Saturday, September 22, 2007

 

SCAT

Old Aeroduct SCAT tubingHere's a bucket of old SCAT. SCAT is a type of flexible ducting made from silicone impregnated fabric around a spiral wire core. It is used to conduct air from various intakes to sources such as cabin fresh air and heat and carburetor air and heat. It's lightweight and pretty durable, but it does tend to come apart after many years, particularly when exposed to things like engine oil. Most of Yellowbird's SCAT predates our relationship and is ripe for replacement. I can't fly her with no engine, so I guess it's time for another grounded airplane project.

Damaged Cessna 177B Cardinal carburator heat ductWhen SCAT goes bad. This is the carburetor heat duct. It runs from the carb heat shroud (the box at top center) to the carburetor air box (the aluminum thing lurking behind the exhaust pipe). This was an inflight failure back in June of 2004, brought about when I applied carb heat during cruise on a humid day. The fabric tube had come unbonded from the spiral wire core, and the sudden suction from the carburetor caused the duct to collapse. This shut down the engine pretty quickly, and fired up my adrenaline glands just as effectively. Shutting off the carburetor heat brought the engine back to life, but it was some time before my pulse was back to normal.

Damaged Cessna 177B Cardinal carburator heat ductAnother view, showing both ends. The duct was completely flattened for several inches. The wire core was squashed like a broken Slinky and the glass fiber cord wrapping the duct had also come loose at both ends, probably due to being soaked with oil from assorted leaks at the back of the engine. This is why you should keep your SCAT clean and have it inspected regularly by a qualified SCATologist.

New Aeroduct SCAT tubingFresh SCAT. Measure twice, cut once is the rule, followed by start over because you transposed the digits in the notebook after measuring. Fortunately, it's not that expensive, but I am stuck with a couple of too-short lengths of brand new SCAT. For a little extra security, I bonded spare SCAT fabric over each end with DC 736 high temperature RTV sealant to keep the ends from coming undone like the old carb heat duct. It's little touches like this that keep one occupied on lovely autumn days when everyone else is up flying.

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