Sonic Boom

Back to Contents of Issue: April 2006

Tokyo to New York in six hours?

by Willhemina Wahlin

"Yes, only rich people can afford to take a Concorde," states There's no doubting the Concorde had its fans, but like all good things, it too came to an end, the curtains closing on the elite's day-tripping flight service on October 24, 2003. In its wake is an industry in post 9/11 turmoil, where it's more common for an airline to go bust than boom. Despite this, a consortium of researchers from the United States, Europe and Japan are exploring new ways of bringing supersonic flight back and better than ever. In October 2005, on a rocket range in the middle of the South Australian desert, far from the glitterati and bubbly-quaffing elite travelers of the Concorde, Japan's Aerospace Exploration Agency (JAXA) tested a fuselage design for a new supersonic jet -- and it was a huge success.

Dubbed the 'Son-of-Concorde, the test of the very practically named 'Scaled Experimental Supersonic Transport (SEST) in Woomera, Australia, was not the first for JAXA. In 2002 the first test ended in spectacular failure. "After attaining a height of about 100 meters, it began spiraling erratically and slammed into the ground and exploded," wrote Daniel Dasey in Sydney's Sun-Herald newspaper in August 2005. "An investigation revealed a computer short-circuit was responsible for the malfunction."

This time JAXA left nothing to chance. In the conference room of JAXA's Aerospace Research Center's Aerodrom Branch, Director of the Supersonic Transport Team, Dr. Takeshi Ohnuki, a PhD graduate in Fluid Dynamics from Tokyo University, proudly showed J@pan Inc. a compilation video of the test taken from 10 different cameras. One can only wonder, after the failure of the previous test and the many years of hard work to correct the problems since, what was going through the minds of the testing team as they watched their precious fuselage take off straight into the air, a fiery tail in its wake. This time, the fire was from the power of the rocket strapped to the body, not a disastrous explosion, and at an altitude 18,000 meters, the rocket separated from the craft, exactly as planned.

The SEST flew for a total of 15 minutes, while computers recorded the aerodynamic characteristics and surface pressure of the craft as it made its trajectory over the red desert below. Reaching a speed of Mach 2, the supersonic craft glided effortlessly before a complex series of airbags and parachutes enabled it to land horizontally in a completely recoverable state, amid the cheers of a relieved testing team. The successful flight of the SEST cleared the way for the further development of the next stage of the craft, named the Silent Supersonic Technology Demonstrator (SSTD), which would tackle the issue of noise and the sonic boom.

Japan's contribution to the great supersonic race is the body of the next generation of supersonic aircraft -- a big contribution. A good fuselage is the key to changing supersonic flight, and its secrets lie in the short-comings of its predecessor. While 34 years is certainly a good run, the Concorde was never going to be financially viable for long because it had far too many limitations placed upon it. These restrictions are what now drive the JAXA team.

That team is composed of around 35 researchers covering such diverse areas as structure, control and propulsion of the rocket, control and propulsion of the rocket. Dr. Ohnuki joined JAXA's supersonic project in the year of its inauguration in 1997, when it was still part of the National Aerospace Laboratory. Prior to this, he was a researcher in drag reduction for conventional aircraft, again with the National Aerospace Laboratory. JAXA was formed in 2003, when the National Aerospace Laboratory of Japan (NAL), the National Space Development Agency of Japan (NASDA) and the Institute of Space and Astronautical Science (ISAS) all merged into a single organization.

Dr. Ohnuki's excitement is obvious when he starts talking about the challenges his team faces in the design of the SSTD and their contribution to the craft he says not one single country will own. "We will design the form, the shape of the aircraft, and it's a big role. The shape is almost equivalent to the brand -- it will become the JAXA brand. We would like to see the Rising Sun Flag symbolically on the craft."

Their yardstick is the Concorde. As the only commercially successful instance of a supersonic aircraft, it is the sole yardstick they have. But as adored as the Concorde was, it had many flaws. The JAXA team intends for its design to correct those.

The Concorde was always going to be an expensive ship to run because it only accommodated 92 passengers. As every international traveler today will tell you, fuel levies on flights are not getting any cheaper, and the Concorde's propensity for gas guzzling was out of step with rising fuel prices. JAXA's design aims to triple the number of seats, which essentially means that 300 passengers can go supersonic for a business class fare.

Another problem with the Concorde was that its characteristic sonic boom and high level of emissions (nitrous oxide in particular) restricted it to routes over the ocean. So, for example, it could fly from London to New York, but not from New York to Los Angeles.

What's more, the Concorde required a much longer runway than a conventional aircraft. Thus its service was limited to airports that could accommodate it.

The long takeoffs and landings also had much more dangerous implications. One of the darkest moments in the history of the Concorde was the Air France crash on July 25, 2000, when a flaming Concorde struck a hotel and burst into flames shortly after takeoff from Charles de Gaulle Airport, killing 113 people, including 4 people in the hotel. Concorde operations on both sides of the Channel were suspended for a year after the accident. While the cause of the accident is still under investigation, it is thought that a small strip of metal that fell off during the previous plane's takeoff was lying on the runway. By sheer chance, one of the wheels of the Concorde ran directly over it, causing a rapid chain of events that would set one of the jet engines on fire. What compounded this problem, and the eventual downfall of all on board, was that the fuel tanks were so close to the engines, and it was only a matter of time before they too burst into flames. Had the takeoff speed been faster, they may have made it to nearby Le Bourget airport, where there were fire crews were standing by, Rob Lewis, in his book Supersonic Secrets: The Unofficial Biography of Concorde, wrote:

"The investigation report that followed on 31 August 2000 implied that a single design defect was to blame for the tragedy. The conclusion was damning for both the aircraft and the generation of designers who had originally put her together."

"There's a reason for the crash that's inherent in the SST design," explains Dr. Ohnuki. "Its triangular wings are fine in flight, but they add weight to the rear of the craft during takeoffs and landings. So the aircraft must maintain a high angle for a long time during these evolutions. This, in turn, requires a long runway.

"Fast takeoffs and landings using a high lift device, as opposed to flaps and slats, reduce the chance of an accident. The inherent design of the craft necessitating a high angle at takeoff is problem enough, but the fact that extra time is needed for takeoff and landing compounds the problem, making these even more risky. Conventional aircraft do not have this long takeoff time, so any structural problems are not exacerbated."

By far the research team's biggest challenge is reducing the craft's sonic boom to the level of noise from an ordinary jet engine. Dr. Ohnuki describes the process as trying to reduce a clap of thunder to a knock on a door. Nevertheless, he maintains that it is the design of the plane's fuselage, rather than the engine itself, that can make the biggest impact on reducing sonic boom, as well as reduce the amount of fuel consumed in flight. Unfortunately, says Dr. Ohnuki, this creates a third problem.

"The technologies needed to solve the problem of the sonic boom and to reduce fuel consumption are different, and actually in conflict with one another, so we have to work out a way to keep these things in balance, as one will affect the other in a negative way."

In a supersonic craft, there are two places that the sonic boom occurs, the nose and the tail. Unfortunately, there is nothing that can be done for the sonic boom at the nose, so the JAXA team concentrated their efforts on reducing that at the tail. They discovered that the second sonic boom can be reduced by changing the under carriage of the craft, so that shockwaves do not accumulate in one place. Much like a CT scan, the plane is made larger segment by segment from the nose, and the unique curvature of the undercarriage raises the air pressure underneath the plane. This increase in air pressure helps to distribute the shock waves along the plane, reducing the sonic boom. However, the increased air pressure creates drag, and therefore the plane requires greater fuel. As the problem of the sonic boom was rectified by the undercarriage design, it gave the researchers the freedom to work on the top section of the plane. They refined the design so that the upper section created the least possible resistance, enabling them to reduce fuel consumption. "It's very aerodynamic", says Dr. Ohnuki, "so it makes up for what's going on below."

The future of supersonics, hyper-sonics, and water-fuelled space travel
One has to wonder why, in an ever-competitive aircraft industry, there is a need for research into supersonic aircraft at all. Certainly the Concorde never became a 'commonly' used mode of transport -- symbolically, perhaps, the most frequent user of the Concorde was an oil tycoon, who made 70 round trips across the Atlantic a year. Eventually the fleet became a financial burden on Air France and British Airways, and as both have since been privatized, it would have certainly been a thorn in their side at the time of sale.

Strangely, for a nation that is a global leader in automobile manufacturing, Japan has never developed an internationally competitive aircraft industry. Perhaps Airbus and Boeing are formidable deterrents to entering conventional aviation development at this late stage. Thus there is a certain logic in Japan's attempt to make a splash in the industry through research and development in supersonics.

JAXA, in their vision statement, has made it a primary goal to establish Japan's aviation industry and develop supersonic aircraft. Not only do they intend to revive aircraft manufacturing, but also to eventually demonstrate the technologies of hypersonic aircraft. While supersonic aircraft are limited to Mach 2 or 2.5, hypersonic aircraft can potentially travel at Mach 5 (some aerospace engineers even claim up to Mach 10), meaning a trans-Pacific flight of just two hours. Hypersonic requires the use of jets known as scramjets ('air breathing rockets'), which work on a different principle from normal jets, which are used in supersonics. Brilliantly, scramjets use hydrogen as fuel, so the future of air and space travel may not even need the smell of an oily rag.

"While a normal jet engine has a fan at the front to suck air in, a ramjet relies on sheer speed to force air into the combustion chamber," wrote the New Scientist Magazine in April 2004. "The difference between a ramjet and a scramjet is that airflow through the engine slows to subsonic in a ramjet, but remains supersonic inside a scramjet. This means that a scramjet can propel vehicles at speeds that only rockets can otherwise attain. But scramjets are far more efficient because they collect oxygen from the air, whereas rockets have to carry an oxidizer such as liquid oxygen."

Scramjet tests in recent years in the US and Australia have clocked up to Mach 7. While JAXA's fuselage design is based on the use of a normal jet engine, investment into superior supersonic fuselage design has obvious advantages. One of the most exciting prospects for scramjet use lies in the futuristic dreams of space travel.

For now we may have to be content with the prospect that the demise of the Concorde is not necessarily a fatal blow for supersonic travel. JAXA hopes that its SSTD will be commercially running by 2025, and being the next generation of supersonic travel after the Concorde, there are sure to be many of the old fans of supersonic travel lining up for a ticket. The question is whether or not the next generation will be commercially viable. For now we can assume that for those willing to fork out a business class airfare, they may want to actually get to their destination in less than half the time. Let's just hope that the glitterati still have time to quaff some champagne between ports. JI

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