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Homebuilt R22 Look-a-like.

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  • Homebuilt R22 Look-a-like.

    Hello to everyone and a merry Christmas.
    I am a new member to ASRA and I am still feeling my way around this site.
    I am in the process of building a side by side gyro that is based on the style of the cockpit of a Robins R22 chopper.
    I would be happy to place a photo or two as the build progresses if anyone is interested. The build is approximately 60% done.
    I am rapidly getting to the point where the main rotor assembly needs to be setup so with this in mind, I do have a question that I just can't seem to find the answer for. I will do my best to phrase it correctly.

    With respect to the main rotor blades, is the RIGGERS ANGLE (angle of attack with respect to the hub bar) set at any particular angle. IE: is there a 1.5 degree positive angle of attack on each blade with respect to the hub bar or is it 3 degrees + or 0 degrees????

    Any help with this would be greatly appreciated.

  • #2
    G'day Electron,

    I refer to the angle you speak of as the Angle of Incidence. I believe he term riggers angle goes back to the days of rag, wood and wire bracing in fixed wings. The angle is the one that is "rigged" into to wing by the fitters during manufacture and measures the angle between the cord line of the airfoil and the horizon.

    In a gyro, instead of the horizon, we use the plane of the hub bar. Most manufacturers set this angle at about 1.8* positive.

    Are you making your own blades? If you're using manufactured blades, do not try to mess with the angle. Leave it as is. One assumes that the manufacturer knows what he's doing.


    In aviation, the only stupid question is the one you don't ask.

    In aviation, the only stupid question is the one you don't ask!


    • #3
      Thanks for the response Waddles.
      I will give you a call today if that's OK. I am still feeling my way around this website and didn't see your message until this morning.

      A little bit of a back story with this gyro for your info:
      I purchased a single seat 2 stroke gyro and a 2 seat EJ25 powered gyro from a fellow aviator after he died. The single seat had to have the small cockpit fitted as that was a project still in progress when he passed away. The 2 seat gyro was nowhere near finished and is the subject of this post. It came with everything to finish it (well.........mostly) and it is well under re-construction now. I have essentially stripped it down to the last nut and bolt and I have been rebuilding it up from there. It is not being "thrown" back together but instead is being built to a high standard mechanically and will have comfort and equipment levels seen in the latest of the factory built machines.

      Angle of incidence is indeed what I am referring to and at last I have an answer, 1.8 degrees positive for each blade. Thank you for that. I am not building my own blades. I have a new set of blades here but I have no idea what brand they are, nor do I have any specifications relating the design of them. I also have a brand new rotor head complete with a hub bar that isn't new. The problem is that the blade mounts on this hub bar do not even come close to being the same as the blade mounts that are on the blades themselves. So, it must be that either the hub bar is off a different craft or the blades were bought at a later date and have yet to be modified to fit the hub bar. The obvious preference for me is to change out the hub bar to suit the blades I have as it would be the easiest part for me to remanufacture accurately here in the workshop.
      I hope you had a good and safe Christmas and hope to speak to you soon.


      • #4
        Good to talk with you yesterday, Electron. I'll look forward to seeing you at Quirindi.


        In aviation, the only stupid question is the one you don't ask!


        • #5
          Please bear with me. I will try and make this as painless as I can!

          It turns out that the brand new set of blades I had that I thought would fit the 2 seater is simply not the case.
          As a result I bit the bullet and bought a brand new set of 30 foot AK blades (still in the crate). I now need to make up the new mast and install them onto it.
          I want to know for 100% sure that I set up the head AND the new mast correctly as the info I have gleaned so far seems a little bit vague & ambiguous to me.

          ALL OF THE FOLLOWING ANGLES ETC is with respect to the KEEL:

          1)I am led to believe that the JESUS bolt (Big vertical bolt through the main bearing on the head) is to be set to 81 Degrees (IE:CLOSE TO VERTICAL but slightly "rearwards") with the controls fully forward. Is this correct??

          2) If that is correct then that would mean that with the teeter bar, resting against its front stop (with the blades orientated "Front to Rear") then the blades will be all but parallel to the keel. This I can visualise and agree with . . . .but is it true?

          3) If that is also correct then without moving the controls, and if the blades were then "tipped" rearwards then they will travel 18 degrees through the teeter and hit their rear stop.

          4) With the blades held against their rear stop, and if the controls are then moved all the way rearwards onto its stops, the JESUS bolt would now be 18-20 degrees rearward from it's near vertical position (63-61 degrees). The teeter will also add another 18 degrees, am I correct in ending up with the blade angle of between 45 & 43 degrees REARWARD???????
          TO BE CLEAR.................. I believe that everything I have outlined here to be 100% correct but hey, am I incorrect in my maths or in my logic or am I good to go???
          PLEASE can someone help me out here as I do not want to do this more than once and I am 1000% sure someone within ASRA knows how to setup a Gyro Head correctly.
          Many thanks


          • #6
            I'm not a scratch builder or designer, but I'll see if I can help here.

            Re (1). I am under the impression that the Jesus bolt lies in a plane parallel to the mast and that the mast to the keel angle is 9* aft or 81* from the vertical. The keel should be parallel to the horizontal in these measurements. However, if the hang test is not within the recommended range, some builders will change the mast to keel angle to achieve the desired hang range. More commonly, the head plates are adjusted to achieve the hang range.

            (2). It is true for the figures you quoted. Your "teeter bar" is commonly called a hub bar. The angle of the hub bar to the horizon is independent of the total angle subtended by the hub bar between the teeter stops. The angle of the hub bar between when it touches the forward stop to when it touches the aft stop is recommended to be a minimum of 16*. Most are set at 18*. When speaking of the HEAD angle, we are referring to the angle that the head rotates through (measured on the ring gear) from when it hits the front HEAD STOP to when it hits the aft HEAD STOP. From ring gear level to aft head stop, this angle must be at least 18*. At the forward stop, the ring gear can be horizontal or about 2* forward (To assist rotor slow down after landing). Once the head movement has been achieved, one must check that rotor blade when pulled down on the aft TEETER stop with controls fully aft such that the head is against the aft HEAD stop, the blade must clear the propeller, the top of the tail and remain clear of the ground. (Check the compliant requirements for the exact figures). Old school figures were 100mm clearances for prop and tail and 300mm for ground clearance. Generally, if the clearances required are insufficient, a new taller mast will be required.

            (3). With your figures, true.

            (4) I think all these angular measurements are over complicating matters. Work with the figures I gave above which I use in all my TA inspections. Really, the only variable is the mast to keel angle if that is the way the designer goes to get the right hang range.

            Give me a call if you think I can confuse you some more!!!!


            In aviation, the only stupid question is the one you don't ask!