Wheel brakes are normally used to slow the aircraft down during
landing roll on the runway and to aid in directional control during
ground handling operations as taxi and parking.In small GA aircraft the brakes are connected to the main landing gear only and are operated independently from each other.The brake systems are operated by hydraulic pressure and the rudder
pedals have the brakes installed on top and are toe operated. Some
aircraft use heel brakes or even with separate levers in the cockpit
operated by hand (e.g. DynAero MCR and Tecnam).
With larger aircraft the weight increases but the force pilots can apply will usually about the same for every human being.It is therefore important that the pilot gets help in the form of brake boosters or power assisted brakes.
The wheel brakes are usually made of the disc type, but on some
exotic aircraft the drum type with two brake shoes inside is still being
used.
Drum type
With this model the two brake shoes are operated by either pneumatic
(air) or hydraulic (oil) pressure or maybe even manually with a cable
(very rare). You won't see these on modern aircraft anymore. Inside
there are a couple of springs attached to the shoes to make sure that
the brake contacts the drum evenly as friction will try to move them
slightly. The springs also make sure that the shoes retracts when brake
pressure is released.
Disc brakes
Very popular as they are lightweight and the disc sits between the
braking pads clamping them when brake pressure is applied. For heavier
aircraft multiple brake calipers and or multiple discs can be used.The brake disc is made from steel and bolted onto the wheel and
rotates. The clamping part, caliper, contains two brake pads and is self
centering. When brakes are applied the pressure moves a piston cylinder
arrangement inside the caliper and the pads will clamp the disc. With
even pressure on both sides.
Brake system
Most light aircraft have two independent brake systems on the upper
part of the rudder pedal. This part is hinged and connected to a master
cylinder. High pressure tubing is used to connect the master cylinder to
the brake cylinder in the caliper. Special hydraulic fluid (DOT4,
AeroShell Fluid 41) is used to transmit the brake pressure. Careful:
this fluid will eat away paint.Make sure that at the start of the take-off run you place your feet
low enough as not to ride the brakes as this would result in a sluggish
take-off roll.As the aircraft has two separate brake systems the pilot can use
differential braking to help steer the aircraft, some aircraft (Pelican
PL, Cessna) have their nose wheel steering connected to the brake system
where the first 10° left or right the nose wheel moves and with further
rudder movement the main gear will help steer the aircraft, helpful
during taxi and parking.
Parking brake
Some aircraft have a sort of ratchet type system where they keep the
brake pressure in the system, holding the aircraft in its place. Others
use a hydraulic valve and after pressing the toe brakes they close the
parking valve, thereby locking the hydraulic pressure. Check the POH to
see which type of system is installed.
Power Assist
The simplest system is the boosted brake. In this systems main
hydraulic pressure is used progressively through a valve to help the
pilot applying the brakes.With power assisted brakes the brake system is fed by the main
hydraulic system with a much higher pressure than the pilot can apply.
Brake pressure regulates main hydraulic pressure to the wheel and
caliper.These power assisted brake systems usually have a backup in case the
main hydraulic pressure fails so the aircraft can still be stopped by
using the brakes.
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