No, just above idle thrust. (N2
in cruise is around 20 to 25% higher)
On the P&W engines, I used to see this during the taxi out.
On aeroplanes with RR
(211-524 with IDG) or GE
CF6 it was during descent, but I don't remember the exact speed. (Should be at faster speed than the JT9D)
|Quoting jetmech (Reply 7):|
I would have imagined that you would want the straight through (direct drive) condition to occur at an N2 close to that associated with typical cruise power settings
Sure, but either way even if it was at cruise thrust setting it was a very narrow speed range in which the oscillations happened (+/- 2 or 3% max) and it didn't necessarily happened on all engines at the same time.
Needless to say the CSD's didn't really spend a lot of time in straight through mode.
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