24 | Flight International | 26 January-1 February 2016 flightglobal.com

COVER STORY

STEPHEN TRIMBLE WASHINGTON DC

Wind tunnel testing of two

advanced designs has led

NASA to conclude it can

deliver supersonic flight,

and reduce tell-tale boom

PLEad foR SPEEd

NASA

B

ack in 2012, NASA thought it had

reached a breakthrough in a

decades-long quest to design a “low-

boom” supersonic aircraft. With left-

over funding from the 2009 financial stimulus

act, the agency commissioned Lockheed

Martin and Boeing to separately develop

preliminary designs and wind tunnel models

of aircraft concepts.

Lockheed aimed its efforts at a 100-seat-

class trijet design similar in scale to the four-

engined Aerospatiale-BAC Concorde, while

Boeing focused on a smaller, 70-seater with

uniquely-configured over-the-wing-mounted

engines. Four years later, Lockheed and

Boeing have reported back to NASA, with

windtunnel runs and simulation data appear-

ing to have validated the agency’s calcula-

tions. NASA may have reached a pivotal

moment in the quest to revive commercial

supersonic air travel, more than 12 years after

Concorde was retired from service by Air

France and British Airways.

Indeed, the data served to persuade the

superiors of Peter Coen – head of the high-

speed project in NASA’s aeronautics research

directorate – to authorise a feasibility study

for a new supersonic X-plane that could

verify the wind tunnel results in real flight.

Critically, data from flight testing could,

finally, force international regulators to

consider overturning a 47-year-old ban on

breaking the sound barrier over land.

Coen says: “We’re very pleased with

[Lockheed’s and Boeing’s] results. Lo and be-

hold, we feel there is a solution using a scaled

X-plane – a 100ft-long aircraft that weighs

about 25,000lb, which is capable of replicat-

ing the acoustic characteristics of a boom of a

larger airplane up to 300,000lb or so.”

A final funding decision may come in Feb-

ruary, with the Obama administration’s fiscal

year 2017 budget request. If the programme is

launched, Coen expects to have a detailed de-

sign study complete by the end of FY2017,

followed by a first flight of the supersonic X-

plane in FY2019.

ExPERIMENTaL vEHIcLE

This low-boom experimental vehicle would

be used in an effort to rewrite the rulebook on

flying over land at supersonic speed. Of

course, not everyone agrees such an effort is

necessary. Aerion, which has partnered with

Airbus, is developing the AS2 business jet to

be optimised to fly at supersonic speeds over

water but cruise at high-subsonic speeds over

land in the USA and potentially up to Mach

1.1 in Europe, where regulations are slightly

less restrictive.

But NASA officials and others in the

industry, including Gulfstream, have said a

commercial supersonic aircraft is only viable

economically if it can fly at top speed over

land. To make that happen, someone has to

give the regulators a reason to change the

rules. The Lockheed and Boeing study results

indicate new technology can reduce sonic

boom noise from 105PLdB to as low as

75PLdB, Coen says.

But while ICAO’s committee on aviation

environmental protection (CAEP) has estab-

lished a supersonic transport task group, it

will need more than NASA-funded windtun-

nel studies – no rules can be changed without

real flight data from a representative aircraft

and a public response.

Aerion’s AS2 business jet

is designed for supersonic

flight only over water

The Lockheed concept

is a 100-seat-class

trijet design

Aerion