Engineering

Beyond the Dreamliner: Blended Wing-Body Aircraft

Pollution is the most significant challenge that the aviation industry encounters nowadays. Air travel is the world’s fastest growing source of greenhouse gases like carbon dioxide, which cause climate change. Globally the world’s 16,000 commercial jet aircraft generate more than 700 million tonnes of carbon dioxide (CO2), the world’s major greenhouse gas, per year. Indeed aviation generates nearly as much CO2 annually as that from all human activities in Africa. One person flying a return trip between London and New York generates between 1.5 and 2 tonnes of CO2. The huge increase in aircraft pollution is largely due to the rapid growth in air traffic which has been expanding at nearly two and half times average economic growth rates since 1960. It is expected the number of people flying will virtually double over the next 15 years. The increasing demand will particularly come from emerging economies, such as China and India. This means increasing airport capacity, more flights, more pollution and increasingly crowded airspace. Moreover, noise pollution has become a serious concern in recent years. Many construction and expansion of airports have faced public resistance partially due to the noise produced from aircraft’s takeoff and landing. For example, the public enquiry of building Heathrow Terminal 5 took 46 months, the longest public enquiry in British history.
Meanwhile, airspace congestion has become an increasingly serious problem in aviation. Saturated airspace intensifies the stress on ground airport control centers, and thus increases the probability of air disaster due to human errors. Meanwhile, airspace congestion cause delays that thousands of travelers encounter everyday. Recent surveys have identified about 60% of the delays are due to the number of aircraft saturating the airspace, as anyone who has been delayed can attest, the ramps and runways of airports.

 

Moreover, the recent skyrocketing oil prices have harmed the profitability of airways as air fuel became more expensive. Airways are trying their best to reduce their fuel cost by purchasing new models of fuel-saving aircrafts. Meanwhile, baffled by pollution, congestion, and the thirst for profit, the two leading aerospace company, Boeing and Airbus, have launched their new models of aircraft that claimed to be revolutionary in fuel economy. However, the technique their new models used to save fuel primarily focused on reducing the weight by using composite materials and installing bigger turbo-fan engines with greater by-pass ratios that would improve the efficiency of engines and reduce noise. As there is no real revolutionary improvement in the aerodynamics of the aircraft, the extent of the improvement, albeit considerable, may not be sufficient to meet the future demand. Drastic re-design in the basic airframe has to be considered.

Size matters

As I have said above, recent surveys have identified about 60% of the delays are due to the number of aircraft saturating the airspace, as anyone who has been delayed can attest, the ramps and runways of airports. Thus the trend is towards larger aircraft that can carry more people economically, while reducing the number of operations from airports. This movement of more people on fewer aircraft has been defined by NASA as “The Lure of Large Aircraft”. However, there are a lot of other infrastructure problems that also need resolving like terminal congestion, parking facilities and, adequate loading gates.
There is a very competitive large aircraft market as illustrated by the AirBus decision to produce the A380 that could carry about 650 people on two decks. The intra-Asian market is another area that can utilize high density loading. They are already doing it with Boeing Super 747s rigged for full economy seating to haul 550 people over the short distances between cities. The trade off is less fuel, but it is not needed for the short runs. This is going to be a problem for the Chinese in about 10 years as they become more affluent and want to travel throughout their country.

 

 

Find out more about lift at Wikipedia http://en.wikipedia.org/wiki/Lift_(force) 

A groundbreaking design

Recently, an aerospace engineer came up with a revolutionary design that combines size, fuel economy and low noise levels, all the virtues demanded by future aviation industry.

This revolutionary design is blended wing body, called BWB for short and was conceived by the McDonnell Douglas Corporation and now is proposed by Boeing. It designates an alternative airframe design which incorporates design features from both a traditional ‘tube with wing’ design into a hybrid flying wing configuration Historically, the flying wing has been defended by many as potentially the most efficient aircraft configuration from the point of view of aerodynamics and structural weight, because flying-wing shape has a thick airfoil-shaped fuselage section to maximize overall efficiency by integrating all the parts of the aircraft into a single lifting surface. For the conventional ‘tube with wing’ configuration, it is only the wing that is generating lift for the aircraft. The fuselage of the conventional configuration does not generate lift. For the BWB design, as the fuselage is incorporated into the flying wing, the fuselage in BWB therefore does generate lift for the aircraft. Thus the lift to drag ratio can be increased from something like the 747’s 17 to 20-plus for the BWB. This means BWB design would significantly reduce drag. This saving in drag translates into substantial economic and environmental benefits. BWB design is estimated to use 20-25% less fuel, while cruising at high subsonic speeds on flights of up to 7,000 nautical miles. It is 10-15% lighter (or will conversely allow for more paying payload), resulting directly in 10-15% lower operating costs than the advanced ‘tube with wing’ aircraft of today. With the development of lighter composite material and more efficient engine design, these figures may well increase substantially, making BWBs even more attractive.

The BWB concept houses a wide double-deck passenger compartment that actually blends into the wing. The experience for passengers will be transformed. Instead of sitting in rows with a window at either side, they will be in a huge, delta shaped cabin that will give airlines great scope for imaginative configurations. Adjacent to the passenger section is ample room for baggage and cargo. BWB aircraft could be developed to carry 800 or more passengers. Thus BWB could reduce the number of operations from airports, and help to alleviate the airspace congestion. An aircraft of this type would have a wing span slightly wider than a Boeing 747 and could operate from existing airport terminals. 
Benefits and Challenges

Al Bowers, a Senior Aerodynamicist for NASA at the Dryden Flight Research Center conclude the benefits and challenges of BWB design:
“The benefits include: lower operating costs; lower production costs; reduced airport/airspace congestion; lower fares; reduced environmental impact and; improved safety. Lower production costs come from not have as many tight bends so the manufacturing costs go down. Although the number of aircraft at terminals is very unlikely to go down, they will be moving more passengers with each departure which will impact congestion by reducing its escalation. It is felt this design concept is at least as safe, and possibly saver, than a convention ‘tube and wing’ design.
“The challenges included: structures and materials; aero-structural integration; aerodynamics; controls; propulsion-airframe integration; systems integration and; infrastructure. Structure is back to the pressurization issues and the integration issue revolves around making the structure clean enough to work aerodynamically and achieve the savings potential.”

Cambridge engineers moot “silent” plane

Recently, a BWB design came from the Silent Aircraft Initiative, an academic-industrial collaboration involving Cambridge University, the Massachusetts Institute of Technology, Rolls-Royce, Boeing and other aerospace companies, and airlines and airports, signal that the era of BWB is just on the door step. The designed aircraft, with four engines on top of a wing-shaped fuselage, should be so quiet no noise would be heard outside an airport’s perimeter. (Detailed information on how this design works to reduce noise, can be read in another article coming soon)

However, the development of BWB still exists in miniature modeling and wind tunnel testing. The commercial launch of BWB passenger aircraft may still take years to come. It is estimated by some aerospace engineers that the first BWB may come in service in at least 20 years time. Now, we should cross our fingers and hope our ingenious engineers can make this groundbreaking design a reality as soon as possible.[6]

References

 

1. GreenSkies: Aviation Emissions and Climate Change
2. http://www.airportwatch.org.uk/briefingsheets/climatechange/index.php
3. http://www.aerosite.net/
4. www.nasa.com http://www.nasa.com/
5. www.silentaircraft.org http://www.silentaircraft.org/
6. http://www.spacedaily.com/

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