mutt, yes, I am indeed talking about all engine performance. Normally, the airplane will take off at max gross, retract the gear while still IGE, and stabilize in a full power first segment climb, flaps 10, at V2+10. The sideline noise measurement occurs during this stable segment. But at lower weights, if I fly the new V2+10, that means a lower TAS and an increased noise exposure time. (I know that's counter-intuitive, but if you review official sideline noise cert data, given the same TO configuration, the lower weight version almost always has a
higher sideline noise level due to the extra time exposure).
You infer that the equal-weight climb rate at V2+18 will be higher than at V2+10. Is that right? I know Vy increases with weight, but not really clear as to its comparison with V2 in general.
I used V2+18 just as an example. The point is, if my TAS is reduced, the noise police will demand a full flight test regime. (Read = costly and impractical). By showing no change in TAS, they'll accept NAC (No Acoustical Change) and I'll avoid actual testing.
Yes, in case of OEI, all bets are off. Fly per the AFM, noise be damned.
You wrote:
"If you are within the Stage 3 limits, why are you seeking a lower noise foot print? If your attempt is to reach the lower limits of certain airports (Paris), then without certified paperwork to prove these lower limits, the French DGAC wont accept your procedure."
I agree with your notion. But we're actually talking about a Stage 2 airplane undergoing some mods and involving a lower weight limitation. An acoustical change, other than a noise
decrease needs to be avoided. Hence the higher TAS requirement. Thrust reduction is not an option until a later second segment climb, during which a much lower noise level will occur. That one, final level, is the only one of any real practical interest, as it is the one most US municipalities are concerned about as they consider Stage 2 curfews and other restrictions. (And they typically measure in a simple dBA, single highest event, scale - not the complex EPNdB time-relative scale).
So, re-stating the question. My GIII weighs 65,000 lbs at takeoff, not the 69,700 for which it was certified. Based on 65,000 lbs, I calculate my V2 and I climb at V2+10. Next takeoff, same weight, same V2, I decide to climb at V2+20 (or whatever higher increment you choose). What will be the performance change, advantages or disadvantages?
PS: Thanks for that link, mutt. Very interesting, and I hadn't seen that before.
Cheers,
Tom