Wind on Take Off

[Skybird]

Hi,

Does anybody know how I can preset a cross-wind on T.O.?

I have tried several times but the wind seems to be all the time in the axis on ground, and once airborne it shifts according to the surface wind value inserted in Local Zone - Surface wind (M green selected so "focused", Set zone by flt... NOT selected)

I selected different airports if this can help:

METAR                -    ND/PROG pge 2( GND Roll)      -         WV at (RA):
EGLL 130/10       -               090/8                          -          2000ft 131/12     RWY09
LIMC 280/18       -               347/6                          -          1700ft 281/18     RWY35
EHAM 290/15      -               236/9                          -          2120ft 288/17     RWY24

To summarize, the surface wind (requested) in the METAR reaches its value around 2000 ft RA.
Did I miss something in the setting?

Thanks
Steve

[Ivo de Colfmaker]

hi,
Don't know if this helps, nut I noticed that when setting a wind direction 90° from the RWY heading and the max. speed, i.e. 75 kts to get the maximum effect,  I get blown of the runway  starting at about 80 kts.
at 100 kts the wind display on the ND kicks in  with , at least so far as I have seen, always with a straight headwind and then turning to the entered value as set in the wind boxes, and as You explained.
No to me this looks like, although the wind indication is not as entered in the boxes before 2000 feet, the actual wind you requested is effective on 80 kts.
Or do I see this wrong?
ivo

[Skybird]

Ivo,
I don't see a lot of difference between 20 and... 75kts...
There is a small drift appearing around 80kts, but the wind on the ND is still showing in the axis.
Taking Off with strong crosswind should give more rudder and aileron work during the TO roll. At lift-off I don't notice any side slip or cross control to be slowly recovered.

For approach and landing (try the 022 situ in Brussels 20kts xwind), however the wind seems to keep its direction (and force?) till the end. But on touch down, the ND is showing it rapidly changing to RWY axis, while I can still feel it coming cross...

Maybe my hardware is also not very good to reproduce the effect of the wind on the flight controls.

[pilotwannabe1]

Steve,

My thought is that the aircraft computes the displayed wind vector from track, heading, airspeed and groundspeed. During the takeoff roll the heading and track are the same, unless the cross wind is so strong that the aircraft is skidding sideways.  So on the ground, the aircraft can only compute the headwind or the tailwind component.

Rushad

[Hardy Heinlin]

Rushad is right.

The wind indication on the flight deck is computed by the IRS.

The IRS doesn't read weather reports.

The IRS senses the aircraft heading, aircraft track, ground speed, and gets TAS data from the air data computers (ADCs), which evaluate pressure data from the pitot-static probes (the probes always point at 12 o'clock, not sideways).

On the ground, aircraft heading and track are nearly equal. They drift apart only when the aircraft is slipping sideways.

As long as heading and track are equal, the IRS cannot detect any crosswind. It can only detect the difference between ground speed and TAS. The computed result can be just a headwind or a tailwind -- no crosswind.

The true wind data is generated by the simulator's weather model and can be set on the Instructor. This true wind data is completely independent of the flight deck indications. The true wind data affects your aerodynamics, while the IRS is just an instrument that may fail or may be inaccurate.

There are 3 IRUs and multiple ADCs and pitot-static probes. And each PFD and ND may be linked with individual data sources. Therefore the wind data on the left and right ND may change depending on the selected sources. Play with pitot failures and other faults and you will see ...


Regards,

|-|ardy

[Skybird]

Rushad, that makes full sense what you mention. Indications cannot show full cross during TO... But I am trying to understand why a surface METAR crosswind is not really sensed on the aircraft control on ground and especially while rotating.

Maybe there was something I did not set properly on the instructor panel. I rechecked the operating manual too  :lol:

[Hardy Heinlin]

I'm not sure what you mean, Steve.

When I lift off in crosswind, the aircraft immediately starts to drift sideways. There is even a weather vane effect on the vertical stabilizer, turning the nose into the wind, and that  makes the wings bank into the wind.

On the takeoff roll, the higher the airspeed, the more lift, the less tire contact: so with the increasing speed you need to hold the aileron into the crosswind in order to stay on the centerline.


|-|ardy

[Skybird]

Hardy, what I mean is that during the lift off, I don't have the feeling of taking off with a strong crosswind and cross controls. I almost can rotate with neutral rudder and stick. The drift appears as soon as the aircraft leaves the ground but there is no roll movement induced by the upwind wing.

For the landing, however, it looks very real to the point that I can decrab while flaring (if less than 20kts), and apply aileron correction into the wind. This is amazingly real!

Thanks for the refresher about the IRS...   :lol:

[Hardy Heinlin]

Steve, I am open to suggestions.

But before we continue, I would like to check if we are on the same page :-)

Are your expectations referring to other flight simulators/theories, or to real-world experience on the 747?


Thanks!

|-|ardy

[Skybird]

I am referring to real world experience on the 747, of course!  

[cagarini]

I believe HH once said the flight dynamics in PSX is completely different from what we had in PS1. In PS1 we couldn't actually feel the x-wind effects as in RL, because, if I'm not wrong, it was only taken into consideration as soon as the nose wheels left the ground, and then the main wheels...

This even caused a "strange" effect where the x-wind component was felt first in the nose of the aircraft, and only latter across the whole 744...

As far as I recall last time I took off with a 30knot 90º component, I even noticed that during the takeoff run the upwind wings were starting to lift, creating a slight bank indication on the PFD AH...  I will try again tonight :-)

[Hardy Heinlin]

Hi Steve,

background: In version 10.0.1 I modified the yaw behaviour for takeoff rotation under asymmetrical eingine-out conditions. In the original version (10.0.0) the yaw axis got an increased turn momentum into the bad engine when the
main gear had left the ground; now since 10.0.1 this increase occurs when the nose gear has left the ground.

Question: Do you expect a similar behaviour for crosswind conditions, i.e. should the increased turn momentum into the crosswind (weather vane effect) already occur when the nose gear has left the ground, instead of waiting for the main gear having left the ground? If that is what you expect, then I think you're right.


Cheers,

|-|ardy


P.S.: During the takeoff roll the crosswind pushes the aircraft sideways off the centerline, and lifts the wing on the crosswind side (hold your aileron into the wind to stay on the runway). The drift angle increases with the rising speed (or with the reduced ground contact). The drift angle increases significantly when the aircraft is airborne, but there will be no jump; the transition is smooth, like during landing, just in the reversed order.

[cagarini]

https://www.youtube.com/watch?v=i1NyUq1HWFY  (see last minutes KLM 744 )

https://www.youtube.com/watch?v=NSXJnM3f1I0

On the following ones, we can clearly see the upwind wing rising and ailerons being used to counter, but the yaw rotation happens pretty much when the main gear starts leaving the rw:

https://www.youtube.com/watch?v=SSozUCS3b5g

and at 0:50 here:

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

Although not involving 744s, this one is great too:
https://www.youtube.com/watch?v=NQ3xZnQNe54

[Britjet]

Interesting discussion..and some great videos! My "tuppence"....

Rw - the upwind wing will tend to lift on the T/O roll. As much as 5 degrees or so if not countered. It is quite noticeable. The control wheel may need to be displaced at least halfway, if not more.
The drift effect kicks in mainly when the main gear comes off. The whole aircraft can move quite dramatically sideways, particularly if the control wheel input isn't increased during rotation. Although there is a "weather-cock" effect, the main displacement comes simply from the sudden 30 kts or so sideways drift, which was previously countered by ground contact.
Additionally, there is an increased roll moment in strong crosswinds caused by the wing sweep, which causes a difference in lift between the upwind wing and the downwind wing (as the angle of attack is increased in the rotation manoeuvre). This need for extra input is a not well-understood effect, in my experience. If you don't allow for it the aircraft will roll downwind..
All this is a slightly different from the engine fail scenario which initially has only a yaw and subsequent very active roll effect, but not a drift effect. The reason that the nose wheel coming off causes increased yaw is that on a split V1/Vr take-off, the pilot has hopefully kept the aircraft straight with a combination of rudder and nose wheel traction. As soon as he rotates, the traction is lost and the yaw continues, but there is no inherent drift as such..

Peter

[Hardy Heinlin]

This at 00:46 is how PSX version 10.0.2 behaves:

https://www.youtube.com/watch?feature=player_detailpage&v=i1NyUq1HWFY#t=42

[Hardy Heinlin]

Additionally, there is an increased roll moment in strong crosswinds caused by the wing sweep, which causes a difference in lift between the upwind wing and the downwind wing (as the angle of attack is increased in the rotation manoeuvre). This need for extra input is a not well-understood effect, in my experience. If you don't allow for it the aircraft will roll downwind.

Is this downwind roll, in your experience, stronger than the upwind roll induced by the weather-cock effect? As we know, when swept wings yaw to the right, the left wing provides a larger area against the air mass -- along the aircraft track -- than the right wing does.


|-|ardy

[Hardy Heinlin]

747 experts, please try this:

http://aerowinx.com/forum/topic.php?id=2637


Thanks!

|-|ardy

[Britjet]

Not sure about that one to be honest Hardy. Will try the Beta 1

Peter

[cagarini]

Feeling extremely plausible!  Very Good!!!

[Britjet]

Hi Hardy

Sorry but I can't get a crosswind on take-off.
I have the airport (EINN 24) focussed in green, wind 330/25 but can't get the crosswind to come in on the take-off roll or just after airborne - it gradually changes to 330/25 by the time I get to 1000ft.

Can you tell me what I am doing wrong here? It's got me foxed..

Peter