Maxaret

Dunlop's Maxaret was the first anti-lock braking system (ABS) to be widely used. Introduced in the early 1950s, Maxaret was rapidly taken up in the aviation world, after testing found a 30% reduction in stopping distances, and the elimination of tyre bursts or flat spots due to skids. Experimental fittings on cars and motorcycles demonstrated mixed performance, and ABS systems would not appear on mainstream, non sporting cars until the 1970s when electronic controls matured.

The Maxaret system had four main parts, all of which weighed only 4.7 pounds and fit within the small confines of a main landing gear wheel. The system was entirely mechanical, and worked by measuring the relative speed of two spinning disks. The first, the "drum", was surrounded by a rubber disk and arranged within the aircraft wheel's internal periphery, so that the rubber maintained strong mechanical contact with the wheel. The second, a flywheel, was attached to the drum with a one-way clutch. Normally, with the wheel turning, the wheel would spin the drum, which would spin the flywheel, so that all of the moving parts were spinning at the same speed.

When a skid developed, the wheel would stop, stopping the drum along with it. The flywheel, driven by the one-way clutch, continued to spin. If the relative angle between the drum and flywheel reached 60 degrees, the drum would be driven forward to press on a valve. This released brake fluid into a reservoir, lowering hydraulic pressure, and releasing the brakes. As soon as the drum started spinning again and reached the (slowing) speed of the flywheel, the valve was released and the brakes re-applied. The system could cycle about ten times a second, and could hold the brakes off for up to four seconds in total before the reservoir filled.

Aircraft have a much lower ratio of tyre contact patch to vehicle weight, and operate at much higher speeds. For these reasons, it is much easier to enter a skid in an aircraft through the over-application of brakes, and threshold braking is essentially impossible as the skid develops so rapidly. This makes landings in marginal conditions very difficult, and leads to many common weather conditions precluding flying. Slippery conditions from heavy rain, or even light snow or ice, will close a field.

In early testing on the Avro Canada CF-100, the Maxaret allowed landings to be safely made on runways covered in ice. Since the operational requirements of most aircraft are defined by the best take-off or landing distances under all weather conditions, Maxaret allowed aircraft to operate at 15% higher all-up weights.

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Wikipedia