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VFR Flexibility

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.

Last Edited by Aviathor at 28 Jun 21:59
LFPT, LFPN

How can the turbo tumble? It runs on a shaft with two end bearings, no?

Administrator
Shoreham EGKA, United Kingdom

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.

huv
EKRK, Denmark

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.

EGTK Oxford

Even if there were gyroscopic related issues (which there surely aren’t), how would you explain this only becoming an issue at altitude?

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.

Last Edited by at 29 Jun 15:28

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.

LFPT, LFPN
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