The ultimate bush hog

[RobJ]

Theoretical question then...
Is there anything..can you go faster than the speed of light?
If you spin the hub at the speed of light, how fast are the blade tips going?

Well it depends on what size mower of course!!!

Geez...

 

[sandman2234]

Don't think it would matter, by the time the sonic boom hit it, from exceeding the speed of sound (which is considerably slower), you would have a mess anyway.
David from jax

 

[Highbeam]

Well if the speed of sound hits somewhere around 1000 fps and the 14000 fpm is really 233 fps then it would be no trouble for the tractor engine to spin things up to the sound barrier If you could get the gears. Cripes, I could grab the 1000 rpm PTO lever and get 500 fps right there. What would happen?

 

[TOMDUALLY]

I don't know but let me stand obout two counties away when you test it and I might be able to tell you which direction it went. LOL

 

[sandman2234]

Remember, the RPM of the pto is measured in minutes, while sound barrier is measured in fps. The diameter of the blade circle for larger single blade mowers has a faster blade tip speed for the same rpm.
I located my calculations for the long gone mower I built. It was designed to run off a gasoline engine, (3500rpm) and blade tip speed was a concern. As it turned out, I sold it without the motor, and adapted it to a 540 pto, so the blade tip speed really wasn't a factor.
I also used 750fps as the speed of sound. Not quite sure where I got that information, but maybe it was my built in safety margin.( or maybe just an error on my part)
David from jax

 

[Highbeam]

It doesn't matter if the pto rpm is measured in revs per year. If you double the pto speed you double it. If the blade tip speed is 14000 fpm at any pto speed and you double the pto input speed then you get 28000 fpm at the tips.

Good fun but the mower blades are plenty fast as they are.

 

[schmism]

I also used 750fps as the speed of sound.

unless your useing your brush hog at like 10K feet thats a bit low

Acoustics Chapter One: Speed of Sound

speed of sound at sea level @ 68deg F = 1128fps

 

[sandman2234]

The finish mower I built years ago was my first, and I was cautioned about blade tip speed, after I had most of it set up. Knowing the guy that gave me the "speed of sound" numbers, he probably allowed for some error on my part, and I probably allowed for some errors in his calculations, and the end result was something way below the speed of sound.
Then I changed from a gasoline engine, to a pto, using the same pulleys, so it was a mute point.
David from jax

 

[Turkeyman]

Brown makes the Utimate Cutter. Mine ( mid 1980's model) is terrible on grass but great on weeds and trees. I think is is rated at 14,000 FPS. The gear box is an old Borg Warner and is only rated for 90 hp. The stump jumper is square and 3/4 thick and weighs in the mid 300 lb range. The blades (4) look like axe heads and are 10" long and 1' thick. At 1600 lbs it is built like a tank.
The rear wheel has a tree deflector built in to push trees off to one side when you back into them.

I would suggest that you build a folding door on yours if you can. It would make it much safer to use.

 

[sandman2234]

Can you describe what a folding door is?
Would really like to see a pic of yours, especially the rear wheel deflector.


I was out tearing up my bush hog again today, and wondered if it is a good idea to consider offsetting the bush hog a foot or so to one side, to cut stuff that you really don't want to drive over? I could build a 7' one, and have it trac even with the wheel on one side, and overhang about a foot on the other side. Probably a little harder on u-joints, but I can stand that (I think).
Anyone ever seen a bush hog with an offset?
Next question... why not?
David from jax