Anti servo tab vs trim tab

Trim tab—you, too, can be a smooth operator

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Trim tab—you, too, can be a smooth operator
Related Articles
What does an anti servo tab do?
What is the difference between a servo tab and balance tab?
What is the disadvantages of servo tab?

My flight instructor was always fiddling with the trim wheel. It was located in the console between our seats, a black wheel with bumps. Rolling it up changed the pitch to more of a nose-down position and rolling it down did the reverse. I understood he was adjusting to keep us level, but it bugged me—and it contributed to my lack of understanding of the trim tab.

Factors such as wind, power settings, airspeed, and attitude affect the control inputs required by a pilot and can lead to herky-jerky overcompensations or constant, tiring pressure on the controls. The ability to adjust the trim and relieve control pressures must be a stress reliever for the ever-patient instructor. Changing the setting of the trim tab adjusts the neutral position of a control surface, such as the elevator or rudder. The trim tab allows its operator (in this case, my flight instructor) to reduce the manual inputs needed to maintain position.

The basic trim tab is attached to the trailing edge of the aircraft’s elevator. The elevator trim is adjusted by rolling the little black wheel forward (up) and the aircraft nose goes down. Roll it backward, and the aircraft nose goes up. Some aircraft have rudder trim, which can be used to help compensate for an airplanes’ left-turning tendencies or adjust for a tendency to pull in one direction in cruise.

My colleague told me she has a trim wheel in her Piper Cherokee 140 that is overhead in her aircraft and when she reached up to crank it on her first flight with her husband he asked, “Now, what are you doing?” But, as she was adjusting for a smooth landing for him, she was too busy to explain. With proper use of the trim tab, you can appear to be a smooth operator when you’re really still a herky-jerky new pilot.

Perfect pitch

The venerable P–51 Mustangs were equipped with a long-range fuel tank behind the cockpit to allow them to cross the Atlantic during World War II. The P–51’s original design was not configured to carry that much weight so far back in the fuselage, so the trim had to be adjusted far forward for the first part of the flight and slowly adjusted back as fuel was used. This avoided the excess drag—and too much fuel consumption—because of the nose-high attitude as the P–51 motored toward Europe.

Julie Summers Walker

AOPA Senior Features Editor

AOPA Senior Features Editor Julie Summers Walker joined AOPA in 1998. She is a student pilot still working toward her solo.

Hello,

Cessna 152/172

PA28

Cirrus SR2*

PA-44

Can anyone tell me what which planes uses what tabs?

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[Ref Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 6-7]

Stabilator is a one-piece horizontal stabilizer;
Elevator is the movable control surface behind the horizontal stabilizer

Stabilator’s control method is almost identical as the elevator and horizontal stabilizer assembly – Pushing the control column forward lowers the trailing edge of the stabilator and pitches the nose of the aircraft down.

Antiservo tabs are incorporated on the trailing edge of stabilator to decrease sensitivity – it is because stabilators pivot around a central hinge point, they are extremely sensitive to control inputs and aerodynamic loads. By using antiservo tabs, an increase in the force required to move the stabilator, it makes less prone to pilot-induced overcontrolling.

In contrast, trim tab is attached to the trailing edge of the elevator to trim off the control force as well as achieve “hand-free” flying purpose.

What does an anti servo tab do?

3) Antiservo Tab In small aircraft, it increases the control feel, and helps prevent you from over-controlling your aircraft's pitch. One of the most popular examples of the antiservo tab is on the Piper Cherokee.

What is the difference between a servo tab and balance tab?

The function of a servo tab is very different from a balance tab. With a servo tab control system movement of the pilots flight controls moves the servo tab. The servo tab at the trailing edge of the main flying control surface produces a aerodynamic force to move the control surface.

What is the disadvantages of servo tab?

The disadvantage of the servo tab is reduced control effectiveness at low IAS. Spring Tabs: The spring tab is a modification of the servo tab. The control column is connected to the tab and through the spring to the main control.