https://www.youtube.com/watch?v=roS6oFjCDhc
Really poor flying. So much for Fly-by-wire.
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!
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
Quote from: Hardy Heinlin on Fri, 6 Oct 2017 16:36
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
Quote from: Britjet on Fri, 6 Oct 2017 14:36
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.
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:
(https://i.imgur.com/BHfWN2P.jpg)
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...
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.
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
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 ...
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.
Quote from: United744 on Mon, 9 Oct 2017 04:24Correct method:
In fairness, this only works up to a point on a 4-holer with a near-300-foot wingspan though... (#pray4eng4 ;))
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...
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.
Quote from: Hardy Heinlin on Mon, 9 Oct 2017 20:15
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.
@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. :o
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.
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.
|-|
Quote from: United744 on Tue, 10 Oct 2017 00:46
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.
|-|
Quote from: Hardy Heinlin on Tue, 10 Oct 2017 01:13
Quote from: United744 on Tue, 10 Oct 2017 00:46
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! ;D
I do see the logic of what Jose is saying; however, in practice I don't think it is really applicable to an aircraft the size of the 744. In a glider (or other light aircraft) one does need to 'fly' the aircraft on the ground because one only needs a relatively light wind to lift a wing (for example, if you are in an aircraft that can fly at an IAS of around 30kt, as is the case for many gliders and microlights, it's easy to see how any significant wind becomes a high percentage of flying speed).
In the Jumbo, however, the wind speed required to lift a wing is much higher. Boeing don't even really like you using in to wind aileron on the takeoff roll at all if you can possibly avoid it: the danger is that if you put too much control wheel deflection in you will start to crack the roll spoilers open and thus destroy your takeoff performance.
Large transport jets aren't generally known for sideslipping very well; again the roll spoilers don't help matters, and as I alluded to earlier it is impractical to land a long wingspan quad jet with underslung engines with any significant amount of bank on as you risk bashing an outboard pod. Hence just fly it down in the crab, squeeze (don't kick!) the rudder to gently remove some of the crab in the flare and just enough opposite aileron to keep the wings level (after touchdown though, you can put in as much as you like).
Fundamentally though you want to be touching down wings level: reference https://youtu.be/HmdrYKIDbSQ or https://youtu.be/I_TgukaMc1U
I agree - I think in an aircraft as large as the 744, initial roll and rudder inputs for wind might be a good idea, but once the aircraft gets any significant forward speed, the aileron can be returned to center. It's the rudder that really matters, to keep things aligned and the aircraft on the runway.
I was just playing with side-slipping to keep the aircraft aligned with the runway and the nose pointing in the same direction, but I think the sheer area of the fuselage prevents it. It feels like the slip angle is limited, which I suspect might be due to the fuselage "sail area".
Imagine you were able to side-slip at 5° bank against a 30 kt crosswind. Now imagine the wind is calm and you still keep this side-slip. Would this tiny 5° bank side-slip make the aircraft move sideways at 30 kt lateral velocity? No. You would need a 30 kt anti-vector against the 30 kt crosswind vector.
Quote from: Hardy Heinlin on Tue, 10 Oct 2017 00:59
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,
at 80 km/h we usually are flying with the tug still on it's takeoff run. Depends on glider and ballast being used or not....
On the Phoebus, a tailwind of near 10 knot ( gusts ) will force me to start my takeoff run with the technique I describe, but as I gain speed, of course the relative wind becomes positive and we do have to apply the usual sort of corrections for x-wind.
I never had thought about the effect being felt on a 744, but in PSX, if I start a situ on rw with a x-wind of 30 knot or more I do see the effect in the tilt of the aircraft, it's upwind wing being up. And... I also found that as I start taxiing, above a certain taxi speed, not necessarily a huge one ( 15 knot G/S will do ) if I deflect the yoke I can see the resulting bank, and try to align the wings, so... I thought to myself that if this is possible at such low speeds, the effect of taxing or taking of with an unusually high cross-tailwind would probably be felt...
So I created SITUs with various wind intensities and tail angles, and started experimenting with it. If the effective axial component is superior to your G/S then there will be negative relative wind. Say you get such a speed up to 30 knot, and you're taxiing at 12 knot. Shouldn't then the aileron ( and rudder ) deflections be sufficient to create the same rolling moment they do with positive relative wind ?
It's a very picky question, I know.... but it just came to my mind :-)
Will think more about the maths of it. And Hardy, I don't think about "lift" in this case, although it is of course necessarily a factor too, but the mechanical effect of the deflected ( down ) ailerons on the upwind wing, getting the blowing wind from behind, will be more of a factor under such circumstances, and do the opposite of what they would do should they be deflected Up, if the yoke was being deflected "into the wind"..
Addendum: Hmmm probably the effect of the dihedral and the way the wind interacts with it, lifting the upwind wing, is much more significant than any possible effect from the "tiny" ailerons....
Tried it in X-Plane 11, and the 744 does tilt like in PSX, and using opposite downwind aileron and upwind rudder Works, but... it's X-Plane, so... it's just another sim, not the real thing ....
and this is how Boeing does it... https://www.youtube.com/watch?v=NfYqs5Bw9RQ :-)
Lot's of theory for something that is widely discussed but hardly ever executed properly... despite what many will claim :-). I didn't read everything above but...
Fly the aircraft the way the designers ask you to.
The Airbus problem is that the stick left/right command is a demand for a mathematical "roll RATE". Landing an Airbus in a crosswind and then compare it to a Cessna landing is likes apples and... you know. Basically you would need to apply the perfect "ticks" to put the aircraft in the correct slip and then don't touch anymore. Fly by wire make sure roll rate remains 0 as long as sidestick is central.
Boeing acts like a Cessna where any rudder application will create secondary roll so the landing remains a cross-controlled maneuver with constant rudder and aileron application. You also have to remember the application point of the rudder "lift" is above the aircraft cg, so any rudder force will make the aircraft roll. There is also the effect of the swept back wing to be taken into account during the "aligning with the centerline with rudder". But in general, during the slip, you will have to maintain some aileron to compensate the rudder force application point.
Also, modern jets with underwing engines (including the classic 737) can only be landed up to certain wind limits "wing low" because of pod strike danger. The values used to be in the FCTM, for a 73 I recall something like 17kts, 25kts depending on flap setting but don't quote me on that... so yes, it is adviced to land in crab, and us pilots end up doing a mixture of "timed rudder and aileron" hoping for the best result. And that best result appears to be harder to achieve on a fly-by-wire Airbus.
So please don't compare gliders, cessna's, fighters, Boeings and Airbusses... :-). And for the record, if you land a Boeing 747 like those Fedex guys, you will scare the shit out of your captain/first-officer. 5° bank max is more limiting than longitudinal axis aligned with centerline. The gear can manage crab. The engine cannot manage concrete, nor grass.
PS: the Airbus 380 video seems to be a case of not really taking care of acft inertia. Too late in, too much correction, too late out, too much correction again. Just my thought :-)
Quote from: Hardy Heinlin on Fri, 6 Oct 2017 16:36
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
---------------------------------
A question: how do the stresses on the tail of the aircraft in this crosswind landing compare with the stresses that broke up an Airbus A300-600 (American flight 587)? The 587 crash was attributed to excessive use of the rudder. Below are some excerpts from an interesting Wikipedia article on this flight.
----------------------------------
http://en.wikipedia.org/wiki/American_Airlines_Flight_587
http://en.wikipedia.org/wiki/American_Airlines_Flight_587#Findings
Aircraft tail fins are designed to withstand full rudder deflection in one direction when below maneuvering speed, but this does not guarantee that they can withstand an abrupt shift in rudder from one direction to the other.
From the NTSB report of the accident:
The National Transportation Safety Board determines that the probable cause of this accident was the in-flight separation of the vertical stabilizer as a result of the loads beyond ultimate design that were created by the first officer's unnecessary and excessive rudder pedal inputs. Contributing to these rudder pedal inputs were characteristics of the Airbus A300-600 rudder system design and elements of the American Airlines Advanced Aircraft Maneuvering Program (AAMP).
Since the NTSB's report, American Airlines has modified its pilot training program.[26] Previous simulator training did not properly reflect "the actual large build-up in sideslip angle and sideloads that would accompany such rudder inputs in an actual airplane", according to the NTSB final report.
And now, we have a view from the inside.
https://www.youtube.com/watch?v=51DkT-S5qpU (https://www.youtube.com/watch?v=51DkT-S5qpU)
QuoteAircraft tail fins are designed to withstand full rudder deflection in one direction when below maneuvering speed, but this does not guarantee that they can withstand an abrupt shift in rudder from one direction to the other.
Correct!
To put it slightly more succinctly, only ONE flight control may be deflected ONCE to full deflection and returned to center, but NOT reversed, and flight control inputs may NOT be combined (e.g. full aileron AND full elevator could exceed either pitching and/or rolling g limits, and snap the wings off).
What destroyed the tail on the Airbus, was the REVERSAL of the rudder. The initial rudder deflection got the aircraft yawing one way, but then they reversed the controls, with the aircraft now in a slip, and the forces were so great (rudder + airflow acting the same way) that it exceeded the structural strength and snapped it off.
Landing can stress the tail in a similar manner, but the speeds are generally lower (landing speed or less), and I would hope the aircraft is well inside what it can handle at that point.
Quote from: andrej on Wed, 11 Oct 2017 09:36
And now, we have a view from the inside.
https://www.youtube.com/watch?v=51DkT-S5qpU (https://www.youtube.com/watch?v=51DkT-S5qpU)
It doesn't look nearly as bad!
Filmed from a seat at the CG, not from a seat in the aft zone.
And even when just watched from the CG position, the fast changing distance to that right, white side strip is impressive. Don't watch the wing, it doesn't depart from the camera; watch the side strip, that's what is changing its distance to the camera. Now extrapolate this side drift to the swinging tail ...
Quote from: Hardy Heinlin on Tue, 10 Oct 2017 06:58
Imagine you were able to side-slip at 5° bank against a 30 kt crosswind. Now imagine the wind is calm and you still keep this side-slip. Would this tiny 5° bank side-slip make the aircraft move sideways at 30 kt lateral velocity? No. You would need a 30 kt anti-vector against the 30 kt crosswind vector.
Understood. I tried it at higher altitude without limits to roll angle, and still couldn't get it to track. It seems the aircraft just can't slip sufficiently.
Quote from: Hardy Heinlin on Mon, 16 Oct 2017 03:49
Filmed from a seat at the CG, not from a seat in the aft zone.
And even when just watched from the CG position, the fast changing distance to that right, white side strip is impressive. Don't watch the wing, it doesn't depart from the camera; watch the side strip, that's what is changing its distance to the camera. Now extrapolate this side drift to the swinging tail ...
Good point. I did watch the how the runway disappeared! I'd find it rather disconcerting if I was a passenger...
Quote from: United744 on Mon, 16 Oct 2017 04:05
I tried it at higher altitude without limits to roll angle, and still couldn't get it to track. It seems the aircraft just can't slip sufficiently.
Yes, it can. Try this:
Wind calm.
Level flight at 200 KIAS at 4000 ft.
Deflect your rudder left 30%.
Control the aileron so that the compass rose is not turning. The bank will be ca. 10°.
Now check the difference between track and heading: It's about 3°. You are drifting sideways while maintaining track and heading in calm wind.
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Quote from: Hardy Heinlin on Mon, 16 Oct 2017 04:54
Quote from: United744 on Mon, 16 Oct 2017 04:05
I tried it at higher altitude without limits to roll angle, and still couldn't get it to track. It seems the aircraft just can't slip sufficiently.
Yes, it can. Try this:
Wind calm.
Level flight at 200 KIAS at 4000 ft.
Deflect your rudder left 30%.
Control the aileron so that the compass rose is not turning. The bank will be ca. 10°.
Now check the difference between track and heading: It's about 3°. You are drifting sideways while maintaining track and heading in calm wind.
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With the necessary adaptation :) the reason why I always perform sideslips in gliders towards the wind, even if faint wind...
You can have one wing a bit lower than the other . . . unless there is a bank of snow next to the runway . . . then you need to keep both wings high :-P
http://avherald.com/h?article=492eaf3a
Hoppie
Quote from: Jeroen Hoppenbrouwers on Wed, 18 Oct 2017 12:20
You can have one wing a bit lower than the other . . . unless there is a bank of snow next to the runway . . . then you need to keep both wings high :-P
http://avherald.com/h?article=492eaf3a
Hoppie
Banks of snow not simulated in PSX ! Ufff!