Specifications

SECTION II
MODEL 560 AIRPLANE AND SYSTEMS
WHEEL BRAKES
Toe-actuated multiple disc brakes are installed on the main gear wheels. Braking can be
accomplished by either of two independent systems: the power brake hydraulic system or the back-up
pneumatic system. Normal braking can be applied from either cockpit seat. The emergency brake control
handle is installed under the left instrument panel only.
DIGITAL ANTISKID/POWER BRAKE
The antiskid system provides power assisted braking with skid protection. It is designed to provide
maximum braking efficiency on all runway surfaces. The system consists of two wheel speed transducers,
brake metering/antiskid valve assembly, digital control box, reservoir, accumulator, an electrically driven
hydraulic pump, filter, pressure and control switches and two indicator lights.
CAUTION
DO NOT PULL THE PWR BRKS CIRCUIT BREAKER TO PREVENT THE POWER
BRAKE PUMP FROM CYCLING. WITH THE CIRCUIT BREAKER DISENGAGED,
THE POWER BRAKE SYSTEM IS INOPERATIVE AND THE RUDDER PEDAL TOE
BRAKES ARE DISABLED. BRAKING IS THEN AVAILABLE ONLY BY USE OF THE
PNEUMATIC BRAKE SYSTEM.
System operation is conventional with power braking available at all speeds while antiskid protection is
available at speeds above approximately 12 knots. The antiskid protection feature is designed to operate
with maximum pilot brake applied pressure. The digital system is tuned to provide optimum performance
with the trailing link gear and brake combination.
The wheel speed transducer is bolted in the main gear axle with the drive shaft connected through a
drive cap to the main wheel. As the wheel turns, the transducer generates a 36 Hz signal for each wheel
revolution that is sent to the control module as a variable frequency. The control module accepts the output
of the left and right wheel speed transducers and converts these signals to a direct current (DC) voltage
that is directly proportional to wheel speed. The voltage from the left and right wheels is averaged to
provide a composite or reference voltage. Any significant variation between either wheel speed voltage and
the reference voltage produces an error signal that activates the side of the antiskid valve assembly which
controls the amount of braking being applied to that wheel. At touchdown, the generator voltage reaches
maximum as soon as the wheel spins up. As long as no skid occurs, the transducer voltage follows wheel
speed and the reference voltage follows the voltage of the transducer. When excessive deceleration of a
wheel occurs, transducer voltage suddenly drops. An error signal is generated which energizes the
appropriate servo valve segment of the antiskid valve for that wheel. The servo valve controls the
movement of spools within the main body of the antiskid valve which modulate the braking effort being
applied by the pilot as required to maintain transducer voltage and reference voltage within the skid limits,
preventing the skid condition. When the airplane speed drops below approximately 12 knots, the antiskid
function disengages.
To ensure proper braking on water, snow and ice-covered, hard-surface runways and all unimproved
surfaces, it is necessary for the pilot to apply maximum effort to the brake pedals throughout the braking
run. When the system anticipates a skid and releases the applied brake pressure, any attempt by the pilot
to modulate braking can result in an interruption of the applied brake signal and may increase stopping
distance significantly. Hydraulic power for the antiskid system is provided by an electrically driven hydraulic
pump located in the left nose of the airplane. An accumulator is installed in the system to maintain system
pressure when the pump is not running. The pump is controlled by a pressure switch that opens when the
pressure approaches 1500 PSI and closes when the system pressure approaches 1000 PSI.
The power brake system is enabled by a switch which is operated by positioning the landing gear
control. When the landing gear is down, the switch is positioned closed, providing a ground for the power
brake hydraulic pump motor. The motor may then run in response to signals from the motor pressure
switch. Upon landing, when the landing gear squat switch senses the airplane is on the ground it signals
the antiskid electronic control box, which enables the antiskid system.
I 56OMB-01 Configuration AA 2-27