| Home | Privacy | Contact |

Pilot's Handbook of Aeronautical Knowledge
Flight Controls

Flight Control Systems

| First | Previous | Next | Last |

Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Balance Tabs
The control forces may be excessively high in some aircraft,
and, in order to decrease them, the manufacturer may use
balance tabs. They look like trim tabs and are hinged in
approximately the same places as trim tabs. The essential
difference between the two is that the balancing tab is coupled
to the control surface rod so that when the primary control
surface is moved in any direction, the tab automatically
moves in the opposite direction. The airflow striking the tab
counterbalances some of the air pressure against the primary
control surface, and enables the pilot to move more easily
and hold the control surface in position.

If the linkage between the balance tab and the fixed surface is
adjustable from the flight deck, the tab acts as a combination
trim and balance tab that can be adjusted to any desired

antiservo tab
Figure 5-21. An antiservo tab attempts to streamline the control
surface and is used to make the stabilator less sensitive by opposing
the force exerted by the pilot.

Antiservo Tabs
Antiservo tabs work in the same manner as balance tabs
except, instead of moving in the opposite direction, they move
in the same direction as the trailing edge of the stabilator.
In addition to decreasing the sensitivity of the stabilator, an
antiservo tab also functions as a trim device to relieve control
pressure and maintain the stabilator in the desired position.

The fixed end of the linkage is on the opposite side of the
surface from the horn on the tab; when the trailing edge of the
stabilator moves up, the linkage forces the trailing edge of the
tab up. When the stabilator moves down, the tab also moves
down. Conversely, trim tabs on elevators move opposite of
the control surface. [Figure 5-21]

ground adjustable tab
Figure 5-22. A ground adjustable tab is used on the rudder of many
small airplanes to correct for a tendency to fly with the fuselage
slightly misaligned with the relative wind.

Ground Adjustable Tabs
Many small aircraft have a nonmovable metal trim tab on the
rudder. This tab is bent in one direction or the other while on
the ground to apply a trim force to the rudder. The correct
displacement is determined by trial and error. Usually, small
adjustments are necessary until the aircraft no longer skids
left or right during normal cruising flight. [Figure 5-22]