Imagine yourself sitting in a European airport, waiting for departure, when suddenly a neon yellow, beacon-encrusted Saab goes howling down the middle of the main runway at ludicrous speed. Too much Akvavit? Nope, just a Saab Friction Tester.
Long, glass-smooth runways can act as unintentional skid pads in the wet - something not quite desirable in a multimillion dollar airliner full of commuter sheep. In the interest of safety, an airport likes to know just how slippery things are out in the field, so that Boeings can adjust their braking distances and don't go skidding off the ends of runways at the first sign of a flurry
In olden days, this task was relegated to a skiddometer (yes, really) — a heavy trailer pulled behind a truck or some other airport vehicle. The shortcomings of this setup were made clear early on, however, so airports began looking around for a more reliable platform from which to test.
Enter Trollhattan. Saab began producing cars specifically with this task in mind in the early 1970's, in conjunction with SARSYS (Scandinavian Airport and Road Systems AB). All models since have been outfitted as friction testers, except the loathsome 9-7X and the too-light 9-2X.
Here's how it works: a fifth wheel is mounted in the trunk, connected to the rear wheels via a chain-drive. This wheel is deployed with about 300lb of downward force once the car is at speed; a built-in 10 to 15% slip of the fifth wheel allows for constantly varying calculations of surface friction. Sensors in the car transmit readings to the towers in almost real-time, allowing for very accurate changes to aircraft braking requirements on demand.
Airports around the world have used Saab friction testers through the years, and continue to do so by the hundreds. Some of the airports that use Saab friction testers include Fargo, Munich, Albany, Oslo, Washington D.C., Chicago, Buffalo – even the FAA owns one for their own tests. The next time you're waiting out the rain in a sky lounge, keep your eyes peeled for a bright yellow Swede tearing down the runway at full tilt boogie.
Photo Credit: Tradewind Scientific
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