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Sud-Aviation Caravelle

The French Sud-Aviation Caravelle was the first really successful short-range jet transport to be developed in the western world. First flight of the prototype took place in May 1955, and the aircraft entered airline service in Europe in April 1959. As with most successful jet transports, the Caravelle was produced in a number of versions; a total of 280 aircraft of all versions were produced before production was terminated in the early 1970's.

The primary technical significance of the Caravelle was its pioneering use of an entirely new and innovative approach in the integration of the engines and airframe. Figure 13.11 shows that one of the two engines is mounted on either side at the aft end of the fuselage. This engine arrangement set the pattern for many future jet transport aircraft of two-, three-, and four-engine design. When the engine location proposed for the Caravelle was first made known, many engineers expressed doubts about the practicality of such an arrangement. For example, questions were raised about the operation of the engines in the wake of the wing as the aircraft approached a stalled condition, or the effect on engine operation of large angles of sideslip. The aft-engine location, however, has proved to be highly workable. Some advantages and disadvantages of this aft-engine arrangement are as follows:

  • The short lateral distance between the engines results in relatively small yawing moments following the loss of an engine. The required vertical-tail size is accordingly reduced as compared with that of an aircraft with wing-mounted engines, such as the Boeing 707.
  • The rear location of the engines results in a relatively low engine-noise level through most of the cabin.
  • Removal of the engines from the wing results in a small [425] increase in the maximum lift coefficient and elimination of wing-pylon-nacelle interference drag. The integration of engines at the aft end of the fuselage, however, requires careful design in order to minimize interference drag in this area.
  • The location of the engines at the aft end of the fuselage, as compared with the underwing position, reduces the problem of interference between the engines and the ground, a problem that becomes particularly important as the size of the aircraft is reduced.

Mounting the engines on either side of the aft portion of the fuselage prevents location of the horizontal tail in a low position. In the case of the Caravelle and a number of other aircraft, the tail is mounted at some location between the root and tip of the vertical-tail surface. Other aircraft utilize the T-tail position in which the horizontal tail is mounted at the tip of the vertical surface. The use of a high tail position offers several advantages: If the vertical tail is swept back, the horizontal-tail moment arm is increased as the tail is moved toward the tip of the vertical surface. The horizontal-tail size, and hence the weight of the tail, may therefore be reduced for a given level of static longitudinal stability. In the T-tail arrangement, the horizontal tail acts as an end plate and reduces the required size of the vertical surface for a given level of static directional stability. Again, a reduction in tail weight may be realized. Structural and aeroelastic problems may, however, cause some increases in weight of the vertical tail. Whether the overall empennage weight is reduced by the use of the T-tail arrangement, as compared with the more conventional low tail position, however, is debatable and depends on the detailed design requirements of the particular aircraft.

The high tail position also has some disadvantages. Certain inherent aerodynamic problems are encountered in the design of an aircraft with a high tail location. Careful attention to the detail design of such a configuration is required in order to achieve reasonably acceptable longitudinal aerodynamic characteristics. Lack of proper care in the design process can result in an aircraft with highly undesirable longitudinal aerodynamic characteristics.

The rear engine location results in large concentrated weights that are a long distance behind the aircraft center of gravity. This arrangement, therefore, causes some problems in balancing the aircraft in certain loading configurations. However, these balance problems have been overcome in a large number of highly successful aircraft that employ the aft-engine arrangement.

Other than the engine arrangement, the Caravelle's configuration is conventional, with the 20 swept wing of aspect ratio 8 mounted in the low position on the fuselage. Two large fences can be seen on each wing in figure 13.11. These fences are intended to control the spanwise flow of the boundary layer on the swept wing and thus improve the stalling characteristics of the aircraft. The wing-pylon-engine arrangement on the 707-type configuration serves the same purpose. The high-lift system consists of trailing-edge Fowler flaps. Large airbrakes are mounted ahead of the flaps on the top and bottom surfaces of the wing. All the flying controls are hydraulically actuated. The aircraft is powered with two Rolls-Royce Avon turbojet engines of 12 000 pounds of sea-level static thrust.

The gross weight of the aircraft is a relatively light 114 640 pounds, even lighter than the Comet, and that it is capable of a range of 1829 miles with a maximum payload of 16 800 pounds. Eighty passengers can be accommodated in a five-abreast configuration. The cost-economical cruising speed of 488 miles per hour at 35 000 feet is somewhat lower than the 550 miles per hour given in the table for the Boeing 707. The lower cruising speed of the Caravelle would be expected in a short-range airplane and explains the low sweepback angle of the wing. The relatively short landing and takeoff field lengths indicate that it was designed to operate from the many small airports appropriate to a short - or medium-range airliner. Again, a wing of low sweepback angle is desirable.

The Caravelle 12R was a re-engined version of the 10R and was only sold to France's Air Inter at Orly. This longer and more powerful version of the classic SE-210 was the most attractive model too. previous models had a fin ridge that ran down the leading edge of the fin and half-way along the top of the fuselage but the Twelve-R variant had a clean fuselage top. A highly successful shortrange jet transport, the Caravelle's place in the history of aeronautical development is secure as a result of its pioneering use of the aft-fuselage-engine location.







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