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  • Fluid Power

    Saw an interesting show on fluid power and all its applications. Anyway, one thing they said was all control surfaces in a modern plane are controlled by fluid power applications. I was thinking "OK, the weakness of this is the same as the vascular system, namely, what happens when fluid leaks out of the hose." Later in the show they talked of the convergence of fluid power, digital systems, and control theory.

    That raised a question for me. In fly-by-wire, what is the extensive part? Does each control surface have a compact unit of digital and fluid components so that the length of hoses is very minor and needs to take a direct hit to lose control? Is the "wire" part what reaches from the flight computer to the control unit so that vulnerability becomes something other than a leak. I know there are many people here who know how this is engineered.

  • #2
    Do you mean hydraulics?
    Tanner Johnson - Owner
    twenty53 Photography

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    • #3
      Fluid power encompasses pneumatics and hydraulics.

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      • #4
        Originally posted by EconomyClass View Post
        Saw an interesting show on fluid power and all its applications. Anyway, one thing they said was all control surfaces in a modern plane are controlled by fluid power applications. I was thinking "OK, the weakness of this is the same as the vascular system, namely, what happens when fluid leaks out of the hose." Later in the show they talked of the convergence of fluid power, digital systems, and control theory.
        That is why they have redundant systems in airliners. It's extremely unlikely to lose all hydraulic power from all systems, although not totally unknown (Sioux City DC-10 for instance). The theory behind redundancy is of course if you lose pressure from one system there will be a separate redundant system to ensure the device being operated functions.

        Originally posted by EconomyClass View Post
        That raised a question for me. In fly-by-wire, what is the extensive part? Does each control surface have a compact unit of digital and fluid components so that the length of hoses is very minor and needs to take a direct hit to lose control? Is the "wire" part what reaches from the flight computer to the control unit so that vulnerability becomes something other than a leak. I know there are many people here who know how this is engineered.
        Not sure. At a guess, hydraulics are heavy, so they'd try and maximise the electrical part and minimise the hydraulic I'd guess. EC, these vulnerabilities have existed regardless of the control system used. In the old fashioned wires and bellcranks system, a bomb or a part fatiguing would mean a snapped wire and a loss of control, hydraulics can mean leaks and a loss of control, electronic wires can be cut. BUT, one thing an FBW system will be able to do that earlier non electronic systems couldn't is compensate for missing control sufaces or part of the network that are 'down'.

        The USAF/USN is experimenting with flightcontrol systems that can compensate for degraded or missing control surfaces (rudders, ailerons etc) - the idea being that if the rudder is completely destroyed other surfaces and engine thrust are used automatically to ensure a basic level of controlability to allow the aircraft to be flown home. The system is transparent with the rudder pedals still making the aircraft behave as though the rudder were still attached for example. There is an FA/18 being experimented on at the moment. I cannot find the video footage but its quite impressive what a rewrite of the FBW software will allow...

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        • #5
          That's a bit queer. No rudder but the controls give the impression it is still there. "Phantom limb syndrome"?

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