Supersonic passenger jets back on the agenda

NASA has commissioned the design of a low-noise supersonic aircraft that could overcome commercial obstacles to profitable high-speed air travel. Bill Condie reports.

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The Anglo-French pioneering supersonic jetliner, Concorde, takes to the skies above Toulouse-Blagnac on 2 March 1969, its first flight. Russia's TU-144 actually beat Concorde into the air with its first flight on 31 December 1968 near Moscow. But the Tupolov-designed plane only flew commercially for 55 flights. The Concorde was in commercial service from 1976 to 2003.
AFP/Getty Images

More than 40 years after the Anglo-French-designed jetliner Concorde made its first commercial flight, NASA has put supersonic air travel back on the agenda, awarding a contract for the design of a “low boom” flight demonstration aircraft.

The test model will be the first in a series of "X-planes" in NASA's New Aviation Horizons initiative and will be designed by a team led by Lockheed Martin.

“NASA is working hard to make flight greener, safer and quieter – all while developing aircraft that travel faster, and building an aviation system that operates more efficiently,” said NASA administrator Charles Bolden announcing the award at Ronald Reagan Washington National Airport in Arlington, Virginia.

“To that end, it’s worth noting that it's been almost 70 years since Chuck Yeager broke the sound barrier in the Bell X-1 as part of our predecessor agency's high speed research. Now we’re continuing that supersonic X-plane legacy with this preliminary design award for a quieter supersonic jet with an aim toward passenger flight.

An artist’s concept of a possible Low Boom Flight Demonstration Quiet Supersonic Transport (QueSST) X-plane design. – Lockheed Martin

NASA's Quiet Supersonic Technology (QueSST) program, under which the contract was awarded, is seeking ways to reduce noise pollution from the "sonic boom" – the ear-shattering sound made from shock waves created by an object travelling through the air faster than the speed of sound.

(You can access a free NASA eBook on the QueSST program here.)

The noise of a sonic boom proved the achilles heel of Concorde, limiting the number of places it could fly to those where the boom took place over the ocean. This limitation is credited for the commercial failure of the aircraft.

The space agency's Commercial Supersonic Technology Project asked industry teams to submit design concepts for a piloted test aircraft that can fly at supersonic speeds, creating a supersonic "heartbeat" – a soft thump rather than the disruptive boom.

Concorde on the runway in 1977. – Manchester Daily Express/Getty Images

“Developing, building and flight testing a quiet supersonic X-plane is the next logical step in our path to enabling the industry's decision to open supersonic travel for the flying public," said Jaiwon Shin, associate administrator for NASA’s Aeronautics Research Mission.

Lockheed Martin will receive about $20 million over 17 months for QueSST preliminary design work. The company will develop baseline aircraft requirements and a preliminary aircraft design, with specifications, and provide supporting documentation for concept formulation and planning.

This documentation would be used to prepare for the detailed design, building and testing of the QueSST jet. Performance of this preliminary design also must undergo analytical and wind tunnel validation.

NASA’s 10-year New Aviation Horizons initiative has the ambitious goals of reducing fuel use, emissions and noise through innovations in aircraft design that departs from the conventional tube-and-wing aircraft shape.

An F/A-18 Hornet photographed just as it breaks the sound barrier. – Ensign John Gay, USS Constellation, US Navy

What causes a sonic boom?

When an aircraft passes through the air it slams into the air, compressing it and creating shock waves at the front and the rear of the aircraft that travel at the speed of sound. These waves are similar to the waves at the bow and stern of a boat as it moves through the water.

As the aircraft approaches the speed of sound, waves from the front and rear of the aircraft are squashed together into a single shockwave travelling at the speed of sound.

The shockwave begins at the nose of the plane and runs to the tail, accumulated in a cone-shape.

The boom occurs from initial sudden air pressure rise from the nose pushing against the air followed by the air pressure suddenly returning to normal right after the plane passes it. All the noise gets squashed into one air tsunami.

The reason it's loud is because all of the sound hits you at once.

In fact, there are two booms – one at the nose of the plane and one at the tail, but they pass over observers at nearly the same time and are almost imperceptible as distinct sounds.

As a plane accelerates through the sound barrier, it is sometimes possible to see the sonic boom as an unusual cloud.

Scientists aren’t entirely sure what creates this cloud but the leading theory is that a drop in air pressure at the plane occurs so that moist air condenses there to form water droplets.

The speed of sound, known as Mach 1, is approximately 1,225 km/h (761 mph) at sea level and 20 °C (68 °F).

The video below gives an idea of the sound and volume of a sonic boom.

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