This example, purchased by a collector of SAAB 900s in 2009 through a Dulles surplus auction, was among the last examples built in-house at the Saab Car Division of Saab-Scania in Nyköping, before General Motors purchased a 50-percent interest in the company and closed the Friction Tester department.
The Saab Friction Tester, introduced in the 99 model in 1977 and continued in production through the 1979-'93 lifetime of the "classic" 900 hatchback
Under the back, the trunk floor contained a hatch panel that covered a chain-driven, friction-measuring wheel that could be hydraulically lowered and raised. This wheel, shod with a tube-equipped 4.00-8-inch tire sporting a rubber composition and tread akin to those on airplanes, was geared to rotate at a constant percentage of slip—usually 10 to 30 percent—relative to the car's steady speed. That speed typically ranged from 40 to 60 mph, although this assessment could be performed at up to 100 mph. A torque sensor read the resistance against the chain drive, and fed this information to an onboard computer that transmitted in real time to Air Traffic Control, which in turn relayed runway condition codes—0 to 6, with 6 being dry and good braking—to incoming and outgoing pilots.
Obviously relevant info for the pilots; once sat in a 747 landing in Oslo, Norway, on a snow packed runway. The pilot use reverse thrusters only to get the plane stopped.
ReplyDeleteYears ago I read in a technical journal that pneumatic rubber tires generate maximum traction at approximately a 10% rate of slip.
ReplyDeleteI would try to explain this to passengers but they had trouble hearing me over the tire noise.
Don in Oregon