A Flying Car in the Future?

Angle of Attack (AOA)

ByMike Hostage January 27, 2020January 29, 2020

You are hand-flying an in-the-weather descent, power back, heading for the FAF. You start a 30 degree banked turn at your lead point to cross the FAF, when your passenger behind you gasps. Looking over your shoulder, you see he has spilled his drink into his lap…too bad for him! However, when you turn your head back to your panel, your inner ear tumbles and you see 45 degrees of bank, 15 degrees nose low, airspeed increasing.

Congratulations! You have managed to get distracted and sucked into an unusual attitude recovery. By the book, you should roll wings level, pull to the horizon, and adjust power as necessary to keep the airspeed within limits. In this scenario, if you had not experienced vertigo, you might have been able to roll to less than 30 degrees of bank, recover your turn, pull the nose up to less than the original descent attitude, pulled a bit of power to slow back to your desired penetration speed and then resumed your desired ground track. However, this would only be appropriate if you had full situational awareness as to the deviations caused by the look over your shoulder, plus full confidence that the moderate corrective actions would put you back on your desired flight path.

As a military aviator, I learned unusual attitude recoveries based upon hard maneuvering at extreme pitch and bank angles. In the hard-maneuvering environment, an unusual attitude could be 90 degrees straight up, airspeed decreasing below 120 kts…or 80 degrees nose low, 135 degrees of bank, airspeed increasing through 500 kts… etc. In these cases, understanding angle of attack, or AOA, is critical to maintaining controlled flight and returning to a normal attitude.

In an extreme nose-high attitude, a military aviator is trained to roll the aircraft to 90 degrees of bank, ease off the back-stick pressure to reduce AOA, add power as required, and allow the nose to slice back towards level, rolling to wings level as the nose approaches the horizon. If nose low, the recovery procedure is to roll rapidly, within asymmetric g limits, until wings level, then to pull at optimum g loading to recover to level flight. For the nose-low recovery, power was normally reduced until airspeed could be assessed and brought under control. However, when doing the nose-low pullout at 7-9 gs, pulling the power for too long would leave you much to slow to resume combat.

The AOA gauge on a fighter’s glare shield is a primary reference during hard maneuvering and for landing. The AOA for optimum maneuvering is 13 degrees, displayed as the green circle or “green donut” on the gauge. The red chevron on top represents a slow condition of 15 degrees or more and the yellow lower chevron represents 11 degrees or less.

For normal landing in the F-16C, the pilot slows to 220 kts and configures abeam the touchdown point while mentally computing the final approach airspeed of 136 kts plus 4 additional knots for each 1000 lbs of fuel. When rolling off the perch and flying the final turn, the pilot would usually only glance once at the airspeed once to ensure final turn airspeed of 180 kts while using the AOA sight gauge as the primary indicator of a best performance turn. As long as the AOA was green donut (13 degrees) or less, you would not stall. If on speed and 13 degrees wasn’t going to get you around the turn to line up with the runway, you knew you were going to overshoot. You never wanted to see the red chevron of 15 degrees or more as that meant you were too slow, pulling too hard, and in danger of building an un-recoverable sink rate!

Few GA aircraft are currently equipped with AOA indicators, though there are several after market devices available for retrofit. However, knowing the impact of AOA and how to manage it is vital to safe aviating, even without an AOA gauge. The bottom line is, as long as you don’t ask the wing to produce more angle of attack than it can handle, you won’t stall.

Practicing final turn stalls, to know what the wing feels like as you get too slow or pull too much on the controls, increasing AOA past the critical point, will keep you safe when you encounter that unexpected overshooting wind or you find yourself inadvertently on too tight of a downwind leg. Better to overshoot or take it around to try again, than to pull too hard and exceed critical AOA.

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Mike Hostage is a retired USAF pilot with 37 years of experience, flying a wide variety of aircraft.  An instructor pilot for more than half of his 4800 flight hours, Mike is currently qualified in a Cirrus SR-22T and regularly flies his two homebuilt sailplanes.