GTE's

[flyjet787]

On a cold day, the idle speed of a GTE without a Fuel Control unit will?

a) Increase
b) Decrease
c) will not be affetcted.

and why?

Same question.. the GTE has a FCU. How will that affect the idle speed?

[barit1]

How do you run a GTE without a FCU??

[Spanner Turner]

On a colder day the air is more dense, so more energy (work) is required to drive the compressor. If no extra fuel is added the engine will slow down.


If you don't want your engine to slow down as temp drops, then a little more fuel is added to keep the engine at the same RPM.
(the upside of this is, you are now producing more thrust as more air is being passed through the engine even though RPM remains the same)


:ok:
.

[barit1]

...the GTE has a FCU. How will that affect the idle speed?

Depends COMPLETELY on the design of the FCU. Some will govern to a constant speed, modulating fuel as required to achieve that. (i.e. colder day, more fuel).

And some will intentionally reduce rpm to maintain constant idle thrust, though not necessarily the same rpm as in the first question.

I have worked on both types.

Incidentally - on a engine for supersonic use, at high Mach (high inlet temp) the idle speed is likely to be increased a great deal - up to 100% maybe. This is to insure that the aircraft inlet keeps "swallowing" all the air rammed into it.