Ground adjustable trim tabs - who can adjust?

Fearless Tower

Fearless Tower

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Fearless Tower
Is an A&P required to adjust ground adjustable trim tabs?

It is not on the list in 43.3, but 43.3 refers to 'preventative maintenance' and I wouldn't exactly consider it preventative maintenance.

It would seem that an A&P is required to adjust, but I'm curious if anyone has seen an FAA reference or interpretation to the contrary.
 
adjusting trim is part of aircraft operation, not aircraft maintenance. what is the difference between adjusting an in flight and a ground adjustable trim tab?
 
tonycondon said:
adjusting trim is part of aircraft operation, not aircraft maintenance. what is the difference between adjusting an in flight and a ground adjustable trim tab?
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My suggestion would be to consult the Maintenance Manual of the aircraft. If it has a reference to adjusting the trim tab, then it is a maintenance function.

For an "inflight" trim adjustment that's addressed in the POH. Rigging of the inflight trim adjustment is defined by the MM.
 
Rotor&Wing said:
My suggestion would be to consult the Maintenance Manual of the aircraft. If it has a reference to adjusting the trim tab, then it is a maintenance function.
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Ah, therein lies the problem....the 1948 Cessna 170 does not have a MM.
 
If you know what you're doing, nobody will notice or care. If you don't, you'd be foolish to try no matter what the book says.
 
tonycondon said:
adjusting trim is part of aircraft operation, not aircraft maintenance. what is the difference between adjusting an in flight and a ground adjustable trim tab?
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You can't put it back real quick if you went to far and made the plane difficult to control:dunno:
 
dmccormack said:
Will someone be dusting it for prints after you adjust it?

:rolleyes:

If not, bend away, but in small increments.
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Even if nobody's "dusting it for prints," your butt will be in the plane, so if you don't know what you're doing, don't do it, even in "small increments," since you may not understand how small "small" is in this context.
 
Ron Levy said:
Even if nobody's "dusting it for prints," your butt will be in the plane, so if you don't know what you're doing, don't do it, even in "small increments," since you may not understand how small "small" is in this context.
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Yeah. Well... I haven't seen a ground adjustable tab that was big enough to make the airplane difficult to handle if gone too far. But that is just me, I guess.
 
Ron Levy said:
If you know what you're doing, nobody will notice or care. If you don't, you'd be foolish to try no matter what the book says.
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There ya go…… bending the tab is actually altering the flight control.. but who cares..
 
Greg Bockelman said:
Yeah. Well... I haven't seen a ground adjustable tab that was big enough to make the airplane difficult to handle if gone too far. But that is just me, I guess.
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+1. I've never seen one that would make the airplane uncontrollable. I suspect that such a beast does not exist on a typical certified light single.
 
Surface area of flight control vs. surface area of tab...

Seems pretty likely on most that I've seen that they can't overpower the main control surface.

Still might make your muscles tired fighting it though. Your mileage may vary...

I'd move it a bit on all the ones I've seen, but without context of what type of aircraft we're talking about, it's only a hypothetical.

Perhaps the OP could share that info.
 
Ron Levy said:
Even if nobody's "dusting it for prints," your butt will be in the plane, so if you don't know what you're doing, don't do it, even in "small increments," since you may not understand how small "small" is in this context.
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How big is this trim tab? Like a barn Door? Then that's a flap -- don't bend that.

Any Cessna bendable tab I've seen is the size of a dollar bill. If that puts you out of control, you need more time in the gym.
 
Greg Bockelman said:
Yeah. Well... I haven't seen a ground adjustable tab that was big enough to make the airplane difficult to handle if gone too far. But that is just me, I guess.
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I have -- on my CP practical test in 1972. Airline was brand new from the factory, and I was the first one to fly it after delivery. Rudder tab was bent the wrong way, and I didn't notice that on preflight (nor did the FAA Inspector giving the ride). You try flying chandelles to the right with the rudder trim set strong left instead of slight right. Even the inspector didn't have enough leg to do it smoothly, and he did try after I told him how the controls felt.

Also, on many planes, if you don't do it correctly, you can do some really expensive damage to the airplane. You can loosen the rivets holding it on, which can pull out damaging jthe surface to which it is attached, or even create a flutter condition. We've seen that before on the aileron tabs on Grummans. So yeah, if you don't know how to do it, don't do it.
 
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The tab on a 170 isn't that big or made of thick heavy material. They do occasionally get bumped or bent on the ground so your adjustment could easily be considered a pre-flight safety check. I do this on my cessna all the time though with a nose wheel the tab is up where it doesn't get bumped much. Remember that adjusting the tab is opposite of the control direction you want. If you want more right rudder with less pedal pressure the tab is bent to the left. Don't do big adjustments and you won't have trouble. If the Fisdo boys say anything tell them it was bent and you're putting it back. Its true after all....they are all bent.
Frank
 
Ron Levy said:
I have -- on my CP practical test in 1972. Airline was brand new from the factory, and I was the first one to fly it after delivery. Rudder tab was bent the wrong way, and I didn't notice that on preflight (nor did the FAA Inspector giving the ride). You try flying chandelles to the right with the rudder trim set strong left instead of slight right. Even the inspector didn't have enough leg to do it smoothly, and he did try after I told him how the controls felt.

Also, on many planes, if you don't do it correctly, you can do some really expensive damage to the airplane. You can loosen the rivets holding it on, which can pull out damaging jthe surface to which it is attached, or even create a flutter condition. We've seen that before on the aileron tabs on Grummans. So yeah, if you don't know how to do it, don't do it.
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Can you show me an entry in any GA airplane logbook by an A&P that reads: "Bent rudder trim tab 0.12 CM to the left..."


:confused:
 
Fearless Tower said:
Is an A&P required to adjust ground adjustable trim tabs?

It is not on the list in 43.3, but 43.3 refers to 'preventative maintenance' and I wouldn't exactly consider it preventative maintenance.

It would seem that an A&P is required to adjust, but I'm curious if anyone has seen an FAA reference or interpretation to the contrary.
Click to expand...

And, may I adjust ground adjustable trim tabs of rental aircraft which are driving me freaking nuts because the ball is out of center to the point that my knee aches after pressing down to keep everything aligned after three hours of flight and my wife is complaining that "everything is slanted" and I know what the problem is but I just want to take my foot off the pedal for a few minutes at cruise up here at 10 thousand feet and who cares about the slant and my coffee is cold now and, no, I don't want a snack!
 
Fearless Tower said:
Is an A&P required to adjust ground adjustable trim tabs?

It is not on the list in 43.3, but 43.3 refers to 'preventative maintenance' and I wouldn't exactly consider it preventative maintenance.

It would seem that an A&P is required to adjust, but I'm curious if anyone has seen an FAA reference or interpretation to the contrary.
Click to expand...

If you need a trim tab on a rag wing 170 some thing is out of rig. go back and set the aircraft up as directed in the 172 M/M. When rudder trim is needed it's a sign of wing incidence angle is wrong.
 
Whatever you do, make sure that if you do bend it, you bend it the right way. I used to train in a 152 that needed constant right rudder and aileron (especially with only me aboard, in the left seat) whenever I forgot to confirm during the preflight that the trim tab was bent to the left, not the right... somebody kept "fixing" it without thinking about how a trim tab works. :rolleyes2:

The most pathetic part of this is that you'd think the offender would realize, after doing this, that the left roll/yaw tendency was even worse... :rolleyes2:

After a while, I'd imagine the thing would be likely to crack from being bent back and forth repeatedly.
 
I MAY have adjusted my trim tabs on the Tiger once, but I was under the direct supervision of my A&P/IA, CFIi, and the guy that mows the lawn around my hangar.
 
Not doing it if you don't know how is a good rule of thumb for airplanes, applies just as well to pilots as owners as to mechanics.

A tab adjustment however, well if you do know how to do it...
 
Tom-D said:
If you need a trim tab on a rag wing 170 some thing is out of rig. go back and set the aircraft up as directed in the 172 M/M.
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Tom, interesting point.....the tab involved is on the right aileron. The tab originally had a VERY healthy deflection upward when I bought it and before it was painted. On the return to service flight, it seemed that it needed aileron input to the right to counter the trim tab, so I had my A&P bend it down to neutral before I flew it home to San Diego.

I've flown it a few hours since then and noticed that it wants to roll right and requires left aileron to keep it level. I assume this is due to the fact that there are two fuel tanks in the right wing vs one in the left and it wants to roll toward the heavy wing.

The paint shop did the control re-attaching and rigging AFAIK. I am wondering if they rigged it for neutral not realizing that the right wing is, by design, heavier than the left.

How big of a job is it to re-rig a '48 properly?
 
The ailerons on the Cessna singles can get distorted and cause wing heaviness, too. People sometimes bang them around when preflighting, or they squeeze the silly things, and that ribbed skin gets a curve in it. If the curve is on the bottom it will try to deflect the aileron upward. If on top, downward. I have seen a tool used to straighten them out. Difficult to use, though, and severe cases need new skins.

Rerigging the 172 wings is a bit of a process. I've never rerigged a 170 but Tom can tell us if it has the same eccentric setup in the aft spar attach in the metal wing versions. Adjusting that changes cable tensions and therefore flap and aileron rigging, too. The ragwing would use strut adjustments.

Dan
 
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