My Sonex panel was spartan. The two luxuries I allowed myself were a stereo intercom with music input (nothing in my life happens without music) and a Lift Reserve Indicator (LRI), an analog version of an angle of attack (AoA) indicator. The LRI, with its sweeping needle, is no longer manufactured, having been replaced by the more conventional light display units, but its functionality was the same. Once calibrated, an AoA indicator will register the same value when all lift has been consumed. Regardless of density altitude. Regardless of bank angle. Airspeed indicators are not so talented.
The LRI had a fixed arc over which the needle swept, providing an indication of how much lift was being produced. As lift decreased, the needle would sweep left, from a green arc (indicating abundant lift), to the white arc (denoting minimal residual lift), and, if allowed, into the red arc. The red arc indicated there wasn’t enough lift to sustain level flight—the airplane would descend until power was added. Pushing the stick forward would reduce the risk of a stall, but you would still be in a downward trajectory.
In an extreme example of flight in the “red arc,” imagine doing a full-throttle vertical climb punctuated with a wingover. At the top of the climb—and for a period of the descent—the AoA would be in the red arc because neither adding power nor pushing the stick forward can stop the airplane from descending; there’s no lift. Only time and loss of altitude, to build airspeed (lift), will allow you to pull back on the stick and return to level flight. This is fun at altitude, deadly in the landing pattern.
My Sonex had a speed ratio of 4:1. It could cruise four times its stall speed. The Lift Reserve Indicator’s needle would quickly enter the green arc and stay there for most of every flight. In a slower airplane, or one with a high stall speed, the needle would be more responsive to smaller changes in airspeed because the scale of the speed range it represented is smaller.
I seldom saw the needle leave the green. Other than a landing or three, when I wanted to see how unnecessarily fast I was bringing my Sonex over the fence, did I use the LRI to slow my approach and shorten my landing. So it went largely unused, but never unappreciated.
AoA Proves Its Value
I used to participate in Sonex Aircraft builder workshop flybys. Together with factory aircraft, I’d launch in my polished Sonex, Metal Illness. We’d fly a pattern that gave workshop attendees a chance to see the airplanes in flight. It struck me that the flybys seemed to stress the all-out speed of the design, but I felt its slow-speed capabilities were just as, or more, impressive. So I’d throw in a low-speed pass.
On one occasion I was flying a low-speed left base for Oshkosh’s Runway 18 (this put me right by the Sonex Aircraft campus and the workshop attendees standing outside, watching the flying circus). I had full flaps deployed and used the throttle to drag through the air at an indicated airspeed of 58 mph. I was nose high. It was classic slow flight. When it came time to turn final I pushed the nose down some and began my left turn to final. The airspeed remained at 58 mph while the LRI’s needle fell quickly out of the green arc and started to flirt with the red. It was eye-opening. I know, of course, that stall speed increases with bank angle, but I had never seen it demonstrated so dramatically. I decreased my bank angle and pushed the stick forward more. The LRI’s needle swept right, into the low end of the green arc, and I completed my turn with confidence.
That was the moment the value of flying with an AoA indicator solidified itself in my mind.
Kerry, I too have an LRI in the panel of my Sonex. I have been working on installing a tailbeacon x with a AV-20 head . I find myself not wanting to remove the LRI for space to install the AV-20, do you think the electronic angle of attack will be as good?
I have nearly 1000 carrier landings and thousands of field landings using a AOA for approaches and landing it. Should be in all GA airplanes and would give student pilots a better understanding of how to maintain airplane energy while in the pattern. Now if we can eliminate the dreaded 2-3 mile final while in the pattern.
“Stall Speed” is no indicator of a stall. AoA is the ONLY indicator and, as we all (should) know, stall AoA can be achieved at ANY bank angle, pitch angle, or airspeed.
You’re mixing up Lift Reserve Indicators (RLI) with Angle-of-Attack (AOA) instruments. They are *not* the same! In your hammerhead example, an AOA would remain firmly in the green since the angle of oncoming air remains completely acceptable with the wing lifting (horizontally). (BTW, to get a vertical up line, the nose of the airplane will be considerably “down” relative to the airflow to get zero lift, otherwise you translate “backwards” over the ground.)
A true AOA unit requires a vane type probe. But if you take the 2-probe differential info from a RLI, add a microprocessor and IAS pitot information, one can make a pretty good approximation of AOA. RLI gives stall warning, that’s it. AOA gives that but also best climb, best glide, approach speeds and is a much better indicator of what the wing is doing.
I like Sparky’s post. Unless it’s an instrument approach, we should be able to make the runway from any position in the pattern in any light aircraft if the engine conks out.