"Mini-Macchi" 24 inch PSS'er - Page 4 - RC Groups
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Jul 07, 2011, 09:31 PM
bjaffee's Avatar
Originally Posted by Tick Point
Neither the hardware store or Tap carries the Woodpecker Pokey Thing. Anybody know what that is?
It's a hobby shop kind of thing, made by Top Flite for use with Monokote covering...

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Jul 07, 2011, 11:32 PM
Sane til the lift starts!
kpeevyhouse's Avatar
Yay! Another mini-Macchi being built!

Yep, that Woodpecker by Top Flite is the one I mentioned. It's a handle attached to a spiked wheel of death. Your local hobby shop might carry it, or you can order it online. It's completely optional, and I only started using it about a year ago. But I feel like it does help to increase the bond between the foam and the skins. When I peeled of a piece of skin from a crashed wing, it looked like a porcupine with all the glue spikes that had been down in the foam. I can't help but believe that gives the skin extra grip.

As far as cutting the mylars: I just use regular ol' scissors. For straight edges I use a metal ruler and an Olfa rotary cutting wheel. The teeth from your tin snips leave a jagged edge, and that might make it harder to peel off from the cured epoxy.

The veil cloth you mentioned will not give any strength to the wing, since the strands are oriented in random directions. I'm assuming you mean it's veil loth, and not chopped strand mat. If it's 3/4 oz, then it's veil cloth. It'll work fine as an outer surface to reduce pinholes and such. Don't bother using that 9oz glass for anything on the wing, it's way too heavy. The 3oz is fine, and I would probably do two layers on 0/90 and one layer on 45/45 bias. Or you can do two layers in each direction for a stiffer wing.

Start thinking ahead about how you'll do the hinge and torque rods. Some people don't like how I do it, or are intimidated to try it.

In fact, I just want to point out that my build thread is meant to show how I build this plane, and is not necessarily the "best" way to do it. Everybody has their own personal preferences on what works best for them. Don't be afraid to experiment or try something new. It might work for you, and it might not, but you won't know until you try.

More pictures coming later tonight. And by all means, feel free to post any questions, or pics of your own progress!

Jul 08, 2011, 05:22 AM
Sane til the lift starts!
kpeevyhouse's Avatar
I felt like such a slacker today, since I didn't get much done. But as long as a little bit gets done each day, then progress is being made... right?

I had glued on the basswood LE on the sheeted wings yesterday, and today I added the wingtip blocks. I had been careful to not get any glue on the LE that extended out past the wingtip, so I didn't have to do any cleanup for a good fit. I used some scrap 3/4" CA'd together to replace the 1.5" of foam that I had cut off when sheeting the wing. A bit of sanding on my 10" disc sander got the angles just right for a tight fit. Some 5-minute epoxy was used to glue the block to the wingtip. I drew the half-circle outline, and will get that sanded to shape tomorrow. I'll also sand the LE to shape at the same time.

Jul 08, 2011, 05:47 AM
Sane til the lift starts!
kpeevyhouse's Avatar
I knew how I wanted to do the hinges and torque rods, but I wasn't sure it would work on such a thin wing and small aileron. So I tried it out on my testing wing that I had made last week. I'm calling it a "testing wing", because it's not one that I'll be using. I had some kind of brain fart, and I more than doubled the amount of fiberglass when I was doing the layup. It's a shame, because the painted mylars really came out nice.

Anyways... I'm using the peel ply hinges along with torque rods. The problem inherent with this setup is that the torque rod cannot be mounted at the hingeline. It has to be offset. This means that it cannot be glued into the aileron, it needs to be able to slide in and out of the aileron to prevent binding.

I'll go into more step-by-step details when I do the real wing, but here's the idea:
This will be a top-hinged aileron. So I cut a slot in the bottom of the wing for the torque rod. I hollowed out a bit of foam in the aileron where the torque rod will go. I applied petroleum jelly to the rod before sliding the brass tube on. I used a bench grinder to taper the rod where it goes into the aileron (important due to the thinness of the wing back there), and reapplied petroleum jelly. I glued the torque tube to the top skin of the wing, and filled the groove with epoxy. Strategic placement of some modelling clay prevented any glue from seeping into the brass tube. Once cured, I filled the little pocket in the aileron with some 5-minute epoxy. As it was kicking off, I was moving the aileron up and down, so the the rod would be sliding in and out of the aileron pocket. Since it was lubed up, it didn't stick to the glue. Once the glue set, it had a perfectly fitting hole for the torque rod.

I have no idea if that made any sense to you, but hopefully I'll get some more detailed pictures tomorrow to explain it better.

Jul 08, 2011, 09:26 AM
Good, fast or cheap, pick two
robh's Avatar
Hey Keith, what a great build thread! Thanks very much for posting this, and ensuring that the "details" are included. I always seem to learn something new from threads like this and Like 1000MPH said, I've got to get into bagging wings someday!

Following closely!
Jul 08, 2011, 09:56 AM
Sane til the lift starts!
kpeevyhouse's Avatar
Well thanks, Rob! As far as vacuum bagging goes... the hardest part is buying all the startup supplies and equipment. After that, it's all pretty easy! Same thing goes for hot wire cutting foam cores.
Jul 08, 2011, 05:31 PM
BillO's Avatar
I haven't seen a build thread like this in a long time -- thanks Keith!

Now, a question: have you tried the "5-minute epoxy torque rod bearing" idea before? I've seen people put a brass tube in there, and I was wondering how long the epoxy would hold up under use...
Jul 08, 2011, 08:06 PM
Sane til the lift starts!
kpeevyhouse's Avatar
Hey BillO,
I have done this before using a piece of brass tube in the aileron, but that was with larger planes. On this little plane, the aileron is just too small to have the brass tube in there. That's why I'm going with embedding it in epoxy. Honestly, I have no idea how long it'll stand up to long term use. I guess I'll find out...

With the wood sheeted wing, I'll be inlaying a strip of balsa and sanding to the airfoil shape. It'll use regular CA hinges and the torque rod will get glued into the aileron like normal.

Jul 08, 2011, 10:35 PM
Sane til the lift starts!
kpeevyhouse's Avatar
Hey Tick,

You're probably already doing the layup... but you're right. The peel ply goes directly on the foam, so that the glass is on the outside. When cured, you'll use a small triangle file and straightedge to score through the glass. If you're worried about cutting through the peel ply, you can add two strips of it to increase the thickness a bit. I've done that with no problems at all.

If you mess it up, you can still cut through the peel ply later and use the E6000 for the hinge.
Jul 08, 2011, 10:40 PM
Sane til the lift starts!
kpeevyhouse's Avatar
P.S. I don't like to tape the mylars along the entire length of the TE like I saw in your photos. It doesn't leave any place for air bubbles and excess resin to escape. I just use two or three pieces. I wait to tape them together until after the layup is done and the glass is trimmed flush with the mylar TE, otherwise the glass tends to bunch up when I fold up the taco.
Jul 08, 2011, 10:44 PM
Registered User
Tick Point's Avatar

didn't pull the trigger

I'm going to stack rocks instead, some new prize winning game. Tomorrow I''ll stack soggy cloth.
Thanks Keith
great thread
Jul 08, 2011, 10:50 PM
Sane til the lift starts!
kpeevyhouse's Avatar
Sometimes stacking rocks sounds better than getting all messy with epoxy.
Jul 08, 2011, 11:32 PM
Sane til the lift starts!
kpeevyhouse's Avatar
Continuing on with the wood sheeted wing:

I got the leading edges and wingtips sanded to shape. You can use a razor plane, a sanding block, a belt sander... whatever floats your boat. I prefer the quick and dirty method of using the belt sander to get it as close as I can, and then finishing up with a block sander.

As much as I focus on the little details, shaping the LE is one area where I just say "that looks about right". I don't bother with LE templates to get the shape within a thousandth of an inch of the actual airfoil. As long as the LE is not sharp, and it kinda looks like an RG-14, then I'm happy.

It's a 3-step process for me. I sand it down so that it's flush with the sheeting, and follows a line tangent to the surface at that point. Then I move the sanding block to a more downward angle and sand another flat spot. Then I just round off the edges. Hopefully you can see what I'm talking about in the pictures below. Then I sand the wingtip blocks flush with the upper and lower wing skins. I then taper them so they get a little skinnier toward the tip, and then just round off the perimeter.

When sanding the LE, I like to place the wing on the edge of the table on one of those non-slip rubbery foam-rubber mats. It helps to keep the wing from moving around. It also helps to prevent denting up the wing on anything like hardened glue blobs, especially important with balsa-sheeted wings. You can find those mats almost anywhere. They are usually in stores next to shelf/drawer liner material.

Now is as good a time as any to get the dihedral sanded in. The wing will have 1.5" of dihedral, so I put a 3/4" block underneath each wingtip. With the sanding block flat against the side of the bench, I just sand away to get the proper angle.

Jul 08, 2011, 11:46 PM
Sane til the lift starts!
kpeevyhouse's Avatar
My wood sheeted wing will use regular CA hinges. Initially, I was going to cut the aileron out and glue some balsa to the wing sub-TE and to the aileron LE. I changed my mind and decided to inlay the balsa into the wing, while not cutting through the bottom ply. I've got it glued in now, and will sand to shape later. I think it worked well, but I might have lost just a tiny bit of the under-camber of the airfoil. Kinda hard to tell.

I marked off the aileron perimeter, and placed a piece of 1/2" balsa along the hinge line. I marked the outline of the balsa, so that there was 1/4" ahead of and behind the hingeline. Using a fresh blade, I cut through the ply and foam, but did not cut through the bottom ply skin. I dug out the foam and used a chisel to remove the glue from the bottom skin. This left a perfect channel for the 1/2" balsa to fit into. Then I smeared some 5-minute epoxy into the channel, put the balsa in there, and held it flat against to foam wing bed to maintain the airfoil's shape. (With all that unsupported ply, it's easy for the aileron to flex up and down.)

This was a little experimental for me, but overall I like how it turned out. Now I just have to be careful when sanding it so that it matches the curve of the upper wing surface, and not have a flat spot where the balsa is.


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