Plane & Pilot
Tuesday, October 25, 2011

Angle Of The Wing


Angle-of-attack indicators, coming to a glass panel near you


I was introduced to an angle-of-attack indicator back in the early '80s. I was ferrying a V35B Bonanza from Atlanta, Ga., to Palo Alto, Calif., where it was to be fitted with one of Victor Aviation's balanced, blueprinted, Black Edition engines. When I climbed aboard at Charlie Brown Airport in Atlanta, that particular Bonanza was an impressive machine. It seemed to have every piece of avionics there was. It also had 2,050 hours since engine overhaul, 350 past TBO.

The AOA indicator (or in this case a Lift Reserve Indicator, same instrument, different name) was a tiny, two-inch gauge tucked away on the far-right panel—and it looked to be the oldest instrument in the airplane, a tired, circular gauge with an area marked in faded red, presumably meaning, "Danger, Will Robinson," a small, yellow/white region in the center and the main space marked in green.

To be honest, I wasn't impressed with AOA on my two-day trip across the country to California. I wasn't flying the V-tail anywhere near the bottom of the envelope, where an AOA does its best work. (A few years later, I was again faced with an AOA, this time on a new 36 Bonanza headed across the Atlantic and Mediterranean to Israel. I came to know it slightly better and gained a greater appreciation for its several talents.)

The state of the angle-of-attack art has come a long way since then. The instruments have improved dramatically, and AOA devices of all descriptions have become more and more common on the aftermarket.

Perhaps of greater significance, aircraft and avionics manufacturers have begun to realize that AOA indicators could help improve the safety record of new general aviation aircraft right out of the box. By definition, experimental aircraft are usually built on a budget, and that often excludes such semi-exotica as AOA instruments. Forgive the selective statistic, but some 45% of all experimental-aircraft accidents are the result of the dreaded stall/spin syndrome. The numbers aren't so bad for certified aircraft, partially a result of more docile airfoils, less enthusiastic stall response and more conservative pilots who probably don't fly so close to the edge.

Mark Korin of Alpha Systems (www.alphasystemsaoa.com) in Ramsey, Minn., has long been an evangelist for angle-of-attack indicators, not just because his company makes some of the best systems on the market, but because he's convinced the devices could help reduce the incidence of stall-spin accidents.

As Korin will be happy to explain to anyone willing to listen, tracking angle of attack is a far superior method of measuring proximity to a stall than is an airspeed indicator. We're all introduced to airspeed indicators as student pilots, but what we're sometimes not told is that, perhaps ironically, ASIs are least accurate in the range where they're needed most.



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