Boeing-Slippery Runway

[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

[uniuniunium]

Not a Boeing driver, but...

I believe that it's due to reduced braking effectiveness, e.g. the lighter you are the more likely anti-skid is going to kick in and the longer it's going to take you to stop the aircraft.

[mangatete]

V1mcg is the minimum speed (on ground) at which the aircraft is controllable by aerodynamic means alone (no credit for nosewheel steering). As it relates to countering
asymmetric engine thrust, it is fundamentally a function of temperature and altitude - i.e. it is independent of
friction characteristics between tyre and runway.
On a contaminated runway, there are two forms of additional drag to consider:
displacement drag and impingement drag.
The former is about the additional drag caused by the force required to move the contaminant from the
path of motion. The latter is about the force on the airframe from airborne contaminant.
The deeper the contamination on the runway, the greater is the
physical resistance to lateral deviation (displacement drag) following engine failure and therefore a weight
"benefit" with increased contaminant depth.
I hope this has been of some help to you.
Cheers Mangatete.

[sebul]

It might have something with a lighter aircraft can hydroplane at a lower speed compared to a heavier one. Thus, if a malfunction occurs before V1 and you are forced to abort takeoff, there is a lower chance of the aircraft hydroplaning at a lower speed and eating up some of your accelerate-stop distance.

[DC-Mainliner]

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.