Friction testing in Sweden
30 November 2007 • Author(s): Fredrik Nilsson, Project Manager, Civil Engineering Department, Swedish CAA at Stockholm-Arlanda Airport and Pär Blom, Training officer, Field Department, Stockholm-Arlanda Airport
In the beginning of air traffic history only propeller aeroplanes were used. They had a landing speed of 60-100 km/h, compared to today’s jet aeroplanes which have a landing speed of 250-360 km/h. Therefore, in the past when friction did not seem as important, the airport personnel used their feet to feel if it was slippery or not. In the 1930’s the friction test began to be performed by a bicycle or a car. After the foot friction test, there came a measuring device called ‘tapleymeter’: a small measuring device located in a car. To get a friction value, the car accelerates to 30 km/h and then the driver hits the brakes. This equipment is still in use at smaller airports today.
When jet aeroplanes began to take over air traffic, the friction coefficient had to be more accurate. A project with the Swedish Civil Aviation Administration (SCAA) and the Swedish National Road and Transport Research Institute, started investigating a procedure for friction testing where the friction coefficient could be compared with a braking jet aeroplane. A trailer was built with a weight of 3300 kg and it was manually programmed and towed by a lorry. This was only in use for a short time because it was very difficult to handle.