Originally Posted by metabolix
If we use Improved Climb (Airport Analyses) tables with a given weight of lets say 55.8t under the 0 wind column, it gives us speeds of v1:150 vr:154 v2:159
Now, although you are more temperature limited for a given weight under the 10kt tailwind column (although not prohibitively in most cases) the speeds for 55.8t are v1:144 vr:150 v2:159
As I said, these are not actual figures, just an example.
So the question is, for a given weight if lower V-speeds (V1 and Vr) are acceptable with a tailwind, then why would those speeds not have been used in the 0 wind column to start with?
The V1 is not a problem - I got that. But why Vr?
A possible suggestion; it's not the Vr which is being limited, it's V2? Which would be consistent with both V2 values being the same.
Then we need to wonder whether there is something about the speed-spread model which is forcing a higher Vr-V2 split with a tailwind.
I haven't thought it through, but if the asumed takeoff technique is the same - rotation speed, target pitch, etc - and the 'tailwind' aircraft is actually at a faster groundspeed, could there be something in the dynamics allowing the aircraft to accelerate more during the rotation phase. Perhaps it's harder to get an accurate pitch target with tailwind takeoffs, so the FT data is worse for speed spread?