ATM & fixed derates... yes again.

[KristianNorway]

Hello guys

Just to square this out from the start: Yes, I've read earlier posts, and yes, I've read the FCOM. I'm still puzzled.

I know that a fixed derate gives you a lower engine rating, resulting in lower Vmcg and Vmca, and therefor a lower V1. So far so good.

I don't understand how a lower V1 can give you more payload on any given takeoff.

Thanks

[Stuck_in_an_ATR]

AFAIK, lower V1 may be beneficial to TOW when stopping distance is an issiue, eg. contaminated runway. Lower V1=> better stopping performance => higher T/O weight.

[rudderrudderrat]

Hi KristianNorway,

The V1 go is able to be lowered (due VMCG being lower).
With full thrust, despite the acceleration being better, you need more runway to accelerate to the higher (VMCG limited) V1 go.

Edit. You only get an improved Take Off Weight on shorter limiting runways. When the runway is longer so V1 stop is beyond V1 go (with Full Power), then reduced thrust has no beneficial effect on RTOW.