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  • Bending the axles allowed?

    Hello All.

    Not sure of the wisdom of this but asking. The GyroBee documentation shows a bent axle strut tube. I am hoping to run this tube straight which would require a bend in the axle itself. Doug Riley has mentioned an insert that allows the axle to be mounted 3 degrees out of alignment of the tube. Unfortunately I will be beyond this 3 degree limit by a significant amount and won't be able to use this method. (Mains are raked back a bit to add nosewheel pressure, in addition to the vertical clearance angle on the plans). I am wary of using any welded components so am entertaining the use of a bent axle. Is there a reason I've not heard of this being done? Searching the Forum yielded no discussion. Thanks in advance for any enlightenment.

    Regards,
    Brian Jackson

  • #2

    What diameter are they?
    I have bent 5/8" solid 4130 with no problem.
    Line up is a challenge when drilling holes for socket alignment.
    I have a hydraulic bender that does a good job, would just need a template to bend them.
    What I did on one machine was to make an axial that had a flat plate on one end.
    Bolted it through a 1/2" plate then bolted it between squeeze plates that held the upper strut, drag link and main strut together.
    I even milled a radius on the top hole to adjust camber.
    Life,The leading cause of Death

    Live and Learn--OR--Die and be an example

    321.252.7705

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    • #3
      Would love to see photos of that. I do have a press brake here at work that is capable of very accurate bends in thick material. I believe 5/8" solid steel rod is what will be used, but I have to coordinate that with the wheels (which I haven't purchased yet). But before I get too far along with this phase of construction I wanted to know from the experienced folks here like you if bending the steel axle was a no-no before giving it more consideration.

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      • #4
        I don't see a problem with the shallow bends under discussion, in non-heat-treated metal such as 4130 N, 1018-1020, etc. The hardened stuff is apt to to crack.

        Dominator landing gears (welded 4130 tubing) are "fine tuned" for toe and camber with a torch on assembly.

        Comment


        • #5
          Thank you Doug and Jake. I see that Azusa also makes axles:
          https://azusaeng.com/product/standar...l-stepped-end/
          This seems reasonable to purchase the wheels and axles from the same manufacturer. However it looks like the shortest length they make is 30" which would mean discarding most of it. No problem. Would have to contact Azusa to inquire alloy and hardness. There are Stepped and Un-stepped varieties. Would seem logical to order them sized for the ID of the tube (1 inch), but I can imagine 3 potential issues with that: 1. Weight. 2. Harder to bend a 1" rod than 3/4". And 3. Deformation of section at bend. I'd be concerned that the slight widening of the rod's diameter outward from the bend point might restrict the full insertion of the axle.

          I'm thinking that aluminum sleeves and a 3/4" non-stepped axle might be the way to go, based on a cursory peruse through Azusa's web site. No decisions made today, just in research and learning mode.

          Comment


          • #6
            Good afternoon Brian,

            Thank you for sharing the fun of your build.

            What is your objection to bending the tube as in the drawing?

            The support for the axle strut assembly is beyond the bend so the axle tube is mostly a guide that is primarily in tension.

            In my opinion the 1.25 inch by .120 wall 6061-T6 tube is more than up to the task even with a bend in it.

            I have no experience building a Gyrobee so this is based on my experience with fabricating structures and is just my opinion from looking at the loads, load paths and materials.

            Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

            Comment


            • #7
              Originally posted by Vance View Post
              Good afternoon Brian,

              Thank you for sharing the fun of your build.

              What is your objection to bending the tube as in the drawing?

              The support for the axle strut assembly is beyond the bend so the axle tube is mostly a guide that is primarily in tension.

              In my opinion the 1.25 inch by .120 wall 6061-T6 tube is more than up to the task even with a bend in it.

              I have no experience building a Gyrobee so this is based on my experience with fabricating structures and is just my opinion from looking at the loads, load paths and materials.
              Hi Vance. Always an honor when you chime in.

              It might be a little nit-picky of me but I share Doug Riley's sentiment about bent tubes under load. In this case it's necessary to have the keel connection portion of the tube aligned with the center of the wheel because of the design of the tube inserts. The rod end bolt that is captured by the insert is allowed to slide in/out by a very tiny amount under tension/compression loads. It's a form of shock absorption that rounds off just the hard transient peaks rather than broadband. If the angle is changed from this arrangement I would expect there to be excessive wear due to the side bending load introduced to the system. The rod end would also be in a bending moment, so it's just favorable to keep things aligned straight.

              There is a way to accomplish this by bending the tube instead of the axle, but it would require 2 bends instead of 1. That idea is still on the table, but if bending the axle itself can accomplish the same thing while leaving the tube straight, that seems like the better option.

              Comment


              • #8
                My inexperience/ignorance with the Gyro bee is showing Brian.

                I do not understand the suspension.

                I only see a single bend in the axel tube itself so it appears I am misunderstanding.

                My thought was if you bend the steel axel there has to be room for the bend giving it more overhang past the support (longer lever) loading both the axel in bending and the putting a load on the connection to the tube.

                My feeling is the less overhang past the support the better and the less length past the joint the better.

                In my opinion a slightly bent tube in tension can be a nice way to provide a little give assuming the force is not enough to straighten out the bend.

                In my opinion a slight bend does not affect the beam strength of a tube much.

                As I read this I am not expressing myself well so I will be quiet and cheer your build.



                Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                Comment


                • #9
                  Originally posted by Vance View Post
                  My inexperience/ignorance with the Gyro bee is showing Brian.

                  I do not understand the suspension.

                  I only see a single bend in the axel tube itself so it appears I am misunderstanding.

                  My thought was if you bend the steel axel there has to be room for the bend giving it more overhang past the support (longer lever) loading both the axel in bending and the putting a load on the connection to the tube.

                  My feeling is the less overhang past the support the better and the less length past the joint the better.

                  In my opinion a slightly bent tube in tension can be a nice way to provide a little give assuming the force is not enough to straighten out the bend.

                  In my opinion a slight bend does not affect the beam strength of a tube much.

                  As I read this I am not expressing myself well so I will be quiet and cheer your build.


                  You expressed that perfectly, Vance, and I apologize for not prefacing my description with the fact it was modified from plans. I do understand that the radius of a bent axle necessarily means it must extend farther beyond the tube end and strut attachment points. That distance is unknown without knowing the safe radius. All things considered it might be wise to leave the axle alone and stick with bending the tube. I will model and analyze both scenarios but am pretty sure a shaped tube is the safer bet with fewer unknowns in the mix.

                  Comment


                  • #10
                    Thank you for working around my sloppy language Brian. I feel we are on the same page now.

                    I feel that the way things appear to me to be designed the steel axle and the joint are the weak links and putting more length on the steel axle exacerbates the weakness.

                    If the first few inches of the axle tube next to the brace are strong enough then putting bends further along the tubes length may be inconsequential.

                    Thank you for allowing me to participate in the fun despite my inexperience Brian.
                    Regards, Vance Breese Gyroplane CFI http://www.breeseaircraft.com/

                    Comment


                    • #11
                      If you Gyro is a single place then the 5/8" axle will be OK,if its a 2 placer the I would if possible go to the 3/4" axle.

                      experience with the RAF bending the 5/8" axle and going to a 3/4" axle has proven to be best.

                      But if your machine is light the the 5/8" will be just fine.
                      Best Regards,
                      Eddie Sigman,Polvadera,nm
                      (575) 835-4921

                      Comment


                      • #12
                        Thanks guys. The practical experience here is invaluable. 5/8" axles would be the way to go for this light ship, along with the Azusalite wheels which are being ordered today. I don't have the bearings in the order yet (just the wheel halves and bolts) because I was told not to use the bearings that normally come with these wheels. I have Aurora bearings used elsewhere on the ship and may see if Aircraft Spruce sells an Aurora sealed precision bearing for this use.

                        EDIT: For correction, I was misremembering the direction about not using Azusa bearings. The direction was "Use the better bearings." I have since purchased the Azusa precision bearings for this wheel group.
                        Last edited by Brian Jackson; 10-19-2018, 05:54 AM. Reason: I was wrong

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                        • #13
                          Brian:

                          I had the same kind of concern for the mains LG bent beam. I too wanted to straighten it out to make it more simple, but my engineering skills are strictly math, not experience.
                          I wanted to bend the tube more near the axle mount point rather than so far in toward the keel. I am leaving it alone...
                          I only know that the bend was supposedly to provide some clearance for the tail boom during TO and Landing without bending the tail boom up a bit. But my info may be wrong.

                          Curtis S.

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                          • #14
                            It appears bending the axle is still on the table as a reasonable option based on the response I received directly from Azusa Engineering:

                            On 10/22/18 10:29 AM, Azusa Engineering wrote:
                            Dear Mr. Jackson:

                            Azusa axles are made from cold-drawn mild steel bars. The cold finishing draw provides a precise diameter, smooth surface, and improves the bar's tensile strength. The steel is not a heat-treatable and requires no heating or quenching after the finish bending.

                            Assembly precaution: Please consider what the bending operation will do to your ability to install ball bearings on the shaft.

                            Regards,

                            Tom Patronite


                            I wrote to Azusa to learn if there would be any heat treating necessary after a bend of approx 10 degrees, and if the alloy had hardness properties that would preclude bending at all. So I am passing this along to the Forum both for posterity and for further consideration. I did work out a preliminary 3D model of the arrangement over the weekend and it appears to work out OK regarding adverse twisting loads, etc. Not making any big decisions until after a few nights sleep, but a viable alternative to bending the strut tubes in my case.

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                            • #15
                              Test: Main page didn't register that the new post above was added. Forum was offline for a short while before posting.

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