Perhaps in five to six years from now, business executives might take off from their home base in the morning, hold a business meeting at a distant location in the afternoon, and return home the same evening

“Arrive before you leave”—a rather intriguing slogan which British Airways used to attract well-heeled passengers during the heyday of Concorde. It meant something. Concorde, the world’s only successful supersonic airliner, needed just three hours 47 minutes to fly more than 4,000 nm from London to Miami with 70 passengers aboard. This was enough to outrace the rotation of the earth, and the travellers reached Miami at a local time earlier than at which their flight had left London. It was a suresell proposition for time-strapped business people, even though they had to fork out that much more for a Concorde ticket.

But after operating for just three decades over limited routes, the expensive, ageing Concorde fleet was grounded for good in 2003. The last seven years have not seen another civilian supersonic aircraft. Fighter jets routinely exceed Mach 1, even Mach 2, but today’s fastest airliners generally clock no more than Mach 0.85 (about 900 km/h), only a little quicker than their counterparts of four decades ago. Business executives, fortunate enough to have flown Concorde, might complain that travel used to be swifter and yearn for the good times to return. Their wish may be granted in the not-too-distant future. A supersonic civilian airliner is still many years away, but considerable research is being done towards a supersonic business jet (SSBJ). Aerion Corporation based in Reno, Nevada, USA, and other companies aim to enable executives to wing their way to distant destinations far faster than the speed of sound (Mach 1.0). And even economy passengers may hope to benefit some day.

World’s Fastest

After Concorde quit the scene, the title of the world’s fastest civilian aircraft was held by the Citation X. Manufactured by Cessna of Wichita, Kansas, USA, the Citation X has reigned virtually unchallenged as the business jet speed king since 1996. It offers a maximum speed of Mach 0.92 and is closely followed by the French Dassault Aviation Falcon 7X at Mach 0.90. Gulfstream Aerospace, based in Savannah, Georgia, USA, recently claimed that it’s ultra-long-range G650—scheduled for first delivery in 2012—is now the fastest civilian aircraft in the sky with a speed of Mach 0.995 recorded in a shallow dive. Of course, diving performance is of little use for business jets, and the G650’s maximum level cruise is a more sedate Mach 0.925. This amounts to a mere Mach .005 faster than the Citation X. Does this matter? It does, if only to wrest the title of the world’s fastest from Cessna. But Cessna has already declared its determination to regain the crown.

What limits the quest for ever greater speeds? Is it the socalled sound barrier? An aircraft’s sound radiates outward in all directions as pressure waves transmitted though the air. As the plane approaches the speed of sound it catches up with the sound waves being projected ahead of it, resulting in a build up of pressure in front of the plane, which forms a shockwave. Shockwaves develop even before the instrument in the cockpit registers Mach 1.0. The accompanying compressibility drag requires additional energy to counter, which means more powerful gas-guzzling engines. This reduces fuel efficiency, lowers cost effectiveness and increases the environmental footprint compared to conventional jets. Compressibility drag can be reduced by a variety of design features—including wings of thinner cross section, sharp sweepback, and wing fences to control the spread of shockwaves. But such features for high-speed flight create their own problems, particularly in the subsonic regime.

Then there’s the vexatious sonic boom. The Mach cone travels with the aircraft and its trail extends to the earth, where it is perceived as a loud double boom or bang. The boom intensity depends on the weather, refraction from different layers of the atmosphere, and most importantly the size of the aircraft. A supersonic airliner is likely to generate a shockwave strong enough to rattle windows and shake up the faint-hearted. For this reason, Concorde was prohibited from exceeding Mach 1 over land—which proved a major obstacle in its ultimately futile quest for economic viability. And Concorde didn’t have the green brigade to contend with.