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  • #16
    So the reason behind choosing it over other materials could be, that when overloaded it deforms - but doesn't break?
    And an open frame gyro is inspected regularly.



    • #17
      I doubt there were any deep reasons for using SS on the Gyrobee. It's rust-resistant as long as it is exposed to oxygen. If cut off from oxygen, it will rust. It provokes serious "wasting" corrosion in aluminum that it contacts if not insulated from the aluminum by plastic, paint or other non-conductive coating.

      Interestingly, my edition of the Bensen plans called out 1/8" 5052-H32 for the cluster plates (and rotor head cheek plates). And that's what came in the kit. This stuff takes and holds a better shine than 6061-T6, but is far more ductile and not nearly as strong. Bensen had us bend some parts out of the 1/8" plate, and I imagine that he used this softer material to reduce the chance of cracking at the bends.

      The Gyrobee cluster plates are strips only 2" wide, mounted with 3/16" bolts. Bensen's, OTOH, are large triangular plates, with far-spaced 1/4" bolts. I'm sure that's why Hollmann and Taggart went to steel.

      Again, I see no need for the steel to be stainless, and a couple good reasons for it NOT to be.


      • #18
        Someone recently told me that he was considering building a gyro from electrical conduit, commonly known as EMT (electrical metallic tubing).

        I was horrified, knowing that EMT is designed for easy forming with simple hand tools, so told him that after a hard landing, heíd have instant spaghetti.

        However, I looked up the physical properties of EMT and to my surprise, its properties are nearly identical to type 304 stainless steel, the material used for fabrication of most Eurotub airframes, the Magni being an exception.

        The yield strength of 304 SS = 31,200 psi; the yield strength of EMT = 35,000 psi.

        The downside of EMT is that itís nasty stuff to weld; with welding heat, the zinc coating vaporizes and creates some noxious fumes. And of course, itís not as pretty as SS.


        • #19
          ...and the yield strength of 6061-T6 alloy is also in the 35,000 PSI neighborhood -- but steel weighs 2.5 times as much as aluminum. It just doesn't make a lot of sense to build an aircraft frame out of 35,000- KPSI steel.

          Once you trade up to 4130, with a yield around 70,000 PSI, it starts to make SOME sense. It's still heavier for a given strength than 6061-T6, but you may be able to earn back that weight penalty because: (1) thin-wall steel tubing welded into trusses can be more precisely deployed, putting just enough metal in each spot to do the job (6061-T6 extrusions are clunkier) and (2) welding is a lighter form of joint-making than bolting (the bolts themselves are heavy, and the wall section must be heavy to carry the high point loads created by bolts and holes).

          By the time you account for the issues of stress relief and corrosion protection of steel, though, it's roughly a toss-up between 4130 truss and Bensen's bolt-n-go construction, for what we do in small gyros.

          In any event, I don't "get" the welded 304 deal at all. It appears to combine some of the unappealing aspects of both types of construction.


          • #20
            With consumer products, Doug, appearance and perception are paramount.

            I expect oxcarts would sell better if equipped with tail fins and high speed hubcaps


            • #21
              I'll buy some 3mm grade 5 Titanium off eBay - strong, light and shouldn't corrode (apart from the barrier layer).
              That should satisfy all requirements - if I can cut and drill it.

              Last edited by rcflier; 12-29-2017, 02:40 AM.


              • #22
                Titanium is strong, tough and chemically inert, making it ideal for use in the human body for such things as artificial hip joints and dental implants.

                It requires care when machining; slow feeds of cutting tools along with plenty of coolant.


                • #23
                  My original bensen had 1/16 cluster plates, I later replaced them with 1/8 due to cracking, the cracking was caused by rough snow and ice conditions while taxi to a takeoff point and not from in flight loads, the bensen had no suspension other than air in the tires and on skis it didnít have that.