Researching the etymology of 'rotate' (that OED lacks!), I chanced on Anas Maaz's Quora answer:

What many does not know is 'rotate' is just not a fancy word, but it involves a real physical rotation. When Rotation speed (Vr) is reached, the pilot pulls the control column which deflects the horizontal stabilizer, causing a rotation along the lateral axis of the airplane lifting up the nose wheel.

  1. Am I correct that Maaz's referring to the 'lateral axis' in the diagram beneath?

enter image description here

  1. Even if yes, what exactly ROTATES? How does the lateral axis ROTATE?

Imagine the wing on the y-axis and time on the x-axis, like the graph beneath. I don't think it's correct mathematically to state that an axis rotates, when it's the function that moves up as time passes?

enter image description here

  • $\begingroup$ An interesting mathematical subtlety is that in general, rotations occur in a plane as opposed to about axis. It just so happens that in 3D, a plane has an orthogonal axis. But there is not axis to a plane in 2D space, although you can rotate things to your heart's content. In 4D and higher, you get all kinds of weird. $\endgroup$ – MikeY May 20 '19 at 16:47
  • $\begingroup$ Note that the quote in your question does not say the axis rotates, but that the plane rotates along the axis. $\endgroup$ – TomMcW May 20 '19 at 17:19
  1. Yes that is the lateral axis of the aircraft.

  2. The aeroplane rotates about the lateral axis, causing the nose to go up/down. The aeroplane then descends or climbs, causing the aeroplane axes to shift relative to earth axes. But the aeroplane axes are all defined relative to the aeroplane.

  • 1
    $\begingroup$ One tiny nitpick. Before liftoff the axis of rotation is actually the landing gear axles rather than the cog as it is in flight. $\endgroup$ – TomMcW May 20 '19 at 17:22

1: Yes, rotation around the lateral axis will make the aircraft pitch. You understood that correct. On the other hand lateral rotation means something else, namely roll.

2: Its not the axis that rotates, its the aircraft that rotates. The axis is in a body fixed reference coordinate system, hence the whole coordinate system (and aircraft) rotates in relation to earth.


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