Quest for Performance: The Evolution of Modern Aircraft
Chapter 4: Design Revolution 1926-39
General Aviation at End of Decade
[96] As the 1930's drew to a close, the general aviation manufacturers offered the private owner and fixed-base operator a variety of high-priced, luxurious aircraft, as well as a number of inexpensive, more austere models. Among the latter, the Piper J-3 Cub is without [97] question the outstanding example. The prototype of the Cub, first flown in 1931 during the early days of the Great Depression, fostered the development of a number of light, low-powered, and, above all, inexpensive aircraft. The aircraft was initially produced by the Taylor Aircraft Company, which was subsequently acquired by William T. Piper and became the Piper Aircraft Corporation. The original Cub was refined and improved through the years and appeared in the definitive model J-3 form in 1937. The aircraft is illustrated in figure 4.15 and is seen to be a conventional, strut-braced, high-wing monoplane equipped with a fixed landing gear. The Cub carried two people seated one behind the other in a small enclosed cabin, one side of which could be opened to provide cooling in warm weather. The aircraft was equipped with brakes and had a steerable tail wheel; but most J-3's had no electrical system, hence, no starter, and, of course, no radio.
Power was supplied by a variety of engines ranging from 40 horsepower to 65 horsepower, with the 65-horsepower version being the most numerous. All the engines were four-cylinder air-cooled types with the cylinders arranged so that two cylinders were oriented at 180° to the other two. This cylinder arrangement, known as a flat engine, is used almost exclusively today on modern general aviation aircraft equipped with reciprocating engines. The cylinders of the engines on...

ground view of a Piper J-3 Cub
Figure 4.15 - Piper J-3 Cub two-place training aircraft; 1938. [Peter C. Boisseau]


[98] ....the J-3 Cub protruded into the airstream to provide the necessary cooling.

An adjustable stabilizer was provided for trimming the aircraft in flight. The Cub had no landing flaps, nor were any needed; the low wing loading of 6.8 pounds per square foot together with the thick, high-lift airfoil section in the wing gave a stalling speed of just over 40 miles per hour. The large air wheels on the landing gear allowed the aircraft to be safely operated from soft muddy fields. The internal structure of the aircraft was conventional and consisted of a welded steel-tube fuselage, together with wings that incorporated metal spars and ribs (at least in the later models). The entire aircraft was covered with fabric. Most aircraft left the factory painted a distinctive yellow, which became almost a trademark for the Cub.
The first cost of the Cub was modest, the operating expenses were low, and maintenance was minimal. A glance at the specifications contained in table II shows that the performance was not spectacular, but the aircraft was completely viceless with respect to its flying and handling qualities. All these factors made the Cub an ideal primary trainer. Thousands of pilots received their first dual instruction and made their first solo flight in the Cub during the explosive expansion of the U.S. Army and Navy Air Forces during World War II In addition to training, the Cub was extensively used for liaison, observation, and other military duties during the war. About 20 000 of the J-3-type Cubs were produced, and a modernized, higher powered version known as the Piper PA-18 Super Cub is still in production at this time. Today, the aircraft is used for crop spraying, glider towing, fish spotting, and various other utility tasks. Many thousands of Super Cubs have also been built. Surely, the Cub and its descendants have had one of the longest production runs of any aircraft in history.
The larger, higher performance monoplane for the private owner and fixed-based operator was typified by the Stinson Reliant SR-8B illustrated in figure 4.16. The Reliant represents the culmination of much experience accumulated by Stinson in the development of a long line of cabin monoplanes. The Stinson Reliant was a well-streamlined high-wing monoplane with a single strut supporting each wing, and a single strut type of landing gear with the wheels enclosed by pants. The radial engine was enclosed by a full NACA cowling and transmitted power to the air by means of a controllable-pitch propeller. The luxuriously appointed cabin accommodated five people and included roll-down windows such as those used in automobiles. The aircraft had...

ground view of a SR-8B
[99Figure 4.16 - Stinson Reliant SR-8B five-place-cabin monoplane; 1937. [Peter C. Boisseau]


....dual controls and a self-starter and was equipped with brakes, flaps, and all the latest flight instrumentation. The aircraft could be purchased with one of a number of different engines that varied in power from 245 to 450 horsepower. The aircraft illustrated in figure 4.16 and described in table II was equipped with the Lycoming nine-cylinder radial engine of 245 horsepower. With this engine, the aircraft had a gross weight of 3650 pounds and a cruising speed of 140 miles per hour at 8000 feet. The performance of the Reliant is not particularly outstanding when compared with comparable general aviation aircraft today. However, the cabin of the Reliant was roomier and allowed elbow and leg room to a degree not usually available in modern single-engine general aviation aircraft. The entire structure of the aircraft was metal, with the exception of the skin which was the familiar doped fabric. During World War II, a version of the Reliant was built as a trainer for the Canadian government. Many of these aircraft reverted to civilian status following the end of World War II. Production of the beautiful Reliant did not resume following the close of the war, and, today, examples of this aircraft are highly prized by collectors of antique aircraft.

Many biplanes manufactured during the late twenties and thirties were still in use in 1939, and several types were in production. Of [100] these, two were high-performance, high-priced cabin aircraft. The most distinctive, and the one that represented the highest level of technology ever achieved In a biplane design, was the Beechcraft D-17. The prototype of the D-17 was first flown in 1932, and the type was continually refined and developed for many years. Production of the D-17 ended in 1948 after 784 models had been produced. The aircraft is illustrated in figure 4.17 and is seen to be a highly streamlined biplane equipped with retractable landing gear, full NACA cowling around its radial engine, and only a single I-type of interplane strut between the two wings on either side of the fuselage. A minimum of wire bracing was employed between the wings. A distinctive feature of the aircraft is the negative stagger; that is, the upper wing was mounted behind the lower wing. This particular arrangement was not unique with the Beech but had been employed on such aircraft as the DeHavilland 5 and Sopwith Dolphin in World War I. (See chapter 2.) However, the arrangement has been rarely used and is responsible for the term "Stagger Wing Beech" by which the D-17 is almost universally identified today. The term is not definitive, however, since most biplanes have the wings staggered, with the upper wing usually being forward of the lower wing; this arrangement is referred to as positive stagger. One may speculate on the reasons why the negative stagger wing arrangement was used in the design of the Beech. If the landing gear is to be...

ground view of a Beech D-17s
Figure 4.17 - Beech D-17S four-place-cabin biplane; 1939. [Peter C. Boisseau]

[101]...retracted into the lower wing, a most desirable feature, then the wing must be placed sufficiently far forward so that the landing gear is well ahead of the center of gravity of the aircraft; this location is necessary for ground stability. (The prototype and the first few aircraft produced had a short, highly streamlined, fixed gear attached to the lower wing.) To place the aerodynamic center of the aircraft in the proper relationship to the center of gravity, the upper wing must then be mounted behind the lower wing.
The Beech D-17 could be purchased with any one of a number of engines, ranging from about 200 to 450 horsepower. The particular version shown in figure 4.17 is the model D17S of about 1939 and was equipped with the 450-horsepower Pratt & Whitney Wasp Jr. engine. The aircraft was fully equipped with all the latest innovations, including controllable-pitch propeller, self-starter, full instrument panel, and, of course, brakes. Plain flaps were also employed on the upper wing. Four passengers were accommodated in the luxuriously appointed cabin. The fuselage of the aircraft was constructed of welded steel tubing and employed wooden formers and stringers to provide the necessary streamlined shape. The wings were constructed of wood, and the entire aircraft was covered with fabric. According to table II, the cruising speed of the aircraft was 202 miles per hour at 9700 feet, and the stalling speed was a relatively low 50 miles per hour. The zero-lift drag coefficient was a very low 0.0182. The Beech D-17 can truly be said to represent the ultimate in biplane development.