Page 25 - Aviation News - September 2017

So perfect was the design there was no after absorbing the energy of stopping such
need for slats and flaps, unthinkable on an a mass from high take-off speeds during an
airliner in normal operation. aborted take-off at maximum weight.
Despite British wing-building pedigree Messier-Dowty produced the undercarriage
(Hawker-Siddeley was brought in for the while Dunlop developed pioneering carbon
inaugural Airbus A300 in 1974) the wing brakes. These electrically commanded,
was French-made. A process of milling hydraulically operated, analogue brake-by-
and shaping specialist aluminium alloy wire systems were lighter, more powerful
produced significant weight saving and and cooled by internal fans. Innovative at
finer tolerances, avoiding the weaknesses the time, they are standard fit on modern
of welds or riveted joints. The constant airliners.
drive for lightweight construction seems The characteristic nose-high approach
particularly prescient in our fuel price attitude was a function of the wing geometry,
motivated climate. Externally, the leading severely reducing forward visibility from the
edge of the wing is so sharp there was flight deck. The only possible solution was
no room for navigation lights; these are to droop the nose to 12.5° for approach and
mounted inside and fed to the leading edge landing, with an intermediate 5° position
by fibre-optics. aiding taxiing and take-off. Furthermore,
In common with predominantly military as the ground clearance getting airborne
deltas (and also the only direct comparison, dictated the undercarriage length, this
the short-lived, Soviet Tu-144) it has only meant gear legs too long to fit into the
a vertical tail. Removing the horizontal available space. Again, an unconventional
stabilizer minimises drag, instead control solution arose: when commanded up, the
was provided by six ‘elevons’ on the landing gear first broke a geometric lock that
wing trailing edge. These provide partial retracted the shock-absorber assemblies
trimming (along with fuel balancing) and into the gear legs, thus shortening them.
via differential deflection all pitch and roll. A tailwheel completed the ‘four greens’
The individual deflections of controls were The nosewheel strut retracts forward necessary for landing and offered a
indicated on an instrument called the ‘Icovol’ conventionally. This allows it to deploy with sacrificial component; excessive pitch
(French origin ‘indicateur a vol’) on the flight the aid of the slipstream in the event of the on touchdown would otherwise result in
deck. A digital version of this instrument is hydraulic system failing. ground contact of the engine nozzles. An
the basis of the Airbus ECAM (Electronic interlock isolated the undercarriage while
Centralised Aircraft Monitoring) Flight UNDERCARRIAGE the visor was raised, preventing inadvertent
Controls display page. Huge forces were involved, not only in mass deployment at high speed.
Flight controls were fly-by-wire, a first (maximum take-off weight was 185 tonnes)
for a commercial airliner – control inputs but the speeds required for take-off. As the FUSELAGE AND MATERIALS
digitized and fed to hydraulic actuators speed and lift generated by a conventional At subsonic speed there is only a slight
electrically, not mechanically. In future, wing increase, the undercarriage is drag penalty from an increase in fuselage
the removal of pulleys and cables would progressively unloaded: this phenomenon width, handy for widebodied aircraft.
save much weight, but physical controls can be observed on take-off in turboprops as Approaching Mach 1.0 however, the physics
remained for this pioneering system, the landing gear struts gradually extend. On change and a slender fuselage (denoted by
though unused in normal operation. Concorde, the vortex lift generated only ‘Fineness Ratio’ – the ratio of the length of a
With one exception, digital systems became significant at rotation speed; streamlined body to its maximum diameter)
were analogue (sine wave) rather than up until that point there was little lift to becomes critical. A specialist aluminium
digital (binary). The first all-digital progressively overcome the aircraft alloy, RR.58, patented by Rolls-Royce was
fly-by-wire system became the heart weight. Another problem specific used as a compromise between cost, ability
of the A320 flight envelope protection to Concorde was that steel brake to be machined and good temperature
system, first flown in 1987. discs tended to fuse together resistance. Production models typically
Condensation briefly billows above the wing on approach. This view
shows the tailwheel deployed and nose droop in landing configuration.
One of the unusual features of Concorde’s design was that it did not
have flaps or slats. Yevgeny Pashnim / Transport-Photo Images

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