Teaching “Invisible Angle Of Attack”

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. We will have a full syllabus of skill-building maneuvers at our SAFE CFI-PRO™ Workshop at AOPA, October 2&3. Fly safely (and often)!


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Basic Physics of Flight Control!

Basic center of gravity is critical to aircraft  control but this is another important concept  most pilots (and some CFIs) don’t solidly understand. And confusion about stability and basic flight dynamics seems to be at the root of many of our LOC-I accidents. To simplify all this concept for students, I call it “balancing the teeter totter.” And this is obviously a “donuts and coffee” level pilot discussion, not a “graphs and Greek letters” deep dive. My hope is to generate some awareness, surprise and more questions for further deep study. Once there is surprise there is learning and these concepts are best learned and mastered in a calm environment (not upside down).

I know from speaking presentations to assembled fliers that this question; “where is the CG” creates consternation and confusion – and half the pilots get it wrong! So obviously this is an “opportunity for growth and learning” if you join in and participate. Ask yourself honestly and pick an option please. Experienced CFIs please use this with your students – you will be surprised. Which end is heavy (and then we will talk about why it matters).

It’s ironic that in pilot training, we spend endless hours calculating and explaining the minutia of moments and moving imaginary baggage around to get into the approved CG range, but we miss the bigger more important picture – the basics of how every familiar GA airplane works. And I can corroborate this from giving flight tests over the last 20 years. Please make your choice…where is the weight? Then click here for the answer.


The nose of the plain vanilla, part 23 GA aircraft is the heavy end and the tail of every plane you fly is “lifting” DOWN. The implication of a heavier nose for most LOC-I situations is that the pilot is (usually) the responsible party creating the LOC-I problem with excessive back pressure. To restore control, step one is to stop pulling on the yoke (which creates and maintains the excessive angle of attack) and RELEASE, to reduce the angle of attack (AOA). There is inherent stability built into a well-designed aircraft if we do not over ride it with a fearful, startled pulling force. Reducing power is also critical (for reasons we will explain later). To simplify, planes don’t stall, but pilots stall planes by pulling. (The one exception being a batched go-around – trim stall!)

So why is it the pilot initiates this problem by pulling and stalling? There is no sure answer available but it seems to be a human tendency that occurs as part of the startle/fear experience. I personally call it the “monkey pull,” since it is an atavistic survival mechanism somewhere in our (ground-based) DNA. Pull away from what is approaching? Unfortunately for flight dynamics, this instinctive reaction in LOC-I is completely wrong for aircraft control and overrides the stability built into the machine. Much of our initial flight training involves attempting to train out this fear/startle response and overcome the pulling response in emergencies. I do not think personally we can ever entirely succeed and the training gets faint if we do not practice continuously.

Bold Method Graphic; click for CFI Tool

Adding a durable intellectual understanding of the how basic CG and angle of attack work on an aircraft (tail force down/heavy nose) is essential, but obviously often missed, in flight training. When you screw up an aerobatic maneuver (and I’m good at this) my mentors always counsel, “reduce power, and let go, the heavy end comes down.” The power part is obvious if you again click here for the CG diagram. High power (often added inappropriately in panic situations) creates induced airflow over the tail that further drives the tail down (and increases AOA). Power also compounds the LOC problem with yaw and torque.

The bigger CG picture and the inherent stability of the plane should be explained and demonstrated to all pilots in training by the professional aviation educator in a very careful and non-threatening manner. We discussed an airplane’s stability in  a turn  – trim and fold your arms and your plane will keep happily turning until it is out of fuel. A stable GA trainer in a stall will recover very nicely if you just reduce power and release back pressure. I personally think this is how the first stall should be demonstrated in training; start gliding power off- gently increase AOA (raise nose too high – not even above the horizon) and the plane will stall gently. Simply release back pressure and the plane starts flying…easy peasy! It is counter productive (and often permanently detrimental) to scare and confuse your new aviator with a complex procedure and wild flight attitude. We want to convey the concept and all the variations can be added later. No learning occurs in a terrified student and we perpetuate the fear that prevents proper recovery later.  The first stalls can be a great confidence builder. When I do that procedure with students they breathe a sigh of relief and comment “that was a stall?” and they can’t believe it. The often also comment “All the other students told me I would hate them and be terrified…”

Next week we will dig further into AOA. For a quiz question to lead that discussion, which of these airplanes here has a higher AOA?

 

 

 

 

 

Did you know that EVERY aircraft actually has an AOA indicator on board? And it might be more reliable than that techno-wizardry you just paid to install? Stand by for that… Fly safely (and often)!


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Join SAFE to support our safety mission of generating aviation excellence in teaching and flying. Our amazing member benefits pay back your contribution (like 1/3 off your annual ForeFlight subscription)! Our FREE SAFE Toolkit App puts required pilot endorsements and experience requirements right on your smartphone and facilitates CFI+DPE teamwork. Our CFI insurance was developed specifically for CFI professionals (and is the best value in the business).

 

 

 

 

Is “Cross-Controlled” Dangerous?

We discussed the turning stall in the last SAFEblog and revealed the (often surprising) fact that in coordinated flight, with lift equal on both wings, a stall simply falls away from the lift vector and is very benign. There is only a burble and a drop of the nose, but no rolling or sudden departure from controlled flight that many people expect (and fear). This maneuver is in the private pilot ACS and should be comfortable for every aviation educator. This maneuver not only builds skills and confidence, but also creates a powerful opportunity to promote the need for coordinated flight and the value of correct rudder usage. Since there is no spin tendency in a turn when we are coordinated, this has a super safety value to every pilot; it opens their minds and gets their attention. But we then need a method to achieve better intuitive rudder coordination.

There is lots of confusion about the airplane’s rudder and its function in flight.  Remarkably, when Rich Stowell surveyed pilots he found 70% thought the rudder was used to turn the aircraft. This is dramatically wrong and should be a wake-up call to every CFI. Quite simply, the rudder cancels unwanted yaw created by the adverse effect of ailerons, power application, or rapid pitching moments. Most commonly, the downward moving aileron creates yaw, pulling the airplane away from the desired turn direction with “adverse yaw.” This can be *very* pronounced in an older (often tailwheel) aircraft but is largely designed out of modern (control blended) aircraft. That is a nice way of saying modern planes mostly tolerate and disguise “flat-footed flying.” Unfortunately, moving the rudders appropriately and learning coordination is the key to safety and preventing LOC-I.

The critical skill is to anticipate yaw not just reactively cancel it after it has occurred. That’s why the advice “step on the ball” – though correct – is too late and creates more problems than it solves. “Step on the ball” means you already created the yaw problem – slewing the plane – and are subsequently forcing it back into balance with a time-consuming, mechanical input. People who utilize this advice not only have their eyes inside but also fly like bad robots in a jerky and uncomfortable fashion. In addition to being clumsy, we just do not have enough mental bandwidth while flying to be cogitating about “stepping on the ball” (which lags badly anyway). It is essential to tune up our kinesthetic yaw sensing and develop automatic anticipation of adverse forces. This will also makes you an amazingly smooth pilot that your passengers will appreciate.

I recommend all flight instructors (and pilots who want to get sharp) demonstrate (observe) a brisk application of power, aileron, or pitch applied independently at a safe altitude. In each case you will see the nose yaw in reaction to this force applied (physics in action).  With practice you can predict which way this will occur (physics!) and discern how much rudder to apply to maintain coordination. I have my primary students initially move the throttle hand and the right rudder together to develop some “muscle memory” while on the ground sitting in the cockpit (works for “chair flying too). This yaw correction will become automatic pretty quickly with directed focus and practice (but is much easier to teach initially than to correct from a bad habit). There is a lot more to this art of learning/teaching rudder and our SAFE CFI-PRO™ workshop has many time-honored CFI tricks to tune up rudder usage.

“As the power increases, you’ll simultaneously press on the right rudder pedal knowing that the entire universe (specifically the airplane’s power induced left turning tendencies) is doing everything possible to yaw the airplane’s nose to the left. But you’ll have none of this nonsense because you are in command of your airplane, right? Right! So step on that right rudder pedal.” Stick and Rudder Mutter, by Rod Machado

But let’s get on to this “cross-controlled bogeyman” we started with. If after we demonstrate that turning stall we ask why the plane did not spin (as expected) in the turn the logical follow up question is “what would cause a stalled plane to spin?” And I guarantee the answer will be “if you stall when you are cross-controlled.” So I demonstrate a stable full slip (power off) and bring the plane to a stall. I love this demonstration, because though the plane is balanced and stable, every pilot anticipates a violent spin entry. In fact with a well rigged trainer, nothing at all happens (except the student finally begins breathing again). Another learning opportunity; why no spin? Because the slip configuration is stable (with no power) with the rudder yaw opposing aileron roll force (perform this only with an experienced instructor and know your plane). This illustrates that the obvious bogeyman is not “cross-controlled” but rather the pro-spin inputs of a skidding turn (ironically the force 70% of pilots think turns the plane) The skid is an excess rate of turn. This usually is created with the rudder but can also be uncompensated force from a go-around attempt (well represented in the NTSB files). The skid is the evil form of “cross-control” and often occurs when people fight yawing force inappropriately with aileron (“driving” again). If there is one aerodynamic principle every pilot must understand this is it; understand thoroughly the difference between a slip and a skid and why one is safe and one will kill you . This is the essence of safety in the pattern. More detail is in this Aviation Safety article I wrote.

Three incidents personally persuaded me to demonstrate these maneuvers and promote this understanding to every pilot. First was repeated flight tests where applicants did not want to “slip to land” because it was “cross-controlled and dangerous.” Then I discovered a website by a respected airline pilot (with great popular following and gravitas) that advised (completely incorrectly) to convert the base to final turn into a slip by applying aileron out of the turn as you lined up on final; “you already have the wing down.” This is of course a skid and very dangerous (pro-spin: do not try this!). The final incident was a young CFI applying for a job at our flight school who demonstrated a massive skid (intending to slip) and confessed he thought you “just cross the controls” to create a slip. This level of confusion is obviously killing pilots and needs to be corrected by every conscientious aviation educator. Again, more here.

Next weekend SAFE will be at the AOPA Fly-In at Frederick, MD (and we would love to meet you there). This blog will cover another misunderstood (and potentially dangerous) aerodynamic force; AOA, CG and pitch (“planes don’t stall, but pilots stall planes”) Fly safely (and often).


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Join SAFE to support our safety mission of generating aviation excellence in teaching and flying. Our amazing member benefits pay back your contribution (like 1/3 off your annual ForeFlight subscription)! Our FREE SAFE Toolkit App puts required pilot endorsements and experience requirements right on your smartphone and facilitates CFI+DPE teamwork. Our CFI insurance was developed specifically for CFI professionals (and is the best value in the business).