B737 Crosswind take off technique

[Hudson]

737NG PF used full control wheel application at start of take off run with 20 knot crosswind comp. Leaves full wheel on and nearing 120 knots the aircraft acceleration slows significantly resulting in obvious performance degradation and V1 now invalid. Obviously a case of spoilers being more effective as speed increases.

While Boeing state that only very small increase will occur in TOD even with extreme crosswind components providing correct lateral and directional input applied, there is little current FCTM amplification on definition of correct input.

A 1976 version 737-200 FCTM has a diagram showing that at 40 knot crosswind only 34 degrees control wheel deflection is needed as against 80 degrees available. In other words a little over one third wheel deflection.

From this, one could assume that no lateral input is required on a crosswind take off until the maximum crosswind limit is approached? I have often noticed that pilots wind the wheel well down into any crosswind above 10 knots. Is this really necessary or a waste of effort?

[alexban]

"Smooth rudder control inputs combined with small control wheel inputs result in a normal takeoff with no overcontrolling.Large control wheel inputs can have adverse effect on directional control near V1(MCG) due to additional drag of extended spoilers."
"during rotation continue to apply control wheel in the displaced position to keep the wings level during liftoff.The airplane is in a slideslip with crossed controls at this point"
All this from FCTM oct2003.
The amount of controll wheel displacement will decrease as speed increase,and usually will be required only a smaal amount of wheel to decrease effort on rudder pedals,avoiding overcontrolling on takeoff.
:ok:

[FlareArmed]

This is an interesting issue. Today, I experimented with crosswind takeoffs in the simulator during recrrent training and may be able to add to the discussion.

Firstly, about 10 degrees of control wheel movement is required to cause spoiler deployment. This is a very small control wheel input, yet I found this was ample to maintain directional control with a 34 knot crosswind (maximum for my model B737).

There was only 2 degrees of bank on the takeoff roll, yet almost full control wheel input (and full spoiler deflection) was required to level the wings. My opinion is that large doses of aileron/spoiler are not required to maintain directional control.

Another interesting point was noted after a takeoff I had recently in a strong gusty crosswind on a wet runway. I needed quite a lot of rudder input (left rudder with a crosswind from the right) to cope with the gusts. After liftoff, the aircraft rolled quite hard to the left because I had failed to release rudder pressure early enough resulting in crossed controls to maintain wings level (it was a very rough night and I had a death grip!). I spent quite a while experimenting with this today and discovered the combination of a very small aileron input on the takeoff roll, and relaxation of rudder input the moment the aircraft unsticks, resulted in a very satisfactory takeoff at the maximum crosswind guideline of 34 knots.

[Human Factor]

We were always taught not to apply more than 10 degrees of aileron into wind for this very reason.

[Hudson]

Thanks for replies. Now, how about the landing case immediately after touch down in 35 knot crosswind? If crosswind from right and full control wheel input (right wing down) is maintained, could someone advise if all ground spoilers rise symmetrically? - and secondly under these conditions do the upwind flight spoilers go fully up or incrementally up depending on wheel deflection angle?

Or do all ground and flight spoilers go fully up regardless of wheel postion leaving only the ailerons to stop any tendency for the into wind wing to rise?

This would seem the obvious thing in order to ensure equal symmetric drag from ground and flight spoilers. The FCTM only mentions aileron application to keep the into wind wing from lifting.

[alexban]

HF: how do you know this '10 degrees" ? I know about this,and I checked today.The spoiler begin to raise at a 0.5 units control wheel deflection. At 6 units ,or less, of control wheel deflection the spoiler is full extended. So,what are this 10 degrees ,the book says about?

hudson: I think ,after landing,the spoilers will go fully up,regardless of control wheel position,commanded by the armed speedbrake,ground sensor,wheel spin.You are right about the drag,I guess.

[NSEU]

"I think ,after landing,the spoilers will go fully up,regardless of control wheel position,commanded by the armed speedbrake,.."

The maintenance manual doesn't seem to suggest this, gents. During a spoiler mixer check, the speedbrake lever is placed in the UP position and the control wheel turned 87 degrees CCW... and one of the checks is to ensure that spoiler No. 9 is "not in the fully down position" (yet specifies that the spoilers 2 and 4 are at 32/37 (+/- 3 ) degrees respectively... around their fully up position).

Other than the spoiler combination 9, 11 and 2 for a clockwise turn of the wheel, no other spoilers are mentioned, but this is not to suggest that others don't move down also.

Rgds.
NSEU.