alwaysontherun
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Don´t Opposite Ailerons Move In Opposite Ways?

Tue Oct 12, 2010 11:48 pm

Hello,

looking at GA aircraft, when the left aileron moves upward the right one goes down and vice versa.

Sitting somewhere in the back (provided people leave their window slides open!!) of an 737NG or A32X they seem to move independly from each other.

I wonder how this works, moving both ailerons up and down at the same time?

Any info would be appreciated.

Cheers,

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DashTrash
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Wed Oct 13, 2010 1:28 am

They work the same way as in a light aircraft. One goes up, the other goes down.

There are aircraft that may deflect the ailerons with the flaps (usually inboard ailerons) which will have both deflect downwards. The principles at work are still the same for every aircraft though.
 
SEPilot
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Wed Oct 13, 2010 1:53 am

As DashTrash notes, most airliners have both inboard and outboard ailerons. The reason is that at high speed the outboard ailerons (which are necessary for low speed flight) actually twist the wing rather than increasing or decreasing lift and lose their effectiveness, or even cause the reverse effect of what they were trying to do. Therefore at high speed the outboard ailerons get locked and the inboard ailerons take over. You may see funny movements when the transition occurs.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
474218
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Wed Oct 13, 2010 2:50 am

Quoting DashTrash (Reply 1):
They work the same way as in a light aircraft. One goes up, the other goes down.


Not all the time: The C-5 and the L-1011-500 have active outboard ailerons. They react to wing loading and position themselves to relieve those loads. So it is possible to have both outboard ailerons in the up position, while the inboard ailerons are displaced one up one down. There are bungees (springs) in the control system that extend or collapse to allow parallel movement of the outboard ailerons.

Quoting SEPilot (Reply 2):
As DashTrash notes, most airliners have both inboard and outboard ailerons. The reason is that at high speed the outboard ailerons (which are necessary for low speed flight) actually twist the wing rather than increasing or decreasing lift and lose their effectiveness, or even cause the reverse effect of what they were trying to do. Therefore at high speed the outboard ailerons get locked and the inboard ailerons take over. You may see funny movements when the transition occurs.


In addition the the active outboard aileron described above: All L-1011 models had full time ailerons, the outboard ailerons were not shut off for high speed flight.
 
SEPilot
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Wed Oct 13, 2010 2:55 am

Quoting 474218 (Reply 3):

In addition the the active outboard aileron described above: All L-1011 models had full time ailerons, the outboard ailerons were not shut off for high speed flight.

I did not realize this; my knowledge is mostly about Boeing jets. Thanks for the info. I guess the L-1011 wings must be torsionally more rigid than Boeing wings.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
474218
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Wed Oct 13, 2010 3:31 am

Quoting SEPilot (Reply 4):
I did not realize this; my knowledge is mostly about Boeing jets. Thanks for the info. I guess the L-1011 wings must be torsional more rigid than Boeing wings.


Correct, because of the L-1011's wing torsional strength dwelling the outboard ailerons was unnecessary. When the -500 wing was lengthened four and a half (4.5) feet structural beef ups were not required and the active controls took care of the additional loads.
 
pilotpip
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Wed Oct 13, 2010 3:44 am

When you look at an airbus at the gate the ailerons on both wings often droop down because there is no hydraulic pressure on them.
DMI
 
soon7x7
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Wed Oct 13, 2010 7:59 am

Airbus uses the "Flaperon" feature on their larger models. Both outboard ailerons also function as flaps with downward deflection during landing while still maintaining roll control effectively. Image one depicts the aileron in flap configuration while image two, demonstrates the same surface doubles as a spoiler upon touch down. The conditions outside the aircraft were winds/ light and variable...g...(pictured was LH A346, D-ABHO@EDDM)
flaperon
spoileron
 
DashTrash
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Wed Oct 13, 2010 8:17 pm

Quoting 474218 (Reply 3):

Not all the time: The C-5 and the L-1011-500 have active outboard ailerons.

I know about the feature, but what are the chances the OP was riding in the back of an L1011 or C-5?
 
KELPkid
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Wed Oct 13, 2010 8:25 pm

The answer, even in GA, is "not always."

One year at a regional air fair, I went to an FAA exhibit, which had a single engined plane out on the ramp, which if you chose to partake, you were asked to preflight and note all the discrepancies you found on your pre-flight inspection. Somehow, they rigged the ailierons to move in the same direction   (don't ask me how...). You would be suprised how many people missed that one...  

Before laughing too hard, be aware that there has been more than one accident where someone has taken off with misrigged ailierons after maintenance, and a few fatalities...
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planewasted
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Wed Oct 13, 2010 9:21 pm

The A380 can do some unusual things with its ailerons, probably some fancy FBW stuff.
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prebennorholm
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Thu Oct 14, 2010 1:02 am

Quoting soon7x7 (Reply 7):
Airbus uses the "Flaperon" feature on their larger models.

And on their smaller ones - all FBW planes including 318, 319, 320 and 321.

Quoting soon7x7 (Reply 7):
Both outboard ailerons also function as flaps with downward deflection during landing...

...and during take-off.

Both ailerons extend 5 degrees down when flaps are extended.

The MD-11 does the same thing.
Always keep your number of landings equal to your number of take-offs
 
tdscanuck
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Thu Oct 14, 2010 2:28 am

Quoting PlaneWasted (Reply 10):
The A380 can do some unusual things with its ailerons, probably some fancy FBW stuff.

Because of the way FBW implements closed-loop control laws, you can get all sorts of weird surface positions. It's entirely possible to have a surface going completely opposite the "normal" direction for the flight crew command.

Tom.
 
soon7x7
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Thu Oct 14, 2010 12:13 pm

Quoting prebennorholm (Reply 11):

   ...I was unaware that the n/bodies also implemented this system...now I am one notch smarter!...thnxmuch...g
 
Tristarsteve
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Thu Oct 14, 2010 12:48 pm

Quoting alwaysontherun (Thread starter):
Sitting somewhere in the back (provided people leave their window slides open!!) of an 737NG or A32X they seem to move independly from each other.

The ailerons on all B737 are connected together by a steel cable. The servoes are in the wheel bay.
They cannot move independently.
 
mrocktor
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Thu Oct 14, 2010 1:47 pm

Quoting tristarsteve (Reply 14):
The ailerons on all B737 are connected together by a steel cable. The servoes are in the wheel bay.
They cannot move independently.

It is worth noting that even on purely mechanical and interconnected aileron systems it is common to arrange the gearing so that for a given input the aileron deflected upward moves more than the one deflected downward (different rates of motion depending on whether the surface is above or below neutral - although they always move together).

This is done because downward deflection is limited by the fact that you can actually stall the wing section if you try to get too much lift out of it, while the upward deflection does not cause this issue. Therefore, to achieve maximum roll rate for a given surface size, you want to deflect the "up" surface more than the "down" surface.

[Edited 2010-10-14 06:49:08]
 
Chese
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Thu Oct 14, 2010 2:04 pm

In school we were taught the rule of thumbs in aileron rigging. Put your hands on the control wheel and turn it either direction and your thumbs should point at 'up' aileron. It may sound silly but it can be possible to rig them backwards, at least for some of use that still work on cable driven flight controls.
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etherealsky
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Thu Oct 14, 2010 3:32 pm

Quoting 474218 (Reply 3):
Not all the time: The C-5 and the L-1011-500 have active outboard ailerons. They react to wing loading and position themselves to relieve those loads.
Quoting PlaneWasted (Reply 10):

The Airbus term for it is Load Alleviation Function (LAF), and on the A320 series both the flight spoilers and ailerons are used for LAF, so if you encounter some windshear, for example, the spoilers and ailerons will deflect to counter it.

http://img839.imageshack.us/img839/7722/a320z.jpg


Quoting soon7x7 (Reply 7):
Airbus uses the "Flaperon" feature on their larger models.

I guess that's a separate feature from LAF but it must still be tied in with the ELACs (control computers for the ailerons)?

Also, it's worth noting that most (if not all?) airliners use flight spoilers in conjunction with (or as a backup for) primary roll control via the ailerons.

Heck, some planes don't even have ailerons to begin with  
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rwessel
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Thu Oct 14, 2010 5:07 pm

Quoting mrocktor (Reply 15):
This is done because downward deflection is limited by the fact that you can actually stall the wing section if you try to get too much lift out of it, while the upward deflection does not cause this issue. Therefore, to achieve maximum roll rate for a given surface size, you want to deflect the "up" surface more than the "down" surface.

I believe the primary motivation for differential ailerons is to reduce adverse yaw.
 
SEPilot
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Thu Oct 14, 2010 5:48 pm

Quoting KELPkid (Reply 9):
don't ask me how..

Very simple. Just reverse the cables on one of them.

There is also a STOL modification for Cessnas that causes both ailerons to move down when the flaps are lowered. This is accomplished by moving the neutral position; the ailerons still respond the normal way to control inputs.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
KELPkid
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Thu Oct 14, 2010 7:59 pm

Quoting SEPilot (Reply 19):
ere is also a STOL modification for Cessnas that causes both ailerons to move down when the flaps are lowered. This is accomplished by moving the neutral position; the ailerons still respond the normal way to control inputs.

Interesting. I presume that that would be the Robertson STOL kit. I flew a few 172's with the Horton STOL craft kit, and never noted that particular behavior on preflight   My former instructor's 172 had the Horton kit with the fences on top, drooped wing tips, cuffed leading edge, and flap gap "seals" (really just a sheet metal job that makes the underside of the wing clean when the flaps are up).
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etherealsky
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Thu Oct 14, 2010 11:44 pm

I'm sure there are probably tons of different kits out there for GA birds, but one in particular with the flaperons (and canards!) for the C182 is the Peterson/Wren kit.


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SEPilot
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Fri Oct 15, 2010 11:34 am

Quoting KELPkid (Reply 20):

Interesting. I presume that that would be the Robertson STOL kit.

I believe that is correct.

Quoting KELPkid (Reply 20):
and flap gap "seals" (really just a sheet metal job that makes the underside of the wing clean when the flaps are up).

I believe that is a separate modification; it actually counters the STOL kit somewhat as it slightly hinders flap performance. I cannot imagine it being included in a STOL kit.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
mrocktor
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Mon Oct 18, 2010 7:24 pm

Quoting rwessel (Reply 18):
I believe the primary motivation for differential ailerons is to reduce adverse yaw.

It helps that too. But stalling the wing tip is a little more serious that adverse yaw (and unless you do some fancy slot arrangement, 40 deg down aileron will stall most wings).
 
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Aesma
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Tue Oct 19, 2010 2:01 am

Quoting etherealsky (Reply 17):
Also, it's worth noting that most (if not all?) airliners use flight spoilers in conjunction with (or as a backup for) primary roll control via the ailerons.

And then you can call them spoilerons. I knew about flaperons on Airbus planes but didn't notice they were also been used as spoilers, so they should be called "spoilflaperons" :d
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Starlionblue
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Tue Oct 19, 2010 4:48 am

Quoting Aesma (Reply 24):
"spoilflaperons"

"Spoilaperons"?'"Flaspoilerons"? "Ailapespoilers"?
"There are no stupid questions, but there are a lot of inquisitive idiots."
 
mrocktor
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Tue Oct 19, 2010 10:54 am

Quoting Starlionblue (Reply 25):
"Spoilaperons"?'"Flaspoilerons"? "Ailapespoilers"?

"Slaperons" has a nice ring to it  
 
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Starlionblue
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Tue Oct 19, 2010 12:17 pm

Quoting mrocktor (Reply 26):
Quoting Starlionblue (Reply 25):
"Spoilaperons"?'"Flaspoilerons"? "Ailapespoilers"?

"Slaperons" has a nice ring to it

              
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Buyantukhaa
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RE: Don´t Opposite Ailerons Move In Opposite Ways?

Tue Oct 19, 2010 8:12 pm

Quoting mrocktor (Reply 15):
Therefore, to achieve maximum roll rate for a given surface size, you want to deflect the "up" surface more than the "down" surface.
Quoting etherealsky (Reply 17):
Heck, some planes don't even have ailerons to begin with
Quoting Aesma (Reply 24):
And then you can call them spoilerons.

Best example that I know of is the B52: no ailerons, just uses spoilers for roll:


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