A320 n1 mode
Joined: Jul 2013
Aviation Qualifications: Non-Aircrew
Posts: 5,679
Likes: 3,341
From: Everett, WA
I assume you're referring to the V2500, since the CFM is 'always' in N1 mode.
When you operate EPR engines in N1 mode, there is greater thrust uncertainty at N1 relative to EPR. So you typically have a performance penalty when operating an EPR engine in N1 mode.
With N1 rated engines, that uncertainty is already accounted.
That's really the advantage of EPR instead of N1 rated engines - less thrust variability at EPR. Hence N1 engines 'give away' more thrust, and for aircraft controllability/handling you need to assume a little more thrust than you're allowed to take credit for.
When you operate EPR engines in N1 mode, there is greater thrust uncertainty at N1 relative to EPR. So you typically have a performance penalty when operating an EPR engine in N1 mode.
With N1 rated engines, that uncertainty is already accounted.
That's really the advantage of EPR instead of N1 rated engines - less thrust variability at EPR. Hence N1 engines 'give away' more thrust, and for aircraft controllability/handling you need to assume a little more thrust than you're allowed to take credit for.
