WBreeze : Aviation and Aerobatics : Introduction to Competition Aerobatics

The popular characterization for this kind of flying is "stunt flying." Pilots who engage in this activity are sometimes thought to be crazy daredevils. This romantic and somewhat sensational view is common in the media because it is exciting. It sells advertising and gets attention. The reality is very different.

Aerobatics competitors belong to the International Aerobatics Club (www.iac.org), an organization of pilots who work to improve their skills and perfect the accurate performance of aerobatics figures and routines to exacting standards.

Judges grade the contestants, much like the figure-skating contests popular in the Winter Olympic Games. Aerobatics pilots are sober, careful individuals who take pride in the attention they give to the safe flying and maintenance of their airplanes.

Aerobatics is a physically and mentally challenging sport that takes years to learn and a lifetime to master. World class pilots start with some natural talent, then dedicate thousands of hours in the air and more on the ground to train to be the very best.

As with the best baseball and football players, many desire the goal and few attain it. Unlike baseball and football players, the financial rewards are few. The primary reward is more like that of Olympic class athletes. It is the pleasure of having succeeded in creating a physical performance that is highly demanding, difficult, and sometimes beautiful to watch.

The Airplanes

Biplanes

Biplanes are popular in all but the highest category of aerobatic competition. Most of the biplanes you will find at a regional contest such as the Kathy Jaffe Challenge were designed by one man, Curtis Pitts, and are generically referred to as "Pitts Specials." The wing construction uses wooden spars and ribs with steel wire reinforcements all covered with fabric. The fuselage is welded steel tubing. The fuselage from the engine to the cockpit has sheet-metal covering. The remainder of the fuselage and tail has fabric covering.

biplane

Photo by Stephen Seidel

Monoplanes

While the Pitts dominated aerobatics in the 1960's, world class aerobatics is now dominated by high-performance monoplanes. There are many different monoplane models. Some of their names are, Sukhoi, Yak, Zlin, Extra, Cap, Edge, and Giles. Most have a welded steel tubing fuselage. Some use fabric covering; some use sheet steel. The latest models use lightweight carbon composite material.

The Aerobatic Box

All of the competitors at IAC sponsored contests perform their aerobatics figures in a safe zone called the "Aerobatic Box." The box keeps competitors in front of the judges.

the aerobatic box

The box lies over a one square-kilometer area on the ground delimited by white markers visible from the air. The markers show the corners, the center, and the center of each side. One kilometer is about 3,300ft.

The altitude for the bottom of the box varies for different levels of competition. The most advanced pilots may descend as low as 300ft above the ground. The beginning pilots must remain over 1,500ft above the ground.

There is a maximum altitude for all pilots of 3,500ft. This keeps the pilots low enough to be seen by the judges.

Pitch, Roll, and Yaw

Most airplanes, and all airplanes in aerobatic competitions, are controllable in three dimensions. The names of the three dimensions are "pitch," "roll," and "yaw."

Pitch is motion of the airplane's nose up and down. An airplane will generally climb as the nose (pitch) goes up and descend as the nose (pitch) goes down. When an airplane rolls the wingtips move up and down. Yaw is motion of the airplane's nose side-to side.

An airplane turns by coordinated use of pitch, roll, and yaw. An airplane that has rolled into a turn is sometimes described as being "in a bank," or "banked," as if following a banked, high speed curve in a road.

Point your web browser to the EAA Young Eagles Web site at www.youngeagles.org for an excellent interactive demonstration of pitch, roll, and yaw.

Aerobatic Sequences

An aerobatic sequence is a series of clearly defined aerobatic figures. Aerobatic figures are individual maneuvers such as loops and rolls that begin and end with horizontal, level flight (upright or inverted). The system of diagramming aerobatic figures and sequences was developed by Jose L. Aresti in the early 1960's. It shows what a pilot is expected to fly in a manner similar to the way music shows what a musician is expected to play.

The paragraphs that follow describe some of the notes, or aerobatic figures that appear in an aerobatic sequence. They show the Aresti symbol, give the name of the figure, and provide a short description of some of the things the judges look for in the figure.

Aresti slow roll The Slow Roll
requires that the aircraft roll without changing its flight path. Judges will deduct points if the aircraft changes direction in the roll, pitches up, or down, or changes rate of roll during the maneuver.
Aresti loop Loop:
The competitor must fly a perfect circle in the sky regardless of wind conditions. Judges will deduct for variations in the radius of the loop and for changes in roll or in heading.
Aresti turn Turn:
The competition turn requires the pilot to roll on heading to a bank of at least sixty degrees, immediately begin a constant rate change of heading without climbing or descending, stop after 90, 180, 270, or 360 degrees, then roll on heading to level flight. Judges deduct for inadequate bank, changes in rate of turn, climbing or descending, and finishing off-heading.
Aresti spin Spin:
The spin is a controlled maneuver in which the airplane essentially falls downward while rolling and yawing at the same time. Judges look for the nose and a wing to drop together, at the same time, in the entry to the spin. They look for a clean vertical down line after an exact number of quarter-rotations.
Aresti Immelman The Immelman
is a half-loop up followed immediately by a roll to upright. The half loop up must have constant radius. The roll must occur on a level line without delay after the half loop up.
Aresti half-Cuban The Half-Cuban
requires a five-eighths loop of constant radius. The pilot must draw a forty-five degree line and center a roll to upright on that line. Judges deduct for changes in radius, steep or shallow lines, and rolls not centered on the line.
Aresti goldfish Goldfish:
The competitor flies two forty-five degree lines connected by a three-quarter loop. Any rolls must be centered on the lines. The loop must have a constant radius.
Aresti wedge The Wedge
has a vertical line and a forty-five degree line. Judges deduct if the airplane is not vertical. If the airplane is slightly on its belly they call it "positive." If it is slightly on its back they call it "negative."
Aresti hammerhead Hammerhead
In the United States we call this a "Hammerhead." Elsewhere it's described as a "Stall Turn." The competitor flies straight up until the plane slows nearly to a stop, then turns the plane on the yaw-axis, with the rudder, and flies straight down. Judges deduct points if the plane rolls or pitches during the turn.
Aresti snap roll A Snap Roll
is a very fast roll caused by rapid change in pitch and yaw, not by the ailerons as in a slow roll. Watch to see the nose move up abruptly just before the rotation begins.
Aresti inverted line Inverted flight:
The Aresti symbol will show a dotted line whenever pilots must push the nose away from them to maintain the flight path.
Aresti rolling turn A Rolling Turn
will have one or more rolls integrated with the turn. The rolls may be inside, in the same direction of the turn; outside, in the opposite direction of the turn; or alternating inside and outside. The rate of turn and the rate of roll must be constant. Both the turn and the rolls must end at the same time after 90, 180, 270, or 360 degrees of heading change.
Aresti four point roll Point roll:
Rolls may contain hesitations, or "points." A two indicates hesitations every half roll. A four every quarter roll, and an eight every eighth roll. The pilot must pause the same amount of time at each point and move between points with a constant roll rate. The points should look like the ticking of a clock.
Aresti tail slide In a Tail Slide
the airplane will briefly fly backward. The competitor flies a vertical line up until gravity begins to pull the airplane back down tail-first. The pilot must cause the plane to flip nose to tail wheels-down (positive) or wheels-up (negative) after sliding at least one-half the length of the fuselage. The pilot must fly a vertical line down before resuming level flight.
Aresti negative snap A Negative Snap Roll
is much like the positive snap roll described earlier, only watch for the nose to move downward (toward the wheels) rather than upward. The nose will move abruptly before the onset of a very rapid roll.

Competition Categories

Powered airplane competitions of the International Aerobatic Club have five categories, or levels of competition of increasing level of difficulty. The five categories are Primary, Sportsman, Intermediate, Advanced, and Unlimited.

The following paragraphs explain each category and show an Aresti diagram of the 2005 known compulsory aerobatic sequence for that category.

Primary

The Primary category is the most basic, entry level category of aerobatic competition. Pilots must demonstrate a spin, loop, roll, and competition turns.

2005 Primary Sequence

Sportsman

The Sportsman category offers a greater challenge to the beginning competitor. It includes a greater number and variety of figures, including the hammerhead (figure 6).

2005 Sportsman Known

Sportsman competitors may design a "free" sequence. A free sequence is a sequence of the competitor's design that satisfies constraints on the type of figures flown, the number of figures, and the total amount of difficulty of the sequence.

Intermediate

The Intermediate category adds the snap roll and some inverted figures. Intermediate competitors must provide a free program. If there is time at the contest they may also be required to fly an "unknown" compulsory sequence.

The Contest Director provides the unknown sequence to the competitors at least 18 hours before the competitors must fly it. Competitors may have practiced many of the figures in the unknown, but have no opportunity to practice the sequence before performing it for the judges at the contest.

You may see competitors doing a strange dance next to their airplanes as they rehearse the sequence on the ground before their flight.

2005 Intermediate Known

The 2005 Intermediate Known included a snap roll on a forty-five degree down line (Figure 7), a roll integrated in a loop (Figure 10), an inverted exit from Figure 5 and entry to Figure 6, and an inverted quarter-turn (Figure 13).

Advanced

The Advanced category includes more challenging figures with multiple rolls and snaps on each figure and more inverted figures. The Advanced category adds the rolling turn.

Advanced pilots fly a known compulsory, free, and unknown compulsory sequence.

2005 Advanced Known

The 2005 Advanced Known included a snap on a vertical down line (Figure 2), a rolling three-quarter turn (Figure 4), and opposite point rolls (Figure 9).

Unlimited

The Unlimited category is the most difficult of all. Only the most capable pilots flying the most capable airplanes can manage the figures required in the Unlimited category.

Pilots flying Unlimited are flying at the level of air-show performers and world competitors.

2005 Unlimited Known

The 2005 Unlimited Known included snap rolls on a vertical line up (Figure 1), combinations of snaps and rolls (Figures 4, 5, and 9), and negative snap rolls (Figures 6 and 9). The sequence also included a tail slide (Figure 8).

Contacts

For more information about the International Aerobatic Club (IAC) see www.iac.org

For more information about the local IAC Chapter 52 sponsoring the Kathy Jaffe Challenge, including membership, aerobatics rides, and getting started in aerobatics see www.iac52.com

This introduction was written by Douglas Lovell and is Copyright 2005, 2006 IAC and IAC Chapter 52.