Originally Posted by
SuperRanger
Can someone enlighten me, why in the slippery runway speeds correction in the QRH, that the lighter the weights the greater the V1 reduction? Thanks.
SR
I'll try to take a stab at it.
A lighter aircraft can reduce V1, and benefit form this, for the following reasons:
We are talking about a slippery runway. That increases the length required to stop beacuse it's "slippery".
So the goal is to reduce the speed at which you are liable to stop from, in a rejected takeoff. Reduced speed means less energy to dissipate from the wheel to runway link on the reduced friction runway - so you can stop in time and not go into the ditch.
We reduce the energy liability by reducing V1. (since we know we continue with the takeoff when we are beyond V1).
With an engine failure, the lighter aircraft may accelerate in a V1 - Go scenario, from a relatively low V1, and still make the screen height of 35 feet at the end of the runway while completing the takeoff run on one engine.
A heavier aircraft would not be able to continue accelerating down the runway from a "low" V1 as smartly, and still make the screen height limit, with one engine inop.
This scenario represents an "unbalanced field" performance example. The distance it takes to stop from V1 will not be the same distance it takes to accelerate on one engine at V1 and make the 35 foot screen height at the runway end OEI. But, the runway required in the performance figures will represent the worst case liability that you are dealing with - be it stopping distance (heavy) or reaching screen height on one engine (light).
I believe Boeing favors a low speed abort on a slippery runway so if V1 can be reduced, they will give you numbers to do so.
Of course no one may reduce V1 below Vmcg or 1.1 Vs - or something like that - I'm winging this but you get the idea.