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  • Bad Design ??

    So doing the final checking today on a Rolls Royce Trent engine compressor blade on ower test bench.







    These are very high value items made from an alloy of Titanium, unobtainium and megsdoshium.



    Hours of work and many knuckles go into these at all points of the manufacturing process before they are fitted to the hub.

    They fit into the hub by the dovetailed machined end clearly shown on ower expensive test fixture.

    However to my mind just a push fit into a hub isn't really good enough for a blade that has to do this amount of work so today I modified the design, prior to RR approval and drilled and tapped two M6 holes in the bottom the take two M6 coach bolts.



    Anyone still following my reasoning ?



    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.




  • #2
    The problem I see is the holes would have to be very uniform to not upset the balance of the assembled rotor. If the main purpose of the holes is to hold the blade in a test fixture, why not merely push against the dovetail with a simple screw with a protective pad? JRW

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    • #3
      Special wooden rotor disk to hold it lol
      Mark

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      • #4
        not balanced now

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        • #5
          You would have thought that they could come up with a better idea than welding a bashed-up waste bin to a piece of old railway line.
          Peter - novice home machinist, modern motorcycle enthusiast.

          Denford Viceroy 280 Synchro (11 x 24)
          Herbert 0V adapted to R8 by 'Sir John'.
          Monarch 10EE 1942

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          • #6
            I remember standing aircraft watch on the flight deck of the America, before I made rank. with the ship under way, there was always a stiff breeze and if the aircraft was nose into the wind, some of the engines turned freely enough that the spools would rotate, pushed by the air flowing through the engine. At this slow speed some of the blades would rattle and tinkle.

            I once reported this and was told that it was normal, go away.
            Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
            ~Practitioner of the Electromechanical Arts~

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            • #7
              Originally posted by Weston Bye View Post

              I once reported this and was told that it was normal, go away.
              And had you not reported the "unusual noise" and a plane came apart, you'd always wonder if you could have avoided a catastrophe with a report. At least you didn't just shrug it off. Some do!
              Krutch


              Mentally confused and prone to wandering!

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              • #8
                Seems to me the vane ought to be held in by some kind of retainer, not just interference fit. The bolt should do it But then rebalance is needed. Hole - bolt + in weight.
                I don't know much about jet engine internals. I see articles in several magazines and thought of the centrifugal force on the vanes but didn't realize the vanes aren't fastened other than by the form and fit.
                Krutch


                Mentally confused and prone to wandering!

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                • #9
                  Just a wild guess, but I don't think John is being entirely serious.

                  Making a display mounting?
                  Bill

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                  • #10
                    I believe that the philosophy behind the original design is to allow the blade to absorb some deflection without fracturing. If the blades are rigidly mounted in the engine then the engine will be susceptible to excessive damage on ingesting seagulls, Canada geese, etc.

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                    • #11
                      Weston, one morning we discovered a length of 4 x 2 stuck in the engine of our Harrier Jump Jet which was parked outside our museum while the hangar was used for a function. Our volunteer security guard sheepishly admitted that the all night tinkling of turbine blades had been getting under his skin.

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                      • #12
                        We sectioned a Rolls Royce Avon engine for our museum and discovered on opening the compressor stage that if care was not taken the stator blades would all run out onto the floor!

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                        • #13
                          You takin a piss, mate?


                          My daughter discovered, "The Misfits" on HULU.

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                          • #14
                            The blades are supposed to be loose. At speed the centrifugal force holds them tightly in place, they turn somewhere in the 15 to 30 thousand rpm range, and as the engine heats up they don't bind. It is however starteling the first time you hear one spool down. Rattler,rattle rattle.
                            Dave

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                            • #15
                              Originally posted by willmac View Post
                              Just a wild guess, but I don't think John is being entirely serious.

                              Making a display mounting?
                              That's a safe bet.
                              The shortest distance between two points is a circle of infinite diameter.

                              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                              Southwestern Ontario. Canada

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