PT6A-27 Question

[Escape Path]

Hi all,

I've noticed that the turbine temperature indicator (T5) doesn't really change throughout the flight. It basically stays at some 650°C; altitude and airspeed don't cause a visible change although torque does change as it should with altitude variations.

Anybody knows the reason?

Thanks in advance.

[twochai]

Perhaps because you haven't moved the power lever??

[Escape Path]

Well, maybe, but doesn't OAT and all the changes that come with increasing/decreasing altitude, ram air and whatnot play a factor as well?

[V1... Ooops]

Originally Posted by Escape Path

...Anybody knows the reason?

The power lever on an aircraft equipped with a PT6A-27 engine sets the speed of the gas generator (compressor portion) of the engine. As long as the power lever is not moved, torque will change if altitude is changed (decreasing with climb and increasing with descent), but gas generator speed (Ng) will always remain the same.

The fuel control unit adjusts fuel flow (Wf) in order to maintain whatever Ng set point that the pilot has selected using the power levers. As the aircraft climbs, fuel flow is reduced, and as the aircraft descends, fuel flow is increased - again, this assumes that the power lever is not moved.

I can only guess that the reduction or increase in fuel flow is more or less proportionate to the reduction or increase in air density, and for that reason, T5 does not change significantly.

Michael