Manifold Pressure Fluctuation

[Pablo Canales]

Last week I flew my T206H up to 21,000ft

But right after crossing 19,000ft the manifold pressure started to Fluctuate between 24in and 30in every time I pitched the nose up or down.
Without even touching the throttle.

On lower (normal) altitudes that never happens, Manifold pressure stays constant.


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[mandm]

Turbo on turbo off?

Mixture?

 

[Bell206]

Fluctuate between 24in and 30in every time I pitched the nose up or down.

My guess would be you were at or near the max turbo output and the pitch movements changed the ram air affect on the intake, ie., caused the MP to show that change.

 

[xander75]

I was gonna say how do you get 30" MAP at 21k ft!
I'd be +1 on @Bell206 that this is likely an air intake situation whereby the turbo can't compress anymore leading to lower pressure alltogether.
Do you have a special cowling or where is the turbo intake, maybe there is something you can do there to maximize the intake.

also when you say nose up, by how much? if it is a small pitch change when this shows I'd be investigating this more, more so then a larger attitude change...

 

[Dan Thomas]

Sounds like fluid in the gauge line, unless it's an electric gauge. Pitching up or down will affect the gravity on the fluid and change the pressure.