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Highest power to weight ratio in an Otto cycle engine I have seen!

Started by mad murdock, January 29, 2014, 09:34:10 AM

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mad murdock

Anyone seen what design engineers at Nissan have come up with?? http://www.dailytech.com/Nissan+Coaxes+400hp+from+88pound+3cylinder+Turbo+Engine+for+Hybrid+Racecar/article34217.htm
Though it is being developed for a Lemans car, technology from this design will mak it into production cars in the future.  Almost all advancements in automotive design and efficiency have come from the racing world.  This engine would be admirable in an aircraft!!
Turbosawmill M6 (now M8) Warrior Ultra liteweight, Granberg Alaskan III, lots of saws-gas powered and human powered :D

John Mc

The power to weight is nice, but getting that power at 7500 RPM or more is a problem, at least for a propeller driven aircraft. You'd have to gear it down around 3:1, and gearboxes in aircraft have not proven all that reliable.
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

mad murdock

John, there are lots of ways to go on reducing the output speed for a propeller, one simple and proven method is a PSRU (prop speed reduction unit), a short prop shaft with some hefty thrust bearings and the appropriate sized toothed pulleys and matching toothed belt to reduce speed from crank to prop.  A lot of aircraft have this type of setup, the belt is similar to the final drive belt on a Harley. They have belts that can handle lots of hp. The other way to go is to build a gear reduction that bolts on to the PTO side of the engine, there are many aircraft that were built with such a setup as well (a lot of radials have them, as well as some opposed lycoming and continentals). Very proven, and dependable.  As far as gear train reliability in aircraft, take a look at any helicopter.  I overhaul the drive train components on our aircraft, reducing gearboxes, main transmissions, tail rotor gearboxes and turbine engine gearboxes, all extremely proven and reliable. The amazing thing about this engine is the power to weight, it rivals a turbine, and outdoes many turbine engines. Something not often seen in an Otto cycle engine. 
Turbosawmill M6 (now M8) Warrior Ultra liteweight, Granberg Alaskan III, lots of saws-gas powered and human powered :D

John Mc

I defer to your greater experience in this area. My experience is limited to piston engine airplanes, and as a user/flight instructor, not a mechanic. I've seen some experimental aircraft with belt driven reductions.  In production airplanes, the gearboxes I've been exposed to don't have the greatest reputations (Cessna's geared version of the 172 is one example).
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

pineywoods

Yeah John, I well remember the geared aircraft engines. Seriously considered putting a 190 lycoming in my old stinson..Designing a gearbox that goes between the crankshaft and the flywheel (propeller) is no small task. Especially if we're talking large displacement 4 and 6 cylinder engines. Without some sort of damping, the power impulses tend to eat up gears. The rolls V12 used in the spitfire and P51 has a built in gearbox and is probably one of the most successful. The biggest belt reduction I ever saw was a 450 hp ford v8 with a 4 inch wide cog belt, mounted on an ag plane.
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mad murdock

Quote from: John Mc on January 30, 2014, 10:34:58 AM
I've seen some experimental aircraft with belt driven reductions.  In production airplanes, the gearboxes I've been exposed to don't have the greatest reputations (Cessna's geared version of the 172 is one example).
Agreed, some experimental stuff is sketchy, others re well though out and designed.  The GO300 continental that was installed in the 175 Skylark got a bad rap, as well as the GO520K engines in the Cessna 421's and the GO520M engines that were installed in the Cessna 404 TitanII.  I have worked on them all quite extensively in my time in aviation, and the failures have alwasy been due to operator error.  The continental opposed gearaboxes were all straight spur gear reduction units, and you cannot reduce powere more than 1" of manifold pressure per second, if you chop power rapidly in one of those engines, the prop will drive the crankshaft, and that sets things up for disaster.  We have several geard engines in our twini fleet where I worked in Kingsford MI, back in the day, and pilots ruined probably 4 engines in the year I worked there.  All from reducing power too fast.  Planetary gear reduction units like are in Radial engines and also Lycoming gear reduction on engines like the GO480, do not have the same problem.  I am not sure of the exact chain of events, but simply put, when the propeller drives the engine in a spur gear reduction unit, it sets up harmonics in the engine, that make the crankshaft dynamic weights come loose, and the engine starts shedding parts from the inside out.  Usually through the case. I saw the results of this as stated several times.  If the geared continental engines were operated as prescribed, they would go to TBO or beyond every time.  Belts seem scary to the uninitiated, but as Piney stated, there are some cogged belt PSRU's in use in failry high HP applications, a less expesive option than a gearbox, and if designed well, durable and dependable.  Sadly, IMO aviation suffers a lot from the onerous regulatory environment, the technology takes decades to work its way into General Aviation circles, except through the Amateur Built/Experimental pathway.  Mch innovation has come in recent years from the Experimenters out there. 
Turbosawmill M6 (now M8) Warrior Ultra liteweight, Granberg Alaskan III, lots of saws-gas powered and human powered :D

John Mc

The 175 Skylark is what I was thinking of... I just blanked on the name/model.
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

hardtailjohn

I used to rebuild radials, and the biggest failures of the gear reduction units were from idling. As long as they kept the idle set where the mfg stated, it didn't do bad.  Of course there were other things, but idling was a biggie. Float planes were bad for that...docking. I rebuilt a lot of 1340 gear cases when the Otters were still mostly recip. 
John
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