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Aug 17, 2018, 09:33 AM
AndyKunz's Avatar
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Build Log

Mark IV Champ - A Tribute to Hal deBolt - FINISHED - FLOWN

When I was a kid, the Midwest Champ was one of those planes that everybody "had to" have. Although I never built one then, I had a wing building jig like that shown in the plans in the top left corner.

My goal is that someone will be able build on those plans. I plan to make an addendum for the various options rather than a complete plan set, and this thread will document the construction of the changes.

The design will support three different wings:

1) The original wing for RET only,
2) A new version with less dihedral and barn door ailerons and flaps, and
3) A new version with strip ailerons.

I will be able to swap on the wing du jour and fly whichever mode I want. The wings will take either bolt-on or rubber bands; I think I can design it so both are well-supported in both the fuselage and the wing.

The basic fuselage construction will remain the same, but I'll be cutting it on the laser so it has tabs and slots for easier building. There will probably be an optional bomb bay door on the bottom. (The plan is for mine to be a candy bomber for all the little munchkins that appear at our family reunions).

I'll also be doing some minor redesign, such as to properly support bolt-on gear instead of the pop-off-every-landing rubber band style that was on the original, adding a servo tray, and guide holes for Nyrods.

The nose will accept electric (Power 15 size) or glow. I'll be putting an OS .20FP in mine.

The tail will be built-up in order to reduce the need for nose weight, built over the original plans.

And the tail wheel will be supported by a bracket.

Last edited by AndyKunz; Jun 05, 2019 at 07:49 AM.
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Aug 17, 2018, 09:34 AM
AndyKunz's Avatar
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Reserved for plans and flight videos.

Fin: 2018-08-29 AM
Stab: 2018-08-29 PM
Wing Tip: 2018-08-29 PM
Gear: 2018-09-07 PM
Windscreen: 2018-09-23 PM
Bill of Materials: 2018-10-06 PM
Last edited by AndyKunz; Oct 19, 2018 at 08:09 AM.
Aug 17, 2018, 08:08 PM
Registered User
You have my attention, I've thought of doing something similar and a good choice of model as well.
Aug 17, 2018, 08:34 PM
B for Bruce
BMatthews's Avatar
I've got one of the TMRC Champ kits here and was looking at building it this winter. I didn't know how I wanted to do it. Got enough RET old timers around that going that way doesn't thrill me. Thought about rudder only with throttle but I've got a little .049 model of my own design that has a lot of Hal's inspiration in it. And what's rudder "only" if we have a throttle to use to bail out of trouble, eh?

So your idea of reducing the dihedral and going with barn door ailerons and flaps hit a nerve. I'm liking that idea. Perhaps I'd even set it up for towing 2 meter gliders?
Aug 18, 2018, 06:31 AM
Registered User
The original kit had a built up stab with no sheeting. So was the rudder. The wing didn't use any te stock. It used sheet on the top and bottom. The fuse was open behind the wing . Look at the Rebel plans. I believe they are on the Outerzone
Last edited by Al M; Aug 18, 2018 at 06:37 AM.
Aug 18, 2018, 07:32 AM
AndyKunz's Avatar
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Thanks, Al. I'm working from the Mk III plans, in case that wasn't clear from the initial post.

The RET wing for this version uses 1 x 1/16" sheet top and bottom for the TE. The stab will be flat, not airfoiled like the Rebel - must easier to build and keep straight. The only wing that will be using and "TE stock"-like material is the strip aileron version.

Aug 18, 2018, 07:35 AM
AndyKunz's Avatar
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Bruce, this will be my RET plane.

I can't wait to have a plane with three wings. Sure beats a biplane!

Aug 18, 2018, 10:24 AM
Culper Junior
Looking forward to this Andy. I have a flying Champ, it would be neat to have another wing with flaps to fool around with.

Aug 18, 2018, 05:55 PM
AndyKunz's Avatar
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I ordered several sets of the OZ plans from Hemi Killer. The price was right, but more importantly, the DIMENSIONS ARE RIGHT!

The fuselage CAD is about done. It will be super quick - it's all tabs and slots for perfect alignment.

Aug 28, 2018, 08:59 PM
AndyKunz's Avatar
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I've been on vacation for over a week. Sunday afternoon I cut the parts on the laser for the RET version I'm building. Monday morning I was greeted by my computer saying "No boot partition" (or some such) and I've finally gotten the machine all back to life, while doing other things like cutting grass, fixing the clothesline, cleaning the shop, ... You know how it goes.

Tonight I finally got to pop the parts out of the sheets and started gluing them together. I'm starting on the fuselage, laminating the firewall and first former. While those dry I inserted the other formers into the notches cut for them in the fuse bottom sheet.

So far everything fits fine. I will make a couple small changes to some parts so they are more universal for glow vs. electric. I'm building for glow.

Aug 29, 2018, 03:48 PM
AndyKunz's Avatar
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Started some serious gluing in on the model today.

I started by dry-fitting the front end. This ties the landing gear, wing mount, and powerplant together. The firewall is the only difference here between the glow and electric versions.

After confirming the fit, the parts were disassembled. The side doublers are added to the fuselage, taking care to align the LG mount cut-outs and the bottom edge of the chin. Next the 1/4" triangle is added along the bottom edge. After the glue dries, lightly sand the triangle/side edge to remove any excess glue.

While that was curing I went about assembling the fin from 3/16" sheet parts. This is one of the places where this plane differs from the Mark III. A single page PDF is available in post 2 for the plans as shown here.

Next I moved on to the wing tips. The triangle-shaped parts T1-T5 are assembled square onto R3.

The firewall that was laminated overnight had the engine mounted onto it using 4-40 blind nuts. There are no holes in it, but there are (now, better) reference lines etched onto the wood that will make it easy to position the motor mount on the firewall.

It's been a few hours, so the Titebond on the fuse sides is cured. Since these parts are all keyed for alignment, you need to assemble them all at once. An extra pair of hands will help. I think this is the only place in the model where a little help could be handy. It can be done without extra hands - my wife was off shopping.

I glued the formers onto the left side and then assembled that onto the bottom (which has some formers on it already). I immediately glued and attached the right side, and pinned things down onto the board. Next I needed to add clamps at several places to keep things tight.

Aug 29, 2018, 08:36 PM
AndyKunz's Avatar
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After the glue dries on the wing tips, the top of R3 and the tips is lightly sanded to conform them to the curve. The wing tip top sheeting is then added to the assembly. If you're working from the kit, the tip sheet splice is aligned with the rear edge of the main spar.

Then I turned my attention to the elevator. The hinge edge is 1/8" laser cut balsa except for the joiner, which is lite ply. Scraps of 1/8" SQ are added as etched on the 1/16" sheet. After that dries thoroughly, the trailing edge is tapered down to the 1/16" sheet. The top piece is added and the edges are taped tightly, and the whole thing is then weighted down to ensure it stays flat. We'll trim sand it to find the stab later on.

That means we need to build a stab! There is a rough outline drawing in post #2 you can refer to. I intended for you to build over the kit plans, but build from 1/4" x 3/8" sticks instead of being over-sheeted. The parts are not an exact match to the original drawings, but are close enough.

Instead of a butt joint at the center of the leading edge, I opted to go with a scarf joint.

Back to the fuselage!

The top has 1/4" SQ stringers as you can see in the photos. These are much lighter than the stock shown on the original plans, and while there is a slight difference in strength it really won't matter much.

After the stringers are in place (I didn't wait for the glue to cure), I attached the sides of the cabin and after fuselage. The cabin portion is added first. Take care when adding them to make sure that there is wood of F3 for the rear portion to glue to. In the old days we used 1/4" triangle on the rear portion, but that's not needed if you are careful at this point. The front portion is flush with the front surface of F2.

The rear top sides were added last. They are NOT attached to formers F4 or F5, only to F3 and to the top edge of the side. I use tape on these joints just as if I were splicing the wood earlier. If you are careful there's no reason you couldn't have assembled the sides before adding to the bottom, it's just different.

There are now more PDFs in Post #2 for your review.

If I hadn't been editing the plans and farting around on RCG all day I could have framed up the wings too.

Aug 30, 2018, 01:12 PM
AndyKunz's Avatar
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This morning the first thing I did was remove the stab from the plans and add a piece of 1/4" SQ in the outermost bay. The intent is to help strengthen the tip against the compression of the covering. It's not exactly the same as shown on the PDF in post 2, but then "plans are just suggestions."

After that I removed the excess wood from the gear mount area. I then sanded the sides so as to carry the rounded shape of the firewall back. I then glued a sheet of soft 3/32" to the bottom, securely at the gear mount and just tacked to the firewall.

I then started on the wings. I'm building over the original plans, using them for rib spacing. The top spars all need to be notched, as shown. This allows them to fit under the wing tip sheeting. I put about 1/4" to 3/8" under there. The LE needs the same thing on the top side.

There is a dihedral block in the kit to set R1's angle properly.

If I had thought a little farther ahead, I'd have made the wings first. That would have saved me several pieces of 1/4" SQ. Instead of using virgin pieces on the fuselage, I could have used the leftover portions from the spars and LE. I guess that's why we build prototypes!

Aug 31, 2018, 07:04 PM
AndyKunz's Avatar
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One thing I forgot to do earlier was add a rib R1 at 1.5" off the root rib. This is to provide extra strength for the rubber bands. I hate it when they crush wood. In the later photos of the wing you will see this rib in place.

After the spars are all in place, I added web between them over the outer 5 bays. The inner portion will have a ply wing joiner that goes in, as shown in the photo. Test fit this, and sand it as necessary to make it snug. You also need to remove the dotted section of the inner two R1 ribs so it can slide through them.

Then add the 1/16" sheeting for the center section. I do the bottom first and let it cure, then the top. After that glue is good and cured, trim off the excess spar and sheeting material and sand so that R1 is flush with them. This allows you to dry-fit the wing panels together.

In earlier steps you saw that I added the chin sheeting, glueing it to the fuselage at the gear mount but only tacking it to the firewall. After that glue cures I use lots of hot water and bend the wood to the firewall curve. It split on each side, but not too badly. I'm happy.

After that cured, I coated the interior of the nose with Z-Poxy Finishing Resin to fuel proof it in case the tank ever leaks.

I'll be off most of tomorrow, so I don't expect to get anything done. Celebrate the end of summer safely!

Sep 03, 2018, 12:29 PM
Registered User
Really enjoying this build Andy, would love to build a Mk IV Champ someday.

Photo of my Champ Mk III that I still fly often, and an in flight photo from this past Saturday of my replica 1952 Live Wire Sr at the VR/CS Spirit of Selinsgrove Reunion.

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