It is not a commentary on crosswind and take-off roll at all.
Where are Adam and Jamie when you need them?? 
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Another way to look at this. Landing is the opposite of take off. Landing in a cross wind, you can crab or sideslip. Let’s say you crab. IAS is 60 kts, cross wind component is 20. This means the SOG is 56.6 kts. The moment you touch down the SOG is only 56.6 kts compared to 60 kts for no cross wind. Clearly braking from 56 kts requires less distance than braking from 60 kts. Therefore accelerating to 56 kts take less distance than accelerating to 60 kts.
Peter wrote:
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Myth busters…
LeSving wrote:
Therefore accelerating to 56 kts take less distance than accelerating to 60 kts.
That is true but takeoff is not the opposite of landing and you will need to accelerate to 60 knots to rotate assuming that is the airspeed needed for rotation.
I think a useful discussion would involve carefully dismantling the points I made in my post #29.
Debating airspeed is a circular argument because that is just an indication on the ASI. It doesn’t directly represent the action of the airflow across the wing.
JasonC wrote:
That is true but takeoff is not the opposite of landing and you will need to accelerate to 60 knots to rotate assuming that is the airspeed needed for rotation.
I would say it depends on how theoretical you want to look at this and what kind of aircraft you fly. What you are saying is merely that we cannot take advantage of it, because we chose not to (for good reasons I guess, but nonetheless). It’s not physically impossible to rise the nose wheel at 56 kts, yaw into the wind and have 60 kts instantaneous, then lift off the main wheel and continue straight ahead in a climbing crab. Accelerating to 60 kts take longer and requires more runway.
Peter wrote:
I think a useful discussion would involve carefully dismantling the points I made in my post #29.Debating airspeed is a circular argument because that is just an indication on the ASI. It doesn’t directly represent the action of the airflow across the wing.
An alternative view might be to consider the effect of increased lift in isolation.
As a thought experiment, consider three tb-20s, two of which were built on a Friday… of which one has shorter wings than standard and the other longer. They are otherwise identical (same weight). The handbook gives lift off at 71kts and 78kts at 50ft, the stall speed in this condition is 65knots, Vx is not given but a reasonable guestimate might be 75kts, i.e. a little less than take off speed. The Friday specials have stall speeds of 63 and 67kts respectively. This difference is chosen to represent the 3kt difference in actual take off speeds, referred to in post #29.
Lets assume the take off roll is not effected and the pilots all operate as per handbook, so how are the take off distances thus effected? I would assert that there would be small differences, as climb angle is dependant on excess thrust versus drag. Indeed the smaller wing variant would be subject to the most drag, the standard one less so, and so on. However these differences are much smaller than if the speeds are recalculated and the correct safety margins used.
I think this makes a number of points.
Has no pilot of Cirrus, Diamond, AA-5, or Columbia/Corvalis contributed?
All of them lacks a steerable nose wheel. So when taking off in max demonstrated crosswind, some differential braking is necessary to maintain direction in all of those airplanes, until the slipstream gives the rudder enough authority. Braking during take-off does only one thing for the distance required.
The above effect is limited as it only applies in the beginning of the take-off run. But during landing in a strong crosswind, the need for differential braking is much more significant since there is much less slipstream on the rudder, so differential braking is required during most of the landing run, obviously increasing the distance required compared to max braking on both main wheels.
Generally I find that the operationally most significant point is that if a strong crosswing is coming 90 degrees on the runway, even a small change in wind direction will change the headwind/tailwind component a lot.
The above two points are on my mind in strong crosswind operations, both calling for bigger margins.
(I did read, or at least skim, all previous posts, and did not really find any convincing argument that a crosswind could benefit take-off or landing performance.)
