Passenger Aircraft Innovations Post Concorde

[Zhang Qi]

Passenger jet aircraft were a marvel when they first emerged. The first passenger jet was the De Havilland Comet. It was released on July 27, 1949, and it included several innovations which would make it 60% faster than the fastest piston engine aircraft of the time, the TWA Constellation. The TWA Constellation clocked in at 500km/h while the Comet could reach a then phenomenal 800km/h.

The innovations used by the Comet are summarized below:

1.) Swept Wing - giving the wings a slanted profile helps to deflect the aerodynamic drag encountered by airplanes at high speed flights by preventing the air from being bound in turmoil at sharp corners between the wings and fuselage.

2.) Integral Wing Fuel Tanks - placing the fuel in watertight wings eliminates the need for separate fuel tanks which add to the weight and drag of the airplane.

3.) Redux Adhesive Bonding Process - this manufacturing process is used to glue the aluminum plates of the airframe together to reduce the usage of rivets which are heavy and cause drag.

4.) Four Wheeled Undercarriages - this type of landing gear configuration is used for greater take off and landing stability because two wheels would not distribute the force experienced by jet aircraft at fast landings as widely as four wheels.

5.) Turbojet Engine - the turbojet is the first jet engine and was developed independently by both Frank Whittle and Hans Von Ohain. The advantage of this type of engine as opposed to a piston engine is that it directly pumps compressed air into a combustion chamber and mixes fuel into it then burns the fuel and uses the explosion to directly produce thrust. This type of engine is more efficient because it harnesses the force of the explosion to push the aircraft not like a piston engine which has more losses because the energy undergoes more transformations such as converting the blast into linear movement, then converting linear movement into rotary movement via a crankshaft and then letting the crankshaft turn a propeller. The additional parts needed to convert the piston engine's internal combustion into rotary motion make the engine heavier and less powerful. Also, propellers cannot run at very high speeds because the pressure of the air at jet aircraft speeds would break the propeller blades.

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After the development of the Comet, an even more ambitious plan emerged which would make passenger aircraft 3 times faster than the Comet and run at Mach 2 which is twice the speed of sound. This plan came to fruition with the introduction of the Concorde. The Concorde is the only supersonic airliner to date and it used two innovations to reach very high speeds but at one great cost: increased fuel consumption. The Concorde, despite achieving a phenomenal top speed of 2,400km/h was withdrawn from service because its fuel consumption was so high that its operational cost could not keep up with rising fuel costs following the 1970's oil crisis.

The design configurations used by the Concorde to achieve Mach 2 are summarized below:

1.) Four After-Burning Turbojet Engines - the Concorde simply increased the number of engines it used to increase its thrust. The increase in the number of engines in use would definitely increase fuel consumption because a conventional jet engine of similar size only uses two engines. Another device that was used to boost the Concord's speed was the afterburner. It injects fuel at the exhaust of the engine and uses the heat of the exhaust gas to ignite the fuel and generate a secondary explosion which will further increase the thrust but would again raise the fuel consumption.

2.) Delta Wing - the Concorde also uses a revolutionary delta wing design because it allows the vehicle to deflect air with minimum frictional loss. The delta wing runs from the fore to the aft of the fuselage, eliminating the need for a tail which gives additional air resistance.

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Because of its extremely high fuel consumption, the Concorde was eventually retired but that did not deter engineers and scientists from finding ways to improve the performance of jet aircraft. Several improvements would later emerge that would make jet aircraft 44% faster than the first jet aircraft and 2.3 times faster than the best piston engine aircraft but without increasing fuel consumption.

The Cessna Citation X passenger jet clocks in at a speed of 1,150km/h and the technologies it used to achieve this speed will be summarized below:

1.) Blade Radiators - these are placed on the jet engine's compressor blades to absorb the heat of the blades generated by its friction when it moves against the air and adds the heat to the air to increase its pressure without making the compressor do more work.

2.) Convex Blades - the jet engine's blades are curved inwards rather than straightened because straight blades do a less efficient job of deflecting and moving air.

3.) Engine Regenerators - the heat of the exhaust gas itself is used to increase the compression of the intake air and further decrease the work done by the compressor by letting the heat be absorbed by a heat exchanger and using it to heat the intake air before it is pumped into the combustion chamber.

4.) Magnetic Bearings - the usual bearings used for roller supports are grease bearings but these have the disadvantage of having viscosity. The viscosity of the oil resists the rotation of the compressor which decreases efficiency and the oil has to be pumped into a heat exchanger after some time because its temperature increases as the compressor's speed increases and if it is not cooled it may ignite. The usage of an oil cooling system further drains the engine's energy so to solve this problem, magnetic bearings are used to suspend the compressor shaft on a magnetic field which gives no friction and eliminates the need for grease.

5.) Flexible Aluminum Alloys - the increase in the flexibility of aluminum has decreased the necessary thickness of aircraft skins which lightens the weight of the aircraft, allowing its speed and efficiency to be increased.

6.) Flexible Cermet Alloys - the increase in flexibility of the cermet alloys used in the turbine and compressor blades decreases the stress exerted on the blades and allows the engine to run at a higher and more efficient operating speed.

7.) Wing Tails - tail fins are placed at the tips of the wings to cut through the drag vortexes exerted on the wingtips and decrease drag.

8.) Vortex Generators - are aerodynamic surfaces consisting of small vanes or bumps that create vortices, the purpose of which is to reduce drag. A control surface without vortex generators experiences more drag because the deflection area of the airflow around the control surface is larger which means that the pressure drop behind the control surface is also higher. The increased drop in pressure creates a suction vacuum behind the control surface which pulls it back and decreases the aircraft's velocity and range. The control surface with vortex generators on the other hand experiences less drag because the vortex generators create a turbulence that causes a larger surface area of the control surface to be covered by the flowing air which decreases the size of the vacuum behind the control surface and subsequently its drag.

9.) Turbofan Engine - the explosion generated in the combustion chamber of a jet engine releases more heat than blast and to increase the power output of the engine without increasing its fuel consumption, an expansion turbine is placed at the exhaust to extract energy from some of the waste heat and convert it into rotary mechanical energy which will be used to run an over-sized intake fan that will be used to pump air into bypass ducts placed around the engine and increase the net thrust of the engine without increasing fuel consumption. This type of engine is called a turbofan. Despite being more efficient than a turbojet, the turbofan still has one limitation: it cannot run at supersonic speeds because the increased air pressure at such speeds will fracture the enlarged intake fan. This is why the Cessna Citation X previously mentioned can only run at up to 1,150km/h which is just 35km/h below the speed of sound. But the increase in speed compared to the De Havilland Comet is still substantial.

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The speed records set by the four passenger aircraft mentioned in this article are listed below:

1.) TWA Constellation - 500km/h

2.) De Havilland Comet - 800km/h

3.) Concorde - 2,400km/h

4.) Cessna Citation X - 1,150km/h