Thread: Build Log SU25K Frogfoot
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Old Sep 18, 2010, 01:18 PM
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you don't have to seal it, as long as the surface is smooth and you are using epoxy as the resin. the only thing you need to watch out for is resin soak. some of the resin will soak into the pores of the wood, so you'll want to wet it out enough to get a good bond and also, just enough to get a good surface. peel ply is the best way to do this, but not absolutely necessary. if you don't use peel ply, you can simply scrape the cured surface with a razor blade and this will help remove any pitting of the resin. it will also save you a lot of sanding time and also strain on your elbows. LOL. if I were you, I would do a few test pieces first, so you can see what the resin soak looks like and you can adjust accordingly. you just need a few scrap pieces of balsa, some cloth and resin. generally, I would wet it out with a brush and then scrape it till it barely puddles at the edges of the scraper. that's usually enough resin soak for bare balsa. if you've got too much, it'll lift the cloth from the surface, which you don't want :^)

as far as weight is concerned, 4lbs is a little bit on the porky side, but not a complete catastrophe in the making. as long as your wing loading is within spec, there is enough power at .75/.8-1 thrust to weight. this isn't a rocket ship afterall, so it doesn't have to be flown like one. remember that many planes of this type (full size), might only have a thrust to weight of .5-1, or roughly there abouts. I think you'll be ok and you'll know for sure on the maiden. LOL. weight is great for penetration, but presents some problems in the landing/takeoff envelopes. for this, you may need flaps if they were marginal, or not needed before. because it hasn't flown yet, you don't know these variables, so it would require some experimentation. I've always gone with flaps, if I've thought that the weight was a bit on the heavy side. yes, they add extra weight, but the lifting capabilities far outweight the weight that they add. especially when your plane is coming on final like a scalded cat without flap. LOL.
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