ITT rise with ECL full forward

[BrianUSMC]

Okay, i have been debating this with my roommate and am not sure of the SPECIFIC reason why this happens.

We all know on the T34 when you are doing the checklist and get to Environmental Control Lever full forward that we are looking for a rise in ITT. Can anyone give me a good 'in the weeds' deep answer as to why that happens?

I am arguing that the bleed air coming off the diffuser affects/decreases the P-3 air to the FCU causing the FCU sense a higher Py3 air ratio and to schedule more fuel.

My roommate thinks that the P3 air is coming from a different part of the diffuser than the bleed air, and that it doesn't notice the pressure drop from the bleed air running off... this keeps the FCU sending the same amount of fuel, which in turn translates to a higher ratio of fuel to the now lower amount of air in the diffuser (going to the combustion chamber)

Two of my IP's want my answer to this question... both of them say the FCU schedules more fuel.

Anyone know the answer?

Thanks
Brian

 

[squorch2]

When you put the lever full forward, it's bleeding off air from the compressor to heat the cockpit. Therefore, you have less air with which to cool the turbine and hence the rise in ITT. The check for rise and subsequent fall in ITT are to ensure that the valve opens and closes correctly, since you might need it in case of compressor stalls.

 

[Fly Navy]

When you put the lever full forward, it's bleeding off air from the compressor to heat the cockpit. Therefore, you have less air with which to cool the turbine and hence the rise in ITT. The check for rise and subsequent fall in ITT are to ensure that the valve opens and closes correctly, since you might need it in case of compressor stalls.

Ding ding ding

I can't believe I remember that... I haven't looked at T-34 systems since.... over a year ago.

 

[Steve Wilkins]

Ding ding ding

I can't believe I remember that... I haven't looked at T-34 systems since.... over a year ago.

Even I remember that....and T-34 systems was a little over 6 years ago for me. Though, we do use gas turbines on ships for propulsion, so that might have something to do with it.

 

[Gatordev]

Fly, you may still remember this because it's the same basic concept for most gas turbines, like Steve is saying. I'd bet your current jet has a similar thing happen, you just don't test for it.

 

[Fly Navy]

Fly, you may still remember this because it's the same basic concept for most gas turbines, like Steve is saying. I'd bet your current jet has a similar thing happen, you just don't test for it.

No I know, it's a basic concept of the jet... it's just associating the procedure of putting the ECL full forward for the test that I was surprised I remembered.

 

[BrianUSMC]

that's awesome guys, thanks.

I was specifically wondering if anyone knows how the bleed air affected the P3 air and the FCU fuel schedule to the compressor. Does the FCU send more fuel because of the pressure change (as the two IPs indicated)? ...Or does the fuel flow remain the same, combined with the subsequent reduction in air available in the compressor, resulting in temperature the ITT increase?

Sullivan

 

[flynsail]

You do not move the PCL or EPL during the ECL test, and the fuel flow needle does not move (at least I have never noticed). Do not know the answer, but just giving you some extra things that may help you.

 

[SteveG75]

The correct answer is PFM (pure f***ing magic).

 

[gaijin6423]

The correct answer is PFM (pure f***ing magic).

Not to be confused with the magic smoke electronic gear operates on. "Magic smoke," you ask? Sure, that's what happens when you break something electronic: You let the magic smoke out, and the damn thing won't work anymore.

 

[BrianUSMC]

PFM! that's the perfect answer. thanks, i am going with that tomorrow.

"PFM, Sir" "absolutely"

How about, "I'm not paid to take it apart sir... I fly it"

 

[East]

Bleedair schedule

that's awesome guys, thanks.

I was specifically wondering if anyone knows how the bleed air affected the P3 air and the FCU fuel schedule to the compressor. Does the FCU send more fuel because of the pressure change (as the two IPs indicated)? ...Or does the fuel flow remain the same, combined with the subsequent reduction in air available in the compressor, resulting in temperature the ITT increase?

Sullivan

As soon as there's a bleed air off take for any reason (i.e. ECS or anti-ice or whatever) the Fuel Control will react by leading more fuel into combustion chamber to compensate for the loss of bleedair. This will result in a higher temporary fuel flow accompanied with the momentary ITT rise. As soon as the compressor reacts on the turbine (action = reaction remember), the ITT will decrease again as it balances out again in function of the air ratio between compressor and turbine.
On the other hand, if you switch off anti-ice or another big source for bleedair you will notice a momentary ITT decrease accompanied with a rpm drop.

It works on GE CF-6 50 engines though (you know the big Tri-jet).
Hope that was any help....