1/8" aircraft ply adequate?

[David_Stack]

Good Evening all;

Looking to install a chute shelf/shock cord mounting point in my Pro Series II Nike Smoke. I've cut bulkheads from 1/8" aircraft ply (not lite ply) to fit inside the body tube about 10" down. Attached photo is what I am envisioning.



The green cardboard ring (~30mm diameter) represents the hole I would cut to allow the ejection charge to pressurize the tube and expel the nose cone/laundry, the small red dot is where I would drill a hole to pass the 1/8" tubular kevlar shock cord through from the top, with a loop/overhand knot on the backside (the knot would be large enough to not pull back through the hole when the shock cord is pulled taut).

This would allow me to fish the kevlar out should it ever be necessary, without the weight of an eyebolt.

Is the 1/8" ply strong enough in this configuration, should I sandwich two layers for a 1/4" thick platform, or do I need to find a 'middle ground' by using the single layer but adding a layer of fiberglass to one or both sides?

Thanks,
Dave

 

[JimByrne]

If it was mine, I would go for 1/4" plywood (that is a lot of shock load for 1/8")

 

[rharshberger]

Good Evening all;

Looking to install a chute shelf/shock cord mounting point in my Pro Series II Nike Smoke. I've cut bulkheads from 1/8" aircraft ply (not lite ply) to fit inside the body tube about 10" down. Attached photo is what I am envisioning.

View attachment 466192

The green cardboard ring (~30mm diameter) represents the hole I would cut to allow the ejection charge to pressurize the tube and expel the nose cone/laundry, the small red dot is where I would drill a hole to pass the 1/8" tubular kevlar shock cord through from the top, with a loop/overhand knot on the backside (the knot would be large enough to not pull back through the hole when the shock cord is pulled taut).

This would allow me to fish the kevlar out should it ever be necessary, without the weight of an eyebolt.

Is the 1/8" ply strong enough in this configuration, should I sandwich two layers for a 1/4" thick platform, or do I need to find a 'middle ground' by using the single layer but adding a layer of fiberglass to one or both sides?

Thanks,
Dave

Just use a large washer on the back for the eyebolt and a ring of body tube or coupler material above and below (mainly in the diection the strain from the eyebolt will come from) to reinforce the edges of the chute shelf. 1/8" ply should be sufficient if used that manner.

 

[David Schwantz]

You could also cut another ply disk the size of a fender washer and epoxy to the 1/8" bulkhead. I also would not use a knot to secure shock cord. If anything, put a washer on the cord to help it from pulling through. Another thought might be tie the cord around a dowel and put a dab of epoxy on the knot. this will keep it from pulling through and you could still fish it out.

 

[dr wogz]

the closer the hole (for the chock cord) is to the side, the stronger it'll be.

I would, add either a large washer to the underside. Or in case you want to just add a knot to stop it, I would add another piece of 1/8" to the area just around the intended anchor point to help spread the load. (I don't feel you need to do the entire disk!) just an inch around the intended hole..

 

[jqavins]

I agree with doubling up for an inch (radius) around the hole. I would also reinforce the edge of the hole with a schmeer of epoxy to avoid chipping. It should be like a formed in place grommet. (Laminate, then drill, then epoxy.)

And yes, I'm talking out of my hat.