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钻石42飞机飞行手册 DA 42 Airplane Flight Manual(98)

时间:2011-10-28 13:17来源:蓝天飞行翻译 作者:admin
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To prevent inadvertent gear retraction on ground, an electric squat switch prevents the hydraulic valve from switching if the master switch is on and the gear extension switch is placed in the “UP” position.
After take-off, the gear should be retracted before an airspeed of 156 KIAS is exceeded. The landing gear may be extended at any speed up to194 KIAS.
The landing gear is designed to be manually operated in the event of failure. Since the gear is held in the retracted position by hydraulic pressure, gravity will allow the gear to extend if the system fails for any reason. To extend and lock the gears in the event of failure, it is only necessary to relieve the hydraulic pressure by means of the emergency gear extension lever, which is located under the instrument panel to the left of the center console. Pulling this lever releases the hydraulic pressure and allows the gear to fall free. Before pulling the emergency gear extension lever, place the gear selector switch in the “DOWN” position.
NOTE
If the emergency gear extension has been pulled due to an emergency, the system has to be checked before pushing the lever in again.
The nose gear is steerable by the use of full rudder pedal travel. A gear damping element, incorporated in the nose gear steering system, prevents shimmy tendencies. When the gear is retracted, the nose wheel centers as it enters the wheel well, and the steering linkage disengages to reduce pedal loads in flight.


Hydraulic gear extension system schematic
The main landing gear of the DA 42 is extended with three hydraulic cylinders. The following schematic figures show the system conditions for each operating mode.
In figure 1 the extension of the landing gear is shown. To reduce the amount of pumped hydraulic fluid during this operation, the return flow is partly led into the feeding flow of
the system.

The figure below shows the system status when the landing gear is extended. All hydraulic cylinders are under high pressure.


The operating mode for the retraction of the landing gear is shown in the next figure. While energizing the right hydraulic valve, the fluid flow in the hydraulic system is started due to different piston areas of the landing gear cylinders although the pressure on both sides of the system is equal.

While the landing gear is retracted both valves are energized and excessive hydraulic fluid on one side is drained into the tank. This configuration of the system is shown in the following figure.


For an emergency extension of the landing gear, the hydraulic fluid can pass through an emergency extension valve so that the gear is extended by gravity. The condition of the system is shown in the figure below.

 

 

7.6 SEATS AND SAFETY HARNESSES
To increase passive safety, the seats are constructed using a carbon fiber/Kevlar hybrid material and GFRP. The seats are removable to allow maintenance and inspection of the underlying controls. Covers on the control sticks prevent loose objects from falling into the area of the controls.
 
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