Trim tab

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Trim tabs are small surfaces that mechanically or electronically manipulate the rudder, elevator, and ailerons to help stabilize an aircraft. They consist of small, movable panels set in the trailing edge of the control surface, looking very much like miniature versions of the control surfaces themselves. Trim tabs free the pilot from constantly adjusting the controls. It is controlled with a trim wheel. When the wheel is rolled forward the nose is held down (used in descents).

When a trim tab is employed, it is moved into the windstream opposite of the control surface's intended deflection. For example, in order to trim an elevator to hold the nose down, the elevator's trim tab will actually rise up into the windstream. The increased pressure on top of the elevator surface caused by the raised tab will then deflect the entire elevator slab down slightly, causing the aircraft's nose to move down.

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