How does the PFD show (calculate) wind velocity during the takeoff roll ?

[aquarium1]

I understand that velocity triangle can calculate wind velocity, but during the ground roll on takeoff how will this be done? Appreciate answers.

[Goldenrivett]

during the ground roll on takeoff how will this be done?
It can't.

In order to calculate the wind it needs to know the ground speed vector, aircraft heading and TAS.

During take off, the difference between ground speed and TAS is displayed as a head wind all of which appears to be on the nose. Once airborne and the aircraft senses the drift then the wind speed vector will be more truthful.

[fantom]

Airbus PFDs display wind direction and velocity during takeoff roll from close to 100 knots and up... Pretty accurate too.

Rubbish. (ten characters added).

[westhawk]

Not being an Airbus guru, I'd have to ask which models are equipped with a side-slip vane? I know I've seen them on at least some models.

If so equipped wouldn't it be possible that measured side-slip angle could be incorporated into the wind triangle calculation?

Takeoff run:
ADC calculated TAS = 100 kts
GPS calculated GS = 80 kts
Weight on wheels = TRUE
Wheel speed sensors = 80 kts
Rwy HDG = 090 deg.
GPS calculated track = 090 deg. (drift angle = 0 deg.)
Side-slip sensor angle = 5 deg.

From the above provided data, can the direction and velocity of the wind be determined?

Of course it can.

Knowing the side-slip angle can also be used to apply pitot/static pressure corrections based on tables derived from flight test data.

So does Airbus incorporate this calculation capability to display actual wind direction and velocity on the PFD during takeoff? It doesn't seem all that daunting a task given the availability of sufficient data processing capability.

I'd like to see what an avionics tech familiar with these systems has to share regarding this capability.

[peekay4]

Previous thread:

http://www.pprune.org/tech-log/273298-a320-wind-indication-pfd-during-takeoff-roll.html

[wiggy]

As an aside it might be worth noting that certainly on at least one Boeing the use of the "wing down" (side slip) technique for final approach /landing stuffs up the wind vector calculations....

[vilas]

It is merely a theoretical question. The very fact wind is displayed on ND and not on PFD means on take off wind display has no meaning. At take off surface wind given by the tower is enough to start with and any change PF will notice by changing rudder requirement. Pilots monitor speed trend arrow which shows the acceleration. Normally the arrow head disappears on top. If it reappears and shortens or fluctuates it is a sign of wind shear and abort should be considered.

[aquarium1]

@peekay4. Nice thread, but still doesn't answer.
Guess must be the different static pressures during roll as there are no sides lip vanes on A320.

[vilas]

So does Airbus incorporate this calculation capability to display actual wind direction and velocity on the PFD during takeoff? It doesn't seem all that daunting a task given the availability of sufficient data processing capability.
Why would airbus use anything complicated to calculate drift etc. when the use of wind display is not meant for the take off run? I don't know how many pilots look at ND during take off run. It is straight calculation airspeed-GS and once airborne it works by including HDG/TRK difference.

[aquarium1]

It's not about why it's done, required or not, should look at it or not BUT HOW DOES IT DO SO.

[mcdhu]

Exactly Vilas. But I used to (retired now) have a quick glance at the ND wind at 100kts just to make sure the indicated component was what I was expecting.

This question is further confused by some sims incorrectly indicating the IOS w/v at 100kts rather than the component.
It does look rather odd though if taking off with 30kts across that the 100kt ND w/v reads 000/00

Cheers all
mcdhu

[Amadis of Gaul]

Exactly Vilas. But I used to (retired now) have a quick glance at the ND wind at 100kts just to make sure the indicated component was what I was expecting.



What did you do in cases when it wasn't?

[westhawk]

Why would airbus use anything complicated to calculate drift etc. when the use of wind display is not meant for the take off run?I don't have any idea. But I thought the original question was interesting from a technical point of view. If it could be done, then how?

For what purpose the information may be useful (if displayed) is another discussion. What useful purpose does allot of the available information serve? How long is a string?

As for myself, if I'm PF I'm almost exclusively eyes outside once the thrust is set. As PM I scan several things.

[vilas]

aquarium1 asked the question and goldenrivet answered. Rest is trying to find the provebial black cat in dark room which is not there. Usefulness of wind vector on takeoff run, has any SOP ever asked you to use it on the run? No.

[vilas]

aquarium1
How does the PFD show (calculate) wind velocity during the takeoff roll ? . It's not about why it's done, required or not, should look at it or not BUT HOW DOES IT DO SO.
To start with is it too much to expect that you should know PFD is not the place to look for wind velocity? It's effects on airspeed is a different matter. To the second question, since it doesn't do it any differently on ground than in the air has errors of that constraint.

[CaptainMongo]

Any pilot thinking of performing a high energy take off abort because of an unreliable calculated wind vector, produced on the ground on the ND should probably buy a six pack, grab a chair, sit in the back yard and rethink his or her whole abort criteria over again.

How many passengers have we, collectively as an industry, killed because of unrequired high speed aborts?

Below 100 knots "Stop, Stop, Stop."

Above 100 knots "Go, Go, Go." (EXCEPT under the conditions your operator specifies, and I have yet to learn of one which references ND wind speed component)

[vilas]

a_pilot
Sure! Trend arrow is a very good indication of wind shear and aircraft acceleration but not the wind on ND. Monitoring of ND wind component is not mentioned in any airbus document nor is it required because there is no way it can calculate the vector correctly on ground. No action is recommended in any document on the basis of ND wind on take off. Normally Trend vector disappears on top but if it reappears, fluctuates or shortens TOGA is an option if stopping in remaining runway is doubtful. But ND wind plays no part in that decision. FCOM below:
The takeoff should be rejected only if significant airspeed variations occur below indicated V1 and the pilot decides that there is sufficient runway remaining to stop the airplane.

[compressor stall]

If Airbus had wanted you to montitor it, it would be on the PFD nice and big. Like a trend vector.

[compressor stall]

On takeoff roll (which as you are aware is the subject of discussion) I don't:
- monitor the E/WD and SD
- monitor navigation/weather returns at all on the ND
- regularly monitor aircraft systems in the SD
- monitor the TAT and SAT and just guess the temperature somehow
- monitor gross weight.

Do you?

The only clarification to the above is that the PM does monitor the E/WD during takeoff. And I'll glance at it at times if I'm PF.

[PEI_3721]

'a pilot', re #19, it's the piloting skill which enables him/her to understand the quality of information and the circumstances (need) for use; not the perceived ability to use all available information.
Skill involves knowledge, such as how the wind speed display is calculated, it's accuracy, update rate, and relevance for flight condition.

Wind-shear during take off is best avoided with preflight assessment and planning; if a warning is encountered during takeoff then stick with the procedures - 'If ... Then', don't invent your own qualifiers, '... Except', (what is the action with a WS warning but no change in wind speed indication).
For every 'good idea' (opinion) the greater the opportunity for ill-considered 'bad' outcomes. Where is the line between stop and go for a 'slight wind change', is it chosen for each takeoff, what is it based on, what speed, ... each additional variable adds to the complexity of operation and the likelihood of misjudgement

[aquarium1]

Guys, plz. It's not about shear, looking at it or not, what will I do etc BUT

HOW DOES A COMPUTER CALCULATE WIND WHEN AC IS ROLLING DOWN A STRAIGHT RUNWAY WITH NO CRAB?

[PEI_3721]

aquarium1, quietly now. It may help by specifying the aircraft type, nav fit, and or particular operation.
There are many methods of calculating a wind vector, and even for the same aircraft type in the choice of which one to display; IRS, GPS, smoothed inertial nav, integrated nav position, etc.
I will not be able to provide an answer re on the ground, as my aircraft did not display a vector until the airborne calculation was considered valid.
The answer to a question is often obvious once the problem behind the question is understood.

[vilas]

From my experience, the wind vector seems to be accurate Seems means you are not sure and you are not the only one that's what the thread is about. According to FCTM:
A rejected takeoff is a potentially hazardous manoeuvre and the time for decision-making is limited. To minimize the risk of inappropriate decisions to reject a takeoff, many warnings and cautions are inhibited between 80 kt and 1 500 ft.
When even failures are inhibited on take off why should anyone include in the decision making an information he is not even sure of it's authenticity. There is no better situation than take off for keep it simple. If you rejected for ND wind and airbus comes out with it's unsuitability on ground you may find yourself very lonely.

[Derfred]

I must be getting old. In all my years I have only ever been interested in 3 things during the takeoff roll:

1. Runway centreline;
2. IAS; and
3. Engine EGTs.

So, in answer to any question about the wind vector during the takeoff roll, my answer must be "what wind vector?"

The IAS indicator will tell me anything I need to know about windshear. I don't care what the wind is. If the IAS is telling me the aircraft can't fly, then that means stop. If the IAS is telling me I can fly, and there is insufficient runway to stop, then I go. The wind might be 50 knots on the tail. I don't care. Letting a wind vector influence your stop/go judgement is asking for trouble. The aircraft doesn't care about wind, it only cares about IAS. It's IAS that makes you fly (or not), not wind. And it's the EGT's that will keep you flying... There is nothing else in the cockpit that is of any interest during the takeoff roll.

Funnily enough, Boeing don't make any mention of the wind vector in the windshear section of their manuals either. And windshear is not the only potential cause of slow acceleration: sticking brakes or incorrect takeoff data could be other examples. Only your IAS will tell you if you have slow acceleration, regardless of the cause.

So, eyes off the wind vector and back to the IAS/EGTs where they belong please folks... :)

[Capt Fathom]

HOW DOES A COMPUTER CALCULATE WIND WHEN AC IS ROLLING DOWN A STRAIGHT RUNWAY WITH NO CRAB?
aquarium1. You'd be better off deleting the thread and start again.

[Derfred]

... or grant yourself the serenity to accept that just because you start a thread you don't own it. Social media has a life of it's own.

You could also accept that the question has already been asked and answered, both on this thread and the previous one... but some have trouble believing the answer...

[compressor stall]

A_pilot, during the takeoff roll, as PIC I occasionally glance (or whatever your copy of Rogets says) at the important bits of the EWD to check if all is ok and that the PM is not asleep. It's his role (as defined in the manuals) but my responsibility at the end of the day.

[Max Angle]

1. Runway centreline;
2. IAS; and
3. Engine EGTs.


Spot on, there really is some complete and utter rubbish being spouted on this thread. Lets just hope that most of these people are not actually involved in flying jet transport aircraft.

[aquarium1]

Thanks All
Wanted a technical explanation of How Its Done.
Someday when I get it, I will put it here.
Once again appreciate those who got my query.

[Derfred]

Thanks All
Wanted a technical explanation of How Its Done.
Someday when I get it, I will put it here.
Once again appreciate those who got my query.

As I hinted earlier, you got your answer in post 2 of this thread. You just didn't like it.

----

A_pilot:
I don't think anyone can dispute this Airbus information

I certainly can dispute your interpretation of it.

Perhaps if you continued reading your document you would have discovered that your page 7 refers to windshear detection in general, not specifically during the take-off roll. For specific take-off phase windshear detection, refer to page 9, which makes no mention of the wind vector:

"Closely monitor the airspeed and speed trend during the takeoff roll to detect any evidence of windshear. "


From your earlier post:
Aren't pilots trained to gather and crosscheck information using all available resources ?

Not during the take-off roll they aren't.

Any decision to reject a takeoff above 80/100 knots (Boeing/Airbus) due windshear is going to be based on the aircraft considered unable to fly (due insufficient IAS). There is only one instrument that can tell you this - your IAS indicator. Your wind vector is irrelevant to that decision. If you continue, stagnating IAS or speed trend is sufficient to carry out the windshear recovery. Again, your wind vector is irrelevant. Page 9 is quite clear. I seriously urge you to reconsider.

[Capt Fathom]

As I hinted earlier, you got your answer in post 2 of this thread
What about post 3 ? Total opposite to post 2.

[vilas]

Quote an airbus document that tells you check wind on ND on ground.

[vilas]

I am not entering into the last post by you because we will further divert from the present topic. In a sense we already have. From the beginning I have agreed with golden rivet's post. FOBN you quoted is an old one and I have it. I will reproduce from the same document below:
Wind shear suspected
Closely monitor the airspeed and speed trend during the take off roll to detect any evidence of wind shear.
Then again
Recovery technique for wind shear encounter during take off:
Before V1:
− Reject the takeoff only if unacceptable airspeed variations occur and the pilot assesses there is sufficient runway remaining to stop the aircraft.
And again　as you quoted:
Monitor speed trend (available on the PFD, depending on the aircraft type)
Note: An unusual speed trend may be an indication of unreliable airspeed or wind shear.


Unreliable speed should lead to reject take off any way. Nowhere the document refers to wind/GS display on ND for any of these decisions.
I don't think any more discussion is required. If you have a document that says how wind direction is calculated on ground I would be interested.

[vilas]

aquarium1
You are not going to find how does PFD show wind but if you meant ND then read an old posts below especially post by brizeguy quoting Collins and see if those conditions are applicable on ground on take off and get your answer.


How does the ADC work out wind components ? [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-433258.html)

[Goldenrivett]

Hi vilas,
We agree that the wind direction displayed on the ND will be in error whilst on the ground. However the displayed nose / tail wind components will be accurate and could be used to confirm suspected wind shear during take off.

[Uplinker]

Dear me !

Aren't we all getting our knickers in a twist? Poor old aquarium1 was only asking HOW the wind arrow was calculated and generated on the ground - a valid question, surely?

Can I just ask - having read the archived tech link - if, as some of you seem to be saying; the wind direction arrow is not to be relied on, why do Airbus display it? It is suppressed below 100 kts, so if it was unreliable they would suppress it until V1 or Vr, or until airborne.

We had a brown trouser moment some years ago taking off from Tobago in a heavyish A330. The man in the tower either gave us the wrong wind or his equipment was faulty. There were no windsocks in our visual field. Captain said nothing between 100kts and rotate, but when we got to rotate, I rotated but nothing much happened. ROTATE shouted Captain again and I hauled on the stick. After a brief struggle, we got airborne - with a significant tailwind, (that we were not expecting).

Now, I always try to glance at the ND wind arrow at 100kts, just to make sure we are not getting a repeat of that day. It is not difficult to do - you have just looked in at your PFD to confirm 100kts, so it is not difficult to glance at the top left of the ND then outside again.

[vilas]

Golden
That takes care of OP. But regarding decision making about reject due to wind shear/ UAR the airbus document points to airspeed fluctuation and trend. No where it guides you to wind display because on take off there is time constraint which is not the case once you are airborne. You don't need any confirmation from any source if there is speed and trend fluctuation because doing so may send you over V1. If the fluctuation is due unreliable speed then even more so. You can gather whatever info you want provided you have time. Notice trend fluctuation on PFD then Check wind on ND then think about what to do if it is different and it is already time to get airborne. he hasn't answered any of the things I have quoted from his documents and is thumping his back. Use of anti ice is not a split second and any one compares that with take off run then I rest my case. However you read the info from Collins that I have given and tell me about your opinion about the accuracy of wind on ground.

[KayPam]

Hello
I haven't had the time to read all the topic but here are some relevant pieces of information :

- It is possible to compute the exact values of the wind if the exact values of TAS GS sideslip are known. (Obviously, you would need heading to and magnetic deviation to get the wind true direction and not only the relative direction)
- There are sideslip probes on most airbus aircraft. (Even 3 on the latest models, at least A350)
- Sideslip is valid from 60kt+
- However, TAS is not completely reliable until 100ft AGL. Under that, ground effect will induce a 2-3kt error on TAS, which will be transferred to wind calculation

However, I don't work in the ATA31 (display) department of Airbus so I have no idea when wind starts to be displayed.
However, it is calculated from 60kts+ and suffers a bit of imprecision until 100ft AGL.

Note : it is also possible to calculate the vertical wind from TAS, flight path angle (Pitch angle - average(AOA)), Vertical speed. But i'm pretty sure this is not displayed.
Which is unfortunate in my opinion.

[john_tullamarine]

Side note .. it would be such a pity were I to be moved to edit any unduly aggressive posts ... please do play the ball rather than the player, folks.

[Uplinker]

Bonjour KayPam.

On A320/A321/A330, the wind strength and direction is displayed on the ND from 100 kts on the take-off roll - I think that is IAS/TAS

Like the OP, I would be very interested to know how these older aircraft calculate the wind direction information while still on the runway, and why the wind vector information is displayed from 100 kts and not later.

Would it be possible to ask your Airbus colleagues?

[Amadis of Gaul]

Gosh, if it gives a_pilot some sort of warms and fuzzies to check the ND on T/O, who are we to tell him not to? We all have our idiosyncrasies, chief among them being that we became pilots in the first place.

[compressor stall]

Why would the aircraft be more difficult to rotate with a tailwind, assuming rotation was commanded at the "bugged" airspeed?

[underfire]

An aircraft can never measure vertical windspeed. The systems rely on the component of the wind in the direction of flight. Winds are not a static flow, but turbulent and gusting, especially though the column near the ground.

However the displayed nose / tail wind components will be accurate and could be used to confirm suspected wind shear during take off.

Component is the operative word, for both horizontal and vertical winds.

it is also possible to calculate the vertical wind from TAS, flight path angle (Pitch angle - average(AOA)), Vertical speed. But i'm pretty sure this is not displayed.
Which is unfortunate in my opinion.

I would have to disagree here, just as the ac cannot provide reliable wind information while crabbing, or in a turn while descending. There is not enough data from the flap settings, latency, and associated lift components to provide vertical winds. (especially when the sensors can be shielded by the manoeuvre such as rotation.)

I believe you will find that AB has some issues with this system, especially on final in winds while it is a start, I would call it far from accurate or reliable.

[KayPam]

Bonjour KayPam.

On A320/A321/A330, the wind strength and direction is displayed on the ND from 100 kts on the take-off roll - I think that is IAS/TAS

Like the OP, I would be very interested to know how these older aircraft calculate the wind direction information while still on the runway, and why the wind vector information is displayed from 100 kts and not later.

Would it be possible to ask your Airbus colleagues?
There is one element I forgot to mention.
In the absence of a sideslip probe, sideslip can be estimated from (left AOA - right AOA).
There have been tests performed and a model or a table has been derived from these tests, the aircraft can then refer to this model or table to compute sideslip, and then wind direction.

underfire : yes, there are many known/admitted limitations to wind calculations.
However, you can derive yourself the formulas and check that what I said is correct if you assume that all measurements are done correctly.

So i wouldn't know any more details about the models/tables used to compute the sideslip angle from the AOA difference, but i'm pretty sure it would lead to a relatively high inaccurracy.
(However, the effect in itself is well documented and should even be included in the flight mechanics part of the ATPL theory : part of the dihedral effect is due to an AOA difference between the two wings in sideslip)

[wiggy]

As mentioned earlier, if you have time in the sim ( and yes, certainly on the Triple it does replicate what happens on the aircraft ).

Fly an approach using crab technique..take a look at the ND wind..then transition to the low wing/sideslip technique (FWIW the Triple will do this on autopilot anyway) and watch what happens to the ND wind as you align the heading with the track..

Then dependent on results consider whether you can really rely on the ND wind display to tell the full story all of the time.

[Uplinker]

Why would the aircraft be more difficult to rotate with a tailwind, assuming rotation was commanded at the "bugged" airspeed?

Fair point, but all I can say is: sod-all happened when I initially rotated and we had 10-11 kts tailwind !

Had we been given the correct wind, we would have used the opposite runway, or a lower flex or TOGA (more engine power) and different Vspeeds. I would also have been very much more 'go' minded had I been aware of the unexpected tailwind.

Like I say, Airbus blank the wind vector below 100kts, so if it was unreliable or if it was a problem for pilots to see it, surely they would blank it until airborne? Easy enough to do.

In the absence of a sideslip probe, sideslip can be estimated from (left AOA - right AOA).
There have been tests performed and a model or a table has been derived from these tests, the aircraft can then refer to this model or table to compute sideslip, and then wind direction.

Could a useable cross wind vector be derived on the runway from the difference in pitot (dynamic) pressure and a look-up table? The pitot probes are not cross linked but digitised at source, so left and right probes could see different dynamic pressures. Owing to the blanking effect of the fuselage on the downwind pitot probe, would it see less pressure than the one on the upwind side?

[compressor stall]

I don't doubt something happened to you that day but I question the relevance to the wind on ND discussion.

If the tower wind was wrong for your calcs, then you would have 'just' rotated normally further down the runway and had slower acceleration.

If you had a shift mid runway, you'd have picked the trend arrow dropping and reacted then.

If you got windshear (or a localised thermal or dust devil sans dust) at Vr, then I'm not sure what checking anything inside is achieving. There is no time to analyse the cause- it might be wind shift, wrong FMS data etc. It's TOGA and out of there.

[underfire]

kaypam, yes, what we look at is the myriad of input variables and combinations that keep the ac straight, horizontally and vertically. The effect of shielding and directional flow on the sensors, and latency in the system.
The sensors that combine the pitot and AOA are particularly, well, an issue. The potential for the pitot and static combination for shielding, especially in crosswinds at loer speed such as on final.
will pm you.

[FE Hoppy]

Anyone flying with honeywell smart probes will be aware of sideslip compensation.
This could certainly be used for a crude wind calculation while on the ground. I wouldn't be looking at it though.

[KayPam]

Anyone flying with honeywell smart probes will be aware of sideslip compensation.
This could certainly be used for a crude wind calculation while on the ground. I wouldn't be looking at it though.
It's exactly like that.

The existence of an aerodynamic effect that could theoretically allow to measure things, does not necessarily mean that in practice the measurement can be done with reasonable accuracy.

However, Airbus will sometimes compute inaccurate things and use them to know "tendencies" i.e. get some insight into how a parameter is changing.

For instance, an increase of 10kts in the measurement of something can be three times higher than the real value, in magnitude, but will most likely represent a real increase of the real value.

[Togue]

For those who wanted an airbus document that suggest the wind direction and velocity can be use in windshear detection; can take a look at the Procedure Data Package, Supplementary Information, Windshear, Detection Clues.

[vilas]

Togue
The issue here is on take off run. All airbus documents including the latest PDP gives detection clues in the air obviously rapidly changing wind speed/direction is definitely a clue in the air. All that the latest PDP says on take off wind shear is:
At take off before V1, only reject take off, if significant speed variations occur below indicated V1, and if the flight crew determines that the runway is sufficiently long to stop the aircraft". Point to note is it only mentions about speed variations and does not ask you to confirm it from ND or any other source. If you want to know about FCOM then below: PRECAUTIONS FOR SUSPECTED WIND SHEAR


FCOM A to B → 18 SEP 12 PRO-SUP-91-20 P 1/2




BEFORE TAKEOFF




Delay takeoff until conditions improve.


Evaluate takeoff conditions :


• Using observations and experience.


• Checking weather conditions.


Select the most favorable runway (considering location of the likely windshear).


Use the weather radar or the predictive windshear system  before commencing takeoff to


ensure that the flight path clears any potential problem areas.


Select TOGA thrust.


Monitor closely airspeed and airspeed trend during the takeoff run for early signs of windshear.


Again no mention of wind speed/ground speed. So those who do are doing on their own and say so. So be it. You won't find anything in airbus documents.

[underfire]

vilas, exactly. Nothing about wind speed or direction...

[vilas]

Reproduced Below is what airbus answered in a symposium about accuracy of displayed ND wind
Q. You gave a possible error for the ND wind. Doyou have Data for a possible error in winddirection indicated on the ND? Thanks for theanswer
Session:Runway Lateral Excursions:The Crosswind Landing Technique
A. wind value on ground or during the flow displayed on the ND may have an error of 5 to 8 kts in speed and up to 10 degrees. The reason of this could be IRS drift and/or the aircraft entering in ground effect.

[lefthanddownabit]

Speaking as an engineer, you could possibly design a system to estimate sideslip on ground to estimate wind vector. But you would have to ask yourself why anyone would do such a thing. It's of little practical use to the pilot and you are only adding more complication to the system for the relatively brief period between 100 knots and Vr. Also, how would you transition from this estimated on ground reading using sideslip to the rather more accurate ADIRS calculations in flight. It would be just one more thing to test and certify with almost no possible use.

The answer to the question, as has been pointed out several times before, is that it doesn't calculate wind vector on the ground. All it is doing is making the best of the data it is receiving and solving the velocity triangle as best it can. It may look like a sensible wind direction reading, but appearances can be deceptive.

[zahnpastaesser]

Back to topic:

Hasn't anyone of you thought about the idea that maybe the computers do just the same as they do in-flight?

Just look up any crosswind takeoff on youtube. You will notice that maintaing centerline will require a considerable amount of crab, hence sideslip. My bet is, that it just simply doenst care about if its still on ground or airborne already. It just does the usual dumb computation.

[vilas]

zahnpastaesser
You will notice that maintaing centerline will require a considerable amount of crab You maintain crab on take off run? You aircraft wheels swivel side ways?

[FullWings]

You maintain crab on take off run? You aircraft wheels swivel side ways?
Only on a B52 ;)

But you do need a slip angle to generate enough reaction force from the tyres otherwise you’ll drift off the runway. So yes, there’s a bit of crabbing on the ground...

[zahnpastaesser]

zahnpastaesser
You maintain crab on take off run? You aircraft wheels swivel side ways?

One would certainly not notice while doing the takeoff-run. At least I haven't so far. But its true. As I mentioned in my post: look it up, you will be impressed about how much angle any a/c will habe to maintain to remain on centerline. I might link a picture later when I have WIFI.

[zahnpastaesser]

http://fs5.directupload.net/images/160929/rmdkd59b.jpg

You're welcome. Although quite exaggerated, it proves my point. The same concept applies to landings as well by the way.

[vilas]

zahnpastaesser
On take off run you maintain RW heading with rudder not crab unless as rightly pointed out by FullWings you were in a B52.