914 RPM/ Boost problem – only 1st flight of the day

I first need to ask if this is fitted with an overload clutch?  If so given what you gave from the log file it appears that the clutch has may have slipped some.  I am not sure why you do not believe the RPM in the log.  Anything over 5800 will cause the turbo to reduce boost and you should have a flashing red lamp in the system.  Remember that the engine TCU is looking at the information you are looking at in the log file.  It thinks you are over rpm and is trying to save the engine from damage.  

Cheers

Just a supplemental comment.  Perhaps you simply have too small a load (pitch) on the propeller.  If this is a fixed prop then for sure it is way too small a load.  if this is constant speed you need to load it more, same if it is inflight adjustable type.  I would look at this before getting into a lot of hunting for strange things in the TCU.  

Cheers

Rotax Wizard wrote:

I first need to ask if this is fitted with an overload clutch?  If so given what you gave from the log file it appears that the clutch has may have slipped some.  I am not sure why you do not believe the RPM in the log.  Anything over 5800 will cause the turbo to reduce boost and you should have a flashing red lamp in the system.  Remember that the engine TCU is looking at the information you are looking at in the log file.  It thinks you are over rpm and is trying to save the engine from damage.  

Cheers

Thanks for the reply - I agree the TCU appears to be doing it's job and saving the engine from excessive RPM, but I don't understand why it only does this on the first flight of the day. I am suspicious of the high RPM data as the TCU thinks it increased 800rpm in 1 second and I don't think the inertia of the engine would allow it to do that, but that's just a gut feel.

Cheers, Mark

Rotax Wizard wrote:

Just a supplemental comment.  Perhaps you simply have too small a load (pitch) on the propeller.  If this is a fixed prop then for sure it is way too small a load.  if this is constant speed you need to load it more, same if it is inflight adjustable type.  I would look at this before getting into a lot of hunting for strange things in the TCU.  

Cheers

Once the engine gets over this glitch, the rpm & everything else is fine for the rest of the day, so I'm pretty sure the prop pitch is OK. It hasn't changed and the engine has done 750 hours. I'm stumped !

Cheers

Marc,

I can follow your concern but do not find the 800 revs jump in the log. 

The comment on the clutch sounds very plausible to me (sudden lack of load). However, the question remains open why this effect only occurs once a day during the first flight.

If I understand your description correctly your prop setup seems OK to me (below 5800 revs at full noise).

Keep us updated.