Building Tips and technical articles. > Building techniques

Fiberglass under or over profile ply doubler?

(1/4) > >>

Dennis Toth:
I am just getting a new very light profile fuse for my electric Ringmaster together to replace the one that the nose broke off in a weird crash. The new fuse is very light and setup for electric from the get-go (the whole fuse weight less the just the old back half). I have a core of 3/8" balsa with 1/16" cross grain sides. This made it very stiff torsional but it's a little soft in bending. I plan on putting light weight fiberglass on with nitrate to stick it down then one scrapped coat of finishing epoxy, then dope finish.

I am at the point of adding the fiberglass or adding the 1/32" nose plywood doubler. Question is do I apply the fiberglass to the balsa fuse first or install the doubler than fiberglass over it and the rest of fuse? I'm going between solid bending strength with no bend that goes under the plywood or doesn't it matter if it goes over the small ply bump? What's your thoughts or experience?

Best,    DennisT

Dave Hull:
Glass on the outside.

Kim Doherty:

--- Quote from: Dennis Toth on April 23, 2021, 03:48:58 PM ---I am just getting a new very light profile fuse for my electric Ringmaster together to replace the one that the nose broke off in a weird crash. The new fuse is very light and setup for electric from the get-go (the whole fuse weight less the just the old back half). I have a core of 3/8" balsa with 1/16" cross grain sides. This made it very stiff torsional but it's a little soft in bending. I plan on putting light weight fiberglass on with nitrate to stick it down then one scrapped coat of finishing epoxy, then dope finish.

I am at the point of adding the fiberglass or adding the 1/32" nose plywood doubler. Question is do I apply the fiberglass to the balsa fuse first or install the doubler than fiberglass over it and the rest of fuse? I'm going between solid bending strength with no bend that goes under the plywood or doesn't it matter if it goes over the small ply bump? What's your thoughts or experience?
Best,    DennisT

--- End quote ---


Dennis
There is no such thing as “light weight fibreglass”
Carefully place the fibreglass in a drawer along with the epoxy and shut it.
You said the fuse is torsionally stiff - that is all you need. I am guessing that you placed the fuse gently on your knee and lightly pressed both ends. Some minor bending occurred.
Do not bend the fuselage over your knee while the model is in flight.
Put the 1/32 back in the wood rack and select a piece of 1/64 ply to be your fuselage stiffener. This is all you need.

Kim 😊

Dennis Toth:
Kim,
I agree with the 1/64 ply but this is only an S1 Ringmaster for some OTS practice and fun. The original kit fuse for the conversion was 8+ oz., my replacement is only 2 oz. built for the electric straight out. Right now it is very stiff in twisting but can bend easily so adding the glass will at best add 1 oz. using the epoxy scrap method then finish with dope. If it were a serious profile stunter I would have gone with a stick/frame/1/64" ply build. I have one of Tom Morris's profile fuses and it is light and stiff with the 1/64" ply sides.

Best,    DennisT

Kim Doherty:

--- Quote from: Dennis Toth on April 26, 2021, 11:52:58 AM ---Kim,
I agree with the 1/64 ply but this is only an S1 Ringmaster for some OTS practice and fun. The original kit fuse for the conversion was 8+ oz., my replacement is only 2 oz. built for the electric straight out. Right now it is very stiff in twisting but can bend easily so adding the glass will at best add 1 oz. using the epoxy scrap method then finish with dope. If it were a serious profile stunter I would have gone with a stick/frame/1/64" ply build. I have one of Tom Morris's profile fuses and it is light and stiff with the 1/64" ply sides.

Best,    DennisT

--- End quote ---

Dennis,
If you want the fuselage to be stiff then run an 1/8” spruce strip through the middle of the fuselage end to end.
If you try to adhere the glass with nitrate dope then you have destroyed the bond that would have been made between the wood the glass and the epoxy. This would have you bonding epoxy to nitrate dope. The glass is adding next to nothing. IMHO you are just adding weight for no purpose with the glass. Pretty much ANY model can be trimmed out to perform at a fairly high level. Certainly a Ringmaster can. Why waste all that time by purposely making something too heavy.  You said the first fuselage weighed about eight ounces. For comparison, my 730 sq/in Shockwave fuselage full built up complete with take-a-parts weighed about 6.5 ounces. ~ 40” long.
Heck, silk span and dope add IMMENSE strength.

Kim

Navigation

[0] Message Index

[#] Next page