Flail Mower Let's talk flail mowers

[leonz]

AH, it is so nice to have my findings proved once more. Thank you Island Tractor.

My Mathews lawn genie has 2 air paddles attached to the flail mower rotor which is almost
six inches in diameter which aid in lifting the clippings up an over the flail mower rotor and
also aid in lifting the clippings into the collection basket while mowing or picking up clippings
that are longer in length due to rain preventing ones mowing as desired.

After I obtain my Dwyer vacuum gauge and tachometer I will take a reading to see how much
of a pressure gradient is generated at full throttle and with the rotor speed of 2,200-2300 RPM.

 

[GManBart]

Nice video. Not so sure about attributing the difference in cut just to "mechanical effect" though. FYI, I just googled flail mower and vacuum and found that several major manufacturers mention the "vacuum effect" in their sales literature. Vrisimo - Super Series Flail Mower Heavy Duty Brush Cutting Tractor Mounted /Tow Behind Flail Mowers 403 Forbidden John Deere materials also mention "vacuum" with their flail mowers/shredders.

Not exactly experimental data but these promotional materials do fit with the notion that flails cut better when riding on their roller in close proximity to the ground due at least partly to a vacuum effect.

The only mention I saw of suction was when they were talking about flails with scoop knives, but I didn't try to go over every line. Then again, we know that promotional materials are always based upon scientific data right? :laughing:

Well, just don't tell them that LouieJunior can't move feathers with his flail...

 

[GManBart]

AH, it is so nice to have my findings proved once more. Thank you Island Tractor.

My Mathews lawn genie has 2 air paddles attached to the flail mower rotor which is almost
six inches in diameter which aid in lifting the clippings up an over the flail mower rotor and
also aid in lifting the clippings into the collection basket while mowing or picking up clippings
that are longer in length due to rain preventing ones mowing as desired.

After I obtain my Dwyer vacuum gauge and tachometer I will take a reading to see how much
of a pressure gradient is generated at full throttle and with the rotor speed of 2,200-2300 RPM.

Findings are what you get after testing.....sounds like you're still at the theory stage. As LouieJunior noted, his flail couldn't pick up and mulch a feather. If a flail can't pick up a feather, there can't be enough pressure gradient or suction to make much difference.

If a standard flail could generate enough pressure/suction, your Mathews wouldn't need those air paddles.

The only readings that would be of any significance are with the PTO running at 540rpm and with the flail stopped. Also, you'd have to take readings in at least four different places for it to mean anything....in front of the rotor, behind the rotor, top and bottom.

 

[leonz]

Using a Dwyer vacuum gauge in a flue connection or a duct which essentially
is what the flail mower shroud is. It is not difficult as all that is needed is a small
drilled hole in the flue is where the readings are taken.

The metal tube which is connected to the rubber hose is inserted in the flue or duct
and the measurement taken for the pressure gradient created "at work with the furnace or
boilers forced draft fan which forces air into and over the burner or through the coal stokers flat grate where the combustion air exits through the holes drilled through the grates and then in to the combustion chamber and then out of the flue into the chimney.

There is actually one place where the readings would be relevant with
regard to the pressure gradient which is the air duct exiting the flail mower rotor where
the air flow travels into the collection hopper.




A couple for things to keep in mind are:

The flail mowers rotor depends on ground effect to a certain extent(which is death for helicopters because they cannot maintain or obtain massive amounts of lift near the ground surface)

The front of the flail mower rotor and the back of the flail mower rotor are the entry and exit points for
the air flow(with the diverter door shut).

The mowers height which is regulated by the rear roller in some flail mowers and the wheel set on my lawn genie are what creates the amount of opening that exists in front of the flail mower rotor.

The height of the mower shroud including the rubber skirt in front of the mower(in my case) or in the case of the debris guard in the case of the Sicma flail mower brand and others is which is going to affect the surrounding airs ability to enter the flail mower shroud.

In the case of the lawn genie the twin air paddles are what aid the flail mower to carry the clippings up the sheet metal duct and into the collection basket and aid in carrying heavy amounts of clippings over the flail mower rotor and into the collection basket.

(the same could be said for the forged scoop knives and the trash door on the Land Pride/Maschio flail mower where the open trash door aids in discharging the clippings quickly in heavy brush mowing conditions)


The Lawn Genie collection basket also has a full width screened vent that is a foot long and four feet wide that releases the pressure gradient/air flow created by the flail mowers side slicer knives and the air paddles and the air disturbance created by the clippings entering the collection basket at the same time.

The only real relevant location for a vacuum gauge reading is in the location above the diverter door
above the flail mower rotor as the sheet metal duct is which directs the clippings into the collection hopper is the furnace flue essentially in the example.

Saying that: feeling and seeing the amount of air and mower chaff/dust moved by the twin air paddles and aerodynamic lift created by the tapered side slicer knives which are also lifting the air into the shroud and into the duct above the diverter door is huge.

The collection basket does not interfere with the clippings like a vacuum bag as the air flow exits directly up and out of the collection basket through the screened opening in the roof of the collection basket.


I will get the ambition to use a smoke generator stick later in the summer to aid in explaining this physics problem (I hope).

Its time for my Perry Mason episode hour and to quote former United States Army General Douglas Macarthur "I will return".


It is always fun to talk about anyway.

 

[IslandTractor]

The only mention I saw of suction was when they were talking about flails with scoop knives, but I didn't try to go over every line. Then again, we know that promotional materials are always based upon scientific data right? :laughing: Well, just don't tell them that LouieJunior can't move feathers with his flail...

Promotional materials certainly are not scientific data as I acknowledged earlier. On the other hand, when JD and Vrismo, both major and competing flail manufacturers, describe vacuum as a significant element in improved cut quality (not only with scoop knives though perhaps more with scoops), I would at least say that the burden of proof shifts towards the naysayers. Perhaps it is simply a flail industry fiction but vacuum or pressure gradient seems to be discussed as important in a number of other types of rotary mowers too so the idea it is important for flails is not exactly without precedent.

 

[GManBart]

Promotional materials certainly are not scientific data as I acknowledged earlier. On the other hand, when JD and Vrismo, both major and competing flail manufacturers, describe vacuum as a significant element in improved cut quality (not only with scoop knives though perhaps more with scoops), I would at least say that the burden of proof shifts towards the naysayers. Perhaps it is simply a flail industry fiction but vacuum or pressure gradient seems to be discussed as important in a number of other types of rotary mowers too so the idea it is important for flails is not exactly without precedent.

I went through all those links more carefully, and the only mention of suction/vacuum is when they talk about scoop or cup shaped knives. A knife shaped that way will definitely move air as it has a large cross-section...they are reasonable fan blades at that point.

"All Super Series Flail Mowers come standard with fine cut scoop knives that create a vacuum effect, lifting debris and vegetation into the unit for improved mulching."

"High-vacuum cupped knives create plenty of suction to draw material up off the ground, assuring neat and thorough mowing and shredding."

I have yet to see a reference to the same thing with side slicer knives....almost certainly because they're thin, sharp, and aren't capable of moving much air at all.

Theory is interesting, but when somebody puts their flail over the top of a feather, and it can't lift it, the theory doesn't matter much.

 

[hunt4570]

 

[leonz]

As i have mentioned previously;

the knife hangers for the matthews lawn genie permit the slotted
mounting hole side slicer knife to become an aerfoil when the speed
of rotation is fast enough to allow the tapered leading edge of this specific
side slicer knife to become an airfoil and travel horizonatally in flight even
though it is traveling in a circle.

These side slicer knife pairs make tremendous racket when the flail mower rotor slows
permitting them to fall ue to the effects of gravity.

currently available knife mounting systems do not do this as the knife pairs are restrained by the
mounting bolts and the narrowed distance between the mounting station weldments.

 

[GManBart]

As i have mentioned previously;

the knife hangers for the matthews lawn genie permit the slotted
mounting hole side slicer knife to become an aerfoil when the speed
of rotation is fast enough to allow the tapered leading edge of this specific
side slicer knife to become an airfoil and travel horizonatally in flight even
though it is traveling in a circle.

These side slicer knife pairs make tremendous racket when the flail mower rotor slows
permitting them to fall ue to the effects of gravity.

currently available knife mounting systems do not do this as the knife pairs are restrained by the
mounting bolts and the narrowed distance between the mounting station weldments.

Even if that's true, I don't think most folks have a Mathews Lawn Genie...haven't really seen any mention of them other than your references.

 

[leonz]

Even if that's true, I don't think most folks have
a Mathews Lawn Genie...haven't really seen any
mention of them other than your references.

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Hello GmanBart,

I have but cannot upload the manual for the
36-48-60 inch lawn genies but I can send it to anyone
who would like one.

I will try and copy and upload a few of the relevant pages for all of you.