Why not more motorcycle engines?

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Ran across this and thought it might be of interest to some others and this seemed like the most logical thread to to attach it?
If you want your brain to hurt think about the balance and resonance problems using this 1L V5 motorcycle engine with a PSRU.

 

PMD

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Not sure what exactly you're driving at with the Jumo-type of engine. The Jumo, by the way, does not have piston like a barbell. They are quite conventional. You're talking about a crosshead type of piston/cylinder arrangement like you find in many ship engines......The Jumo-type opposed piston engines are large, heavy, slow turning engines and best suited for large, long range aircraft. Although there is a vast amount of room for improving these, I believe they are best suited to driving propellers directly, not through generators and electric motors.
The Junkers pre WWII engines were anything but large, heavy or slow turning. OPOC (Opposed Piston, Opposed Crankshaft) are used specifically because they have very light weight and small size for the power they can produce. Here is a bit of a summary:
One might conclude they would be the ideal technology for jet fuel aircraft engines. PSRU is integral to the design.
 
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PTAirco

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There is not a whole lot you can show me about opposed piston engines that I haven't seen or read, since this is a pet subject of mine. Compared to spark ignition engines like typical 1930s V12s and radials, they were indeed large and slow turning. 1300lbs for 700hp wasn't bad but not in the same league as a Merlin. They definitely had their niche though. And no doubt could be improved upon nowadays.
 

sotaro

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There is not a whole lot you can show me about opposed piston engines that I haven't seen or read, since this is a pet subject of mine. Compared to spark ignition engines like typical 1930s V12s and radials, they were indeed large and slow turning. 1300lbs for 700hp wasn't bad but not in the same league as a Merlin. They definitely had their niche though. And no doubt could be improved upon nowadays.
The Junkers 207 redlined at 2800-3000 rpm, in versions A-C. This was a common maximum rotational speed for German V12's.
 

PMD

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The OPOC Junkers engines were heavy relative to their spark ignition contemporaries because they had next to no funding available to develop. Prof Hugo was NOT well connected within the Nazi party, so he was forced to concentrate on his SI designs. The 4 bank 223 would have moved OPOC WAY up the scale of comparative power density. Even so, the 205 and 207 series accomplish some pretty impressive feats and compared with DIESEL engines of the era, were VERY light indeed.

Using modern injection and materials technology, OPOC engines can easily get down to Rotax 9xx series power densities - something that direct drive SI engines can NOT do at this time.
 

Geraldc

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A 1000cc sport bike engine weighs 150lbs dry and produces 170hp. Why not reduce rpms to bring it down to ~125hp and have a package that weighs under 200lbs?

A suzuki 1300cc weighs 20lbs more an gets another 20hp running at a lower rpm for an extra 20lbs. And people modify those to over 500hp, seem like 150hp and ~220 lbs would be doable.

Is it the rpm or packaging issues? Stock motors are used for racing, so they should be fairly durable. Maybe not 2000 hours durable, but they are also cheap to replace. the built in transmission could even be used as a psru.

What issue am I missing?

I know some smaller engines (eg BMW) have been used in lower power applications, but haven't seen the newer high power ones used.
There are plenty of potential motorcycle engines but most have the gearbox built in and need more work to fit a redrive because of this.
The BMW had a separate gearbox .
 

PMD

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KK: THANK YOU for posting what has to be one of the most interesting stories in early aviation history. Significant to me as IMHO aviation and outboard marine engines happen to share a lot of technology - or at least they should. Very similar operating requirements....except of course for cooling. What makes a good outboard should make a good genav power plant.
 

Dan Thomas

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The first air brake compressors manufactured by Bendix-Westinghouse were converted outboard motors. They had the intake ports in the cylinder walls, with the discharge valves in the head. I have one of these old things (circa 1945-1950) as a homemade compressor in my shop. It's obvious why Bendix soon abandoned the design: the suction created in the cylinder as the piston descended sucked oil past the rings, contaminating the air, and the holes in the cylinder wall limited the effective displacement, reducing its CFM capacity.

The lesson: purpose-designed and built stuff is always superior. I am not aware of a converted outboard that worked out well. The Scorpion helicopters used a couple of converted Evinrude outboard models, but RotorWay eventually designed their own four-stroke engine for their helicopters. The homebuilt Spratt Control Wing (Spratt 107) used a converted Mercury outboard.

I've had outboards, had them apart. The powerhead is not light at all. It doesn't need to be. Cast iron is heavy. The newer four-strokes are even heavier. And expensive. Used outboards are a crapshoot, with the chances of serious wear caused by irresponsible or careless owners. Forgetting to mix oil into the gasoline, or using the wrong oil, is a good way to wreck it. The outboard is designed to use stone-cold water from the lake or river, and a radiator setup has to be able to adequately cool it. My two-stroke Johnsons have thermostats that open at around 140 degrees. That's a lot cooler than an auto engine.

I did the design and installation of an already-converted Subaru into a Glastar. By the time it was done, the owner could have bought a nice Lycoming and been flying sooner and safer and faster, and the resale value of the airplane would have doubled. The mileage of others may vary, but that was my experience.
 
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