Plane & Pilot
Tuesday, October 25, 2011

Angle Of The Wing

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

Mark Korin of Alpha Systems believes that his company's angle-of-attack indicators, seen here installed on a Cirrus SR22, can help to reduce the incidence of stall-spin accidents.
Most of the rest of us mere mortals need help in identifying minimum approach speed. Many general aviation pilots with a need to land short or on a precise point use a formula approach speed of 1.1-1.2 Vso. Through long hours of experience with a specific airplane, a pilot may know that his aircraft stalls at 50 knots IAS in full dirty configuration. This usually means an approach at 55-60 knots.

Trouble is, if conditions aren't exactly as planned at 1.1 and circumstances have raised the airplane's stall by only two knots, they may be flying as slow as 1.05 Vso without knowing it, operating with essentially no margin above stall. For that reason, some pilots mount an AOA indicator on the top left panel, so it's practically in their line of sight during the approach. No matter what the load, the temperature, the wind or the CG, pilots can monitor the AOA indication during approach and maintain a proper margin between approach speed and stall. They can adjust the needle or light position during the approach and move higher or lower on the scale depending upon conditions.

If angle-of-attack indicators are basically foolproof, they lack glamour. Prior to the advent of light displays, they were typically small, innocuous gauges with no or few numbers. AOAs suffered from not showing us what pilots live by, numbers. They lacked the excitement of airspeed indicators that informed us of the magical speed with which we were traversing the planet.

It has taken a while for Mark Korin's message to catch on, but the advent of the glass cockpit has made a color display of angle of attack the most logical of instruments. Prior to the advent of flat-panel displays, AOA indicators were separate gauges, often mounted in the panel itself or on top of it. That situation may be about to change big time.

At least three major aircraft manufacturers and the world's largest glass-panel company have contacted Korin regarding the possibility of incorporating an AOA readout as part of the airplane's PFD. These displays already include colorful representations of attitude, altitude, airspeed, groundspeed, vertical and horizontal position with reference to a GPS or VOR, the phase of the moon and Vegas odds on the World Series, so AOA could only improve positional awareness.

The plan would be to make the Alpha AOA system standard equipment, presenting visual warnings in the pilot's peripheral field of view, plus audio advisories, so pilots would have the benefit of angle of attack, regardless of their knowledge of its operating principles.

Korin's Alpha Systems presents AOA information in a variety of visual and audio formats, offering military chevron displays, horizontal or vertical light displays or a needle on a sliding scale. Perhaps best of all in this age of avionics that can easily cost $50,000 or more, Alpha's instruments are relatively inexpensive, typically costing under $1,500 plus installation. The system utilizes an independent, nonmovable probe that requires virtually no maintenance and should last as long as you do.

Glass panels such as the Garmin G1000 and Avidyne R9 have dramatically revised the way pilots fly both VFR and IFR. Scan problems have diminished exponentially, since so much information is now available on a single screen. In the near future, a pilot may be able to monitor his aircraft's precise margin of stall on the same instrument.


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