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Business Jets Race for the Supersonic Prize

[+] Author Notes

Greg Freiherr is a writer based in Fond Du Lac, Wis.

Mechanical Engineering 138(03), 36-41 (Mar 01, 2016) (6 pages) Paper No: ME-16-MAR2; doi: 10.1115/1.2016-Mar-2

This article explores efforts that are being put into developing a business jet called AS2 and various challenges in developing the same. Aerion’s 12-seat tri-engine AS2, unveiled in spring 2014, is designed to have a range up to 5000 nautical miles; reach 51,000 feet; and cruise at speeds between Mach 1.2 and Mach 1.6. About the time it is ready to fly commercially, possibly as early as 2023, the market could support annual sales of 30 supersonic business jets. NASA and Lockheed Martin have been exploring a variety of options for quieting sonic booms. In its Strategic Implementation Plan, released in 2015, NASA states that ‘the viability of commercial supersonic service depends on permissible supersonic flight over land.’ It is however noted that the success of the next generation of supersonic transport will ultimately come down to economics. Prospective buyers of supersonic business jets will include corporations and ultra-high net worth individuals.

Shock wave of the supersonic T-38C over the Mojave Desert.

Photo: NASA

The market for supersonic business jets such as the AS2 is expected to be only about 30 per year.

Illustration: Aerion Corp.

Grahic Jump LocationThe market for supersonic business jets such as the AS2 is expected to be only about 30 per year.Illustration: Aerion Corp.

Last September, a delegation of executives from Airbus Defence and Space, the European aerospace consortium, spent four days in the offices of Renobased Aerion Corp. Though the companies had been partners for more than a year, this was the first time senior engineers and project managers from both companies had met to discuss their joint development, a business jet called the AS2. Executives and managers from the two companies reviewed the engineering on every structure and system on plane.

If all goes as planned, in 2023 business travelers be able to board an AS2 and fly faster than the speed of sound.

“It showed us the great progress we had made in one year of collaborative effort and set a clear path for our next steps,” said Aerion's CEO, Doug Nichols, who described the effort as the “only supersonic program to have shifted into the aircraft development program phase.”

It will be Aerion's job to build the business jet. Airbus, a premier manufacturer of commercial aircraft, will be a “tier-one supplier of aerostructures,” Nichols said. Airbus is already providing Aerion with design tools, as well as advising the company “in a number of engineering and program management areas.”

The partnership will bear fruit with the first supersonic flight of its AS2 business jet in 2021, Aerion spokesman Jeff Miller said. He said the company expects certification and entry into service in 2023.

The Aerion-Airbus partnership is one of a half dozen or so ventures looking into supersonic transports. Among them is Spike Aerospace, whose slick artist renderings show an 18-passenger business jet that company founder Vik Kachoria promises will one day cruise at Mach 1.6. Spike is targeting 2018 for the first supersonic test flight of a “rudimentary, proof of concept” prototype and 2022 for delivery of its first production model, Kachoria said.

The schedule is “very aggressive, very ambitious,” he said. “But we also recognize that our investors have a time horizon.”

Gulfstream, which makes the G650 Flexjet, a leading business jet, has conducted supersonic research, but has not publicly discussed plans for a supersonic aircraft since the early 1990s. Its former partner, Russian aircraft maker Sukhoi, however, may still be interested, having displayed a model of a supersonic business jet two years ago at a Moscow air show.

Dassault Aviation, the French maker of business jets and military fighters, showed interest in the late 1990s, but has said little since.

Research by Boeing and NASA has been aimed at increasing fuel efficiency and reducing noise.

Photo: NASA

Grahic Jump LocationResearch by Boeing and NASA has been aimed at increasing fuel efficiency and reducing noise.Photo: NASA

Dark horses with a declared interest in developing supersonic business jets are Reaction Engines and Supersonic Aerospace International.

Although Reaction Engines focuses primarily on propulsion, the company claims to have designed two airframes, one capable of Mach 5, another of suborbital flight.

The CEO of Supersonic Aerospace is J. Michael Paulson, who has said that he wants to carry on the vision of his father, Allen Paulson, the one-time owner and CEO of Gulfstream who, before his death in 2000, worked with Lockheed Martin to design a supersonic business jet.

The AS2 business jet: Aerion and Airbus hope to have it in the air by 2021,

Grahic Jump LocationThe AS2 business jet: Aerion and Airbus hope to have it in the air by 2021,

Two aerospace goliaths with supersonic transport programs, Lockheed Martin and Boeing, are decidedly old school. The N+2 design by Lockheed Martin would seat 80 passengers; the Boeing ICON-II would seat 120.

Their designs have a place in the past but not the future, according to Richard L. Aboulafia, vice president of analysis at the Teal Group, an aerospace and defense consulting company. The chief reason is that their designs would require public subsidies to operate.

“The Concorde-size SST will never ever happen again,” he said. “The good old days of taxpayers generously giving billions of dollars to rich people have become passé.”

The Concorde, which last carried passengers in October 2003, was first conceived in the 1950s. The French and British governments paid Aérospatiale (whose assets were acquired by Airbus) and the British Aircraft Corp. billions of dollars to develop and build the Concorde, then provided subsidies to Air France and British Airways to operate the planes. The Concorde existed in “a moment in time when technology was funded by the state without any thought to earning money,” Aboulafia said.

Current efforts to return civilians to faster than sound travel are all privately funded.

Aerion's 12-seat tri-engine AS2, unveiled in spring 2014, is designed to have a range up to 5,000 nautical miles; reach 51,000 feet; and cruise at speeds between Mach 1.2 and Mach 1.6. About the time it is ready to fly commercially, possibly as early as 2023, the market could support annual sales of 30 supersonic business jets, according to Aboulafia. That's enough volume for one provider.

“But it has to be just one player,” he said. “If it's two, they are going to lose their shirts.”

With fewer passengers, business jets would be far smaller than the Concorde. Along with improvements in design and engineering and the use of lighter materials, they promise improved performance and increased range. This makes for an economically viable supersonic transport with a price in the range of $120 million per plane, according to Aerion.

This stratospheric price—about twice that of a Gulfstream G650—won’t be hard to swallow. Aboulafia said interest in top-end business jets “has exploded in the last couple of decades, not only in terms of total demand but in what people will pay.” The market may be willing, but the next generation of SSTs must meet several technical challenges to get off the ground. Supersonic business jets will have to combine a powerful engine with a fuel-efficient design; demonstrate low emissions, especially at high altitudes where the ozone layer is vulnerable; and abide by tough airport noise standards.

An even bigger concern, say many in the aerospace industry, is what they believe led to the downfall of the Concorde: a ban on civilian supersonic travel over land and territorial waters. This ban, enacted in the mid-1970s by the Federal Aviation Administration and stretched around the globe by international regulators, limited demand for the Concorde to airlines with ocean routes.

Aerion, on the other hand, contends that fuel efficiency is more important than reducing sonic booms. Aerion's market surveys have documented demand for a “not everywhere” supersonic business jet that would fly efficiently at subsonic speeds over land and supersonically over oceans.

NASA and Lockheed Martin have been exploring a variety of options for quieting sonic booms. This artist's conception of the N+2 concept shows a vehicle shaped to reduce sonic shockwaves and reduce drag.

Image: NASA/Lockheed Martin

Grahic Jump LocationNASA and Lockheed Martin have been exploring a variety of options for quieting sonic booms. This artist's conception of the N+2 concept shows a vehicle shaped to reduce sonic shockwaves and reduce drag.Image: NASA/Lockheed Martin

To achieve those efficiencies, Aerion relies on what it calls natural laminar flow, said Richard Tracy, the company's chief technology officer. It protects the boundary layer, the thin sheet of air that flows over the skin of the airframe. Increasing speed can disrupt this layer and increase drag.

Natural laminar flow, which smooths the boundary layer, requires an unconventional wing design.

A cross-section of a conventional wing looks like the top half of an elongated teardrop, with a flat bottom and a curved top that tapers toward the rear. Aerion's natural laminar flow wing looks like a complete teardrop, with tapering curves on both top and bottom.

This design breaks from 100 years of aviation history. It is what has put Aerion on the map.

“As our investor Bob Bass likes to say, laminar flow and the tools for designing and optimizing the aircraft design to achieve it is really our secret sauce,” Tracy said.

The impact of natural laminar flow is immediately visible in the AS2's design. In conventional subsonic aircraft, wingspan roughly equals fuselage length. Aerion's SST design calls for a long, thin fuselage with stubby thin wings. In fact, it resembles the Starfighter 104, a 1950s high-performance combat aircraft.

“The Starfighter actually can generate laminar flow and NASA did some tests back in the late 1950s with Neil Armstrong flying the plane,” Tracy said. “We were pleased to find that it [laminar flow] happened before, but we found those reports after we had settled on our wing shape.”

Unlike the AS2's stubby wings, the delta wings that characterize competitors’ designs are “swept” to minimize drag at supersonic speeds. Natural laminar flow, leveraged in the AS2 design, reduces drag at supersonic speeds, as well as at subsonic, thereby improving fuel efficiency and range, Tracy said. The jet will also be able to cruise efficiently just below the speed of sound, at Mach 0.95 to 0.96.

And that just might be necessary.

In its Strategic Implementation Plan, released in 2015, NASA states that “the viability of commercial supersonic service depends on permissible supersonic flight over land.”

The wording of the Federal Aviation Administration's ban on supersonic flight actually gives SST boosters hope. FAA prohibits jets from exceeding the speed of sound except when such operations will not cause a “measurable sonic boom overpressure to reach the surface.” NASA has been working with corporate partners to tame sonic booms for decades, refining low-boom technologies as it hatches plans to research how much boom is too much for the American public.

To further its studies, NASA photographed the formation of shockwaves at the nose, wings, and fuselage. These shockwaves appear as the aircraft nears Mach 1 and are fully developed as the aircraft reaches Mach 1.2, according to Peter Coen, project manager for the NASA commercial supersonic technology project.

“To reduce the boom you want the shockwaves to be as equal in strength as possible and spaced fairly evenly along the length of the airplane,” Coen said.

In one of the more interesting tests, performed in 2006 and 2007 in collaboration with Gulfstream, NASA gauged the effect of a telescoping device called the “Quiet Spike.” Like the nose of a supersonic Pinocchio, it extended and retracted. In a NASA wind tunnel test, changes in length and diameter produced a more even set of shockwaves that could reduce sonic booming. Researchers also flighttested the device on a NASA F-15B for stability.

Since then, NASA has discovered other ways to reduce sonic booms. “We have been able to achieve similar types of shockwave control by shaping the fore body of the airplane,” Coen said. “Our new designs have a series of subtle ’steps’ in area growth that produce small shocks that do not coalesce.”

Low-boom innovations might keep the noise to about 70 decibels, according to Coen, about a third quieter than Concorde-created booms. Such sonic “thuds” might not be much of a problem in cities, he said, but they could be a problem in rural America, especially in the quiet of national parks. NASA hopes to have a better handle on what the American public will accept after exposing people on the ground to sonic booms and then surveying them about their opinions. Controlled boom tests could take place in the next few years.

“There are always going to be people who find any noise unacceptable,” Coen said. “It will be up to the regulators to decide where to draw the line.”

Meanwhile, Aerion is building an aircraft that can operate efficiently within today's regulatory framework.

“That is the most sensible starting point for introducing a new generation of supersonic aircraft,” Miller said. “Without clear regulatory definition, manufacturers lack sufficient guidance for designing a low-boom supersonic jet.”

Also on the noise front, supersonic business jets will have to meet restrictions applying to take-off and landing. Aerion claims it will achieve airport noise levels as quiet as the quietest business jets today, adhering to what are known as Stage 4 noise standards.

The AS2 will also be able to land on standard runways at just 120 knots.

To get off the ground, a supersonic business jet needs a high-performance engine. Unfortunately, that engine does not exist. Reaction Engines says it has a design, but not a working model. Several years ago, Aerion had settled on a design built around two Pratt & Whitney JT8D engines, off-the-shelf models that propelled Boeing 727 and MD-80 jetliners. But the JT8D has since been phased out of production. Jet engines built for combat aircraft are too inefficient for supersonic business jets. But commercial jet engines—with the proper modifications—might do the trick. Aerion is counting on it.

The success of the next generation of SSTs will ultimately come down to economics. Demand for business jets in the United States is strong, but less so in other parts of the world. During the first half of 2015, global shipments of business jets fell 4.1 percent compared with the same period one year earlier, according to the General Aviation Manufacturers Association. Business has suffered the effects of the Great Recession. The 722 business jets that shipped in 2014 were little more than half the 1317 that shipped in 2008.

Prospective buyers of supersonic business jets will include corporations and ultra-high net worth individuals, according to Aboulafia. Others may be the providers of fractional ownerships and premium charter services.

“Perhaps the most intriguing would be heads of state or military buyers,” he said. “The world is filled with crises and trouble. The faster you can get a rapid reaction team there, the better.”

While demand will play a big role in the success of supersonic business jets, so will keeping a lid on operational costs. Maintenance and training issues will have to be addressed. The greatest technical challenge to commercial supersonic flight, however, is the sonic boom, industry experts agree.

If the boom can be tamed, the ban on supersonic flights over the U.S. and other countries might be lifted.

And business jetsetters will be free to set speed records as never before.

Copyright © 2016 by ASME
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