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