"Rotate"
- Thread starter BCTAv8r
- Start date
The Gardener
Terrafirma Phobic
Rotation (Vr) by no means represents the moment the aircraft leaves the ground. That would be 'lift off' speed.
It strictly refers to the speed that the nose wheel leaves the runway and the plane is pitched to the takeoff attitude.
Of course, I'm not flying Jets either. Might be something different there...
It strictly refers to the speed that the nose wheel leaves the runway and the plane is pitched to the takeoff attitude.
Of course, I'm not flying Jets either. Might be something different there...
kellwolf
Piece of Trash
Nah, that's pretty accurate. Jets are just really big airplanes. Something I think that gets lost in the shuffle when some of the new guys with low time came up at my airline is the thing is still just an airplane. Turn the yoke left, it goes left. Push forward, houses get bigger and all that. It still even follows the laws of physics like coordinated turns and ground effect. Though those two get forgotten about a LOT around here.
Despite my poor choice of words, I know that rotation happens when the nose leaves the ground. My question was why it was called rotation. The answer apparently being "because the aircraft pivots around the axis of its main landing gear".
Bumblebee
Commodore
This was another reason someone came up with...I cannot vouch for the validity of this explanation.
Rotate is one of those words that have been handed down from the days when there was a physical mechanism at the bottom of the airplane control console (the "stick" in smaller aircraft). When the aircraft reached a certain taxi speed where it could begin actual flight (the so-called Vr speed) the pilot would pull back on the stick and a mechanism at the pivot point of the stick would rotate slightly and send that "command" to the control surfaces, particularly the elevator in the back, causing the nose fo the plane to come up and the plan to begin to lift off the ground. If the aircraft then reached the acceleration speed, where it was safe to begin the take-off climb, then things were good. If it didn't reach that speed, the pilot could easily abort the takeoff by pushing forward to lower the nose. The device has been replaced by electronics and remote actuators, but the terminology remains, and is still important as an indication of attaining the speed necessary for takeoff.
Rotate is one of those words that have been handed down from the days when there was a physical mechanism at the bottom of the airplane control console (the "stick" in smaller aircraft). When the aircraft reached a certain taxi speed where it could begin actual flight (the so-called Vr speed) the pilot would pull back on the stick and a mechanism at the pivot point of the stick would rotate slightly and send that "command" to the control surfaces, particularly the elevator in the back, causing the nose fo the plane to come up and the plan to begin to lift off the ground. If the aircraft then reached the acceleration speed, where it was safe to begin the take-off climb, then things were good. If it didn't reach that speed, the pilot could easily abort the takeoff by pushing forward to lower the nose. The device has been replaced by electronics and remote actuators, but the terminology remains, and is still important as an indication of attaining the speed necessary for takeoff.
The Gardener
Terrafirma Phobic
Perfect. It wouldn't quite be correct to say that the plane rotates around the lateral axis at Vr since that would technically be centered on the location of the CG, which we can assume would be higher than the main landing gear.
Regarding planes being planes I always hear guys ask "whats Vr?" when they are getting checked out in something new. I always tell them pitch the nose to the horizon when you have the airspeed to do so; it will lift off when it is ready to fly. Vr can be anything we want it to be and the plane will fly when it is ready too.
PeanuckleCRJ
Poodle Wrangler
The action taken at "rotate" speed is simply to begin to bring the aircraft's nose up during the takeoff roll. Derotate is what you do during the flare when you bring the nose back down to the ground.
The speed that "rotate" is called during a large aircraft's takeoff roll is the calculated speed to get the aircraft into the air and stabilize at the appropriate pitch attitude to maintain V2+10 to 15 with a 2 degree per second rate of pitch up.
This is theoretical of course....in real life, on both the 757 and 767 I bring the nose to 7.5-9 degrees nose up and stop rotation until I break ground. This ensures that the airplane will fly and keeps me from dragging the tail if we have a bunch of fatties in the back whose weight wasnt accounted for... Once I break ground, then I continue pitch up to normal attitude (15-20 degrees nose up typically).
As far as the physics of it.... during the first part of rotation you are pitching around the main wheel trucks.... they are situated aft of the true lateral axis. Once the weight is relieved off of the trucks, then you are pitching directly around the lateral axis of the aircraft.
The speed that "rotate" is called during a large aircraft's takeoff roll is the calculated speed to get the aircraft into the air and stabilize at the appropriate pitch attitude to maintain V2+10 to 15 with a 2 degree per second rate of pitch up.
This is theoretical of course....in real life, on both the 757 and 767 I bring the nose to 7.5-9 degrees nose up and stop rotation until I break ground. This ensures that the airplane will fly and keeps me from dragging the tail if we have a bunch of fatties in the back whose weight wasnt accounted for... Once I break ground, then I continue pitch up to normal attitude (15-20 degrees nose up typically).
As far as the physics of it.... during the first part of rotation you are pitching around the main wheel trucks.... they are situated aft of the true lateral axis. Once the weight is relieved off of the trucks, then you are pitching directly around the lateral axis of the aircraft.
The Gardener
Terrafirma Phobic
Brilliant. I love it.
SIUav8er
Narcosis
fo4ever
Well-Known Member
Well said sir.
That's the same reason I often see "Alpha speed" at the speed book value. Yep, we are a tad bit heavier than advertised. click the speed up one knot at at a time until it goes away and fly that 'till touchdown. Or just click the throttles off and turn the MD into a DC-9....Self serve!
What's an "axis"? is that what I saw on WWII in HD on discovery?
:crazy:
Maddog1974
Well-Known Member
Is fatties an official or technical term. And btw I do not take offense to that remark...I resemble it.
R
Roger, Roger
Guest
Rudder? That's for when you lose an engine right?
PFGiardino
Well-Known Member
I've always hated "rotate" in the 172.
Student: "Vr, Rotate."
Me: "Guffaw, et cetera."
Rotate, to me, means that the airplane's angle of incidence is so low (transport category) that it needs to be physically ROTATED about it's axis to produce an AOA which will allow a CL high enough to fly. If you don't have enough elevator authority, it can't be done, hence the need for speed (don't drop a movie reference). That's why you see airliners sitting there at 150 kts or so with their nosewheel in the air for a few seconds.
A 172, on the other hand, just starts flying when it's fresh and ready, and it's your job to guide it along.
Student: "Vr, Rotate."
Me: "Guffaw, et cetera."
Rotate, to me, means that the airplane's angle of incidence is so low (transport category) that it needs to be physically ROTATED about it's axis to produce an AOA which will allow a CL high enough to fly. If you don't have enough elevator authority, it can't be done, hence the need for speed (don't drop a movie reference). That's why you see airliners sitting there at 150 kts or so with their nosewheel in the air for a few seconds.
A 172, on the other hand, just starts flying when it's fresh and ready, and it's your job to guide it along.