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Feb 18, 2020, 08:31 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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Cartoon Scale Monocoupe (skeletonized foam)


I have been meaning to do this plane for quite a long time. This is intended to be a somewhat aerobatic light weight cartoon Monocoupe with oversize control surfaces. It will be similar in size at 20 inch span and hopefully similar in weight to Adam Woodworth's very nice Cartoon Scale skeletonized foam J3 Cub.

For whatever reason the Monocoupe is one of my favorite planes from the Golden Age. This will be my fifth Monocoupe. Below are my earlier Monocoupe's and basic details.

This thread will also serve to document the steps for my good friend Pete Foss, who will get a set of pieces to build when I've got this one done and in the air. He will benefit from any tweaks needed. The goal is for us to fly these together at NEAT this year.
Last edited by Gordon Johnson; Feb 18, 2020 at 10:31 PM.
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Feb 18, 2020, 08:38 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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Here are the bits so far. This is after about two weeks of design work on the computer, and cutting, assembling, tweaking the drawing, cut, assemble, and so on. Lots of pieces cut with scrap foam, dry fit, removed, redesigned, and on and on. I have made and assembled four versions of the fuselage, some were just the cabin and nose area. Wings and tail have not been designed up yet. Those will come when I get to them.

But, first the fuselage.
Last edited by Gordon Johnson; Feb 19, 2020 at 09:06 AM.
Feb 18, 2020, 10:15 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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First up to assemble is the motor mount, which will be attached to the firewall, which in turn will be attached to the front cabin former. It is made from 1/32 ply, and will mount one of Vladimir's 1.85g BL gearboxes on two carbon fiber tubes.

The ply pieces are glued together on the ply firewall. The mount for the motor goes in the middle and the two pieces slide in and "capture" the CF rods. I glue it with Super Phatic so it gives me time to move things around compared to CA.
Last edited by Gordon Johnson; Feb 19, 2020 at 06:54 AM.
Feb 18, 2020, 10:30 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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The next step is assembling the Depron pieces that will join the front cabin former to the firewall.

The two side pieces have different length tabs. The shorter tab is inserted into the slots on the cabin former. The longer tab goes through the firewall. It is longer because it has to fit through 3mm Depron and a piece of 1/32 ply.
Feb 18, 2020, 11:23 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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On to the skeletonized fuselage sides and top and bottom. These are skeletonized foam. I used 3mm Depron for all the formers inside the fuselage because Depron has a stiffer skin and gives more rigidity. For the fuselage sides I used Gediplac because the skin is softer and the foam is easier to bend. I have only skeletonized the aft section of the fuselage. I want to reduce weight at the tail to help with the CG due to the light weight gearbox up front.

I used the same technique of applying RA Microlite mylar "panels" to the skeletonized regions, and the rest of the fuselage is bare white foam. The process is to adhere printer paper with the barest hint of 3M77 dusting to the shiny side of the Microlite. Then, these are cut out in panels. A corresponding template is cut out which also has a hint of 3M77 dusted on it. This is positioned on the skeleton piece so when spraying a regular amount of 3M77 for adhering the covering, only the area being covered gets 3M77. Then, the carrier sheet is pulled off leaving the mylar covering.

The reason I covered just regions was I wanted to leave the corners of the aft portion of the fuselage bare so I can sand them rounded and get a nicer look. We will see how this works. I did the sanding on a non-skeletonize fuselage as a test.
Last edited by Gordon Johnson; Feb 19, 2020 at 09:08 AM.
Feb 18, 2020, 11:31 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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I adhered red Microlite to backing paper, and laser cut the stripes. I saved the triangular pieces from the fuselage and inserted them on the back side to give a firm surface for orienting and then pressing down the red stripes. Stripes were dusted with 3M77 and applied, and then backing paper peeled off.

The same process was followed to make the top and bottom fuselage caps. Note the laser cut grooves that go half way through the foam. These make it easier to curve and bend the foam.
Last edited by Gordon Johnson; Feb 19, 2020 at 09:09 AM.
Feb 18, 2020, 11:35 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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Installing the fuselage sides. Apply Uhu to all joints, install in slots, and then use thin strips of masking tape to hold together while it dries. I use green tape. The blue tape is too strong and leaves marks on the foam as it peels off a bit of foam.
Feb 18, 2020, 11:38 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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Next the windshield frame is installed. This serves to pull the forward upper part of the fuselage together because the front cabin windows tilt in slightly on a Monocoupe.

And, now it sits over night for the Uhu Por to completely dry.
Last edited by Gordon Johnson; Feb 19, 2020 at 12:21 AM.
Feb 19, 2020, 12:38 AM
Aircraft Designer Guy
AJWoods's Avatar
Really impressive work Gordon!
Latest blog entry: Star Wars A-Wing Submarine
Feb 19, 2020, 09:19 AM
in pursuit of low wing loading
Gordon Johnson's Avatar
Thread OP
Thanks Adam. It's inspired by your Cub. It's only taken me 10 years to get around to doing this plane. The full three-dimensional fuselage out of foam is the most difficult foam design and construction I have ever done. No wonder I've done so many skeletonized profile planes. They are way easier!

Do you remember when you did a profile Fokker DVIII with a round cowl and I did a profile Nieuport 17 with a round cowl? I'm using those techniques again for the round cowl on this Monocoupe, except with a full fuselage behind the cowl this time.

The scale'ish details such as a round cowl, wheel pants, wind screen and side windows, etc are going to add weight to this plane. I'm doing my best to minimize them. But, I know they will add up. The horizontal former just under the windows in the cabin insures the fuselage is not assembled twisted or crooked. But, that is also where I will glue the printed Calvin and Hobbes pilots inside the cabin.
Last edited by Gordon Johnson; Feb 19, 2020 at 01:59 PM.
Feb 19, 2020, 08:10 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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After curing over night, time to wrap the fuselage around the area before the firewall. At this point I am switching from Uh Por to FoamTac so I do not have any yellow in the glue. The pieces are oversized, so I trimmed one, glued it in place. Then, trimmed the other side, sanded to fit, and glued in place.
Feb 19, 2020, 08:12 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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The upper rear deck and fuselage sides have tabs to assist with assembly. These required some final sanding to fit, and then it goes together easily.
Feb 19, 2020, 08:16 PM
in pursuit of low wing loading
Gordon Johnson's Avatar
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The bottom deck and belly of the plane is one piece, and the only tab is up at the firewall for centering purposes. The edges of the sized between the front and back cabin former needs to be sanded at an angle, the same angle as the curved formers are where they meet the fuselage sides. The bottom deck/belly is oversized. It will get glued on, and trimmed and sanded to fit after the glue cures.

At this point I also cut two rectangles of 3mm Depron and glued in behind the landing gear ply for a bit more reinforcement.
Feb 19, 2020, 08:28 PM
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Petefoss's Avatar
Looking great Gordon!


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