Cross wind take-off. Spoiler drag.
There is opinion out there that says we should minimise control wheel displacement beyond a couple of units during a crosswind take-off as this will cause the flight spoilers on the up-wind wing to raise, causing additional drag. It has been said that this extra drag will reduce Vmcg and adversly affect take-off performance.
I can understand these concerns to some extent however with regards to Vmcg, unless V1 is equal to minimum V1 (due to Vmcg considerations), it doesn't really matter that Vmcg increases does it? For example if V1 is 130 kt, the Vmcg quoted in the manual for a particular take-off is 120 kt and due to spoiler deployment the actual Vmcg increases to 125 kts, if I suffer an engine failure at 120-125 kt I am going to be closing the thrust levers and stop anyway. Closing the thrust levers immediately removes the assymetric thrust
How often is V1 any where near Vmcg? For the vast majority of the time I would say it is not. And during my search on the subject before typing this post I read on an archived thread that Vmcg assumes nil crosswind in Europe and just 7 kts in the USA anyway. It seems the simple fact that a crosswind exists makes all the Vmcg data invalid even before I consider puting aileron into wind.
Now my question is, if I put in the required control wheel displacement such that it is roughly in proportion to the amount of rudder input and the wings stay level during the take-off roll and rotation, how much extra drag will there be? (I'm talking B737, B767, B747, A320, A330, A340.)
How would you quantify it in terms of head wind component or assumed temperature? That is to say if there is a 10 kt headwind and we make the take-off calculations assuming nil wind, would that be enough compensation to make the extra spoiler drag a non-issue? Or if the actual temperature is 30 degrees C and the assummed temperature is 45 degrees C, would using an assumed temperature of 40 degrees C be enough to compensate for the extra drag.
The reason I ask is because my gut feeling is there's more risk to the operation by not puting in enough aileron during a crosswind take-off for fear of spoiler deployment than there is by puting in aileron in proportion to rudder displacement and accepting the extra drag. This risk by under doing the ailerons comes during rotation.
I have seen first hand the 1-2 degrees roll during the take-off run (yes you can see it on the ADI) suddenly become roll of 5 to 10 degrees during rotation because there was insufficient aileron into wind. How we didn't get a pod scrape I do not know.
This sudden requirement to adjust the ailerons to where they should be to prevent the roll also causes a subsequent tendancy to rush the rotation. Is it any wonder many tail scrapes happen during crosswind conditions!
May I say having to REACT to a sudden roll at such a critical moment in the flight to prevent aircraft structural damage rather than having the correct aileron input to begin with seems like bad operational policy to me!