ITT indications

[norwester33]

Hello
I have just converted to turbines and we have a PT6-34A.
When advancing the power lever the ITT initially rises around 40 degrees then drops back around 40-50 then off it goes up steadily.
is this normal and what is the reason??

Thankyou

[Dufo]

I don't know specifically about this model but on some other turbines this is due to airflow changes when prop governor increases the Np RPM with the same fuel flow (initially), gradually changing position of start valve and various bleed ports and is completely normal.

[Piltdown Man]

As the engine spools up, it is getting more efficient. So with a higher fuel flow, more torque and more RPM you have a lower ITT. My own engine does that (CF34) as did the PW125 I used to fly with. I've forgotten what the Tay used to do.

[604guy]

In very simplistic terms, remember that only about 25% of the air going through your engine is used for combustion, the remainder is used for cooling. As you advance your power lever, particularly at lower Ng's(N1's), your increase of fuel to the fire is momentarily ahead of the increase of airflow.

[Escape Path]

It happens on the PT6A-27 too. When starting the takeoff, initial power lever movement to around 10PSI torque will give a rise in temperature which immediately reduces to "normal" value. I've been told to accelerate to 10PSI, wait for the temperature decrease after the peak and then applying takeoff power as that will make it less hard for the engine.

[Nepotisim]

Not knowing anything about a PT6, but having jet engine licence.
Its not a bleed valve closing at a set point?

[Escape Path]

Its not a bleed valve closing at a set point?

I don't think so, the bleed valve in the gas generator turbine closes fully at 80%Ng. The peak is roughly at 20% of the engine's full power.

I'm leaning for this one:

As you advance your power lever, particularly at lower Ng's(N1's), your increase of fuel to the fire is momentarily ahead of the increase of airflow.

[VFD]

In very simplistic terms, remember that only about 25% of the air going through your engine is used for combustion, the remainder is used for cooling. As you advance your power lever, particularly at lower Ng's(N1's), your increase of fuel to the fire is momentarily ahead of the increase of airflow
604 has explained it as simple as it can be made.
When you start a turbine you are always looking for a "hot start" because you are only turning the turbine with the starter to supply air and the fuel control is in the process of ramping up the fuel flow for idle with the air flow catching up as N1 comes up to speed.
norwesters question is just the same only higher up the rpm range.

VFD