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Oct 29, 2017, 07:42 PM
Jer. 29:11
jeffsch's Avatar
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Build Log

North american f-82 twin mustang (41" wingspan)


Sometimes inspiration comes from a picture, and in this case, a picture of a P-51 Mustang and F-82 Twin Mustang flying in formation. I have enjoyed building dz1sfb's SEMFF WWII models, and I wanted to build an F-82 Twin Mustang in the same scale as the SEMFF WWII P-51D.

The model has a 41 in. wingspan, uses two 300-class motors, a pair of 2S batteries, and comes in around 18 oz. all-up weight.

Kits include eleven cut sheets of Model Plane Foam and are available for $40. Send me a PM to order. (Shipping details to be determined.)
Last edited by jeffsch; Jan 31, 2018 at 07:53 PM.
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Oct 29, 2017, 07:42 PM
Jer. 29:11
jeffsch's Avatar
Thread OP

Shopping List


Here are the parts I used on the prototype.

I did my shopping at Heads Up Hobby because they have a good selection, include prop test data, and have fast and inexpensive shipping (at least here in the U.S.)

* Two 300 'Blue Wonder' 1600kv motors
http://www.headsuphobby.com/HURC-300...or_p_1980.html

* Two 12A ESC
http://www.headsuphobby.com/Sky-Powe...EC_p_1543.html

* Two APC 7x4E propellers
Feel free to substitute propellers based on your experience or Heads Up RC propeller test data
http://www.headsuphobby.com/APC-7-x-...er_p_1089.html

* Three 9-gram servos
http://www.headsuphobby.com/Emax-8g-...vo_p_1180.html

* Two 2S 800mah batteries
To keep the model balanced laterally, you'll want to put a battery in each fuselage.
http://www.headsuphobby.com/74v-850m...ry_p_2353.html
Last edited by jeffsch; Oct 29, 2017 at 07:54 PM.
Oct 29, 2017, 07:43 PM
Jer. 29:11
jeffsch's Avatar
Thread OP

Other F-82 Plans and Kits


Last edited by jeffsch; Jan 10, 2018 at 07:38 PM. Reason: Found another related build thread.
Oct 29, 2017, 07:55 PM
Jer. 29:11
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Building the Fuselage


The fuselage assemblies should be built first.

Each fuse is created by laminating seven layers of foam; each layer is numbered.

Start by removing the tabs that hold the seven parts of each fuse from the kit sheets. You might want to leave the hatch and servo covers attached to the outside laminations -- Parts 1 and 7 -- for now (and remove them later).

I recommend using a spray adhesive like 3M 77 -- a light coat on both pieces is all that is required. (I have used White Gorilla glue for this, and while it adheres well, since it dries harder than the foam, it is difficult to shape afterwards.)

While gluing, the alignment of the motor mount and wing slot in each layer is fairly critical. Careful work here will save time later getting everything straight. To help keep things lined up, I made a simple jig from a scrap of foam that was the same length as the wing slot; I held the jig in place while I glued each layer to the others.

Laminate the fuse parts from the middle toward the outside. First laminate Parts 3, 4, and 5. Make one left and one right fuse! Then glue in the tongue depressor reinforcements just above and forward of the wing slots. Then laminate Parts 2 and 6.

In the second build, I glued the laminations for one fuselage with Deluxe Products Foam to Foam glue. The other with 3M77. The came out nearly identical in weight at 71 grams (2.5 oz) each (before sanding or shaping).

Before adding the outside laminations -- Parts 1 and 7 -- you may wish to attach your motor mounts to the 1/16" light ply mounts and glue them in place. This would also be a good time to double check the length of your motor mounts and make any adjustments necessary. The kit places the motor mounts in the right place for the recommended motors to give a close gap for a 1-1/2" spinner.

After all the layers are glued (and the glue has set up), it is time to shape the fuselage by sanding. Find a picture (or two or three) of the F-82 Twin Mustang to use for reference, and round the fuselage as much as you have patience. The model should fly fine without any shaping, but it does look nicer if you do. The shaping saves a (little) bit of weight. In the second build, a fuselage dropped by 5 grams (0.2 oz) after shaping.

If you have a mind to do it, this is also a good time to spackle the fuse. I like to use the Freddie B's miracle whip, but here are some other options.

And, this is a good time to paint the fuse. Keep in mind that a lighter plane will fly better.
Last edited by jeffsch; Jan 31, 2018 at 07:49 PM. Reason: Adding build pictures and notes.
Oct 30, 2017, 08:18 AM
Retired CAD guy
birdofplay's Avatar
Last time I saw the F-82 was at Lakland AFB, TX back in 1968.
It was part of the Base museum collection.

Although at first glance it looks like they just joined two Mustangs
there are lots of differences.

Looks like you've captured the essence of F-82 ness ;>}
Oct 30, 2017, 08:32 AM
Jer. 29:11
jeffsch's Avatar
Thread OP
Thanks Bob! It sure looks the part when flying.

I saw two at the USAF Museum after a pilgrimage to the Toledo show. I was surprised how big they are in real life.
Oct 30, 2017, 12:39 PM
Retired CAD guy
birdofplay's Avatar
Dayton is a favorite destination of mine now that I live closer than WA state.

I believe that the F-82 from TX was relocated to Dayton when the museum built more space
a few yrs back.
Oct 31, 2017, 07:39 PM
Jer. 29:11
jeffsch's Avatar
Thread OP

Building the Wing


The wing has two parts, the main wing and the KF step. For packaging reasons, each part is made of two outer and one inner span that fit together with a jig-saw cut. When finished, the wing seams will hide inside the fuselages.

The wing and the KF step each have a groove cut to fit a 5 mm x 1 meter carbon spar. The center spans also have a wide groove cut to allow servo wires to pass from one fuse, through the wing, to the other fuse.

To help keep things lined up well, it's best to glue the wing in a single session. Glue the outer and inner spans for the main wing together. Then glue the outer and inner spans for the KF step. Then glue the spar into the main wing, and glue the KF step over top of the main wing. Keep the wing and KF step aligned with each other with pieces of tape, apply weights, and set aside until the glue has thoroughly cured.

Pro tip: Sparks points out that when you pull tape off foam, it can leave a rough finish you have to deal with later. When removing the tape, he recommends using a hair dryer to soften the tape's adhesive.
Last edited by jeffsch; Dec 19, 2017 at 12:43 PM. Reason: Add build pictures
Nov 21, 2017, 01:56 PM
Jer. 29:11
jeffsch's Avatar
Thread OP
The fuselage hatches are held at the front with a Popsicle stick and magnets at the back.

Cut a 1-1/4" long section off one end of a Popsicle stick and glue it so half is on the front end of the hatch.

For the back of the hatch, I used 1/8" magnets, like these from banggood.com. You can cut holes with a hobby knife, but you might want to invest in a piece of 1/8" brass tubing; sharpen the end of the tubing, and it cuts nice holes in foam.

To make it easy to open the hatch, cut a 1-1/2" piece of hinge tape, fold over one end, and fasten to the magnet-end of the hatch. When the hatch is closed, you can grab the folded end of the tape to open the hatch.
Last edited by jeffsch; Dec 29, 2017 at 08:48 PM. Reason: Added build pictures
Dec 22, 2017, 01:33 PM
Jer. 29:11
jeffsch's Avatar
Thread OP
At some point, you need to hinge the ailerons and elevator (and rudders if you choose to cut them out). I chose to do this before painting.

Hinge tape works well. Another option is so-called CA hinges, where thin strips of plastic form the hinge and are attached with CA glue.
Jan 04, 2018, 02:15 PM
Jer. 29:11
jeffsch's Avatar
Thread OP
For the second build, I used Emax CF2805 motors, and together with the spinners I found, they are a bit too short. So, I printed a mount that had a 1/4" offset. See attached.
Jan 31, 2018, 07:52 PM
Jer. 29:11
jeffsch's Avatar
Thread OP
A few finishing details.

After you glue the wing to the fuselages, you can fish a string through the slot in the wing between the two fuselages. I do this by tying a small washer to a piece of dental floss and dangling it through the opening in one fuselage, through the wing, until I can pick it up with a pair of tweezers in the opening in the other fuselage. Of course, if you go with two receivers -- one in each fuselage -- you don't need to do this step.

Attached are some pictures of how I hooked up the control linkages.


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