Use of rudder during aircraft rotation

[Rainboe]

I'm still trying to work out why my answer was not 'approved'!

[one dot right]

Upset someone Rainboe?

[Blip]

Originally Posted by one dot right

What did Rainboe say that was so incorrect? Seemed like a perfectly reasonable course of action.

Rainboe said:

Because of the crosswind element, as the aeroplane lifts off, it becomes in a slight yaw situation as the relative direction of the wind is not aligned with the runway direction, which is what the aeroplane is pointing in.

How did Rainboe manage to track the runway centreline up to the point of rotation? Why is the aeroplane pointing in the direction of the runway and not the direction of the relative wind? Was it not with rudder opposing the:

aeroplane naturally turning slightly into wind by itself

?

If you have a crosswind from the right, you will have left rudder opposing the "aeroplane turning into wind by itself". You have right aileron to counter the right wing producing more lift than the left wing. You maintain this cross control during the rotation. You do not just suddenly abandon the rudder!

Once airbourne you still have these crossed controls. The aircraft will still be heading in the direction of the runway centreline, while sideslipping to the right (into wind). This sideslip will equal the crosswind and the two cancel out. The aircraft is therefore tracking the runway centreline.

Now at this point all you need to do now is slowly relieve the pressure on the rudder pedals until they have naturally come back to the centre. When you say:

I don't think you should use rudder- you are causing another yaw situation, and when you remove the rudder input, you are creating a reverse yaw situation in the other direction.

it seems to me you might be unclear as to where the rudders are at this point in time. I might be wrong but it seems you are visualising the pilot [b[initiating[/b] rudder input at this time to cause the heading to change. This is not the case. At this point in time the rudder input is already there and is in fact now being reduced back to centre.

While the rudder displacement is reduced, the ailerons are reduced too. While this happens, the aircraft has a natural tendency to turn ever so slightly and assume the correct heading to continue tracking the runway centreline. You initiate the movement of the rudder first and then the ailerons in response to the reduction in induced roll. In other words you consciously move the rudder in a deliberate and controlled manner, and move the ailerons with whatever response is required to keep the wings level.

At this point in time, the wings are now level, all the controls are centred, and the correct heading is established which causes the aircraft to continue to track the runway centreline.

I hope what I have written is clear. Being able to demonstrate it in the real world would be so much easier!

[Intruder]

Another way of looking at the situation is that it is exactly the same as a crosswind approach/landing situation, in that there are 2 ways to fly the approach: Wing down/top rudder (slip) or crab.

Both have the same net effect, in that they allow the airplane to track the localizer or extended runway centerline. Both require some kind of transition from the airborne to the runway environment. Both allow some combination of the basic 2 techniques. Both become "intuitive" to the experienced pilot, who may not overtly realize which [combination of] technique he employs, and in what sequence.

The one difference is that in the takeoff case, a slip is not normally seen as a "proper" technique once airborne, so a transition to balanced flight is "always" required. The choice is then to maintain runway heading or to "crab" into the wind to maintain the extended runway centerline track. Both are "proper" techniques, and one or the other may be required in specific departure procedures (though it appears that maintaining track is becoming the more frequent requirement).

IMO, the bottom line is that a controlled transition from runway to airborne environment must be made, and specific techniques for doing so depend on the airplane and installed equipment.

[Rainboe]

Once airbourne you still have these crossed controls. The aircraft will still be heading in the direction of the runway centreline, while sideslipping to the right (into wind). This sideslip will equal the crosswind and the two cancel out. The aircraft is therefore tracking the runway centreline.

Now at this point all you need to do now is slowly relieve the pressure on the rudder pedals until they have naturally come back to the centre. When you say:

Blip, once airborne, almost immediately you have to reduce rudder input to zero. I have found that the aeroplane will not weathercock enough into wind to counter the drift by itself. You see this when watching planes sliding downwind after take-off when they haven't applied enough drift- very few ever move upwind. So my answer to Snakes initial query in the first post:

Would you use rudder during aircraft rotation in crosswind conditions to push the nose into the wind? This in purpose to assure a correct drift angle to maintain runway track after lift-off.

Or...., wait until after lift-off and then bank slightly into the wind to maintain runway track.

....was not to then use rudder into wind to apply further drift required but to bank slightly towards the crosswind keeping balanced flight until you have the full heading offset required to maintain runway track.

[Blip]

Ok Rainbow. I think we are on the same page more or less.

The technique I describe works very well for me. The whole process of rotation and initial climb always feels under control and therefore I have no inclination to rushing the rotation and risking a tailscrape.

Also you might be right about there being some crosswind not being accounted for by the crossed controls once airbourne, however the aircraft type I fly has a map referenced to track and it does not ever indicate any drift more than a degree or so.

Also to clarify, I begin to reduce rudder input as soon as I am finished with the rotation and am at the correct attitude for initial climb (15 - 18 degrees nose up). This would be at about 100 ft AGL. The time it takes me to then centre the rudder pedals is about 3 - 5 seconds depending on how much they're displaced. So even if I was drifting a degree or so, it would only be for a matter of seconds.

Of course as you climb, the wind tends to strengthen and change direction as well. Once the rudder is back to centre I would certainly be using aileron to adjust the heading in an attempt to maintain runway track.