The Insane Engineering of the Concorde

This episode of Real Engineering is brought to you by the CuriosityStream & Nebula package. Watch the latest episode of our new series 'The Battle of Britain' on Nebula for just €14.79 a year. In 1969, a pioneering vision of the future made its public debut. In a few years, if all goes well, seeing the Concorde at international airfields around the world will be commonplace. There will then be 130 passengers on board. Flight times will be cut in half. From 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 that 40 years ago, at a time when color television was a luxury, passengers were flying across the Atlantic at the speed of sound.

The Concorde was 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, its development funded entirely by the British and French governments to the tune of $2.8 billion. The Concorde's legacy is tarnished 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 crazy

engineering

of the Concorde.

Introduction Sequence The Concorde engineers had several unique challenges. Developing a supersonic aircraft is difficult enough due to military design requirements, but developing a supersonic aircraft that satisfies the wealthy customers it is intended to serve is a completely different ball game. Aerial refueling makes fuel efficiency a secondary concern for the military. Airline passenger comfort is an afterthought at best, and the price tag associated with these special, often limited-operation planes exceeds a commercial airline's budget. Those needs are reflected in Concorde's unique design. An elegant exterior that hides powerful engines. Engines developed from the iconic British warplane, 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. These engines, when introduced for the Avro Vulcan, were capable of generating only 49 kilonewtons of thrust (11,000 pounds), but over the course of their adaptation for use in the Concorde, their thrust more than tripled to a whopping 169. kN (38,000 pounds). pounds). 20% of this thrust increase was provided by newly installed afterburners, a technology typically reserved for military aircraft. Afterburners work by injecting fuel directly into the superheated, high-pressure exhaust of the turbine section. Despite this air traveling through the combustion chamber, only about half of the oxygen in the air is consumed.

Leaving untapped energy in the engines' exhaust. To capture this energy, fuel can be injected directly into the turbine exhaust and ignited. It basically acts as 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 aircraft engines have a fixed nozzle, because these aircraft are expected to be efficient in a relatively low range of subsonic speeds. But the Concorde, with its enormous speed range, needs not one, but two controllable nozzles to properly control the engine's power. The main nozzle connects directly to the outlet of the jet tube and consists of petal-shaped structures that can be closed or opened to vary the diameter and therefore the jet outlet area.

When the afterburner, or superheat as British engineers called it, was turned on, it caused a massive increase in pressure in the engine exhaust. This increase in pressure could cause obstructed flow in the engine, where a high pressure zone in front of lower pressure zones will prevent air from flowing properly through the engine. To prevent this, the primary nozzle opens wider when the afterburner is active, to decrease pressure and ensure that the mass flow rate through the engine does not change. However, sometimes we do want to affect the flow upstream of the nozzle. The Olympus 593 was one of the world's first twin-spool turbojet engines, preceded only by the Pratt and Whitney J57 engine by just a couple of months.

Two spools means that the engine contained two compressor sections, driven by two turbine sections, each acting on their own concentric drive shafts, 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 turbine closest to the primary nozzle. When the primary nozzle was actuated, it caused a pressure change across the low-pressure turbine, causing the low-pressure compressor to spin faster or slower. This provided a method of engine control that allowed the aircraft to optimize its performance over its wide speed range.

The function of the secondary nozzle is equally complex. The lid doors look like some kind of steampunk blast shield, and for good reason. The force that these secondary nozzles had to withstand influenced their appearance. Withstanding enormous forces at both supersonic and subsonic speeds, they could even close completely upon landing to function as reverse thrusters. By actuating these nozzles, the aircraft could carefully manipulate the exhaust velocity and thus maximize thrust, because, together, the torque acts as a controllable converging and diverging nozzle. Converging and diverging nozzles are typically used in rocket nozzles to accelerate combustion products to the optimal speed and pressure.

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 accelerates as the cross-sectional area decreases to a critical area called the throat. This is where Mach one would be reached. At this point no further acceleration of the air can occur, as the flow is throttled. Now, as expected, if that same subsonic air flows through a diverging duct, the air slows down as the area of ​​the duct increases. This is Bernoulli's principle at play. The strange thing is that the exact opposite happens 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 to maximize the acceleration of our exhaust gases, we first want to pass the subsonic engine air through a converging nozzle, the primary nozzle, until it reaches mach 1 at the throat. Then we want it to pass through a divergent duct, the secondary nozzle, at supersonic speeds, so it can continue accelerating. This pair of nozzles allowed Concorde to carefully optimize the nozzle profile for different flight conditions. A wonderful work of engineering. The same principles were used for the entry.

No engine can operate with supersonic flow. The shock waves that would form inside the engine would cause all kinds of chaos. So the Olympus 593 needed some way to slow down the supersonic air coming through its unique square inlets. These square inlets were designed to simplify the complicated task of creating a nice laminar subsonic flow for the engine compressors. Inside there were a series of ramps and doors that could open and close depending on the flight regime at the entrance. On takeoff, the engine required all the air it could get to accelerate the plane enough for those cumbersome delta wings to generate enough lift to take off.

To channel as much air as possible into the engine, the two variable ramps were retracted to their closed position. A spill door in front of the engine inlet was kept open to allow additional airflow into the engine, while two bypass doors controlling the air around the cooling duct around the engine were also closed. The afterburners were also active during takeoff, but shortly thereafter the Concorde was required to enter a noise reduction stage of flight where the afterburners were turned off and power was reduced as the aircraft climbed. At this point, the bypass doors open to allow cooling air to travel around the outside of the engine.

As speed increases, the primary and secondary nozzles adapt, gradually beginning to form the converging diverging nozzle ideal for supersonic cruising. In parallel with these changes in the nozzles, the inlet ramps are activated to create a converging inlet that slows and compresses the supersonic air entering the engine. The fuel consumption of supersonic flight is enormous, but it is mainly due to aerodynamic drag, not thermal efficiency. This supersonic air being introduced and compressed into the engines greatly helps the engine achieve its high thermal efficiency. The thermal efficiency of jet engines is largely determined by the pressure ratio achieved by the engine.

That is the pressure ratio between the engine inlet and the compressor outlet, which in the case of the Concorde flying at cruise is 80:1. An incredibly high pressure ratio. The Boeing 787's highly efficient GEnX engines only achieve a ratio of 58:1. The two spools of the Olympus 593 each contained 7 compressor stages, each driven by a single-stage turbine. The low- and high-pressure compressors together provided a 14:1 pressure ratio, a moderately high pressure ratio that would provide moderate efficiency at subsonic speeds. However, the pressure ratio multiplied to 80:1 in cruise as supersonic air hit the unique square-inlet engines. This high pressure ratio resulted in extreme temperatures within the engine that required the use of high-temperature alloys normally reserved for turbine blades.

Titanium blades were used for the early stages of the compressor and high temperature nickel alloys in the even hotter later stages. Cooling the driveshaft bearings became another engineering challenge. Increasing the mass flow rate of cooling oil was not sufficient 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 at some changes that the engineers were forced to make. In the Olympus 593 there is no longer a central bearing located immediately after the high-pressure compressor, and the advancing drive shaft takes the shape of a bottle, increasing in diameter in the new space between the bearings.

This center bearing had to be removed because the temperatures were too high in this location immediately after the high pressure compressor, but without the bearing support the drive shaft became too flexible. To accommodate this change, the driveshaft needed to increase in diameter to increase rigidity. The Concorde is full of strange little design details like this. Solutions to unique engineering problems caused by immense cruising speed. To reduce fuel consumption as much as possible, it was necessary to minimize the front area of ​​the aircraft. Delta wings allow the wingspan to be drastically reduced and reduce the drag created in supersonic flight.

However, it creates some major problems for low-speed flight, where they have difficulty generating enough lift. Making takeoffs and landings difficult. This is where the Concorde's pointed delta wings come into play. This is a form of compound delta wing where there are two sections of the wing, with the forward section having a higher sweep angle than the rear section, connected with an ogee curve that goes 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, the separated airflow would roll over the wings to form two stable cone-shaped vortices where the air speed was high and the air pressure was low.

Effectively creating lift. However, those high angles of attack needed for low speeds created serious visibility problems for the pilots, whose cockpit would have a beautiful view of the sky if it weren't for the iconic droopsnoot. The droop snoot is a unique solution. A mechanized nose that could descend 12.5 degrees to provide pilotsa clear view of the runway during these high-angle attack maneuvers. 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 specialized thermal protection visor used to protect the cockpit windows from the heat of supersonic flight.

When placed in this position, the hydraulic visor actuator retracts, causing the visor to retract into the front fairing. The next position was the 5-degree down position, used for takeoff and taxiing. Expanding this hydraulic actuator. And the final configuration pushes the nose down to the 12.5-degree configuration needed for landings. The plane also had an extendable tail landing gear, which on most takeoffs and landings was not necessary, but was present to protect the plane's engines, which would be the first point of contact for what would normally be a hit. queue for other planes. . Tail strikes are not that uncommon and usually occur during landings in difficult conditions.

Some aircraft, such as the 777, also have extendable protective measures in the form of tail skids, as an impact can, at best, force a plane to undergo maintenance, costing the airline money. , or in the worst case, cause serious damage to the pressure bulkhead and endanger lives. of passengers on board at risk. In fact, a tail strike is responsible for the accident that claimed the most lives of any aviation accident in history. In 1985, a Japan Airlines Flight 747 crashed in the mountains of Japan, 7 years after a tail dent occurred, which had not been properly repaired. With the high angles of attack that the Concorde required for landings, this protection was vital to keep the plane safe.

The visor was necessary during supersonic flight because the nose of the plane experienced temperatures of around 130 degrees Celsius, while cruising at an altitude of 60,000 feet, where ambient temperatures are typically lower, around -56 degrees Celsius (or -70 Fahrenheit degrees). The Concorde went through several design iterations with this forward-facing protection. Early prototypes simply eliminated the forward-facing lower windows entirely. But it turned out that pilots like to have a view of where they are going, so this was not an option for the production model. However, a version of the droopsnoot with an all-metal heat shield was originally considered for the Concorde, which would have eliminated forward visibility during cruising, which was not considered essential, but fortunately 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 problems, especially with the frequency of flights required to make a commercial airliner financially viable. The thermal expansion caused by these temperatures caused the plane to grow 20 centimeters with each flight. The fatigue that this thermal stress could cause would eventually result in catastrophic failure if not properly accounted for. The first question was to find a material capable of withstanding this heat. Titanium could have been used, which was used for the SR-71, but due to its cost and weight it was soon discarded. Traditional aluminum would not be able to withstand these conditions, but a special aluminum alloy, Hiduminium RR58, developed in Britain during World War II for the newly invented gas turbine engines, could.

The alloy is made up of copper, magnesium, silicon, iron, nickel and titanium and the remaining percentage is made up of aluminum. Although this material had been developed decades before Concorde, it had never been used in this application. With lower average temperatures than its traditional use inside gas turbine engines, but with much longer life requirements. Parts would also be manufactured using different techniques, such as the cold rolled sheets needed for the fuselage. This 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 "creeping" of the internal crystalline structure when under stress and heat.

To adapt this material to the Concorde's cold-rolled skin, Rolls Royce engineers had to develop new manufacturing methods to maximize the grain size of these cold-rolled components. Manufacturing knowledge that Rolls Royce has undoubtedly used for more modern applications. Now that a suitable material had been developed, it was crucial to shape it in a way that allowed for expansion. Most of this expansion was imperceptible to the Concord's crew and passengers. The interior panels could slide against each other to hide the expansion from passengers and, crucially, prevented tension from forming as a result of uneven expansion between the hot exterior and the cold interior.

The wiring around the plane was loosened to prevent it from breaking as the plane expanded, and many components around the plane were corrugated, meaning the parts were given a curved shape. This allowed these parts to stretch and flatten the curves like a spring. However, an expansion gap was quite obvious to the Concorde crew. As the flight approached its cruising speed, a gap began to form between the flight engineer's console and the cockpit bulkhead. A gap large enough to slide your hand into, or as became tradition for retired Concordes, the flight engineer's cap would be placed inside the gap as it closed.

Leaving him permanently shod. Like the SR-71, this continuous cycle of expansion and contraction caused some serious problems with the fuel tank sealants. To cope with expansion cycles, a sealant must be flexible. Even the usual plastic sealants for domestic windows need this quality to prevent small movements from allowing drafts to pass through. The problem is that high temperatures tend to harden the sealants over time and then, as the expansion cycles continue, the sealants begin to crack and allow fuel to leak out. While the temperatures the Concorde experienced were much 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, about every 1,100 flight hours, about once a year, the Concorde was forced to perform maintenance, which could take three weeks to complete. Maintenance of the Viton sealants was one of the many procedures required. The fuel tanks would be emptied and then vented for 24 hours to allow technicians to come in and manually inspect and replace the sealant. This was a huge job and often required technicians to work by touch as access to the 5A and 7A tanks on the outermost part of the wing was impossible.

The Concorde had a total of 13 separate fuel tanks. Making the most of the large amount of interior volume that the delta wings provided. Without these fuel tanks, with a capacity of 119,000 liters of fuel, the Concorde would not have been able to cross the Atlantic and would have been completely useless. To put that volume in perspective, a typical Boeing 787, holder of the world record for longest commercial flight, can hold only 34,000 liters of fuel. These fuel tanks also played a vital role in controlling the aircraft. As speed increases, a wing's center of pressure, the point through which all lift forces act, tends to move rearward. : This is not usually a major problem for slower commercial airliners, but the Concorde's center of pressure moved back up to 1.8 meters.

More than enough to cause major control problems that would push the plane into a tailspin if not taken into account. Typically, such a change would be counteracted by the elevator, which could stabilize the pitch of the aircraft due to changes in the center of pressure; but the Concorde did not have a horizontal tail, and adding wing elevons large enough to counteract this change would have resulted in high levels of aerodynamic drag at such high speeds. So the Concorde engineers used the huge tanks they had at their disposal to solve this problem. As the aircraft approached Mach 2, fuel would begin to be pumped from the forward trim tanks to the rear trim tanks and wing header tanks.

Move up to 20 tons of fuel rearward and shift the center of gravity rearward to match the change in center of pressure. Keep the airplane balanced without adding any additional resistance 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 a strange sense of nostalgia for a plane I never got to fly. Hundreds of thousands of passengers can see one of the last remaining Concordes as they arrive and depart 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 was made to retire all Concordes, leaving the aircraft stranded there indefinitely. Alpha Bravo has been in limbo ever since and was never able to undergo planned upgrades to prevent another Air France 4590 disaster from happening again. An inadvertent monument to the storied history of British aviation. Accidental monuments like this are scattered throughout Britain. All over Britain you can find gigantic radar towers that are no longer working. These towers were among the first radar systems ever built and played a vital role in the defense of Britain during the Battle of Britain.

A system that the Germans greatly underestimated, not only thanks to the technology, but also to the logistical and strategic systems that supported it. This is the story of the latest episode of our Battle of Britain series, which delves into how British 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 D-Day Logistics series, by signing up for CuriosityStream for just over a dollar a month. With this annual subscription to CuriosityStream you can enjoy the mountain of award-winning documentaries on CuriosityStream and support independent content creators like me at Nebula.

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