RCU Forums - View Single Post - Basic Skils: Turns using rudder

03-07-2014 | 07:42 AM

#233

Rob2160

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From: Sydney, AUSTRALIA

Quote:

Originally Posted by JPerrone

Ok, with all the knowledgeable people weighing in and confirming that cross wind exerts no force or acceleration on the aircraft, I'll accept that as fact.

This original post was regarding making turns, and the reason, partially, for that was to improve landings. The next question/observation is related to that, so we aren't off topic.

I'll present two cases
Case A: Aircraft is lined up with strip, wind is on the nose, straight on. The airplane heading is aligned with the strip and it lands nicely (with practice of course)
Case B. Aircraft is lined up on the strip, wind is off to the side a bit. Just for this case, lets say its 30 degrees off, coming from right to left. Observation of a real model airplane is that, holding rudder straight and ailerons flat, the airplane will tend to drift a bit to the left, away from the wind..

There is no sideways force from the cross wind, no acceleration, the wind is coming straight on the nose even though the true wind is coming 30 degrees off the nose.

So why does it drift like that? The plane should continue going straight.

There's 3 elements in there: the plane, the wind, the ground. I'm going to go out on a limb and say the ground is not moving any differently than it is moving in case A. So it has something to do with either the plane or the wind.

Regards

That is a fair question and easily answered.

You are right, in B, the ground is not moving any differently.

But the wind is. The wind is moving sideways relative to the runway in B.

The plane is being carried sideways by the wind. At the same speed as the wind, IE no acceleration and no force being applied to the aircraft.

The apparent wind is directly from the front of the plane, but the entire air mass is moving across the ground, carrying the plane with it at the same speed and not accelerating the plane.

The path through the air is straight, relative to the air, but the path across the ground is forward and sideways (relative to the runway)

The wind is carrying the plane sideways, not accelerating it sideways. There is a difference.

Last edited by Rob2160; 03-07-2014 at 08:12 AM.

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