A trim tab or trim tab is a small rudder to aileron , elevator or rudder of an aircraft . With the trim , rudder forces can be neutralized for different flight situations, e.g. B. for different positions of the elevator depending on the speed or the rudder in the start phase of powered aircraft or for single-engine flight. The picture of the Boulton Paul Overstrand shows an early form of such trim tabs. Other variants of aerodynamic auxiliary surfaces are, for example: Recognizable by the ailerons of the Dornier Wal or the elevator of the Dornier Do X.
The Flettner rudder, shown schematically, has been the usual design since the mid-1930s , as it hardly creates any additional resistance.
The trim rudder pulls the trailing edge of the rudder to which it is attached from the original neutral position into a new "normal position" with the air force it generates itself and the large lever arm. This neutralizes the force on the control stick / on the pedals for this new flight attitude. The trim rudder is one of several technologies for adjusting the trim using a control element in the cockpit .
The edge of the bow, which is common in sport aircraft and on the rotor blades of helicopters, has a similar effect as the trim rudder , usually simply a sheet metal riveted to the rear edge of the rudder / rotor blade . The aerodynamic function is the same as with the trim tab, but the edge of the bracket cannot be adjusted during flight. This bracket edge is therefore only suitable for permanently compensating for structural inaccuracies or (e.g. with pendulum elevators) to generate a certain rudder force that gives the pilot the feeling of a neutral position.
- Götsch, Ernst - Luftfahrzeugtechnik , Motorbuchverlag, Stuttgart 2003, ISBN 3-613-02006-8