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Henry Mignet HM 360 Project

By Gene Frost, EAA 431006, for Light Plane World


What got me started on building an HM 360 Pou de Ciel (Flying Flea) goes back over 55 years to the mid to late ’50s. Back then, we kids were called ramp rats, and we were always welcome because we would do any kind of work for a little flying time, or better yet, some flight instruction. One day I saw a picture of an HM 14 on the front page of a magazine in the airport office, and I said to my friend John, “If I live to be an old man, by gosh, I’m going to build me one of those planes.”

Yep, it’s that simple. Now 55 years and 10,000-plus flight hours later, here I am. I still can’t believe I’m in one piece after all I’ve done. It proves God does have a sense of humor, to let me live to see the follies of my youth.

I purchased plan set number 300 from Henry Mignet’s son Pierre about six to seven years ago. My plans were in French and they were beautiful. So good, as a matter of fact, you could have built the aircraft just by looking at the pictures! Henry was by trade a master wood craftsman and furniture manufacturer. I made no major or significant changes from the plans. The more I studied the drawings, the more I saw the logic and just good common sense in everything Henry did. This was to be proven to me over and over more times than I would care to admit! Every time I attempted to take a shortcut or do something my way (some times twice), I felt like Henry was looking over my shoulder saying, “I did not design my airplanes to be built by imbeciles. Do it my way and it will be easy.” I heard the small voice of the master craftsman.

Building the Wings
I did use a bit of Stephen Wood’s Sky Pup technology in my building methodology. Ribs are 1-inch-thick construction foam (pink) with 1 x 1/16 three-ply wood cap strips glued with Titebond III to the foam. I did this for all the “A” ribs. There are 15 total for the front and rear wing center sections. This was done in an effort to save both a little weight and mostly time. Not much if any was saved. If I was to do it over again, I would do it the old-fashioned way: Just make a rib jig and cut and glue. It can’t get any simpler, and it’s easier and more fun, too. Lesson learned again. Do it Henry’s way! I still hadn’t totally learned. You cannot, as in no way, make the folding elliptical wingtips with foam ribs. You’ll never get your twist and washout correct!

Main wing assembly
First setup of the main wing assembly.

I checked with two structural aeronautical engineers, members of another EAA chapter, on how I could devise a method to test the results of the glue bonds, just to be safe. They were an awesome help. Got to love our EAA! I followed their instructions and conducted several shear tests. I had been informed that if a pull test between 1/16 plywood and the foam held to at least 45 pounds before it sheared, it was very acceptable. Both times I stopped, havingnever being able to get the glue bonds to part in shear at (hang on) 105 pounds. I applied the glue by rubbing it on with my finger so as to get good saturation in the foam. Then I did the same with the cap strip. I suspect that the wood, because it breathes, allows the glue to fully set up overnight and cure, thereby completing the bond. After six years the test samples are, if anything, stronger. Even now the wood can be pulled away, but in doing so it will take big chunks of foam with it.
I found out that if you just follow the plans it will come together fairly easy, correctly, and faster! When I was a young lad, the only way you could build a model airplane was from scratch. Stick and tissue were the only materials, period. So, from my point of view, the wood and fabric construction of the Flying Fleas is easy to build. The reason for much of the lamination of the primary structure was simply because of the sometimes poor quality of wood that was available to them at the time. By cutting shorter pieces, and then laminating, they were able to gain strength plus inspect the wood.

Flea wingtip
Flea wingtip showing curved construction of the tip.

Spruce certified for aircraft building can cost as much as $10 a board foot. Or you can educate yourself with some great literature and articles on woods from our own source, the EAA bookstore. I found great spruce from - of all places - sheet-metal shops just by looking at the wooden shipping skids that the sheet metal was delivered on from the Oregon and Washington state areas. Yes, the pieces are usually short (2 x 4 to 4 x 4 sizes), but when it has the correct annular growth rings and runout, and you have used your handy-dandy Harbor Freight moisture tester, it is free. Who wouldn’t rip it and use it to save a few hundred bucks in trade for a couple of hours of fun? Surprisingly I found Douglas-fir that met all the correct criteria at high-end hardwood stores and even Lowe’s lumber departments. Of course, you may have to move a few hundred 2 x 4’s and replace the ones that you didn’t select, but for your labor and a few dollars you can literally save $50 to $60 depending on how you rip and use it! There’s a world of fun and education in wood - after all, it’s nature’s perfect engineering material. The moral here is study, read, and learn as much as you can, for life is exceedingly fast and short.
The fabric covering will be Superflite for the wings and maybe two coats of aircraft silver paint. I want just enough to provide ultraviolet protection and still keep the weight down. The fuselage presently has only two coats of clear varnish for looks and moisture protection. My Flea will be hangared when not flown, and if traveling any distance it will be in an enclosed trailer that I have just for it.

Prop Turns the Wrong Way
I was very fortunate that recently one of the chapter members sold me a new 38-hp Kawasaki TA440A engine, complete right down to the correct carburetor and tuned exhaust. A few years back another member had given me two redrives. Good fortune, I’d say. The story only gets better for a guy like me whose luck is like needing a restroom that requires one quarter and then finds that he only has two dimes and a nickel. I went on Barnstormers and purchased a left-hand four-bladed 56-inch propeller (needed because of ground clearance). Now comes the funny part, so please have a good laugh on me. I went to the hangar the next day, excited of course, placed the prop temporarily on the redrive just to look at my great find, and lo and behold, it turns the wrong way! I, the maintenance guy, had been thinking of the PTO end of the two-stroke, the seller was a pilot thinking like a pilot. I called and shared the humor with the seller who promptly offered to take it back. I said thank you, but it’s hard to find a good used prop that fits my need for ground clearance. So I’ll just reverse the two-stroke engine rotation, and the propeller will work just fine. After a short pause came the “uh-huh” reply.

Hangar photo shows four-blade prop and mockup of the pattern for the windshield.

So how do you reverse the Kawasaki engine rotation? Simply reverse the recoil starter from right-hand pull to left-hand pull. Next, take off the magneto ignition and flywheel and replace it with a 12-volt DC electronic-triggered ignition system (saving 10 to 11 pounds). Next, reverse the timing from 22 degrees before top dead center (BTDC) hand rotation to 22 degrees BTDC left-hand rotation. If interested, check out this great website about ignition systems for small engines at www.GardenTractorPullingTips.com. If you're an EAA member, call 314-520-2815, and I’ll be happy to share what I have learned and have done to the Kawasaki.

The original HM 360, and all that I am aware of, were powered by VW 1200 to 1600 engines. I have spoken with several people who worked and were employed by Henry Mignet. However, I haven’t found anyone that had built the HM 360 as a FAR 103 ultralight. You can find plenty of HM 290s or 293s worldwide that were built as ultralights (many with VW engines), but no true HM 360s built as ultralights.

This completed VW-powered HM 360 shows what mine will look like.

This was one reason that I decided to make my little boy’s dream of an HM 360 come alive as an ultralight. Most of 290s, 293s, and 360s were of the same wing area (140 to 150 square feet) and overall dimensions. I came to realize that if I simply reduced the average weight from 370 to 380 empty by replacing the four-cylinder VW engine with a lighter engine, this could be a fine FAR 103 ultralight. Right now I’m on track to come in at 252 to 254 pounds.

There are many excellent websites with information about the Flying Flea. One of the best (because it’s in English) is www.NestOfDragons.net/flying-flea. Also check out PouGuide.org and the Jolly Roger website at Jolly.Roger.free.fr. It has a collection of photos of completed Flying Fleas and a link to flight simulator software for the unique airplane. There’s a great video of an HM 293 in action here on You Tube .

Gene Frost

Everybody has a favorite; to me of course it is Henry’s 360. It was the prettiest of all his designs, plus he had finally worked out all of the issues of his previous designs. Before then, there was the nasty habit of whenever the control stick was pushed too far forward, the aircraft just continued over to the shortest route home, usually straight down. Everybody knows that makes for a hard landing! The aircraft even seems to cuddle you when you sit in it. It’s truly a labor of love. To me it looks like a beautiful butterfly. The only aircraft in my life that perhaps I loved almost as much was the series of Bell AH-1 Cobra helicopters that I flew for over 2,000 hours. It was called the “Snake” for a very good reason, and it could bite or kill very quickly if you did something really stupid.


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