Page 68 - AA 2018_09

hen the Wright brothers Gone but not forgotten, it is now
first took flight in 1903, they 15 years since the Concorde’s
initially mastered the skies retirement. british airways the aircraft were more spaced. It can
Wfor 12 seconds and a distance
of 37m. Over nearly three times that
distance, Usain Bolt runs three times
as quickly, while that entire history-
making flight covered the wingspan of
a Boeing 737.
But that momentous occasion at
Kittyhawk gave birth to a human
endeavour that has continually strived
to go higher, faster and further. Sixty
years later, aviation seemed to be
upon a new threshold – the dawn of
commercial supersonic transport.
History has shown that it was not
meant to be, but in the 21st Century,
it may just be possible that history is
about to be rewritten.
A wall in the sky
When lightning strikes the
ground in the distance, it may
take some seconds before the
‘crack’ is heard. Like light, sound
travels in waves, but the difference
in the speed at which they travel is
highlighted by the pause between ‘The
the sight and the sound.
speed of sound, or sound barrier, was phenomenon
For the first decades of flight the
overhead in unison with the noise that was at odds
not an issue and an aircraft would pass
subsonic flight. Even so, the change with many
it generated. These were the times of
in sound from high to low pitch as aspects
the aircraft flew by did pose some
This change in sound came to be of aircraft
questions.
known as the Doppler effect, and it design at the
was subsequently explained by the
aircraft were pushed closer together as time.’
fact that the sound waves ahead of the
68 AUSTRALIAN AVIATION
the source of the sound, the aeroplane, waiting to decimate those test pilots
caught up to them. The waves behind foolhardy enough to enter its realm.
The truth was that the sound
be compared visually to the congested barrier had already been broken by
bow wave and the dispersed wake everything from the cracking tip of a
of a boat moving through the water, stock-whip to the bullet that strikes
although sound waves radiate from an the soldier before he ever hears the
aircraft as a cone. shot. The reality was simply that the
The speed of sound, which is phenomenon was at odds with many
around 1,190km/h at sea level, actually aspects of aircraft design at the time.
varies depending on environmental Generously curved, or cambered,
conditions. Consequently, as the quest wing cross-sections needed to be
for speed drove aircraft ever-faster made sharp to penetrate the air and
and towards the sound barrier, the conventional tailplane controls with
speed of an aircraft was given a Mach hinged elevators were replaced by
Number. This number described all-flying tails, or stabilators. Shock
its speed as a ratio, relative to the waves had been prone to forming
speed of sound under the ambient on the hinge-line of the tailplane,
conditions. For instance, a Boeing 747 significantly increasing the load on
cruising at Mach 0.86 is travelling the flight controls and causing pilots
at 86 per cent of the speed of sound, to say that their controls ‘froze’ as they
while the sound barrier is at 100 per approached the sound barrier.
cent – or Mach 1.0. These were just some of the
At the speed of sound, the problems that designers needed to
molecules in the air could no longer counter before Chuck Yeager was able
get out of the way, and the sound to officially exceed the speed of sound
waves in front of the aircraft were on October 14 1947 in the Bell X-1
effectively compressed into a single – an aircraft whose fuselage closely
wave – or shock wave. The shock wave resembled the shape of a .50 calibre
forms with an abrupt increase in air bullet.
pressure and density, resulting in a aviation, conquering a frontier opens
As with all advancement in
sonic boom. There is in fact a second
boom when the tail passes through up even further research and a range
the shock wave and the air pressure
of new applications. The breaking of
rapidly returns to normal, although the sound barrier was no exception,
the human ear sometimes only detects
and soon swept wings were emerging
a single boom. as the norm on fighter aircraft and
In flight, the shock wave initially jet engine technology developed at
aerodynamic airflow over the wing eye was cast beyond the ranks of the
proved to be a barrier to the smooth a tremendous pace. Inevitably an
that had always been sought to military, and a new challenge dawned
generate lift. Consequently, for some, on the civil aviation horizon. Did the
the sound barrier was perceived as an future of air travel lie in the supersonic
domain?
invisible wall in the sky, a finite limit