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In 1969, a pioneering vision of the future made its debut to the public.
In a few years time, the sight of the concorde on international airfields all over the world
will be common place if all goes well.
Then there will be 130 passengers on board.
Flying times will be cut iby half.
London to New York from 7 hours 40 minutes to 3 hours 20 minutes.
The juxtaposition between this dated footage and the futuristic plane is strange.
It’s hard to believe passengers, 40 years ago, in a time when colour TV was a luxury,
were flying across the Atlantic at the speed of sound.
The Concorde was well ahead of its time.
An anomaly in the history of commercial travel.
A byproduct of misguided government funding, a joint effort between Britain's BAC and France’s
Aerospatiale, and it’s development funded entirely by the British and French governments
to the tune of 2.8 billion dollars.
[1]
The Concordes legacy is marred by its commercial failure, but this engineering marvel was a
triumph of ingenuity.
Nothing remotely close to it had flown before, and nothing like it has flown since.
Turning what had been a military only technology into a luxury flying experience required innovative
thinking.
This is the insane engineering of the Concorde.
Intro sequence
The engineers of the Concorde had several unique challenges.
Developing a supersonic plane is difficult enough with military design requirements,
but developing a supersonic plane that would satisfy the wealthy customers it intended
to serve is an entirely different ball game.
Aerial refuelling makes fuel efficiency a secondary concern for the military.
The comfort of the plane's passengers is an afterthought at best, and the price tag attached
to these often limited-run speciality planes is beyond the budget of a commercial airline.
Those needs are reflected in the Concordes unique design.
A sleek exterior, hiding powerful engines.
Engines developed from the iconic British war plane, the Avro Vulcan.
Fuel efficiency and supersonic flight are two opposing ideas, but these engines, the
Rolls Royce Olympus 593, when flying at Mach 2, were the most efficient engine ever created.
[2]
These engines, when introduced for the Avro Vulcan, were capable of generating just 49
kilonewtons of thrust (11,000 lbs), but over the course of their adaption for use in the
Concorde, increased in thrust by over triple to a whopping 169 kN (38,000 lbs).
[3]
20% of this thrust increase was provided by newly fitted afterburners, a technology typically
reserved for military planes.
Afterburners work by injecting fuel directly into the superheated and high-pressure exhaust
of the turbine section.
Despite this air’s journey taking it through the combustion chamber, only about half of
the oxygen in the air is consumed.
Leaving untapped energy in the exhaust of the engines.
To capture this energy fuel can be injected directly into the exhaust of the turbines
and ignited.
Basically acting like a rocket stage of the engine, causing further expansion and acceleration
of the exhaust through the exhaust nozzle.
However this system is useless without a controllable nozzle.
Typical airliner engines have a fixed nozzle, because these aircraft are expected to be
efficient at a relatively low range of subsonic speeds.
But the Concorde, with its massive range of speeds, needs not one, but two controllable
nozzles to adequately control the engine's power.
The primary nozzle connects directly to the jet pipe’s exit and consists of petal-like
structures that can close or open to vary the diameter and therefore the area of the
jet’s exit.
When the afterburner, or reheat as the British engineers called it, was ignited, it caused
a massive increase in pressure at the engine's exhaust.
This increase in pressure could cause choked flow in the engine, where a high pressure
zone ahead of lower pressure zones will prevent air from flowing through the engine correctly.
To prevent that, the primary nozzle opens wider when the afterburner is active, to decrease
pressure and ensure the mass flow rate through the engine is unchanged.
[4]
However, at times we do want to affect the flow upstream of the nozzle.
The Olympus 593 was one of the world’s first two spool turbojet engines, predated only
by the Pratt and Whitney J57 engine, by just a couple of months.
Two spool means the engine contained two compressor sections, driven by two turbine sections,
each acting on their own concentric drive shafts [3] Allowing the two sections to operate
at different rotational speeds.
The high pressure compressor was driven by the high pressure turbine, and the low pressure
compressor was driven by the low pressure turbine, which was the closest turbine to
the primary nozzle.
When the primary nozzle was actuated it caused a pressure change across the low pressure
turbine, which would cause the low pressure compressor to spin faster or slower.
This provided a method of engine control that allowed the plane to optimise it’s performance
across its wide speed range.
The secondary nozzle function is just as complex.
The eyelid doors look like some kind of steampunk blast shield, and for good reason.
The force these secondary nozzles had to endure influenced their appearance.
Withstanding huge forces at both supersonic and subsonic speeds, they could even close
completely on landing to function as reverse thrusters. [4]
By actuating these nozzles the plane could carefully manipulate the exhaust velocity,
and thus maximise thrust, because, together the pair acts as a controllable converging
diverging nozzle.
Converging diverging nozzles are typically used in rocket nozzles to accelerate the combustion
products to the optimum speed and pressure.
The opposite shapes are needed because air acts completely differently at subsonic and
supersonic speeds.
For example, when subsonic air travels through a converging duct, it speeds up as the cross-sectional
area decreases until some critical area which is referred to as the throat.
This is where Mach one would be reached.
At this point no further acceleration of air can occur, as the flow is choked.
Now, as you would expect, if that same subsonic air flows through a diverging duct, the air
slows down as the duct area increases.
This is Bernoulli's principle at play.
The bizarre thing is, the exact opposite occurs when air travels at supersonic speeds.
A converging duct will result in a decrease in velocity and a diverging duct will result
in an acceleration.
So, in order to maximise the acceleration of our exhaust gases we want to pass our subsonic
air from the engine first through a converging nozzle, the primary nozzle, until it reaches
mach 1 at the throat.
Then we want it to pass through a diverging duct, the secondary nozzle, at supersonic
speeds, so it can continue to accelerate.
These pair nozzles allowed Concorde to carefully optimise the nozzle profile for different
flight conditions.
A marvellous piece of engineering.
The same principles were used for the inlet.
No engine can operate with supersonic flow.
The shockwaves that would form inside the engine would cause all kinds of chaos.
So, the Olympus 593 needed some way to decelerate the supersonic air entering its unique square
inlets.
These squared inlets were designed to simplify the complicated task of creating nice laminar
subsonic flow for the engine's compressors.
Inside were a series of ramps and doors that could open and close depending on the flight
regime the intake was encountering. [5]
At take off the engine required all the air they could get to accelerate the plane enough
to get those cumbersome delta wings to generate enough lift to take off.
To funnel as much air as possible into the engine, the two variable ramps were retracted
into their closed position.
A spill door in front of the engine intake was held open to allow additional airflow
into the engine, while two bypass doors which controlled the air around the cooling passage
around the engine were also closed.
[6]
The afterburners were also active during takeoff, but soon after the Concorde was required to
enter a noise abatement stage of flight where the afterburners were turned off and power
was reduced as the plane climbed.
At this point the bypass doors open up to allow for cooling air to travel along the
outside of the engine.
As speed increases the primary and secondary nozzles adapt, gradually beginning to form
the ideal converging diverging nozzle for supersonic cruise Parallel to these changes
in the nozzles the inlet ramps actuate to create a converging inlet that slows down
and compresses the supersonic air entering the engine.
The fuel consumption of supersonic flight is massive,but that is primarily driven by
aerodynamic drag, not thermal efficiency.
This supersonic air being rammed and compressed into the engines helps the engine immensely
in achieving it’s high thermal efficiency.
Thermal efficiency in jet engines is largely determined by the pressure ratio achieved
by the engine.
That is the ratio of pressure between the inlet of the engine and the outlet of the
compressor, which in the case of the Concorde flying at cruise is 80:1.
An incredibly high pressure ratio.
The highly efficient GEnX engines of the Boeing 787 only manage 58:1.
The Olympus 593’s two spools each contained 7 compressor stages, each driven by a single
stage turbine.
The low pressure and high pressure compressors together provided a pressure ratio of 14:1,
a moderately high pressure ratio that would provide moderate efficiency at subsonic speeds.
However, the pressure ratio multiplied to 80:1 at cruise as the supersonic air rammed
into the unique square inlet engines.
This elevated pressure ratio resulted in extreme temperatures inside the engine that necessitated
the use of high temperature alloys that are typically reserved for the turbine blades.
Titanium blades were used for the early compressor stages and high temperature nickel alloys
used in the even hotter later stages.
[7]
Cooling the drive shaft bearings became another engineering challenge.
Increasing the mass flow rate of cooling oil was not enough to keep the bearings within
a safe operating temperature.
Looking at the differences between the original Olympus engine used in the Avro Vulcan and
the Concordes, hints towards some changes the engineers were forced to make.
A centre bearing located immediately after the high pressure compressor here no longer
exists in the Olympus 593, and the drive shaft proceeding it takes a bottle-like shape, increasing
in diameter in the new gap between bearings.
This centre bearing had to be removed because the temperatures were too high in this location
directly after the high pressure compressor, but without the support of the bearing, the
drive shaft became too flexible.
To accommodate this change, the drive shaft needed to increase in diameter to increase
stiffness. [7]
The Concorde is full of strange little design details like this.
Solutions to unique engineering problems caused by the immense cruising speed.
In order to decrease fuel consumption as much as possible, the front area of the plane needed
to be minimised.
Delta wings allow wing spans to be decreased dramatically and reduce the drag created in
supersonic flight.
However, it creates some major issues for low speed flight, where they struggle to generate
enough lift.
Making takeoffs and landings difficult.
This is where the ogival delta wings of the Concorde come into play.
This is a form of compound delta wing where there are two sections to the wing, with the
forward section having a higher sweep angle than the rear section, connected with an ogee
curve going from concave to convex curves smoothly.
This shape allowed the Concorde to generate additional lift and low speeds through the
use of vortex lift.
When flying at high angles of attack, separated air flow would roll over the wings to form
two stable cone shaped vortices where air speeds were high and air pressure was low.
Effectively creating lift.
However those high angles of attack needed for low speeds created some serious visibility
problems for the pilots, whose cockpit would have a lovely view of the sky if not for the
iconic droopsnoot.
The droop snoot is a one of a kind solution.
A mechanised nose that could drop by 12.5 degrees to provide the pilots a clear view
of the runway during these high angle of attack manoeuvres. [8]
The mechanism had four positions, controlled by the pilot with this lever.
The top position was the fully retracted position used in supersonic flight.
The second position lowered a specialised heat shield visor used to protect the cabin
windows from the heat of supersonic flight.
When placed in this position the visor hydraulic actuator would retract, causing the visor
to retract into the nose fairing.
The next position was the 5 degree down position, used for takeoffs and taxis.
Extending this hydraulic actuator.
And the final setting pushes the nose down further into the 12.5 degree setting needed
for landings.
The plane also had an extendable tail landing gear, which on most take-offs and landings
was not needed, but was present to protect the plane's engines, which would be the first
point of contact for what would normally be a tail strike for other airliners.
Tails strikes aren’t all that uncommon, usually happening on landings in difficult
conditions.
Some planes, like the 777, also have extendable protection measures in the form of tail skids,
as a strike can at best force a plane into maintenance costing the airline company money,
or at worst cause serious damage to the pressure bulkhead and put the lives of the passengers
aboard at risk.
In fact a tailstrike is responsible for the crash that claimed the most lives out of any
aviation single crash in history.
In 1985, a Japan Airlines 747 flight crashed in the mountains of Japan, 7 years after a
tail strike had occurred, which had not been correctly repaired.
With the high angles of attack demanded by the Concorde for landings, this protection
was vital to keeping the plane safe.[9]
The visor was needed during supersonic flight because the nose of the plane experienced
temperatures of around 130 degrees celsius,
while cruising at an altitude of 60,000ft, where ambient temperatures are usually around
-56 degrees celsius (or -70 degrees fahrenheit).
The Concorde went through several design iterations with this forward-facing protection.
The earliest prototypes simply removed the lower forward facing windows completely.
[12] But it turned out that pilots like having a view of where they are going, so this wasn’t
an option for the production model.
However, a version of the droopsnoot with a fully metal heat shield was originally considered
for the Concorde, which would have eliminated forward visibility during cruise which was
considered non-essentially, but thankfully these heat resistant glass visors were used
in the final version.
Working with such high temperature variations between takeoff and landing causes some serious
structural issues, especially with the frequency of flights needed to make a commercial plane
financially viable.
The thermal expansion caused by these temperatures made the plane grow by 20 centimetres (8 inches)
on each and every flight.
The fatigue this thermal stress could cause would eventually result in catastrophic failure
if not properly accounted for.
The first issue was finding a material capable of dealing with this heat.
Titanium, which was used for the SR-71, could have been used, but due to its cost and weight
was ruled out early.
Traditional aluminium would not be capable of withstanding these conditions, but a special
aluminium alloy, Hiduminium RR58, developed in Britain during World War 2 for the newly
invented gas turbine engines, could.
[10]
The alloy consists of copper, magnesium, silicon, iron, Nickel, and titanium with the remaining
percent being made up of aluminium.
Although this material had been developed decades prior to the Concorde, it had never
been used in this application.
With lower average temperatures than its traditional use inside gas turbine engines, but much longer
life requirements.
The parts would also be manufactured using different techniques, like the cold rolled
sheets needed for the fuselage.
This one process alone affected critical material properties that improved heat resistance
Forged parts tend to have larger crystal grain sizes than rolled components, which helps
forged components resist the internal crystal structure from “creeping” when under stress
and heat.
To adapt this material for the cold rolled skin of the Concorde, the engineers at Rolls
Royce had to develop new manufacturing methods to maximise the grain size of these cold rolled
components.
Manufacturing knowledge that has no doubt been used by Rolls Royce for more modern day
applications.
[10]
Now that a suitable material had been developed, shaping it in a way that allowed expansion
was crucial.
Most of this expansion was imperceptible to the crew and passengers of the Concord.
Interior panels could slide past each other to hide the expansion to the passengers, and
crucially prevented stress forming as a result of uneven expansion between the hot exterior
and cool interior.
Wiring around the plane was given slack to prevent the wiring from snapping as the plane
expanded, and many components around the plane were corrugated, meaning parts were given
a curved shape.
This allowed these parts to stretch and flatten the curves like a spring.
However, one expansion gap was quite obvious to the crew of the Concorde.
As the flight approached its cruise speed a gap between the flight engineer's console
and the cockpit bulkhead began to form.
A gap large enough to slide your hand inside of, or as became tradition for retiring Concordes,
the flight engineer's cap would be placed inside the gap as it closed.
Leaving it permanently wedged.
Like the SR-71, this continual expansion and contraction cycle caused some serious issues
with fuel tank sealants.
In order to deal with the expansion cycles a sealant needs to be flexible.
Even the mundane plastic sealants on household windows need this quality, to prevent small
movements from allowing drafts getting through.
The issue is that high temperatures tend to harden sealants over time and then as the
expansion cycles continue the sealants begin to crack and allow fuel to spill out.
While the temperatures the Concorde experienced were vastly lower than the SR-71, it was still
a maintenance issue.
The Concorde used a high temperature sealant called Viton, but even this sealant hardened
and cracked over time.
And so, approximately every 1,100 flying hours, roughly once a year, the Concorde was forced
into maintenance, which could take three weeks to complete.
Maintaining the viton sealants was one of many procedures needed.
Fuel tanks would be emptied and then vented for 24 hours to allow technicians to climb
inside and manually inspect and replace sealant.
This was a massive job and often required the technicians to work with just touch as
access to tanks 5A and 7A on the outermost part of the wing was impossible.
The Concorde had 13 separate fuel tanks in total.
Taking full advantage of the large amount of interior volume the delta wings provided.
Without these fuel tanks, capable of holding 119,000 litres of fuel [11] , the Concorde
could not have made it across the Atlantic and would have been completely useless.
To put that volume into perspective, a typical Boeing 787, the world record holder for longest
commercial flight, can hold just 34,000 litres of fuel.
These fuel tanks played a vital role in control of the plane too.
As speed increases, the centre of pressure of a wing, the point through which all lifting
force acts, tends to move backwards.
: This is usually not a significant issue for
slower commercial airliners, but the Concorde’s centre of pressure moved back by as much as
1.8 metres. [11] More than enough to cause significant control issues that would push
the plane into a nosedive dive if not accounted for.
Usually, such a shift would be counteracted by the elevator, which could stabilise the
aircraft in pitch from changes in the centre of pressure; but Concorde did not have a horizontal
tail, and adding elevons on the wing big enough to counteract this change would have resulted
in high levels of trim drag at such high speeds.
SO, Concorde engineers instead used the huge tanks they had at their disposal to deal with
this issue.
As the plane approached Mach 2 fuel would begin to be pumped out of the forward trim
tanks and into the rear trim tanks and collector tanks in the wing.
Moving up to 20 tonnes of fuel rearwards and shifting the centre of gravity backwards to
match the shift in centre of pressure.
Keeping the plane balanced without adding any additional drag with control surfaces.
An elegant solution, using the tools at hand
The Concorde is an icon in the history of aviation.
I can’t help, but feel an odd sense of nostalgia for a plane I never got to fly in.
Hundreds of thousands of passengers can see one of the last remaining Concordes while
arriving and departing from Heathrow.
Nicknamed Alpha Bravo, this concorde made its last flight a month after the tragic loss
of Air France 4590.
It was undergoing major interior upgrades when the decision to retire all Concordes
was made, stranding the plane there indefinitely.
Alpha Bravo has been in limbo ever since, never getting to undergo the planned upgrades
to prevent another disaster like Air France 4590 from ever happening again.
An unintentional monument to Britain’s storied history in aviation.
Accidental monuments like this are scattered across Britain.
Gigantic, no longer functional, radar towers can be found all over Britain.
These towers were among the first radar systems ever constructed, and played a vital role
in the defence of Britain during the Battle of Britain.
A system that the Germans vastly underestimated, thanks to not just the technology, but the
logistical and strategic systems that supported it.
This is the story of the latest episode of our Battle of Britain series, that delves
deep into how Britains radar systems worked and how those systems were integrated into
an effective intelligence system.
You can get access to the entire Battle of Britain series, our Logistics of D-Day series
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