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rondon9897

Flight control locks

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Hello folks,

 

My question is why did the Fokker 70/100 have flight control locks when all of the primary flight controls were hydraulically actuated? Surely the controls couldn't flap in the breeze with no hyrdaulic power?

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actually they can. When hydraulics are not powered, the pressure will bleed off over time. Most actuators are balanced and have hydro power to both sides of the actuator. When you displace a control, one side is variably bleed to return back to the reservoir which allows the actuator to move in the selected direction. The actuators also have a normal bleed through which keeps the fluid circulating. This aids in temperature control and helps keep the actuator warm. When powered, there is more volume to the control than the normal bleed allows. So after shut down, the pressure will eventually bleed back allowing the controls to flap around. The DC10 and other jets I've flown had hydraulic snubbing in the actuator that cushions the flight control when it flaps to its extremes. In this type system, a gust lock isn't required. In the Gulfstreams that I fly, you set it after shut down when the pressure has bled free. To ensure no pressure, we usually move the yoke fore and aft, left and right before setting the lock.   

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