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SWS-AlexVletsas avatar image
SWS-AlexVletsas asked SWS-AlexVletsas answered

Turboprop engine fuel consumption

After reading the topic on Jet Engine fuel consumption, I have a question regarding turboprops and their fuel consumption modelling. In flight_model.cfg we have three constants for fuel flow at low idle, high idle and max fuel flow.

Low idle fuel flow is always close to what we're putting in the cfg, but high idle is some value that is completely irrelevant to it. Can you lay out the formulae used for fuel flow calculations when we have a turboprop engine?

aircraftflightmodel
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FlyingRaccoon avatar image
FlyingRaccoon answered

Hello.

Here's some info about how fuel flow is handled, with some particularities for turboprop.

Basically, we determine a target N1 with the throttle and the fuel flow is adjusted to reach that N1.

If tp_high_idle_throttle_pos is not set, the target idle N1 is computed as:
idle_Ne = tp_idle_range * mixture_lever_pos + low_idle_n1

The corrected commanded Ne is given by:
corrected_commanded_Ne = idle_Ne + (100 - idle_Ne) * Effective throttle

The final idle fuel flow is given by:
final_idle_fuel_flow = (idle_high_fuel_flow - idle_fuel_flow) * mixture_lever_pos + idle_fuel_flow

One thing you have to consider is that if in idle, you have a target N1 that is high enough to be beyond what the idle fuel flow can allow, then the fuel flow will be adjusted to reach that N1 and will not correspond to what you specified.

Let me know if that answers your question.
Regards,
Sylvain

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SWS-AlexVletsas avatar image
SWS-AlexVletsas answered

@FlyingRaccoon thanks, that covered it!

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