Gear door operation must be controlled so that it occurs after the gear is stowed. Two sequence valves (C and D) also receive fluid pressure. This drives the gear into the wheel well. At the same time, the actuator cylinder on each gear also receives pressurized fluid to the gear-up side of the piston through an unrestricted orifice check valve. The three downlocks are pressurized and unlocked so the gear can be retracted. In the system illustrated in Figure 4, when the flight deck gear selector is moved to the gear-up position, it positions a selector valve to allow pump pressure from the hydraulic system manifold to access eight different components. If pressure declines, the pressure switch closes to run the pump and raise the pressure until the pressure switch opens again. The gear are held in the retracted position with hydraulic pressure. When the three gears are fully retracted, pressure builds in the system, and a pressure switch is opened that cuts power to the electric pump motor. Fluid from the gear-down side of the actuators returns to the reservoir through the shuttle valve. As the cylinders begin to move, the pistons release the mechanical down locks that hold the gear rigid for ground operations. Fluid from the pump flows thought the gear-up check valve to the gear-up sides of the actuating cylinders. In this direction, pump inlet fluid flows through the filter. This sends current to the electric motor, which drives the hydraulic gear pump in the opposite direction causing fluid to be pumped to the gear-up side of the actuators. To raise the gear, the flight deck gear handle is moved to the gear-up position. Electric limit switches turn off the pump when all three gear are down and locked. When the gear reach the down and locked position, pressure builds in the gear-down line from the pump and the low-pressure control valve unseats to return the fluid to the reservoir. While hydraulic fluid is pumped to extend the gear, fluid from the upside of the actuators returns to the reservoir through the gear-up check valve. Restrictors are used in the nose wheel actuator inlet and outlet ports to slow down the motion of this lighter gear. Pump pressure moves the spring-loaded shuttle valve to the left to allow fluid to reach all three actuators. The motor turns in the direction to rotate the hydraulic gear pump so that it pumps fluid to the gear-down side of the actuating cylinders. When the flight deck gear selection handle is put in the gear-down position, a switch is made that turns on the electric motor in the power pack. An all-electric gear retraction system is illustrated in Figure 1. This is possible only with the relatively lightweight gear found on smaller aircraft. The rotary motion of the motor is converted to linear motion to actuate the gear. An all-electric system uses an electric motor and gear reduction to move the gear. Use of a roller chain, sprockets, and a hand crank to decrease the required force is common.Įlectrically operated landing gear systems are also found on light aircraft. Through mechanical advantage, the pilot extends and retracts the landing gear by operating the lever. The simplest contains a lever in the flight deck mechanically linked to the gear. Thus, many light aircraft have retractable landing gear. Small Aircraft Retraction SystemsAs the speed of a light aircraft increases, there reaches a point where the parasite drag created by the landing gear in the wind is greater than the induced drag caused by the added weight of a retractable landing gear system.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |