737-800 Aileron Movement

[WindSheer]

Hi,

Recently flew return sectors in the pax cabin of a 738.
Was sat on the wing both ways and noticed something intersting about aileron movement.
Scenario:

Sat on the right wing.
A/C banks LEFT.
To return to wings level, the aileron on the right wing lowered slightly as opposed to raising. I doubted myself at first, but observed it again on the return.

Could somebody clarify this? Obviously the aileron on the low ring would lower to return return to wings level, but why didn't the high wing aileron raise, and in fact lower instead?

I am aware of some of the aileron logics built into some of the newer FBW a/c, this was incidentally a brand spanking new 738.

Cheers all...:ok:

[Johnny Tightlips]

It could be to do with the roll spoilers or else near the end of the turn the control column was turned left to level the wings thus causing the aileron on the right wing to lower for a second or two. Then I could be completely wrong.....

[WindSheer]

I was considering it could be oppposite aileron applied to prevent the wings 'over-levelling', but it was consistent throughout the whole movement.

Is it an updated Boeing logic?

[STBYRUD]

Nope, that shouldn't be the case, since there flight controls are controlled directly only a sideslip or maybe badly rigged ailerons could be a reason.

[Chu Chu]

I'm SLF, so I'm sure this will be a learning experience for me. But I'd have thought that to level off from a bank, the pilot would return the stick to neutral, not feed in opposite aileron. It would seem to follow that a little left aileron at the end of a left bank would just mean that the stick hadn't yet been returned completely to neutral.

[STBYRUD]

No, the plane would not maintain bank by itself, but return to level flight only very slowly - therefore a little aileron against the turn is necessary to level the wings.

[WindSheer]

Okay, maybe I am slightly misunderstood.

What I am getting at is that maybe it was the LOW wing that was doing all the levelling, and that the high wing was conforming with some form of low drag aileron logic.
Obviously, if you are banking left and give some right yoke to level the wings, you can assume that the right aileron will raise to provide what is required by the yoke.
What I observed on this brand new 783-800 wasn't the case.
What I am asking is does the newer version of the 738 have a form of FBW built in?

:ok:

[aviatorhi]

Is there a chance you were seeing the trim tab in action? Or possibly the aileron returning to it's regular "dropped" position (I forget if that's on the NGs or not, it was on the 200 as an STC)?

IIRC the aileron system is linked together by cables (left and right ailerons), the "action" of one side has a directly related "response" from the other side.

[STBYRUD]

No droop, no FBW in the 737. There are no aileron trim tabs either, the aileron trim directly recenters the aileron mechanism.

[aviatorhi]

Sorry STBY, but there are trim tabs (servo tabs, or whatever technical name you'd like to assign them) on the entire 737 line. Furthermore, the aileron trim recenters the artificial feel, it doesn't center the bus drum mechanism.

What do you think drives the ailerons in manual reversion? Take a good look at a picture and try to say there's no tabs on the aileron.

http://www.airport-data.com/images/aircraft/large/100/100273.jpg

[MarkerInbound]

There's a world of difference between servo tabs and trim tabs. Granted, Boeing tends to have the servo tabs revert to a trim tab function to drive the control surfaces with a loss of hydraulics.

[captjns]

Negative... Either Balance Tabs with hydraulics or Control (Servo) Tab sans hydraulics.

[Yeelep]

What do you think drives the ailerons in manual reversion? Take a good look at a picture and try to say there's no tabs on the aileron.
While the balance tabs in conjunction with the balance panels reduce the force to move the ailerons. The now human driven PCU's are what actually move them during manual reversion.

There's a world of difference between servo tabs and trim tabs. Granted, Boeing tends to have the servo tabs revert to a trim tab function to drive the control surfaces with a loss of hydraulics.In the case of the 737, there are no trim tabs on any control surface. The balance tabs are servo tabs, but have no connection to the control system.

Negative... Either Balance Tabs with hydraulics or Control (Servo) Tab sans hydraulics.Not true, the aileron balance tabs are not influenced by powered or unpowered aileron control input. They are connected to the wing trailing edge through tab rods. The powered/unpowered control input is applied directly to the aileron.

[latetonite]

Probably reverse rigged ailerons. Happened before...Just takes extra training to fly.

[RCav8or]

WindSheer,
Since you were "sitting" on the right wing, you were throwing off the balance of the aircraft in the roll axis, so no "up"aileron on the right wing would be needed to roll back to the right:O. I have to guess the FBW computer was adding some crazy aileron differential to counteract the SLF on the right wing:uhoh:
In all seriousness, I have no clue:). But inquiring minds would like to know.
My limited knowledge of aeronautics tells me you would have adverse yaw if only the aileron on the low wing were deflected downward to roll back to level, but then I don't know if that applies to swept wing jet transports.

latetonite,
I don't quite see how reversed rigged ailerons would result in WindSheers observations. Only the PF would be painfully aware the ailerons were reversed.
I've been involved in R/C flying for 25 years, so I've seen all too many cases of reversed controls being discovered a moment after rotation. They rarely end well, but alt least only someones pride is dinged.

Pete