Wow... This is crosswind...

[cagarini]

https://www.youtube.com/watch?v=roS6oFjCDhc

[Britjet]

Really poor flying. So much for Fly-by-wire.

[Will]

These movies and photos taken with super-telephoto lenses always make the angles look really exaggerated. I'm not saying it wasn't a bumpy landing... but seen with your naked eye, from a natural perspective, these same landings don't look all that bad.

There are any number of these videos on YouTube, and they're all shot with 300mm lenses or even more. You won't find any shot with a 50mm lens (or something else that's close to how the eye sees things naturally), because the landings don't look that impressive anymore.

Get a camera with a 500mm lens, and you can turn an average crosswind landing into an EXTREME CROSSWING LANDING!

[Hardy Heinlin]

The zoom lens exaggerates the angle, but the swing of the tail, in my opinion, is still enormous: the pax in the aft zone must have been thrown sideways over a distance of ca. 10 meters in less than 2 seconds. And then back. And then again. I'm not sure how much of the effect was induced by a crosswind gust and how much was caused by the pilot who tried aligning the aircraft before touchdown; that overshooting yaw-swing actually started when the rudders were kicked to the left. The rudders stayed in that position during the entire swing. It looks like the pilot didn't stop this turn by the rudders; the rudders rather supported it.


Regards,

|-|ardy

[martin]

The zoom lens exaggerates the angle, but the swing of the tail, in my opinion, is still enormous

That was my first thought, too. The actual landing seems not too far out of the normal, but then that S curve (or possibly chicane)...

To correct for well-known tele-lens effect, focus on the main gear: the aircraft comes down slightly left of the centre line (inner right main gear on the line), but then the first "curve" of that swerve (nose left, tail right) has a radius (shift) more than the half width of the main gear "span" (outer left wheel touches line), and the second one to the opposite side is not much smaller.

And this is a shift more or less perpendicular to te tele-lens axis, so it can't be much exaggerated.

Cheers,
Martin

[frumpy]

Really poor flying. So much for Fly-by-wire.

Can you explain this a little? I think the flare was messed up (too late, too strong),
while the rudder was principally used correctly for touchdown, it resulted in the swinging motion.

I think there was also some overcorrection on the rudder after touchdown.

[United744]

Airbus...

* The aircraft can't stall
* The rudder is only for engine failures

The training sucks. Whoever was flying that is clearly out of practice using the 3rd primary flight control, and doesn't know how to conduct a proper crosswind landing.

Correct method:

[cagarini]

Speaking of crosswinds, there's a detail I would like to see replicated in PSX...

From my RL experience I know that starting a takeoff with a considerable tailwheel component ( we sometimes opt for that in glider operations due to field restrictions and ease of operation, provided within acceptable limits ) at the beginning of the takeoff run we use counter-intuitive  "away from the wind aileron", "into the wind rudder" inputs, reverting it to the usual crosswind technique ( into the wind aileron, away from wind rudder and whatever required regarding the elevator ) as relative wind speed becomes positive...

In PSX if we set a good x-wind on ground, the aircraft will correctly tilt on the rw / taxiway, it's upwind wing being lifted. But if you set a considerable cross tailwind, the usual inputs will work as if the relative wind speed was always positive - aileron into the wind will level the wings.... at any taxi speed, when indeed under such conditions we should use away from the wind yoke to force the wings evel.

Probably also related to the same way it is modelled in PSX's FDM, the aircrfat as it get's airborne under such a considerable tail crosswind situ will also "weathervane" in the oposite direction - downwind - when it should actually weathervane upwind.

A picky detail, I know...

[Hardy Heinlin]

In PSX, the crosswind from the left lifts the left wing not because of a certain aileron angle but because the wing tip is higher than the wing root. If it were because of the aileron, and if the aileron influenced this effect in up or down direction depending on the tail or head wind component only, the aileron would be ineffective if the wind came from 9 o'clock. Also, the weather vane is not induced by the lifting wing but by the vertical stabilizer. The air mass always meets the aircraft from the front, even on a tailwind takeoff; the aileron has always a positive effect even when the aircraft flies in tailwind with the groundspeed higher than the airspeed. Even a windshear won't make the aircraft fly backwards, it will just stall the aircraft.

[cavaricooper]

Hardy-

I believe Jose is mentioning weathervaning that occurs in the light and ultralight aircraft he is experienced in. Aileron and elevator down into the wind is standard practice there.The 300+ tons mitigates this in the 744...

Best- C

[Hardy Heinlin]

I think it's not so much the weight but the wing shape having a dihedral or anhedral or flat construction. The 747 is dihedral. Jose's fighter jets are probably anhedral ...

[localiser]

United744,

I would say that Airbus type training has recently show the signs that they are coming to terms with the fact that a Fly by Wire aircraft can stall - at least in my experience.

Also (at the risk of starting Boeing vs Airbus, which is not my intention), far be it from me to defend a manufacturer, however the Airbus FCTM does recommend the decrab technique for landing in crosswind conditions, and states:

"The objectives of the lateral and directional control of the aircraft during the flare are:

To land on the centerline, and
to minimize the lateral loads on the main landing gear.

The recommended de-crab technique is to use all of the following:

The rudder to align the aircraft with the runway heading during the flare
The roll control, if needed, to maintain the aircraft on the runway centerline. Any tendency to drift downwind should be counteracted by an appropriate lateral (roll) input on the sidestick.

In the case of strong crosswind, in the de-crab phase, the PF should be prepared to add small bank angle into the wind in order to maintain the aircraft on the runway centerline. The aircraft may be landed with a partial de-crab (residual crab angle up to about 5 °) to prevent an excessive bank. This technique prevents wingtip/sharklet (or engine nacelle) strike caused by an excessive bank angle.

As a consequence, this may result in touching down with some bank angle into the wind (hence with the upwind landing gear first)."

...not a million miles from anything Boeing says, and matches your photo of the MD-10 quite nicely.

Personally I also find if you fly with autothrust disconnected it tends to fly and land better as you aren't fighting the oscillations created by the stick and the engines being out of sync. Of course that depends on SOPs.

[skelsey]

Correct method:

In fairness, this only works up to a point on a 4-holer with a near-300-foot wingspan though... (#pray4eng4 )

[cagarini]

Hardy,

I believe you didn't get my point.

To start with, I never flew fighter jet's, but rather - gliders :-)  IRL that's what I've been flying for decades...

Wind effects on ground are common to all types of aircraft, at least in as far a fixed wing aircraft are concerned.

Of course what lifts the wings of the 744 and tilts it on ground is exactly what tends to lift the upwind wing of my Phoebus B1, if there is a crosswind component. The question is, what control inputs should actually be used while the relative wind has a negative sign, when taking off with tailwind.

If we set, in PSX, the ground wind from, say, 8 o'clock like in my example above, at at 40 knot ( yes, the crew shouldn't even try to takeoff under such extreme conditions ... ) while taxiing along the runway, or during the initial takeoff run, yoke to the right and rudder to the left might have to be used, changing progressively to the usual compensation for a "positive crosswind" when the relative wind transitions from negative to positive.

I don't know it the full deflection of the yoke to the right would be sufficient, at taxi speeds, and low GWs to level the aircraft, which in this example would start tilted to the right...

The bellow observation results ** only ** from my lack of attention and interpretation of the ND :-/ - my bad.... It's showing Track, not heading which is displayed by the triangle symbol... Sorry about that...

The other aspect is weathervane once airborne. Say I continue my takeoff with a tail crosswind component from port side. As I leave the rw will the aircraft weathervane to the left ( port ) or right ( starboard ) ?

I believe port is the only possible outcome, because the effective x-wind component is from the left irrespective of being tail or not...

[Hardy Heinlin]

When the wheels are on the ground, crosswind from left pushes the vertical stabilizer to the right causing the nose turning to the left, i.e. the aircraft turns anti-clockwise.


Edit: You edited your post while I was writing mine. Track and FPV indications on the 744 EFIS are centered when below 80 kt groundspeed.

[cagarini]

When the wheels are on the ground, crosswind from left pushes the vertical stabilizer to the right causing the nose turning to the left, i.e. the aircraft turns anti-clockwise.


Edit: You edited your post while I was writing mine. Track and FPV indications on the 744 EFIS are centered when below 80 kt groundspeed.

Yep, edited the part regarding the heading after takeoff, when wheels no longer in contact with ground, which of course is correct in PSX - no matter if comming from the front or tail, the x-wind always results in the aircraft aligning / weathervaning when that contact is lost on takeoff. I was incorrectly interpreting the ND symbology, and mixing Track with Heading... sorry for that :-/

Regarding the use of ailerons if, for instance you set a wind of 45 or more from, say left and back ( 07:30 o'clock ) I still believe yoke downwind would indeed create a CCW rolling moment, compensating the aircraft "tilt" to the right a bit, because the ailerons on the upwind wing move down and the relative flow, moving at a higher speed than the aircraft is moving fwd, until it accelerates past the tailwind speed component, would "push" the left wing tip down. Also, using into the wind rudder, which is the opposite of what should be used if the x-wind was from the front, will create a CCW yaw moment, again due to the interaction of the faster than aircraft fwd speed tailwind component.

[United744]

@localizer: Yes - after AF447 it was a wake-up call for them. The way it was trained wasn't strictly as per the manuals, and the attitude was "fly the FBW" and not "fly the aircraft". They learned the hard way...

The part about the rudder was more tongue-in-cheek, though I have heard of pilots being told exactly this about the rudder on A32x. 

I find I can't land the 744 in a crosswind as well as the autopilot. Not sure why, but I seem to have insufficient rudder authority, and the aircraft drifts to the side in short order, and I usually land just to the side of the runway. I've yet to strike a pod though!

It seems impossible to fly the 744 in a max-limit crosswind in a side-slip and still remain aligned with the runway (assuming forgetting the landing and just trying to keep it straight down the runway). It should be possible - it's just a matter of balancing yaw and roll angles.

[Hardy Heinlin]

Jose, a few rhetorical questions for you:

At what airspeed does a glider start to fly?
At what airspeed does a 747 start to fly?

When rolling on the ground at heading 360° and the wind is 210° at 50 kt ...
... and the groundspeed is 10 kt, do the wings get air from the front or from the aft?
... and the airspeed is 10 kt, do the wings get air from the front or from the aft?

In PSX, when parked, the ailerons are only effective if there is a strong headwind component. Unlike you thought, they don't lift anything when parked in tailwind. So there is nothing to reverse. Zero is zero.


|-|

[Hardy Heinlin]

It seems impossible to fly the 744 in a max-limit crosswind in a side-slip and still remain aligned with the runway (assuming forgetting the landing and just trying to keep it straight down the runway). It should be possible - it's just a matter of balancing yaw and roll angles.

You can only bank up to 5°. To be safe in stormy turbulence, maybe even just 3° to 4°. This tiny bank angle is not great enough for an exact runway alignment with a side-slip into a 30 kt crosswind at 130 KIAS. If that would work, the ailerons would be very sensitive, causing fast turns whenever the wings are not level.

In strong crosswinds you always need to add some crab. Side-slip alone is insufficient, and usually not even done in manual flight.


|-|

[United744]

It seems impossible to fly the 744 in a max-limit crosswind in a side-slip and still remain aligned with the runway (assuming forgetting the landing and just trying to keep it straight down the runway). It should be possible - it's just a matter of balancing yaw and roll angles.

You can only bank up to 5°. To be safe in stormy turbulence, maybe even just 3° to 4°. This tiny bank angle is not great enough for an exact runway alignment with a side-slip into a 30 kt crosswind at 130 KIAS. If that would work, the ailerons would be very sensitive, causing fast turns whenever the wings are not level.

In strong crosswinds you always need to add some crab. Side-slip alone is insufficient, and usually not even done in manual flight.


|-|

I just tried it again - it doesn't seem possible.

Cross-wind from the left; full right rudder and 11 degrees of left roll is still insufficient to align with the runway at approach speed. The aircraft is simply too large!