Control Stick for 3 axis push pull tube.

Discussion in 'Tube and Fabric' started by blane.c, Jul 28, 2019.

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  1. Jul 31, 2019 #21

    Dan Thomas

    Dan Thomas

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    The Jodel has the aileron torque tube with nothing running through it. The top elevator cable passes over the spar and the bottom cable passes through slots in the fore and aft spar plates under the torque tube.
     
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  2. Jul 31, 2019 #22

    blane.c

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    View attachment 87265
    That is very nice.
     
  3. Aug 13, 2019 #23

    blane.c

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    Can someone talk about this in plain English.

    https://cad.timken.com/item/tapered...arings-ts-tapered-single-imperi-2/a2031-a2126

    I am trying to figure out if the bearing is as strong as a 1/8" cable in push pull, the cable is rated as I understand it to support 2,000 lbs hanging on it and the bearing is rated at 437 lbf. I don't understand if lbf is the same as hanging a weight on a cable or if it is something different.
     
  4. Aug 13, 2019 #24

    FritzW

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    ...a 200 pound guy exerts 200 LBf on a bathroom scale.

    If I'm looking at the right bearing...
    You can apply 2070 pounds of force sideways to the bearing (static radial load) and 437 pounds along the axis of the bearing (thrust load).

    I don't know the geometry of your system but I'd bet it'll never see 100 pounds of force.

    EDIT: There's more to it than that. Tapered roller bearing setups should have two bearings facing each other etc., but if you have two bearings you can double the allowed load.

    IMHO, unless your just wanting the smoothness of the bearings, tapered roller bearings are way overkill. And they add cost, complexity and weight.
     
    Last edited: Aug 13, 2019
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  5. Aug 13, 2019 #25

    blane.c

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    A couple thrust washers would work, but I'm thinking clearance? So the torque tube can rotate back and forth around the push pull tube. A couple bearings can be preloaded and then no axial play. Any clearance would be multiplied by the hinge line to the stabilator trailing edge length so about 16.75" times. So that could end up being with washers anywhere from around a 1/16" to 3/16" depending on how much play it actually takes to make it work properly. Flutter? Or just plain sloppy?

    Another way? There are 4 connections from and including the control stick to the first either bell-crank or idler connection (one at the stick/link another at the link/pass thru rod another at the opposite end of the pass thru rod and one at the bell-crank or idler). They could all be spherical rod ends and some rod ends have 14 degrees to 18 degrees of movement both ways from centerline. So cumulative 56 to 72 degrees of motion each way. I just see one rod end going to its stop then the next and back the other way, not all of them taking rotation evenly and how kosher is that?

    Evans, in the VP-1 plans and handbook page 63, Stabilator, it says about the flight load on the stabilator that it is at 6.6 g's 300lbs. Like the eyebolts he's referring to in the same paragraph all of the rod ends would need to be magnafluxed. The VP-1 Stabilator is 26" long total and the VP-3 22"
     
  6. Aug 13, 2019 #26

    blane.c

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  7. Aug 13, 2019 #27

    blane.c

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    With rod ends the torsion would be forced through the rod ends by the first bell-crank or idler. So that bell-crank or idler would have to be "beefed up" to do that job.
     
  8. Aug 13, 2019 #28

    FritzW

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    He's just making the point that each eyebolt is rated for 7000 pounds but the max load that will be applied to (and shared by) all 6 eyebolts is only *300 pounds.

    That 300 pounds IS NOT transferred to the control system, it's transferred to the stern post. Just like the weight of your 500 pound refrigerator isn't transferred to the handle on a furniture dolly, it's transferred to the axle on the dolly.

    The force on the handle of the control stick would be more like 5 pounds. That means there's only something like 50 pounds of tension in the elevator cables/rod. ...and that could never happen because you'd pass out and let go of the stick way before you could put that many G's on the airplane.

    I don't see any reason to Magnaflux rod end bearings that will never see 50 LBf (that's 2.5 psi on a 1/4" shank) ...your shoe stings probably see higher loads than that.
     
  9. Aug 13, 2019 #29

    FritzW

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    No offense intended at all
    but I don't think you fully understand the loads in the control system. Do you have a sketch of your system?
     
  10. Aug 13, 2019 #30

    blane.c

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    There isn't any way that I understand the loads, no offense taken. I understand the mechanical motion and the geometry. I don't want to end up with an overweight Codwallager, I would like to end up with something simple and more elegant than that. I have sketches, iterations of sketches, and I am still reducing the size and trying to make it simpler so nothing is finished. I will take a picture of a front spar sketch and a rear spar sketch neither are finished ideas just works in progress. Using spherical rod ends I wouldn't try to fix the internal push pull shaft from rotating as shown in the drawing were I was intending to address the rotating motion past the rear spar for example.

    On the left end of the control stick sketch the radius is 1 3/8" which thru 45 degrees forward and 45 degrees back movement will have a total up down movement of about 7/16" and longitudinal movement of about 1 15/16" . It has a 3" link (rod) between the stick and the push pull tube. The angles on the rod pushing in and pulling out on the tube do not seem excessive. I just ruffed the idea out at this end and I know it needs more refinement but I have no doubt it is workable so moved to aft end.

    I included a swivel sketch which most likely will be abandoned, I have spent much of my spare time worrying about dealing with the rotation of the torque tube not unduly affecting the push pull tube.
     

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  11. Aug 14, 2019 #31

    blane.c

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    I was thinking I needed much more rotating motion on the torque tube than I do. Considering aileron bell-crank differential the amount of lateral movement needed on the torque tube amounts to about 15/16" to put the aileron to the stops (touching false spar) this is about 26 degrees of rotation each way. So all of the compensation for the torque tubes rotation can be compensated for by using two spherical rod ends that in combination exceed that 26 degrees. This realization (finally) simplifies. I am changing the threaded extension of the rod in the center photo for a tapped 1/4" -28 hole in the end instead and changing to a male rod end, the Aurora GMM-3M-470 has 17 degrees of movement and weighs 0.05lbs. A second of these rod ends will be at the end of the push-pull tube connected to the first bell-crank for a total of 34 degrees each way. This should be adequate?
     
  12. Aug 14, 2019 #32

    blane.c

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    I chose 4340 for the rod in the bushing because it is the hardest of the common alloys in the normalized condition and it wears in the bushing, the bushing is 7075-T6 for similar reason and that it is dissimilar metal and that it is also a nut plate.
     
  13. Aug 14, 2019 #33

    FritzW

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    I'm trying to add all this to the VP-3 center section model but, man, there's a lot going on in there. Are you sure your not channeling the spirit of Ladislao Pazmany? ;)
     
  14. Aug 14, 2019 #34

    blane.c

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    I am trying to reduce the total size of the hole in the spar. Is that crazy?
     
  15. Aug 14, 2019 #35

    blane.c

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    In the middle photo I made the tube 1 1/16" outside dia. In the first photo I hadn't enlarged the tube dia. yet and was still trying to stuff it all in 7/8", increasing outside dia. to 1 1/16" through and aft of the front spar will make it easier, also on the front side of the front spar outside dia. is not limited by spar hole dia. I was going to make tube from a turned down piece of 1 1/8" and leave it original thickness on front side of front spar because it will be easier to weld to a larger thickness. They don't make a tube 1 1/16" outside and 15/16" inside but do make a tube that is 1 1/8" outside and 15/16" inside in the 4130 normalized.
     
  16. Aug 14, 2019 #36

    BJC

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    I’ve lost track of what you are building and why you want a smaller hole. Can you cover that info again?

    Thanks,


    BJC
     
  17. Aug 14, 2019 #37

    blane.c

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    Increasing the tube diameter to 1 1/16" and leaving the top of the hole the same as the top of the hole for 7/8" moves the center of the hole for the larger tube down 3/32" which moves the aileron crank down 3/32". It still fits in the 3/4" space below the spar but the first push pull tubes going out to the aileron bell-cranks may need to be lengthened.
     
  18. Aug 14, 2019 #38

    blane.c

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    A VP-3 control stick, modifying from cables to push pull tube. To eliminate 3/4" diameter holes in bottom area of both spars. Push pull tube to go thru center of torque tube.

    Because less holes in spar center section is better?
     
  19. Aug 14, 2019 #39

    FritzW

    FritzW

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    Fewer/smaller holes are always better but there's a balance between "ideal" and "practical". You may be going to great lengths (added weight, cost, complication and hassle) to solve a problem that's not really a problem. If Bud Evans was okay with those holes then it's a safe bet those holes are okay.

    Controlling the stab on a VP with cables is perfectly fine. It's simple, easy, cheap, bullet proof, and light.
     
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  20. Aug 14, 2019 #40

    blane.c

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    It has a cool factor too.
     

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