When the Mowing Gets Rough

When it comes to cutting the tough jobs — those jobs with tall strands of thick grass, weeds and even small trees — the flail mower steps to the plate. Such heavy-duty cutting tasks would normally stall the most powerful deck mowers, so these jobs call for the token flail mower that can be found in most grounds managers' sheds.

By definition, a flail mower uses banks of flails (or “knives”) instead of blades. A flail is a short piece of metal that operates by beating the grass (flailing it) and breaking it off. At high speeds, the job is done quite efficiently.

“Just by their nature, flail mowers have a tendency to minimize the bunching and the lumping of cut material,” said Jerry Sechler, vice president of sales for Hector, Minn.-based Loftness US Attachments. “The rotor is spinning at a pretty good rpm.”

Standard Loftness models, which fit on skid steers and on rear-mounted, three-point-mount tractors, go through material up to 1 inch in diameter at a speed of 2,190 rpm. “That can be anything from grass to vines, sumac and cattails,” added Sechler.

Flail mowers are typically mounted on heavy tractors, stopping short of being able to cut anything woody larger than young saplings or small limbs. Some flail mower heads, such as Tiger Corporation's attachment for its Saber Tooth boom mower, can cut limbs and trees up to 4 inches in diameter. Cutting heads are the rotary or drum type, and may be mounted on an articulated arm or boom and placed at the front or back of the tractor or the side. Some cutting head attachments are available mounted on the arm of an excavator.

Boom attachments are available in various sizes to match a variety of jobs. Using a boom allows the operator to reach over culverts or other obstacles to mow steep hillsides or other overgrowth such as tree limbs or brush. Booms can be found to attach to the rear or side of the tractor.

As with other types of mowers, flail models are matched to the job usually based on size. With most other mowers, the size is measured in deck width; for flail mowers, the size is measured by the width of the rotor (or drum). Drum widths generally range from 48 to 102 inches. Depending on the manufacturer, sets of knives vary per foot of drum length. Triple-gang flail mowers, with two side attachments and one rear attachment, offer the widest swath for the largest jobs, from more than 200-inch widths to just under 300 inches.

The power requirement for flail models is another factor. According to a 2004 university extension report written by Graeme R. Quick, former adjunct professor of Agriculture and Biosystems Engineering at Iowa State University, flail mowers require the most power when compared with other mower types. This, in turn, will determine the size of tractor needed.

Tractors can be either the rubber-tired or track variety. The recent proliferation of rubber-tracked machinery has been favorable for flail usage.

“Flail cutters have been around for a long time,” said Sechler. “But with the advent of skid steers having rubber tracks, you now find more interest in these attachments. What rubber tracks give you is more versatility on golf courses and other places where you don't want to disturb the ground as much as you'd do with wheels or a steel track. That lends itself to using flail mowers even more so.”

The cut from a flail mower is very distinctive and different from that of a rotary mower. The flails are often Y-shaped, or sometimes a half-Y, giving the mowed grass a combed or ridged appearance. Flail heads are available as rough, fine and smooth cuts. This too depends on the end usage — the fine or smooth knives are ideal for large-scale cutting for jobs such as golf course rough or large, upscale lawns or even soccer fields. Control of cutting height may depend on the tractor's three-point hitch, although some models have an adjustable rear roller to control height, which normally ranges from 0 to 6 inches.


There's more to using flail mowers than just tackling young jungles.

Highway mowing and park maintenance crews often use flail mowers because they are less likely to throw objects during cutting.

“Using a flail mower minimizes any bunching and doesn't throw anything to the left or to the right,” said Sechler. “So, if you're cutting in an area where you don't dare throw things out into the street or highway, or out into the fairway or up against a building, then you would use a flail.”

On a flail mower, the knives are free-swinging as they rotate around the horizontal axis, catching the cut material in a cylindrical hood, though the basin can also be angular. Some hoods are curved and claim to have better suction, thereby discarding trimmings virtually where they were cut, just behind the forward-moving machine. Loftness models feature rotors with reverse rotation, which picks material up and off the ground as the skid steer travels forward, cutting as it goes.

The lowered likelihood for thrown objects because of a contained and limited trajectory allows operators to mow in areas with heavy trash and where there might be large numbers of bystanders.

Flail mowers can also handle wet grass better than most rotary mowers because the discharge area runs the full width of the machine. Operators have also used some flail mowers for closer cutting of fine lawns by reversing the drums, positioning blades to swing forward at the bottom and up in the front, though this is not possible or recommended for all models.

Other uses for flail mowers include removing thatch and jobs involving turf renovation. Joe Marsh, past president of Environmental Care, Inc. noted on www.progardenbiz.com, “If you must renovate a large turf area occasionally, use efficient equipment to do the work. An excellent technique is to use 40-hp tractors with turf tires pulling 6-foot flail mowers equipped with slicing knives. This unit will do the verticutting while 6-foot aerifiers pull the 6-inch-long plugs.”


In May 1999, a field mechanic working at a vineyard near Napa, Calif., was crushed by the rear wheel of a farm tractor as he repaired a three-point, hitch-mounted back flail mower. The employee died. Almost exactly a year later, at the same location, a tractor operator's coattail was caught in the spinning driveshaft that drove a PTO-driven three-point mounted flail mower. He was more fortunate than the previous accident victim, living but suffering fractures to the arm that was pulled in, as well as a dislocated elbow.

Such incidents involving flail mowers are easily preventable when specific measures are followed. Consider the following tips from the University of California's Research and Extension Centers when using flail mowers:

  • Before using the equipment, inspect the flail mower for damage or disrepair and make sure all shields and guards are securely in place, including the power take-off shaft guard.

  • Make a visual inspection of the area before starting. Note uneven surfaces, or large ground depressions that may be sinkholes or contain large rocks.

  • Allow no one on the machine other than the operator when the machine is in motion.

  • When operating the machine on a hillside, allow no one to remain down slope while the flail mower and/or tractor is in motion.

  • Never allow the machine to coast downhill with the transmission in neutral.

  • When working with the machine in unfamiliar territory, heavy brush and trees, or areas of poor visibility, the operator should enlist the assistance of an observer on the ground. The observer should be especially careful to stay clear of the machine and any falling trees or limbs.

  • Never back up without looking to the rear first.

  • When parking, set parking brakes, lock transmission, let blade down, leave in full float position, turn off switch and remove key.

Long-arm flail attachments present another potential safety issue — proper balance. In England and Ireland, concerns about the stability of tractors powering large side-arm flail cutters have prompted manufacturers to help operators stay safe and keep within the law. Manufacturers such as Spearhead Machinery, Bomford Turner, Renault Agriculture and Michelin have devised equipment and formulas, such as support wheel systems and proper weight distribution figures, to overcome ballast problems.

Solutions have come in the form of ballast-correcting combinations of tractor weight and tire size and type. When operating side-arm attachments, always check with the manufacturer to ensure the driving tractor is adequate for proper ballast, and that the tires are capable of the specified load.

Tracy Powell is a freelance writer who resides in Jeffersonville. Ind.

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