Angle of attack (AOA) is the most misunderstood concept in aviation – just raise the topic casually in a hangar flying session to sample the confusion. Our previous two blogs on tail-down force and the basics of a turn demonstrated the many scary gaps in the average pilot’s knowledge. Some CFI somewhere has failed these pilots in training. Ignorance and misunderstanding, along with lack of solid skills are at the heart of many of our fatal loss of control accidents. Most pilots are fine and happy in the limited “comfort zone” of their 5% flight envelope, but terrified when forced by surprise events to maneuver. (I highly recommend Rich Stowell’s Emergency Maneuver Training to every pilot. This book will fill many “gaps” and is written in wonderfully clear language)
Controlling AOA is the central tool in the generation of lift and essential to everything we do as pilots defying gravity. Understanding and managing AOA is indisputably the most important knowledge and skill set we (should) learn as students. But unfortunately, if AOA exists at all in a pilot’s vocabulary it seems to represent only the feared excess of the stalled condition. And even the simple stall is clouded in mystery and fear and hidden behind an over-reliance on technological protections. Now that minimum controllable airspeed (MCA) has been removed from the private pilot ACS, educators often don’t teach this important skill and sample “the feathered edge” of critical AOA. Learning to maneuver in MCA not only teaches coordination, it teaches all the kinesthetic cues of the impending stall.
I have been privileged to own a 7AC Champ for the last 30 years. This plane has no stall warning device at all – and no blue button or “envelope protection” either. Demonstrating AOA and teaching stalls is so easy in a Champ or Cub (or glider); pilots in training learn it early and fairly painlessly. Add all the distractions of a technologically advanced airplane and the slow flight/stall process can take longer and be disguised by distractions. Don’t get me wrong, technology is wonderful and necessary in a “go fast” machine, but the physics of lift is identical and more easily learned in a simple plane.
Angle of attack is most commonly confused with flight attitude (an aircraft’s relationship to the horizon) but there is no relationship between AOA and attitude. I think this misconception is a deeply embedded “natural” human assumption. And it is essential to eradicate these misconceptions during flight training. This requires knowledge, demonstration and practice; but we often don’t get there. Any plane can be in level flight attitude and stalled, be pointed straight down and also be stalled (both exceeding the critical AOA). Air France 447 was a landmark case study of a very experienced crew mishandling AOA.
As illustrated above, in a still photo of an aircraft, you just can’t determine the AOA from the outside view; it is invisible. To discern AOA you need motion and trend; it is the difference between where the airplane is pointed and where it is actually traveling. And that is another good reason for a pilot to keep their eyes outside for more than infrequent glances; you need to see the trend to achieve control. If it’s going down out of control you need to unload and push it further down to recover. “Unloading” (reducing AOA – especially when nose down already) is so unnatural and at first it is incomprehensible to new pilots.
A secondary stall is a excellent tool to illustrate the difference between AOA and flight attitude and train unloading – the student is confused p“the nose is down below the horizon but the plane is stalling? How can that happen?” This initial confusion (cognitive dissonance) is a “learning opportunity” for full explanation, full understanding and training muscle memory in the learner. And here the aviation educator has to be patient and kind but also somewhat relentless in achieving understanding and proficiency (DPEs do not evaluate this skill on flight tests). If pilots do not fully grasp this “unload” concept, they will never be safe in emergencies.
My personal familiarity with AOA is largely from many hours of “dual given” watching people misunderstand and mishandle the physics of flight. And my passion is guiding them back to comfort, knowledge and control in their aircraft. But this takes commitment on both sides of this instructional relationship. Our natural human tendencies (called “naive rendition”) of how flight works is initially all wrong. Our intuition fails when it tries to “do physics.”
Everyone seems to “know” the nose high aircraft is “high AOA” (the crime of flight school demonstrations). But nobody seems to comprehend that a nose-low A/C can have an equally “high AOA” and be just as close to a stall (it mistakenly appears safe). The untutored knowledge that is “natural” to new pilots does not work and only gets worse when fueled by fear in an upset (pull away from the ground). Flying is largely applied physics and requires proper counter intuitive knowledge and understanding. Flight training is a careful process of discovery as we overwrite what humans intuitively guess is going on. And that takes trust and willingness on the part of the learner and requires a strong CFI/learner relationship to work through these issues completely – also rare.
After many years of flying and teaching, we know most people can drive a plane down the center of the flight envelope with very little guidance – “look mom I learned to fly in a week!” We’ve all seen this on the cover of Popular Mechanics and I would love it if it was that easy. Unfortunately, if these marginally trained pilots experience displacement from “normal” or are startled, loss of control is a certainty. Even the most experienced pilots can fall into AOA traps. The video below is of an Air Force Thunderbird F-16 that suffered a very predictable LOC problem. Watch carefully and see if you can figure out why this happened (no one was severely injured here and the pilot ejected in time)
I often present this video at gatherings and call this “the perfect stall.” It demonstrates that even the most amazing military machine with endless power can’t make an airplane do the impossible and defy physics. Below is a screen shot that looks like a “fly by” – but in a static picture AOA is invisible – it takes motion and trend of a video to reveal the 7G stall.
And the question we left you with in last week’s blog; What is the AOA device installed in every airplane? AOA corresponds with how much chrome you see on your yoke (how far you are pulling back); and how much back pressure you feel on the stick (right side up). “Unloading” (overcoming that dangerous “monkey pull”) allows the reduction of AOA and is the first step to recovery of control (or don’t go there in the first place). To me personally, this huge, universal AOA device is more obvious and compelling in an emergency than a small electronic AOA device hidden somewhere in a busy panel. But there are many good Upset Recovery Schools for you to try this for yourself and decide while experiencing upsets safely. There is also excellent technical guidance on LOC-I in our SAFE public resource center (available to everyone) and in the FAA Airplane Flying Handbook. Fly safely out there (and often)!
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All the elevator ever does is change angle-of-attack. The problem is there is only a small difference in aircraft attitude and direction of motion…it just can’t be seen.
Upon releasing the control wheel the machine immediately goes to the trimmed AOA. Learn to fly hands off controlling direction with smooth rudder input.
An excellent review of this can be found in the Mar/Apr 2014 FAA Flight Safety-Brief, page 13.