ch3-3

Quest for Performance: The Evolution of Modern Aircraft

Part I: THE AGE OF PROPELLERS

Chapter 3: The Lean Years, 1918-26

High-Speed Racing Aircraft


[72] The national and international air races helped stimulate and maintain public interest and support for aviation during the years immediately following World War I. The races also provided a focus for the development of new, high-performance aircraft. Many of these special aircraft were government sponsored. The Army and the Navy sponsored such developments in the United States, as did the air forces of France, Great Britain, and Italy in Europe. The most successful of these aircraft were highly developed forms of the biplane configuration. Typical of such aircraft is the 1923 Curtiss R2C-I racer shown in figure 3.4. Standing beside the aircraft is Navy Lieutenant Alford J. Williams who flew it to first place in the 1923 Pulitzer race. The aircraft is seen to be extremely clean aerodynamically and had a phenomenally low zero-lift drag coefficient of 0.0206 (table II). The aircraft achieved a maximum speed of 267 miles per hour with a liquid....



Figure 3.4 - Curtiss R2C-1 racer; 1923. [NASM]

[73] cooled engine of about 500 horsepower. Some of the features that accounted for the low drag coefficient and consequent high speed are the minimization of the number of wires and struts to support the wings, the smooth, highly streamlined sernimonocoque wooden construction of the fuselage (this type of Construction is briefly described in chapter 2 in connection with the Albatros D-111 fighter), the all-metal Curtiss Reed propeller, and the very interesting skin-type radiators that were used to provide heat exchange surface for the water-cooled engine. The external surfaces of these radiators, which formed a part of the surface of the wing, were of corrugated skin with the corrugations aligned with the direction of air flow. The remainder of the wing surface was covered with plywood. The Curtiss PW-8 fighter, of which about 30 were produced in the mid-1920's, also employed the skin-type surface radiator. Although the skin radiators contributed significantly to obtaining a low drag coefficient, and hence to improving performance, they were not practical for use on operational combat aircraft. In addition to being prone to leak as a result of flexing of the wings, they were extremely vulnerable to battle damage, which was probably the deciding factor in their elimination from future combat aircraft.

A number of racing aircraft were developed that employed the monoplane configuration. Some of these aircraft had cantilever wings; others employed strut-braced wings; such advanced concepts as retractable landing gear were sometimes seen. For one reason or another, however, none of these monoplane racers was particularly successful. The Dayton Wright RB racer developed for the 1920 Gordon Bennett race was perhaps one of the most advanced concepts developed during the entire period. The aircraft is illustrated in figure 3.5, and some of its characteristics are given in table II. The pilot was entirely enclosed in the fuselage, which was of wooden semimonocoque construction. The cantilever wing was constructed entirely of wood an employed leading- and trailing-edge flaps. These flaps in effect provided variable camber so that the airfoil section could be adjusted to its optimum shape for both high-speed and low-speed flight. This extremely advanced feature did not appear on production aircraft until the development of the jet transport in the 1950's. The landing gear on the Dayton Wright racer retracted into the fuselage in very much the same way as that used in later Grumman fighters of the thirties and forties. The drag coefficient at zero lift of the Dayton Wright racer was 0.0316 (table II), which is considerably higher than the value of 0.0206 for the Curtiss R2C-1 but very much lower than the value of 0.0496 given in table I for the DH-4. Although highly advanced for its time, the....




[74] Figure 3.5 - Dayton Wright RB-1 racer; 1920. [NASM]


....Dayton Wright racer was not successful in the 1920 Gordon Bennett race. The aircraft was somewhat underpowered and during the race had to withdraw because of a broken rudder cable. Unfortunately, the type was not further developed.

Another highly advanced monoplane racer, developed by the British for the 1925 Schneider trophy race, was the Supermarine S-4. The Schneider race was an international event for seaplanes. Shown in figure 3.6, the S-4 is a beautiful, highly streamlined, cantilever monoplane mounted on twin floats. The wing, constructed of a wooden framework covered with plywood, employed flush radiators that, unlike the previously described Curtiss racer, were not of the skin type. The wings had landing flaps that could be geared to the ailerons. The rear of the fuselage was of wooden semimonocoque construction, and the forward portion containing the engine was of metal. The engine had 12 cylinders arranged in 3 banks of 4. A front view of the engine gave the appearance of the letter "W"; accordingly, this cylinder arrangement was referred to as a W-type engine. A glance at the characteristics of the aircraft contained in table II indicates a drag coefficient of 0.0274, which must be considered quite low in view of the large amount of surface area of the exposed twin floats. The wing loading of about 23 pounds per square foot was high for the period and accounts for the use of the wing trailing-edge flaps. Another important factor that allowed the use of such a high wing loading was the relatively long take off...




[75] Figure 3.6 - Supermarine S-4 seaplane racer; 1925. [NASM]



...and landing runs possible with the use of rivers and harbors, as compared with the confined land airfields of the day. The aircraft was destroyed by wing flutter before the 1925 Schneider trophy race (ref. 117). According to reference 114, the ailerons on the S-4 were unbalanced, which no doubt contributed to the onset of wing flutter at the high speeds of which the aircraft was capable. Flutter and divergence of cantilever monoplane wings were not understood at that period in the development of aeronautical technology. Later Supermarine racers, which were quite successful in subsequent. Schneider trophy competitions, employed the more predictable wire-braced monoplane wings. The designer of the Supermarine S-4, R. J. Mitchell, later designed the famous Spitfire fighter of World War II. For those familiar with the Spitfire, some resemblance between the S-4 and the famous fighter can be seen in figure 3.6. The national and international air races and the aircraft of the early 1920's are described in comprehensive detail by Foxworth in reference 51.