Quote:
So that`s my question... if you have a clearway you`re supposed to get more weight off the runway... right? Because you can achieve V2 at 35ft beyond runway end, on the clearway.
[Unquote]
Yes: it will certainly never reduce it, and would probably increase it in the case you describe. But I think you may be misunderstanding the idea behind decrements. Correct me if I'm wrong, but the weight decrement you are talking about is meant to be applied to the RTOW that you have already calculated separately for a dry runway on the day?
Taking your figures:
TORA = 1800m
TODA = 1980m
On the dry runway, the 1980m TODA will give a noticeably higher RTOW than if there was no clearway (TODA 1800m)
The clearway is also useful for the contaminated runway case, but not as useful as it is in the dry runway case. The contamination has a big effect on runway performance (usually the stopping), but none on the airborne performance (theoretically). In other words, the length of the runway is the more critical thing in the contaminated case. So – when applying the weight decrement (CORRECTION) for the contaminated case – there has to be a greater penalty than if the TORA was as much as the TODA.
Once again: if the TODA and TORA were 1800m, the dry RTOW would obviously be lower than with your TODA of 1980m. Despite applying a smaller decrement to get the contaminated RTOW, the resulting contaminated RTOW would still be lower than the one you would obtain in your case, where you are applying a slightly bigger decrement to a higher RTOW.
Quote:
If option "no clearway" gives you best weight (more weight for takeoff). Can you actually use it, instead of "with clearway" option?
[Unquote]
NO!! 
That would be like keeping your fat, and eating it as well.
Hope this helps...
Last edited by Chris Scott; 4th November 2008 at 00:35.
Reason: Minor changes to reflect the fact that the extra clearway MIGHT not improve the theoretical RTOW in the contaminated case.