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Airbus Control Stick Sensitivity  
User currently offlinePhxplanes From United States of America, joined Feb 2005, 436 posts, RR: 0
Posted (8 years 11 months 3 days 15 hours ago) and read 4441 times:

I was wondering how sensitive the control stick on the airbus aircraft. Do light movements turn the plane or do you have to move it pretty far. Also do the different aircraft have different sensitivities?
Thanks

16 replies: All unread, jump to last
 
User currently offlineGmidy From United Kingdom, joined Jun 2005, 48 posts, RR: 0
Reply 1, posted (8 years 11 months 3 days 14 hours ago) and read 4434 times:

Every movement goes through a computer so "it" computes a small movement of the stick as a small movement of the flight surfaces, however if you applied full sidestick to the left the aircraft would bank left to the max bank angle, the best thing is you can let go of the stick and she'll happily fly back to straight flight, plus no trimming is required as its automatic, everything is very smooth with no noise dropping as is usual during a turn.  Smile


Lawrence
User currently offlineWing From Turkey, joined Oct 2000, 1559 posts, RR: 24
Reply 2, posted (8 years 11 months 3 days 12 hours ago) and read 4415 times:

The side stick as we call it is truly a marvel.Its very sensitive,easy to use and very easy to adjust.The FBW makes the airplane obey very small sidestick inputs so you dont even need to grasp the stick you only use some finger movements to make small adjustments,very easy to fly in great precision.To maintain a certain attitude all you have to do is give the necessary command nice and easy and hold it there for a second and the FBW does the rest.


Widen your world
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 3, posted (8 years 11 months 3 days 7 hours ago) and read 4360 times:

Quoting Phxplanes (Thread starter):
I was wondering how sensitive the control stick on the airbus aircraft. Do light movements turn the plane or do you have to move it pretty far. Also do the different aircraft have different sensitivities?

This is my understanding:
As Wing is hinting, the Airbus stick is not equivalent to a yoke in normal law. It's a roll and pitch rate selector. That is, a given deflection on the stick is not equivalent to a certain position of the control surfaces. With the Airbus stick, a given deflection is equivalent to a given roll or pitch rate regardless of speed. the flight control system decides how much to deflect the control surfaces based on the position of the stick and the speed of the aircraft.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineMandala499 From Indonesia, joined Aug 2001, 6760 posts, RR: 76
Reply 4, posted (8 years 11 months 3 days 5 hours ago) and read 4345 times:

As Wing is hinting, the Airbus stick is not equivalent to a yoke in normal law.
Sounds like FBW = fulltime CWS with envelope protection doesn't it  Smile (sorry, had to use Boeing lingo to describe the Bus FBW)...

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlinePihero From France, joined Jan 2005, 4388 posts, RR: 76
Reply 5, posted (8 years 11 months 2 days 7 hours ago) and read 4222 times:
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Starlion,
I'm impressed with your grasp of the A flight controls.

Mandala499,
Can't compare apples and strwberries. But you can enjoy them both.

Wing, my dear,
Are you still enjoying it?
I still intend to pay you a visit once the summer season madness is over.

Cheers.



Contrail designer
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 6, posted (8 years 11 months 2 days 6 hours ago) and read 4205 times:

Quoting Mandala499 (Reply 4):
Sounds like FBW = fulltime CWS with envelope protection doesn't it

Somewhat but not quite.

On an Airbus (except the A300 and A310) when you move the stick, the computers interpret pilot deflection to mean "oh, you want the plane to change direction by x degrees per second in the roll and pitch axes". The computers then move the surfaces to give you that desired change in direction rate (unless said desires are beyond what is allowed by flight envelope protection). This is regardless of outside (the cockpit) factors such as airspeed.

On a Boeing, when you move the yoke (or the stick in a C-17 ) pilot deflection is directly reflected in control surface deflection. It has a certain correlation with directional change rate, but this correlation is highly affected by external factors. (Note that there are surface movement limiters. Just like on a car, if you move the wheel/yoke x degrees, this is equivalent to a smaller deflection at higher speed.)

So. On the Airbus you have replaced the human brain compensating for outside factors with automation.

But, and this is a very important point, the Airbus system does not "replace the pilot". The pilot is still very much in charge of what happens. Unless he or she does something stupid like try to break the plane of course. Flight envelope protection can be somewhat compared to stability systems in some modern cars. If you try to drive your four wheel drive Mercedes through a turn on a gravel road too quickly, the stability systems will intervene to ensure you have maximum grip. Until you get to that point ("the point of stupidity"), the Mercedes will let you do what you want. Beyond that point there's s an extra insurance, but it doesn't mean that the plane (or car) will rescue you from really really stupid behavior (A320 Mulhouse crash).

Not to raise a hornet's nest here, but could Airbus flight envelope protection have saved AA587 by preventing rudder movement beyond structural limits? I'll go out on a limb here and say that it would have prevented the fin from snapping off. Whether this would have saved the plane is another matter. But this illustrates my point. It's an extra insurance, but if you do something wrong any plane can bite you in the ass.

One pilot I spoke to recently put it quite well. I paraphrase: "In the military, I was taught to fly to the very edges of the envelope. Here, we try to fly as close to the middle of the envelope as possible." Or in other words: "A good pilot will use his superior skills to keep himself out of situations where he might have to use them." This is true regardless of model.

Quoting Pihero (Reply 5):
Starlion,
I'm impressed with your grasp of the A flight controls.

Thx. I guess all the time on A.nut is paying off

[Edited 2005-08-26 16:24:05]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineVuelingAirbus From Spain, joined Aug 2005, 113 posts, RR: 2
Reply 7, posted (8 years 11 months 22 hours ago) and read 4080 times:

It is more or less accurate what was posted here so far, nevertheless I would like to clarify something concerning the normal law (means flight envelope protection is working).

It is true that you command a roll rate by moving the stick to left or right. The more you move the stick the more rate you get. Bring the stick back to neutral and the aircraft is keeping the bank angle (only above 33 degrees of bank you need to hold the input - if you release the stick to neutral the bank goes back to 33 degrees. With more than 45 degrees of bank the flight director bars disappear from the primary flight display as this is considered a evasive maneuver by the engineers)

However, changing the pitch (pulling or pushing the stick) DOES NOT command a rate. It commands a g load which is held by the aircraft and limited to a maximum of 30 degrees up or 15 degrees down (unless you hit another protection like alpha floor (stall) or overspeed)


User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 8, posted (8 years 11 months 5 hours ago) and read 4003 times:

Quoting VuelingAirbus (Reply 7):

However, changing the pitch (pulling or pushing the stick) DOES NOT command a rate. It commands a g load which is held by the aircraft and limited to a maximum of 30 degrees up or 15 degrees down (unless you hit another protection like alpha floor (stall) or overspeed)

Thanks for that clarification. However if it commands a G load how is it measured in degrees. Do you mean change in angle (degrees per second)? How is this related to G rate?



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineVuelingAirbus From Spain, joined Aug 2005, 113 posts, RR: 2
Reply 9, posted (8 years 10 months 4 weeks 1 day 21 hours ago) and read 3956 times:

Well - i try to explain it plain and simple but maybe a aeronautical engineer reads the post and can explain it better than i can. I will give you two examples. In spite of the fact that bank is a roll rate command it is still based on g load same as the pitch. The certification limit for a civil aircraft in clean configuration is 2,5 g. Thats the reason why fly by wire limits the bank angle to 67 degrees in the airbus because if you keep the aircraft level with mentioned bank you have a resulting g load of 2,5 (nice to know - the Airbus Engineers were actually thinking when they designed the aircraft). In pitch it works similar. All four forces are balanced when in straight and level flight (its a one g condition). however - you basically have to pull more than 1 g if you increase pitch and the computer maintains that g load - works reverse if you decrease pitch. Having said all that - for you as a bus driver you don't really have to know or understand. combined with auto trim i pull/push the stick till i have my desired pitch (as indicated on the primary flight display) - release the stick to neutral and the plane maintains that pitch. Its a pleasure flying the Bus on a visual approach cause with the so called bird (shows your flight path angle) you just intercept the papi and keep the bird at three degrees below horizon and you get the most stable and perfect approach you can dream of... Its a fu#@!ing smart peace of metal (sorry but I just love the BUS)

User currently offlineGmidy From United Kingdom, joined Jun 2005, 48 posts, RR: 0
Reply 10, posted (8 years 10 months 4 weeks 1 day 19 hours ago) and read 3943 times:

The bus is loved indeed mainly only though by bus flyers!  Wink


Lawrence
User currently offlineVuelingAirbus From Spain, joined Aug 2005, 113 posts, RR: 2
Reply 11, posted (8 years 10 months 4 weeks 1 day 3 hours ago) and read 3898 times:

Well - thats because the other's don't know better i would guess. To be honest, i was full of doubts coming from MD-83. The stick, the protections and so on. But having a meal on a proper table can't be replaced by anything. The actual flying makes about 20 percent of the job and as an office place the Airbus is unbeaten. And by the way we have 7 flight control computers in the A320. If we turn off 6 of them we are in "737 mode" with direct control of the control surfaces. And even with only one engine and 3 of those computers gone we can still make an autoland in Cat 3 conditions... Like I said before: Its a fu#@!ing smart piece of metal...

User currently offlinePihero From France, joined Jan 2005, 4388 posts, RR: 76
Reply 12, posted (8 years 10 months 4 weeks 1 day 2 hours ago) and read 3884 times:
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VuelingAirbus, Hi!

I like your posts.
With a proviso :Starlionblue has it right in a dynamic sense, i.e during maneuvers, a stick input controls a rate of x degrees per second, be it on pitch or in roll.( you are right, the factor in pitch is the g load, which means the pitch change would be smaller with an increasing speed)
Remember if omega is the angular velocity, the acceleration -thence the load factor will be : omega squared x radius.

Regards.



Contrail designer
User currently offlineSWISSER From , joined Dec 1969, posts, RR:
Reply 13, posted (8 years 10 months 2 weeks 21 hours ago) and read 3665 times:

Moves smooth and feels like it listens to your input,( it does actually!)

when you pitch up and move the BA, stop the tilt on the stick, move it to neutral and the Bus will maintain the BA until you recover or Alpha floor is reached, when certain adjustments are made it computes what you need the aircraft to do, feels complex and simple to use at the same time, quite like the automatic gearbox of a car compared to a manual gearbox explained in simple terms!


User currently offlineSWISSER From , joined Dec 1969, posts, RR:
Reply 14, posted (8 years 10 months 2 weeks 21 hours ago) and read 3662 times:

Quoting Starlionblue (Reply 6):
Somewhat but not quite.

On an Airbus (except the A300 and A310) when you move the stick...

Nicely explained Starlion!


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 15, posted (8 years 10 months 2 weeks 10 hours ago) and read 3621 times:

Did someone ask for the pitch angle change rate vs load factor? Napkin algebra using non-standardized symbols:

V – airspeed (m/s)
r – radius of curve followed in the vertical plane
nz – z axis load factor (G load)
az – z axis acceleration
g – gravitational constant
A = pitch angle (deg)
w = angular velocity in pitch (deg/s)

First, you have nz due to gravity:

nz_gravity = 1*cos A

Then you pull on the stick, adding to nz:

az_pull = g*nz_pull = V^2/r <=> nz_pull = V^2/(r*g)

nz = nz_pull + nz_gravity = cosA + V^2/(r*g)

r = V^2/(g*(nz-cos A))

w = 360*V/(2*r*pi) = 180*V/(r*Pi) = 180 * g*(nz-cosA)/(V*Pi)



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineKlaus From Germany, joined Jul 2001, 21406 posts, RR: 54
Reply 16, posted (8 years 9 months 1 week 5 days ago) and read 3401 times:

Quoting Starlionblue (Reply 6):
Not to raise a hornet's nest here, but could Airbus flight envelope protection have saved AA587 by preventing rudder movement beyond structural limits? I'll go out on a limb here and say that it would have prevented the fin from snapping off.

I'm not so sure. If the official investigation report is correct in its conclusions, the cause of that was the ultimate result of dynamically inciting an increasing oscillation in the yaw axis which ultimately subjected the tailfin to excessive side loads due to a sideslip angle which could not have been reached by a single deflection.

Prevention of the fatal oscillation would have needed to have a dynamic damping mechanism in there. It would of course be possible to develop such a damper software (basically a sort of high-authority yaw damper for emergencies), but I'm not sure the current Airbus FBW mechanism actually has this class of dynamic damping built into it. It's a class of control that's complex to master and probably difficult and expensive to certify.

As far as I'm aware, only the A340NG and the A380 actually have rudder FBW, and it might be interesting to find out if that actually had the same level of "intelligence" as aileron/elevator control or if it was basically just an electronic replacement for a simple ratio changer with mechanical wire links to the servos. Is anyone in the loop for that kind of information?


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