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Mar 30, 2018, 01:54 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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Discussion

Carbon Bender (First Molded CF Plane)


I'm starting this thread on my first attempt at a molded CF plane. First some background.

I've done skeletonized foam planes for many years. One I did in 2010 was my Air Bender
https://www.rcgroups.com/forums/show...8-inch-Aerobat
That one had a wing span of 18 inches and weighed 19g.

And, I've done many other cartoon scale skeletonized foam planes. I am for some reason drawn to the Fokker Dr-1 triplane. I've done so many of them I've lost track. They are usually about 11 inch span, and generally weigh about 19g.

One I did that weighed 9 grams, and would fly in my family room. See this thread for a video.
https://www.rcgroups.com/forums/show...-with-Video%29

Most recently I did a cartoon version of a Super STOL, with working flaps. It flies nicely, and the flaps are effective and it really flies slow with them deployed.
https://www.rcgroups.com/forums/show...804-Micro-STOL

I used to mold my own CF props about 12 years ago. And, I first worked with fiberglass molding back in high school. So I have worked with composites. But, molding curved CF rod, and then the construction techniques that go along with it are new to me.
Last edited by Gordon Johnson; Oct 11, 2019 at 09:40 AM. Reason: changed name of thread
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Mar 30, 2018, 02:18 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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I've been following what has been going on with CF construction, and then molding in the F3P area for a while. And, finally, I have taken the plunge.

First, I want to thank Ruslan Ermolin (29rus) and George (Ampbomber) for all their help. I've asked about a million questions as I got started. And, all the other people who post their information here. I've read lots of it.

What I'm going to build is a slightly larger version of Ruslan's lime green plane (below). His plane has a 420mm (16.5 inch) span and weighs 9.7g. Using pictures he has posted and shared with me I'm drawing up my own version of his plane, and scaling it to 20 inch span. I'm pretty much a Micro guy, and this size is at about the upper end of the size planes I generally build and fly indoors. The other reason for this size is unlike Ruslan's green plane I will be using one of his Coaxial drives with 9-inch props. According to Ruslan 20 to 22 inches is about right for the 9-inch props and his drive. He has other planes about this 20 to 22 inch size, but I like the looks of his lime green plane, so am scaling this one up.

I'm sure I'll make a few tweaks as I go along. For example, I added about 0.5 inch to the chord to give it a bit more wing area.

Equipment will be Ruslan's 9-inch props and Coaxial drive, which weigh about 3.7g total for drive and props. Control will be two of Nick Leichty (Micro Flyer Radio) 0.395 servos for rudder and elevator and one of his 0.50g servos for the ailerons. Receiver will be Deltang. And, brushless ESC is the Chinese 3A unit that a lot of people use. Battery will be either 70mAh or 100mAh, I'm not really sure yet. I will post pictures of equipment as I get to those stages. I have all the equipment on hand now, so it's time to do CF construction.

I don't know what I'll call this plane yet. Ruslan's doesn't have a name. I've always liked Air Bender, so it could end up being Air Bender II. Or, maybe it should be Carbon Bender. Time will tell.

Please feel free to make comments and suggestions as I go. I have lots to learn.
Last edited by Gordon Johnson; Mar 31, 2018 at 07:36 PM.
Mar 30, 2018, 02:25 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
Thread OP
First how to mold the CF. I've decided to use a method similar to what George and Ruslan are doing, where the CF is not pulled into heat shrink. And, to start I'm using a variation of George's poster board form method.

As I draw up the parts on my computer, I also drew up the forms for the curved pieces. I laser cut the pieces from poster board. Then, I got to thinking that the outside pieces could be used to hold the CF in place, similar to the routed grooves in wood technique used by some people who go with the heat shrink tubing method. So, I saved those and cut them up into three pieces that could be placed around the outside.

the first two pictures are of a wing panel. The third is of one side of the elevator.
Mar 30, 2018, 02:36 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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Finally, I started molding. I'm using 3k tow and WEST epoxy. I mixed up a batch in 5:1 ratio, and applied a line down each length of tow, which had the ends CA'd, and then taped with Gaffer's tape. I think I'll mix up less epoxy next time. I wanted to be sure I had enough for my first try, and I had plenty.

Similar to George, I hung the CF tow segments up from the rafters in my workshop. First I wiped them down lengthwise with folded up pieces of paper towel. Then, I followed George's method of "palming" them after about 20 minutes. And, then I "paddled" them at about the 1-hour mark. At 2 hours (per George's recommendation) I cut them down and wrapped them around the forms (which I put mold release wax on while waiting for the epoxy to begin curing).

I did push the exterior pieces of poster board in place to help hold the CF tow in position. But, honestly, I'm not sure this is needed. I may skip this step on the fuselage unless I see that a segment needs it.
Last edited by Gordon Johnson; Mar 30, 2018 at 07:39 PM.
Mar 30, 2018, 02:41 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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And, finally, this morning, my first molded sections of curved CF. I suspect everyone who has done CF molding felt the same when their first pieces were done. These need to be trimmed as there are excessively long pieces out past where they are needed. And, after 24 hours of curing I need to bake these in the oven. And, then I need to sand then lightly.

What comes next is gluing these curved pieces together with straight lengths of commercial CF. The method I will be using is similar to what others have done. I will be laser engraving grooves in Depron or similar foam for each of the curved and straight pieces of CF, with a hole cut through at each joint. I will use thick CA on the joints, following the method pioneered by others on this forum.
Mar 30, 2018, 02:46 PM
Registered User
to bake, it is necessary to fix the bent parts or weights or between two equal glasses, otherwise to be warped, deformed
Mar 30, 2018, 02:50 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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Thanks. Now I need to get some glass.
Mar 30, 2018, 04:49 PM
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crossup's Avatar
Pretty cool, I presume the maiden will be Monday? I have a feeling I vastly underestimated your enthusiasm. What I can not wait for is a real video of one of these minis in a normal venue, the living room flight videos give me no idea how they perform.
Mar 30, 2018, 07:32 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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This will be a long build. Our last indoor of the season is in May. And, there is no way this will be done by then. Chances are it will fly for the first time at the indoor at NEAT. I travel a lot on business, generally about 60 days a year. And, I'm in the middle of a six week stretch of travel every week. So, for those watching, progress will not be fast. I may go weeks with no progress. The other reason for going slow is I'm trying out various methods. For the fuselage molded pieces I may try a laser cut variation of what Ruslan does. I also have never done any airbrushing. I just got an airbrush. So, that's one more thing I have to learn.

But, I just picked up two sheets of glass that will fit in our oven. So, I'm now set for baking the CF moldings I have tomorrow.
Mar 30, 2018, 08:22 PM
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Ampbomber's Avatar
Knowing more than what you have posted about the beginning of your project I don't feel that obsessed any more with my projects Have at it and enjoy. .

BTW, obsession is a good thing
Mar 30, 2018, 10:12 PM
Registered User
Looks like it will be a great project! Already looking forward to seeing her fly at NEAT.

Joe.
Mar 31, 2018, 04:10 AM
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joao's Avatar
What a great project, thank you for sharing all this information. The Fokker flight is super.
Joao
Mar 31, 2018, 04:18 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
Thread OP
I have baked the CF rod pieces. Time to assess. I would not give myself a very high grade.

I pulled the semi-cured tow/epoxy lengths tight to make sure they were tight against the form. Well it may have been too tight. On some of my corners the rod deformed to a flat shape, not nice and round. There are also a couple of places where the rod waves up and down a few times. So, I must not have gotten it down right in the joint between the pieces of poster board. I did sand the poster board beveled.

I also think I should have let the CF epoxy/tow cure longer before forming them. I kept checking the small amount of epoxy in the bottom of the mixing cup to see how it was setting up. It was somewhat beginning to set up, but could still be moved around. Ruslan recommends closer to four hours curing before molding the CF rod. I had kept checking how flexible the hanging rods were as I approached the 2-hour mark, and they were very flexible. Now I know that I could have gone longer. I'm not sure how much longer with WES and 5:1 ratio with hardner.

I will go ahead and glue straight pieces with these formed pieces, and I'll cover them as well. At this point I'm considering these practice pieces.

I'm going to try lazering grooves in foam and see about on my next attempt molding the CF rod in the grooves. This is a variation of the method Ruslan uses. This will also probably keep me from pulling the lengths of CF rod too tight.

On to my second attempt ...
Last edited by Gordon Johnson; Apr 03, 2018 at 12:58 AM.
Mar 31, 2018, 05:52 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
Thread OP
This is Ruslan's method. All I've done is to use my laser to score the lines that I trace over with a hand-held tool. I used Depron Aero (Gediplac) because it has a softer skin than true Depron. Then, I took a wood tool and widened and deepened the grooves.

The last picture is not actual CF tow molded in the grooves. It is the pieces I made a couple of days ago, placed into the grooves.

What is next is to make another batch of epoxied tow and try this again. And, I still need to put mold release wax in all the grooves. With any luck I can start this second try tomorrow morning.
Mar 31, 2018, 05:54 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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Quote:
Originally Posted by joao
What a great project, thank you for sharing all this information. The Fokker flight is super.
Joao
You might like this one of my first version of the Blue Dr-1, complete with "Snoopy vs. the Red Barron" background music.

Fokker Blue Max (2 min 7 sec)


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