Good question!
Even 4 cylinder motor bikes have rubber hub dampers in their rear wheels - or at least my 600 cc Yamaha did. More of a problem to incorporate in an aircraft engine where the prop is bolted onto the end of the crankshaft, but should be possible where there is a gearbox in between which, I believe, is the case with most modern engines.

The Technify (Thielert Centurion) engine has a reduction gearbox with a dual mass fly wheel and clutch.

Indeed a slipper clutch is the usual answer to vibration in aircraft piston engines. It is especially critical in engines with few cylinders but with a reduction gearbox; the Thielert indeed but the Rotax 912 also. Though ISTR only the later 912's have one.

Mine certainly has one, too, and I have had reason to be grateful for that when I milled the prop to pieces yet the engine came to no harm.

Some smaller engines, especially car conversions, use belt drive, which serves as reduction gear and as a damper all in one.

I never heard of using some block of rubber as a vibration damper, curious as to why - it seems a viable idea.

IIRC some of the earlier versions of Rotax engine had slipper clutches. There was some problems with them and for a while they didn't. Then they put them in again so I suppose they cured whatever the problem was. (Mine doesn't.)

Lotus cars and, I think the Triumph Herald line used to have rubber 'doughnut' flexible drive. One of its problems was that it could 'wind up' and then release causing uneven drive.

I'd expect that in a propeller at some frequency the rubber drive could be expected to create an oscillation where instead of smoothing out small vibration it actually caused a much bigger one.

As I understand it one of the ways of minimising vibration is to have more cylinders of smaller size, making the oscillating parts smaller in relation to the mass of the block and head. That is another reason I am surprised no one has tried the Tuareg 10 cyl. Al. engine.

The Junkers design had a problem with vibration as the piston timing was offset so the valves were opened and closed more efficiently. I don't know if that was still so in the Deltic design but it did have more cylinders and lots of pistons! Probably the sheer size and weight of the block and the locomotive it was mounted in had a lot to do with making the deltic engine acceptable in railways.

The basic problem with virtually all of the diesel designs is weight.

Looking at the VW V10 engine, its weight is variously given at between 600 and 800lbs. And this is a new weight saving design using through bolts down into the crankcase to strengthen it. To that has to be added a gearbox.

The equivalent 300hp Lycoming an IO-540 has a dry weight of 480lbs. So a massive difference.

The V6 VW TDI has a weight of 420lbs, plus gearbox, but it 'only' makes 220 hp.

The same comparison has been made between the O-320 and the Thielert, although with the lower power engines the differential, whilst still there, is smaller proportionately. The Thielert conversions made much of lower fuel consumption - which does mask the additional weight.

I'm disappointed to hear the Toureg engine weighs so much. Further reading that wasn't available last time I looked (years ago) says that it has a balance counter shaft and the crank is loaded with extra counterweights too. One would have thought that an all aluminium and rather compact engine would weigh less.
There is, of course the weight of all the extra bits, two turbos etc.

You probably wouldn't need a gearbox. Apparently the engine give its full power and enormous torque all the way down to 2,000 revs.

I think the devil is always in the detail. The Ford Ecoboost engine had a tremendous write up in the press. Carried to Detroit as excess baggage, footprint no large than an A4 page.

All unfortunately completely untrue!

The excess baggage engine actually is marginally smaller than the unit is replaces - its footprint is actually larger than A3! Even better its dry weight is over 200lbs, so it must have been a robust handbag the chap was carrying(?)!

So the Ecoboost is somewhat lighter than the engines it replaces, it is somewhat smaller than the engines it replaces - but the Rotax 912iS is significantly lighter and more compact than the 1.0 Ecoboost.......

@ChrisVJ: these balance weights and balance shaft all have their weight, too, and MUST have their weight to be any good. Here comes in the natural superiority of the boxer engine, which doesn't need all these additions to run smoothly.

As for needing a gearbox: yes, modern diesels develop maximum torque at very low revs - the 3,0 Iveco in my van even at 1400 rpm! - but, though torque is important, we still want power at the prop, and power is torque multiplied by rpm. Revving up the engine will still bring improved performance. Whether a gearbox brings enough improvement to justify the added weight/complexity/maintenance is any designer's decision.

Jan

I was suggesting that the V10 could be used at, say, 2,300 revs as it gives easily 200hp at that speed. It would also get over the usual problem with Auto engines, that they are not designed to give their rated power for more than a few seconds.

At 200hp and 3,200 revs I was looking at the V10 for an RV, maybe an RV8. However if it weighs 600lbs plus it won't work. And why would one build a V10 needing all that balancing when you could build a V8 and not have it? Were the 2 extra cylinders that important?

What I don't understand about engines could be written in a book the size of the bible.

http://www.weslake.eu/news/newspages...reoengine.html

Patience chaps :)
the modern version of Junkers opposed piston, supercharged two stroke high power to weight diesel is on the way.

There have been numerous false starts like DieselAire, Gemini, Zoche, etc.

One thing for sure, to simply take a Lycosaurus avgas design and turn it into a diesel is not going to work well. Any more than trying to put a Mercedes car engine into an aircraft. The amount of technical fixes needed to make these false starts work defeats the object. The object being simplicity, reliability, economy, and safety.

Perhaps wisely Weslake are avoiding the certified route for development and using LAA type aircraft for initial flight tests.

The Weslake diesel has successfully run at 80HP on the dynamometer. It will be on display at Sywell for the LAA rally, where the company plan to run the engine fitted to a Gruppo Trail aircraft.

This engine is similar to an already operating marine version. The aviation version will have the belt driven water pump and injection pump relocated at the rear, and driven from the two cranks. This will give a more streamlined frontal area.

The Weslake diesel could become a direct replacement for Rotax , Limbach, and VW type, 80HP engines. No more carb heat, ignition systems, valve gear adjustments, AVGAS/MOGAS problems, fire danger, etc. Lets hope the development goes smoothly and quickly.

The Weslake diesel has successfully run at 80HP on the dynamometer. It will be on display at Sywell for the LAA rally, where the company plan to run the engine fitted to a Gruppo Trail aircraft.

This engine is similar to an already operating marine version. The aviation version will have the belt driven water pump and injection pump relocated at the rear, and driven from the two cranks. This will give a more streamlined frontal area.

The Weslake diesel could become a direct replacement for Rotax , Limbach, and VW type, 80HP engines. No more carb heat, ignition systems, valve gear adjustments, AVGAS/MOGAS problems, fire danger, etc. :ouch:
Lets hope the development goes smoothly and quickly. :ok:

The 912 ULS has an installed weight of about 64kg. Any info on what the Westlake currently weighs?

Here's the spec for the marine version:

Its hard to tell if Weslake (who designed the engine) have gone for the simplicity of a mechanical injection system, or the preformance and efficiency of common rail. Maybe they will offer both?

The output RPM of the marine version could be reduced for aircraft applications by changing the ratio of the geartrain between the outboard crankshafts and the central propeller driveshaft. This should be neater than adding another reduction gearbox on the front.

I wish them well with this project. They have been working on the concept for years.

Curious: elsewhere the same marine engine is stated to produce 100 BHP?

BWM Ribs - BWM Diesel Marine Engine

Self-correction: the company announces a 80 BHP engine and a 100 HP one - both with the same bore and stroke and producing their power at the same RPM. Addition of a second stage turbo? Different compression ratio?

The report in LAA mag suggests plenty of scope for weight saving in the aviation engine. At present it is some 5 kilos heavier than the Rotax, but thinner castings, lighter gears, etc, could reduce the weight a lot. Mechanical injection systems can be optimised for max efficiency at the most used rpm. Being independent of an electrical system would score for reliability.

Jan, it may well be a difference in injection system, or simply the application for each engine in terms of longevity vs. performance. There are so many variables on a turbocharged diesel, such as boost pressure, porting, number of injector pulses and their duration plus emissions considerations that the cylinder capacity is not an overriding factor.

Yes. Come to think of it, IF the engine has FADEC, it can be easily tuned to a wide range of max power limitation.

Regarding FADEC dependency on electrical system, reliability &c: Rotax have a nice solution there, powering their ignition system from magnets rotating on a flywheel over pickup coils. Surely something akin could be done for powering a FADEC? Even doubled (i.e. two sets of coils), to further increase reliability?

Small Marine Diesel ??? They have a completely different application scheme. They usually run at best economic RPM, which is quite often around 25-30% power setting. They usually never run at 65+%, as in aviation.

Chickenhouse, Bear in mind the application for the BWM marine diesel engine is in rigid inflatables (RIBs) which tend to be use higher power settings than engines in displacement vessels.

Given Weslake's history and track record, I'm confident that they know what they are doing.

Regarding the difference in output between the BWM 80 and BWM 100 engines, I've just found the answer in the 'company pedigree page.