misfitsailor

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This morning I flew my propane powered airplane for the first time.

I have seen full-size powered paragliders powered with propane, but I have not seen anyone else fly a piston engine R/C plane on propane. I think this is a first!

I converted a new 40cc Briggs to R/C, then adapted a Lehr propane carb and regulator. (I had converted a Lehr 24cc engine first, but it had no power, so I moved the carb to this engine.) Power is moderate, 7000 rpm on 18x6 for a static thrust of 14.5 pounds. (20x8 yielded only 5300 rpm) A standard 14oz propane cylinder resides in the fuselage area normally used to house an expansion exhaust. It can be swapped out in a couple of minutes, and can be refilled at home.

The airframe is a 30% Yak that came up for sale cheap. (I hope to build more of a "floaty" airframe for this engine someday.) The all up weight of the Yak is 19 pounds 8 ounces. Take offs look just like the Spirit of St Louis, but it does fly! The engine starts easily, and runs reliably. With propane, throttle response is instantaneous.

The purpose of this exercise was merely to see if I could make it work!

1QwkSport2.5r

Now THAT is cool. Kudos!

adrian222

My Feedback: (1)

What flight time do you get?

aspeed

How is it lubricated? Good to see some fresh ideas.

1QwkSport2.5r

Looks like a wet sump oiling system. Note the oil cap with the two posts on either side of the cap. Very common among small Briggs 4-stroke engines.

misfitsailor

My Feedback: (6)

Yes, it's wet sump. I don't know the run time potential yet, my guess is 90 minutes or more with this airframe. This is the worst type of airplane possible for duration testing, as you have to really fly it all the time. For that I would prefer a huge 3 channel design that I can trim to fly in a big circle overhead, hands off. I could save some weight if I modify a propane cylinder shorter, as I carry much more fuel and tank than needed for normal flying.

I have also a converted Honda GX35 (also wet sump) that doubtlessly would have made greater power on the propane, but I wanted the novelty of flying a plane with this flathead engine.

av8tor1977

My Feedback: (6)

Pretty neat. I was wondering when someone would get around to trying this. Looks like besides your propane tank, that regulator could do with some downsizing and lightening as well. The Honda engines work pretty well, and are all position, but low on power. I'm guessing they have more power than the flathead though. I'd have to look back through my posts to see what my GX31 that I converted turned. For real fun, try a Stihl Four Mix engine, as they are quite powerful. Well, on second thought that wouldn't work without coming up with an oiling system because they use oil in the gas like a two stroke.....

AV8TOR

Scota4570

I wonder if it would run on butane? The bottles are smaller and of lighter construction.

I converted a Briggs a while back. It gave 5700 rpm with a 20x8 running on gas. You are not far off with the propane. I also did a poulan 4 stroke. It gave 5400 with the 20x8. It is much lighter than the Briggs. I saw the Lehr brand propane weedwackers on clearance about a year ago. I almost bought one to mess with.

I would probably make an aluminum refillable tank. I can't advise that due to possible bursing hazards, just saying what I would do.

dcflysrc

Very Cool! Great to see that you were able to continue on with this idea and congratulations! I'm surprised by your choice of airframes for this project and wonder how long it will be before your new trailer arrives. LOL! Take care and hope to see you sometime soon. DON

misfitsailor

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Don, I am more surprised than you by my choice of airframe! This one came up for sale cheap at the club field, and I thought I would give it a try. The 3D guys probably think this is a sacrilege! By removing one stab (and the wings) I can actually get this thing into the Jeep! The rudder is at the windshield and the prop is at the tailgate! 1400 sq in sounded like a lot of wing area, but now I long for about 2500 sq in... You know me, I prefer old timers and Lazy Bees.

misfitsailor

My Feedback: (6)

Scota, The Lehr trimmer I converted was too weak with propane to swing a useful prop, but it makes good power with gasoline. I used a Walbro WYK-194 carb, the same as the one I bought for the Honda GX35 conversion. It turned 6400 RPM with a 18x6 prop on gasoline and magneto. Not bad for 25cc! The Lehr is a Chinese clone of the Subaru Robin EH025 engine. Here is a shot of it making wind;

rangerfredbob

My Feedback: (13)

That's cool! looks like something I would do

aspeed

There is a Soda Stream tank for CO2 that may be a bit smaller or at least lighter than the propane tank. They have used odd threads to make things difficult though. I think to get real power, a huge carb would be needed. I never knew there was a propane weedwacker.

Flight Risk

My Feedback: (1)

Hey Misfitsailor, i was hoping to find a thread like this. I happened across a Lehr propane trimmer at a recycle place, tossed in with a lot of dirty 2-stroke trimmers. I first noticed the propane and then that it was a 4-stroke, and it seemed fairly clean and turned over nicely, so for $10 thought it was worth a try for something. It even had a mostly full propane tank. I cleaned it a bit and changed the oil, and it eventually came to life. It's running real nicely now but the throttle needs to be open more than I can set it to idle. I can't find any settings other than the idle screw, and wonder if our 6000 ft. altitude may be a problem. Anyway, I will probably try it as a trimmer for awhile, but am wanting to convert it into something. I may go the gas carb route. and try it on a floater plane. I've always wanted a 4-stroke gasser. I converted a Briggs 29cc years ago but it was only turning a 16-6 prop at 5k or so and is sooo heavy. Since this Lehr even has a clutch I thought an RC buggy may be fun.
Have you ever found an oldtimey floater for your engines? Also I noticed these engines were rated at 101 octane. Is that typical for propane, and would that mean these are higher compression than a normal engine? I notice these came out about 2009 and were gone in a few years. Now Lehr seems to be only doing propane outboard boat motors.

thx
Rod

misfitsailor

My Feedback: (6)

No, I am still in the market for some big 3 channel design to put my Honda 35cc in.