Merlyn Graves’ Kawasaki KI-100 Project


I have been building and flying 144” Kawasaki KI-61 Toni’s since about 1980. My first was powered by a Homelite 5.3 chainsaw that I bought and cut off all the parts until it looked like an engine. It was a real shaker but it did fly the Toni well. Since then I have had three of them over the years. It’s been several years since I got rid of my last one and I was thinking about building another when I became aware of the RCS215 5-cylinder gas radial engine. I had seen it fly in a Stearman, and it seemed the perfect choice for a large scale warbird. Near the end of WWII, the Japanese were unable to obtain any more in-line engines for their KI-61’s and had over 200 complete airframes with no engines just sitting on the ground. The decision was made to covert the air frame to accommodate the Mitsubishi HA-112, a 14-cylinder two-row radial and the KI-100 was born.


Over the last 20 years, my original shop drawings for the KI-61 had either turned hard and yellow or disappeared. I thought the easiest route to go would be to purchase some smaller plans and enlarge them. I bought a few sets from various plan drawers and went to the expense of enlarging one set up to the 144” size required. As I started to get ready to cut parts, it became obvious that like most hand drawn plans; the parts would never fit correctly, especially when enlarged by 25%. It was going to require a lot of tweaking, cutting, sanding, and guessing to get things right. I do a lot of scratch building and this has always been a problem.

I had recently completed a 132” Vulcan Bomber from my own plans that I had drawn in AutoCad. I was extremely pleased with them because everything fit like a glove when I cut out the parts. Thus, I decided to bite the bullet and draw my own for the KI-100. Using three views from a 1977 Arco Publication and a Hasegawa plastic model kit, I set out to draw up a set. It is fairly easy to draw the three views, but that doesn’t give you the fuse former profiles. To get those, I assembled the plastic model fuse and then cut through it at the former locations to get a former plan. Then I enlarge it on a copier to a size that allows me to measure it out and transfer it to AutoCad. 43 hours of drawing time later, I had the plans done.

Reference book
3-View reference
Cad drawing


I decided to begin construction on the fuse first, because I wanted to get it framed to the point that I could start making the molds for the canopy and the cowl early in the project. This would allow me to work on them piecemeal as framing construction went along rather that have to stop everything for 2-3 weeks while I made the molds.

I decided to built the fuse around the engine box and add the remainder of the fuse on a crutch. After cutting all the fuse parts, I found that as I had imagined, the use of AutoCad enabled the parts to fit together so well that I was able to completely assemble the fuse with out any glue what so ever. This allowed me to verify that everything would line up true, before gluing.

Engine box
Engine box and wing saddle

Complete fuse

CONSTRUCTION: Step 2-Canopy molds

Since no canopies are available for this airframe, I will have to vacuum form my own. Since the largest plug that I can get into my over is about 15” land and the finished canopy is nearly 30” long I will have to make it in two pieces.

The hardest part of that process is the making of a good mold. It is very time consuming with a lot of waiting time for things to dry. This is why I wanted to be able to work at it as the project went along. The process that I use is as follows:

1 .Hot wire the basic shapes out of pink insulation foam.
2. Temporarily fix them to the fuse and sand to the final shape.
3. Fill with drywall joint compound and sand smooth.
4. Add balsa end caps to make them over size and additional caps to change any undercuts so that the mold will come out of the finished canopy.
5. Fiber glass with 1.4 oz cloth. Prime and seal until you have a glass smooth finish.
6. Make a female mold plug out of Ultra-Cal 30 plaster. This is done by laying on a 1/8” thick layer of Ultra-Cal. After it has set up, apply fiber drywall tape and more Ultra-Cal until you have 3/8” to ½” built up so it is strong enough that it won’t crack as you handle it. Remove the plug from the Ultra-Cal mold. After it has completely cured, sand out any imperfections. It is difficult to sand so it is important that you have a really good plug to start with. Then prime it with a filler-primer and 400 wet sand it.
7. Wax the inside of the Ultra-Call mold and then fill it with Durham’s Rock Hard Water Putty. I like this product because after you pull it from the Ulta-Call mold and it has cured (7-10 Days depending on the size of the plug) you can final sand it as it isn’t as hard as the Ultra-Cal.
8, Once you have sanded it out it is ready for vacuum forming.
9. I use 0.040 PETG plastic for all my canopies. Some times I use 0.060 if the pull gets too thin.
10. The secret to getting a really clear final canopy is to pull one canopy on the mold. Then remove it, trim all the ragged stuff off and wet sand it with 400 wet/dry sandpaper. Then put it back on the plug and pull another over it. This way it comes out like clear glass.

Front canopy section being cut and sanded
Rough plugs filled for sanding prior to fiber glassing

Plugs ready for first casting

CONSTRUCTION: Step 3-Hortizonal stab and elevators

Since the stab has a symmetrical airfoil, you have several choices for alignment. Usually I glue on little legs to each rib and then build it over the plans. This time I decided to cut the ribs in half and build them on a flat sheet of 1/8” balsa. You actually have to cut out a 1/8” thick piece from the center of each rib to compensate for the balsa center.

1. After gluing the ribs onto the sheet, add the upper spar.
2. Sheet with 1/8” balsa. Turn it over and add the lower spar and sheet the bottom.
3. Add the leading edge and sand to shape.
4. Cut out the elevators, add hinge blocks and cap off the edge with ¼” and 3/8” balsa.
5. I use functional boost tabs on the elevators to minimize flutter, so cut those out and finish the edges.
6. I run the leading edges of the elevators and boost tabs through the band saw at the proper angle and then hinge them.
7. Fiberglass it and it is ready for gluing to the when the fuse is complete

Top half of stab
Sheeted stab

Glassed stab, elevators, and boost tabs


1. I begin wings by gluing legs to each rib to align the center lines.
2. I set up the root, tip, and a center wing on the plans with the top spar in place. When everything is in alignment I glue the top spar to the root and tip ribs. I always built a wing upside down so that I can add servo mounts, retract rails, etc. before removing the wing from the bench.
3. Another advantage of drawing your own plans is that you can set your rib spacing anyway you want to. I decided on a 4” spacing which would give me 17 ribs in each half. Since I buy all my balsa from Lone Star, the sheets are oversized. This allows me to rip them to exactly 4” for use as shear webs. I like to build a box spar as it is extremely strong. Using 3/8” x ¾” balsa spars I glue in each rib while adding the front and rear shear webs. This keeps everything at right angles and automatically puts each rib at the proper location.
4. I cut the shear web between the root and rib#2 at a five degree angle and this sets my dihedral.
5. Next I add the servo rails and tube for servo wires and retract plumbing. I have my local hobby store save the 1” tubes that K&S metal sends their music wire and brass tubing in for use in the fuse and wings.
6. Add the rear spars
7. Sheet the top of the trailing edge and the bottom of the wing from the front spar to the rear spar.
8. Add landing gear blocks. For an airplane of this size, I use Annco retracts. The first set that I bought back in 1980 lasted through all three of my Ki-61’s. They are still available from Ed Cochran at E&J Hobbies.
9. Sheet the bottom from the front spar to the leading edge.
10. Remove the wing from the plans and sheet the top.
11. Add leading edges and sand round.
12. Add wing tips.
13. Cut out the ailerons, and flaps, finish and hinge them.
14. When I build a box spar I use a ½” thick plywood dihedral brace that sides through ribs 1 and 2 between the top and bottom spars.
15. Join the wing, fiberglass the center with 6 oz cloth, and then cover the wing with 1.4 oz. cloth



Completed Wing halves


Join Our Email List

Become an RCWarbrids site supporter by making a donation.


The Web