DeFelsko Corporation produces a handheld non-destructive ultrasonic Thickness Gauge that is ideal for measuring aircraft window thickness during window restoration.
measurement challenge
When evaluating the effects of wear and corrosion on substrates, the main objective is to measure the remaining thickness non-destructively. Due to safety considerations associated with aircraft inspections, high speed sampling and data logging may be required.
Substrate Thickness Measurement Solutions
The ultrasonic positector UTG C is ideal for non-destructive testing of acrylic substrates with a thickness between 1 mm and 50 mm (0.04 and 2). Figure 1 is a photograph of a maintenance technician using the positector UTG C to measure the remaining thickness of a window in an aircraft being repaired. By measuring the surface across the window, it is possible to identify areas that have experienced significant in-flight erosion or wear from the window restoration process.
Figure 1 Aircraft window measurement
The positector UTG C has several pre-sonic common substrates. When measuring the thickness of an acrylic window, the user can select "Plexiglass" from the table menu, or Fine Precision makes a simple adjustment to a known sample thickness or sound velocity. The positector UTG C can be tuned to a wide range of sound velocities from 0.0492 to 0.393 ml/µS (1250 to 10000 m/s).
The positector UTG's preset Aluminum Sonic is ideal for measuring the thickness of aluminum alloy plates on aircraft wings.
When multiple measurements are required, the sweeping instrument mode function enables 20 readings per second to be taken when the coupled probe is dragged across the window. The result is a high-detail window thickness map. As shown in Figure 2, the scanned instrument mode shows the total number of readings as well as the highest and lowest readings. Not only does this provide the user with a thinnest and thickest reading attainable from the substrate sampled, but the readings can also be stored and downloaded to the instrument with optional posisoft computer software.
Figure 2 - Scan Mode:20 readings per second. Desirable rapid detection in large areas.
Background of the window restoration process in an airplane
What is it for?
During normal operation of an aircraft, microcracks form in the cabin windows due to common elements such as dust, sand, pollution, onboard volcanic acids and deicing compounds. Preventive maintenance programs, such as microcrack repairs before they become visible prevent high repair and replacement costs.
Global Aviation Services has patented a mechanical computer-driven system for window restoration called the Global CS1 Restoration Machine. CS1 height is directly on the outer surface of the aircraft with suction cups. The CS1's four polishing heads are impregnated with a special formula that is used by the robot's pickup and controls to polish and remove micro-cracks from windows. After about 15 minutes, CS1 was able to automatically complete the repair, restoring the clarity of the windows for passengers to see. When the CS1 starts to work on the next window, the operator only wipes the remaining window with a light clean soft cloth.
Why measure?
While the window restoration process can be repeated many times beyond the manufacturer's recommended tolerances, it is still necessary to monitor the window by measuring the remaining thickness after each restoration. Such safety checks are critical in aviation applications due to the potentially catastrophic events associated with failures.
Considering that passenger aircraft can have over 200 windows per aircraft, and that maintaining cabin windows is rated as the third highest maintenance cost in the industry, a quick and affordable method of measuring window thickness was needed. Unlike mechanical surveying, ultrasonic inspection can take place from the side of the window while it is in place, reducing maintenance costs and aircraft downtime.
Where is the market?
Global CS1 passes 321 series in Boeing 727, 737, 747, Airbus 757, 767, 777300; Fokker 100; MD80, MD90 series; and DC-8 and Dash-8. Due to its versatility, this positector UTG can be used to measure recovery window thickness on these or any such aircraft.
