How much power is needed for a Baker Fan?

Discussion in 'Prony Brake' started by Jerry Christiansen, Jul 11, 2007.

  1. Jerry Christiansen

    Jerry Christiansen Mega Poster WMSTR Lifetime Member

    The question, “How much power is needed to spin a Baker Fan?” has been asked many times. I have also heard people say that they will not belt their engine to a Prony Brake because the Brake is too hard on the engine. Then later I have seen the same engine slaving away, spinning a Baker Fan sounding like it is pulling for all it is worth.

    Last winter I approached Gerry Parker about doing an experiment with his steam engine, a Baker Fan and a Prony Brake to determine how much power is needed to spin a Baker Fan. My hypothesis was: A Baker Fan is a very large load that will hold the engine’s speed down far below the maximum horsepower value and will work the engine VERY hard.

    The amount of power needed to spin a Baker Fan depends on the size and number of the blades, and how fast the fan spins. Because of these factors, the results of this test are true for the Baker Fan at Rollag which has four 24 inch X 24 inch blades. It has two pulleys, one has a 24 inch diameter, the other has a 16 inch diameter.

    On 15 June 2007 Gerry Parker, Jeff Edin and Colt Edin belted Parker’s 28Hp Minneapolis Steam tractor to the Baker fan at Rollag, MN. When belted to the larger pulley, the Minneapolis went right up to the governed speed when throttle was opened. Then they belted to the smaller pulley and opened the throttle again. This time the engine was held to 240rpm. Using the diameters of the pulleys, we can calculate that the Fan was spinning at 630rpm.

    The same crew brought the engine to the Red Brake at Rollag and we did a “horsepower run” for the engine. We took 28 readings of Force and RPM that allowed us to calculate 28 horsepower values for the engine. We started at 230lbs and 249 rpm, which calculates to 57.3Hp. From there we took a series of measurements that went up to a maximum of 108Hp at 470lbs and 230rpm. We continued to tighten the Brake until the scale read 510lbs at 205rpm, which calculated to 104.6Hp. The complete list of values for the run are in the table below.

    When belted to the smaller pulley of the Baker Fan, the Minneapolis was held to 240rpm. If we assume a 1% error (assuming 1% error is assuming that our measurements are VERY good!) in the readings, the engine was running between 238rpm and 242rpm. If no error is assumed on the Prony Brake the Minneapolis produced 70.2Hp to 100.0Hp in that rpm range. If we also assume a 1% error in the Horsepower calculations, the range extends from 69.5Hp to 101Hp.

    From this experiment we can conclude that the Baker Fan requires somewhere between 70Hp and 100Hp when the Fan is spinning at 630rpm. This implies that engines that produce less that 70Hp (and possibly as large as 100Hp) will be held below their maximum power and the smaller the engine, the farther below the maximum it will be held.

    The next step to determine the minumum power needed to run a Baker Fan is repeat this process with different sizes of engines that are smaller than the 28Hp Minneapolis.



    The table is difficult to read. If someone knows how to put spaces in, please let me know. Tabbing doesn't work and if I put extra spaces in with the spacebar, they disappear when I submit the post. The first three digits are the pounds of force, the next three are the rpm and the last number with the decimal point is the horsepower.

    Force(lbs) rpm Hp
    230 249 57.3
    240 246 59.0
    250 245 61.3
    260 239 62.1
    270 240 64.8
    280 241 67.5
    290 242 70.2
    300 242 72.6
    310 240 74.4
    320 238 76.2
    330 237 78.2
    340 235 79.9
    350 235 82.3
    360 236 85.0
    370 238 88.1
    380 233 88.5
    390 236 92.0
    400 240 96.0
    410 238 97.6
    420 238 100.0
    430 235 101.1
    440 234 103.0
    450 235 105.8
    460 233 107.2
    470 230 108.1
    480 224 107.5
    490 216 105.8
    500 210 105.0
    510 205 104.6

    Thanks for your patience in reading this.

    Jerry Christiansen
     
  2. DMahalko

    DMahalko Intermediate Poster

    Just a comment on your table creation problems.

    To retain your table spacing, enclose the text block with the [noparse]
    Code:
    ...
    [/noparse] tags. The font style needs to be changed to a monospace font like Courier New or Lucida Console, or the spacing is going to come out totally wrong in the text editor.

    Code:
    [FONT=Courier New][B]Force(lbs)  rpm  Horsepower[/B]
      230       249    57.3
      240       246    59.0
      250       245    61.3
      260       239    62.1
      270       240    64.8
      280       241    67.5
      290       242    70.2
      300       242    72.6
      310       240    74.4
      320       238    76.2
      330       237    78.2
      340       235    79.9
      350       235    82.3
      360       236    85.0
      370       238    88.1
      380       233    88.5
      390       236    92.0
      400       240    96.0
      410       238    97.6
      420       238   100.0
      430       235   101.1
      440       234   103.0
      450       235   105.8
      460       233   107.2
      470       230   108.1
      480       224   107.5
      490       216   105.8
      500       210   105.0
      510       205   104.6[/FONT]
    
     

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