No announcement yet.


  • Filter
  • Time
  • Show
Clear All
new posts

  • #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.


                  • #24
                    Well, Starbee just wrote me, they use cluster plates of 3/16" 6061-T6. And the lap belt end fittings are of 1/8" 6061-T6 also.
                    That leaves only the shock plate.



                    • #25
                      Also the rod end U-brackets are typically stainless. Has anyone made theirs from aluminum as well? I wondered about making them from a section of 2x.125 square extruded tube but worried about stress cracks at the sharp inside corners. What alternatives to stainless U-brackets have builders used, if any?


                      • #26
                        Brian: I wouldn't use cut-up bits of extruded al. alloy tubing for any sort of angle bracket (despite what the Gyrobee plans say). The inside corners are sharp, as you observe, but also they are, in effect, welded into being during the extrusion process. It's not a great idea to subject these corners to a prying-apart load.

                        Depending on the loads involved, I'd use brackets bent from either sheet aluminum alloy or non-stainless steel -- in either case with a nice inside bend radius, bending across the grain.


                        • #27
                          Hi Doug (and the rest) - I'm sorry to be such a large bundle of questions.
                          But LEAF has some nice 7075-T6 brackets - wouldn't they be great?
                          (although it'll all add up to a thick wad of dollar bills)



                          • #28
                            Erik: I believe that LEAF's aluminum U-brackets were/are used in the Air Command series gyros -- in places quite equivalent to the similar Gyrobee: trailing links, vertical struts.

                            I've never known of one breaking on an A.C., and some of them took a fierce load just from the misalignment that was originally built into that design.

                            U-brackets are actually a fairly awful way to connect tubes together from the structural viewpoint. A U-bracket forces the loads off-center compared to the bolts at the base of the U. This in effect wastes much of the strength of the tubular strut that's bolted to the U.

                            But they were very widely used in hang-glider-based ultralight planes, and the early designers of ultralight gyros took over the practice from Quicksilver, Teratorn, Drifter et al. They are easy, cheap and fast to install. You just have to beef up the joint to compensate for its inefficiency.

                            Getting back to cluster plates for a sec, my copy of the Bensen material specs called out 5051-H32 for cluster plates and all other plates on the gyro. This alloy polishes beautifully and holds a shine, but it's much softer than the 6061-T6 of the tubes. But Bensen's plates were massive. The Gyrobee's cluster plates, in contrast, are just 2" wide strips. Moreover, the 3/16" bolts have a smaller bearing area inside their holes than Bensen's 1/4" bolts. I suspect that's why Martin Hollmann specified steel instead of 1/8" aluminum for the 'Bee cluster plates.


                            • #29
                              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.
                              Neither do I. The European gyro manufacturers attempt to justify SS 304 by claiming that 4130 isn't readily available.
                              I doubt that's true, as Aircraft Spruce buys some of their 4130 from Germany.

                              What they also ignore is that SS work hardens easily from vibration. I suspect that's been a factor with masts and tail booms cracking.

                              I mentioned to my TIG welder (who build custom Cubs, works with SS, 4130, etc.) about ELA's tails falling off, ostensibly due to failed welds.
                              He shook his head and said, "
                              No, it's the wrong material."

                              I know nothing about the Gyrobee, but offer my 2 cents about SS in general.

                              Regards, Kolibri
                              Last edited by Kolibri; 04-03-2018, 04:12 PM.
                              PP - ASEL complex (Piper 180, C206, RV-7A), SP - Gyro (Calidus, RAF, SC2), soloed in gliders

                              Wasn't happy with my RAF's pitch instability, so I installed a Boyer H-Stab to my great satisfaction!

                              When an honest but mistaken man learns of his error, he either ceases to be mistaken -- or he ceases to be honest."


                              • #30
                                In Europe you can ask for DIN 1.7218 steel. It's the equivalent of SAE 4130.