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Throttle Vs n2

Posted: Fri Dec 26, 2014 2:06 pm
by vololiberista
I have a couple of questions regarding the relationship of throttle position to n2.
Assuming ISA conditions at a sea level airfield.

Does the throttle position equate to engine n2? For example does 80% throttle=80%n2?
And, does slamming the throttle to full take n2 to above 100%?

Am I correct to assume the engine limitations schedule is valid at sea level?
Buon natale e felice anno nuovo a tutti.

Re: Throttle Vs n2

Posted: Sat Dec 27, 2014 5:23 pm
by bobisqueen
The throttle position is relative to thrust produced. Ie, throttles at half = approx half thrust. Off the top of my head the HPRPM speed at half throttle would be approx 90%.

Slamming the throttle to max, the engine could go over 100% at isa conditions but the engine would normally be limited by the max P3 pressure (HP comp outlet pressure).

The engine limiters and controls are valid thoughout the aircrafts entire flight envelope inc on the ground.

Hope that helps!

Re: Throttle Vs n2

Posted: Sat Dec 27, 2014 7:46 pm
by vololiberista
Many thanks that's useful. I'm surprised though that 90%n2 was at half throttle. I though it would have been around 80%plus. For a full throttle take-off the engines would be limited to at or below 100% then. Would I be correct in assuming that engine limitations could be more easily achieved in hot conditions?
Before your reply I did some calculations to obtain CN2 and got the graph below. If 50% throttle equates to 90%n2 then then the second half of throttle travel would only be 10% of n2 90-100%. and the graph would effectively be a horizontal straight line. It's easily changed if that is indeed the case.
cn2.jpg