Opinions on this Crosswind Take-off from heavy metal flyers please

[BugSmasher1960]

Video of crosswind take-off of a JAL 738 doing the rounds.

https://www.facebook.com/TheAcquaPlanet/videos/1631095577182053/

Some are saying "just a normal crosswind takeoff" - others are saying "Waaaay over the limit". It's looking pretty dicey to me - just wondering what you chaps who fly these think of this in terms of aircraft and airline operational limits?

[BleedingAir]

Typical of Facebook commenters, most of them thought the tires were smoking as well.

It's hard to make a call from one video, and telephoto lenses such as that used here can make things look worse than they do out the front windows.

Our takeoff crosswind limit on the 738 is 33 knots including gusts. This takeoff could certainly have been hovering around that number, so while looking a bit dicey, was within the requirements.

[BugSmasher1960]

Our takeoff crosswind limit on the 738 is 33 knots including gusts. This takeoff could certainly have been hovering around that number, so while looking a bit dicey, was within the requirements.

Thanks BleedingAir - is that limit only for a dry runway (this one was obviously a bit on the damp side)?

[ACMS]

Looked fine to me, quite well controlled down the centreline. Maybe a little more Aileron into wind perhaps at around 100 kts where you can see the into wind wing ( left ) rising up a little. That's not a big deal and they did a good job.

[BugSmasher1960]

Looked fine to me, quite well controlled down the centreline. Maybe a little more Aileron into wind perhaps at around 100 kts where you can see the into wind wing ( left ) rising up a little. That's not a big deal and they did a good job.

Thanks.

I was somewhat concerned about the side-loading / slipping put on the tires (admittedly a little less in this situation with the damp runway).

[ANCIENT]

Actually ACMS I thought there was too much left aileron because you can see the spoilers deploying on the left wing. The increased drag then requires more right rudder to keep straight.
Overall I think they did a good job, must have been on the limit.

[compressor stall]

A good training video reference aileron use in crosswind. Certainly one of the better ones I have seen.

Following on from Ancient's comment - from the 737-800 FCTM

"Large control wheel inputs can have an adverse effect on directional control near V1(MCG) due to the additional drag of the extended spoilers."

[BleedingAir]

Yes the limit is lower on a wet runway, but moisture on the runway doesn't automatically qualify it as "wet". It may have been justified to use dry limitations on this occasion. And different operators specify different limitations.

As for side loads on the tires, the gear is designed to handle that.

[FullWings]

Looked OK to me. Didn’t let the into-wind wing pick up, tracked the centreline more-or-less, didn’t try and snatch it off the ground, reacted well to gusts.

It doesn’t look like full control deflection was used at any point, so they had more authority if they needed it. I’d say that was a well-flown crosswind takeoff in the prevailing conditions.

[Capn Bloggs]

Facebook drama queens.

[JammedStab]

Kept the wings level during rotation which is desired.

[BugSmasher1960]

Thanks everyone.

So just to clarify, a degree of visible tyre side-slip is OK?

I kinda liken it to applying a bit of opposite steering when power-sliding a car around a corner; on one hand the vehicle is still under control, but on the other, the very fact that tyres are slipping does indicate that it's reached a "new level" when compared to normal cornering.

Just wanting opinions on whether that is considered "OK" from a heavy metal point of view? (in an industry that's generally considered to be very conservative).

[Capn Bloggs]

Just wanting opinions on whether that is considered "OK" from a heavy metal point of view?
Opinions given above...

[Capt Fathom]

I was somewhat concerned about the side-loading / slipping put on the tires
Don't the later 737's have main wheels that castor slightly? They seemed to maintain the centre line reasonably despite the way the aircraft was pointed!

[PENKO]

I see ab-so-lu-te-ly nothing wrong with that video.*
There is no tire slip.
And I'm almost sure that it wasn't even near the limits.
As a passenger you would have felt some rocking and rolling along the runway, not much else. Certainly no scratching and scrapping tires.

If this benign takeoff video gives rise to concern, then better don't watch the landing videos!
As someone posted before, the telelens distorts what is really happening. The plane is hurtling at more than 200 kilometers per hour down the runway but all you see is a plane 'sliding' left and right from behind.


(*other than maybe a tad too much into wind aileron+spoilers, but that's a different story)

[Mikehotel152]

Spot on PENKO.

A long lens down the runway gives a highly exaggerated perspective. Just look at all the crosswind landing videos posted on youtube to see how 'exciting' routine landings can look.

None event, but for competeness, I'd love to hear what the wind was doing at that time.

[TURIN]

Don't the later 737's have main wheels that castor slightly? They seemed to maintain the centre line reasonably despite the way the aircraft was pointed!

Not sure about the later ones, but the classics (100-500 series) had a shimmy damper between the torque link knuckles that allowed a certain amount of castoring. I don't think it was designed for easier crabbing but I could be wrong.

[LLuCCiFeR]

The take off looks fine! Well done! :ok:

p.s. Don't listen to Fb 'experts'! As a matter of fact, just cancel your account, it's pure KGB/NSA/Stasi! ;)

[Mikehotel152]

The 800 series do too.

[PENKO]

Judging by the (little) work this guy was doing to track the centreline and the apparent ease had keeping wings level on rotation I'd say 25 knots cross, no more. But that's just a guess, every crosswind is different. Max is what, 38?

[oceancrosser]

Agreed, pretty well done. Gusty winds.

[oicur12.again]

"There is no tire slip"

You sure about that?

[TowerDog]

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..

[PENKO]

"There is no tire slip"

You sure about that?

Yes. Very sure.
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.

[oicur12.again]

Penko,

When i change lanes in my car the car is moving laterally across the road.

The 737 does not. It tracks the centerline whith its nose displaced into wind.

[PENKO]

Don't you think you would see at least a bit of smoke coming from the tires if that was the case?

[BugSmasher1960]

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.

[Goldenrivett]

Hi PENKO
Full traction of the tires.
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/commercial/airports/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.

[PENKO]

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 :)

[BugSmasher1960]

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 :)

I hear what you're saying - totally.

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.

[PENKO]

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.

[Goldenrivett]

Hi BugSmasher1960,
So no slippage.
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)

[BugSmasher1960]

Thanks GoldenRivet - I appreciate your input & explanation.

[nick14]

Limits vary by operators, 25kts wet up to I have heard 34/35ish?

[BugSmasher1960]

Thanks GoldenRivet - I appreciate your input & explanation.

Found this thread on a good site ;)

http://www.pprune.org/questions/443278-max-crosswind-b737.html

[PENKO]

Wet or dry, we have the same 38kt limit.

[Mikehotel152]

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.

[FullWings]

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.