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  1. Feb 7, 2013 #41

    Jay Kempf

    Jay Kempf

    Jay Kempf

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    I am not talking about a $5 model airplane servo. I am talking about a linear or rotary actuator. And they are not heavy or expensive. The robotics world is full of this stuff. There are some high end model airplane servos that would work for some applications but not for a large amount of area under a large load unbalanced. The DIY CNC world has come a long way due to advances in robotics. The stuff exists. The example of model airplanes is an example where long control runs have been replaced with putting actuators at the control surface. It is done because it is less complex, lighter, more accurate input to output and gives a tone of flexibility in setting up mixed control scenarios. It has been that way for decades now. If you are after that complexity it makes sense. Almost all of my designs could benefit from and are limited by the mechanical solutions for those complexity decisions. I don't think I need to rethink my thinking. If it was better to build complex mechanical systems that would be the trend line in every industry. It is not. If you are happy with a simple cable then this discussion really doesn't apply to you. Electrical systems if designed properly have been proven at this point to be more reliable in systems with added complexity in almost every industry and application you can think of including aviation.
     
  2. Feb 7, 2013 #42

    autoreply

    autoreply

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    I read a lot of "can't, won't and don't" in your reply.

    Before every step in aviation, many have proclaimed similar things. Let's see what Jay wrote and go from there:
    So let's look at the facts. For the plane I typically fly, I need about 4 of those for both aileron control and elevator control (max deflection at Va, completely out-of-trim):
    HS-645 MG Super Torque Servo from Hobby Lobby

    That's a whopping 8 ounce. Let's change that to 15 servo's for the elevator surfaces and 20 for the flaperon surfaces (redundancy). Now I'm down a shocking 3.5 lbs. That's less than the weight of one push-pull tube system, let alone 3 of them. What would the power consumption be, 10 Watt? That's less then my Ipaq's screen....

    Shall we now go back to the discussion how it can be done?
     
  3. Feb 7, 2013 #43

    Jay Kempf

    Jay Kempf

    Jay Kempf

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    There are all levels of servos with all levels of internals and they aren't really all that expensive. It is amazing how strong and fast they are.

    HerkuleX DRS-0101 Smart Robot Servo - RobotShop
     
  4. Feb 7, 2013 #44

    cavelamb

    cavelamb

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  5. Feb 7, 2013 #45

    Dan Thomas

    Dan Thomas

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    No FBW system will be more reliable than a simple non-boosted pull-pull cable system.

    Dan
     
  6. Feb 8, 2013 #46

    Jay Kempf

    Jay Kempf

    Jay Kempf

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    No I really am not kidding. Are you just having an impression or have you resolved the hinge forces for the control system you have in mind cannot be done? Imagine how small the force your hand puts in to a side stick, then travels through the cables and rods and is then resolved into the actual moving panel. How much force/torque do you think you can put through the control system? Hundreds of foot-lbs?
     
  7. Feb 8, 2013 #47

    cavelamb

    cavelamb

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    Stall torque: 12kgf.cm@7.4V


    How old are you, Jay?
     
  8. Feb 8, 2013 #48

    Himat

    Himat

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    The fastest RC sailplane have been measured to 498mph ground speed.
    Aircraft Speeds

    The plane I think was similar to this: k100 Page

    With the right design those small servos are good for a larger airplane too.
     
  9. Feb 8, 2013 #49

    Jay Kempf

    Jay Kempf

    Jay Kempf

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    Yeah, I got it, you don't understand that they make linear and rotary actuators in all sizes and strengths. Sheesh.
     
  10. Feb 8, 2013 #50

    Jay Kempf

    Jay Kempf

    Jay Kempf

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    Yup,

    But that doesn't mean you can use a small capacity servo for everything. There are also huge RC planes and large drones using servos. There are actuators for everything now. Off the shelf.
     
  11. Feb 8, 2013 #51

    cavelamb

    cavelamb

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    Pass...
     
  12. Feb 9, 2013 #52

    Pops

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  13. Feb 9, 2013 #53

    cavelamb

    cavelamb

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    Little better price here maybe...
    Surplus Center
    I found these to remote steer the outboard on my sailboat.

    While strong enough for the job they are WAY too slow for primary flight controls,

    Richard
     
  14. Apr 27, 2013 #54

    Hot Wings

    Hot Wings

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    I've got a question relating to FBW and can't seem to find any information, probably because I can't even come up with any good search terms. What I'm attempting to do is to figure out how much energy would be needed to operate control surfaces of a FBW system. If I had some idea of of the frequency and amplitude of the inputs needed during a "normal" flight during periods of high control activity, I could then integrate the resulting curve. Has any such study been done, maybe with regard to pilot fatigue? Even data from RPVs/UAVs/RC might be helpful.
     
  15. Apr 27, 2013 #55

    Jay Kempf

    Jay Kempf

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    Not sure what you are asking. Are you looking at control forces meaning hingeline torque/moment?
     
  16. Apr 27, 2013 #56

    Hot Wings

    Hot Wings

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    No. I can figure the force needed to move the surface. What I need is the number of times the control surface is moved per unit of time and the average amplitude of those movements during that time period. For example how long will a battery of X amp hours last, if the generator were to fail, assuming normal trimmed flight control inputs or while on autopilot in turbulence.
     
  17. Apr 27, 2013 #57

    Jay Kempf

    Jay Kempf

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    Gotcha, have to think about that or find a govt study.
     
  18. Apr 27, 2013 #58

    Himat

    Himat

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    I am sure several such studies much has been done to find the power consumption by the flight control system. The very simplest on model airplanes by charging the receiver and servo battery to full, fly a certain amount of manoeuvres during a set time and then recharge the battery to see how much energy that have been used. The F3A people do this to size the battery. I guess the same is done on smaller UAV’s. Maybe published like UAV power consumption breakdown or something like that?

    On full size aircraft with boosted control such a study must be done to size the hydraulic or electrical system providing the “boost”. Now, how to formulate search terms in this direction? Some more general notes might be public like in university lectures on the subject. The NASA server is down, if not that would be one place to search.
     
  19. Apr 28, 2013 #59

    Kristoffon

    Kristoffon

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    For that you need to know the frequency response of the autopilot and of the control surface actuators. Autopilot freq response is probably a programmable setting to suit to each aircraft but the manufacturer should be able to give you an idea. For the actuators you can get that data from their spec sheets. The highest low cutoff frequency gives you the most actuations per unit of time possible on that system. For amplitude assume full deflection -- this gives you a worst case scenario.

    Then you have force * distance = work, work * speed = power and you should reach a ballpark figure.
     
  20. Apr 28, 2013 #60

    Hot Wings

    Hot Wings

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    Thanks! That may be a lot more help than you might realize.
     

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