ortac wrote:
But the turbo will definitely not “tumble”
It will of course not tumble in the sense a gyroscopic instrument will. My interpretation was that the clearance between the turbine and the surrounding housing was so tight that the turbine could rub against it, in addition to the load on the bearings, or wobble.
I also got the impression that it won’t happen until a very much higher altitude.
On another forum the cost of certifying an engine or aircraft above 18000’ was mentioned as another probable cause.
Hmm, I should have thought some more before posting. The turbine speed will potentially increase with altitude (less back pressure). Higher speed, higher gyroscopic precession forces when the aircraft manoeuvres around its own axes. Which means more load on the bearings.
But the turbo will definitely not “tumble” and I’m still not convinced this is a real world issue.
Even if there were gyroscopic related issues (which there surely aren’t), how would you explain this only becoming an issue at altitude?
Peter wrote:
How can the turbo tumble? It runs on a shaft with two end bearings, no?
I agree with Peter, this sounds like rubbish. It isn’t a gyroscope.
The DA-40 altitude limit of 5000m ~ 16400 ft does not appear to be engine related, as the Lycoming DA-40 has exactly the same limitation. And that is what it is, a POH limitation, not a “max demonstrated” value. Nevertheless, at FL 180 the diesel runs just fine and the aircraft flies well, and the reason for the limitation is not obvious at all.
How can the turbo tumble? It runs on a shaft with two end bearings, no?
lenthamen wrote:
The Centurion engine is certified up to 18K feet so I take that as a limit
Actually I always wondered about the reason for that restriction, and somebody close to Austro recently explained that to me. As the atmospheric pressure drops with altitude, the turbo may, due to gyroscopic effects, tumble and get damaged. This happens at a much higher altitude, but in order to keep a safe margin to the phenomenon, the limit was set at FL180.
Just out of curiosity, what is the service ceiling of your DA40, and what engine is it equipped with?
This was at FL170. Engine is a Centurion 2.0s.
POH speaks about a “demonstrated operating altitude of 5000m (16400ft)”.
The Centurion engine is certified up to 18K feet so I take that as a limit.
lenthamen wrote:
We were at the max of our service ceiling
Just out of curiosity, what is the service ceiling of your DA40, and what engine is it equipped with?
That’s the only attitude i can imagine is right. ATC has no power to send you into a CB.
