Building Tips and technical articles. > Building techniques
Fiberglass under or over profile ply doubler?
Brent Williams:
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.
Serge_Krauss:
FWIW: I disagree that fiberglass is too heavy. .56-oz glass is thinner and takes less matrix that some other coatings, and my tests show that with fiberglass attached with the right amount of epoxy or dope, it can weigh less than silkspanned surfaces. I've posted this before, with data and photos. I know it's too late, but the fuselage would be less flexible with laminated balsa grain applied longitudinally (fore <-> aft) and really stiff torsionally with glass applied over it biased at 45 degrees. Dope application is easy and less messy, but sheets of glass or silkspan can float, while applying glass to squeegeed epoxy will not do so, and the glass/epoxy is noticeably stiffer. You can use 1/16" plywood butt-jointed to 1/16" balsa with a slanted seam and not have an appreciable stress-riser. - SK
Dave Hull:
Completely agree with SK's answer.
D
Ken Culbertson:
--- Quote from: Brent Williams on April 29, 2021, 09:52:50 AM --- 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.
--- End quote ---
You are making a convincing argument. The stress I am not addressing adequately is the twisting that may/will occur which will eventually crack the wing/fuselage joint. It is stressed internally with CF rods but....
For reasons that probably won't make much sense to most I am not able to use anything that produces strong lasting odors in building this ship. That rules out dope and even rattle-can. I even avoid prolonged CA applications. Everything is going to be MonoKoted. I have done this before so I know how to do the fuselage (not fun) and joints. Problem occurs when you use a surface that MonoKote doesn't like much so I try and keep everything it touches Balsa. Plywood, even Bass, doesn't adhere well. It also doesn't do well over epoxy. The fiberglass option may be the way to go but I will probably have to skin it with some 1/32 balsa or find something to stick it on that doesn't smell - any ideas?
Ken
Brent Williams:
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
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