The Latest Developments of Air Transport
The commercial airline industry has grown from a few aircraft to that of a multi-billion pound industry. The Boeing 707 began a revolution in air travel when it entered service in1958.It was the first commercially successful jet aircraft. Since then aircraft manufacturers have strived to provide larger and more economical planes to aircraft companies.
The basic appearance of commercial airliners has not changed much for over 50 years. Nevertheless, there has been a considerable increase in innovations and new technology within the aerospace industry. Advancements in engine efficiency, aerodynamics and new materials have all led to a significantly lower operating cost per seat mile of commercial aircraft.
There have been a number of significant innovations, especially on the Boeing 787, the latest wide body jet to enter service. Composite materials are now been used in the commercial aircraft industry. The Boeing 787 is primarily constructed from composite materials. They are used in most primary structures, particularly the fuselage.
By using a unique one piece composite barrel construction, the 787 eliminates the need for any fuselage lap joints, doubler longitudinal skin splices. This has a dramatic reduction in weight and drag. In addition, it also significantly reduces the amount of maintenance and inspections required. Panel construction in aircraft such as the Boeing 707 requires additional joints, fasteners and splice plates, resulting in increased weight and inspections.
The most critical expense areas for aircraft fleets are fuel, maintenance and its residual costs. New aircraft have been designed and manufactured to lower these costs. Maintenance tasks have been reduced by 30 per cent, and inspections are required less frequently. A good example of this is the 787 which does not require its first heavy maintenance check until after 12 years of service.
Another advantage of using composite materials, especially in the wing structure is that it gives aircraft such as the 787 a higher aspect ratio than previous aircraft, resulting in a higher Coefficient of Lift. A lighter aircraft will reduce fuel costs and therefore have a positive effect on the range equation.
Advancements in aerodynamics have led to an increase in the overall efficiency of aircraft, becoming more fuel efficient by reducing drag. Components such as winglets and wingtip fences decrease vortices created at the wing tips which cause aerodynamic drag.
Raked wing tips create a greater degree of sweep on an aircraft wing. This enhances the wings efficiency, by increasing the aspect ratio of the wing, therefore decreasing the amount of lift induced drag produced by the aircraft. This kind of drag can be reduced by up to 6%.with the implication of raked wing tips.
Blended winglets can be attached to the wing giving a level curve in place of a sharp angle reducing interference drag at the wing.
Recently Airbus has completed the first flight of its A320 test aircraft equipped with ‘sharklet’ wing-tip. The sharklets can cut fuel burn by up to 3.5% over the current configuration with wing-tip fences and increase the maximum take-off weight by up to 3 tonnes.
The engine with the higher value of specific impulse (Isp) is more efficient because it produces more thrust for the same amount of fuel. A higher or more favourable L/D ratio is typically one of the major goals in aircraft design. Using these higher values will obviously increase the range of an aircraft.
The latest propulsion systems have advanced, improving the economics of aircraft. Early jet airliners had turbojet engines. These engines operated well at high altitudes and speeds, but had had a high fuel burn rate. When the turbo fan engine was introduced it could move a greater amount of air at lower speeds, than the turbo jet engine, as it had a large fan attached on the front. By enclosing the fan inside a cowling, the aerodynamics was better controlled. This reduced fuel consumption, compared to a turbojet. The next-generation engine technology is provided by Boeing’s engine partners, General Electric and Rolls-Royce. The latest engines being the Rolls Royce Trent 1000 and the General Electric GEnx.
These engines incorporate a bypass ratio of about 10, compared to the first turbo fan engines having ratios of about 7. The higher bypass ratio allows the engine to be quieter, with significantly reduce fuel consumption. This lowers cost for the 787 operators and reduces emissions, lessening the environmental impact of the aircraft. Chevrons on the nacelles significantly reduce shock cell noise in the aft cabin.
Both the Trent 1000 and the GEnx engines are interchangeable at the wing of the 787. This reduces operating costs and gives the 787 liquidity and strong residual value.
Both the Rolls Royce Trent 1000 and the GEnx eliminate the engine bleed air system and associated pneumatic system. This improves the reliability and efficiency of the aircraft by further reducing fuel consumption and maintenance costs. The electric system improves efficiency by removing only the power actually needed during each phase of flight. The aircraft have a health management system which monitors the electrical systems, improving the aircrafts productivity.
General Electric recently delivered a new innovation in technology producing advanced composite material fan blades .The process results in a 100% defect-free, carbon-reinforced epoxy blade , which means no voids in the fibres. In order to accomplish this, advanced sensor and data acquisition systems were used. This technology will continue to be used on wide-body aircraft of the future, Resulting in lower cost, and greater efficiency. Duncan, Tom, 2010. Engines of Today. Commercial Airliners, 2, 8.
An innovation to watch out for in the near future is the use of Titanium aluminide turbine blades. Titanium aluminide’s low density means that a turbine blade will be about half the weight of a blade made from a traditional nickel alloy blades. Reducing the density and the weight of an aircraft engine has huge benefits.
Using the range equation you can calculate the range of an aircraft, if you have the value of the following components.
- R = distance flown (m)
- u = velocity (m/s)
- Isp = specific impulse (s)
- L/D = lift-to-drag ratio (dimensionless)
- Winitial = gross aircraft weight at the start of cruise (kg)
- Wfinal = gross weight at the end of cruise (kg)
The engine with the higher value of specific impulse (Isp) is more efficient because it produces more thrust for the same amount of fuel. A higher or more favourable L/D ratio is typically one of the major goals in aircraft design. Using these higher values will obviously increase the range of an aircraft.
The appearance of aircraft has not changed much over 50 years because when it was first designed the cone shaped fuselage with wings attached had good design and technology features.
The process of designing and producing a new aircraft is very expensive and risky. There is enormous economic risk along with a large investment and liability risk. The (you bet your company curve) plot below shows the cumulative gain or loss in an aircraft project during its life. It was recently estimated that a new large airplane project at Boeing would take 20 billion dollars to develop.
Aircraft manufacturing companies are not likely to take risks on projects that rely on unproven technology. This is the reason that innovative concepts are not likely to be tried out on the next generation of commercial airliners and why aircraft such as the 787 look so much like the Boeing 707. Customers of commercial aircraft manufacturers can sell their planes which are basically the same appearance as 50 years ago. There is not enough financial gain to design an aircraft with a different appearance. In addition, passengers may prefer to board an aircraft that consist of a tube with wings rather than an aircraft in the shape of a large triangle.
The new 787 Dreamliner is a prime example of how innovations in new airframe and propulsion technology can lead to a more efficient aircraft. From innovative composite materials to aerodynamics to propulsion technology the 787 has become 70% more fuel efficient than the 1950s-era four-engine Pratt & Whitney JT3D-powered Boeing 707s.
This has considerably increased revenue potential through significantly better performance, improved fuel efficiency and lowered maintenance decreasing operating cost per seat mile of commercial aircraft.
