Building Tips and technical articles. > Building techniques
Fiberglass under or over profile ply doubler?
Ken Culbertson:
For an electric, I am starting to question the need to use plywood at all. I am building my "One Ship for Everything" plane right now and all I could get locally was 8lb balsa. By the time I was ready to add the 1/32 plywood doublers on the nose it was already so strong that I left them off. Balsa is incredibly strong for its weight. I use large fillets at the wing joint so I am about to finish my first plane with zero plywood. ~^
Ken
Dennis Toth:
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
john e. holliday:
As short as the fuselage is of the S-1 Ringmaster you should have no worries about side loads. Remember we used to fly these in combat years ago. Also when racing these we have not torn a nose off. Build it light and straight. As stated earlier a srip of hard wood running the length of the fuselage will stiffen it up considerably. If you are worried that some one will complain because you left off the ply wood, go with lite ply. Also put hard wood inserts where landing gear will be strapped to. D>K
Ken Culbertson:
--- Quote from: Dennis Toth on April 28, 2021, 08:43:44 AM ---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
--- End quote ---
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! LL~
Dennis Toth:
Ken,
You didn't mention if it is a profile or full fuse. I agree if full fuse with some hard 8 lb balsa should work. If profile, if it is a full 1/2" might be OK. My profile is 3/8" core with cross grain 1/16" overlay. It was very light but not stiff. I agree with what Kim wrote about adding the spruce strip would do the job but I am to far along to add that. I also agree that if you built the fuse strip and cover would be very strong and light but again I'm to far along.
Right now glass is on the fuse and it is still only 2 1/4 oz. It is now very stiff and should be a pretty good fuse for my use.
Best, DennisT
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