Balsa F-22 - RC Groups
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May 07, 2017, 02:36 PM
AndyKunz's Avatar
Build Log

Balsa F-22


I was digging around my computer the other day and happened on the plans and photos I made 9 years ago for an F-22 pusher prop jet. This is a pretty quick build, and flies nicely. It should also convert to flat foam construction should you be so inclined.

Attached are the plans as revised after flying.

It took three tries to get the balance right (started out way nose-heavy), but eventually we got it right.

Andy

2009 08 29 First Flight Model F 22 (2 min 8 sec)
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May 07, 2017, 06:26 PM
AndyKunz's Avatar
Construction is straightforward.

Cut the wing pieces to rough shape first and glue them together. I prefer to use tape over the seam, and then apply a thin layer of Titebond (blue, original flavor), then fold it flat and apply pressure to cure it straight.

While that cures, I cut out the remaining pieces. Some, like the fins, will need to be joined in like manner. The wing tips also need to be attached. The chordwise grain helps keep the wing from cambering itself.

Sand the bottom of the wing flat and smooth, then flip it over and sand the airfoil. Rough-sand the strakes and stab to airfoils as well.

Next I marked the centerline of the wing, stab, and strakes and then glue these together. The center reference will be needed as we add the formers. Blend the airfoils where the different parts meet one another.

Andy
Last edited by AndyKunz; May 07, 2017 at 06:45 PM.
May 08, 2017, 04:40 PM
AndyKunz's Avatar
After the glue holding the inner formers has cured, add the fuselage sides and then the outer F2 and F3 formers. Follow this with the outer sides.

Add former F1, aligning the bottom of the former with the inside edge of the balsa sides, then set it aside to dry.

After it dries, you can sand the bottom surface so that the sides are flat/flush with the bottoms of the formers. In the photo you can see that I added some shims onto F5 and to the stab area. Those have been fixed on the plans in the first post.

Add the motor mount tubes (CF or glass), epoxying them to the bottom of the stab. Cut a wire access hole in F4.

Andy
May 09, 2017, 10:43 AM
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jimm1962's Avatar
Subscribed. Looking forward to following this one. Love that it is balsa.
May 09, 2017, 12:39 PM
AndyKunz's Avatar
Thanks, Jim. This is inspiring me to build another - I have a kit sitting on my workbench, waiting ...

Continue construction by starting the bottom sheeting at the air intakes and working to the back, and then from there forward.

The turtledeck is a block of soft balsa or foam, shaped and finished prior to adding it to the top of the wing. Temporarily attach the top block and nose blocks to the fuselage and continue sanding. The nose block needs to be hollowed out so you can add some weight up there - the LiPo pack isn't enough to counter the motor so far back.

Sand the top/nose blocks to shape, and add filler as needed around the seams.

Andy
May 10, 2017, 03:57 PM
AndyKunz's Avatar
It takes a good bit of sanding to get the nose shaped properly. Remember to block-sand flush the corners on the underside of the fuselage. I should have mentioned that earlier.

The canopy can be made from a balsa block. I hollowed it, but could have left it solid just as well because I ended up needing a good bit of forward ballast.

That forward ballast need means a good strong nose is essential. To that end, I used 2oz glass on the interior of the forward section.

Tomorrow I'll cover control installation, and then it'll be done!

Andy
May 12, 2017, 09:10 AM
AndyKunz's Avatar
Temporarily tape the elevator halves on, with the control horns installed. Mark and then open up holes in F4 top to bottom so that the horns can pull inside (full down) and so that there's clearance for the clevis or Z-bend.

Also make a hole for the motor leads to come through.

The ESC in mine is midway between the motor and the receiver, straddling the big hole made in F3. To hook it to the motor I first taped its output leads together and to a long piece of music wire, which I then fished through the motor lead hole. Using that music wire, I pulled the ESC to the back until the leads were outside and then plugged them into the motor (make sure the motor spins the right way for your prop!) Then I pulled the ESC back to the front and plugged it into the receiver.

I opted for elevon control on this plane, so there are only two JR DS285 servos in it. Roll is not as fast as it could be if it had separate ailerons, but it's fast enough for me to enjoy - watch the video.

Install your battery and balance the model as shown on the plans. My first attempts at flight were a big nose-heavy, as you can see in the video. The plans show where the balance ended up - it's still slightly on the nose-heavy side, but it's a great place to start.

I had my best launch results underhanded, between my legs as you can see in the video. We tried dolly launches but the dolly itself was a problem. I'll try it again with the next model.

Andy
May 16, 2017, 07:49 PM
AndyKunz's Avatar
To help cool things off, I opened a small hole in the bottom of the nose. Because the plane has to fly slightly nose high (flat plate wing) there is enough pressure to flow some air in.

The hatch is held down by an alignment pin in the front and a 4-40 bolt into tapped balsa at the rear.

The fins are marked parallel to the center line of the model and blue tape is applied to make it easier to remove the covering cleanly later. After covering the fins are added, using an angle gauge made from the front view on the plans.

Watch the video to show how we launched it (it took a few tries to get the balance right). We also tried some dolly launches - those didn't work at all, but I think it was the soft suspension of the dolly that made steering difficult.

Andy


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