Aviation News — September 2017

So perfect was the design there was no

need for slats and flaps, unthinkable on an

airliner in normal operation.

Despite British wing-building pedigree

(Hawker-Siddeley was brought in for the

inaugural Airbus A300 in 1974) the wing

was French-made. A process of milling

and shaping specialist aluminium alloy

produced significant weight saving and

finer tolerances, avoiding the weaknesses

of welds or riveted joints. The constant

drive for lightweight construction seems

particularly prescient in our fuel price

motivated climate. Externally, the leading

edge of the wing is so sharp there was

no room for navigation lights; these are

mounted inside and fed to the leading edge

by fibre-optics.

In common with predominantly military

deltas (and also the only direct comparison,

the short-lived, Soviet Tu-144) it has only

a vertical tail. Removing the horizontal

stabilizer minimises drag, instead control

was provided by six ‘elevons’ on the

wing trailing edge. These provide partial

trimming (along with fuel balancing) and

via differential deflection all pitch and roll.

The individual deflections of controls were

indicated on an instrument called the ‘Icovol’

(French origin ‘indicateur a vol’) on the flight

deck. A digital version of this instrument is

the basis of the Airbus ECAM (Electronic

Centralised Aircraft Monitoring) Flight

Controls display page.

Flight controls were fly-by-wire, a first

for a commercial airliner – control inputs

digitized and fed to hydraulic actuators

electrically, not mechanically. In future,

the removal of pulleys and cables would

save much weight, but physical controls

remained for this pioneering system,

though unused in normal operation.

With one exception, digital systems

were analogue (sine wave) rather than

digital (binary). The first all-digital

fly-by-wire system became the heart

of the A320 flight envelope protection

system, first flown in 1987.

UNDERCARRIAGE

Huge forces were involved, not only in mass

(maximum take-off weight was 185 tonnes)

but the speeds required for take-off. As the

speed and lift generated by a conventional

wing increase, the undercarriage is

progressively unloaded: this phenomenon

can be observed on take-off in turboprops as

the landing gear struts gradually extend. On

Concorde, the vortex lift generated only

became significant at rotation speed;

up until that point there was little lift to

progressively overcome the aircraft

weight. Another problem specific

to Concorde was that steel brake

discs tended to fuse together

after absorbing the energy of stopping such

a mass from high take-off speeds during an

aborted take-off at maximum weight.

Messier-Dowty produced the undercarriage

while Dunlop developed pioneering carbon

brakes. These electrically commanded,

hydraulically operated, analogue brake-by-

wire systems were lighter, more powerful

and cooled by internal fans. Innovative at

the time, they are standard fit on modern

airliners.

The characteristic nose-high approach

attitude was a function of the wing geometry,

severely reducing forward visibility from the

flight deck. The only possible solution was

to droop the nose to 12.5° for approach and

landing, with an intermediate 5° position

aiding taxiing and take-off. Furthermore,

as the ground clearance getting airborne

dictated the undercarriage length, this

meant gear legs too long to fit into the

available space. Again, an unconventional

solution arose: when commanded up, the

landing gear first broke a geometric lock that

retracted the shock-absorber assemblies

into the gear legs, thus shortening them.

A tailwheel completed the ‘four greens’

necessary for landing and offered a

sacrificial component; excessive pitch

on touchdown would otherwise result in

ground contact of the engine nozzles. An

interlock isolated the undercarriage while

the visor was raised, preventing inadvertent

deployment at high speed.

FUSELAGE AND MATERIALS

At subsonic speed there is only a slight

drag penalty from an increase in fuselage

width, handy for widebodied aircraft.

Approaching Mach 1.0 however, the physics

change and a slender fuselage (denoted by

‘Fineness Ratio’ – the ratio of the length of a

streamlined body to its maximum diameter)

becomes critical. A specialist aluminium

alloy, RR.58, patented by Rolls-Royce was

used as a compromise between cost, ability

to be machined and good temperature

resistance. Production models typically

http://www.aviation-news.co.uk 25

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

The nosewheel strut retracts forward

conventionally. This allows it to deploy with

the aid of the slipstream in the event of the

hydraulic system failing.

22-26_concordeDC.mfDC.mfDC.indd 25 04/08/2017 13:03