ch13-4

Quest for Performance: The Evolution of Modern Aircraft


Part II: THE JET AGE


Chapter 13: Jet Transports


Second-Generation Transports


[426] The second-generation jet transports are considered to be those [427] which first flew in prototype form in the 1960's. The following 11 aircraft constitute the second-generation jet transports:

Country Manufacturer Model First flight ^a Engines United States Boeing 727 1963 3 United States McDonnell Douglas DC-9 1965 2 United States Boeing 737 1967 2 United Kingdom British Aircraft Corporation 1-11 1963 2 United Kingdom Hawker Siddley Trident 1962 3 United Kingdom British Aircraft Corporation VC-10 1962 4 Netherlands Fokker F-28 1967 2 U.S.S.R. Tupolev Tu-134 1964 2 U.S.S.R. Tupolev Tu-154 1968 3 U.S.S.R. Ilyushin Il-62 1963 4 U.S.S.R. Yakolev Yak-40 1966 3

Country	Manufacturer	Model	First flight ^a	Engines
United States	Boeing	727	1963	3
United States	McDonnell Douglas	DC-9	1965	2
United States	Boeing	737	1967	2
United Kingdom	British Aircraft Corporation	1-11	1963	2
United Kingdom	Hawker Siddley	Trident	1962	3
United Kingdom	British Aircraft Corporation	VC-10	1962	4
Netherlands	Fokker	F-28	1967	2
U.S.S.R.	Tupolev	Tu-134	1964	2
U.S.S.R.	Tupolev	Tu-154	1968	3
U.S.S.R.	Ilyushin	Il-62	1963	4
U.S.S.R.	Yakolev	Yak-40	1966	3

First flight dates for prototype of first version



Most of the aircraft listed are representative of about the same level of technology and have no large state-of-the-art advances over the first-generation jet transports previously discussed. All the aircraft are equipped with turbofan engines of relatively low bypass ratio that are of about the same level of technical sophistication as the fan engines that powered the first - generation transports. Basically, with a few evolutionary refinements, the second - generation aircraft represent an application of the technology developed in the first - generation aircraft to transports specifically tailored to various types of airline route structures and payload requirements. All the aircraft, except the Boeing 737, employ aft-fuselage-mounted engines in either two - , three - , or four-engine configurations. Four of the aircraft are briefly described in the following paragraphs; they are the three-engine Boeing 727, the twin-engine McDonnell Douglas DC-9, the twin-engine Boeing 737, and the four-engine British Aircraft Corporation VC-10.

Boeing 727

By any standard, the three-engine Boeing 727 must be considered the most successful jet transport aircraft yet produced. The prototype first flew in 1963, and the type was introduced into service by Eastern Airlines in early 1964. Total orders to mid-1982 numbered 1825, with [428] the aircraft being produced at the rate of 2 per month¹ . The 727 is operated all over the world by some 85 airlines; It is rarely possible to - visit a domestic airport served by a scheduled airline without seeing a Boeing 727 during the course of a day. The 727 is popular with the airlines primarily because it can be operated profitably over range segmerits of various lengths and passenger-load requirements, and its relatively short field capability permits operation from a large number of airports too small to accommodate 707 class aircraft. Many studies were made over the years in an effort to find a replacement for the ubiquitous Douglas DC-3; though with different range and payload characteristics, and with different field length and cruising speed capabilities, the 727 may be considered as the modern-day counterpart of the DC-3 that first appeared in 1935.

The aircraft was first produced as the 727-100, and a later stretched version designated the 727-200 was introduced. Of the 1825 aircraft so far ordered, over 1300 have been for the 727-200, which is the only version now in production. The aircraft is produced in both passenger and convertible cargo-passenger configurations. A 727-200 in American Airlines markings is shown in figure 13.12, and the characteristics of this version of the aircraft are given in table VII.

The choice of three engines for the 727 was dictated by a compromise between cost and airport performance. For operation on hot days from airports located at high altitudes, the three-engine arrangement...




Figure 13.12 - Boeing 727-200 medium-range airliner. [mfr]



[429] ....offered significantly better takeoff and climb performance with engine out than was practical for an efficient twin-engine design, but at a great deal lower cost than for a four-engine aircraft. An interesting discussion of this trade-off, as well as other aspects of the design and development of the 727, is contained in reference 145.

The most distinguishing recognition feature of the 727 is probably the mounting of the three engines, which are located at the aft end of the fuselage. The inlet for the center engine is on top of the fuselage ahead of the vertical tail. The engine itself, however, is located in the fuselage in the same horizontal plane as the two outboard engines and exhausts through the tail end of the fuselage. Placement of the three engines in this way simplifies maintenance and servicing and allows a high degree of commonality in ground-support equipment. This arrangement, however, necessitates the use of an S-shaped duct to deliver air from the upper-fuselage-mounted inlet to the front face of the center engine. The design of inlet and duct for the center engine requires careful attention if unacceptable internal aerodynamic losses are to be avoided. The advantages and disadvantages of the aft-fuselage-engine location have been discussed in connection with the twin-engine Caravelle and apply equally well to a three-engine design like the 727. Arrangement of nacelles and exhaust nozzles are shown in the rear view of a 727-100 presented in figure 13.13. Also note the rear-loading stair. Flight tests of a rear-fuselage-mounted engine were made on the Boeing 367-80 to prove acceptable engine operation with the wing in a stalled condition. This test arrangement is shown in figure 13.14.

Power for the 727-200 is supplied by Pratt & Whitney JT813-17 engines of 16 000 pounds thrust each. These engines, which have a bypass ratio of 1.06, have probably been used to power more jet transport aircraft than any other engine.

The 727-200 is seen from figure 13.12 to be a low-wing design; according to the data given in table VII, the wing planform geometry is similar to that of the 707. The engine arrangement results in a horizontal tail mounted at the tip of the vertical fin in a T-tail configuration. Some of the advantages and disadvantages of this arrangement are briefly discussed in chapter 10 as well as in this chapter in connection with the Sud-Aviation Caravelle. The lateral and longitudinal control surfaces are of the same type as those employed on the 707. In contrast to the 707, however, all the controls on the 727 are hydraulically actuated. In order to allow operation from airports of medium size, the 727 is equipped with very powerful high-lift devices. The...




[430] Figure 13.13 - Rear view of Boeing 727 airliner. [mfr]



....trailing edge of the wing has triple-slotted flaps of the type shown schematically in figure 10.25(a) and illustrated in figures 10.26 and 10.27. The leading edge has a slat on the outboard two-thirds of the span and Krueger flaps on the inboard portion of the wing. With these high-lift devices, a stalling speed of 121 miles per hour is obtained at the maximum landing weight of 160 000 pounds. The main landing gear employs two-wheel bogies instead of the four-wheel type used on the 707. The gear retracts inward into the wing at the root. The leading - and traling-edge high-lift devices are shown in the takeoff position in figure 13.15. Also note the large negative deflection of the horizontal tail and the flame trailing from the tail skid as it drags along the runway. The dramatic high-angle-of-attack takeoff illustrated in figure 13.15 was made for test purposes and is not typical of normal operating practice.

The Boeing 727-200 has a gross weight of 210 000 pounds and in full tourist configuration can accommodate 189 passengers in a 6-abreast arrangement. The upper fuselage diameter of the aircraft is the....




[431] Figure 13.14 - Fuselage-mounted engine under test on Boeing 367-80. [mfr]




Figure 13.15 - Takeoff test of a Boeing 727-100 at maximum rotation angle. [mfr] [Original photo was in color, Chris Gamble, html editor]



....same as that of the 707 and the shorter range Boeing 737. Thus, to the passenger, all three aircraft appear to have the same cabin size except for length. The 727-200 is capable of a maximum range of 3738 miles with full fuel tanks; with maximum payload, it has a range of 3335 miles. The cruising speeds of the aircraft are comparable to those of the 707 and the DC-8.

[432] McDonnell Douglas DC-9

The twin-engine McDonnell Douglas DC-9, in its many versions, generally has a smaller passenger capacity, shorter range, and shorter field length capability than the Boeing 727. It has been produced In six major versions and is now in operation on airlines all over the world. The six versions now in operation vary in (1) passenger capacity from 90 to 172, (2) length from 104 to 147 feet, and (3) gross weight from 80 000 to 148 000 pounds. Perhaps more than any other aircraft type, the DC-9 represents an entire family of aircraft. The prototype of the DC-9 first flew in February 1965, and nearly 1100 examples have been produced to date. The type is still in production at the rate of four or five per month, and it seems destined to roll off the production lines for several more years to come.

The DC-9-30, one of the most numerous versions of' the aircraft, is illustrated in figure 13.16 in the Royal Dutch Airlines livery, and some of the characteristics of this aircraft are presented in table VII. Basic configuration of the aircraft is similar to that of the Caravelle in that the two engines are mounted in the aft-fuselage position. The T-tail arrangement employed by the DC-9, however, is different from that of the Caravelle. The engines that power the aircraft are the same basic Pratt & Whitney JT81) turbofans as are employed on the Boeing 727. For this particular version of the DC-9-30, the two engines have 15 500 pounds of thrust each.

The sweptback wing of the DC-9 has a somewhat smaller sweep angle than that of the 727, and the cruising speeds given in table VII...




Figure 13-16 - McDonnell Douglas DC-9 twin-engine short-range airliner. [mfr]



[433]....for the aircraft are correspondingly lower than those of the 727. As pointed out in the discussion of the Caravelle, the lower cruising speed of the DC-9 results from tailoring the characteristics of the aircraft to relatively short range segments and small airports for which it was intended. The high-lift system on most versions of the DC-9 consists of trailing-edge double-slotted flaps and leading-edge slats (the DC-910 had no slats). The lateral control system utilizes inboard and outboard ailerons, with the outboard ailerons being used only at low speeds as in the DC-8. Speed brakes are mounted on the upper surface of the wing. With the exception of the elevators, all the control surfaces are hydraulically actuated. As in the DC-8, the elevators of the DC-9 are manually controlled through aerodynamic servotabs.

The gross weight of the DC-9-30 is 109 000 pounds, which is about half that of the 727-200, and the 115 tourist-class passengers are seated in a 5-abreast configuration. The higher thrust loading and lower wing loading of the DC-9, as compared with the 727, result in a much lower takeoff field length for the Douglas aircraft; the landing field lengths for the two aircraft, however, are about the same. The range at maximum payload for the DC-9-30 is 1812 miles, which is about half that of the Boeing 727. Clearly, the DC-9 and 727 are intended for different types of airline-route structures and passenger-load requirements. Both highly successful aircraft complement each other in airline operation, and both seem destined to fly on together for many years.

Boeing 737

The twin-engine Boeing 737 was developed as a direct competitor of the McDonnell Douglas DC-9 but did not fly until about 2 years after the latter's introduction. The 737 has been produced in two versions, the 737-100 and the 737-200. Except for 30 units, all the aircraft produced have been the 737-200 version, which is a stretched, higher capacity, and heavier aircraft than the 737-100. The total number of orders for the 737 was 978 by mid-1982, and the type is currently being manufactured at the rate of 8 per month (ref. 150).

A Boeing 737-200 in United Airlines' markings is shown in figure 13.17, and some of the characteristics of the aircraft are given in table VII . The two engines are mounted under the wings in a manner similar to that of the 707. The proximity of the engine nacelles to the under surface of the wing highlights the problem, previously mentioned, incurred by the underwing engine location as the size of the aircraft is reduced. The desire to avoid a high-mounted horizontal tail, and its...




[434] Figure 13.17 - Boeing 737-200 twin-engine short-range airliner showing underwing location of two engines. [mfr]



....possible stability problems, apparently was largely responsible for the choice of this engine location instead of the aft-fuselage-mounted arrangement. As figure 13.17 shows, the horizontal tail is located on the fuselage below the root of the vertical tail. The 737 uses basically the same Pratt & Whitney engines as those employed on the Boeing 727 and the McDonnell Douglas DC-9.

The 737 fuselage appears short and stubby, due to its large upper-fuselage diameter, which is the same as for the 707 and the 727, and its short length, which is less than for the 707 or the 727. The higher fineness ratio fuselage and greater length of the DC-9 results from the use of a five-abreast seating arrangement and consequent smaller fuselage diameter. The short fuselage length of the 737 along with the wide lateral separation of the underwing-mounted engines result in the large vertical tall on the aircraft.

The geometry of the 737 wing is very similar to that of the DC-9 as is shown by the data in table VII. The high-lift and control systems of the 737 are like those described for the 727.

An examination of' the data in table VII for the 737-200 and the DC-9-30 shows a close similarity in the size, weight, and performance of the two aircraft. This similarity Would be expected since they were designed for similar operations. The major difference in performance of the two aircraft is the longer range of' the 737 with full fuel tanks.

[435] A major new derivative of the Boeing 737 is under development and scheduled for initial deliveries late in 1984. Designated the 737-300, the new aircraft will be a stretched, heavier variant of the 737-200 powered with the GE Snecma CFM turbofan engines of 20 000 pounds thrust and bypass ratio of 6.0. Lower seat-per-mile costs and reduced noise are among the advantage offered by the improved aircraft.

British Aircraft Corporation VC-10

Two long-range, four-engine, heavy jet transports were developed in the 1960's. These were the British VC-10 developed by Vickers Armstrongs, which later was absorbed into the British Aircraft Corporation, and the Soviet Ilyushin Il-62. The two aircraft closely resemble each other in configuration and employ an engine arrangement different from any existing four-engine jet transport. On each aircraft, the four engines are mounted at the aft end of the fuselage, two on either side, in a four-engine adaptation of the twin aft-engine configuration pioneered by the Caravelle. Both aircraft weigh over 300 000 pounds, and both were designed for long-range operation.

The VC-10 was developed in response to a requirement of the overseas division of British Airways, formerly the British Overseas Airways Corporation (BOAC), for use on its long-range routes to Africa, India, and Australia. First flight took place in June 1962, and the type entered service with BOAC in April 1964. Production of the aircraft was terminated in 1974 after 54 units were manufactured.

The VC-10 is shown in figure 13.18, and some of the characteristics of the aircraft are given in table VII. The four aft-mounted engines are, of course, the most distinctive feature of the configuration. The power is supplied by Rolls-Royce Conway turbofan engines of 21 000 pounds thrust each. These engines have a bypass ratio of 0.6 and employ a four-stage front-mounted fan.

Like all aircraft that employ the aft-mounted engine arrangement, the wing of the VC-10 appears quite clean and uncluttered. The sweepback angle is 32.5% and the aspect ratio is 6.9. Although the sweep angle is slightly less than that of the Boeing 707, the wing-plan-form geometry employed on the two aircraft is nearly the same. The high-lift system consists of trailing-edge Fowler flaps, which are similar to the double-slotted flap shown in figure 10.25(b) with the small middle element removed, and leading-edge slats. Three leading-edge fences are employed on each wing, as can be seen in figure 13.18. Lateral control is provided by a combination of ailerons and spoilers. The....




[436] Figure 13.18 - British Aircraft Corporation VC-10four-engine long-range airliner. (Note engine arrangement.) [Flt. Intl.]



....spoilers are also used as air brakes and can be seen deployed as such in figure 13.18. All control surfaces are hydraulically actuated.

A comparison of the performance data of the VIC-10 and the Boeing 707-320B given in table VII indicates that the maximum payload and corresponding range are significantly less than those of' the Boeing 707-320B. The cost-economical cruising speeds of the two aircraft are also about the same; however, the maximum cruising speed of' the 707 is somewhat higher than that of the VC-10. Many of the airports served by British Airways are located in tropical or subtropical areas characterized by high temperatures. Such temperatures increase the ground speed required for takeoff and reduce the maximum thrust produced by the engines. The VC-10 was accordingly designed to cope with these difficult takeoff conditions that, in some cases, were aggravated by airport elevations considerably above sea level. As a consequence, the takeoff field length for "standard day" conditions given in table VII is about 2000 feet shorter for the VC-10 than for the 707.

The VC-10 is no longer in airline service, but a few are in the Royal Air Force inventory. The economics of' the aircraft apparently could not compete successfully with those of the Boeing 707 and McDonnell Douglas DC-8; hence, the VC-10 enjoyed a relatively limited production run. The Soviet 11-62, counterpart of the VC-10, is still in production and is widely used on Aeroflot's long-range routes. According to reference 150, about 190 of these aircraft have been constructed.
¹ The last Boeing 727, a cargo version, will be delivered in August 1984; the total number of 727 aircraft produced will be 1832.