2 stroke alternative ?

Discussion in '2-Stroke Aircaft Engines' started by MadProfessor8138, Jun 6, 2019.

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1. Jun 6, 2019

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I wasnt sure what section to post this in so here goes........just some of my thoughts on engines.
If this thread needs to be moved..........

There seems to be a need for 35-50hp 4 stroke engines but very few options available.......everyone wants to get away from 2 strokes these days for some reason.
If you want high hp with low weight then looking for engines that were developed with that from the beginning would be the logical choice.
It's a shame that nobody has taken advantage of the R&D that has been done by the Japanese engine designers....they build great engines.

As an example......Yamaha YZF dirtbike engines are 4 stroke,around 45-55hp depending on year,around 60 lbs,rev to around 11,500 rpm,water cooled.....etc.
Strip the kick starter,clutch and transmission off and drop probably 10 lbs or more.
The needed coolant and radiators are pretty light.....under 10 lbs probably.
Design a gearbox or belt drive to mate up with the cases and you have a 60 -70 lb 45-55hp 4 stroke that can take any rpm that you care to throw at it all day long..........and you can walk into any dealer or surf the net to find parts.

Has anyone pursued this avenue before?

I know there was a Yamaha Virago street bike engine flying on a Nieuport for a while...and then you have the Yamaha snowmobile engines being converted now....larger engines than what we are shooting for but still the same principal....

Kevin

Last edited: Jun 6, 2019
2. Jun 6, 2019

Vigilant1

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Most folks wanting a relatively inexpensive 4-stroke aero engine in this 35-50 HP range will still go with the options we've had for a few decades: a 1/2VW or a full VW 4-cyl. And they still work fine.

The O-100 will come to market soon and be putting out a bit more than the 50 HP you've requested. Some people will find it meets their needs.

On paper, there are a lot of good motorcycle engine that could work. Unfortunately, none of the major manufacturers sells crate engines, so a builder faces the task of finding a wrecked bike for a donor engine. There's no real problem with this (after all--you only need to find one good one), and the folks at the Moto-air Yahoo group have been discussing it for a long time. If you haven't been there (and if you can put up with Yahoo), you might check out what folks have posted there, if you want to try adapting something yourself.

As far as a "here it is" kit or complete engines: Having to make use of used engines is an big impediment to the development of a standard aero engine of this type for wide adoption. It's too hard for a company to make money doing it as a business, since finding, evaluating, and adapting used engines just makes it uneconomical. The VW continues to live as an aero engine because we can still buy all parts new and at economical prices.

Maybe there's a manufacturer of reliable, modern, simple, light, mass-produced 45HP engines that can be bought new in a box and adapted for aircraft use. But, unless the whole thing, with a prop hub, reliable carb, PSRU, etc can be done at a weight and/or price less than a 1/2VW or full VW, then there will be limited demand.

The Valley Engineering Big Twin did use a Big Block Generac and a PSRU to provide up to 50 HP for short periods--but just 32 HP continuous. I don't know how many they sold, but no one else has jumped into that market space since they left. At a price of about $5500 (40HP for takeoff) to$6200 (50HP for takeoff), undoubtedly some buyers decided instead to get a VW engine and pay less money for double the continuous HP.

Last edited: Jun 6, 2019
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3. Jun 6, 2019

pictsidhe

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I'm not sure how long one of the motocross engines would last at 12krpm. But detune down to 9k, it could be worth looking at. It seems tempting to use the primary reduction, though they aren't low enough on many engines.
My pick would be harley cylinders and heads on a more aero bottom end. There is a Texan attempting to graft harley cylinders to a half VW bottom end. But judging by his website, he doesn't know what he is doing...

4. Jun 6, 2019

Hephaestus

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Wouldn't the BMW K series fit in here? It's been done...

5. Jun 6, 2019

pictsidhe

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BMW Rs are popular in Europe. Ks have been done too. IIRC, there are 2 valve per cyl versions that are somewhat lighter.

6. Jun 6, 2019

BBerson

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Electric is an alternative. Kitplanes has an article about some guys that removed the two-stroke and installed electric in a Strojnic S-2. The electric system came from a Zero motorcycle. About 200 pounds. So not light enough for an ultralight.

7. Jun 6, 2019

TFF

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Everyone takes advantage of advanced technology. The question is always is better better for the case. 11,000 +rpm motorcycle engines are cool. A prop gearbox for an 11,000 rpm engine is an answer in search of a question. It’s one thing if you start whittling it all on your own because you just need to cut some steel or aluminum. It is a bad idea when it would take millions of dollars to make a commercial product for one of the smallest set of buyers out there. Great for the home scientists engineers; bad bad bad business. I put the O-100 in the just have to scratch the itch category with someone very capable to pull off limited production,just because he wants to see it. Profitable profit has to be the last thing on the list of goals for that thing.

8. Jun 6, 2019

jbiplane

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May be use 1/2 of 1300cc rotary wankel engines of Mazda?
This 650cc 4-stroke will beat VW by specific power. The only drawback will be relatively big oil consumption.

9. Jun 6, 2019

Vigilant1

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This has been done, and it works "okay." The challenge is that a single rotor requires a large counterweight, so it is relatively heavy. Plus, you need two end plates and rotor housing, so just the case has 3/4ths of the weight of a twin rotor (that has twice the power). And you still need the water cooling, etc just as for a twin rotor. You can reduce the counterweight a bit if you go with a lightened AL rotor, but that adds cost. Altogether, the HP/LB isn't nearly as good with a single rotor as it is with a twin rotor (things get more favorable going the other way, with 3 rotors, for the same reason). Maybe a single rotor could still compete on a HP/lb with a VW 4 cyl, I don't know.

Last edited: Jun 6, 2019
10. Jun 7, 2019

Hot Wings

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Went down this road. The ONLY advantage to the Harley top end is that they are available for a reasonable price......Especially if you go by the pound. I still have the parts on the shelf. Need to sell them........

Oops, they do have one other advantage compared to 1/2 VW, 2CV or BMW components. They can be had in 100mm+ bore sizes so building a narrow opposed engine with the same displacement as a stroked VW is possible.

A little 1200 cc 4 cylinder made with Ural/Denpr parts might be interesting?

11. Jun 7, 2019

pictsidhe

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What about Harley top ends on a 1/4 of a V8 crank in custom cases?

12. Jun 7, 2019

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Frankensteining an engine together is the exact path that I'm trying to avoid.
My intention was to find an existing engine that could be mated up with a redrive to make an acceptable combination for an aircraft.
An engine is nothing more than exactly that.....just an engine.
It weighs something,it uses fuel/air/compression and spark to create power,it has a set hp,torque and rpm range....etc.
Find an engine that meets the parameters that you need and an appropriate redrive and youre good to go.
Frankensteining an engine and then praying that it holds together is madness.......
Use an existing engine,that has been designed/built by some of the best engineers in the world,and dont try to make it something that it isn't and it should be extremely reliable if its ran within the manufacturers parameters.
The engine isn't the problem,because they are all over the place and meet the weight and hp envelope needed.....the redrive is the issue.
As an example....particular dirtbike engines are 4 stroke,60-70lbs,45-55hp,will take rpm all day long,\$cheap,and will be pretty near bulletproof in an aircraft.........
Now.....figuring out how to mate a redrive to one is the trick....figure that out and you'll have a great power package for an aircraft.
Have I mentioned that the Japanes spend millions upon millions to research,develop and make constant improvements for engines that don't break........they are pretty good at what they do.
The Yamaha snowmobile engine is an excellent engine for conversion but heavy for ultralights....
Yamaha dirtbike engines are in the ultralight territory....
Kevin

Last edited: Jun 7, 2019
13. Jun 7, 2019

Sockmonkey

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Do they make 2-cylinder 4-stroke chainsaw engines in the 30-hp range?

14. Jun 7, 2019

mm4440

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Hi, this thread does not belong in the two stroke area despite "two stroke" being in the heading. the firewall forward area with the B&S conversions and other threads. The V-2 industrial engines are flying in trykes and ppgs and some fixed wing aircraft. Worth a look.
Murry

15. Jun 7, 2019

dino

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16. Jun 7, 2019

pictsidhe

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Motorcycle engines are mostly designed for high power to cc ratio. This yields engines that are complex and have a high piston speed, thus wear quickly if held at peak power. We want high power to weight. While that also favours a high piston speed, it often does not favour complexity.
If we are going to adapt a motorcycle engine, expecting peak power for long periods seems a little over ambitious. Motorcycles spend very little time at full throttle and max revs. You will run out of road if it is over 100cc. Detune it and it may last a respectable time. If we aren't wringing every last hp out of an engine, we can tune it for peak torque at our rpm.
Hotwings, what is wrong with Harley top ends?

17. Jun 7, 2019

Hot Wings

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Biggest problem is they are HEAVY. Also the valves tend to be too large and they have antiquated combustion chamber shape. This partial mass of HD head weighs 15 pounds.

Edit: For comparison a 1/2 VW head, minus rocker cover, weighs a little less than 1/2 the HD.

Last edited: Jun 7, 2019
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18. Jun 7, 2019

pictsidhe

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The 883s have smaller valves, but work with 1200 pistons, though maybe they are huge, too... The weight is going to be a problem.

19. Jun 7, 2019

mcrae0104

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While I generally agree with what you're saying, piston speeds are a mixed bag. The bikes I've owned have been in the 52-60 ft/sec range (also true for the two EJ255 cars I've owned). Modern liter bikes are more like 78-80 ft/sec. Many modern street car engines have higher average piston speeds than this.

A Lycoming O-360's pistons loaf along at a leisurely 33 ft/sec, and a Rotax 912 at 39. I wouldn't be afraid of an 80 ft/sec engine falling out of the sky, but I would choose something other than a motorcycle engine for other reasons than piston speed.

20. Jun 7, 2019

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