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Oil Door Stiffening?

avrojockey

Well Known Member
Patron
Builder had good intent with his clean design but the oil door wasn't good so I installed a hidden hinge and camloc. However the door flexes enough that around 140 KIAS the door pops open because the lock interference is lost.

I'm looking at stiffening the door with foam sandwich, but ACS is out of stock of foam cores and minimum size is 2' x 4'...I don't need that much.

Any thoughts on different stiffening technique or alternative material to foam? I was thinking about using end grain balsa as it has superior strength and rigidity to foam.
 
I used...

I used SORIC. It is about 1/8" thick and when properly wet, forms hexagons.

I put one layer on the door and covered it with one layer of cloth.

Planning to use it on the inside of my wingtips, as well...
 
Since the oil door is small, you can do a thin float coat of epoxy and microballoons of about 1/8 to 1/4 thick and lay another ply of fiberglass over it. It should create a stiffer door and more heat resistant than foam.
 
Since the oil door is small, you can do a thin float coat of epoxy and microballoons of about 1/8 to 1/4 thick and lay another ply of fiberglass over it. It should create a stiffer door and more heat resistant than foam.

I'm guessing flox be stiffer/stronger? Should I use it? I have both...and silica. Of course, if using flox I might as well just layer up glass...the balloons would be lighter
 
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I used short pieces of very thin angle aluminum--maybe left overs from elevator or rudder stiffeners--that I riveted onto the fiberglass door. Also, make sure you have enough of a lip on the opening to catch the latches firmly.
 
I'm guessing flox be stiffer/stronger? Should I use it? I have both...and silica. Of course, if using flox I might as well just layer up glass...the balloons would be lighter

The required sheer strength isn't that great but the weight penalty using cotton flox is small for the size of the oil door. one thing, microbaloons is easier to sand and smooth than cotton flox.
 
Vans has foam core for just this purpose. It is sized just large enough for the oil door and works great. Look it up on their store.
 
I'm guessing flox be stiffer/stronger? Should I use it? I have both...and silica. Of course, if using flox I might as well just layer up glass...the balloons would be lighter

The foam is there only to create a gap. The rigidity comes from the box structure. Think of how much stronger a 1X1X1/16" square tube is, relative to bending forces, than a 1x1/8" piece of flat stock. It is not the doubling of the thickness, but the tubular structure.

Larry
 
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Builder had good intent with his clean design but the oil door wasn't good so I installed a hidden hinge and camloc. However the door flexes enough that around 140 KIAS the door pops open because the lock interference is lost.

I'm looking at stiffening the door with foam sandwich, but ACS is out of stock of foam cores and minimum size is 2' x 4'...I don't need that much.

Any thoughts on different stiffening technique or alternative material to foam? I was thinking about using end grain balsa as it has superior strength and rigidity to foam.

Click on my VAF name and send me an email with your address. I will send a strip of Soric. It is not that wide, but strength is not reduced with a seam anyway - I have tested that. It will be plenty for the oil door.
 
A simple solution is to epoxy a couple of pieces of cotton rope to the inside of the door, then lay cloth over those strips. You've basically created hat sections to stiffen the structure so it doesn't deflect so easily.
 
The foam is there only to create a gap. The rigidity comes from the box structure. Think of how much stronger a 1X1X1/16" square tube is, relative to bending forces, than a 1x1/8" piece of flat stock. It is not the doubling of the thickness, but the tubular structure.

Larry

You might think that, but I made 2 "beams" with 3mm Soric sandwich with where the single layer of reinforcement on each side met on the ends, and cut off the edge exposing the core around the perimeter. Both pieces failed at nearly identical loads.

Conclusion - the Soric core (specifically) is well attached to the reinforcement and does a good job of carrying the shear load independently of a closed edge.

The area moment (I) of the material is greatly increases with the core, similar to and I beam, but the core must carry shear loads between the reinforcement or it will bend like a ream of paper as each sheet shears against the others. In your example the sides of a square tube or center web of the I beam contribute to the stiffness primarily through shear loads. Not precisely, but handwaving.

Basic solid mechanics.
 
Thanks for all the ideas lads! I'm going to try the Soric strips Bill is sending. I love this community!

I really liked the idea of corrugations with straws or cotton rope...gave me the idea of laying up a part with couple ply and modeling clay then epoxying it to door...this would be the least weight solution.
 
Straw rope

Thanks for all the ideas lads! I'm going to try the Soric strips Bill is sending. I love this community!

I really liked the idea of corrugations with straws or cotton rope...gave me the idea of laying up a part with couple ply and modeling clay then epoxying it to door...this would be the least weight solution.

Straw idea is pretty neat. Since it may not stick, I would pack the straw inside with floxed epoxy then tape the stray in place to cure. Remove and cut away the plastic straw and you have stiffener rods that will bond. I haven't tried it so no idea if it will work. I did stiffen my wing tips with dowels. It worked well.
 
Conclusion - the Soric core (specifically) is well attached to the reinforcement and does a good job of carrying the shear load independently of a closed edge.

Agree. It seems to form a hexagonal epoxy honeycomb when infused. Finished product is heavier than paper honeycomb by a lot, but that doesn't matter much for an oil door. Definitely a lot more crush resistant.
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For the soric can you do a wet layup or should I vacuum bag it? I you thing I need to bag it...what common materials could use for the process instead of purchasing peel ply and breather fabric

EDIT: I just searched and found you can use polyester fabric and paper towels for bagging.
 
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Since Bill is sending me soric, I decided to redo the door because I didn't like the fit of the original.

  1. Used the original door as a mold (I guess the pros call them "tools") with some wax paper
  2. Three layers of glass
  3. Micro exterior to smooth
  4. Thought 3 layers was the original thickness but need to add 2 more to interior after I trimed the door to fit
  5. Sanded micro smooth...much nicer fit now
  6. Awaiting Bill's soric
 

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Nice work Tim. I am about to do the same. The hinge is worn out and the door is slightly misaligned. Good motivation thanks!
 
Aluminum

Only one entry for an aluminum door?
There are no compound curves in the oil door and bending a shape to conform is very simple and just what I did on my 10. I kept the fiberglass oil door and riveted an aluminum back plate to it, leaving the flange fiberglass only. There is no flex in my oil door and the "flat" and solid structure of aluminum gave me an ideal attachment for a hidden hinge as opposed to a hollow honey comb or flox cage.Latch attachment is also much less complicated with a flat door vs a honeycomb structure.
I used .063 AS.
 
End grain balsa will work OK. If it doesn't conform to the curve, cut parallel slots part way through it on the concave surface.
 
Some left over parabeam works well too. I covered mine with a layer of carbon fibre cloth after shaping it. It looks and works great.
 
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Only one entry for an aluminum door?
There are no compound curves in the oil door and bending a shape to conform is very simple and just what I did on my 10. I kept the fiberglass oil door and riveted an aluminum back plate to it, leaving the flange fiberglass only. There is no flex in my oil door and the "flat" and solid structure of aluminum gave me an ideal attachment for a hidden hinge as opposed to a hollow honey comb or flox cage.Latch attachment is also much less complicated with a flat door vs a honeycomb structure.
I used .063 AS.

My James Cowl required a compound curve, and few minutes with an english wheel (.063 2024) did the trick, but it would have been better that the cowl & wheel were in the same place for fitting.:eek:

Tim, you do not need to vacuum bag it, I made some hand layup samples for test (strength) to be sure.

These photos are infused, but show the relative stiffness improvement with the 3mm Soric. The non core was touching the table.
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Parabeam

James Aircraft sells small pieces of parabeam. We buy it by the roll and we love it. It makes the cowlings stiff with less weight than the soric. We use both in our products.
 
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