Opinions on this Crosswind Take-off from heavy metal flyers please
SkyGod
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Agree, well done.
Hopefully he was heavy with less than Max T/O flaps.
I have done a few cross-wind take offs on snow and ice where I had to abort at slow speeds, but this one seemed within limits..
Hopefully he was heavy with less than Max T/O flaps.
I have done a few cross-wind take offs on snow and ice where I had to abort at slow speeds, but this one seemed within limits..
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"There is no tire slip"
You sure about that?
You sure about that?
All I can see is a well executed takeoff in moderate to strong crosswinds. This happens hundreds of times a day. The plane is fully in control. Full traction of the tires. If they had to reject the takeoff they would stop in a few hundred meters.
Why would you think there are slipping tires? Do your tires slip when you switch lanes on the highway? Even when you do it a bit abruptly? No.
I've seen lots of evidence on the tires of 'bad' landings. I have yet to see bald spots caused by crosswind takeoff. Sure there will be some scratching but not to the extent that is alluded here.
Last edited by PENKO; 18th Aug 2016 at 19:07.
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Thanks again folks.
As a professional photographer I can say that long lenses compress distance, but they don't really change angles at those distances (they definitely change speed perception though which, as people rightly mention, makes some things look a lot worse than they really are).
I'd have to disagree about "There is no tire slip." though - I can't see an alternative for those moments where where the aircraft was pointing left but wheels moving right whilst still on the ground (assuming that there's not THAT much castoring available).
Personally, I always disliked on-the-limit cross-wind take-offs a lot more than on-the-limit cross-wind landings, although I imagine it's something you get more comfortable with after doing several hundred (or more) of them.
Thanks again - I've learned something.
As a professional photographer I can say that long lenses compress distance, but they don't really change angles at those distances (they definitely change speed perception though which, as people rightly mention, makes some things look a lot worse than they really are).
I'd have to disagree about "There is no tire slip." though - I can't see an alternative for those moments where where the aircraft was pointing left but wheels moving right whilst still on the ground (assuming that there's not THAT much castoring available).
Personally, I always disliked on-the-limit cross-wind take-offs a lot more than on-the-limit cross-wind landings, although I imagine it's something you get more comfortable with after doing several hundred (or more) of them.
Thanks again - I've learned something.
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Hi PENKO
I don't think so.
At time 30 secs, the nose wheel is tracking the centreline with the left main gear on the centreline. The main wheels are therefore displaced downwind by 2.86m. The distance between main wheels and nose wheels is 15.6m, therefore the aircraft is crabbed by about 11 degrees. (http://www.boeing.com/assets/pdf/com.../acaps/737.pdf
Since the aircraft is approaching VR with the ground spoilers not deployed, then the wing is generating some lift (left wing is rising despite left aileron and some spoiler). The load on the tyres must less than the weight of the aircraft and the tyres must be slipping.
Full traction of the tires.
At time 30 secs, the nose wheel is tracking the centreline with the left main gear on the centreline. The main wheels are therefore displaced downwind by 2.86m. The distance between main wheels and nose wheels is 15.6m, therefore the aircraft is crabbed by about 11 degrees. (http://www.boeing.com/assets/pdf/com.../acaps/737.pdf
Since the aircraft is approaching VR with the ground spoilers not deployed, then the wing is generating some lift (left wing is rising despite left aileron and some spoiler). The load on the tyres must less than the weight of the aircraft and the tyres must be slipping.
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Sure Goldenrivet, there will be slipping eventually when you lift off. But that is not what all the people on Facebook are oooh-ing and aaaah-ing about! In this topic there is even talk of 'power sliding'. No such things going on on ANY takeoff in max crosswind conditions that I have flown. Even in the worst crosswinds the plane will generally follow where the nose is pointed. I have never done a crabbed takeoff roll 
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Sure Goldenrivet, there will be slipping eventually when you lift off. But that is not what all the people on Facebook are oooh-ing and aaaah-ing about! In this topic there is even talk of 'power sliding'. No such things going on on ANY takeoff in max crosswind conditions that I have flown. Even in the worst crosswinds the plane will generally follow where the nose is pointed. I have never done a crabbed takeoff roll
With the nose pointing, say, 11 deg left of the centreline - the video shows nose left / tail right - but what it DOESN'T show (due to the angle) is the aircraft (probably) changing it's direction of travel (so it's still aligned with the direction it's pointing). So no slippage.
There are some moments where the nose goes left but the wheels slip to the right though. On a dry runway I'd expect that to either (a) not happen due to increased grip or (b) smoke / squeal as it happened (not that you'd see the smoke in that wind). That wasn't a dry runway though - I suspect that the dampness "lubricated" the slip quite nicely.
I've accidentally left power on during a cross-wind landing once (in General Aviation) and had a similar thing - tyres definitely didn't like it.
To my "general aviation" eyes that take-off looked a bit "on the limit" - but reading through your comments and watching it again I can now appreciate that it was well controlled. I'm not sure that all pilots would have the confidence & competence to pull it off though.
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I agree with you that a wet runway is more forgiving and you are right, the tires will slip a bit on a wet pavement but overall there will be full traction. So technically my statement of 'no slipping' might be a bit too bold. But looking at the takeoff run as a whole: there is no slipping and sliding along the runway.
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Hi BugSmasher1960,
How do you think a tyre develops a sideways load?
https://en.wikipedia.org/wiki/Slip_angle
The average direction of the aircraft was somewhere between straight ahead and about 10 degrees Left (into wind). At no time did the aircraft steer right to regain the centreline.
The tyres were slipping sideways in order to develop the force required to balance the cross wind loads.
Edit:
(Imagine a rolling tyre slip angle / skid as being equivalent to angle of attack / stall of a wing)
So no slippage.
https://en.wikipedia.org/wiki/Slip_angle
The average direction of the aircraft was somewhere between straight ahead and about 10 degrees Left (into wind). At no time did the aircraft steer right to regain the centreline.
The tyres were slipping sideways in order to develop the force required to balance the cross wind loads.
Edit:
(Imagine a rolling tyre slip angle / skid as being equivalent to angle of attack / stall of a wing)
Last edited by Goldenrivett; 21st Aug 2016 at 11:57. Reason: extra text
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In terms of maintaining centreline tracking, if there was tyre slippage, I don't think the pilots would be able to tell. All they can feel through the controls is gusts pulling the nose into wind and they would instinctively counter the yaw with rudder.
If the main gear tyres were slipping slightly at that time, that would have been caused by the overall wind effect exceeding the grip from the tyres. It's possible. The pilots aren't 'power drifting' a sports car, so I suspect any slippage of the main wheel tyres 75 feet behind them wouldn't be obvious. Those with more experience than I on slippy runways would be better placed to comment.
However, I don't think the video shows tyre slippage. Even at 100 knots the plane is covering 50m a second. If lateral displacement were 2-3 metres over the course of 2 or 3 seconds of video (over 100m of runway) that's well within my expectation of the aircraft tracking downwind of the centreline due to a gust before the pilots can correct.
Disclaimer: I have only just started my morning coffee and my brain is only engaged in 1st gear while typing.
If the main gear tyres were slipping slightly at that time, that would have been caused by the overall wind effect exceeding the grip from the tyres. It's possible. The pilots aren't 'power drifting' a sports car, so I suspect any slippage of the main wheel tyres 75 feet behind them wouldn't be obvious. Those with more experience than I on slippy runways would be better placed to comment.
However, I don't think the video shows tyre slippage. Even at 100 knots the plane is covering 50m a second. If lateral displacement were 2-3 metres over the course of 2 or 3 seconds of video (over 100m of runway) that's well within my expectation of the aircraft tracking downwind of the centreline due to a gust before the pilots can correct.
Disclaimer: I have only just started my morning coffee and my brain is only engaged in 1st gear while typing.
As Goldenrivett has pointed out, slip is an inherent feature of a conventionally constructed tyre. To get any forces from it (lateral, braking) you expect to have some measure of slippage, i.e. the direction the tyre is pointing and the direction it is going are different and/or there is average relative motion between the tread and the surface.
This is completely transparent to the pilot as they simply apply enough steering to track down the centreline and the slip angle looks after itself.
This is completely transparent to the pilot as they simply apply enough steering to track down the centreline and the slip angle looks after itself.
