Trim Tab question
05-30-2007, 08:37 PM
#1
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Trim Tab question
Most piston singles that have trim tabs have it only on one elevator. Why dont they have a tab on both and why doesnt having one tab lead to a flight imbalance?--shouldnt the airplane want to roll just as if one aileron was deflected?
05-30-2007, 08:47 PM
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because the trim tab effects the elevator which rotates at one common point. The elevator is one piece...if it were separated into two then yes it would need two...but it isn't...pretty simple but good question.
05-31-2007, 08:41 AM
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One tab on one side is adequate to trim the elevator, and the forces are light enough that the imbalance does not create a structural problem for the elevator.
As you suspected it would impart a very slight roll moment on the airplane as a whole, but on a light airplane it's a small force and not really noticeable. Ideally an airplane should be rigged to fly straight-and-true at normal cruise speed, so the trim-tab roll moment might be cancelled out by the design and rigging of the other control surfaces.
Larger airplanes would probably not have asymetric control tabs.
As you suspected it would impart a very slight roll moment on the airplane as a whole, but on a light airplane it's a small force and not really noticeable. Ideally an airplane should be rigged to fly straight-and-true at normal cruise speed, so the trim-tab roll moment might be cancelled out by the design and rigging of the other control surfaces.
Larger airplanes would probably not have asymetric control tabs.
05-31-2007, 12:29 PM
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Originally Posted by Texandrvr
I think that the "slight roll moment" provided by having the trim tab only on one elevator is engineered that way on purpose in order to counteract the torque from the prop.
05-31-2007, 01:01 PM
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Originally Posted by Lowtimer77
Most piston singles that have trim tabs have it only on one elevator. Why dont they have a tab on both and why doesnt having one tab lead to a flight imbalance?--shouldnt the airplane want to roll just as if one aileron was deflected?
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