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Variable Pitch Propeller

November 9th, 2013 Leave a comment Go to comments

Variable Pitch Propeller

A propeller hub with adjustable blade pitch concept.

Many propellers in common planes (or boats) allow adjusting pitch of all blades at any moment – and even reversing it, in some designs. I was interested in recreating it, seeing it as a challenge that was apparently never approached in the official Technic sets, as opposed to a regular helicopter rotor. The designs are actually somewhat similar, with the primary difference being that a rotor has the pitch-changing mechanism exposed and located near the blades, usually below them, while a propeller has the same mechanism enclosed within the hub housing for better aerodynamic properties.

The building instruction for this design can be found here.

My hub design used four blades and was based on a small Technic turntable, which was rotated by a 20-tooth double bevel gear next to it, and through which a pitch-controlling axle was put. Pushing this axle and pulling it back controlled the pitch of all four blades at once, also allowing reversing it. The design was somewhat bulky, but sturdy, except for the fact that the centrifugal force could pull a blade out of it at higher speeds. I have used a rubber band to counteract this effect, but it still occurred at very high speeds, with near-zero pitch.

I have used the hub primarily to test the thrust generated by the blades from the 9396 Helicopter set, and it turned out to be highest at near-zero pitch, when the rotational speed of the propeller was highest. According to my imperfect measuring method involving a kitchen scale, the total thrust achieved with 1.2V batteries was sufficient to lift over 50 grams of load. It could most likely be noticeably higher with regular 1.5V batteries.

Photos:

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Video:

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Categories: Aircraft, Ideas Tags: ,
  1. Sandesan
    November 12th, 2014 at 21:20 | #1

    @Sandesan
    Otherwise, make triangles, 4x6x6 studs. That resultaat in approximately 72,72,36 degrees.

  2. Sandesan
    November 12th, 2014 at 21:07 | #2

    @Artwodeetwo
    Ehm, no sorry, I can’t… But I could send you an e-mail of a rough set up showing how to get the 72-degree angle. I just build it for you. Not to eager to just put my private mail address on a chat forum though. And mocpages is down. Perhaps Paul could link us through….

  3. Artwodeetwo
    November 12th, 2014 at 19:12 | #3

    @Sariel Thanks

    @Sandesan Can you explain this in a simpler way, I’m really struggling to understand this

  4. Sandesan
    November 12th, 2014 at 15:10 | #4

    @Artwodeetwo
    You might use a “tangent 3 approach” where each blad is connected to an other blade, where for two studs distance on one balde, you’d connect it on the sixth stud of the other blade. It won’t fit perfectly, but with a little tension, it might work. It’s only 2.5 percent of.

  5. Sariel
    November 12th, 2014 at 14:14 | #5

    @Artwodeetwo
    I don’t see any easy 100%-Lego way, but you could use this custom Lego-compatible part by Efferman: https://www.shapeways.com/model/1737527/rotorhead-for-5-blade-helicopters.html?materialId=6

  6. Artwodeetwo
    November 12th, 2014 at 13:58 | #6

    Hi Sariel, I’m interested in making a Technic Sea King helicopter, any ideas how to make a variable pitch rotor with 5 blades?

  7. ethan24
    February 12th, 2014 at 15:24 | #7

    thanks i think i will go with m

  8. Sariel
    February 12th, 2014 at 14:24 | #8

    @ethan24
    M or L, definitely not XL. You need speed more than torque.

  9. ethan24
    February 12th, 2014 at 12:35 | #9

    hi paul
    i want to make a boat i have given it two propellers should i use the pf M motor or should i go bigger-L or XL motor

  10. Neko
    December 19th, 2013 at 09:17 | #10

    You should try with the part No. 89509 ;)

  11. Sariel
    November 21st, 2013 at 18:38 | #11

    @Lennart
    The 9688 blades are worse. That’s why I said the 9396 blades are best.

  12. Lennart
    November 21st, 2013 at 18:12 | #12

    You say that the blades from 9396 are the best, maybe you can try the blades from 9688.

  13. Sandesan
    November 14th, 2013 at 11:12 | #13

    @Sariel
    I was just jesting… ;-)
    I’ve built a few of these, from Monogram, Italeri, Revell, if I recall well.
    And stull a few in the box to be built as attic insulation. A great plane, can’t wait it to be finished. Mustang high on my ‘coolest planes ever’ ladder as well… how to replicate that whistling noise in Lego….?

  14. Sariel
    November 14th, 2013 at 10:59 | #14

    @Sandesan
    I have seen all these things before. The Warthog won’t have propellers, it’s a jet plane.

  15. Sandesan
    November 14th, 2013 at 09:50 | #15

    Not to prove it has been done before, but for inspiration, please look at these.
    http://www.youtube.com/watch?v=rwTvn2dY2uY
    http://www.youtube.com/watch?feature=player_embedded&v=qxR7JVQAYsc

    I guess it will be an awesome Warthog; I’ve never seen one with variable pitch propellors….

    Keep a look out for the Antonov 140 built entirely from axles, scale 1:15. It surely will have variable pitch props as well I reccon…. but I think he hasn’t built the engines yet…

    Lots of projects running now simultaniously now you’ve added the (winged) Mustang. Looking forward to your posts. My building process of a ‘bus’ is just ever so slow…. Hope to finish it before I retire (and we’re about the same age, so….)

  16. Sariel
    November 10th, 2013 at 13:27 | #16

    @bj51
    As explained at the very beginning of the video, a variable pitch propeller has all the mechanics inside the hub, not outside the hub like the 9396 does.

  17. bj51
    November 10th, 2013 at 09:48 | #17

    I don’t get it. The set from which you took the blades (9396) has a mecanism that does exactly that. Why then say it was “never approached in the official Technic sets” ?

  18. Pierre
    November 9th, 2013 at 23:24 | #18

    you have done an error on your PDF ;-)
    One of your cross axle 3M (at steep 2) could be a connector wrong friction 3M :-)

  19. Srdjan Grbovic
    November 9th, 2013 at 13:03 | #19

    I built a 6 propeller hub, and used 8×4 plates as propeller blades, and a fixed pitch of 45 deg. I then geared 3 PF M motors 1:3, to achieve an rpm of nearly 1300, and got a lift force of nearly 65g :D I was unable do drive it faster because the propellers would fly away at over 1500 rpm :/
    Great design, i might use it in my helicopter, i will give you credit for it :)
    PS. On another note here is my finished TAM 150 truck which uses the front suspension of the Jeep Wrangler, http://mocpages.com/moc.php/368414 :)

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