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Old 02-26-2012, 08:12 AM   #1
NFA Fabrication
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Default Planning Scratch Fiberglass Plane Build. Have ?'s...

I am planning to build a fiberglass plane based on being a fairly simple high wing Cessna style 5 channel plane (Elevator, Rudder, Ailerons, Throttle, and Flaps). I will be loosely basing this on the dimensions of the E-Flight Apprentice, as I like how it flies as a trainer, and will be using it for leisurely flying and for training friends how to fly.

I will alter the design as needed until I like how it all works, and once it meets my wants, I will make molds of the individual pieces for easy replication of parts. I have a few questions regarding the tail control surfaces. I see that the "Apprentice" (A fully foam based airplane), has a very flat elevator and rudder control surface, but it has about a 4mm thickness to it. Is this simply because the panels are foam based with a laminate? If I was to make them out of flat fiberglass ~1mm thick, would there be any negative effect?

I will have more questions I am sure, and understand the importance of the main wings form/shape. I will post pics and any ?'s i have as this progresses.

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Old 02-26-2012, 02:24 PM   #2
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Originally Posted by NFA Fabrication View Post
I see that the "Apprentice" (A fully foam based airplane), has a very flat elevator and rudder control surface, but it has about a 4mm thickness to it. Is this simply because the panels are foam based with a laminate? If I was to make them out of flat fiberglass ~1mm thick, would there be any negative effect?
I wonder if they would be stiff enough not to flex excessively. I think if you made tail surfaces out of solid glass you'd find they were heavy, making the plane hard to balance.

Most GRP kits use a molded fuselage only and conventional construction for the wing and tail to save weight.

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Old 02-26-2012, 05:54 PM   #3
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I agree, tailfeathers might get just a bit too heavy and "brittle" if they were totally made out of FG. Kinda thinkin that FG would make a good laminate. The main wing would definitely get heavy and might not be able to deal with the loads without some sort of bracing or just plain ol foam core with a thin glass overlay ......maybe .060.... .040?? might have to be thinner???
IMHO I think a glass fuse with maybe balsa ribs or structure would probably work.
After a few miles and twist and spill the App's tail feathers do get creased and warped pretty easily. Did the App crash? Can it be fixed???......That wing for the App has a ton of lift and dihedral built in it, I just don't know how much total weight it could take.

Saying all that, I think it would be interesting if you tried this. Be a little bit of work.

Also I remember Rockin Robins had found/used this GOOP stuff, that was brushed on over foam and was pretty strong and in thin layers didn't weigh much....tryin to find link....

http://www.scalemodelguide.com/guide/hints/poly-goop/

Not sure how safe it is with foam???

have a good one
cr
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Old 02-27-2012, 12:28 AM   #4
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I am thinking that I might start with the very forgivable Apprentice platform, and start by making tail surfaces and test them on this working plane. I have made a lot of flat fiberglass panels for various things, and they are very light and rigid (Maybe not as light as the foam, but not bad by any means).
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Old 02-27-2012, 05:05 PM   #5
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Definitely be interesting what you come up with. After installing a Cermark NeoDym-15, silly power for a trainer, (and, ummmm, a lot of un-needed yankin/bankin) I found out the weak point in the wing is where the ailerons and the anti-stall strake outmost point line up, its right where the CF tube ends also, very rare to fail, but IMVHO with FG it might be a problem.

As you already know, the weak tail feathers are not attached very well to the fuse, little bit of epoxy and CF along leading edges, middle area and into the fuse itself it was better.
Even with a larger motor and the additions to the stab and elev, I had problems with it being tail heavy.

Didn't mean to sound harsh, not sure it wouldn't be a bad idea, just giving my one penny!

.....waiting to see what you come up with

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Old 02-28-2012, 10:47 AM   #6
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Keep in mind that every gram of weight you add in the tail means you will need to add an additional 5 or so extra grams of lead in the nose to balance the model.

Also, keep in mind, the typical construction methods for airplanes and our models have been developing over many many years. They are the way they are for very good reasons - they work

Solid FG is not a good idea. Its going to be too heavy by the time you get it thick enough to be stiff enough. Thats why no models are built that way now.

Thin layers of FG as a skin over foam to create a stressed skin structure can work very well - if you keep it light. You will need to use the minimum ratios of resin to glass and vacuum bagging techniques to achieve the lowest weights. Hand layups simply cant come close.

Think of it this way, unless you want the model you're building to fly like a lead sled, it needs to be no heavier than it is now. Weight is your enemy in models.

Right now its a foam structure with a little carbon fiber as spars. If the fiberglass and resin you add weighs any more than the few grams those carbon spars weigh, then your going in the wrong direction.

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