Why does a DA42 Engines have a Clutchs and whats the purpose of them

[nezzer]

Hi does anyone have any thoughts on my question above

[Jan Olieslagers]

Yes. I do have some. Several in fact.
For a beginning: I think it could be said more properly that the DA42's engines have a clutch. The DA42 being a twin, it actually has two clutches.

[ashdaman]

maybe its to simulate engine failure!!:uhoh:

[Pilot DAR]

The "clutch" is not there in "the disconnect the transmission so you can change gears" sense, but rather to absorb some of the shock of the strong diesel engine power impulses, to lessen the strain on the propeller blades. These clutches seem to have been a less than ideal maintenance feature of the Thielert engine.

This version of the DA-42 does not have clutches - direct drive!

http://i381.photobucket.com/albums/oo252/PilotDAR/Jims%20DAR%20Testing/File0262.jpg

[FlyingStone]

As Pilot DAR says. It's a lot easier to start an engine with the gearbox decoupled and then progressively couple it once the engine speeds up to idle. Similar thing happens in car with manual transmission - you never start the car in a gear with the clutch coupled. Having the clutch has another advantage - in case of prop strike, it decouples the gearbox from the engine and thus you only have to do a shock load inspection on the propeller and gearbox - saves money. On the other hand, if the infamous Thielert clutch fails, you end up with the engine delivering power/torque, yet none of it (or not all of it if the clutch has just started slipping) is delivered to the propeller.

For a beginning: I think it could be said more properly that the DA42's engines have a clutch. The DA42 being a twin, it actually has two clutches.

Let's not confuse anybody - each engine in a diesel DA42 has a single clutch. There are engines used in cars which have two-clutch transmission (for a single engine), but this design would be completely unnecessary for a single-gear reduction gearbox used on aircraft diesel engines.

[RTN11]

I thought the primary reason was so in the event of a prop strike, the clutch would take the strain rather than the engine being shock loaded. Same system as the Rotax 912. However, the load being taken off the starter does also make good sense.

[madlandrover]

A bit of all of the answers. Main use is to smooth out the power pulses - anyone who's seen one of the clutches removed after its 300 hour service life will understand how hard it works!! Let alone at least one that's worn in flight due to a misfire so rapidly that it was struggling to transfer drive after 30 hours... The Thielert clutch does not disconnect the prop pre/during start, it's effectively direct drive via the gearbox but just a little smoother. The Austro Engines AE300 replacement used in DA42/DA40 NG aircraft does away with the clutch and replaces it with a torsion damper to achieve the same effect without a consumable part.

[Pilot DAR]

It's a lot easier to start an engine with the gearbox decoupled

Just to be clear, the clutch in the diesel propeller engines does not decouple under pilot control for any reason. It simply absorbs any shock in the drive line. When you start and fly the Theilert diesel, it is very similar to a simplified gasoline engine (just fewer knobs, and things to get wrong!)

On the other hand, helicopter piston engines are all decoupled from the rotor drive train for start. Once running, the pilot engages the clutch (a fussy process in some models). That is simply because there is not a hope of the starter motor turning over the engine and rotor drive system!

[A and C]

Both the diesel engines in the DA-40/DA-42 have a way of damping the torsional pulses that the engine produces.

The Thielert uses a clutch that slips at a pre set load.

The Austro uses a torsional damper. ( I can assure the readers of this that there is no hydraulic damper fitted to the Austro)

The damper fitted to the Austro is an attempt to decrease the maintenance requirements that are a disadvantage of both engines. One advantage that the Thielert has is that as the clutch totally disengages the gearbox from the engine, a prop strike is not usually a reason for any more than a gearbox inspection, a prop strike on the Austro engine will require the strip inspection of the engine.

It will be interesting to see what comes of a Thielert engine that was recently involved in a mid-air, the prop and part of the gearbox departed the aircraft but due to the FADEC control the engine did not overspeed. I await the inspection report from Thielert with interest!