The Need for Speed | Flight Today | Air & Space Magazine

The Need for Speed

Everything is in place for the development of a supersonic business jet-except U.S. Federal Aviation Regulations.

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I CAN'T IMAGINE A MORE HUMBLING END for an aviation legend.

Late last November, the national TV news shows all carried footage of a Concorde supersonic transport being barged slowly up New York's Hudson River to the Intrepid Sea-Air-Space Museum in Hudson River Park.

The image of the airplane, perched atop the barge like a wounded stork, still proudly holding its head high for all the media's cameras and crowds of onlookers, will be forever in my memory.

For many years I marveled as the Concordes swooped to a landing at Washington Dulles International Airport in northern Virginia. I was thrilled not only by the grace of their approach but by what they symbolized about the future of civil air transportation—a future defined by speed. With the retirement of the Concorde, was that future invalid? Did the Concorde's demise indicate that air travelers don't value speed and time?

This issue was addressed at a recent workshop on the future of supersonic flight sponsored by the Federal Aviation Administration. Richard Smith, executive vice president of Netjets, an organization that sells shares of business jets, recounted that fractional owners of aircraft sometimes find that their airplanes are not available when they want them because they are already in use by another owner. In such a situation, Netjets, like all fractional providers, will offer the owner an upgrade to another aircraft.

Smith noted that when owners of the fastest business jet available today, the Cessna Citation X, which cruises at Mach .92, need a substitute airplane, they are not interested in upgrading to a larger airplane; they want one equally fast. Their need is speed. There was no doubt in Smith's mind that a supersonic business jet would have buyers, and Netjets would surely be one of them.

Business jet manufacturers have been exploring the idea of a supersonic business jet for many years, but they realized that for customers to take full advantage of it, the craft would need to be able to fly supersonic over the world's landmasses, not just its oceans. The Concorde was not permitted to fly supersonic over the continental United States because federal regulations forbade it.

Currently, Part 91 of the Federal Aviation Regulations prohibits all civil aircraft operation at speeds greater than Mach 1 over the United States and imposes flight limitations to ensure that civil supersonic flights entering or leaving the country will not cause a sonic boom that could reach the surface of the landmass of the United States. Even if a supersonic aircraft slows to subsonic speed, its sonic boom plows on ahead of it, so this rule creates a buffer zone offshore.

In 1990, the Federal Aviation Administration proposed to amend the noise standards and operating rules for future civil supersonic airplanes. After analyzing the comments that this proposal received, the FAA determined that further investigation and research was necessary before a final rule could be developed. Specific noise standards have therefore not been established yet for future civil supersonic airplanes. The FAA anticipates that future proposed standards will require that an airplane's noise impact on a community not exceed that of a civil subsonic airplane certified to the most restrictive current noise levels. Is this feasible?

It may be. In 1999, NASA efforts to develop technologies for a supersonic large transport were terminated after all the manufacturers involved cited the high cost of development and what were anticipated to be stringent federal regulations regarding noise and emissions.

In 2000, the National Research Council conducted a study to identify breakthrough technologies for overcoming key barriers to the development of a commercial supersonic aircraft that would be both environmentally acceptable and economically viable. The study,

"Commercial Supersonic Technology, The Way Ahead," concluded that none of the anticipated obstacles to commercial supersonic aircraft are insurmountable. It went on to note that while NASA should have its eye on supersonic commercial transport, research was also needed to determine the impact of sonic booms produced by smaller supersonic business jets.

The Quiet Supersonic Platform (QSP) program, sponsored by the Defense Advanced Research Projects Agency, began in 2000 and is a Congressionally mandated effort to develop technologies that could reduce the impact of a sonic boom to 0.3-pound-per-square-foot pressure propagated to the ground by the shock wave. This is significantly less than the 2.0 pounds per square foot created by the Concorde, an impact that restricted it from flying at supersonic speeds over land.

Last year, the QSP Program, in conjunction with Gulfstream Aerospace and Raytheon Aircraft Company, demonstrated that aerodynamic shaping of a modified Northrop F-5E fighter reduced the craft's sonic boom signature in flight. The modification consisted, most visibly, of an enlargement to the forward fuselage to make it more bulbous. The test also confirmed that the size of the aircraft has a direct effect on the noise heard on the ground. The QSP demonstration was a success in that it indicated that by simply altering the shape of the fuselage and other aerodynamic elements, designers can dramatically reduce the noise produced when an aircraft exceeds Mach 1.

Even without advanced shapes, the smaller the airplane, the smaller the sonic boom it will create. In fact, the overpressure produced by advanced designs may not be described accurately by the term "sonic boom." Those familiar with the QSP demonstration flights suggest that "sonic whoosh" or "sonic poof" may more accurately convey the sound.

Therefore the development of a quiet supersonic business jet is not only feasible, it is likely.

In light of this research, and because the FAA's rules had not been re-examined for more than two decades, last November the agency requested public comment on the issue and sponsored a workshop on supersonic flight. Gulfstream Aerospace, long interested in developing a supersonic business jet, submitted substantial details for what it calls a Quiet Supersonic Jet. The initial design requirements for the QSJ are presented in the sidebar (opposite).

At the FAA workshop, Gulfstream Aerospace was the most vocal company among the participants, but all manufacturers of business jets attended, along with the makers of business jet engines. The General Aviation Manufacturers Association (GAMA), which chaired the panel of airplane manufacturers, will place a high priority on getting the FAA to change the regulations that govern operation and design of this important new class of airplane.

GAMA told the FAA that it is essential to begin immediately the process of changing the regulations that prohibit supersonic flight. Since these rules were established in the 1970s, technologies have advanced significantly, and recent studies have shown that safe and environmentally acceptable designs for aircraft and engines are not only possible but likely to have sufficient market demand. The first new supersonic airplanes are likely to be advanced general aviation aircraft—business jets.

GAMA also noted that it is essential that the FAA maintain sufficient research and development activities to support this rulemaking process. And as most supersonic civil operations will involve international flight, the FAA should also begin negotiations with its counterpart agencies in other nations to revise international standards and recommended practices to allow advanced supersonic aircraft to operate internationally.

In November 2002 the Commission on the Future of the United States Aerospace Industry issued a report stating, "Superior mobility afforded by air transportation is a huge national asset and competitive advantage for the United States. Because of the tremendous benefits derived from a highly mobile citizenry and rapid cargo transport, the United States must make consistent and significant improvements to our air transportation system a national priority."

Because they have already done some preliminary work and because they serve a market that needs and can afford supersonic aircraft, business jet makers are uniquely positioned to create one such improvement: the next generation of high-speed transport. No company can make that move, though, under the current FAA regulations.

In order to ensure that new vehicle technologies are introduced into service efficiently and safely, the FAA's regulations must keep pace with the technologies that are both here and near. They must enable—not restrict—improved safety and mobility.

When I look at the Wright brothers' 1903 Flyer, I see a beginning, not an end. And when I look at the Concordes that are now being placed in museums, I'd like to think of them in the same way.

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