WANTED: Angle of Attack Managers

This is one in a series of posts by special guest authors about SAFE’s new CFI-PROficiency Initiative™ (aka SAFE CFI-PRO™). The goal of the initiative is to make good aviation educators great!

Aviators, airmen, aviatrices—a few of the other words used to describe pilots. Yet none of these words reflect what we really do. Ultimately, pilots are angle of attack managers. Let’s have another look at AOA.

As David St. George notes in “Invisible Angle of Attack,” AOA is the difference between where the airplane is pointing and where it is going. Wolfgang Langewiesche describes the importance of AOA thus:

“If you had only 2 hours in which to explain the airplane to a student pilot, [AOA] is what you would have to explain. It is almost literally all there is to flight. It explains all about the climb, the glide, and level flight; much about the turn; practically all about the ordinary stall, the power stall, the spin. It takes the puzzlement out of such maneuvers as the nose-high power approach; it is the story of the landing.”

AOA implies two things: wind and an object around which the wind is flowing. Most everyone has played with AOA before. Remember sticking your hand out of the car window when you were a kid? What happened when you tilted your hand into the oncoming wind? “It went up!” is the common response. Reflect more deeply on the experience, however, and you’ll notice that your hand actually moved upward and backward. If we want to get technical about it, we could call the “up” part Lift and the “back” part Drag.

We’ve all seen examples of unusual things being forced to fly, too. For example, tornado-strength winds can cause even the most reluctant Holstein to go airborne.

A high velocity jet of air precisely aimed at a Snap-on screwdriver can cause it to hover (courtesy of SAFE member Shane Vande Voort—please don’t try this at home!).

And though we might describe a wing as having a “top” and a “bottom,” Lift- and Drag-producing AOAs are possible on either side.

AOA is discussed primarily in the context of the airplane’s main wing. But at the correlation level of learning, we see the entire airplane as an assembly of wings all of which are subject to the principles of AOA. The propeller, for instance, is a rotating wing. Main and jury struts are often symmetrical wings streamlined to minimize drag. “Aileron” is French for “little wing.” And our primary flight controls are AOA controls. The elevator controls the AOA of the main wing (aka pitch control).

Ailerons control local AOAs (typically the outboard part of the wings, aka roll control).
Rudder controls the AOA of the fuselage (aka yaw control).

Our job as instructors is to teach our trainees how to manage these AOAs to achieve desired performance outcomes. Although AOA itself may be invisible, changes in AOA can be sensed and its trend interpreted. In the visual flight environment, this means coupling aeronautical knowledge with sight, sound, and feel to manage our controllable AOAs.

Before we climb into the airplane, for example, we know that the combination of a high power setting and a slow airspeed during the takeoff phase will yaw the airplane. But we want coordinated flight during this particular takeoff. That will require a certain amount of rudder to manage the AOA of the fuselage to cancel the yaw. What does yawed flight look like during takeoff? What does it sound like? What does it feel like? What does it look and feel like if we try to use aileron to correct for the yaw instead of rudder? All of these questions can be explored in the practice area without staring at the slip/skid ball. The lessons learned can be applied during subsequent takeoffs.

Whether it’s pitch, roll, or yaw, changes in AOA manifest as changes in one or more of the following: attitude, G-load, control pressure, control displacement, and often sound. In the case of elevator inputs, add airspeed to the list of cues.

For fun, test your understanding of AOA with the following thought experiments. Imagine you are at an airshow watching a competent aerobatic pilot fly a capable aerobatic airplane.

1. The airplane makes a knife-edge pass from your right to your left at precisely 90 degrees angle of bank.
a. Where is the nose of the airplane pointing relative to its flightpath, and how is the pilot making that happen?
b. What is the pilot doing with the elevator to make the airplane fly down the runway?
c. What is the AOA of the main wing?
d. What is the pilot feeling?

2. The airplane climbs along a perfect vertical line.
a. In order to remain on the upline before pivoting in a Hammerhead, what is the pilot doing with the elevator?
b. Ultimately, what is the AOA of the main wing during the upline?

Want to learn more ways to push learning to the correlation level? Attend SAFE’s inaugural CFI-PRO™ workshop in Frederick, MD on October 2–3, 2019!

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

“Artful” Control Usage; Pattern Precision

Rudder use in climbing turns is critical to safety in the pattern!

Flying around the pattern with perfect coordination is more difficult than most pilots think. Its also essential to safety because this is where the majority of accidents happen either from collisions or loss of control. Aviation educators must be insistent on thorough understanding and proper control usage if we are going to make better, safer pilots.

The correct actions and control pressures required in the pattern often go against what initially seems “natural” to new trainees; their “naive rendition.” Aviation educators need to patiently unpack and overwrite naive assumptions with correct theory and control usage. These are “trained responses” and require lots of practice to become embedded, implicit scripts that are constantly ready for use by the savvy pilot. There are lots of negative transfers from our more common transportation activity; driving.

Every educator will get arguments that mastering the correct control application is unnecessary because what they are doing “already works” or they will correct sloppy control later; neither is true. The basics must be mastered early and practiced often in flying or you have embedded a ticking bomb in your procedures that will surface later when a critical surprise situation requires immediate and accurate control skills to save the day. Marginal performance from power loss or density altitude challenges can suddenly require us to squeeze every ounce of performance from our aircraft. For safety and efficiency we need to unpack some of these less studied effects and work to master correct coordination.

A common example of “instinctual control” is seen in new pilots on initial power application and rotating to climb for take-off. These new learners counter left yawing tendencies with aileron;  a powerful negative transfer from driving. Many experienced but rusty pilots still exhibit a trace of this incorrect control input. Correctly canceling the yaw with rudder is a trained response that has to overwrite “intuition” and driving habits through continual reinforcement. With practice, the nose should rise straight and steady to a know climb attitude with outside reference and rudder pressure canceling yaw. (Extra points are awarded for not wagging left and right as the climb progresses) As the plane leaves the ground and starts climbing, some even more subtle control pressures are necessary to stay coordinated.

After rotation the pivot point for elevator shifts from the wheels to the CG point (forward of the wing) so a release of back pressure (lower nose) is required (nosewheel plane). Additionally, the increase of induced drag upon leaving ground effect requires a subtle relaxing of back pressure. The proper climb picture required should be memorized and acquired with visual outside reference. The view outside will also allow a pilot to see that left aileron is necessary to keep the wings level in the climb. Right rudder pressure causes a proverse roll to the right (more prominent in some planes than others). This subtle force surprises even experienced pilots when it is pointed out. Climbing coordinated requires some cross control pressure to keep the ball centered and the wings level; “cross-coordinated.” In the proper configuration, most planes exhibit 15% greater climb rate when correctly coordinated on the takeoff since they are stramlined and more efficient. (Try gliders to experience how necessary proper coordination is to performance) Though 300-700 HP can pull almost anything airborne even sideways, bad coordination in emergency situations is the killer. It is amazing that 24% of fatal accidents occur on the take-off and initial climb. Many pilots just don’t value all the challenges here – “hard to miss the sky!”

During the initial high-power, low-speed climb, most singles require right rudder pressure to center the ball. This induces a right rolling moment. Left aileron input against the right rudder is subtle but necessary to keep the wings level as the ball is centered. Once the plane is “subtly cross-controlled” in this manner, it will climb much better because drag is minimized.

The standard left crosswind turn in the patterm  is an even greater challenge to keep properly coordinated for new pilots; right rudder is required! Recent accident data indiates the climbing crosswind turn in the pattern may be even more dangerous than the well known base-to-final turn. Pilots turning left in a climb usually don’t apply the proper right rudder pressure to cancel the prominent left-turning forces since is initially “so unnatural.” As mentioned in many of these blogs, flying well requires many counter-intuitive trained actions to be safe. Remember, since both wings have equal lift in a stabilized turn, and the left-turning tendencies are still present and require right rudder – we are still climbing! Unfortunately, many pilots skid around their left climbing turns (standard right-hand patterns would be safer for control). Pilots who have tried chandelles – a more extreme climbing turn – are very familiar with the cross-coordination concept here. But even in less extreme left crosswind climbing turn, right rudder is essential. But why is flat-footed flying dangerous here?

In skidding turns, the force of roll and yaw are both acting in the same downward direction; they are coupled and adverse in effect – pro-spin. And when pilots inappropriately counter this skidding force in a climbing left turn with more aileron, this incorrect control application increases the angle of attack on the lower, slower wing. This makes the lower wing more likely to stall first and tuck into a spin. This illustration from Bold Method provides a depiction of the many problems with a skidding turn. Correct control application must be taught relentlessly by a committed aviation educator and studied carefully by the pilot in training to become an embedded habit. And this is particularly hard to master since it is a llearned action that is initially completely counter-intuitive. But anything less is clearly unsafe.

The skidding turn seems to be always depicted in a nose low, base-to-final turn in the pattern. This is where pilot action creates the skid with rudder to inappropriately increase the rate of turn. But you will see far more skidding turns in a climbing left turn if you pay attention. The skid here only requires pilot inaction. All the powerful left-turning tendencies create the skid that must be corrected by pilot action. These left-turning forces must be actively countered with right rudder to prevent a skid. This dangerous tendency is especially common in bigger planes and more powerful engines in the climbing turns. Do the math and you can discern that this is often demonstrated by the “captain of industry” – an affluent step-up client who bought a big new plane. This person is allegedly a “trained pilot” but often really requires remedial instruction to be safe. The professional aviation educator must be firm here to address and fix these coordination problems. Acquiescing to poor control or bad technique is unprofessional and unsafe; it’s how we are losing control in our aircraft every day. Fly safe out there (and often)!

An appreciative nod to Michael Maya Charles and his amazing book “Artful Flying” (SAFE members get 20% off) which continues to inspire me daily. Flying well is more than just being safe. It is the daily joy of pursuing excellence in aviation; flying artfully!

 

 


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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).