Kraków 2014-03-02
Wide-body planes.
In the period 1960-1980, transport planes with a turbojet drive dominated air transport. This period culminated in commercial passenger airliners; Boeing 707, Douglas DC-8 and Convair 880/990 which were powered by turbojet engines. The first two designs were designed to take as many passengers on board as possible. Convair 880/990, on the other hand, were advertised as the fastest passenger airliners. It is impossible to hide. Two trends emerged; more passengers or faster. In this chapter we will present the development of wide-body airplanes, or the trend of more passengers.
Fuselage widening.
After the commercial aircraft Boeing-707, Douglas DC-8 and Convair 880/990 were put into service, pragmatic Americans quickly calculated that if more passengers were placed on board the aircraft, the profitability of connections would be higher. The actual analysis of the fuselage width and the number of passenger seats in a row began during the design of the Boeing 707. Airplanes designed at the turn of the 1940s and 1950s usually had a fuselage diameter of 10 ft (3.048 m). Such a width of the fuselage allowed to place seats (standard width 50 cm) in a 2×2 arrangement, with a passage (corridor) about 70 cm wide. However, it is too narrow to place the seats in a 3×2 arrangement. Therefore, airplanes with a fuselage of 11 ft (3.3528 m) began to be designed. Thanks to this, in the economy (tourist) class it was possible to accommodate five seats in a row. This is how the Convair 880 aircraft was developed.
Boeing then went even further. The extensive work on the future B 707, based on the Dash 80 / Boeing 367-80 design, was decided to suspend and redesign the fuselage by widening the fuselage from 11 ft (3.3528 m) to 12 ft (3.6576 m). This width allowed (for the first time in the history of aviation) to place 3×3 seats in the economy (tourist) class.
Ultimately, the exterior of the B 707 hull is 12.33 ft (3.759 m) in diameter. The greatest width inside the cab is 11.32 ft (3,450 m). A set of three armchairs is approximately 145 cm wide and the passage is approximately 55 cm. This arrangement has another significant advantage; It allows great possibilities of arranging the cabin in the higher classes (I class, business class). Not only can the seats be made much wider, they can also be folded out to a lying position. This layout from the B 707 was transferred to other structures; B 727 and B 737. Also in the DC-8 aircraft it was possible to put 6 seats in one row, with a passage in the middle.
Naturally, planes with the traditional 2×2 or even 3×2 layout were becoming less economical. Such seat layouts began to be used in smaller aircraft, which came to be called regional aircraft.
The designers, following this lead, began to consider placing even more armchairs in one row. The idea of a 4×4 layout has become controversial. A passenger sitting by the window would have to apologize to three people to go out to the corridor. Additionally, the flight attendant could not serve the meal to the person sitting by the window. Remember that a flight from one US coast to the other coast is a 6-hour government flight, not a cinema, where we watch a movie for only 2-2.5 hours. That is why there was an idea to make two corridors (two passages).
The planes already have an outer fuselage diameter of 3,750 m. Of course, you can add further fuselage segments by extending it. And so it was done. The elongated fuselages of the aircraft had, among others, the following designs: DC-8 (versions -61, -62, -63), Boeing 707 (versions -320B and 320C), Boeing 727 (version -200) and DC-9 (versions -30, -40 and -50), which could accommodate more passengers than their predecessors. Additionally, extending the fuselage gave even more luggage space on the lower deck.
Wide-body aircraft.
The vast majority of wide-body fuselages have a circular cross-section. There are two main reasons for this shape; firstly – the round hull most effectively resists the loads resulting from the pressure difference inside and outside the hull. It handles tensile stress better. There are also no bending stresses that occur in non-circular sections. Secondly – the round cross-section of the fuselage has a positive effect on the air flowing around it when flying at a greater angle of attack or during side-sliding. The air is not detached, and thus turbulence, which disturbs the aerodynamics of the flight.
At this point, it is worth describing the cross-section used, similar to the number 8, and in the USA referred to as Double Bubble. Several transport aircraft were built with such fuselages. The turning point was the giant Lockheed R6V Constitution (First flight on November 9, 1946, 2 built). It turned out that the technologies used at that time worked well for airplanes with altitudes of up to 25,000 ft (7,620 m). However, further increasing the ceiling requires the use of higher cabin pressure, which makes it necessary to strengthen the airframe structure. The weight of the plane increases. The comparison of the Double Bubble cross-section with the circular cross-section with the same surface areas showed that the latter is clearly lighter, with the same strength parameters.
It has been assessed that it is technically possible to build such a hull, with a circular cross-section, where one row will fit from 7 to 10 seats with 2 passages (corridors). The diameter of such a fuselage must be about 6 m. In this way, the idea of wide-body airplanes was born, which is still valid (2014). Although today it is assumed that a wide-body aircraft is used for long-haul flights: transcontinental and transoceanic.
Wide-body planes take on board from 200 to 550 passengers, and in the new Airbus A 850 (2005) even 850 passengers (although none of the airlines has ordered such a capacious version of the plane yet).
Construction work.
In 1966, the American airline American Airlines developed the requirements for a future commercial short-, medium- and long-range aircraft to serve passenger lines with heavy traffic. Due to the fact that the plane was to serve connections at distances from about 500 km, it had to be accepted by airports with weaker infrastructure and with a slightly shorter RWY (runway). This increased the requirements for the equipment of the future aircraft. There were also strict requirements as to the distance to be covered; from 500 km to 11,000 km. The plane was to take 380 passengers on board in a one-class arrangement (economy class) and about 270 passengers in mixed arrangements. Such requirements were difficult to reconcile in one machine. Other major air carriers have set high demands as well. Among others, the airline Pan Am (Pan American Airlines), which held talks with the Boeing concern (1965). The airline was interested in an aircraft capable of taking 400-500 passengers on board and with a range of up to 10,500 km. The determinant was the route New York – Rome, 6,897 km (4,286 miles, 3,724 NM), which the plane was supposed to cover with full passengers.
The tasks were undertaken by three companies; McDonnel Douglas (DC-10), Lockheed (L-1011), and Boeing (747). The first two companies were developing machines powered by three turbojet engines. The Boeing company worked on the B 747 colossus. It is significant with the B 747, because it was a design being developed as a transport plane for the USAF.
The DC-10 plane was created as the first joint project after the merger of McDonnell Aircraft Corporation and Douglas Aircraft Company. The new company was named McDonnell Douglas. McDonnel Douglas signed an agreement with American Airlines, which approved the proposed solutions.
Written by Karol Placha Hetman