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Old Jul 11, 2013, 09:33 PM
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Denver CO
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ive tried monokote over foam and it never sticks, whats your secret?
Just awesome! and quick too!
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Old Jul 11, 2013, 10:17 PM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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I dust a light coat of 3M77 onto the foam. That needs to dry thoroughly, maybe an hour or so. It should be dry to touch with your finger with no tenancy for your skin to stick. The Monokote will stick to it some, but can be easily pulled up and repositioned. Then the heat activates the glue on the film and also the 3M77. It`s a pretty good bond.

If the 3M isn`t dry enough it tends to cause more gas underneath the film than normal, and it never seems to stick as well as when the 3M is allowed to dry completely. Even overnight drying is OK, probably even better, as long as the surface stays clean.

Also as noted earlier, Econokote is even better because there is more of a range between shrinking,sticking temps and the temp that will melt the foam. Low heat films are the best, but I`ve used regular Monokote here because that`s all that the LHS had in the color I waned, and I didn`t want to wait to order it.
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Old Jul 12, 2013, 08:17 PM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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Airfoil Choice

Here`s the airfoil that I`ve chosen. It will be aprox a 10% thickness at the root and more like 13% at the tip.
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Old Jul 13, 2013, 08:03 AM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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Airfoil Templates

This won`t be a tutorial on cutting foam wing cores, but I am going to show a couple of time/expense saving things that I`ve learned over the years.

This is a new idea, but I`m going to cut each panel as an upper and lower section. It will have several advantages.

One is that I can match a good top with a good bottom and that will save some waste. It`s very frustrating to get a nice cut on the top and then screw up the bottom , then have to throw the whole panel away.

Another thing is that I plan to add as much of the structure as I can to the inside of the panels before the top and bottom are joined. That will leave a smoother outer finish which will be good since I`m just covering the wing with Monokote.

Last, since I`m working with 1" foam, it will be easy to do. If I had 2" foam, I`d probably just go with a more conventional cut, but it`s fun to try something new, and sometimes I come up with a keeper.

Here are some pics of the templates. They are just printed out, then I glue them to aluminum flashing material, like is used in roofing. I bought a 25ft roll from Home depot about 10 years ago for $10. You can cut the stuff easily with just regular scissors.

I used bamboo skewers, left over from my combat building, to strengthen them, but any kind of dowel would work fine.

Then I sand the edge of template with fine sand paper, like 400 grit. Make some holes in them for pins or screws to hold them to the foam. Then they are ready to use.
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Old Jul 13, 2013, 11:36 AM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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Well I`ve got the cores cut. Some trial and error, but not too much waste. On a wing where the tip cord is 50% of the root cord or less (this one is about 33%) it`s hard to get a smooth cut because the wire is moving so much faster at the root the wire gets too hot at the tip and causes grooves and foam loss.

So I ended up adding about 1/4" to the center of my tip template, with the upper and lower curves staying the same. That helped compensate for the foam loss from the hotter wire and gave me some added thickness so that I could sand out the grooves.

With a little more adjusting of the templates and some practice I could do much better, but these sanded out OK and will work fine for now.

I have the outline of the actual foam core marked except for the LE which will need to be trimmed for the balsa LE. I`m going to wait until I have the wing all glued together before I add the balsa LE, TE, and tips, and do the final sanding. So these are ready to install some spars and hard points for the main gear retracts.
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Old Jul 13, 2013, 12:02 PM
Lee Liddle
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Carrollton, Tx
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Quick note......I`m estimating that the total weight of the bare airframe will come in at 3lbs or a little less. If I can do that I should be near my 10lb AUW target with about 4.5lbs of lipos included.
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Old Jul 13, 2013, 12:38 PM
DELTAS RULE
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tehachapi, CA
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Dang that looks great!
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Old Jul 13, 2013, 02:44 PM
“Do it Right The First Time!”
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United States, MN, Hermantown
Joined Dec 2008
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Quote:
Originally Posted by Knife Liddle View Post
Quick note......I`m estimating that the total weight of the bare airframe will come in at 3lbs or a little less. If I can do that I should be near my 10lb AUW target with about 4.5lbs of lipos included.
Lee, at 4.5lbs of lipos, is that going to be a 2s2p set-up? And what monster fan have you built for it?
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Old Jul 13, 2013, 03:06 PM
2014 EDF JET JAM We be Jamming
Kevin Cox's Avatar
St. Louis Intl, Missouri, United States
Joined Jan 1997
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Nice work Lee!
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Old Jul 13, 2013, 04:09 PM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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Quote:
Originally Posted by Knife Liddle View Post

Fuse weight is still just under 16oz. I`m shooting for an AUW weight of around 10lbs with a very large lipo pack 10 to 12s 8000 for very long flight times of 7 min or so. So far I seem to be on track.

:
I'm planning for about 3.5kw, but long flight times. I'm getting tired of 3min flights.
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Old Jul 13, 2013, 07:03 PM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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OK, I`ve got the structure figured out. The main ancor for everything is a 5" X 16" piece of 1/8" ply. This part will tie into both the front and rear spar, and the retract mounting beams will also mount to it.

It`s kind of like the BVM flex plate system except that it won`t require a big hatch to work. The whole part won`t be able to be removed if/when it gets broken, but there is enough room so that a repair piece could be laid in and tied to it if it gets broken too badly.

The part weighs 4oz by itself, but I think it`s weight well spent. It should make the wing center and gear mounts plenty strong enough to withstand some of my poor landings without punching the gear through the top of the wing.

The spars will be 1/4" basswood/spruce, and will be slotted in the center to slip over the main plywood plate.
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Old Jul 13, 2013, 07:54 PM
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Lee:

Great job. plane looks very nice.

Ed
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Old Jul 13, 2013, 08:40 PM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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Here is the plate and spar assy mounted into the upper half of the cores. Just need to cut the recesses in the lower cores, check the fit, and it will be ready to glue together.

The glue will be a combo of Gorilla Glue and 3M-77. Then 5 min epoxy to glue on the LE, TE, and tip balsa.
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Old Jul 14, 2013, 01:42 AM
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Hampton, VA
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Really appreciate the time spent showing how you do your wing cores.

Ksqm
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Old Jul 14, 2013, 02:18 AM
Lee Liddle
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Carrollton, Tx
Joined Dec 2006
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Quote:
Originally Posted by ksqm View Post
Really appreciate the time spent showing how you do your wing cores.

Ksqm

No problem, it only takes a few minutes and it`s a good record for me too. I`ve gone back and checked my own threads many times because I forgot one thing or another.

This method did work out pretty well,especially for a wing that`s just going to get film directly over foam, because I was able to preserve almost all of the surface without any need for any filler.
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