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Building Tips and technical articles. => Building techniques => Topic started by: Greg L Bahrman on October 07, 2010, 09:31:18 PM
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I fiberglassed my flaps per Al Rabe. I thought they flexed to much etc. Boy what a difference it made. I used Z-Poxy finishing resin and 1/2 oz. glass cloth. This was the first time I have done it. I like it and will do it again whenever I have a weak flap.
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D'ya know how much weight you added?
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Well, that's the issues, isn't it. How much weight. I suspect it can be done without adding a ridiculous amount of weight, but I like Howard Rush's approach better. Carbon tube just doesn't flex much.
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Good question Timmy........I really don't know. I should of weighed them before and after. I pulled them both off as they were not glued in place yet and the 2 of them together weigh a whopping 1 5/8 oz. Wingspan is 51 inches and will be powered by a Aero Tiger 36 so I didn't want any unnecessary flex. They are glassed on both sides and sanded to the point where they are smooth and ready for prime and paint. Flaps, before I started were 1/4 in. thick at the pivot and are sanded to taper back to about 3/32 at the trailing edge of the flap.
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WARNING: I assume this is not a built up flaps.
Glider trick. If you take Mylar’s and you wax them (McGuire’s gold wax Kmart 9$) you paint the Mylar then you put the glass on .75oz/yd bias 45 degree put resin on the glass. After that you put paper towels to extract most of the resin with some pressure (I use a hard roller). You put the Mylars on the wood and vacuum bag it. when you peel up the Mylars you have a painted shimmy flaps ready for some LE detailing with not much extra work.
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D'ya know how much weight you added?
Hi Tim,
As you well know, a touch of extra weight can make or break a model. If the flaps are really flexible, the plane might just be a real dog. So adding an extra ounce might be the game breaker.
A compromise is sometimes well needed. If you are really careful, yuo can usually build the model plenty light enough, and just a *bit* more doesn't really affect the flight characteristics. I have often heard Billy Werwage (known as one of the planet's lightest builders) give a *range* of weight the model will be best at. Say "56-59 ounces". If you are at "56 ounces, then the ounce of extra is well with in the design parameters.
It is better to be a minute amount overweight than to have a crappy flying model! (and I always build as light as I can)
Mongo
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did the same thing with the flaps of my Strega and it worked really well. So far haven´t seen any Strega ARC or ARF do corners like this, and I am not very good in corners, some are good most arent, but I guess you can have an idea.
http://www.youtube.com/watch?v=pYkywY3eYrw
Martin
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I have seen laminated ailerons and flaps on high performance gliders, the same thing could easily be applied to flaps on a C/L model! 3 pieces of 1/16" or 1/8" with the grain on center piece 90 degrees to the top and bottom pieces, its very rigid. When its sanded down to a section, you'll be surprised how sharp the T/E is with the grain in the opposite direction. I've started to glue a length of 1mm carbon rod to the T/Edges to make them ding proof !!
Cheers Neville
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Why not use carbon matt? It should be stiffer and lighter than fiberglass cloth. You'd have to decide between .2, .3, and .5 oz carbon. I'd use .5 oz, probably. I like Neville's idea of the 1mm rod on the TE of the flap, but spruce or basswood should work and probably be lighter. H^^ Steve
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I use the carbon rod on all T/edges, elevators, fin and wing tips. It sticks very easily with CA. even around tight bends, just lightly sand the rod to remove the glossiness and start at the tightest part of the curve. I use the rod as a guide for sanding the elevators etc, to a section, then cover the lot with tissue or silk.
Cheers Neville