Quest for Performance: The Evolution of Modern Aircraft
Chapter 13: Jet Transports
New Transports of the 1980's
[448] The year 1982 saw the introduction into airline service of an entirely new American-built jet transport, and a second new aircraft by the same manufacturer began service in 1983. Neither aircraft is of the "jumbo-jet" size such as discussed above. Both are designed to supplement and ultimately replace current transports in use on medium- and short-range stage lengths. In the design of both aircraft, increased fuel costs led to great emphasis on improved flight efficiency and careful matching of range-payload capabilities to specific airline needs. A few details of the two new aircraft are given below.
Boeing 767-200
With a first flight date in September 1981, the Boeing 767-200 entered airline service in the late summer of 1982. The aircraft is shown in figures 13.27 and 13.28, and physical and performance data for one version of the aircraft are given in table VII.
The Boeing 767-200 is a 290-passenger, double-aisle, wide-body airliner designed to replace the aging Boeing 707 and McDonnell Douglas DC-8 transports now used on domestic and foreign medium range route segments. Average stage lengths over which the aircraft will be operated are estimated by Boeing to lie between 850 and 1150...

overhead ground view of a B767-200 surrounded by people
[449] Figure 13.27 - Rollout of Boeing 767-200 wide-body, twin-engine airliner. [mfr] [Original photo was in color, Chris Gamble, html editor]

....miles. Maximum range is, of course, much greater and includes a nonstop United States coast-to-coast capability; the twin-engine 767-200 is not intended for long over-ocean flights.
As can be seen in figures 13.27 and 13.28, configuration of the Boeing 767-200 is conventional with the wing located in the low position at the bottom of the fuselage and with one of the two engines pylon mounted beneath each wing. Location of the engines under the wing, rather than to the rear of the fuselage, allows the horizontal tall to be mounted in the low position. As discussed in chapter 10, a low tall position is helpful in minimizing pitching-moment nonlinearities that are often characteristic of sweptback wings at angles of attack in the vicinity of the stall. The main landing gear consists of two struts, each with a four-wheel bogie, that retract inward into the wing root.
Although of conventional configuration, the detailed aerodynamic design of the 767-200 is highly refined, as might be expected by the nearly 25 000 hours of wind-tunnel time required in the development of the aircraft. To place this wind-tunnel effort in perspective, 14 000 and 4000 wind-tunnel hours were expended in developing the Boeing 747 and 727, respectively.
The Boeing 767-200 has been widely advertised as being much...

aerial photo of a B767-200
[450] Figure 13.28 - In-flight view of Boeing 767-200 airliner. [mfr] [Original photo was in color, Chris Gamble, html editor]

....more fuel efficient than earlier generations of jet transports. Although the careful aerodynamic design just mentioned contributes to the efficiency of the aircraft, the high-bypass-ratio turbofan engines employed on the 767-200 are primarily responsible for its high fuel efficiency. At present, the 767-200 is offered with two versions of both the Pratt & Whitney JT9D and the General Electric CF6 turbofan engines. Both of these engines are in the 48 000- to 50 000-pound thrust range and have bypass ratios between 4.5 and 5.0 and compressor pressure ratios between 25 and 30. Specific fuel consumption of these engines, expressed in pounds of fuel per pound of thrust per hour, is between 20 and 25 percent lower than that of the Pratt & Whitney JT3D engine that powers both the McDonnell Douglas DC-8 and the Boeing 707.
Comparison of certain characteristics of the 767-200 with those of the older Boeing 707-320B is of interest. Examination of the data in table VII shows that the wings of the two aircraft are nearly the same size, with only small differences in area and span. Sweepback angle and aspect ratio of the new 767-200 are 31.5° and 8.0, respectively, as compared with 35° and 7.1 for the 707-320B. These differences in wing geometry would be expected to increase aerodynamic efficiency by a small amount. Incorporated in the wing of the 767-200 is a new Boeing-developed supercritical-type airfoil section. The basic technology of the supercritical airfoil section was pioneered by Richard T. Whitcomb of the NASA Langley Research Center. Use of such sections allows increased wing thickness ratio without corresponding reductions [451] in the Mach number at which large adverse compressibility effects begin to occur. Reduced wing structural weight, increased aspect ratio and reduced wing sweepback angle-or some combination of the three-are accordingly possible. Incorporation of this new type of airfoil section on the Boeing 767-200 contributes to high overall efficiency.
High-lift devices on the wing consist of full-span leading-edge slats and a combination of both single- and double-slotted flaps on the trailing edge, with the double-slotted flaps placed on the inboard part of the wing. Inboard and outboard ailerons in combination with spoilers are used for lateral control. When deployed symmetrically, the spoilers help decelerate the aircraft on the landing rollout and aid in rapid in-flight descents. An elevator and adjustable stabilizer are used for longitudinal control, and a conventional rudder is provided for control about the yaw axis. All controls are of the fully powered, irreversible type.
New techniques for navigation and flight control are used on the 767-200. These techniques herald an entirely new relationship between the aircraft and the flight crew. An automatic flight control system coupled with a computer allows storage of an entire flight plan and gives automatic guidance and control of the aircraft from takeoff to landing. Included in the system are not only navigation functions but vertical flight-path control to minimize fuel consumption. To a large extent, the traditional electromechanical instrumentation has also been replaced by more simple cathode-ray-tube displays that provide different types of information at the command of the crew. A detailed description of this new equipment and its use are beyond the scope of the present discussion. Let it be noted, however, that aircraft such as the 767-200 may herald the end to most hands-on flying of transport aircraft and introduce an age in which the pilot is increasingly a button-pushing systems manager. Automatic flight management techniques such as those employed in the new Boeing transports will certainly result in more efficient fuel utilization in future airline operations.
All versions of the 767-200 can accommodate a maximum of 290 passengers seated in a 7-abreast double-aisle configuration. The aircraft is now offered in six variants, with gross weights falling in the range from 302 000 to 337 000 pounds. Listed in table VII are the characteristics of the 337 000-pound version of the aircraft, which is powered by two Pratt & Whitney JT9D-7R4E turbofans of 50 000 pounds thrust each. This particular variant of the aircraft, available in 1984, has nearly the same gross weight as the Boeing 707-320B but [452] carries about 100 more passengers over a much shorter range. Maximum cruising speed of the 767-200 is about 40 miles per hour slower than that of the 707-320B, and takeoff and landing field lengths of the new aircraft are significantly shorter than those of the 707. These differences in speed and field length reflect the differing requirements of a long-range aircraft designed for international operations and one designed for medium-range domestic use. Aerodynamic efficiency of the 767-200 can be judged by the maximum lift-drag ratio, estimated to be about 18. The larger ratio of wetted area to wing area of the 767-200, as compared with that of the 707-320B, results in a value of (L/D) max somewhat lower than that of the older aircraft. The much larger passenger capacity and more efficient engines, however, make the new aircraft more efficient in terms of cost-per-seat-mile.
The Boeing 767-200 has just entered airline service, and although its characteristics seem highly promising, its ultimate place in the spectrum of successful transport aircraft has yet to be determined.
Boeing 757-200
The second new Boeing jetliner of the 1980's, designated the 757-200, made its initial flight in February 1982 and is scheduled to enter airline service in the spring of 1983. Intended as a fuel-efficient replacement for the long-lived Boeing 727 on short-range route segments, the 757-200 can accommodate as many as 239 passengers in a single-aisle six-abreast cabin arrangement. Average route segments are expected to be about 575 miles or less and to require less than 2 hours' flight time. A narrow six-abreast single-aisle configuration usually has slightly less wetted area, and thus less drag, than a six-abreast twin-aisle arrangement designed for the same number of passengers. Apparently, passengers are willing to accept the single-aisle layout for short flights but prefer the more spacious wide-body design for flight times greater than several hours.
The first 757-200, photographed on the occasion of its rollout in January 1982, is shown in figure 13.29, and data for one version of the aircraft are given in table VII. Configuration of this twin-engine aircraft is seen to be very similar to that of the 757-200 shown in figures 13.27 and 13.28; however, the data in table VII show that the 757-200 has a smaller wing of less sweepback angle and is much the lighter of the two aircraft.
Like the 767-200, the fuel efficiency of the 757-200 derives largely from the high-bypass-ratio turbofan engines employed on the aircraft.

photo of a B757-200 being pulled fro the hangar
[453] Figure 13.29 - Rollout of Boeing 757-200 narrow-body, twin-engine airliner. [mfr] [Original photo was in color, Chris Gamble, html editor]

Listed in reference 150 are the characteristics of three versions of the 757-200. The aircraft currently in production are powered by the Rolls-Royce RB211-535C engines of bypass ratio 4.36 and thrust of 37 400 pounds. By the end of 1984, the aircraft will also be available with the Rolls-Royce RB211-535E4 engine of 40 000 pounds thrust, or with the all-new Pratt & Whitney 2037 turbofan of 40 000 pounds thrust. All three of these engine types offer a 20- to 25-percent reduction in cruise-specific fuel consumption as compared with the various versions of the Pratt & Whitney JT8D engine that powers the 727.
Many of the design features of the 767-200 described above are incorporated in the 757-200. The same supercritical airfoil section is employed in the wings of both aircraft. The high-lift and lateral control systems of the two aircraft are nearly the same, although some differences are evident in the trailing-edge flaps and ailerons. In contrast with the 767-200, the trailing-edge high-lift system of the 757-200 consists almost entirely of double-slotted flaps, and no inboard ailerons are used. Cockpit layout and automatic flight control and navigation systems are essentially identical on the two aircraft.
Gross weight of the version of the 757-200 now in production is 221 000 pounds. With the more advanced Rolls-Royce and Pratt & Whitney engines, gross weight will be 241 000 pounds. The data in table VII are for the heavier version of the aircraft powered with Pratt & [454] Whitney 2037 engines. As compared with the 727-200 it has been designed to replace, the 757-200 is shown by the data in table VII to be larger and heavier and to have a larger passenger capacity. Wing sweepback angle of the new aircraft is 7° less than that of the 727-200, and the maximum cruising speed is 49 miles per hour lower than that of the older aircraft. This speed differential is relatively unimportant on the short-range segments for which the aircraft is intended; also, it reduces fuel consumption.
As with the larger 767-200, only time and experience will measure the success of the 757-200 in airline operation and in the domestic and international marketplace.