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Building Tips and technical articles. => Building techniques => Topic started by: Jim Morris on August 28, 2011, 06:17:24 PM
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Ive been hearing some talk about using cf tubing or rods on flap le or te. Can someone explain or post pictures of how you do that. How do you install the hinges? The Vector flaps I was going to redo because they ar too soft, I was thinking I can put the CF tubing on them to fix the problem ? They are 1/4in thick, tapered at the TE.
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Howard Rush is the guy to ask. He's been doing flaps with carbon tubes for a bit.
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I did carbon tubes in the last 2 models.
Carbon tube along the leading edge - When I make the ribs for the flaps I make the cutout a 1/2 moon shape to allow the fitting of the carbon tube along the leading edge. This in turn makes up the leading egde radius.
I mount the hinges the exact same way as I would normally. One key addition is to carve a round balsa dowell and slide it down the middle of the carbon tube to allow you to glue the hinge internally.
I cut the hinges down by 1/2 to allow them to sit inside the carbon rod. I still recess out a square to allow the barell to sit flush to the leading edge.
Fit and finish as you see fit.
Advantages are increase stiffness.
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If I recall the vector 40 uses solid flaps. The ones that came in my kit were just fine as is. Once you cover them they stiffen up just fine. They are not large enough to stress over. If you still wish to stiffen them cover them with Carbon Fiber veil instead of silkspan. That will be more than stiff enough for a Vector 40. CF tubes are more for built up, large model flaps with high loadings. Complete overkill on the vector.
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Hi Jim,
Howard, and Al Rabe seem to be the guys who really are keen on the CF tubes/flaps.
One thing Al seems to always do is cover the flaps with a layer or two of .5 fiberglass to stiffen them up. If you really work on getting all the excess resin out of the cloth, the weight gain is not much. I had to fiberglass the flaps on my P-51B "big" stunter.
On SSW Al had a tutorial abut using the CF tubes and the fixture he made to cut the hinge slots. Don't know the URL for it off hand, but it's there.
Big Bear
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Thanks guys, thats all I needed to know. I will not use this method on the Vector. Yes the flaps have been glassed, but using dope, very soft. i will remake them in C grain. I wish I would have used CF veil, but still not sure it would be stiff enough.
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Thanks guys, thats all I needed to know. I will not use this method on the Vector. Yes the flaps have been glassed, but using dope, very soft. i will remake them in C grain. I wish I would have used CF veil, but still not sure it would be stiff enough.
Would have been more than stiff enough for a Vector 40. Mine came in at 40 ozs dry, using only the wood from the Brodak kit
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Thanks guys, thats all I needed to know. I will not use this method on the Vector. Yes the flaps have been glassed, but using dope, very soft. i will remake them in C grain. I wish I would have used CF veil, but still not sure it would be stiff enough.
It would be easy enough to strip the dope/fiberglass off the existing flaps. Use thin epoxy finishing resin with either .75 oz fiberglass (on a 45 deg. bias), or .5 oz CF mat. If one layer isn't stiff enough to suit you, add another.
FWIW, Howard was not satisfied with torsional stiffness of the usual unidirectional CF tubes, so rolled his own with the CF on a 45 degree bias. That's Howard for you. When PW test flew Howard's plane, he reportedly said the flaps were too stiff. y1 Steve
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The JCT is coming to town.
We're plenty stiff from the flaps on down.
I was going to make some torque tubes tonight, coincidentally, but the carbon prepreg I had was too short. I'll try again tomorrow and maybe take pictures. I wrap the prepreg on an aluminum arrow shaft, then cook the prepreg to harden it, then dissolve out the aluminum with HCl. Then I slit the carbon tube with a Dremel dangerous disk and cram balsa plugs down inside so the hinges have something to hold onto. It's easier than it sounds.
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Here are some pictures:
1. A roll of carbon-epoxy prepreg from the local airplane factory surplus store and aluminum arrow shafts from Lancaster Archery.
2. Wrapping a strip of prepreg on the arrow shaft. Width is calculated to make a 45-degree wrap.
3. Wrapping a ply in the opposite direction. This time I left the backing paper on until I did the wrapping.
4. Wrapping the tube with polyester shrink tape. The pink stuff on the tube is .001" Teflon to keep the shrink tape from sticking to the part.
5. Putting the tubes after cooking in the autoclave into the Reactor. Note the authentic chemical ring stand.
6. Adding water to the Reactor.
7. Add acid to water, not the converse. Remember that?
8. After a little time, the reaction starts to go fast. I shoulda used a bigger diameter Reactor.
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And notice the upscale shop.
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But no operational stunt planes like this shop:
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I gotta axe...how do you dispose of the HCl and aluminum chloride solution? Per JCT regs, I'm sure. LL~ Steve
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Five months on, I've made a little more flap progress. Here are pictures:
1. Slitting the tubes for nylon hinges. This is a Dremel Dangerous Disk mounted in a router on a router table. The block, rod, and arrow shaft segment taped to the carbon tube hold the tube orientation so the slits line up.
2. Using a plug cutter to cut balsa dowels for hinge anchors.
3. Cutting the dowels in two with a band saw. A piece of 1 x 2 with a hole the size of the dowel is clamped to the saw table in front of the blade. A ramrod pushes the dowels through the blade.
4. Cramming the split dowels into the torque tube using the other end of the ramrod, which has an old X-Acto blade glued to it to align the splits in the dowels with the slits in the tube.
5. When the split-balsa-dowel hinge anchors are in place in the tube, I use a piece of Teflon to hold the split open while I Hot Stuff them in place.
6. You can see the end anchor. I finish the flap before installing hinges.
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What has proved more difficult was trying to include carbon tubes into foam core flaps.
Somehow I managed...
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Did you make the hole in the foam first, then stick in the tube, then cut the flap?
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Thanks guys, thats all I needed to know. I will not use this method on the Vector. Yes the flaps have been glassed, but using dope, very soft. i will remake them in C grain. I wish I would have used CF veil, but still not sure it would be stiff enough.
I believe you will find the fiberglass to be stiffer than the CF veil even when both are applied with 30 min. Epoxy or Finishing resin.
"C" grain with biased layers (2) of .5 FG cloth and finishing resin squeegeed off will more than suffice on even a 700 sq.in. model. Weight gain is miniscule compared to the benefit.
BIG Bear
RNMM/AMM
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Howard ;
Sheeted the flap, made a front LE from 1/4 - bevelled out the balsa leading edge to accommodate the carbon torque tube - which is precut for my hinge slots ( which is a pain to do! ). Epoxy it in, epoxy that to the foam finish as per normal.
To cover the flaps, I lay .58oz Glass cloth over the whole flap, then .3 oz carbon veil - standard PTG finishing method from there on.
VERY stiff flaps.
With the addition of my Rush boost tabs of course!