The EconomistJanuary 27th 2018 Science and technology 692W
HEN a British Airways Concorde
travelling from New York touched
down at Heathrow airport, in London, on
October 24th 2003, supersonic passenger
travel came to an end. Concorde was a
technological marvel, but never a commer-
cial success. Only 14 of them entered ser-
vice. Yet the idea of building a successor
has never quite gone away. Aircraft-makers
review the idea from time to time. A num-
ber of groups are working on small execu-
tive jets intended to travel faster than the
speed of sound. The trouble is, something
else has also refused to go away: the shock
wave known as a sonic boom that ema-
nates from a supersonic aircraft.
That boom was one of Concorde’s fail-
ings. It rattled windows and frightened an-
imals, which meant the plane’s flights over
land were restricted to subsonic speeds.
Throttling back an aircraft that is designed
to fly fast is inefficient and causes it to guz-
zle a lot of fuel. If supersonic air travel is
ever to return, Concorde’s successors will
thus have to quieten their act.
Several groups are trying to do this by
tweaking designs to take account of ad-
vances in aerodynamics. By 2021NASA,
America’s aerospace agency, hopes to fly a
small experimental supersonic plane fitted
with some of these modifications, such as
a long, slender nose and engines blended
into the fuselage. The agency expects this
to reduce the sound of the shock wave to
what it describes as a “low boom”. But
John Schlaerth, an aerospace engineer
based in California, thinks he can take
such modifications much further. He and
his colleagues have filed for a patent on a
set of designs which they believe might
eliminate the boom’s sound altogether at
ground level.
A sonic boom is the product of a series
of shock waves arising from various parts
of an aircraft—particularly its nose, wings
and engines—as it flies faster than the
speed of sound (1,240kph, 770mph orMach 1, at sea level). Those waves are
caused because air molecules cannot get
out of the way fast enough during super-
sonic flight, and thus build up in front of
these parts of the plane. The consequent
change in pressure then propagates
through the air and, when it reaches the
ground, is heard as a distinctive boom.
Mr Schlaerth’s idea is to reflect and muf-
fle the worst-offending waves. He would
do this not by blending the engines into the
fuselage, but rather by placing them well
forward of the leading edge of the wing.
That could be done either by mounting
them on pylons extending from below the
wing, or by attaching them to the fuselage.
Both configurations would cause the en-
gines’ exhaust plumes to reflect any shock
wave forming in front of a wing up-
wards—ie, away from the ground.
Further shock waves, caused by the ex-
haust’s counter-reflection downwards by
the wing’s wave, could be dealt with by
modifying the engine casings to create a
slower-moving stream of air below the
plume. This slower air should form aboundary layer which, Mr Schlaerth says,
would act as a “pneumatic cushion” that
softened and impeded downward-propa-
gating shock waves. The aircraft’s long
nose, meanwhile, would be shaped to di-
rect its shock waves upwards and side-
ways. Waves from the engine inlets would
be directed upwards too, and put to good
use. Adding an appropriate downward
curve to a wing would trap the wave and
create an area of high pressure that would
give the wing additional lift.
To find out whether all this would
work, Mr Schlaerth recruited two experts
in computational fluid dynamics to act as
independent consultants. Tim Colonius of
the California Institute of Technology and
Luigi Martinelli of Princeton University
each carried out a series of tests. Using so-
phisticated computer modelling, one test
found that the shock wave from the wing
could be reduced by 63% at Mach 1.5, and
that a similar reduction would be expected
at Mach 2 (Concorde’s cruising speed). An-
other test showed that shock propagation
below the engine was virtually non-exis-
tent. Further analysis, Mr Schlaerth says,
indicates that the overall shock wave
might be almost inaudible at ground level.
The next step is to replicate the comput-
er tests using models in a wind tunnel, a
task which the group hopes to take on later
this year. Mr Schlaerth and his business
partner, Mark Bryan, have founded a firm
called New Century Transportation and
Aeronautics Research to exploit the idea. If
all goes well, it could lead to an experimen-
tal aircraft to demonstrate the technology.
Reducing sonic booms to an acceptable
level would allow overland flights, which
should make the return of supersonic pas-
senger travel more plausible. Much would
depend on the cost of building and operat-
ing such aircraft. But the prospect of being
able to fly from New York to Los Angeles in
less than two hours, instead ofa tedious
six or so, would be welcomed by many a
weary traveller. 7Supersonic flightBoom boxed
A new idea for quietening sonic boomsTomorrow, yesterdaygether—for a replacement set of these is re-
quired with each new liver stored.
In the future, OrganOx hopes to expand
its activities by building a metra for kid-
neys, and perhaps also one for pancreases.
Meanwhile, the firm has competition in
the form of TransMedics, of Andover, Mas-
sachusetts. This company is developing
similar devices for livers, hearts and lungs.
Besides increasing the supply of organs,and improving patient outcomes, metras
and their competitors can also help ease
the psychological burden on surgeons.
One such, of some 30 years’ experience,
still admits to having sleepless nights after
performing a liver transplant. Even if he
has done the surgery perfectly, he cannot
be sure thatthe liverhe has transplanted
will actually work. Metra-storage makes it
quite likely that it will. 7РЕЛИЗ
ГРУППЫ"What'sNews"