Resizing a flywheel

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Resizing a flywheel

Home Forums Stationary engines Resizing a flywheel

Viewing 14 posts - 1 through 14 (of 14 total)
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  • #338241
    Stephen Follows
    Participant
      @stephenfollows82099

      I am building a stationary steam mill engine. I'm resizing the plans upward to do this. The original cylinder is 1/2" bore x 1". this gives a capacity of 0.196 cu. in. and a surface area of the piston of 0.196 sq. in.

      Mine will be 1" bore x 2". this gives a capacity of 1.570 cu. in. the piston will have a surface area of 0.785 sq. in.

      The capacity increases x 8, the surface area x 4.

      The original flywheel is 3" x 1/2". (3.534 cu. in.)

      What size should my flywheel be? Doubling the size the same as all other measurements gives me 28.274 cu. in. or 8 times the volume hence weight. it seems a lot for a small engine to drive.

       

      Edited By Stephen Follows on 25/01/2018 19:31:23

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      #3331
      Stephen Follows
      Participant
        @stephenfollows82099
        #338244
        JasonB
        Moderator
          @jasonb

          6" flywheel is about right for a 1×2 cylinder assuming it is spoked, just look at all the Stuarts that use that cylinder size and they all have 7" flywheels.

          I've enlarged and reduced quite a few engines in my time and every part gets enlarges or reduced by the same amount, not had one that did not run well. Only time were a reduction of mass may be worth doing is where you want the engine to pick up or loose speed quickly but that will be at the cost to smooth slow speed running.

          J

          PS New capacity will be 1.57 cu in or if double acting 3.14cu in

          #338250
          Stephen Follows
          Participant
            @stephenfollows82099

            Thanks Jason. Point in the wrong place blush, put it right now. Any idea where I might get a 6×1" fly wheel? Making everything else but a spoked wheel is beyond my machining skills.

            #338252
            Neil Wyatt
            Moderator
              @neilwyatt

              The difference is that as engines get larger, they generally run slower so they need a proportionately heavier flywheel.

              Your double size engine probably should not run as fast as the little one.

              Care needs to be taken not to dangerously overspeed flywheels on mid-sized engines. If speed is what's needed a small diameter solid flywheel is safest.

              Neil

              #338258
              JasonB
              Moderator
                @jasonb

                There is not a lot of choice for a 6" flywheel from the UK suppliers, Engineers Emporium do a 6" brass one with curved spokes and that's about it. Nothing from Reeves or Stuarts that fits the bill

                 

                RC Machine in Germany do quite a good range that includes a 154mm x 24mm one and these come part machined at reasonable cost. Also from Germany, Torsten at TS Model does a 150mm one, I've had 3 flywheels from him and they are really nice quality, the only downside is he needs international bank transfer so will add the charge from his bank to the invoice and you are also likely to get a charge from yours which does make them a bit spendy,

                The Swiss company Atelier do a 140mm one that may do the job

                Edited By JasonB on 25/01/2018 19:58:29

                #338262
                Oldiron
                Participant
                  @oldiron
                  Posted by Stephen Follows on 25/01/2018 19:33:41:

                  Thanks Jason. Point in the wrong place blush, put it right now. Any idea where I might get a 6×1" fly wheel? Making everything else but a spoked wheel is beyond my machining skills.

                  You could always make a solid flywheel, relieve the portion between the rim & the hub then drill a series of holes to make it look more like a spoked wheel. Easy enough to do on the lathe & mill.

                  regards

                  #338274
                  Neil Wyatt
                  Moderator
                    @neilwyatt

                    Or get a blank laser cut.

                    for john.jpg

                    Neil

                    #338283
                    vintagengineer
                    Participant
                      @vintagengineer

                      If you need to lighten a flywheel the more you take off the outer diameter the more the effect.

                      #338344
                      Howard Lewis
                      Participant
                        @howardlewis46836

                        From a theoretical point of view, doubling the dimensions of the parts of an engine should quadruple the weight, so it would seem appropriate for the Flywheel to have a Moment of Inertia four times greater than the original.

                        This should provide the same cyclic irregularity as the original, assuming that the materials used for every part are the same.

                        Howard

                        #338347
                        Mick B1
                        Participant
                          @mickb1

                          When I couldn't turn the 7" flywheel for my Stuart Beam Engine in the Myford Speed 10 I had at the time, Reeves sold me the flywheel from a 'Lady Stephanie', which is about 5 1/2" diameter.

                          I added a thick brass rim to bring it up to 6", plus a broad and heavy brass pulley wheel on the far end of the shaft.

                          This runs a bit faster than I'd like, but works quite well.

                          #338356
                          duncan webster 1
                          Participant
                            @duncanwebster1
                            Posted by Howard Lewis on 26/01/2018 10:35:55:

                            From a theoretical point of view, doubling the dimensions of the parts of an engine should quadruple the weight, so it would seem appropriate for the Flywheel to have a Moment of Inertia four times greater than the original.

                            This should provide the same cyclic irregularity as the original, assuming that the materials used for every part are the same.

                            Howard

                            doubling the dimensions increases the masses by factor 8 (2 cubed) and the moment of inertia by 32 (mass * radius of gyration squared). I'd stick with the scaled up flywheel, the engine will run more smoothly. It doesn't actually take significant power to drive a flywheel, just wind resistance and bearing friction, both pretty small

                            #338358
                            Martin Kyte
                            Participant
                              @martinkyte99762

                              Thinking in the opposite direction (as usual) if the proportions of the model were taken from a typical full size original (not an unreasonable assumption) and both the big one and the little one worked then any scale in between should work too. In practice ,in my limited expirience, rim thicknesses tend to be proportionately thinner on full size engines (particularly noticeable on traction engines). I suspect actually they have been thickened up on models to achive smother running. So proportionate flywheel and thin the rim a little so it it looks right if you really want too.

                              regards Martin

                              #338363
                              Ian S C
                              Participant
                                @iansc

                                The bits needed to make a fly wheel for one of my hot air engines, it started out as three discs of 10 mm hot rolled plate(cut outs from another job), the centre on drilled out for spokes, and a hub brazed in, the other two made into rings to form the rim, the three bits bolted together with 10-32 UNF bolts, the outside skimmed in the lathe.

                                Ian S Cdsc01091 (800x600).jpg

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