Drop the Dunlops,
The key to contaminated performance is an understanding of the range of available V1s. Most V1s given by a decrement from a table are produced for simplicity, using a mid-range V1. Unless at limiting weight, there will be a minimum and a maximum possible V1; calculating and choosing the most appropiate is the nub of the issue. If the contaminent is such that there is an acceleration problem (slush) then V1=Vr is the safest conditon - ie you are not trying to accelerate through the contaminent with an engine out. Conversely, a stopping problem (ice) requires a (properly calculated) low V1, but this must not be lower than Vmcg/Vmca. In your case you don't have to actually increase the weight - just use a V1 equal to or less than the V1 for the max weight achievable in the conditions, provided it is above Vmcg.
A simple technique to solve your problem may be:
1. Calculate the maximum T/O weight for the contaminated runway and then calculate the associated V1.
2. Compare the speeds given by your (lighter) actual T/O weight to those for the max weight for the conditons.
3. If required you can enhance your V1 up to that for the max weight for the conditions in order to achive V1>Vmcg. If the max V1 is higher than your intended Vr then you can use a V1/Vr of unity.
My company uses this technique to produce a single Wet/Dry V1, rather than uneccesarily sacrificing screen height by having a lower V1 than necessary in the wet.
Do not use a V1 lower than Vmcg - this would be dangerous.
I would not use less than full power for a contaminated take-off.
Regards
Last edited by Brain Potter; 27th December 2006 at 18:44.