Aerobatic Flight

 

All eyes on the ground are fixated on the vintage World War II Stearman as it plummets from the sky, spiraling downward toward certain disaster. The antique biplane falls faster and faster, the growl from its powerful engine growing ever louder. The doomed pilot has obviously lost control and is about to crash when suddenly, just inches above the tarmac, the Stearman pulls back up and roars off into the sky to the cheers of an admiring audience. Welcome to the world of aerobatic flying!

 

Aerobatic flight, a specialized area of general aviation, is defined as “precise maneuvering in three-dimensional space.” Maneuvering is broken down to three components—position, velocity, and attitude. A textbook aerobatic aircraft's position would be precisely controlled along all three axes (pitch, roll, and yaw) and could be quickly reoriented to any other position. Such an aircraft is a theoretical impossibility since it must travel through, and is influenced by, an unpredictable ocean of air. An idealized example of a true aerobatic vehicle can be conceptualized by observing the Space Shuttle Orbiter's ability to maneuver on all three axes when operating in the weightless vacuum of space and using this image as a yardstick to measure earthbound aerobatic maneuvers.

 

Lincoln Beachey is widely recognized as the “father” of aerobatic flying, even though his feats were, at first, dismissed by none other than Orville Wright as mere “optical illusions.” All such doubters were converted during a now-legendary 126-city barnstorming tour in 1914 when Beachey, known as “the flying fool,” dazzled crowds across the country flying stunts in his airplane, the Little Looper. Luminaries such as Thomas Edison and Carl Sandburg became aerobatic fans and even Orville Wright retracted his original comments, describing Beachey's exhibitions as “poetry.”

 

Evolving directly from the early air racing and military training airplanes, these initial aerobatic aircraft were usually oversized but underpowered. Such factors combined to produce rather lackluster aerobatic performances (by today's standards) since aircraft maneuverability was sluggish and the ability to climb vertically was limited.

 

In spite of equipment refinements that allow inverted flight capability (such as upgraded airfoils, fuel, and oil systems), even the best aerobatic aircraft cannot fly for long periods in unnatural flight attitudes. Engine torque and wash from a spinning propeller cause an aircraft to respond differently when maneuvering to the right than it does to the left—forcing aerobatic pilots to learn their maneuvers in both directions. These aerodynamic limitations are such that no aerobatic aircraft in existence can efficiently fly on its side—the glowing claims of “knife edge” climbs or spins notwithstanding.

 

Improved control during stall, snap roll, and spin maneuvers cannot completely offset the effects of engine torque during the ascent and descent phases of flight. An aerobatic aircraft with sufficient thrust to briefly “hang” on its propeller for a moment is soon overcome by engine torque that, in turn, rotates the aircraft. The skilled aerobatic pilot understands these design limitations and learns never to yield control of an aircraft in order to escape from an aerobatic maneuver.

 

A robust aerobatic biplane, the Grumman Gulfhawk II, generated considerable excitement on the air show circuit from 1936 to 1948, performing at the New York World's Fair, the Cleveland Air Races, and the Miami All-America Air Show. Originally built by Grumman for Gulf Oil, the Gulfhawk II was specifically designed to bear up under the high structural stresses of aerobatic flying and modified to endure inverted flying for durations of up to 30 minutes.

 

A German-built biplane, the Bücker Bü-133 Jungmeister, became the dominant force in aerobatic competitions in the United States and Europe from the mid-1930s until the outbreak of World War II. Agile and responsive to its controls with ailerons on both upper and lower wings, the Jungmeister was ideally suited for aerobatic flying because of its high power-to-weight ratio. The Jungmeister also has a darker side to its history—it was used as a training aircraft by a civilian German flying club known as the Luftsportverband, whose pilots later formed a clandestine Air Force that eventually evolved into the Nazi Luftwaffe.

 

The face of aerobatic flying changed forever in 1945 when Curtis Pitts built the first aircraft specifically designed for aerobatics—the Pitts Special S-1. Pitts envisioned an aircraft that could flout gravity and respond crisply on its controls—a smaller aircraft than the war-era biplanes that could climb, roll, and maneuver swiftly. Pitts abandoned the concept of a large radial engine and designed a swept-wing aircraft powered by a smaller, lighter, horizontally-opposed engine with a center of gravity that allowed for tight snap rolls (A snap roll is produced by flying just above the stall speed, applying a sudden yaw with the rudder, applying the opposite aileron, and pulling back on the yoke. One wing stalls and the plane rolls over).

 

The resulting Pitts line of aerobatic aircraft—small (with only a 17-foot (5-meter) wingspan), lightweight, and extremely agile with a high power-to-weight ratio—soon dominated aerobatic competitions. One of the more famous Pitts aircraft, a hand-built S-1C model known as the Little Stinker, was flown by another pioneer in aerobatics, Betty Skelton, who won her first women's International Aerobatics Championship in 1949 at age 23 and won it again the following year. At a time when there were few women aerobatic pilots, Skelton was a trailblazer and achieved acclaim as the first woman to complete an aerobatic maneuver known as the “inverted ribbon cut” in which an airplane flying upside down, only a few feet off the ground, slices a two-foot (0.6-meter)-wide ribbon strung between two poles. In fact, during her first attempt at the inverted ribbon cut, the engine of her airplane stalled when flying upside down very close to the ground. Somehow, she amazingly recovered from the stall, righted the aircraft, and landed safely. From then on, the ribbon cut was the highlight of her act.

 

An aerobatic kit plane named the Stephens Akro inspired similar monoplane designs that overcame the Pitts' major design drawback, the inability to climb vertically. The lower drag from the single wing configuration translated into higher airspeeds. Speed is not a necessity for an aerobatic aircraft but it is often desirable since it can be translated into altitude.

 

The Akro-derived aerobatic designs were quickly overshadowed by specialized aircraft, such as the German Extra 300, that continued the evolution process by incorporating design refinements that separated them from other conventional light aircraft. Increased structural strength (including the use of composites), more powerful engines (which generate a higher power-to-weight ratio), larger propellers, and improved aerodynamic surfaces and controls have yielded aircraft that are well suited to the demands of aerobatic flight.

 

Patty Wagstaff won the 1991 U.S. National Aerobatic Championships flying an Extra 260 aerobatic aircraft, becoming the first woman to win the title since the men's and women's competitions were combined in 1972. She went on to defend her title for the next two years, flying an Extra 260 in 1992 and an Extra 300S in 1993.

 

Air shows featuring aerobatic flying demonstrations have become enormously popular in the United States and throughout the world. More than 27 million people annually attend air shows in the United States, making it one of the country's top three spectator sports, ranking right alongside Major League Baseball and NASCAR auto racing. It is also one of the most dangerous: each year, several aerobatic pilots are killed due to pilot error or equipment malfunction.

 

Aerobatic pilots accept and understand the inherent dangers of their occupation. Striving to minimize their risks, professional aerobatic pilots have honed their skills with years of constant practice and through an in-depth understanding of both the physics of flight and the performance characteristics of their specific type of aerobatic aircraft.

 

A dictionary of aerobatic flight, first published in 1961, listed every conceivable aerobatic maneuver and position defined at that time, 3,000 in all. Today, this list has grown to more than 15,000 maneuvers as pilots experiment with the capabilities of their aircraft. This demonstrates that aerobatic maneuvers conform to the natural evolution of flight that has occurred throughout history—as aircraft capabilities continue to improve, skilled pilots learn to exploit those improvements.

 

—Roger Guillemette

 

Sources:

 

Marrero, Frank. “Lincoln Beachey: The Forgotten Father of Aerobatics.” Flight Journal (March/April 1999).

Szurovy, Geza, with Goulian, Mike. Basic Aerobatics New York: McGraw Hill Professional Publishing, 1994.

Wagstaff, Patty, with Cooper, Ann L. Fire and Air: A Life on the Edge. Chicago: Chicago Review Press, 1997.

Williams, Neil. Aerobatics. North Branch, Minnesota: Specialty Press Publishers & Wholesalers, 1993.

 

Online Sources:

 

“Aerobatic Champions.” National Air & Space Museum. http://www.nasm.si.edu/galleries/gal104/aerochamps/

Allison, Rick. A Short History of Aerobatics. Model Aviation, August 1999. http://jmrc.tripod.com/fa/aero/aero1.htm

British Aerobatic Association. http://www.aerobatics.org.uk

“Bücker Bü-133C Jungmeister.” National Air & Space Museum. http://www.nasm.si.edu/nasm/aero/aircraft/buckerbu133.htm

Carter Hummingbird Aerobatic Aircraft. http://www.esotec.co.nz

Dininny, Paulette. “The Little Plane That Could.” (abstract from Smithsonian Magazine, December 2001.) http://www.kidscastle.si.edu/channels/air-space/articles/air-spacearticle11.html

“Extra 260 Aerobatic Aircraft.” National Air & Space Museum. http://www.nasm.si.edu/nasm/aero/aircraft/extra260.htm

“Grumman G-22 Gulfhawk II.” National Air & Space Museum. http://www.nasm.si.edu/nasm/aero/aircraft/grumman_gulfhwk.htm

International Aerobatic Club. http://www.iac.org

“Pitts Special S-1C Little Stinker.” National Air & Space Museum. http://www.nasm.si.edu/nasm/aero/aircraft/pitts.htm

 

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International Technology Education Association	Standard 8	Students will develop an understanding of the attributes of design.
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