76-00-00
page 10
May 01/2007
Effectivity 912/914 Series
Edition 1 / Rev. 0
d02626
BRP-Rotax
Maintenance Manual
2.1.2.3) Target pressure reduction by limiting the compressor
pressure ratio
To prevent vibration resonance, the max. turbo charger speed
of approx. 165 000 rpm must not be exceeded . Since the
turbo charger speed can be deduced exactly enough from the
pressure ratio, this ratio is limited to max. 2.6.
Example: e.g. at density altitude of 5500 m
ambient pressure approx. 500 hPa
max. permitted airbox pressure (regarding deactivation)
500 x 2.6 = 1300 hPa
i.e. no reduction of the target pressure, since this boost
pressure cannot be reached at all at this altitude.
Explanation:
The critical flying altitude for max. continuous power is reached
at 4500 m. Because of the low density at this altitude, the
actual boost pressure is only approx. 1140 hPa, although the
wastegate is completely closed.
Deactivation would not start until airbox pressure of 1300 hPa
is reached.
â—† NOTE: Deactivation happens very rarely and only
under certain climatic conditions and at certain
altitudes.
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