(CL-600) N1 Indicator Compensation

[TurboCompound]

Hi all, this is my first post, so apologies if it's in the wrong thread/has been asked before (though I didn't find it in a search).

So I'm working on a detailed computer simulation of the Canadair Challenger 600 based on data from an actual flight manual, and I found a small detail that isn't particularly well explained. Here is the excerpt:

"T. O. / NORM SWITCH:
(Two position toggle switch)
T.O. - Fan speed indicator compensation is on. NORM - Fan speed indicator compensation is off. Actual N1 speeds are shown on indicator."

This is a caption labeling the corresponding switch on a diagram of the engine display unit.

The function is briefly described later in the document:

"For engines that produce more than rated thrust at a given N1 rpm, the system will bias the affected N1 %RPM indicators to read up to 2% high if the T.O./NORM switch is in the T.O. position."

I'm afraid that I'm not quite sure I understand how the indicator will behave differently with this system on, but hopefully one of you can help me out.

Thanks

PS: If you've piloted the classic Challenger before, feel free to tell me any quirks I should know that the flight manual wouldn't have covered.

[AerocatS2A]

With compensation off the indicators show actual N1 %. With compensation on they show an N1 equivalent to the actual thrust produced. Setting take-off power with compensation off will give you more than rated thrust on an engine that performs better than it should. With compensation on you will get rated thrust.

Does that help? I don't fly the 600 but it seems that it works the same way as other types.

[TurboCompound]

Thanks for the info, so for clarity:

If comp. is off, the actual N1 speed of the fan is shown, and if it's on, the thrust is measured and the N1 that would normally provide that thrust is shown?

What factors would affect said thrust significantly enough? Would the OAT have any effect, or is it just a maintenance thing?

Thanks

[AerocatS2A]

If it's anything like the BAe146 N1 compensation, it is not "live", it doesn't measure thrust directly. Periodically the engines are checked for performance and their thrust output vs N1 is measured. on the 146 you can see the compensation values when the engines are shut down. The N1 gauges will read small values rather than zero. These are the compensations.

So it is not related to any ambient temps or pressures, it's all to do with how the engine performs under test conditions compared to the nominal engine performance.

[TurboCompound]

Thanks for the clarification. I feel like you are probably correct, as the CL-600 actually has the same engines as the 146. I will have to find more documentation to see if there are any differences.

[Mad (Flt) Scientist]

I honestly can't believe there are any engines left for a 600 that perform better than "normal" any more....