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Old 12-17-2013, 04:45 PM
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Can Someone Calculate My Tip Speed?

I used a laser tachometer to find my blades tips are 4445 RPM. My blades are 15.50" long.

I used a DT-2234C+ to find the RPM's. I compared it to a stroboscope we use at work and its very accurate. I painted the tips matte black and placed the reflective tape on one of the tips.

The 23 HP Briggs V-Twin spins @ a 3600 RPM no-load speed.

What does it calculate to?

Thanks.
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Old 12-17-2013, 06:01 PM
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Where's your math skills?

The simple method to find blade tip speed:

Blade tip speed(in Feet per minute) = RPM X blade length(in inches) X .262

Unless you're mathematically inclined, you may not know, or even want to know, why or how the number .262 magically appeared in the formula. If you desire a complete mathematical explanation, PM me.

So in your case, BTS= 4445 X 15.5 X .262 or 18,051 Feet/minute

As I recall the Comsumer Protection laws have the maximum set at 19,000FPM so you're under the wire.

Since you know your blade RPM, engine speed has nothing to add to the calculation.

Last edited by dutch1; 12-17-2013 at 06:03 PM. Reason: Add
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Old 12-17-2013, 06:20 PM
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Dutch...... Didn't know you could type French !
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Old 12-17-2013, 06:28 PM
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Thanks for solving that for me.

As for "Where is my math skills?" Heh! I admit to being seriously mathematically challenged when it comes to anything more advanced than basic.

Thanks Again
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Old 12-17-2013, 06:31 PM
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Quote:
Originally Posted by dutch1 View Post
Where's your math skills?

The simple method to find blade tip speed:

Blade tip speed(in Feet per minute) = RPM X blade length(in inches) X .262

Unless you're mathematically inclined, you may not know, or even want to know, why or how the number .262 magically appeared in the formula. If you desire a complete mathematical explanation, PM me.

So in your case, BTS= 4445 X 15.5 X .262 or 18,051 Feet/minute

As I recall the Comsumer Protection laws have the maximum set at 19,000FPM so you're under the wire.

Since you know your blade RPM, engine speed has nothing to add to the calculation.
Bonus points for where CPS came up with that limit of 19k FPS?
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Old 12-17-2013, 07:05 PM
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Patriot, I heard the info at one time but my recollectin' ain't to good and I have a dang good excuse--the odometers rolled over too many times--refresh my memory and drop the extra credit.

Rob, it may have been French but better yet did you understand it? I think yer still feelin' yer oats after the week in the lawn chair, on supervisory duty!
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Old 12-17-2013, 07:18 PM
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ANSI testing found that the chances of the blade shattering upon impact are greatly reduced below this speed. Contrary to many home engineers, deck design and setup are the paths to a better cut.
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Old 12-17-2013, 07:41 PM
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That's likely what I'd guessed had I been forced to do so. I remember a span of years when there were several injuries related to blade breakage/shattering, probably leading to lawsuits, leading to testing and finally leading to the limit on BTS. Thanks, Patriot.
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Old 12-17-2013, 08:09 PM
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In reality, the max tip speed is not a law. It's a recommendation only. And it only covers consumer products, commercial decks over a certain size aren't covered.
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Old 12-17-2013, 08:50 PM
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Quote:
Originally Posted by Patriot Services View Post
Contrary to many home engineers, deck design and setup are the paths to a better cut.
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I agree on this. I don't know about how great my Cub Cadet 44" Z-Force deck is designed but until I really got into setting it up it didn't cut that great.

Once I took the time to get it level side to side with a 3/8" lower blade tip at the front the cut began to look like carpet and moving speed was no longer that critical. I finally figured out a 3/8" drop at the front is really more like 1/4" with my 225 lbs sitting on it.

The tip speed is more of a curiosity because I just went from a 3200 RPM 18 HP engine to a 3600 RPM 23 HP.

A U-Tube of the blade RPM data collection The beginning shows me looking at the history of the previous run. I also panned the Tiny Tach and my oil pressure gauge.
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