V1 and weight
 

Guys

As we know V1 increases with weight if not field length limited.

What if field length limited ? i have seen a book stating that in that case V1 will decrease ! is it correct ? when field length limited with higher weight which requirement is the most critical ? stopping or accelerating single engine ?

thanks

For a balanced field length, as weight increases V1 must decrease due to brake energy limits. In other words, the more weight you have, the more brake energy required to bring it to a stop within the confines of the balanced field, and hence the earlier decision required.

i understand
however i recall Vmbe is like V1 max . so if we are not approaching V1 max what happens ?

Just to add to what chimbu said: At a higher weight you will also take longer to accelerate. If you were to accelerate like normal and then reject the takeoff at the same point (along the runway) that correspondes with the lower weight V1, as chimbu said, you will run out of runway! But at that point along the runway, at a heavier weight, you will be at a lower speed. So you need to have a V1 speed that's even lower than that so that you reject the takeoff at a point along the runway that is sufficiently before the V1 point of the lower weight, to guarantee that you will stop on the remaining runway.

Both accelerate-go and accelerate-stop are equally important with regard to balanced field. Are you flying a commuter or transport category airplane? In the US, Canada or different country?

If you have a balanced field length, you are at your maximum performance limited take-off weight.

You cannot, therefore, increaes the take-off weight any further.