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25 Cards in this Set
- Front
- Back
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Briefly describe the DA42's landing gear system.
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It's a fully retractable, hydraulically operated, electronically powered landing gear system.
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Describe the main gear on the DA42.
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A tubular strut with a trailing link suspension system. The wheel attaches to the trailing link. A gas/oil filled damper attaches to the rear of the tubular steel strut and the landing gear.
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Describe the nose gear on the DA42.
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It is a steel strut damper willed with gas/oil to absorb the shock. It is steerable with the rudder via a steering linkage. A string assembly attached to the tubular steel strut centers the gear when deflected.
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Do the rudder petals always steer the nose gear?
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No, when the nose gear retracts, it rudder linkage disconnects from the nose gear.
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How does the nose wheel center itself?
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A small nitrogen filled piston on the right side of the nose wheel pushes down on the centering unit. The centering unit looks like a valley; as the nose wheel turns, it compresses the piston. The piston then wants to extend, centering the nose wheel.
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What is the main purpose of the centering unit?
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To center the nose wheel when retracting the gear off the ground.
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How far do the steering stops limit the nose wheel?
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30 degrees
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What makes up the hydraulic control block and where is it located?
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It consists of:
-Electric motor -Hydraulic pump and pressure switch -Hydraulic reservoir -Hydraulic accumulator -Hydraulic regulating valve -Hydraulic relief valve It's located rear of aft cockpit bulkhead, left side. |
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What is the purpose of the hydraulic pressure switch?
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It turns the hydraulic pump on at 1400psi and off at 1650psi.
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What is the capacity of the hydraulic reservoir?
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It holds 1.5L of hydraulic fluid; normal level in the reservoir is 0.9L, so 0.6L in the "system".
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Describe the hydraulic accumulator.
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Cylindrical container divided by a diaphragm: system pressure on one side, nitrogen at 1150PSI on the other.
Used to dampen pressure changes that occur during normal operation to reduce the number of pump cycles. |
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What is the purpose of the Hydraulic Dump Valve?
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Releases fluid from accumulator and hydraulic system back into reservoir: used for MAINTENANCE & GEAR SERVICING
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What is the purpose of the hydraulic pressure regulating valve?
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Limits normal operating pressure to 1800psi.
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What is the purpose of the hydraulic pressure relief valve?
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Limits max pressure to 2600psi.
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Describe how the landing gear operates.
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The electronically controlled valves provide the required hydraulic pressure to move the actuators on each gear leg.
Main gears retract inward toward the wing. The nose gear retracts forward into the nose. System is always pressurized; the hydraulic pressure keeps the gears retracted. |
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Why are their different speeds for extension and retraction?
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Because hydraulic pressure is used to retract the gear, at very high airspeeds (156 KIAS), there will not be enough force to raise the gear with the amount of airflow.
The gear can be extended at a higher airspeed (194 KIAS) because the airflow will actually help pull the gear down. |
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What happens when the gear selector is moved to the up position?
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-Retract solenoid valve allows fluid to flow from pump to retract side of actuator;
-Extend solenoid valve allows fluid to flow from pump to extend side of actuator -Fluid acts on both sides of actuator but the retract side has larger surface area than extend side; so more force acts on the retract side -Actuator movement unlocks the folding stays and the latching mechanism on each gear leg causing the gear to retract |
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What happens once the gear is fully retracted?
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-All three "up switches" operate. The nose gear is the last to come up.
-It sends a signal to the extend solenoid. -The extend solenoid energizes causing fluid from the extend side of the actuator to return to the reservoir through an extend solenoid valve -Gears are held in the retracted position with full pressure on the retract side of the actuator. |
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What happens when the gear selector is moved to the down position?
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-Extend solenoid valve allows fluid from hydraulic pump to flow to extend side of actuator
-Retract solenoid valve allows fluid from retract side of actuators through regulating valves and back into the reservoir -Pressure on extend side of actuators extends the gear -At extended position, latches on the folding stays operate against spring pressure which locks the stays in the unfolded position. |
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What is the max speed of the emergency gear extension lever?
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156 KIAS
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What happens when the emergency gear extension level is pulled?
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-Emergency control lever opens the emergency extension valves AND it operates a micro switch to isolate the hydraulic pump, so pump cannot run
-Open emergency valves allows the fluid on the retract side of each actuator to flow through the bypass valves -The by pass valves allow the hydraulic fluid flowing from the actuators to bypass the regulating valves and return to the reservoir. -Folding stays unfold, tension springs located in each bay ensure they fully unfold -Spring operated latching mechanism positively locks the folding stay open holding the gear legs in the extended position |
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What happens to the gear when the electrical system fails?
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-Failure of electrical system causes gear to extend because hydraulic pump is not powered anymore and both solenoid valves open.
-With no hydraulic pressure holding the gear up, gravity pulls the gear down. |
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Describe how the landing gear indicating system works.
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Green lights: Illuminate if gear handle is set down and gear is down and locked
Red unsafe light: Stays on if one or more of the gear has not reached the selected position -Down switches are located on folding stays on each of the gears. -Up switches are located at the top of the landing gear bays. These switches open when the gear is fully retracted to isolate the ground to the red unsafe indicator. Gear/Fire Test: Illuminates the lights and sounds the warning horn. |
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What are some of the safety features of the landing gear system?
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Squat switch:
-A Squat switch is located on the trailing arm of the left main gear. -With weight on the aircraft, the dampener compresses and opens the switch to isolate the solenoid valves from the system to prevent extension and retraction. Gear warning horn: When flaps are NOT in the LDG position and either power level is below 25%, the gear warning horn will sound if the gear is up. |
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Describe the brakes system?
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-Two sets of master cylinders: Pilot and co-pilot
-Fluid reservoirs are behind the co-pilot's rudder pedals; fluid flows from the co-pilot's reservoirs, into the pilots master cylinders, then through the parking brake valve into the brake calipers. -When toe of rudder pedal is pressed, fluid is pumped through hoses into the brake calipers, compressing the disc. -Parking break lever traps the fluid pressure in the hoses so the calipers stay compressed. |
