Engine selection - Ultralight

I just placed an order for the tubing to build my first ultralight. It's a really simple, back-to-basics, design. The suggested engine is a 2-stroke that's not in production any longer that is about 65# plus the weight of a re-drive. I never have had much luck with 2-strokes so want to go 4-stroke and have pretty much narrowed my engine selection down to 3 different engines. All would be used tractor configuration and direct drive. They are;

Kohler 27 HP Command (94#)

Briggs and Stratton 23 HP (77#)

2A042 Teledyne 18-20 HP? (about 79# stripped, I understand)

I'm basing my assumption that the plane will perform to suit me with any of the engines on others' reports of performance figures with this HP level in ultralights, and also some performance calculations based on wing span, gross weight, climb and cruise performance, etc.. I expect to have to work out weight and balance since any of them are heavier than what's spec'd. I also have done enough math on the construction side of the project to feel confident that I can come in under the magic 254# weight limit.

That was a long way around to my question and it is....
Does anyone here have experience with, or knowledge of, any of the engines listed and would you either recommend, or dissuade me from using, any of them? Here are my thoughts on the various engines.

2A042 Teledyne - The 2A042 is attractive as a inexpensive choice and it "looks like an airplane engine". The Yahoo groups on the internet that discuss the 2A042 and other surplus engines have several members reporting that they are currently flying them and THAT is very attractive from a experience and support standpoint. I talked with TN Props this AM and they verified having cut props for them, and they were of the length and pitch I had heard about on the Yahoo groups

Kohler - A local seller of commercial engines, who I trust, has a preference for the Kohler as being smooth and economical, compaired to the B&S. It is the one that needs to go on the biggest diet though. He does feel it can be stripped of a lot of weight, including the electric start, and thinks it could get in the +/- 80# range.

Briggs and Stratton - It is very attractive from a weight and price standpoint. From a #/HP standpoint it would also seem to be an attractive choice.

I'll look forward to getting input and certainly appreciate you sharing your knowledge and experience. I'm asking my question here since it seems there is an absolute wealth of knowledge on this board, and I'd feel that opinions given would be well-informed and un-biased.

Thanks

Lynn

The thought that comes up first, is to look at the torque curve, and pick the one that gives best hp and torque at the speed your prop needs to turn.
Might not be worth two cents, but others will speak up.

RonL

I'm with RonL, at what rpm do the engines achieve those HP figures and which has the best ft/lb?

Thanks for the suggestions to look at the torque and HP charts. I know that peak HP at 3600 RPM is not very useful if the torque curve does a nose-dive at 2200. I'll check it out and post back with some info. What I learn may make the choice more obvious. Then again, it may tell me to look at something else. The engine/prop is probably going to be 50% of the cost of my ultralight and I'd like to make the best selection.

Having another look at the engine choices... not much bang for the weight there. Are you really sold on 4-stroke? 2-strokes tick a lot more boxes in the ultralight category, and you get a lot more choice.

I have a rotax 377 in a Hi-Max. I always worry about the engine quiting if I make a rapid power reduction. Due to lubrication starvation. I have heard of others that have had that experience. I don't know first hand. It may be a myth. The noise level is unreal on the old 377. I think the newer version must be a lot less. The power is good at estimated 35hp at hi rpm. I would change to a 4 cycle if I could. Good luck on your project. Others I am sure have more experience that I do with 2 cycles.

Thanks again for the responses. Regarding 2-stroke vs. 4-stroke, I wouldn't, and haven't, completely ruled out a 2-stroke but certainly have a strong preference toward the 4-stroke. Part of it is the sound issue, and I know that's petty. Part is the reliability question and I'm only basing my skepticism on things I've read that talk about engine-outs all too often with 2-strokes. Maybe it's because of the % in use on ultralights, maybe it's poor maintenance...? Part is familiarity in that I feel fortunate when my daughter's 80 Suzuki 2-stroke is running OK and I don't have to try to fix it. I finally switched it to pre-mix and all is well, for now at least. On the positive side of a 2-stroke is the advantage of their power in a more compact, light-weight package.

That being said, below is some HP and torque data on the various engines I listed before plus one more;

2A042 Teledyne
Peak HP (as best as I can tell from info found) 17.5 @ 3600 with 24 Ft# torque
17 HP @ 3000 with 28 Ft# torque
Peak torque 32 Ft# @ 2000 with 12 HP
Dismal figures compaired to the rest!

Kohler 27 HP
Peak HP 27 @ 3600 with 37 Ft# torque
24 HP @ 3000 with 41 Ft# torque
Peak torque 41.5 Ft# @ 2800 with 23 HP

Briggs 23 HP
Peak HP 23 @ 3600 with 30 Ft#
21 HP @ 3000 with 32.25 Ft# torque
Peak torque 32.7 Ft# @ 2600 with 19 HP

New to the list - Honda 24 HP
Peak 24 HP @ 3600 with 33.5 Ft# torque
21.5 HP @ 3000 with 36 Ft# torque
Peak torque 37.5 Ft# @ 2500 with 18 HP
I had to do some conversion of the torque figures on the Honda to Ft# ratings but think I converted them right. It is about the same weight as the Kohler and has probably the flattest HP and torque output of the lot.

All of the V-twins present a similar, large frontal area which would of course be a disadvantage from a drag standpoint. Also their size would present a bit of a problem with forward vision. The ultralight design I'm planning has the engine mounted on a fuselage tube in front of the high wing, and to keep the whole plane from getting too top heavy I'd feel the engine mount would need to be built to drop the crankshaft centerline well below the centerline of the tube, right into my field of forward vision. That makes the weakest HP engine, the 2A042, very desirable with it's more horizontal configuration.

The engines range from $650 to about $1800 in cost. I'm not wealthy but won't let money make my decision. I want reliability from whatever engine I end up with, 2 or 4 stroke.

I feel that even the lowest power unit will fly my ultralight (based on reports of 2A042 powered planes of similar weight). I'd like to hear of anyone's experience with any of the engines listed, recommendations or warnings.

Thanks, in advance!

Lynn

My preference would be the Honda. I've been riding a Honda 250CC bike for the past month on the highway - it's a loaner from my mechanic, and despite riding it for two hours each day at the red line, I can't seem to break it! What a bore! Honda has a reputation for excessive reliability.

One last thing you might look at (if you like doing stuff like this) is to make a list on each engine, they all have their peak hp at 3000 rpm, compare the bore, stroke, and compression ratio, (if you can find c. ratio) this might give you an idea of what air/fuel mix is giving what power. Each pound of fuel has a BTU value of just so much, all this being said, you can likely spot if one is really a gas hog before you buy it.

Of course you have to consider which might have the longest life ( most likely the one with the most weight )

RonL

Thanks....I have thought about doing an overlapping HP and torque graph of all the engines using different color lines for each engine in consideration. Might be a "busy" graph but the information would be easy to compair. I also need to decide what performance I'm willing to accept. The 2A042 is the least powerful but can still make the plane fly just a little more slowly than the others. It seems to be considered, by some, a real workhorse and stone reliable. It, and the larger 4A084 appear to have more useage than the V-twins by what I've found searching the 'net. I seem to be off the beaten path already, wanting a 4-stroke, but at least the 2A042 path has a few more tracks....I hope they aren't marks left by un-planned landings!

Regarding fuel consumption; Since it's an ultralight with it's relative restricted flight area, local sight-seeing, 5 Gal of gas will probably fly me as long as I'd care to stay in the air at one time. I certainly don't want a gas hog but (pardon my opinion) any of the 4-strokes should have a lower Gal/Hr burn than a 2-stroke.

Thanks to all...

Lynn

Lynn, I'm building my latest ultralight with the Honda GX670TDW, it's a superb engine. It's a 90º twin as well, so you can look down the "V" and have the cylinder heads protrude out either side of the cowling. I'm having a 3 angle valve job done, and likely port and polish on the heads too, it should turn almost 30hp at 3600rpm by that point. It's not an overly heavy engine once all the cooling ducting and fan system is removed, and has a TON of features the others you've listed largely don't. It has high pressure lubrication, aluminum connecting rods, a flat torque curve, an oil cooler, an automotive oil filter, is already set up for remote throttle and choke (the TDW model), a 20 amp charging system, and stand alone unit ability from the get go. Plus, it is likely more fuel efficient than a lot of the lower power engines listed.

Best part? Tulsa Engine Wharehouse has a few on sale for $1199 including fed ex freight to your door. I bought one, considering a second. It's a smoking deal, 1/2VW type power, much better engine ready to roll, cheap, and with great features.

I'm also trying something new with mine... nitrous oxide. I'm setting it up with a motorcycle nitrous oxide system I'll use on climb out. I'll give it 10-15 extra HP for take off with a wet nitrous system.

I just stripped all the housings, cooling ducting, starter motor assembly, air box and all the other things you won't use on the GX670 in a plane off and it now weighs in around 75lbs.

I was considering the use of a Briggs V twin in the future. I was wondering if you plan on keeping the flywheel on the Honda as-is or using a lighter version. The flywheels add considerable weight to the engine but also dampen out the torque impulses to the propeller. Any thoughts?

Ardent....Are you building a Hummel Ultra Cruiser that you're using the Honda in? I visited Hummel in Jan. and they mentioned someone doing that and wondered if it's you. I have the UC plans, ordered some of the aluminum for bulkheads, etc., enough to get started building, and then had 2nd thoughts about making my 1st plane construction project one of that magnitude. I am started a little bit now finally on a Beaujon Minimac ultralight. Very simple but hopefully I can fly it in much sooner. I still do want to build the UC "someday". I'll be watching various groups and forums for your progress and results with the Honda. Best wishes.

Lynn