Control surfaces like elevators and rudders are attached to the rear spar of the stabilizer structure using hinges or fittings to allow movement. Their construction resembles wing construction, using spars, ribs, and skin made of composite materials like epoxy and honeycomb cores. Control surfaces are built to be light in weight with minimal structure behind the front spar. Both mass and aerodynamic balancing are important to prevent flutter, achieved by placing the center of gravity at the hinge line using mass balances and reducing hinge movement through aerodynamic design features.

1. CONTROL SURFACE
ATTACHMENT & CONSTRUCTION

2. CONTROL SURFACE ATTACHMENT
• Similar to wing-aileron attachment, rudder,
elevators are also attached to stabilizer
structure.
• They are attached at rear spar.
• On most a/c, this will be hinges or fittings that
allow the back & forth movement of surface.
• A rear or false spar may be built into TE of
flight control area when trim tab is fitted.

3. CONTROL SURFACE CONSTRUCTION
• These resemble wing construction of a/c.
• They use spar, ribs, skin all.
• Commonly they use epoxy reinforced
composite construction & honeycomb core
construction covered with aluminium skin.
• Epoxy is thermosetting polymer which
possesses unique mechanical & resistance
properties.

4. CONTD...
• Honeycomb core is manufactured from
composite materials like fibre class, reinforced
plastic or from a metal such as aluminium.
• Control surfaces are built, keeping in mind
that they should be light in weight.
• They have minimal structure aft of the front
spar in honeycomb core.

5. MASS & AERODYNAMIC BALANCING
• Both the balancing is important to avoid
FLUTTER.
• FLUTTER is an severe oscillation in control
surfaces as they are mounted on flexible
structure like wings.
• This can be cured by bringing the CG of the
control surface to the hinge line.
• This can be accomplished by adding mass balance
weights to LE of control which is mass balancing.

6. CONTD...
• Aerodynamic balancing means of reducing
hinge movement & thereby the physical effort
needed to control an a/c.
• Eg. In elevator if a portion of control surface
would extend in front of hinge line at
outboard end of surface, the portion ahead of
hinge line will tend to reduce force needed by
pilot to operate the same.

7. CONTD...
• So there must be a setting to set the hinge
into the control surface so that when
deflected from neutral, the part of the surface
forward of hinge line projects into air stream.
• This is aerodynamic balancing.
• They may be inset hinges, horn balance,
internal balance & tab balance.