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Hydraulic Controls

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Jay Fortner
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#1 Posted: 1/10/2010 18:29:23

Hey folks, Has any one ever used or thought about using simple non-pressurized hydraulic control systems similar to a brake system? I was reading a thread on teleflex cables and I agree they bind and reduce feedback. I'm in the process of converting a Quicksilver MX to conventional rudder to pedal controls. I had thought to hook the t-flex to the spoilerons but I don't like the lack of feedback inherant with them. I have a lathe and am not afraid to use it. I could build the cylinders quite easily. It would be a double acting cylinder on the joy stick with single acting cylinders for the slaves. I've already installed lightweight springs to park the spoilerons instead of the bungees Eipper used so the master could be ported to relieve pressure when the stick is in the middle. Of course you wouldn't  do this with ailerons, rudder or elevator. Fluid could be DOT-5 brake fluid or light hydraulic oil. So am I crazy or is this a viable alternative to cables, pulleys,bellcranks and linkages? Tell me what you think.    Thanks,            J.



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Joanne Palmer
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#2 Posted: 1/10/2010 20:45:33

Other than it will be heavy heavy heavy, it could be made to work.  Leakage could be a serious issue, but a simple check valve and reservoir system will take care of that.  And you have to have a method for air bubbles to work their way out.



Jay Fortner
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#3 Posted: 1/11/2010 09:52:04

Hey Joanne, When you say heavy are you talking about the feel on the stick or the weight of the system. I don't plan on using iron and steel and feel on the stick can be controlled by the volumes of the cylinders. On my little MX I would use nylon air line tubing so that should help keep the weight down, the cylinders and fittings would of course be Al I'm thinking .625 bore, .75 OD. Remember I've got to keep this thing at 254lb. or less. Bleeder screws are a must.

Thanks for your input,        J.



Joanne Palmer
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#4 Posted: 1/11/2010 11:19:37

Heavy as in weight.  your .625 bore relates to a .3 sq inch area.  You have two areas to consider. 

 

Stick forces.    These should probaly NOT exceed 100 lbs EVER and in most phases of flight these should be 50 pounds or less otherwise flying the plane will by like wresling Hulk Hogan.  I'm not sure that .3 Sq inch can give decent control feel and response.  And your hinge moments of your control surfaces have an effect.  Large throws (to get the forces down) will have large volumetric flow requirements.  Short throws have high forces and low flows, but now they can be "touchy" in pilot response.

 

you also have to consider response and that means hydraulic flow.  In order to get flow velocities down you have to have large tubes.  Since these have oil in them all the time, it can get heavy.  For 1/4 ID tubing, you'll have weight of .02 lb per foot length for OIL alone .  And you have that in BOTH directions.  Weigh that with a push rod system and I think you'll find that there are LESS headaches with a mechanical system and it weighs less.



Jay Fortner
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#5 Posted: 1/11/2010 11:38:57

Oh Youv'e done it now, The challenge is on. The E in EAA stands for experimental doesn't it. The MX has quite a lot of dihedral in the wings so if the spoilers were to fail chances are pretty good that I'm not going to crash. Hope to have my system on there and tested by Sun-n-Fun. Hope to see you there.        J.



Ried Jacobsen
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#6 Posted: 1/11/2010 12:57:20 Modified: 1/11/2010 13:00:19

I suspect you might be able to make it work.  I have two suggestions for E experimentation:

1. Set up a "benchtop" test rig to trial the application.  A joystick connected to the cylinder, with a 20' poly tubes to each "aileron cylinder".  I assume that if you have some type of accumulator at the aileron cylinder, no return line would be required.

2. Unless you "benchtop" is subject to freezing temperatures, run your tests with water initially.  If it does not work, the cleanup will be a lot simpler.

Good luck and let us know how you make out with the experiment.  Get a tech counseler or other independant witness to confirm what you see, then try it in the air. 

 



Jay Fortner
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#7 Posted: 1/11/2010 13:23:18

Hey Ried, My MX uses bungee cords to pull the spoilerons down and I have replaced them with springs because the bungees were stretched out and useless(I'm not a big fan of consumable parts). Do you think these will be a good enough subsitute for accumulators. I,m trying to keep this system lightweight. I like your H20 idea. Y'all bear in mind this is an ULTRALIGHT and I'm not trying to move large surfaces. Thanks,      J.



Ried Jacobsen
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#8 Posted: 1/11/2010 15:37:26

Keep in mind that water is probably 25% heavier than oil or brake fluid.  Guessing about 1.5 lbs of water vs. 1.2 lbs of oil as a guess.  Your results may vary. 

And your controls will get real stiff if you fly at 2o degrees F!  And they won't work after the ice thaws.  (But you knew this already, right?)

Water will work well for debugging the system, and if you like it (and get all the leaks out) switch to brake fluid)



Jay Fortner
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#9 Posted: 1/11/2010 15:57:31

No. I was only going to use water for testing, DOT-5 fluid is expensive.  I always thought water froze at 32deg?



Ried Jacobsen
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#10 Posted: 1/13/2010 21:55:40

In high school physics (up in North Dakota during the winter) we managed to sub-cool water to 10 degrees.  However, once a sub-cooled liquid is disturbed it will crystalize very quickly.  Anyway, water at 20F is "stiffer" than water at 32F.  I apologize for my poor attempt at sarcastic humor!



John McGinnis
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#11 Posted: 1/13/2010 23:23:35

Jay,

I'm using a master/slave nonpressurized hydraulic system together with more conventional control linkage in a way that allows the (redundant) hydraulics to damp the system and allow a convenient lockout. Since we're not using much pressure, it is totally unnecessary to use heavy, high friction hydraulic cylinders. In addition to the kind of parts used in automotive brake systems, I wanted you to note that many air cylinder manufacturers support the use of their products in low pressure hydraulic operation (generally under 200 PSI), provided the seals are oil compatible. Don't use any that aren't. You'll probably find the friction is still high unless your hoses are large and slick, but there can be a ton of advantages to this strategy, especially in terms of feel. Make sure if you have a lockout, as I do, that it can't vibrate closed on you in flight!



Jay Fortner
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#12 Posted: 1/14/2010 06:54:32

That's alright Ried, I've never been one to take life to seriously anyway.(i'll never grow up, I'm a toys-R-us kid).

North Dakota? Man you must be freezing. I feel for you brother.



Jay Fortner
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#13 Posted: 1/14/2010 07:14:12 Modified: 1/14/2010 07:18:48

Hey John,  Thanks for the feedback. You're correct about using low pressure pneumatic cylinders. I found some in an industrial supply catalouge they're not to pricey either. The master I will have to fab myself. I was planning to use aluminum to keep the weight down, 1/4" SS for the ram rods. Plastic air line tubing to plumb it with. Explain lockout?   Thanks,      J.

 



Kenneth Bailey
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#14 Posted: 1/15/2010 22:48:46

Jay, there was a kit plane, i believe the Bateleur, a composite pusher, with a delta wing and canard, that used hayraulics as the primary controls.  there might be information there..

 

Ken



Jay Fortner
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#15 Posted: 1/16/2010 06:24:14

I'll look that up,  Thanks Ken.       



John McGinnis
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#16 Posted: 1/17/2010 03:26:04

Lockout:  a valve mechanism able to stop the fluid flow through the circuit. This gives an 'any position' gust lock for parking, display, or maintenance. Handy but an obvious liability.