Spin Masters

Helicopters and boats fly in a furious duet

August 1, 2006

A hawk soars off the shelf of green — the last bench of the Cumberland Plateau before the forest gives way to farmland, and to the stretch of Tennessee below. On this shelf sits the town of Sewanee, home to the University of the South, and the Franklin County Airport, home to William Kershner. The former Navy pilot and Piper Aircraft flight-test engineer who has authored numerous flight-training manuals — and sold more than a million of them, with six books still in print — set down roots here in 1964.

The hawk we watch stays in a rather sedate flight regime; it rarely exceeds 30 degrees pitch up or 60 degrees of bank in its quest for dinner. Momentarily flightless "birds" that we are, we'll still pull more Gs than the hawk does in the days to come.

Most pilots these days don't stray much past straight and level either, after the checkride — practicing emergencies or "abnormal" maneuvers plays second fiddle to the primary melody of getting from point A to point B. But we pay for it when circumstances lead us into the corners of the V-G diagram (the graph that illustrates the load factors and limiting airspeeds of a particular airplane), and play an unfamiliar tune.

But extreme aerobatics (the kind easily served up by a Pitts or an Extra) isn't necessary to explore and appreciate — and learn the skills to survive — an out-of-straight-and-level experience. In fact, using a purpose-built aerobatic machine in this exploration may not serve the average general aviation pilot best. The airplanes most of us fly don't have the horsepower-to-weight ratio or the roll rate of common aerobatic steeds. We need to know how our aircraft respond in accelerated stalls, spins, rolls, and loops to understand how to recover from them without bending ourselves or the sticks and struts keeping us aloft.

To this end, Kershner has been providing spin and aerobatic training in a one-airplane operation, Ace Aerobatic School, for several decades. He served once as its sole instructor, but the right person came along, and now he has a partner. After Kershner serves up several helpings of wisdom on the ground, Catherine Cavagnaro takes over and puts students through their paces in the 1978 Cessna 152 Aerobat.

The two met before Cavagnaro had started flying lessons, in 1998, when she went for an airplane ride at Franklin County. "Bill gave me the basic aerobatic manual [that he had written], and I thought, 'What kind of nut case would do such a thing?'" After she finished her private certificate in September 2000, she scheduled a flight with Kershner, and, as she says, found out she is one of those "nut cases." She quickly progressed through certificates and ratings, completing her commercial and flight instructor certificates and instrument rating within a year — she's since added instrument and multiengine instructor ratings as well. Cavagnaro has a doctorate in math, and she's associate professor and chair of the math and computer science department at the University of the South. But besides that, she has something else. Says Kershner, "She's the only person I know that I have full confidence in [to teach] in my airplane; she's got the math background.... We have people who haven't graduated from high school [who come to fly with us], and we have people with doctorates, and we can handle it — you've got to change your approach."

Kershner and Cavagnaro offer two basic outlines for aerobatic and upset training. The first is a basic aerobatic course that teaches primary maneuvers such as the aileron roll, loop, and upright spin. This course can serve either as a springboard to further aerobatic flying or as the foundation for an emergency upset training course, depending on the student's needs. A spin course focuses on the spin itself. The course can be used by any pilot who wants spin training, but it's of particular interest to flight instructors for the initial CFI certification (spin training is required for this certificate) or as a refresher or for additional training.

Spins

Good training begins on the ground. I'm in the presence of a master, that's certain, even before the first marks go down on the whiteboard in front of us. Kershner starts by reviewing the mechanics of the spin, particularly how a spin differs from a spiral. And his deadpan — and sometimes downright silly — humor peppers every technical discussion. There are those who say that levity has no place in training; what a sorry band of kill-joys, that bunch. Kershner's my kind of guy.

Here's a quick whiteboard tour of what we reviewed: A spin requires that at least one wing is stalled, and that the wings vary in the amount of lift they produce at that time. Typically this occurs when, during a stall or other high angle-of-attack maneuver, there is a difference in the angle of attack on each wing, usually brought on by a lack of coordinated control inputs — the ball isn't centered — which creates unequal airflow over the wings. With the difference between the two wings in lift created, rotation begins.

The first stage of the spin, the incipient phase, normally comprises the first two turns, and describes the stage in which the spin is setting itself up — forces of pitch, yaw, and roll increase. The second stage, the developed spin, is when the airplane reaches a constant rate of rotation and steady pitch attitude. Often the recovery is referred to as the third stage of the spin cycle — and has such a profoundly good effect on a pilot's psyche that it deserves separate (and high) billing when discussing the stages of the spin.

Conversely, in a spiral, the airspeed is high, or increasing, whereas in a spin, the aircraft wings are stalled — and the airspeed is low and steady. The deflections of both the ball and the airplane in a turn coordinator (TC) won't be as extreme in a spiral as they typically are in a spin — and the ball will deflect to the side of the airplane in which the turn coordinator is located in the panel, away from the airplane's center of gravity, regardless of the direction of the spin.

Kershner's Aerobat has a slip indicator (the ball part of the TC) installed on each side of the panel to demonstrate this principle: During a spin, the ball in the slip indicator on the left side of the panel goes to the left, and the one on the right shows a right deflection.

To recover from a spiral, you use normal inputs: Level the wings using coordinated rudder and aileron, and then smoothly pull out of the dive using back-pressure on the yoke or stick.

Recovery from the spin is logical, but not as immediately apparent to the pilot who sees the ground rushing up at her for the first time. First, "pro" spin conditions need to be rectified: The throttle comes back to idle (power tends to pitch the nose up in most airplanes), the flaps come up, and the ailerons go to neutral. Then, full opposite rudder, nose down to break the stall, and a smooth pitch back to level.

Aircraft specifics

In the Aerobat in particular, Kershner notes, the fuel gauges read "empty" during a spin because of the centrifugal reaction — it literally sloshes fuel to the outer side of the tank, away from the fuel-quantity-indicator floats, and, yes, the lines leading to the engine.

Which begs the next question: How long will the fuel in the lines last during a spin before the engine quits? Anywhere from eight to 13 turns, as the pair has demonstrated thousands of times over the years. The prop usually stops, but can be induced to windmill — and the engine to start again — at roughly 120 knots during the recovery. This is one reason why Cavagnaro sets up spin practice within gliding distance of an airport.

The behavior of the fuel system during a spin starts a top-level discussion regarding the difference between classic tailwheel aircraft and modern nosewheel designs. Which leads us to an important point about pushing the control wheel forward during spin recovery in most modern aircraft.

"If you take two objects, and one's shaped sort of like an ellipse, and we have another one with the same mass, but the weight distribution is different, like a peanut," notes Kershner, "and we get them spinning at the same frequency — the 'peanut' one resists stopping.

"In the old days, the little trainers were more or less a 'fuselage-loaded situation,' like an ellipse, and they had big rudders because of the tailwheel. Modern airplanes [with smaller rudders] have to get the nose over to get the streamlined airflow over the rudder — it's a smaller rudder, but it makes sense: Why drag a big rudder around in a trike?

"In modern airplanes, there's also the difference in mass distribution — with fuel in the wings, people in the middle — and the rudder isn't effective enough to stop the mass going this way (because of the 'peanut' shape centered on the wings) — plus the rudder is blanketed out of the way by the elevator until you get the nose down."

Testing the theory

In the airplane, we start spin training with a couple of power-on departure stalls. Then Cavagnaro demonstrates how the Aerobat will recover itself from an incipient spin. In fact, she laughs and, as she pats the glareshield lovingly, says, "The Aerobat has to be talked into the spin. You have to light some candles, play some soft music...." To effect an "automatic" recovery, we trim the airplane a little nose up before we put it up into the spin: At the first toot of the stall horn, I give the yoke another little tug and make a sharp application of left rudder, and we smoothly roll over to an attitude I last saw during a student's uncoordinated stall attempt many moons ago. After one turn, I pull back the throttle as instructed, and release the controls. The airplane, true to its stability-seeking design, stops rolling and yawing almost immediately. With the trim as we've set it, it also pulls out of the dive, though I can't help but help it along a bit.

Next, we set up three- to five-turn spins until I get the hang of the recovery. Heck, it almost feels normal to see the ground filling the windscreen, twirling on an invisible axis. I'm beginning to understand how Cavagnaro can sit so calmly through the airplane's machinations.

The spin course provides three hours of ground instruction and two hours of flight training in the Aerobat, but it can be easily tailored to the pilot's experience and goals.

Acro intro

Back at the whiteboard, Kershner writes out a series of V-speeds for the Aerobat: V Y, V X, and V S1. We'll look at some other speeds in a minute — the entry speeds for loops and rolls — but first he explains how every maneuver we practice in the basic aerobatic course exacts positive Gs, and we'll remain more or less coordinated. This is important, as for new aerobatic pilots (and seasoned ones), it's the negative Gs that feel the most uncomfortable. Even at the top of the loop, where we tread most closely to negative territory, we see only 0.7 Gs — enough to feel light in our seats, but not enough to float loose objects around the cozy cockpit.

Kershner picks up a red marker and draws a series of figures in a practiced hand. The first is a diagram of an aileron roll to the left, which he uses to explain at which point in the maneuver I'll relax back-pressure, and vary rudder input — in the Aerobat, the control wheel stays all the way into the roll (and then some) until it's time to fly upright.

Then comes a trio of graphs upon which he lays out the relative amount of control deflection for the ailerons, elevator, and rudder throughout the roll, as it passes through 90, 180, and 270 degrees and comes back to straight and level. Throughout he emphasizes the use of smooth control inputs. "I don't know why people think you've gotta jerk the airplane around — you don't."

But most of all, his tone and demeanor deliver the message he closes our discussion with: "It's going to work out, and it's predictable." This addresses directly common concerns, and downright fears, that many students carry with them to the school. What we don't understand we often view as chaotic. But what happens during these elementary aerobatic maneuvers — spins included — can be explained and replicated. Kershner is careful to break down each maneuver into its simplest elements so that understanding comes more easily, and a student's questions are answered as much as possible before getting into the airplane.

Flying the basics

Back in the airplane the next day, Cavagnaro and I ready ourselves for our third flight, in which we'll do more rolls, loops, and spins. Like each time before, we've done a complete preflight of the airplane — though Kershner has owned this airplane for a couple of decades, he still attends to it like a new patient each time he approaches it for flight, and we do the same. And once strapped in, I review the means by which we'll exit the airplane if we need to. This, too, we run through each time.

"Unlatch the door, grab the D-ring securing the door hinges, and pull," says Cavagnaro, as she steps through each motion. "Push the door free if you need to, and then put your right hand on the door jamb. Grab the seat-belt release with your left hand and pull it across you. Reach for the gear strut with your left hand, and pull yourself out and clear of the aircraft." Got it.

We climb out of Franklin County Airport, over the trees and off the bench. The ground falls away and gives us an instant 1,000-foot advantage. That's good, because even with a Lycoming O-235 110-horsepower engine, the Aerobat still takes its time to climb. We need to achieve 6,000 feet msl to start today's practice; that gives us roughly 5,000 feet of clear air to play with. Throughout the maneuvers, we never get below 3,500 feet.

I try a couple of aileron rolls to the left to warm up, then I do one to the right, which isn't quite so pretty. As Kershner had explained prior to our flight, the deck is stacked against you a bit during the right aileron roll: You must roll against the engine's torque, and you sit on the outside of the roll (if you sit in the left seat of the side-by-side Aerobat). However, the control wheel is easier to use in this direction. But the upshot is that you're going to lose a little more altitude in the right-hand roll, and it's going to take a couple of seconds longer to execute.

Next, we do some loops. We dive to pick up airspeed: 120 knots. During the first loop, Cavagnaro retains control of the throttle while I work my way through the combination of elevator and rudder pressure required to keep things, well, vaguely circular in profile. Then I get the throttle, which goes to full as I pull up into the first 90 degrees of the loop. We lighten up at the top, and I relax back-pressure a little as the airspeed decays to about 65 knots and the stall horn sounds. I switch from looking at the left wing tip to looking through the top of the aircraft — eyebrow windows in the ceiling provide a view to the ground straight down. I pick up some railroad tracks to align the nose, and I get ready to reduce the power as we come past 135 degrees. (I hear Kershner's voice from the lesson: "Throttle back, throttle back, for God's sake, throttle back!") We pull about 3 Gs in the bottom of the loop and finish it off.

The spin and roll practice could honestly get you out of trouble — whether from an encounter with a heavy's wake on final or from a bout with spatial disorientation in the clouds. But the loop is pure fun. And if you like it enough, there's plenty more to explore. Kershner and Cavagnaro offer continued instruction for pilots who wish to explore snap rolls and square loops in the Aerobat. The airplane, which is a reinforced version of the standard 152 (Aerobat versions of the 150 also were built), is certificated to basic Aerobatic category limits, plus 6 and minus 3 Gs.

Just the beginning

As with most of the training I've taken over the years, after three hours in the hot seat I feel like we've just seen the tip of the iceberg. But by going at a measured pace (the pair lets the student call the shots) we avoid the common pitfalls of nausea, intimidation, and regressional fear that can come from tackling too much too soon. Can't hardly wait to come back for more — and that's the goal.

Kershner figures that he's taken 659 students through his courses at last count. If you figure a couple of dozen spins per course, and five turns per spin, that's...well, that's a whole lot of seeing the world go round.


E-mail the author at julie.boatman@aopa.org.


Walk through a Cessna Aerobat preflight and hear more wisdom from spin master William Kershner on AOPA Online.


You can get more information on the Ace Aerobatic School by calling the Franklin County Airport at 931/598-1910 or by visiting the Web site.


Variations on the Stability Theme

Some scientists will take a perfectly good airplane and muck with it — all in the name of "research." However, at the University of Tennessee Space Institute (UTSI) near Tullahoma, Tennessee, the results of such tinkering are a greater understanding of what makes a particular aircraft behave the way it does under specific conditions. Two North American Navions have been modified so that the stability designed into the airplanes can be adjusted and flight-tested.

Rich Ranaudo, project leader and test pilot, and Catherine Cavagnaro, flight instructor and professor of mathematics at the nearby University of the South in Sewanee, regularly fly students in the UTSI Flight Research Center program so that they can see firsthand the effects of varying stability on aircraft handling, comfort, and safety. "We set the Navion up to share the same short-period longitudinal-stability characteristics as the Twin Otter in various configurations," says Cavagnaro. Engineering students gain a lot from the ability to experience various flight regimes in an actual aircraft, rather than simply modeling the aircraft behavior on the ground.

UTSI's variable-stability aircraft is used in particular to simulate actual icing conditions. "Students were asked to maneuver the aircraft at altitude, fly instrument approaches into the Tullahoma airport, and evaluate the handling characteristics in the various configurations (to model various ice accretions)." In fact, the Flight Research Center will offer a short course on aircraft icing, to be held from October 16 through 20 at Tullahoma Regional Airport/William Northern Field. First introduced in 2004, the course uses in-flight and ground simulations using NASA icing data and includes a combination of guest lecturers and UTSI staff who are experts in various fields of icing technology, flight testing, and flight operations. A one-hour ground-based simulator training session in NASA's ice-contamination-effects flight-training device is included. Enrollment for the one-week course is limited to 17 participants; the fee is $1,765 plus $440 for the training flight. Early enrollment is suggested. For more information or to register, contact Becky Stines, director of continuing education, at 931/393-7276, or e-mail bstines@utsi.edu.