At the dawn of the last century, it didnt take the Wright brothers long to figure out that wings stall at a measurable angle of attack. Student pilots are taught this concept, then promptly trained to forget about it and use airspeed to detect an impending stall.

Thats because light aircraft have airspeed indicators, but they don’t have angle of attack indicators. Yet there’s no reason they shouldnt have these gadgets and, in fact, there are four companies hawking such prod- ucts. The argument for AoA indicators is convincing. By learning to fly angle of attack rather than airspeed, an airplane can be flown more precisely at slow airspeeds, improving short field

performance and reducing stall/spin surprises.

Lift Reserve

Angle of attack indicators are old hat for military and commercial jet aircraft, but their history for small aircraft is recent. The product that first gained notice in this arena was conceived by Morgan G. Huntington and marketed in the 1980s. Huntington developed a gauge that used differential air pressure to determine when an aircraft was approaching, reaching or passing the stall angle of attack. This device was originally called the Huntington Airspeed Director, but was later rechristened the Lift Reserve Indicator. Huntingtons work and his product capitalized on the principle that regardless of weight, temperature or altitude, stall angle of attack is constant. If you have a means of flying at that angle, you can extract peak low-speed performance and land on a dime or climb at best efficiency.

An LRI is technically not an AOA indicator. Rather its a purely mechanical pitot-type device that uses subtle differential pressure measurements to surmise angle of attack. More sophisticated lift reserve instruments used a computer module into which the pitot tubing is routed and the pressures are transposed into electronic signals for LED readouts, but the principle is the same. True AoA devices-which are also available for light aircraft-use a vane sensor to directly measure AoA and are both more complicated and expensive than LRIs.

If anything has kept the LRI from becoming more popular, its probably a misunderstanding of what it does and the unconventional size of the indicators. The original Huntington LRI was a hulking 2 1/4-inch instrument designed to be mounted on the glareshield.

But despite the tiny niche these products occupy, the display technology has improved recently. One-entry level LRI still uses the 2 1/4-inch round instrument, but other providers have developed gauges to fit both large and small panel holes and LED or LCD indicators that take up little panel space. Heres a rundown on the four players in the LRI/AoA field. Bear in mind that LRIs are not certificated and will require an FAA Form 337 to install, although one company is seeking certification.

InAir Instruments, LLC, of Westerville, Ohio, seems to be the go-getter in the LRI business. You can tell from talking to InAirs owner, Al Mojzisik, that he wants you as a customer. Mojzisik was partnered for a while with Jim Huntington, son of the