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oldannyboy
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A/C type behaviour in turbulence

Tue Mar 30, 2021 2:21 pm

Hi Guys,

I am reaching out *mainly to pilots out there* to see which aircraft type(s) they think handles rough and turbulent weather better, and why.

I know there have been prior discussions on this, but always more on the pax perspective, back of the cabin kind-of thing.
So now I am reaching out to pilots to see whether they think one type is better than another.

Mods: feel free to move to Tech/Ops if deemed necessary.

many thanks,

Daniel
 
Flow2706
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Re: A/C type behaviour in turbulence

Tue Mar 30, 2021 2:39 pm

Regarding the A320 family, the A320 flies better in turbulence compared to the A319 and A321. The A319 is very light and therefore very sensitive. The A321 tends to yaw a lot in moderate turbulence as the fuselage is quite long compared to the A320. Also the cockpit and aft cabin is further from the CG which increases the turbulence felt. I heard from people who have experience in 737s and A320s that the 737s are generally nicer in turbulence, probably due to the wing design. I think B757s, especially the 757-300 is terrible in turbulence. The whole aircraft flexes a lot and due to the long fuselage the turbulence can be felt strongly in the aft cabin.
 
baje427
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Re: A/C type behaviour in turbulence

Tue Mar 30, 2021 3:18 pm

Flow2706 wrote:
Regarding the A320 family, the A320 flies better in turbulence compared to the A319 and A321. The A319 is very light and therefore very sensitive. The A321 tends to yaw a lot in moderate turbulence as the fuselage is quite long compared to the A320. Also the cockpit and aft cabin is further from the CG which increases the turbulence felt. I heard from people who have experience in 737s and A320s that the 737s are generally nicer in turbulence, probably due to the wing design. I think B757s, especially the 757-300 is terrible in turbulence. The whole aircraft flexes a lot and due to the long fuselage the turbulence can be felt strongly in the aft cabin.

In my experience I found that the A319 felt pretty secure in turbulence whereas the A321 felt a bit dramatic in turbulence it doesn't help that a heavy A321 has a hard time climbing above the turbulence.
 
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Re: A/C type behaviour in turbulence

Tue Mar 30, 2021 3:48 pm

IMO, the aft cabin of the 753 is pretty bad in turbulence. Even in non-turbulent conditions I thought it was a rough ride in the aft cabin (the mini cabin by the supplemental exit doors).

The 735 was pretty bad in turbulence, and although I have never flown in it, I have heard the 736 handles poorly in turbulence as well.
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TW870
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Re: A/C type behaviour in turbulence

Tue Mar 30, 2021 4:02 pm

Flight attendants also have a keen perspective on turbulence, which is interesting to contrast with pilots.

When flight attendants work, they are working in multiple places related to the center of gravity - forward of it, on it, and behind it. Therefore, they really get to feel how different parts of the aircraft ride so differently in turbulence. On long aircraft where the aft fuselage is far aft of the center of gravity, you get a "wagging" tendency that is particularly pronounced. I flew for United pre-merger, so I have never worked the 757-300. But even the -200 had a tail that very much wagged. My older colleagues said the DC-8-61/-71 had en even more pronounced tendency. In the cockpit, though, the turbulence feels completely different on the 757, with shorter, more abrupt feeling bumps. Generally it is harder to perceive the yawing tendency of the airplane in the cabin without a visual external reference, so pilots are generally more knowledgeable about how airplanes yaw in turbulence.
 
airbuster
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Re: A/C type behaviour in turbulence

Tue Mar 30, 2021 7:09 pm

I was in the back of the 330 I fly a couple of flights ago. It was turbulent and I was surprised how bad it was, not only the movement but the sound of turbulent air around the stabilizer also caught my attention. It’s way more smooth and quiet in the front of the plane.
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Starlionblue
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Re: A/C type behaviour in turbulence

Wed Mar 31, 2021 4:56 am

TW870 wrote:
Flight attendants also have a keen perspective on turbulence, which is interesting to contrast with pilots.

When flight attendants work, they are working in multiple places related to the center of gravity - forward of it, on it, and behind it. Therefore, they really get to feel how different parts of the aircraft ride so differently in turbulence. On long aircraft where the aft fuselage is far aft of the center of gravity, you get a "wagging" tendency that is particularly pronounced. I flew for United pre-merger, so I have never worked the 757-300. But even the -200 had a tail that very much wagged. My older colleagues said the DC-8-61/-71 had en even more pronounced tendency. In the cockpit, though, the turbulence feels completely different on the 757, with shorter, more abrupt feeling bumps. Generally it is harder to perceive the yawing tendency of the airplane in the cabin without a visual external reference, so pilots are generally more knowledgeable about how airplanes yaw in turbulence.


Cabin crew indeed. We can sit in what we feel is light chop, and get a call from the aft galley to please turn the seat belt signs on. It is 60+ metres behind us so there's quite a difference in feel.

airbuster wrote:
I was in the back of the 330 I fly a couple of flights ago. It was turbulent and I was surprised how bad it was, not only the movement but the sound of turbulent air around the stabilizer also caught my attention. It’s way more smooth and quiet in the front of the plane.


I get this impression in most long planes. The back seems to snake around more.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
oldannyboy
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Re: A/C type behaviour in turbulence

Wed Mar 31, 2021 9:45 am

As a passenger I recall the more violent reactions for what seemed moderate chop at best when flying on a Condor 757-300....it seemed like we were riding a bull, with the fuselage bending left, right and center. Fun for a bit, but not after a while.
 
T54A
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Re: A/C type behaviour in turbulence

Wed Mar 31, 2021 10:02 am

A330-600 was a nightmare in turbulence. It was just too long and all oscillations were exaggerated in the nose
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Starlionblue
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Re: A/C type behaviour in turbulence

Wed Mar 31, 2021 11:04 am

T54A wrote:
A330-600 was a nightmare in turbulence. It was just too long and all oscillations were exaggerated in the nose


A340-600?

IIRC, Airbus introduced some automatic pitch inputs to counter the effect, but that didn't completely "solve" the issue.

The 787 and A350 have active damping as standard, and I think the entire Airbus FBW range has maneuver load alleviation, which uses the spoilers to unload the wing during turbulence.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
T54A
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Re: A/C type behaviour in turbulence

Wed Mar 31, 2021 11:30 am

Starlionblue wrote:
T54A wrote:
A330-600 was a nightmare in turbulence. It was just too long and all oscillations were exaggerated in the nose


A340-600?

IIRC, Airbus introduced some automatic pitch inputs to counter the effect, but that didn't completely "solve" the issue.

The 787 and A350 have active damping as standard, and I think the entire Airbus FBW range has maneuver load alleviation, which uses the spoilers to unload the wing during turbulence.


Ha ha. You see, it shook so much I can’t read numbers anymore. I remember something about the installation of accelerometers on Eng 1&4 to help. It didn’t really
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stratclub
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Re: A/C type behaviour in turbulence

Thu Apr 01, 2021 10:43 am

Starlionblue wrote:
TW870 wrote:
Flight attendants also have a keen perspective on turbulence, which is interesting to contrast with pilots.

When flight attendants work, they are working in multiple places related to the center of gravity - forward of it, on it, and behind it. Therefore, they really get to feel how different parts of the aircraft ride so differently in turbulence. On long aircraft where the aft fuselage is far aft of the center of gravity, you get a "wagging" tendency that is particularly pronounced. I flew for United pre-merger, so I have never worked the 757-300. But even the -200 had a tail that very much wagged. My older colleagues said the DC-8-61/-71 had en even more pronounced tendency. In the cockpit, though, the turbulence feels completely different on the 757, with shorter, more abrupt feeling bumps. Generally it is harder to perceive the yawing tendency of the airplane in the cabin without a visual external reference, so pilots are generally more knowledgeable about how airplanes yaw in turbulence.


Cabin crew indeed. We can sit in what we feel is light chop, and get a call from the aft galley to please turn the seat belt signs on. It is 60+ metres behind us so there's quite a difference in feel.

airbuster wrote:
I was in the back of the 330 I fly a couple of flights ago. It was turbulent and I was surprised how bad it was, not only the movement but the sound of turbulent air around the stabilizer also caught my attention. It’s way more smooth and quiet in the front of the plane.


I get this impression in most long planes. The back seems to snake around more.
I have heard that one of reasons for class dividers was so that passengers don't notice fuselage flex so much. In long skinny planes like MD-80s, the flex can seem extreme in turbulence , so it could make sense.
 
N965UW
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Re: A/C type behaviour in turbulence

Thu Apr 01, 2021 2:05 pm

The E190 and 195 can get rough in the back for the same reasons as above (longer fuselage). The E-Jet series is also prone to fishtailing.

Without knowing this, my buddy who has a fear of flying once booked a seat in the back of a 190 from BOS to DCA. They hit turbulence and it wasn't a good time.
You can always go around
 
mxaxai
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Re: A/C type behaviour in turbulence

Thu Apr 01, 2021 2:35 pm

Starlionblue wrote:
The 787 and A350 have active damping as standard, and I think the entire Airbus FBW range has maneuver load alleviation, which uses the spoilers to unload the wing during turbulence.

The A380 has this feature very visible with quite large independent deflections of the ailerons to automatically counter gusts. https://youtu.be/MsV6c5GdxNQ
This split-aileron activation was developed for the A380.

The A330 and A340 all have a simpler "Comfort in Turbulence" function that controls the rudder and elevator in addition to the A320's load-alleviation function. https://www.flightglobal.com/long-time- ... 04.article
The A320 only uses the spoilers and ailerons (not split like the A380), and only since 2008. https://www.flightglobal.com/airbus-exp ... 67.article

However, you don't need FBW for this. The C-5A already had such a system (ALDCS) that would deflect the ailerons symmetrically. https://ntrs.nasa.gov/citations/19760024060
A similar system was on the L1011-500.

For Boeing, the 787 was the first to use active damping and load control.
 
GalaxyFlyer
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Re: A/C type behaviour in turbulence

Thu Apr 01, 2021 6:14 pm

Oh boy, ALDCS! I’m having flashbacks and tremors. It was early computers that integrated all kinds of very analog, very mechanical systems. Lots of problems as flying it with ALDCS INOP was either prohibited or very restrictive.
 
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DocLightning
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Re: A/C type behaviour in turbulence

Thu Apr 01, 2021 6:31 pm

Generally, aircraft with higher wing loading will experience less jostling in the cabin (a rock thrown through the air is much less susceptible to turbulence than a leaf falling from a tree), and the seats further from the wing will move more with yaw/pitch.

The worst throwing around I ever experienced was in a BAe-146 going DEN-ASE. It was even more terrifying because it was at night and there was no view of the ground. So when we hit negative Gs (and we did), I was convinced we were going to slam into a mountaintop.

The second worst was on a NW 744 flying SYD-ITM in August of 1994 (NW's very last flight out of SYD and I had the "privilege" of laying over for a few hours at the outdated ITM only a week before KIX opened). The flight deck announced that we might be experiencing a "little turbulence" and asked the F/As to suspend service and be seated and then we flew between a line of thunderheads over the ocean and bounced around like a rubber ball. It was amazing (and a bit disturbing) to see just how much the engines jiggled on their mounts and the giant wings flapped like a sparrow's.
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Max Q
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Re: A/C type behaviour in turbulence

Fri Apr 02, 2021 12:37 am

It’s not just wing loading that affects ride in turbulence

The 757 has a very stiff wing and a terrible ride in turbulence, i think the -300 series is actually better with its longer, more flexible fuselage soaking up the bumps, the 752 is the only large transport aircraft I’ve operated in which I’ve experienced severe turbulence, it was really bad, the 767 with its far more flexible wing and of course higher weight is much better


The MD80 wasn’t too bad in turbulence but the 727 set the bar highest, the highly swept, flexible wing, high wing loading, massive vertical fin and general control responsiveness made for the best ride possible, it went through turbulence like a hot knife through butter
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r6russian
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Re: A/C type behaviour in turbulence

Fri Apr 02, 2021 6:15 pm

rode in an A346 once, seated by where the stairs to the cargo bathrooms are. looking down the isle just to the front of cattle class you could see the whole plane twist and yaw and move a good couple feet every way. i bet it scared alot of people that didnt know it was supposed to do that.

bulkheads between sections of cattle class were mounted on pins that went up thru the cabin ceiling. pins were like a half inch diameter, holes they went thru were probably an inch. i thought they were missing grommets or something then i saw how much the airframe moves around and realized why the holes are twice as big as the pins going thru them
 
VMCA787
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Re: A/C type behaviour in turbulence

Fri Apr 02, 2021 8:30 pm

DocLightning wrote:
The second worst was on a NW 744 flying SYD-ITM in August of 1994 (NW's very last flight out of SYD and I had the "privilege" of laying over for a few hours at the outdated ITM only a week before KIX opened). The flight deck announced that we might be experiencing a "little turbulence" and asked the F/As to suspend service and be seated and then we flew between a line of thunderheads over the ocean and bounced around like a rubber ball. It was amazing (and a bit disturbing) to see just how much the engines jiggled on their mounts and the giant wings flapped like a sparrow's.


Interesting, I have just over 15,000 hours on the 747 and found it to be just the opposite, especially when compared to other aircraft with much lower wing loading. The 400 wasn't as good as a 200 in turbulence, but it sure beat just about everything else.
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dennypayne
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Re: A/C type behaviour in turbulence

Sat Apr 03, 2021 2:29 am

stratclub wrote:
TW870 wrote:
My older colleagues said the DC-8-61/-71 had en even more pronounced tendency.

I have heard that one of reasons for class dividers was so that passengers don't notice fuselage flex so much. In long skinny planes like MD-80s, the flex can seem extreme in turbulence , so it could make sense.


I used to enjoy sitting in the back of the DC-8-71 in turbulence - you could look forward and see the tops of the seats in the front of the plane twisting the opposite way from the seats in the back. The cabin dividers definitely did nothing to disguise that.



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arcticcruiser
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Re: A/C type behaviour in turbulence

Sat Apr 03, 2021 10:51 am

Max Q wrote:
It’s not just wing loading that affects ride in turbulence

The 757 has a very stiff wing and a terrible ride in turbulence, i think the -300 series is actually better with its longer, more flexible fuselage soaking up the bumps, the 752 is the only large transport aircraft I’ve operated in which I’ve experienced severe turbulence, it was really bad, the 767 with its far more flexible wing and of course higher weight is much better


Agree. The 752 will throw coffee sideways out of your cup in the cockpit whereas on the 753 it does more of an up and down motion. And agree again that the 763 is an overall better ride.
 
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747classic
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Re: A/C type behaviour in turbulence

Sat Apr 03, 2021 11:47 am

Having operated the 747 for 17.000+ hrs and having been send to all places in the world at most Airbus, Douglas and Boeing types, i have the following experience :

The 747, especially the 747 -200/300, has a perfect ride in turbulence, even in moderate turbulence , using the turbulence mode of the autopilot
The very flexible wing, relative high mass and moderate wing loading contributes IMO to the good turbulence ride.
The 707 has also a good ride in turbulence (as far i can remember, more than 25 years ago !), No experience at the 727 series.
737 series have also a stiffer wing and are more prown for turbulence.

Most airbussen (A300/310/320/330/340 have a stiffer wing and are more prown to tutbulence. Note : I have not been on board of a A380 during turbulence, so no experience on that type
.
Also M(DC) aircraft have a stiffer wing structure and are more prown to turbulence
Note : the DC8- 61/63 are the champion of fuselage bending, like all over-stretched variants (757-300, 767-400ER, etc.) and are prown for turbulence in the aft section of these aircraft.
DC10 has also a stiffer wing platform, especially the MD11 has a harsch ride in turbulence (high wing loading)
DC9 series , i have no negative turbulence memory, but its also more than twenty years ago.

My worst 747 turbulence experience was heavy (clear air) turbulence overhead Greenland (mountain waves ?), to the point it was impossible to focus your eyes on the instrument panels, a slow wings level decend finally cured the situation, but we experienced moderate turbulence for over an hour after decend to a better level.
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BowlingShoeDC9
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Re: A/C type behaviour in turbulence

Sat Apr 03, 2021 4:10 pm

mxaxai wrote:
Starlionblue wrote:
The 787 and A350 have active damping as standard, and I think the entire Airbus FBW range has maneuver load alleviation, which uses the spoilers to unload the wing during turbulence.

The A380 has this feature very visible with quite large independent deflections of the ailerons to automatically counter gusts. https://youtu.be/MsV6c5GdxNQ
This split-aileron activation was developed for the A380.

The A330 and A340 all have a simpler "Comfort in Turbulence" function that controls the rudder and elevator in addition to the A320's load-alleviation function. https://www.flightglobal.com/long-time- ... 04.article
The A320 only uses the spoilers and ailerons (not split like the A380), and only since 2008. https://www.flightglobal.com/airbus-exp ... 67.article

However, you don't need FBW for this. The C-5A already had such a system (ALDCS) that would deflect the ailerons symmetrically. https://ntrs.nasa.gov/citations/19760024060
A similar system was on the L1011-500.

For Boeing, the 787 was the first to use active damping and load control.



Whats the advantage of the splitting aileron control on the same wing? It it due to transient control limitations or a way of decoupling a roll moment and and lift (to counteract vertical movement by having one of the aileron inputs be symmetrical on both sides) control inputs? Or C, non of the above? Haha
 
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DocLightning
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Re: A/C type behaviour in turbulence

Sat Apr 03, 2021 7:25 pm

VMCA787 wrote:

Interesting, I have just over 15,000 hours on the 747 and found it to be just the opposite, especially when compared to other aircraft with much lower wing loading. The 400 wasn't as good as a 200 in turbulence, but it sure beat just about everything else.


I think the point is that you can't generalize an airplane's behavior based on a few incidents. Strong turbulence is going to toss a plane around and it doesn't matter how big or small it is. Some planes do take turbulence slightly better, but in the end it's what's happening in the air around the plane that will define what is experienced in the cabin.
-Doc Lightning-

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Max Q
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Re: A/C type behaviour in turbulence

Sun Apr 04, 2021 12:15 am

Boeing generally seems to build a stiffer fuselage with a more flexible wing (757 excepted)

Whereas MD built a stiff wing and a flexible fuselage

With only outboard ailerons on the 757 I suspect the wing had to be stiffer in order for them to retain effectiveness across the entire speed / Mach range
The best contribution to safety is a competent Pilot.


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Starlionblue
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Re: A/C type behaviour in turbulence

Sun Apr 04, 2021 1:29 am

BowlingShoeDC9 wrote:
mxaxai wrote:
Starlionblue wrote:
The 787 and A350 have active damping as standard, and I think the entire Airbus FBW range has maneuver load alleviation, which uses the spoilers to unload the wing during turbulence.

The A380 has this feature very visible with quite large independent deflections of the ailerons to automatically counter gusts. https://youtu.be/MsV6c5GdxNQ
This split-aileron activation was developed for the A380.

The A330 and A340 all have a simpler "Comfort in Turbulence" function that controls the rudder and elevator in addition to the A320's load-alleviation function. https://www.flightglobal.com/long-time- ... 04.article
The A320 only uses the spoilers and ailerons (not split like the A380), and only since 2008. https://www.flightglobal.com/airbus-exp ... 67.article

However, you don't need FBW for this. The C-5A already had such a system (ALDCS) that would deflect the ailerons symmetrically. https://ntrs.nasa.gov/citations/19760024060
A similar system was on the L1011-500.

For Boeing, the 787 was the first to use active damping and load control.




Whats the advantage of the splitting aileron control on the same wing? It it due to transient control limitations or a way of decoupling a roll moment and and lift (to counteract vertical movement by having one of the aileron inputs be symmetrical on both sides) control inputs? Or C, non of the above? Haha


Decoupling roll and lift is certainly part of it.

As mxaxai mentioned, ailerons on both sides deflecting in the same direction is standard on FBW Airbus. That's "step one", if you will. Deflecting both sides upwards unloads the wing and is used to smooth out bumps.

"Step two" is splitting aileron control. With this method, wing bending in turbulence can be more accurately controls, even further smoothing out bumps.


As least, that's how I understand it.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
CeddP
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Re: A/C type behaviour in turbulence

Sun Apr 04, 2021 3:52 pm

Starlionblue wrote:
BowlingShoeDC9 wrote:
mxaxai wrote:
The A380 has this feature very visible with quite large independent deflections of the ailerons to automatically counter gusts. https://youtu.be/MsV6c5GdxNQ
This split-aileron activation was developed for the A380.

The A330 and A340 all have a simpler "Comfort in Turbulence" function that controls the rudder and elevator in addition to the A320's load-alleviation function. https://www.flightglobal.com/long-time- ... 04.article
The A320 only uses the spoilers and ailerons (not split like the A380), and only since 2008. https://www.flightglobal.com/airbus-exp ... 67.article

However, you don't need FBW for this. The C-5A already had such a system (ALDCS) that would deflect the ailerons symmetrically. https://ntrs.nasa.gov/citations/19760024060
A similar system was on the L1011-500.

For Boeing, the 787 was the first to use active damping and load control.




Whats the advantage of the splitting aileron control on the same wing? It it due to transient control limitations or a way of decoupling a roll moment and and lift (to counteract vertical movement by having one of the aileron inputs be symmetrical on both sides) control inputs? Or C, non of the above? Haha


Decoupling roll and lift is certainly part of it.

As mxaxai mentioned, ailerons on both sides deflecting in the same direction is standard on FBW Airbus. That's "step one", if you will. Deflecting both sides upwards unloads the wing and is used to smooth out bumps.

"Step two" is splitting aileron control. With this method, wing bending in turbulence can be more accurately controls, even further smoothing out bumps.


As least, that's how I understand it.


I'll drift slightly off topic here but it's a quite interesting discussion (I hope :tongue2: ).

Contrary to popular beliefs, A380 ailerons behaviour is not the result of a load alleviation function per say nor a turbulence damping one but was primarily designed to solve a wing elasticity issue. During flight test they discovered that during roll command, wings would oscillate at 2 specific frequencies which would sometimes resonate leading to huge discomfort, especially noticeable in the aft of the aircraft, even in calm air. To neutralize these oscillations, they programmed this function they called VDA for "Valse Des Ailerons" (= Ailerons Waltz) and which, in its final iteration, would result in having the inner aileron to deflect 2,5x the amount of the outer one, with the middle one following the inner with a 350ms delay.
Something similar was designed for the rudder as well, called VDR (Valse Des Rudders).

For those interested, I highly recommend Claude Lelaie's book, "The A380 flight test campaign, a pilot's view".

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