why do some planes have....

Maximilian_Jenius

Maximilian_Jenius

Super User
...trim tabs on all of some control surfaces and others don't.

For example the MD-80-90, 727's,737's,747's,777's all have trim tabs on control surfaces yet 757's,767's do not.

When I fly Southwest whenever were turning/banking I always see the control tabs at work maunevering the alierons.

What is the advantage in having control tabs on control surfaces vs. not having them is there even an advantage at all?

Anyways back to my original question why do some jetliners have control tabs and yet and still others do not.

Thanks in advance for your replies.


Matthew
 
Depends on the airplane. On some you don't actually move the aileron...you move a the servo tab (your "trim tab") and the forces created by that actually move the control surface.
 
[ QUOTE ]
Depends on the airplane. On some you don't actually move the aileron...you move a the servo tab (your "trim tab") and the forces created by that actually move the control surface.

[/ QUOTE ]


Yea like on 737's...anyone ever take a good real long close look at the rudder of the 727. It just looks complex.

It isn't just a simple one piece rudder like the 757/767.

It has two pieces and can move together as one unit or the bottom half can be used as a rudder I would suspect at higher speeds.

Also I believe that the trailing edge of the rudder has hinges allowing the trailing edge to move about and act like a rudder.

And in addition to all that the rudder has a trim tab on it.

Anyone want to tell me why the 727 rudder is so complex?

Very neat tho....


Matthew
 
Well I can just speak for the -88 because I can't risk saying something incorrect about the 727 or 737, getting 'googled' and enduring 500 nastygrams daily about how I'm screwed up, but on the -88/90, the yoke just moves 'control tabs' and the surfaces are aerodynamicslly 'flown' to the desired positiion.

For example, if you turn the yoke left, the 'control tab' on the aileron moves down, which will "fly" the aileron to the 'up' position, and vice versa.

The horizontal stabilizer works roughly the same way. Basically, for the most part there is no hydraulic roll or pitch control, it's easier to manually move a smaller control, which uses aerodynamics to move a larger surface.

Now if you've got a LOT of roll input in, the flight spoilers will articulate on the wing on the inside of the turn.
 
***500th post Alert***


Well yea thats what I thought...but wondered why some airliners have "trim tabs" and others don't.

I looked up what I said bout the 727 rudder and it is mostly right...wouldn't want to be "flamed".

lol...."control tabs".


Matthew
 
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