Learning Project Piper Cherokee - Page 2 - RC Groups
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Oct 04, 2017, 04:58 PM
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Extreme, the only document laminating film I'm familiar with goes on at a high temp. I've tried it over blue foam, but the iron melted the foam.

I guess I'd say that I'm starting this process as if it were a wooden model, but built from foam. The wings are the same as I've done for decades; white foam and balsa (although this is my first try at using Gorilla Glue for sheeting a core --- I'm very happy with it!).

In fact, my original intention was to convert one of my wooden designs into foam, but I've long wanted a Cherokee (and my wife has a thing for Pipers -- as she's also an active flier, I want to keep her happy!).

Next project, I'll probably go for a pink foam wing, with a SMALL balsa TE, a spar (gotta figure out what size to use!), wooden aileron bay edges, and fiberglass covering.

CD
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Oct 04, 2017, 09:24 PM
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Did a comparison of wing weights on the Cherokee versus two wooden models. The Cherokee wing, with ailerons and servo (but not finished and missing hinges and pushrods) weighs 207 grams. That's a lot more than you guy's foam wings, but it's still less than the 356 grams of one model and 400 grams of a second. All three have the same wing area (432 in. sq.) and the two wooden wings have two servos, each. Hopefully, the finished Cherokee wing will still come in under 300 grams!

Now to start doodling the next and (hopefully) lighter design!

CD
Oct 06, 2017, 04:53 PM
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Got a little work done, then the mailman delivered the Orange module I'd ordered for the Turnigy 9XR I won at NEAT.

Spent a couple of hours, before I was able to confirm that the module was DOA...<sigh>. On the good side, HobbyKing is sending another module, but, time is getting precious at my age.

Anyway, the fuse is rough-sanded and the ailerons are shaped.

As of this time, the fuse is 242 grams (still need to hog out some of the interior). It started at 259 grams. The wing is 226 grams, ready to cover, and the whole airframe (wings, fuse, and tail feathers) is 497 grams.

CD
Oct 06, 2017, 08:31 PM
treefinder
springer's Avatar
no dihedral?
Oct 07, 2017, 06:23 AM
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Doesn't look like it, but there's 4 degrees of dihedral. I reduced it from scale because I want a plane I can toss around. I guess I'm a wannabee Pattern Pilot.

CD
Oct 07, 2017, 06:55 PM
treefinder
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You may get the chance, my low wingers like lots more dihedral than the high wingers. Certainly with ailerons you can compensate, of course. I just think low wingers look "right" with lots of dihedral.
Oct 08, 2017, 03:25 PM
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Another personal first, using finishing epoxy to fiberglass a wing (I used polyester MANY years ago, and Polycrylic a few times, but his is the first time I've tried epoxy). Of course, I mixed up much too much, so I wound up scrambling to do a few other bits before the epoxy cured. (BTW, I used Jim Ryan's tutorial, from here on R/C Groups, as my info source).

I thought about using polyurethane, but went with the epoxy as I have a new package of it.

I also hogged out some of the fuse and did a lot of little spackling chores. I should be ready to glass the fuse and the rest of the tail feathers, shortly. The fuse is really pretty stiff, so I think I'll hold to 1 layer of 1/2 oz. glass, using Polycrylic or Polyurethane as the 'resin'.

I did the wing bottom in 1/2 oz. glass and will use the same for the top. I plan to use 3/4 oz. for the HS, as it's a bit flexy (even with the carbon fiber strip I added this morning).

The bare fuse weighed 259 grams when I started; it's down to 230, with the addition of some filler at the wing roots. I plan to cut open the bottom aft fuse to install the pushrods, at which time I'll also carve out some of the inner block.

CD
Oct 08, 2017, 08:37 PM
treefinder
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Be careful adding a lot of weight to the tail!
Oct 09, 2017, 11:02 AM
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Iím kinda liking the way you built the fuselage but I think you could get away with half the thickness of the sides. Itís giving me some ideas though.
Oct 09, 2017, 07:28 PM
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Having never built a fully foam fuse before (isn't that alliterative?), I followed the recommendation in Keith Sparks' book. If I read it correctly, he recommended the minimum thickness be 1/2", so that's what I hollowed the 1" thick foam to between the joints. I was cautious as I wasn't sure how rigid it would be and I wasn't sure how much would be left after rounding the corners.

After I assembled it, I (crudely, I must admit) hollowed out the cockpit area. I plan to glass the fuse, then cut a hole in the aft underside for access to the pushrod installation. Whilst the fuse is open, I intend to hollow out more of the rear. I'm hoping that it won't weaken it so that I need to add stiffeners. Right now, without any fiberglass, the aft fuse is easily as rigid as any of my balsa models (and about the same weight).

Got 1/2 oz. glass polyurethaned to one side of the rudder and the elevator. Tomorrow, I hope to get the wing top, vertical stab (fin), HS (tailplane), and rest of the ailerons epoxy glassed.

CD
Oct 10, 2017, 02:11 PM
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Ok just how sculptable, sandable, and paintable is the pink foam you’re using?
Oct 10, 2017, 06:44 PM
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Dewey, it's very pleasant to work with. I've used blue, pink, and green foam for pilots, engines, machine guns, etc. A knife is of limited use in carving it, but the best cutter is sandpaper. Emery sticks (i.e., fingernail sanders) are great carving tools for finer details. If you carve off too much, some spackle can be added to build the foam back up. For glues, I like Foam-Tac (or it's Bob Smith imitation) if the glue might wind up leaking onto the surface as it's easier to sand than aliphatic or CA. If I'm sure I won't goof and let the glue squeeze out, I use Gorilla Glue or aliphatic.

It's like very soft balsa, only it has no appreciable grain. It is awfully soft, so once you've carve and fine sanded it, a protective coat (Polyurethane or Polycrylic) are good.

I've heard that the different color foams have different properties, but I've yet to notice it. I have used blue foam for foam wing cores. Its a bit heavier than white, beaded ('Styrofoam') foam, but it also seems to be a bit stronger.

CD
Oct 10, 2017, 09:23 PM
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Great info thanks.
Oct 11, 2017, 05:56 AM
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My pleasure!

BTW, for years, my main source of foam was work. Not AT work, but driving TO work -- I drove along a major highway in NJ (Rt. 295) and routinely saw large blocks of foam along the side of the highway. So, when safe, I'd stop and pick the stuff up -- quickly had enough for several models.

CD
Oct 12, 2017, 10:01 AM
Registered User
I went to Lowe’s last night and they only had 4x8’ sheets of the green foam. No pink stuff at all. I was hoping to find some 2x4’ sheets of it.


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