Chinese v-twin diesel.

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lear999wa

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Whilst doing the rounds on Alibaba, as you do. I came across the hercules dv210 diesel v-twin. It's weight for what it's worth is quoted at 85kg. And having had a quick chat with the merchant, apparently they are working on a 60 kilowatt version of the engine. All in all I believe that this engine could potentially fit in the Rotax 912 UL niche, at about 190lbs and 80hp. Potentially encouraging for those interested in burning diesel or Jet a.
 

PMD

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Sad to see the Chinese squat on the famous Hercules engine name. Company built about a million engines between 1915 and 1999 - 750,000 of them for WWII effort.

I would second the comments on NVH for such an engine. On top of that: the redrive needed would add considerably to weight - and complexity. To dampen out such large torque pulses is not a small engineering task. While China CAN build high quality stuff, bottom feeding in 3rd world industrial and ag markets is hardly the path into an airplane cowling.
 

blane.c

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At the time our (USA) tractor engines were being developed into airplane engines we were considered by many to be a third world country.
 

wsimpso1

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Vibration isolation for the engine mount and along the driveline will be essential to making this powerplant feasible for turning a prop. The firing sequence must be 450-270, which would mean those big Diesel firing pulses at both 2/3 and 4/3 orders. Maybe bifilar torsional pendulums at 2/3 and 4/3 orders. Isolating with a spring damper would get interesting indeed with having to get below about 6Hz for first resonance.
 
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PMD

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Vibration isolation for the engine mount and along the driveline will be essential to making this powerplant feasible for turning a prop. The firing sequence must be 450-270, which would mean those big Diesel firing pulses at both 2/3 and 4/3 orders. Maybe bifilar torsional pendulums at 2/3 and 4/3 orders. Isolating with a spring damper would get interesting indeed with having to get below about 6Hz for first resonance.
For those who wonder why some people make such an issue over torsional vibration and resonance: The devil may be in the details, but the big deal is when you have complete reversals of angular momentum due to lack of overlapping power pulses. This means a 4 cycle starts to get a bit easier with 5 cylinders and a 2 stroke a lot easier with 3. Worth remembering that several F1 bright people (thinking Frank Thielert here) screwed up horribly trying to tame a 4 cylinder 4 cycle diesel. I know of some other REALLY bright people who ran a 2 cylinder 2 cycle diesel into a marine drive train and thought they had the world by the tail....until the put an aircraft propeller on the flange. Successful re-drives are actually quite a rare thing - and probably what made Rotax the most successful aircraft engine manufacturer on the planet (remember that even Lycosaurus and Clunkinental engines once came with gear reduction - and had their share of problems).

Of course, the simple solution is to build 60 degree 12 cylinder 4 cycle engines and get pretty easy torsional damping problems to solve. I don't think Merlins or even Allisons had any real issues with their PSRUs.
 

Martin W

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Twisting crankshafts

Something the average person does not realize ... some engine designers too.
I will use the Lycoming 540 cu in 6 cylinder as an example.

Under full load each piston power impulse causes a slight torsional twist in the crankshaft ,
when added up it can be 11 degrees of twist at the flywheel end (prop flange)

Keep in mind each connecting rod journal is now slightly skewed from parallel and ignition timing is slightly different for each cylinder .... not a big deal , engineers account for that and the engine will run forever without issues.

However if a pilot accidentally overspeeds the engine here is what happens .... the crankshaft will twist beyond 11 degrees and then spring back to less than 11 degrees as a high frequency vibration and the engine will fail within 100 hours.

Same physics as quickly bending a coat hanger 10 times and it will break in two.

Fixed wing fixed prop engines are not easy to overspeed but in cases of helicopters an overspeed can occur on startup because the clutch is not yet engaged .

Automotive engines have a very wide rpm band so the destructive harmonic vibration is tamed by the harmonic balancer on the front of the crankshaft.
 

Vigilant1

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For what it is worth, this source says:
Original Equipment Manufacturers find that oscillatory crankshaft movement should be less than 0.2 degrees or the crankshaft is likely to break due to fatigue failure.
I have no idea if it is right, but it is more consistent with what I would have guessed. And it would have been a guess.
 

lear999wa

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Interesting. Is it oversimplified to assume that a direct drive chunky wood prop would be able to overcome some of the potential TV problems?
 

Markproa

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.......... Worth remembering that several F1 bright people (thinking Frank Thielert here) screwed up horribly trying to tame a 4 cylinder 4 cycle diesel.
Successful re-drives are actually quite a rare thing.........
Over the years, while building my Gazaile2, I have read these sort of statements over and over on hba. My Peugeot 4 cylinder diesel has a torsional damper and a 1.66 to 1 tooth belt redrive. There are plenty of these planes flying in France with various size diesel engines with no issues reported, many with hundreds of hours some with over 1000 hours. How does this align with your statement, how worried should I be?
 

wsimpso1

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Over the years, while building my Gazaile2, I have read these sort of statements over and over on hba. My Peugeot 4 cylinder diesel has a torsional damper and a 1.66 to 1 tooth belt redrive. There are plenty of these planes flying in France with various size diesel engines with no issues reported, many with hundreds of hours some with over 1000 hours. How does this align with your statement, how worried should I be?
Doing exactly the thing that a bunch of other folks have done is pretty likely to produce similar results. The operative word in the last sentence is "exactly". Run different inertia, spring rates, or maybe even different belts, and bad stuff can happen...
 

Markproa

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Doing exactly the thing that a bunch of other folks have done is pretty likely to produce similar results. The operative word in the last sentence is "exactly". Run different inertia, spring rates, or maybe even different belts, and bad stuff can happen...
Thanks Bill, I get that but what I don't get is these French guys are using three or four different diesels with different ratio redrives and none are having the problems I keep reading about here. I'm getting close to flying so would like to understand why theory and practice isn't aligned here.
 

wsimpso1

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The neat thing about those diesels selected is they are all very similar in size, output, vibe character, rotating part (mostly flywheel) mass moment of inertia, and suitability for available giubos for isolators.

One interesting thing about props - we tend to operate them all around the same tip speeds. Turn 'em slower and make 'em bigger, turn 'em faster and they must get smaller.

At similar power, the reflected inertia of the prop side is similar. Prop inertia is heavily influenced by mass and tip radius squared, and reflected inertia is prop inertia times speed ratio squared. Speed ratio goes down while tip radius goes up, not much difference in reflected inertia.

So, similar inertia at each end of similar giubos - similar vibe management. Then the belt drives are most likely oversize for the power, regardless of the engine picked.

Once we have a successful recipe for one, we could well have a pretty good recipe for several. The danger lies when you go from a 4 to a twin or worse to a 90 degree v twin or double the power. Big changes in firing orders or in torque can run pulse trains frequencies and natural frequencies together with bad results.

Billski
 

wsimpso1

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Good to hear, thanks. There are already enough unknowns to be concerned about while test flying. I'll keep an eye on the flexible coupling.
If it turns out you are operating too close to a resonance, and the coupling is rubber or elastomer, it will cycle excessively, overheat, and failure mode will by hardening and cracking. Overheat might be possible from engine heat too. If symptoms of overheat occur slowly enough, forcing cooling air over it may help the life of the next one. If quickly, you have a much bigger problem...

Looking for any signs of deterioration in the giubo should probably be part of every preflight inspection. If the coupling is steel springs then look for bottoming, battering, etc.

Billski
 
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