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

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

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 😊

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

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

Ken,
My concerns with not having the plywood are for the side loads imposed by the prop gyroscopic forces. Granted in electric we use very light props but some use CF props that are very stiff but close in weight to a wood prop. On hard corners the side force could be considerable so for me I still use thin 1/32" ply doublers. I have been tempted to go to 1/64" but since I can afford the weight I haven't had the guts to try it.

Best,    DennisT

Ken,
My concerns with not having the plywood are for the side loads imposed by the prop gyroscopic forces. Granted in electric we use very light props but some use CF props that are very stiff but close in weight to a wood prop. On hard corners the side force could be considerable so for me I still use thin 1/32" ply doublers. I have been tempted to go to 1/64" but since I can afford the weight I haven't had the guts to try it.

Best,    DennisT

I share your concern but I think that the thickness of the balsa structure and the large fillets should hold.  Won't know till I try it and if you are right I will paint a huge "I TOLD YOU SO" on the nose!

 Seems a bit risky on a 10" nose with a 3515 or 3520 motor and a 12" prop.  There's a lot of torque being applied from the motor/battery weight in the G-force of a hard square, triangle, hourglass, ect, and a lot of force from the motor's torque as it increases power to maintain the governor rpm.  1/64 or 1/32 ply doublers seems like good strength insurance and a good way to keep certain harmonics and other potential ills from developing.

Completely agree with SK's answer.

D

If you are needing some extra adhesion for the film on your fuselage and fillets, here is a good option. 

Deluxe Materials from the UK makes a water soluble, heat activated covering adhesive called Cover Grip.  A no-stink version of Sig Stix-It or Coverite Balsarite.  Cover Grip is readily available online in the USA.  Deluxe Materials has a lot of effective water based products.

https://deluxematerials.co.uk/products/cover-grip

Ken,
Is your ship going to be electric? That gives you lots of options for finish, acrylic water based paint (check YouTube for model car or aircraft finishing), even the MonoKote trim sheets can be used.

For my project which is a rebuild of an S1 Ringmaster electrified, I chose the very light 3/8" balsa core (what I had in the shop), cross grain 1/16" skins with light weight Deluxe Material fiberglass (only stuff the local shop had). I adhered the cross gain and the fiberglass with 20 min Finishing Resin scraped thin. I put it on under the 1/32" ply nose reinforcement to give smooth continuous cover. It worked very well and the fuse is very stiff in torsion and bending and only 3 oz. (original S1 Sterling kit fuse was 8 oz.). I will finish with some Zinc steroid (Randy Smith Aero lite) and dope then dope color and clear. Should be less then 4.5 oz. big weight savings over the original.

Best,    DennisT