According to Sweet, the sensor consists of conductive strips built into the surface ply of the boot. "They're actually strands of graphite, embedded into conductive rubber. What happens is when ice forms on the surface, one of the electrodes (called the driver or positive electrode) sends a signal to the receiving electrode, and through this, we can measure the impedance, which gives us the thickness of the ice. Polyurethane has very good erosion resistance. We are finding, through testing, that the boots are equivalent in erosion resistance to our standard boots. However, the boots are activated less because you only turn it on when you have an indication, so life expectancy is expected to increase. One of the things we're looking at in the future is installing a closed loop system (automatic activation). But for now, the de-ice has to be activated manually."
Maintenance of the SMARTboot
Sweet says that SMARTboots are maintained as other esthane/urethane boots are.
"In terms of maintenance, the SMARTboot is an esthane/urethane surface material, so you don't use the AgeMaster™ product, but you can use the Icex™ and the ShineMaster™ with it," he says.
The electrical sensing system does require testing periodically by checking the continuity of the Ice Thickness Sensors, to confirm there are no intermittent shorts within the air connection and manifold area. To check continuity of the SMARTboot de-icers, BFGoodrich provides a procedure requiring the use of a digital ohmmeter and an air pressure source capable of 6 psi.
Pneumatic Impulse Ice Protection
Young says a product which BFGoodrich has in development is called Pneumatic Impulse Ice Protection (PIIP). The key improvements in this system over the standard pneumatic systems is that it could remove smaller accretions of ice, called "rime ice." With standard pneumatic systems, you need to let the ice build to .040 inches before activating the system. PIIP is able to break ice off at .025 inches. The other advantage is that the leading edge is made of Titanium, which could conceivably last forever.
Sweet says BFGoodrich began development of the product in the early 80's. "It is considered to be the next generation system designed to upgrade the Pneumatic de-icers. Installation of the system basically involves removing the aluminum leading edge strip on the aircraft and installing the new PIIP leading edge in its place. This new leading edge has the ice protection system built right into it.
"The PIIP edge is basically a composite panel with a titanium surface. It contains a tube or tubes which are opened to the atmosphere at the end," he says. The way it works is we build a high pressure charge (600 psi) with a valve. This charge is released and creates a shock wave in the tube. As that shock wave travels down the length of the tube, high surface acceleration is generated on the titanium and this expels the ice from the surface. The acceleration is actually quite dramatic. In fact, if you would place your hand on the surface when the air is expelled, it feels like when you fall down and slap your hands on the concrete. In wind tunnel tests, with a high speed camera, you can actually see the ice come off and go forward in the airstream, before it's carried away. So, it's launched with quite a bit of acceleration," he explains.
Sweet says PIIP is activated upon detection or when icing is suspected. "The number of cycles you can get out of the system is about four times what you would get out of a pneumatic de-icer, then the tubes have to be replaced," he says.
"We are currently working with a business jet manufacturer who is testing it onboard an aircraft, but I can't give you a date when it will be certified. It will originally be targeted for business aircraft. We feel it will offer quite a few advantages over the conventional systems that are out there," says Sweet.
Two other systems in development at BFGoodrich are Electro-Impulse De-icing system (EIDI), and Eddy Current De-Icing Systems (ECDS).
EIDI uses a spiral wound coil placed in proximity to the inner surface of the protected airfoil. When electrical current is discharged into the coil, opposing magnetic fields are generated between the coil and skin. The result is a rapid outward motion of the airfoil surface, and shedding of accreted ice.
ECDS systems contain a flat ribbon coil distributed over the airfoil surface. An electrical discharge into the coil produces eddy currents, causing the surface of the de-icer to move rapidly away from the airfoil. This method is better suited for stiff, complex shapes that may not "flex" as easily as two-dimensional airfoils.
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