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What is the blade tip speed, of a push mower.

Discussion in 'Lawn Mowing' started by instyle, Jan 26, 2006.

  1. instyle

    instyle LawnSite Senior Member
    from Canada
    Posts: 380

    Just for comparison to a riding mower. Just looking for a rough idea.....I know they will all be differant.
  2. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    Let's see...

    21" blade times 3.14 equals 65.94". Multiply that by 3600 RPM and you get 237,384" per minute. Let's divide that by 12 to get the feet per minute and make the numbers shorter. So we come up with 19782 FPM multiplied by 60 minutes equals 1,186,920 feet per hour. Divide that by 5280 and we get 224.8 MPH.

    Now I guess we know why push mower engines are always set below 3600 RPM.
  3. chimmygew

    chimmygew LawnSite Senior Member
    Posts: 576

    All I have to say is WOW!!!! That is pretty impressive Mr. Martin.
  4. mcwlandscaping

    mcwlandscaping LawnSite Gold Member
    Posts: 3,164

    The speed may be there, there sure are times where i wish there was more torque!! Impressive math mr martin!
  5. instyle

    instyle LawnSite Senior Member
    from Canada
    Posts: 380

    So, when a 7 iron deck is spinning 18500 feet per minute this is in fact slower than the push mowers.
  6. Jason Rose

    Jason Rose LawnSite Fanatic
    Posts: 5,858

    No... Like pointed out, 21" mowers are set up to turn, usually around 3400 rpm, that puts the BTS at the osh approved speed of 18,683. I say "around" I'm sure it's not an exact thing but + or - a hundred or so. That's close enough to 18,500
  7. mulcahy mowing

    mulcahy mowing LawnSite Senior Member
    from ma
    Posts: 721

    With that math problem forget my "us landscapers are not so smart" comment
  8. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    This is easy stuff. Here's one I did last week when someone asked how fast air moves through a Mustang 5.0 intake manifold. It's not a perfect answer but it gave the person who asked a pretty good idea of how fast the air is moving.

    A 302 uses 446 CFM of air at 6,000 RPM (302 X 6000 X 3.456 X .85 VE)
    The opening between the upper and lower is about 1.25" by 1.5" X 8 for .105 SQ FT
    446/.105=4247 feet per minute of airflow X 60=254847 feet per hour/5280 (feet in a mile)=48.29 MPH or 8 MPH for every 1,000 RPM.

    Of course VE is variable from engine to engine and it even changes in a particular engine as the RPM changes but .85 is a good average for a street engine
  9. steve45

    steve45 LawnSite Bronze Member
    Posts: 1,325

    Quick! How many revolutions does a dragster engine make during it's quarter mile run??? (approximately)
  10. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    Depends on the tune like final drive ratio, tire diameter, clutch setup etc. 550 to 575 is close enough for this discussion.

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