Turboshaft Fuel Flow/Altitude

[Brian Abraham]

I flew the things in helicopters for many a year but have no idea of the correct answer, perhaps should have paid more attention.
Question. As you climb with a fixed torque setting (constant horsepower) does the fuel flow (a) increase (b) decrease (c) remain the same. And of course the inevitable "why". Obviously the N1 increases as does the EGT. Searched the web without a direct answer and an authoritive link would help.
Thanks in advance.

PS Good to see you back Old Smokey, you've been missed. Did the leash leave any marks?

[rigpiggy]

can't answer to turboprops, but the pt6 fuel flows at a given torque are almost constant, however efficiency goes up due to TAS increase. At least up to temp limits.

[pjvr99]

As with any engine, the air/fuel ratio has to be maintained. So increase in altitude = decrease in air pressure = decrease in fuel required. However this is only a very small correction, and is therefore not as noticable .....