Wide-body aircraft

A wide-body aircraft is a large airliner with two passenger aisles, also known as a widebody aircraft or twin-aisle aircraft. The typical fuselage diameter is 5 to 6 m (16 to 20 ft). In the typical wide-body economy cabin, passengers are seated seven to ten abreast, allowing a total capacity of 200 to 850 passengers. The largest wide-body aircraft are over 6 m (20 ft) wide, and can accommodate up to eleven passengers abreast in high-density configurations.

By comparison, a traditional narrow-body airliner has a diameter of 3 to 4 m (10 to 13 ft), with a single aisle, and seats between two and six people abreast.

Wide-body aircraft were originally designed for a combination of efficiency and passenger comfort. However, airlines quickly gave in to economic factors, and reduced the extra passenger space in order to maximize revenue and profits.

Wide-body aircraft are also used for the transport of commercial freight and cargo and other special uses, described further below.

The largest wide-body aircraft, such as the Boeing 747 and Airbus A380, are known as jumbo jets due to their very large size.

History
The Bristol Brabazon was a widebody transatlantic design that first flew in 1949 but never reached production. Following the success of the Boeing 707 and Douglas DC-8 in the late 1950s, airlines began seeking larger aircraft to meet the rising global demand for air travel. Engineers were faced with many challenges as airlines demanded more passenger seats per aircraft, longer ranges and lower operating costs.

Early jet aircraft such as the 707 and DC-8 seated passengers along either side of a single aisle, with no more than six seats per row. Larger aircraft would have to be longer, higher (such as a double deck), or wider in order to accommodate a greater number of passenger seats. Engineers realized having two decks created difficulties in meeting emergency evacuation regulations, with the technology available at that time. They opted for a wider fuselage as one solution (the 747, and eventually the DC-10 and L-1011). By adding a second aisle, the wider aircraft could accommodate as many as 10 seats across.

The engineers also opted for creating "stretched" versions of the DC-8 (61, 62 and 63 models), as well as longer versions of the B-707 (-320B and 320C models), B-727 (-200 model) and DC-9 (-30, -40, and -50 models), all of which were capable of accommodating more seats than their shorter predecessor versions. The full length double-deck solution had to wait until the 21st Century (A-380).

The widebody age began in 1970 with the entry into service of the first widebody airliner, the four-engined, double-deck Boeing 747. New trijet widebody aircraft soon followed, including the McDonnell Douglas DC-10 and the Lockheed L-1011 Tristar. The first widebody twinjet, the Airbus A300, entered service in 1974.

After the success of the early widebody aircraft, several successors came to market over the next two decades, including the Airbus A330-A340 Series and the Boeing 777. In the jumbo category, the capacity of the Boeing 747 was not surpassed until October 2007, when the Airbus A380 entered commercial service with the nickname Superjumbo.

Design considerations
Although widebody aircraft have a larger frontal area (and thus greater form drag) than a narrow-body aircraft of similar capacity, they have several advantages over their narrow-body counterparts:


 * Larger volume of space for passengers, giving a more open feeling to the space
 * Lower ratio of surface area to volume, and thus lower drag on a per-passenger basis
 * Twin aisles that accelerate loading, unloading, and evacuation compared to a single aisle
 * Wider fuselage that reduces the overall aircraft length, improving ground manoeuvrability and reducing the risk of tail strikes.
 * Greater under-floor freight capacity
 * Better structural efficiency for larger aircraft than would be possible with a narrow-body design

British and Russian designers had proposed widebody aircraft similar in configuration to the Vickers VC10 and Douglas DC-9, but with a widebody fuselage. The British Three-Eleven project never left the drawing board, while the Russian Il-86 widebody proposal eventually gave way to a more conventional wing-mounted engine design, most likely due to the inefficiencies of mounting such large engines on the aft fuselage.

Engines


As jet engine power and reliability have increased over the last decades, most of the widebody aircraft built today have only two engines. A twinjet design is more fuel-efficient than a comparable trijet or four-engined aircraft. The increased reliability of modern jet engines also allows aircraft to meet the ETOPS certification standard, which calculates reasonable safety margins for flights across oceans. The trijet design has been effectively dismissed due to higher maintenance and fuel costs, and only the heaviest widebody aircraft today are built with four engines (the Airbus A340, Airbus A380 and Boeing 747).

The Boeing 777 twinjet features the largest and most powerful jet engine in the world, the General Electric GE90, which is 128 inches (3.25 m) in diameter. This is almost as wide as the entire fuselage of a Boeing 737 at 148 inches (3.76 m).

The massive maximum takeoff weight of the Airbus A380 (560 tonnes (1,200,000 lb)) would not have been possible without the engine technology developed for the Boeing 777 (such as contra-rotating spools). The Trent 900 engine pictured, used on the Airbus A380, has a fan blade diameter of 116 inches (2.95 m), only slightly smaller than the GE90 engines on the Boeing 777. An interesting design constraint of the Trent 900 engines is that they are designed to fit into a Boeing 747-400F freighter for relatively easy transport by air cargo.

Interiors
The interiors of aircraft, known as the aircraft cabin, have been undergoing evolution since the first passenger aircraft. Today, between one and four classes of travel are available on widebody aircraft.

Bar and lounge areas which were once installed on the Boeing 747 have mostly disappeared, but a few have returned in first class or business class on the Airbus A340-600, Boeing 777-300ER, and on the Airbus A380. Emirates Airline has installed showers for first-class passengers on the A380; twenty-five minutes are allotted for use of the room, and the shower operates for a maximum of five minutes.

Depending on how the airline configures the aircraft, the size and seat pitch of the airline seats will vary significantly. For example, aircraft scheduled for shorter flights are often configured at a higher seat density than long-haul aircraft. Due to current economic pressures on the airline industry, high seating densities in the economy class cabin are likely to continue.

A comparison of interior cabin widths and economy class seating layouts is shown below under widebody specifications. Further information can be found under external links.

Wake turbulence and separation


Aircraft are categorized by ICAO according to the wake turbulence they produce. Because wake turbulence is generally related to the weight of an aircraft, these categories are based on one of four weight categories: light, medium, heavy, and super.

Due to their weight, all current widebody aircraft are categorized as heavy, or in the case of the A380 in U.S. airspace, super.

The wake-turbulence category also is used to guide the separation of aircraft. Super and heavy-category aircraft require greater separation behind them than those in other categories. In some countries, such as the United States, it is a requirement to suffix the aircraft's call sign with the word "heavy" (or super) when communicating with air traffic control in certain areas.

Special uses


Widebody aircraft are used in science, research, and the military. Two specially modified Boeing 747 aircraft, the Shuttle Carrier Aircraft, were used to transport the U.S. Space Shuttle. Some widebody aircraft are used as flying command posts by the military, such as the Boeing E-4, while the Boeing E-767 is used for Airborne Early Warning and Control. New military weapons are tested aboard widebodies, as in the laser weapons testing on the Boeing YAL-1. Other widebody aircraft are used as flying research stations, such as the joint German-U.S. Stratospheric Observatory for Infrared Astronomy. Airbus A340, Airbus A380, and Boeing 747 four-engine widebody aircraft are used to test new generations of aircraft engines in-flight. A few aircraft have also been converted for aerial firefighting, such as the DC-10-based Tanker 910 and the 747-based Evergreen Supertanker.

Some widebody aircraft are used as VIP transport. Canada uses the Airbus A310, while Russia uses the Ilyushin Il-96 to transport their highest leaders. Germany replaced their Airbus A310 by Airbus A340 in spring 2011. The specially modified Boeing 747-200 used by the President of the United States is known as Air Force One, or the Boeing VC-25. More information can be found under: Air transports of heads of state and government.

Future development


Airbus and Boeing are racing to market with two new widebody designs, currently in development. Both manufacturers have been under significant pressure to see which obtains the most orders.

In 2005, the Boeing 787 Dreamliner had received more orders than Airbus, and was scheduled to be the first to enter into airline service. The 787 is also the first large commercial aircraft to utilize a monolithic composite fuselage.

The initial Airbus A350 design was only a minor upgrade to that of the A330/A340 series, but Airbus was forced to make significant design changes in response to feedback from the airlines. In addition to being a few inches wider than the Boeing, Airbus claims that the A350 final specifications will be better than that of the 787.

The article on competition between Airbus and Boeing further discusses the rivalry, while order counts between the two aircraft can be compared under Airbus A350 orders versus Boeing 787 orders.