Trim Tabs

[minitour]

...so...what's up with them?

I get the elevator trim tab...makes it easier for me to be a p*ssy and hold altitude/pitch...

Rudder trim: The only aircraft I ever got to control with rudder trim was a 172 and I left it centered the whole time...but from what I understand it was a linkage thing in the 172 where on bigger stuff you actually have a tab to trim out the pressure

Aileron trim: Okay...not sure where this one comes from...

I guess my main questions are:
If you could give me a general example of why you would use alieron trim?

I remember reading a book a while back about what order to trim the aircraft in, but I can't remember it...Elevator, Rudder, Aileron? Elevator Aileron Rudder? any reason that you trim the way you do (in a certain order)?

Thanks for answering another nerd question.

-mini

 

[avbug]

Minitour,

Both rudder and aileron trim have their most obvious value in a multi engine airplane that is experiencing an assymetrical thrust problem (engine out or reduced power on one engine).

On airplanes that feature a three-axis autopilot the autopilot controls the aircraft by several means, one of which is usually the trim motors.

Aileron trim has value in a fuel imbalance situation, or any time that aileron pressure must be held for an extended period. An engine failure in a multi engine airplane that isn't centerline thrust means that typically a slight bank is held into the "good" engine(s), as well as typically a lot of rudder. It's usually a whole lot easier to trim this out and concentrate on flying the airplane, than to keep fighting the airplane and holding the control inputs.

Fuel imbalance isn't a big issue with a light single engine airplane, but a larger multi engine airplane may have several hundred pounds difference in the fuel balance for varying reasons.

Any time you're going to have to trim out the rudder to any great degree, you're probably going to have to readjust the aileron trim, too.

 

[Fury220]

I use aileron trim all the time.

First of all, the jet displays different rolling tendencies at 180KIAS than it does at 500KIAS. It differs from jet to jet, mostly because the T-38s I fly are all 30+ years-old. After day to day work at 5+Gs, the wings get ever-so-slightly bent. Trim helps out a lot for small rolling tendencies like this.

Second, aileron trim is pretty huge when you're flying fingertip. At 350KIAS, the wingtip vortices off lead's wing can actually push you away. I always tap a couple clicks of aileron trim INTO lead to counter this. It helps out quite a bit.

I probably use rudder trim the least, so I guess the order I use trim (from most to least) goes like this: Elevator, Aileron, Rudder.

Hope that helps.

 

[mar]

Don't forget the junk factor

Trim (aileron and rudder) is also helpful when flying junky-crooked airplanes.

You know, once they've been crashed and put back together again they never fly like they used to.

 

[Illini Pilot]

trim tabs can also have an anti-servo function...

for example on a cherokee with a stabilator, it is such an effective control surface that the trim tab moves up or down as you move the stabilator further from neutral. it is in effect acting against the control surface, and as it has been explained to me, this is to give the elevator a "heavier" feel and resist the movement of the surface against the airflow. without it, moving the stabilator a small amount would cause larger pitch changes, so the trim tab (which of course can also be used in the normal manner of trimming for an airspeed) actually acts to make it "harder" to move the stabilator against the air.