ive been thinking about doin a conversion and think i have figured every thing out exept one potential project killer. will the an engine designed for glow stand up to the heat of gas? the main question that is probly going to be asked is "what about oiling" well i think i can plumb an engine and using either a gear driven pump (as on a enya 120 gp im playing with) or a tme smoke pump. the engine is normaly just oiled by the blow by from combustion and i think it would get just as much if not more oil by a fairly simple oiling system made by placing a few pressure nipples and one way valves in the proper areas(rocker arms, cam gear, and crank/rod area) and just 1 return line at the bottom of the engine. the system would use a small tank to store the oil. the system would not need to be very complex and a small 1 ounch tank visible thru the cowl would be all you need to monitor fluid levels. since the blow by oil is the only normal oiling system i think the plan ive come up with would provide plenty of oil to the engine. the ignition system is easily obtained and that just leaves the problem or the actual engine componets themselves.....CAN THEY TAKE THE HEAT.

any ideas, experinces, comments appreciated.

There was a group converting just the engine you have to run on gas to try and make an unmanned Atlantic crossing. They seemed to hold up well running a gas/oil mix and very easy on fuel. It's a shame none made across (that I know of). Unless you're in 110 deg heat, it should be ok. The only drawback might be with your method of oiling. If the engine is inverted, you may have a problem with oil running by the rings. Most 4 cycle engines have some sort of oil control ring that keeps the oil out of the combustion chamber. I'll take a look at my Ryobi and see what it has. Sounds interesting though, keep us posted. Ya never know you might just have something here!

BTW, a splash system should work just as well. Most smaller engines use this method.

i agree on runnig it inverted, it would not be posible unless you rememberd to turn your plane upside down after every flight, it would work on upright and horizontal engines. the splash is a good idea, it could easily be done with a sight glass added to see oil level.....that could be an even easier method, just have to determine the maximum level you could put oil inthe crankcase before it would cause problems with the moving componets..ie too much pressure. would have to make the vent exit above the oil level too. this could be a good way to go also.

another thought is to what kind of oil would be best, just automotive motor oil, or perhaps some high viscosity oil....marvel mystry oil, or what about a super lubricant like prolong?

why not mix the oil at 15% and forget the rest.

Darin

Darin has the best idea. Without an oil control ring and valve stem seals and a front crank seal and added weight it wouldn't be practical, but it would be a good experiment. Check out how it's done on a full size radial. They have two or three scavenge pumps.

Problem with mixing oil in with the 4stroke gasoline is three fold:

1. The stochiometric or ideal air-fuel ratio for gasoline engine is much higher than that of methanol engines. So much less oil gets inroduced into the combustion chamber; therefore, much less of it gets blown past the rings into the crankcase.

2. The induction cycle occurs only every other down stroke. Again, less oil.

3. Gasoline engines run hotter, and so more of the oil gets vaporized and blown out the exhaust.

The typical glow fuel 4stroke relies strictly on blow-by lubrication. Unless you redesign the fuel induction path to run through the crankcase, you'll invariably need to retrofit a wet-sump splash or a dry-sump pumped system.

There is certainly a lot of fun in the challenge, and that's what this forum is all about, but some projects are much more involved than others. This one, I would suggestion you leave to the folks at Ryobi, Honda, etc. and get one already designed for it.

i think the idea here is that they need so little oil to begin with that i could just install a sight glass and fill tube in the crankcase and keep about a 1/4 ounce of oil in there. it would be able to be mounted horizontal or verticle but not inverted(becasue the oil would have to be pulled back to the bottom of the crankcase by gravity between flights). it could run in any attitude. it wouldnt need a crank seal or valve stem seals since its not a pressure system. any leak thru would be minimal and desired for the lubrication. i think the only 2 questions that remain are

1 what viscosity oil to use?
2 can the piston/cylinder wall handle the extra heat?

As far as oil, try standard 30w air cooled mower oil. It's designed for the higher running temps of air cooled engines. The engine should handle the heat otherwise it would not have been practical for a Trans-Atlantic Crossing.

Jody,

Just a question about your purpose. Suppose it works out and you can run your four-stroke glow engine on gasoline, with whatever works for lubrication...

Are you prepared to have that engine running with about half the power as the same engine on glow fuel? That's roughly what you'll get.

You might want to give some thought to what you'll be flying with this engine.

Good luck,
Dave Olson

Scar where are you getting your information?

Most of the College aerodynamic competion and long distance record holders use four stroke model engines converted to gas. They just mix 2 stroke oil with the gas and forget it. I don't know how much oil, but I would think 5% or less. The mineral oil used for gas engines doesn't need to be mixed in high percentages. Especially since the oil remains in the crankcase till its blown out of the vent.

Maynard Hill, holder of many model records (also the group that attempted to fly the Atlantic) used a regular O.S. .52 4cycle for his duration record airplanes in the early-mid 1980s (current record is 33+ hours, set in 1992 by Mr. Hill and friends ). These had been converted to burn Gas/Oil using a standard flywheel type ignition system (these engines turned at low RPM with big props 16"-18" I think). As far as I know, the only modifications he made to the engine, other than ignition type, was to replace the original push-rods with a harder material (some said it was just drill rod).

I have a Picco .40 2 cycle, converted to burn gas/oil that has run continuously for 40 hours on 100/1 regular 2cycle Aimsoil, 14x6@6000, no heating or lube problems.

the reason i want to go with a dry fuel(no oil in the fuel) is that i dont like the oily mess that gets everywhere. the reason i was worried about the engine materials holding up is that it was designed for glow and it runs cooler. the reason i want 4 cycle is that is more realistic. as for the gasoline containing less power than glow i dont know where that came from, gasoline actualy contains more power.

as for the gasoline containing less power than glow i dont know where that came from, gasoline actualy contains more power.

Gas has more btu per pound of gallon, but methanol and nitro are run at much mixtures say a mix of alcohol and nitro is about 4 to 1 VS gas at around 14 to 1. Even though nitro has less btu per pound more btu's get into each charge, thus more power but very poor efficiency. Because gas has more btu per tank you can go much further per tankfull, which is why the distance record holders use gas or diesel.

glow fuel is not 100% nitro..... more like 10%-15%, the rest is methanol and additives.

100% nitro may be more powerful, the dragster people seem to think so, but i think the cooling problem with it would be terrible. cost would probbly be prohibitive too....


youve brought another idea to me...... what about a dry nitro methanal mix.....it would be able to be run with no special ignition at all. still use glow plugs, use the splash oiling system.

Nitromethane adds power to an engine because it carries with it it’s own oxygen supply, so it’s less dependent upon the volumetric efficiency of the engine (which is essentially an air pump) to intake the correct amount of air per combustion cycle. However, this power boost is derived from added heat generated during the combustion process, and as IC engines are fairly inefficient at converting all the combustion heat energy into mechanical energy, much of that heat is wasted and needs to be removed from the engine. Most of it goes out the exhaust, but a good portion of it still has to be conducted away by the engine block. Add too much nitro and you can watch your normally well mannered engine turn into a self-detonating machine.

As for running methanol + nitro only and no oil, it’s certainly doable, but since neither of the two has any inherent lubricity, you might run into upper cylinder lubrication problems with a splash-only oil system. Gasoline, being essentially a light-weight and multi-fractioned oil, has a good bit of lubricity to it. A good compromise might be a “gasohol” or gasoline-alcohol mixture on a spark ignition system with any of the new commercial 4stroke weedie engines for a better power/weight ratio. More and more of these industrial engine manufacture are coming out with 4stroke engines to meet the increasingly tough environmental regulations. Even Zenoah/Komatsu/Redmax is coming out with one. Maybe after a while, they will be refined to a point where they are competitive with 2strokes on power/weight ratio. My Ryobi 26cc sure runs nice and sooo miserly on gas, but it sure is a big ol' porker.

Glow engines don’t have needle bearings on the conrod and so needs too much oil to do what you want to do easily.

glad you posted Volfy, i have the same ryobi but havnt got an airframe for it yet, im still deciding what it can handle, any recomendations, im assumming it is the same power as a 120 4cycle glow.....

The WW1 rotary engines metered oil into the intake pipe separately from the carb into the crankcase through the end of the crankshaft. They used castor oil because it wouldn't mix and dilute the gasoline. Thats the reason why they had to run to the John after a mission. Must have been a hoot with full flying garb on. Just food for thought.

Glow engines don’t have needle bearings on the conrod and so needs too much oil to do what you want to do easily.

I don't quite buy that one. Although I am sure it may effect the percentage of oil to some extent, I can't see it bringing the oil down from 20% to less than 3%. I think the dry fuel and differances in castor/synthitic and mineral oil is the main reason.

Jody, I would think the Ryobi 26cc has a bit more power than a 1.20 glow 4stroke, but probably not by much. It does swing a big old prop though. Mine is still doing actual weed wacking duty, as I'm been patiently waiting for other parts of the weedwacker to die/break before setting the engine free.

Sport, you're certainly free to believe what you like, but the conrod bearings (particularly the lower end) do carry by far the largest load per bearing surface than any other bearing in the model engine. Without the forced lubrication (i.e. oil pumped under pressure directly onto bearing surfaces) in larger scale engine like automobiles, these small plain bearing rely largely on the excellent properties of the bronze material (often oil-impregnated) to retain a thin oil film under load. Needle bearings OTOH are much better at retaining splash lubrication and recoating the bearing surfaces.

You are correct, though, that there are other reasons for the difference in oil requirements between methanol and gasoline engine. Upper cylinder lubrication, which I mentioned in an earlier post, is another. However, conrod bearing is by far the dominant factor.

The big Super Tigres require only about 10-12% oil mostly because the load per bearing surface on the conrod is lower, so are the operating rpms vs. smaller glow engines. Convert them to needle bearing, though, and they can be safely operated at 4-5% oil content.

Old Sachs snowmobile engine wristpin brg. was bronze, made to run on 20 to 1 mix. Guys tried to run on 40 to 1 mix, siezed up the bushing before the tank was empty.

Hi, guys - thought I'd chime in with some more info.

Check out this link.

http://www.nelsonhobby.com/ignition/samples/samples.htm

The guy that designed this system flies at the same club I do and I've had many discussions similar in content to this thread regard lubrication, heat, bearings seizing, etc.,...

I've seen first hand 3 engines that he's converted (a Super Tigre 91, OS91 and a Saito 180), all work fine (so far). There are some drawbacks, see the link for more info (not all carbs are good enough, hall sensor install, etc.,...)

Later!

DB