Air Surface Friction Tester

Air Surface Friction Tester

The VW Sharan Multipurpose Continuous Friction Measuring Equipment (CFME)

1. The computer system
The ASFT computer system includes measurement computer, main computer with printer and an operator's panel with only six keys to simplify the handling of the system.

The computer is pre-programmed for measurement and presentation in accordance with ICAO, FAA, and CAP 683. The computer system controls the measuring procedure and presents the results on the computer display and/or on paper printout.

2. The self-watering system
The ICAO and FAA clearly state that a CFME must have a self-watering system. The ASFT self-watering system sprays a water layer on the runway surface in front of the measuring wheel. The tank volume is sufficient for measuring more then 10,000 meters runway with a water layer depth of 1 mm (0,04").

3. The measurement computer
This reads signals from the vertical and torque transducers (sensors) which are then converted into digital form and sent to the main computer together with the pulses from the pulse transmitter. The measurement computer also performs automatic tests on the system, which makes any tedious adjustments unnecessary.

4.The relay box
Relays and fuses for the measurement system are centralised to a service box which is very easy to reach. Here you also have the new system usage counter.

5. The torque sensor
When the measuring wheel slips on the runway surface, the friction creates a torque which is transferred to the chain system and measured by a load sensor.

6. The vertical load sensor
This monitors the vertical down pressure created by the hydraulic system, and makes any necessary adjustments to it. It ensures that an absolute constant ground contact pressure is kept.

7. The measuring wheel
A special high pressure tyre, the Friction Tester "Aero" tyre has been developed for operational measurement purposes. Measuring results with this tire have been shown to correlate well with aircraft braking characteristics. For calibration purposes a low pressure tyre can be used. 
The slip ratio of the measuring wheel is about 13%, the exact value depending on the wear of the measuring tire and the car tyres.

 

8. The hydraulic system
This system provides constant pressure for the wheel retraction mechanism and for the vertical load on the measuring wheel.