Mowing mowing wow that fast? finish, rotary and flail

rdam · Sep 4, 2003

Henro,

I understood you perfectly. I think a similar theory applies to helicopters (increased lift moving forward due to relative speed) and hurricanes (Counter clockwise rotation means the right side of the huuricane will have faster "relative" wind speed equal to the forward speed of the storm).

I disagree with your definition of "perfect". The wife is getting your seat time. /forums/images/graemlins/smirk.gif

Soundguy · Sep 4, 2003

As long as power isn't a restriction due to thick material being cut, and I can keep my RPMS at the pto mark on my tach, I usually mow in 3rd range 2nd gear on my NH 1920.. though I'm not sure what speed that is.. but I can tell you.. it is a good clip. Luckilly my acerage is flat with only a few large obstacles, and occasional bump/drop. That is about as fast as I can practically mown... And If I get into tight areas, it is 3,1 or even 2,3.. of which there is a huge differences in speed.. 2,3 is still slow.. whereas 3,1 moves along ok.

Soundguy

CTyler · Sep 4, 2003

( ...that perfect mowing should occur at zero speed. )

I'd opt for around 180mph with a stationary blade. To much wind at 200 /forums/images/graemlins/tongue.gif

Kelvin · Sep 4, 2003

( Is that blade working like a scissor? Isn't that blade following a rotational motion? If so, then how is it (blade tip speed) slowing on one side and increasing on the other side? Maybe, I didn't understand what you told here. By the way, the blade speed relative to the grass is the same as absolute blade speed as the speed of grass is zero. )

I think that I want to disagree with you, but can't as I'm not sure I fully understand what you're trying to say. Something tells me that I should stay out of this discussion, but I'll venture out and throw in my 2 cents worth:

If the tractor is moving linearly at 200 mph, and the mower blades are rotating such that the blade tip is 200 mph, then...

(1) the blade tip speed of the 1/2 of the blade moving in the same direction as the tractor would be 400 mph (200+200) relative to the ground, and
(2) the blade tip speed of the 1/2 of the blade moving in the opposite direction of the tractor would be 0 mph (200-200) relative to the ground.

Now for some potentially useful information: The high blade tip velocities are needed for the blades to aerodynamically create the proper "Lift" in order to uniformly cut grass. Push mower also have high blade tip velocities, but I don't think that they were designed to mow at high velocities across the ground.

Kelvin

chrisjbell · Sep 5, 2003

tractor is moving linearly at 200 mph 

I don't think that even Jesse on Monster Garage got his mowing Mustang to get to 200MPH! /forums/images/graemlins/grin.gif But I suppose that now we'll have to have mowing speed contests... /forums/images/graemlins/laugh.gif

nomad · Sep 5, 2003

Have fun. This is why we are here. I think we aren't talking same thing. Maybe, I made a mistake that I rarely do. Anyways, I drew a simple figure to understand each other. See image. Now, are you saying that tractor speed V0 (the question of this thread) isn't related at all to the blade tip speed V1=V2=V3=V4? I made a mistake at my first post by connecting tractor speed to V4. Actually, the blade is cutting the grass at the point 1, isn't it? So, V0 and V1 are related to each other or not? I mean if V1 is known (and known), then doesn't tractor speed V0 have anything to do with V1? - We know V0 which is approx. 5-10 mph is negligible comparing with V1 which is approx. 200 mph. But this is high speed motion in which even small quantities can cause some unwanted turbulence in the air around the blade. So, we can not neglect the relation between V0 and V1. So, if V1 is given (~200 mph), what is the value of V0 which is also question of this thread? Anyone here who would answer this?

Blade cuts the grass at point 1?

JerryG · Sep 5, 2003

When does this mower take off????? /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

Hambone · Sep 5, 2003

If you are driving down the road at 55 mph, and there is a fly in the back seat.
How fast does he have to fly to get to the front seat?

MossRoad · Sep 5, 2003

Actually, the blade is cutting the grass at the point 1, isn't it? 

The point that the grass is cut is the entire area between V4 and V2. It is an arc. If you move forward, the blade cuts an arc starting at V4, not V0. So I'm guessing the tip speed in relation to the grass will be V0+V4.

Henro · Sep 5, 2003

any comments? Ideas on mowing speeds with finishing,rotary or flail mowers? 

At first I thought this thread got hijacked...but then I looked back and see we are right on track! /forums/images/graemlins/grin.gif

When does this mower take off????? 

Has to be when you put the blades on upside down, and suction becomes lift... /forums/images/graemlins/smile.gif

Also take-off speed is somewhat dependent on deck airfoil shape relative to the forward travel travel [V0] direction...