NASA Developed The Supercritical Wing In The 1960s - BUT - No One Was Interested - March 29, 2013

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NASA Developed The Supercritical Wing In The 1960s – BUT – No One Was Interested – March 29, 2013

“Robert Novell’s Third Dimension Blog”

Good Morning and Happy Monday—I hope everyone had a good Easter and had a little time to enjoy life, family, and friends. I was off the grid for the last four days so this is why the blog for Friday is a little late.

Today I want to talk about a man whose contributions to military, commercial, and corporate aviation in the twentieth century are second to none. This man is NASA scientist Richard T. Whitcomb who brought us the “Area Rule,” supercritical wing design, and winglets.


Richard T. Whitcomb

Airfoil research in the United States had reached a standstill by the late 50s, and aerodynamicists had become more interested in other research questions such as how the air flowed over an aircraft’s skin when it traveled faster than the speed of sound, and how much wings should be swept back. Although designers still developed new airfoils, they only did so on a case-by-case basis for use on specific airplanes. Few aerodynamicists, or manufacturers, undertook basic research on airfoil shapes for a whole class of aircraft.

That changed in the 1960s when NASA scientist Richard T. Whitcomb developed the supercritical airfoil. Whitcomb was already famous for developing the “Area Rule” of supersonic flight which resulted in some fighters of the mid 1950s having a pinch midway along their fuselage like an hourglass. Probably no one understood how air flowed over an aircraft as it approached the speed of sound better than Whitcomb, and he applied that knowledge to a new problem associated with the compressibility of air over an aircraft wing as it approached the speed of sound.

At the time, commercial passenger jets like the Boeing 707 cruised at speeds of around Mach 0.7 to Mach 0.8. The people who ran the airlines wanted planes that could fly faster, at Mach 0.9 or 0.95, and still be fuel efficient; however, as an aircraft approaches the speed of sound it reaches a point where the air flowing over the wings reaches supersonic speeds, although the plane itself is still moving slower than Mach 1, causing a dramatic increase in drag. The airspeed at which this occurs is called the critical Mach number for the wing. For example, if the air flowing over a wing reaches Mach 1 when the aircraft is only moving at Mach 0.8, the wing’s critical Mach number is 0.8. The spot where this happens on the wing is usually about halfway between the leading edge and the trailing edge of the wing.

Designers deal with this dramatic increase in drag by angling the wings back from the fuselage, making them thinner, and using other features designed to reduce drag. But all of these solutions increase structural weight, decreasing range and fuel economy, and making them unattractive for commercial use. In addition, thinner wings cannot be used to store fuel, a common location for fuel tanks on passenger planes.

In the early 1960s, Whitcomb sought to develop a new airfoil shape that would allow the wing to reach a higher speed before the airflow over it reached the speed of sound. He proposed a new airfoil shape featuring a well-rounded leading edge, relatively flatter upper surface that pushed the critical Mach point farther back on the wings, and a sharply down-curving trailing edge that increased lift. He called this the “Supercritical” Airfoil.” Whitcomb tested this wing in NASA’s 8-foot transonic pressure tunnel at Langley, Virginia, and the tests suggested that the supercritical wing might allow planes to travel up to 10 percent faster.

The wind tunnel tests, however, involved small models with low Reynolds numbers making tests of the supercritical wing unreliable. For full-scale tests, NASA engineers chose a Navy F-8U fighter as a test aircraft. The F-8U was normally a fighter aircraft capable of supersonic flight, but NASA engineers wanted to use it to determine if an aircraft could cruise just below the speed of sound in the transonic region. NASA engineers equipped the plane with a slender, graceful supercritical wing and tested it in 1971. The F-8U flight tests proved that Whitcomb’s wind tunnel results were correct: the supercritical airfoil would allow planes to cruise at higher speeds. Passenger jets could be equipped with wings that would allow them to fly at Mach 0.9 or 0.95, instead of Mach 0.7 or Mach 0.8, and still be relatively fuel efficient.

NASA presented the resulting wind tunnel and flight test data at a conference in 1972. Industry designers were intrigued by the data and started to evaluate it. They then came up with a surprising conclusion: instead of increasing cruise speed to around Mach 0.9, they would keep the speed around Mach 0.8, but use the supercritical shapes to increase fuel efficiency. A more efficient aircraft could travel farther on the same amount of fuel. A good example of this is the Boeing 787 which was originally proposed to cruise at Mach.90, but after careful consideration, and collaboration with their customers, they adopted Mach .85 which gave them a twenty percent fuel savings over the B-767 and the A-330-200 which Boeing considered to be the dominant players in the long haul market for those operators using, or wanting to use, twin-engine transports.

Below is the Wall Street Journal’s tribute to Richard T. Whitcomb after his death in 2009:

He Sparked Supersonic Flight

with a Coke Bottle and File

Richard T. Whitcomb dreamed up techniques that made supersonic flight possible and innovations that endure on passenger jets today.

Mr. Whitcomb, who died Oct. 13 at age 88, solved a problem that had bedeviled aviation engineers, whose designs couldn’t achieve supersonic flight even though they seemed to have enough power. Increased wind resistance at speeds approaching the speed of sound was the problem. Engineers took to calling it the “sound barrier.”

Mr. Whitcomb’s solution was to taper the airplane’s fuselage in a manner he often likened to a Coke bottle, which dramatically reduced drag. Within three years of Mr. Whitcomb’s discovery in 1951, U.S. Air Force interceptors were flying at supersonic speeds.

It was the first of three revolutionary advances Mr. Whitcomb designed. Another was a new and more efficient wing shape used today on nearly all passenger jets. And he designed “winglets” — small drag-reducing vertical panels found at the wing-tips of many commercial jets.

“I think he was the most significant aeronautical engineer operating in the second half of 20th century,” says Tom Crouch, a curator at the Smithsonian National Air and Space Museum. “His fingerprints are on every jet plane flying today.”

Mr. Whitcomb made his discoveries as a government engineer at the Langley Research Center in Hampton, Va., which had developed state-of-the-art wind tunnels where he could test his ideas in supersonic winds. He would spend hours at his desk chain-smoking.

In the 1960s Mr. Whitcomb developed the specially shaped wing known as the supercritical wing, an improved design that increases fuel efficiency at near-supersonic speeds. He filed down the model edges, flattening the top of the wing and rounding the bottom to find the optimal shape. He had a reputation for being able to visualize airflow.

During round-the-clock wind-tunnel testing, he lived in the laboratory and slept on a cot. Although he never married, he would sometimes emerge from marathon sessions for Sunday dinner with family who lived nearby. “Uncle Dick rarely showered,” recalled a nephew, David Whitcomb.

Richard Whitcomb inaugurated himself as an aeronautical engineer at age 12, commandeering the basement of his parents’ home in Worcester, Mass., as a workshop where he sought to improve common model planes.

“There’s been a continual drive in me ever since I was a teenager to find a better way to do everything,” Mr. Whitcomb told the Washington Post in 1969. But it was the technical problems involved and not flying himself that interested him.

“It had nothing to do with Lindbergh or anything like that,” he said. “It was just the fascination of making a model that would fly.”

Mr. Whitcomb said his first innovation was a method of doubling the power available from the rubber bands that powered his early models. After studying at the Worcester Polytechnic Institute, he went to work at Langley, in 1943, where he quickly acquired a reputation as a wunderkid, according to a National Aeronautics and Space Administration history of the lab.

When he had the idea for the Coke bottle-style fuselage, “It was like a bulb lighting up but it wasn’t out of the blue,” Mr. Whitcomb said in the Washington Post interview. Others at Langley had been working on the same problem.

His method for sculpting a plane to reduce drag became known as “Whitcomb Area Rule” and was kept secret at first. After it was made public, he won the 1954 Collier Trophy, awarded by the National Aeronautics Association for “basic knowledge yielding significantly higher airplane speed and greater range.”

In 1973, President Richard Nixon conferred the National Medal of Science on Mr. Whitcomb. His secretary had to remind him to buy black shoes to wear with his tuxedo, and he forgot his suspenders, so he met the president with his shirt pinned to his pants.

Mr. Whitcomb retired in 1980. He worked as a consultant to the aviation industry as well as for yacht designers, whose innovative keels borrowed winglets in the 1980s.

Although he did much to define modern flight, Mr. Whitcomb never learned to fly.

Source Document

That’s it for now. Have a good week, watch the video below, and remember to keep family and friends close. Life is short and when I woke up this morning I reminded myself that mine is one day closer to coming to an end. I need to work on my list a little harder.

Robert Novell

March 29, 2013