Quest for Performance: The Evolution of Modern Aircraft
Chapter 13: Jet Transports
Pioneer Transports
[409] The age of jet transportation began on May 5, 1952, with the inauguration of scheduled service from London to Johannesburg, South Africa. Later in the year, service was established from London to Ceylon and from London to Singapore. Then, in April 1953, scheduled flights were begun from London to Tokyo, a distance of 10 200 miles. The flying time was 36 hours, as compared with 85 hours for the propeller-driven aircraft then in use on the route. The pioneering jet transport that began commercial operations in 1952 was the DeHavilland Comet 1.
The design of the Comet airliner had its origins in the waning days of World War II, and the layout of the aircraft was completed in 1947. The first flight of the prototype took place on July 27, 1949, with John Cunningham as pilot. The performance and physical characteristics of the Comet 1A are given in table VII, and a three-view drawing of the [410] aircraft is presented in figure 13.2. A photograph of a Comet 3, similar in appearance to the Comet 1A, is given in figure 13.3. The configuration, of the Comet was not significantly different from that of contemporary long-range propeller-driven aircraft. A comparison of the characteristics of the Comet given in table VII with those of the Lockheed Constellation given in table III indicates that the Comet was a somewhat lighter aircraft, had a lower wing loading and a wing of lower aspect ratio but had a cruising speed of 490 miles per hour at 35 000 feet as compared with 331 miles per hour at 23 000 feet for the Constellation. The range with maximum payload of 44 passengers was 1750 miles. At a much reduced payload, a range of slightly over 4000 miles was possible. By present-day standards, the Comet 1A was a small, relatively low performance aircraft. By comparison with other aircraft of the early 1950's, however, it was extremely fast.
The Comet 1A was powered with four DeHavilland Ghost turbojet engines of 5000 pounds thrust each. The takeoff thrust-to-weight ratio was a very low 0.17. As a consequence of this low thrust-to-weight ratio, very precise control over the aircraft attitude was required during the takeoff roll to prevent overrotation and subsequent high drag and loss of acceleration. At least one aircraft was lost as a result of overrotation during takeoff. The four engines were mounted in the wing roots, two on each side of the fuselage. This engine arrangement has the advantages of placing the engines near the longitudinal center-of-gravity position and of minimizing the asymmetrical yawing moment that accompanies loss of an engine during takeoff; at the time, it was also thought to be a low-drag arrangement. The proximity of the engines to each other and to the passenger cabin, however, posed a possibly hazardous situation in the event one of the engines disintegrated. Engine disintegration was a very real concern in 1950. Engine maintenance was also complicated by the wing-root mounting arrangement.
The aerodynamic design of the wing was conventional except for the use of 20° of sweepback. The aspect ratio of 6.6 was low, as compared with contemporary long-range propeller-driven aircraft. The high-lift system consisted in a combination of simple plain and split trailing-edge flaps. Some aircraft employed fences on the wings. The aerodynamic controls were hydraulically boosted. The passenger cabin was pressurized to maintain a cabin altitude of 8000 feet at an aircraft altitude of 40 000 feet.
The Comet I was sold to British, French, and Canadian airlines, and it appeared that Great Britain had produced a truly outstanding new aircraft that would be sold in large numbers throughout the world.

frontal, overhead and side view drawing of  a Comet airliner
[411] Figure 13.2 - Dehavilland Comet airliner prototype.

Prospects for the Comet dimmed, however, when three accidents occurred in which the aircraft disintegrated in flight. All Comet 1 aircraft, over 20 in number, were withdrawn from service in 1954. Extensive laboratory studies were undertaken in an effort to diagnose the problem. Fatigue failure and subsequent rupture of the pressurized fuselage as a result of pressure recycling was finally identified as the cause of the accidents. The Comet was completely reengineered and emerged as....

ground view of a DC-3
[412] Figure 13.3 - DeHavilland Comet 3 airliner. [David A. Anderton]


....a much changed and improved aircraft in 1958. This version, identified as the Comet 4, was not really competitive with the new generation of jet transports coming into use at that time, and only 74 were built.

The commercial success of the Comet was limited, but it was the first jet transport and represented a large step forward in our concepts of air transportation and its utility. It is unfortunate that the pioneering work of the designers and builders of the Comet was not rewarded with greater success. The Comet, in highly modified form, survives today as a marine reconnaissance aircraft known as the Nimrod. An interesting account of the development of the various versions of the Comet is contained in reference 169.
The Tupolev Tu- 104 is the second of the pioneer jet transports. This aircraft was first flown on June 17, 1955, and went into scheduled airline operations in 1956 on the Moscow-Omsk-Irkutsk route. In 1957, an improved version of the aircraft, the Tu-104A, captured a number of records for speed, altitude, distance, and load-carrying capability. The Tu-104 transport was developed from the "Badger" bomber and utilized the same wings, tall surfaces, engines and inlets, landing gear, and fuselage nose section as the earlier bomber aircraft. Figure 13.4 depicts a Tu-104B, and the data in table VII are for this version of the aircraft.
As can be seen in figure 13.4, the Tu-104B is a low-wing aircraft with a conventional tall arrangement and a wing incorporating pronounced sweepback. The transparent nose adopted from the bomber version of the aircraft is clearly visible in the photograph. The two engines that power the Tu-104 are located in nacelles that are faired into [413] the wing roots. This arrangement is somewhat similar to that employed on the Comet; however, the nacelles are larger and the circular inlets extend forward of the leading edge of the wing, as contrasted with the leading-edge inlets on the Comet. The two main landing-gear struts are fitted with four-wheel bogies and retract rearward into pods on the wing. The aircraft has a seating capacity of 100 passengers arranged in a 5-abreast configuration. The sweepback angle of the aspect ratio 6.5 wing is 40° from the root to about the midsemispan position and is 37.5° from there to the tip. Each wing has two large fences located in the streamwise position on the top surface of each wing. One of these is at the position where the sweep angle changes, and the other is farther outboard. As indicated in chapter 10, these fences help control the boundary layer and, hence, improve the stalling characteristics of the wing. Lateral control is provided by conventional ailerons that are operated manually; manual longitudinal control is also used. The rudder is actuated hydraulically. The wings are equipped with trailing-edge Fowler-type flaps and have no leading-edge devices. A Fowler flap is similar to the double-slotted flap shown in figure 10.25(b), but without the small segment between the wing and the main portion of the flap.
The Tu-104B is powered by two Mikulin turbojet engines of 21 385 pounds thrust each. The engines are equipped with thrust reversers, although some of the early models did not have this equipment. These early aircraft employed two braking parachutes to assist in stopping the aircraft on landing. Insofar as can be determined, no other commercial transport aircraft (except early versions of the Tupolev...

photo of passengers boarding a Tu-104B airliner
Figure 13.4 - Tupolev Tu-104B airliner. [Flt. Intl.]

[414]....Tu-134) has utilized braking chutes as a routine operational procedure. The gross weight of the aircraft is 167 551 pounds, which is somewhat heavier than that of the piston-engine transports at the end of the era in which these aircraft dominated the world's airlines. With the large turbojet engines, the thrust-to-weight ratio of the aircraft, 0.26, is nearly as high as any of the large transports whose characteristics are given in table VII. The wing loading of 84.8 pounds per square foot is relatively low compared with more modern designs; however, comparison of the data given in table VII for different aircraft indicates that the combination of low wing loading and relatively simple high-lift devices on the Soviet aircraft give stalling speeds comparable to those of more modern high performance jet transports.
The range of 1500 miles given in table VII for the Tu-104 aircraft with maximum payload places it in the short-range category. The cost-economical and maximum cruising speeds are 497 and 590 miles per hour, respectively; these speeds correspond to Mach numbers of 0.75 at 35 000 feet and 0.85 at 25 000 feet.
The Tu-104 was built in a number of versions, and some are still in use on domestic routes inside the Soviet Union. Production of the aircraft ended after 250 units were constructed. The development history of the Tu-104 series of aircraft is completely described in reference 190.
Both the DeHavilland Comet and the Tupolev Tu-104 were pioneers in a new and exciting concept of air transportation, and both have a well-deserved place in the history of aeronautical development. In many respects, however, the design of these aircraft reflected the philosophy of contemporary propeller-driven aircraft. For example, the low wing loadings, unsophisticated high-lift devices, and simple control systems are typical of high-performance propeller-driven transports. The need for high wing loadings and powerful high-lift devices in order to permit cruising at near maximum values of the lift-drag ratio, but at the same time retaining satisfactory stalling speeds, is discussed in chapter 3 of reference 176. The engine location on the Comet and the Tu-104 are no longer used on modern jet transports and must be considered obsolete for this type of aircraft. The advantages and disadvantages of mounting the engines in the wing roots are discussed above in the description of the Comet. This aircraft, as well as the Tu-104, employed turbojet engines of relatively small diameter. The beginnings of the high-bypass-ratio turbofan engine with its large diameter fan poses an additional problem with the wing-root engine location because of the difficulty of integrating the large engine into the wing root.