Nose Gear Steering Flashcards
What are components for steering
The nosewheel steering system consists of an arming switch, a handwheel and rudder control RVDT, a steering control unit, steering hydraulic manifold and steering actuators. The steering system provides electrically controlled and hydraulically powered actuation of the nose landing gear steering actuators for taxi, takeoff, and landing operations. When steering is not selected or under failure conditions, the system provides a free castering (shimmy damped) mode of operation to ensure dynamic stability of the nose landing gear. The steering handwheel on the pilot side console can turn the nosewheel 75 degrees either side of center while the rudder pedal input is limited to 7.5 degrees either side of center. If inputs are received from both systems at the same time, they will be summed if they are in the same direction or the difference will be the resultant if the inputs are opposing. In no case can the nosewheel turn more than 75 degrees, a mechanical limit at the actuator. For towing purposes, the torque links shall be disconnected, using the quick-disconnect mechanism available.
What is SCU
The steering control unit (SCU) is located in the underfloor avionics compartment for both the Global series aircraft and the Global 5000. It processes the steering command input and feedback signals, engages the solenoid selector valve, provides an output signal to the electrohydraulic servovalve, and also performs built-in-test and diagnostic functions.
What is Nosewheel arming switch
Nosewheel Steering Arming Switch
The nosewheel steering arming switch is a latching, two-position OFF/ARMED toggle switch mounted to the left of the landing gear selector lever. It provides control of the DC power to the steering control unit.
Does the rudder control have an RVDT
Rudder Control RVDT
Figures F1 and F4
Movement of either set of pedals drives an RVDT attached to the top of the pivot shaft of the rudder pedal assembly of the copilot. The pedal authority is ±7.5 degrees of nosewheel angle, corresponding to full rudder pedal deflection. The RVDT must be rigged when installed on the pedal assembly. The spline shaft has a missing tooth, corresponding to a missing tooth on the mounting bracket to ensure the windings are aligned before final rigging.
Where are steering components
L/h side fwd of nose u/c door
What are the feedback transducers
Feedback Transducers
One feedback transducer, a linear variable differential transformer (LVDT), is mounted in each steering actuator to provide a feedback signal, representing nosewheel position, to the steering control unit. The LVDTs are provided with excitation signals from the SCU.
How does it operate
With the nosewheel steering switch in the OFF position, the solenoid selector valve and the steering control unit are unpowered. Within the steering manifold, the bypass valve spring has moved the spool to the flow position, providing shimmy damping. As the nosewheel position changes, the fluid being forced out of the actuators is allowed to flow through restrictors into the other side of the actuators. With the two NLG WOW signals, the nose downlock signal and the nosewheel steering switch in the ARMED position, the steering control unit provides power to energize the command circuits, feedback transducers, and the monitoring subsystems. When the nosewheel steering switch is armed, a BITE check is carried out by the steering control unit to check the integrity of the system. The steering control unit then energizes the solenoid valve. Hydraulic system no. 3 pressure (provided by the “gear down” side of the landing gear no. 3 selector valve) repositions the bypass valve to configure the system for steering operations. The steering control unit constantly monitors the steering input RVDTs and the feedback LVDTs. Pilot inputs from the handwheel provide a steering authority of ±75 degrees. Pilot or copilot inputs from the rudder pedals provide ±7.5 degrees steering authority. When a steering input is received, it is summed with the feedback signal, and the resultant command (error) signal is applied to the torque motor coils of the electrohydraulic servovalve (EHSV).
What is free castering mode
Free Castering Mode Inoperative steering (selected off or failure condition) causes the system to revert to free castering mode. In this mode, the hydraulic pressure is blocked by the closing of the solenoid selector valve (SSV). During taxi maneuvers, there is no steering actuator force available to center the nosewheels, but they respond to asymmetric braking in order to turn the aircraft.
