Originally Posted by
GOMMY
To all our helicopter Brainiacs' out there, a question if I may ask please?
Why does the Maximum Continuous Power (OEI) available (and even 2.5 minute rating) reduce in a turbine helicopter with an increase in altitude?
Example: After an engine failure at Lafayette Regional Airport(42 ft AMSL), the AW139, MCP OEI at 20°C is 140% Tq (PI).
Lets also assume Standard Adiabatic Lapse Rate of 1,98°C (2°C) up to 10 000ft.
1. Why at 10 000ft ASMSL (0°C) with one engine failed after being in the cruise with 70% / 70% PI AEO, will the MCP OEI drop to 113% PI? (most likely ITT limit due to altitude and not TQ)
2. Will the PI Limiting also be reduced from 140% PI to a value of 113% (PI) maximum?
3. Is there a possibility of harming the remaining good engine coming of 70% PI AEO in cruise to an OEI condition in the cruise?
I can unfortunately not post URLs but if someone can help, the Graphs are in AW 139 RFM, Section 9, Fig 9-59 (OEI CRUISE - PA 0 Ft at 20°C) and Fig 9-86 (OEI CRUISE (PA 10 000Ft at 0°C)
Thank you.
I think short answers would be:
1. You’re torque limited AEO and ITT/NG limited OEI (ITT hot and high,N1 cold and high)
2. Not sure how the AW139 FADEC works but is PI Limiting a function that works AEO and OEI. If both then your answer is yes, otherwise no.
3. No, that would have been covered in flight test.