Aviation News — September 2017

clocked up 20,000  ight

hours (about half the

design life) but were also

monitored by a ‘reference

 ight’ index that factored

cycles based upon

weight.

Additional fatigue

modelling accounted

for the thermal cycles

experienced: initially

cooling at altitude, then

heating upon supersonic

acceleration, reversing

upon descent and

deceleration. Kinetic

heating restricted the

maximum speed (nose

and leading edge

temperatures typically

peaked at 130°C and 105°C) but at Mach

2.0, heating was also by solar radiation,

hence a white livery to re ect maximum

heat. With increasing speed, the balance

changes, requiring more heat to be

radiated, hence the colour of the SR-71

Blackbird.

POWERPLANT

The term ‘powerplant’ is most appropriate

for a unique combination of three elements:

intake system, engine and exhaust nozzles.

Olympus: even the name for the heart of this

unholy trinity evokes the crackle of thunder,

tracing a pedigree from the Avro Vulcan and

BAC TSR2. Rolls-Royce produced the  nal

Mk.593 using titanium and nickel-based

superalloys to resist huge temperatures and

compression ratios. Engines were analogue

thrust-by-wire, the predecessor of Full

Authority Digital Engine Control (FADEC)

 tted even to light aircraft today.

The intakes are huge, containing ramps

that would extend inwards beyond Mach

1.0 slowing the incoming air to a speed the

engines could ingest. As a by-product, this

also compressed the air ow, boosting the

efficiency of the system. In a world  rst,

ramps and their related ducts were digitally

controlled (computers lifted from BAC guided

weapons systems) due to the critical nature

of their precise position in response to Mach

shockwave onset.

Snecma Moteurs contributed the reheat

and nozzle mechanisms. A variable

geometry nozzle allowed reverse thrust

upon landing and was synchronized with

the intakes to boost system efficiency.

Reheat was used for take-off and transonic

acceleration above Mach 1: design elegance

and the hugely efficient intake system

allowed a sustained supercruise (without

reheat), a feat only matched in the civilian

market by the Tu-144.

An unusual problem was detected very

late on: vibration of engine No.4 caused by

the opposing rotations of the wing vortex

and the engine compressors. The port

engines received a vortex rotating the other

way and No.3 was inboard, further from

the leading edge air ow. A modi cation of

inlet vanes and a thrust restriction at low

speeds resolved this. On take-off, the reheat

 ame of the No.4 engine could initially be

seen to glow weaker than the other three:

the relevant gauge on the  ight deck had a

coloured tab  tted as a reminder.

Whilst already understood prior to

Concorde, actively

mitigating the ‘bowing’

of the Olympus main

shafts was critical, given

their  ne construction

tolerances for optimum

performance. A function

of metallurgical diversity,

variable rates of thermal

expansion could cause

a slight warping along

the length of the shaft,

resulting in vibration

and more insidiously,

metal fatigue. This effect

was most apparent

post-shutdown after

several hours on the

ground, when the effects

of variable cooling

were most pronounced. To combat this

phenomena, engines could be started and

latched at a speed below idle, allowing all

components to equalise: hence the  ight

engineer’s de-bow function. A pre-start

motoring sequence for thermal stabilisation

still occurs on some jet engines, including

the CFM LEAP-1A  tted to the A320neo.

There is no auxiliary power unit (APU)

as the bulk of the tail contains the tail-wheel

unit and fuel trim tank, impractical in the high

intensity, faster rotations of modern airline

operations. For the  ight crew Concorde

offered a full-regime autopilot and linked

autothrottle, permitting a reduced workload

in all phases of  ight. This was harnessed

to a complex air data computer that

automatically monitored parameters and fed

them to related systems. Both are key in the

modern, integrated  ight deck.

Aerospace has changed a lot since the

1960s; progress now focuses upon metrics

such as economy, turnaround times and

load factor. Appropriately for the decade

concerned, there are clear parallels with

President Kennedy’s speech that instigated

Project Apollo – “we choose to go to the

moon...not because it will be easy, but

because it will be hard”. Never before had the

giant leaps of a terrestrial aircraft pioneered

so many smaller steps along the way.

26 Aviation News incorporating Jets September 2017

We wish to thank the Runway Visitor Park at

Manchester Airport and Aeroscopia Musée

Aéronautique at Toulouse Blagnac Airport for their

assistance in accessing their Concordes to take

some of the images used in this article.

The variable geometry engine nozzles

rotate for use as thrust reversers and, when

airborne, work in combination with the

engine inlets to optimise engine efficiency.

Here Concorde is rapidly accelerating after take-off. The reheat is not yet

switched off for noise abatement, the main undercarriage is retracting and

already telescopically withdrawn. AirTeamImages.com/Philippe Noret

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