Quest for Performance: The Evolution of Modern Aircraft
 
 
Part I: THE AGE OF PROPELLERS
 
 
Chapter 8: Boats in the Sky
 
 
Design Transformation, 1930-40
 
 
 
[187] The 1930's saw a transformation in the American flying boat from a clumsy biplane of low aerodynamic efficiency, typified by the Martin PM-1, to the highly efficient monoplane types, like the Boeing 314, which appeared near the end of the decade. The impetus for this metamorphosis came from military requirements for increased performance as well as from the stimulus of commercial competition. As indicated in chapter 4, rapid advancements in aeronautical technology were being made in this time period that provided the basis for improved flying-boat design. In the following discussion, attention is first directed toward two early monoplane developments; after which three, large, long-range, passenger-carrying boats are described; and finally, three general-aviation-type flying boats are presented.
 
Early Monoplane Developments
 
Nonstop flights between the mainland of the United States and Panama, Alaska, and the Hawaiian Islands were major performance objectives for future Navy flying boats as the decade of the 1920's drew to a close. In response to the requirement for this mission capability, the prototype of a new breed of flying boat, the Consolidated XPY-1, appeared in January 1929. The aircraft, which represented a marked change in patrol-boat design, was a twin-engine strut-braced monoplane built to Navy plans and specifications. The prototype offered sufficiently improved performance so that bids were sought by the Navy for production of a number of similar boats. The Martin company was the winner of the production contract, and the resulting aircraft was designated the P3M-1. With this start, both Martin and Consolidated began a series of patrol-boat developments that extended into the 1950's.
 
Not to be outdone by the loss of the Navy contract, Consolidated offered a passenger-carrying version of their aircraft, which became [188] known as the Commodore. A photograph of' this flying boat, figure 8.12, depicts a parasol monoplane with the wing mounted well above the hull on a bridgelike arrangement of struts that also served to support the two engines located below the wing, as well as the lateral stabilizing floats. The entire layout suggests a high-drag aircraft; this is confirmed by the zero-lift drag coefficient of 0.0562, which is about 18 percent higher than that given for the Martin PMI-1 biplane. The actual drag area of the two aircraft, however, is seen to be nearly the same. The high-aspect-ratio monoplane wing of the Commodore give it a maximum lift-drag ratio about 22 percent higher than that of the PM-1 and thus offered the potential for higher cruising efficiency and longer range than the older aircraft. On the other hand, values of both the zero-lift drag coefficient and the maximum lift-drag ratio of the Commodore compare unfavorably with those of the Hall XP2H-1 biplane. Going to a monoplane configuration was a step in the right direction, but the aerodynamic data for the Commodore indicate that the potential of the monoplane wing arrangement was not realized because of the many drag-producing elements, such as struts and uncowled engines, that were present in the design.
 
Other features of the Commodore were its single-step all-metal hull that could accommodate 32 passengers and a crew of 3. The full complement of passengers, located in three cabins, could only be carried...
 
 
a Cosolidated Commodre in flight
 
Figure 8.12 - Consolidated Commodore 32-passenger flying boat,- 1931. [NASM]
 
[189]...on relatively short-route segments. For a 1000-mile flight, the boat probably could accommodate no more than 14 people including the crew (author's estimate). Wing and tail construction consisted of metal-frame structure covered with fabric except for metal-covered leading edges.
 
With a first flight in 1931, a total of 14 Commodore boats were built. They were used in airline service from the United States to South America where routes extended as far south as Buenos Aires, a distance of 9000 miles from Miami. They were out of service by 1935, having been superseded by more efficient aircraft such as the Sikorsky S-42. The Commodore may be considered as a first step in the United States along a road that was to lead to the highly efficient monoplane-type patrol and transport flying boats later in the 1930's. The XPY-1 and its civil counterpart the Commodore may be considered as progenitors in a series of flying-boat developments that led to the famous Consolidated PBY Catalina of World War II fame.
 
Although emphasis in the present volume is placed on aircraft developed in the United States, no discussion of the evolution of the monoplane flying boat would be complete without mention of the pioneering work of Dr. Claude Dornier, the German designer. As described in reference 68, he envisioned large, all-metal flying boats before the end of World War I, and such an aircraft was designed, but not built, before the end of that conflict.
 
In 1922, a twin-engine monoplane flying boat known as the Dornier Wal (whale), very similar to the earlier 1918 design, was first flown. This aircraft featured a single wing located a short distance above the hull with the two engines mounted in a single nacelle, tractor-pusher fashion, on top of the wing. This arrangement reduced the number and length of struts inherent in the Consolidated Commodore-type of arrangement in which the wing was high above the hull with the engines mounted below. So successful was the Dornier Wal that variants of the basic design remained in production until 1936, and Dornier flying boats of the same general configuration were used by the German Luftwaffe throughout the years of World War II. Even today proposals have been made for production of a refined version of a World War II Dornier flying boat equipped with turboprop engines.
 
The ultimate in the Wal configuration concept found expression in one of the most remarkable aircraft, either landplane or flying boat, ever built: the Dornier Do X, which first flew in 1929. This unique flying boat was the largest aircraft ever constructed up to that time and had a gross weight variously listed as 105 820 or 123 459 pounds. The [190] lower value was probably the design gross weight: the higher, likely an allowable overweight condition for special long-range flights. In the United States, no aircraft exceeded the gross weight of' the Do X until the one-of-a-kind experimental Douglas XB-19, at a gross weight of about 140 000 pounds, flew in 1941, and the Boeing B-29 bomber of on World War II fame was the first production aircraft to have a higher gross weight. Incredibly, the Do X was powered by 12 engines. They were positioned in six nacelles, tractor-pusher style, strut-mounted on top of the wing. Tests were made with several different engines in the three Do X aircraft that were built. The data in table IV are for the version powered with 12-cylinder Curtiss V-1570 water-cooled engines of 640 horsepower each, a total of 7680 horsepower. Perhaps fortunately, no other aircraft has ever been equipped with so many engines. One can only guess at the difficulties encountered in keeping all of them operating simultaneously in an efficient manner.
 
A photograph of the Do X is presented in figure 8.13. As can be seen, the monoplane wing was mounted flush with the top of the hull-fuselage, and the six engine nacelles were located on struts above the wing. Instead of lateral stabilizing floats, short stub wings, called sponsons, projecting from the sides of the hull near the waterline provided lateral stability in the water. Each wing was braced by three struts extending upward and outward from near the tip of the sponsons. In turn, the sponsons were braced by three additional struts extending downward and outward from near the top of the hull to about the mid- point...
 
 
aerial view of a Dornier Do X
 
Figure 8.13 - German Dornier Do X-flying boat with 12 engines; 1929. [NASM]
 
[191]...of the sponsons. Two sets of horizontal tail surfaces of different size were configured in a sesquiplane arrangement, and directional stability and control were provided by a single fin and rudder. To reduce pilot control forces needed to maneuver so large an aircraft, small surfaces connected to the main control surface, called park-bench balances, were mounted above and ahead of the elevator and aileron hinge lines.
 
The all-metal hull had a modified vee bottom with a single transverse step and an afterbody that tapered to a sharp vertical stern post. To assist in maneuvering on the water, a small rudder was mounted at the stern post. Accommodations in the hull were divided among three decks. On the top deck were the pilots' compartment, navigation room, captain's cabin, and flight-engineers' compartment. Instruments and controls for operating the battery of 12 engines were located at the engineers' station. The passengers were carried on the second deck, which had several cabins with seats and sleeping accommodations as well as a bar and smoking and writing rooms. Cabins were spacious, and appointments included wood paneling, rugs, and other features of contemporary luxury liners of that day. Perhaps some of the weight of this equipment was more appropriate to a surface ship than an aircraft where lightness is an essential ingredient of efficient flight. But the 66 passengers for which the aircraft was configured no doubt traveled in a regal style unknown today. (On one occasion, 150 passengers, 10 crew, and 9 stowaways were carried on one short record flight.) Fuel and stores were carried on the lower deck.
 
The wing and tail surfaces consisted of a metal framework covered mostly with fabric. Having an area of 4844 square feet and a span of 157.5 feet, the large wing was sufficiently thick to incorporate walkways on which a person could pass through the inside of the wing. Access to the engines for maintenance was provided by hatches above the walkways at each engine nacelle position. Whether or not work on the engines was performed in flight is not known.
 
With a maximum speed of 134 miles per hour and an estimated cruising speed of 122 miles per hour at 75 percent power, the performance of the Do X appears, at first glance, to be very creditable (table IV). The zero-lift drag coefficient of 0.0472 was also as low or lower than most contemporary flying boats. Because of the low wing aspect ratio of 5.12, however, the maximum lift-drag ratio was a low 7.7, a full 22 percent lower than that of the Consolidated Commodore. In addition, the useful load fraction (ratio of payload weight plus fuel weight to gross weight) was only 27 percent for the 105 820-pound gross [192] weight condition. By comparison, the useful load fraction for the Commodore was 35 percent and for the World War I vintage NC-4, 42 percent. The useful load fraction of modern jet transport varies between 45 and 55 percent, as can be seen from the data given in part II for transport aircraft. The combination of low maximum lift-drag ratio and small useful load fraction doomed the Do X as a commercial airplane capable of carrying an economically attractive payload on transoceanic routes. For example, estimates (by the author) suggest that at a gross takeoff weight of 105 820 pounds, including 66 passengers and a crew of 6, the maximum achievable range was between 600 and 650 miles at a cruising speed of 108 miles per hour at sea level.
 
A total of three Do X aircraft, including two for the Italian government, were constructed. None of these proved to be commercially viable. Yet the aircraft must be considered as an engineering achievement of considerable magnitude for the time; it showed that very large aircraft could be built and indicated some of the problems of such aircraft. Preserved for many years in a Berlin museum, the original Do X was destroyed in an Allied bombing raid during World War II.
 
The Flying Clipper Ships
 
Operated by Pan American Airways with substantial support from the U.S. Government, three types of large, four-engine flying boats pioneered long-range commercial flights across the Atlantic and Pacific Oceans in the latter half of the 1930's. In honor of the fast sailing ships that crossed the Pacific from China in the 19th century, these aircraft were collectively known as Clipper ships and each had a specific designation such as China Clipper or Dixie Clipper. Even today, Pan American applies the name Clipper to each of its jet transports.
 
The three legendary Clipper types of the 1930's were the Sikorsky S-42, the Martin 130, and the Boeing 314. These aircraft types are illustrated in figures 8.14, 8.15, and 8.16, respectively. Their appearance suggests a technical era far in advance of that of such earlier boats as the Martin PM-1 and the Consolidated Commodore. Indeed, as described in chapter 4, aeronautical technology had made significant advances by the mid-1930's; and just as the Boeing 247 and Douglas DC-3 represented a higher level of technology than the earlier Ford trimotor, so too were the Sikorsky, Martin, and Boeing flying boats the products of an advanced technological age.
 
 
ground view of a Sikorsky S-42
 
[193] Figure 8.14 - Sikorsky S-42 four-engine 32-passenger flying boat; 1934. [NASM]
 
Some of the significant design features of these flying boats were the following:
 
 

(1)

All three aircraft were equipped with four radial air-cooled engines enclosed in drag-reducing NACA cowlings and were mounted, side by side, in the wing leading edge. This type of installation resulted in significant aerodynamic drag reductions as compared with strut-mounted engine nacelles located above or below the wing. In addition, the leading-edge engine installation allowed the wing to be mounted on or slightly above the top of the hull, thus reducing the length and drag of any supporting wing struts while, at the same time, keeping the propellers sufficiently high to avoid a major spray problem.

(2)

Some form of variable pitch propeller was employed on all three boats. Their use resulted in an important increase in available power and efficiency over the speed-altitude operating envelope of the aircraft.
 
 
aerial view of a Martin 130 China Clipper
 
[194] Figure 8.15 - Martin model 130 China Clipper class passenger-carrying flying boat;1934. [mfr]
 
a Boeing model 314 taking off from the water
 
Figure 8.16 - Boeing model 314 four-engine passenger-carrying flying boat; 1938. [NASM]
 

(3)

Wing flaps were incorporated on all three aircraft. Flaps permitted the use of higher wing loadings for more efficient cruise flight, together with smaller and thus lighter wings, without increased stalling speeds.
(4)
All three aircraft were constructed of metal with certain small portions covered with fabric.

(5)

[195] The Sikorsky S-42 had tip floats for lateral stabilization, whereas both the Martin and Boeing aircraft utilized sponsons for this purpose. These small surfaces were also used for fuel tanks and served as convenient ramps for embarking passengers.

(6)

While the Boeing 314 had full cantilever wings, the Sikorsky and Martin aircraft were characterized by a limited number of supporting wing struts.

(7)

The S-42 and Martin 130 had hulls with two transverse steps. The Boeing 314 had a single-step hull with an afterbody tapering to a sharp stern post.
 
 
The features cited above do indeed illustrate marked advances in flying-boat design as compared with aircraft discussed earlier. Some of the important quantitative characteristics of the three aircraft are compared in the following tabulation (other data are given in table IV):
 

 

Aircraft

Wg

Vmax

CD,O

(L/D)max

useful load fraction, 1 -(We/Wg)

Rh

Sikorsky S-42

38 000

182

0.0362

12.2

0.37

2914

Martin 130

52 252

180

0.0303

11.9

0.53

4816

Boeing 314

84 000

201

0.0274

13.0

0.43

4059

 
where
 

Wg

gross weight

Vmax

maximum speed

CD,O

zero-lift drag coefficient

(L/D) max

maximum lift-drag coefficient

useful load fraction, 1 -(We/Wg)

useful load fraction, I - (We/Wg), where We is empty weight

Rh

hypothetical range
 
 
The hypothetical range was estimated on the assumption of the weight of a four-member crew, with the remainder of the difference between gross and empty weights being taken up by fuel. The hypothetical range gives an indication of the range potential of the aircraft but corresponds to no real value because of restricted fuel-tank volume.
 
[196] The tabulation shows that the Sikorsky S-42 was the lightest of the three aircraft, with a gross weight of 38 000 pounds. To lend perspective to this weight, the heaviest landplane transport in production in the United States at the time the S-42 first flew was the Douglas DC-2; it had a gross weight of 18 560 pounds. At a gross weight of 84 000 pounds, the Boeing 314 was by far the heaviest of the three boats. The maximum speed of the Boeing boat was also about 20 miles per hour faster than the 180 miles per hour of the other two aircraft.
 
Although the zero-lift drag coefficients varied significantly for the three aircraft, the corresponding values of the maximum lift-drag ratio showed a more modest variation, with the Boeing 314 having an improvement of about 8 percent as compared with the other aircraft. The useful load fraction of the Martin 130, however, was higher by 43 and 23 percent than for the S-42 and 314, respectively. As a consequence, the hypothetical range of the Martin 130 was the greatest of the three aircraft. Although the maximum lift-drag ratio of the Boeing 314 was somewhat higher than that of the Martin 130, the large useful load fraction of the Martin gave it a 757-mile, or 19-percent, advantage in hypothetical range over the Boeing. These comparisons of hypothetical range suggest the careful attention the designer must give to detail trade-off studies of weight and aerodynamic efficiency. An interesting indication of progress in flying-boat design during the 1930's is given by a comparison of the 4816-mile hypothetical range of the Martin 130 to the corresponding value of 1760 miles for the Consolidated Commodore, which first flew only a few years earlier.
 
The great flying clippers occupy a permanent place in the annals of transport aviation history. Present-day accounts by passengers who once flew on these aircraft speak of them with great affection and nostalgia. In spaciousness and comfort, they offered a means of air transportation as outmoded today as the luxury railway trains and steamships of the distant past.
 
First of the new-generation flying clippers was the Sikorsky S-42, which made its maiden flight on March 29, 1934, and began airline service between Miami and Rio dejaneiro on August 16 of that same year, an indication of the rapidity with which a transport aircraft could be flight tested and certified in that long-gone and technically simpler age. As the range-payload characteristics of the S-42 did not suit it for passenger service on the long overwater routes of the Pacific, the aircraft was used primarily on South American segments of the Pan American system. Equipped with extra fuel tanks, however, the S-42 made route-survey flights in the Pacific in 1935 and in the North Atlantic in [197] 1937. For normal passenger operations, the aircraft was configured to carry 32 passengers, with 8 in each of 4 compartments, and a crew of 4 or 5. With this payload, the aircraft is estimated to have had a range of about 1200 miles. A total of 10 S-42 flying boats were built; 4 of these survived World War II and were broken up for salvage in 1946.
 
Chronologically, the second of the flying clippers, and the one most often associated with early trans-Pacific passenger-carrying operations, was the Martin 130, which made its first flight on December 30, 1934. Three of these aircraft were constructed and were christened China Clipper, Philippine Clipper, and Hawaiian Clipper. Generically, the type is referred to as the China Clipper. Proving flights were made in the Pacific during 1935 and the first part of 1936. Between November 22 and December 6, 1936, the China Clipper made the first commercial crossing of the Pacific Ocean from San Francisco to Manila. The 8210-mile flight was divided into five stages with intermediate stops in Hawaii, Midway, and Wake and Guam Islands. Five days and 60 flying hours were required for the flight. Later, the route was extended to Hong Kong.
 
The Martin 130 was configured to carry 41 passengers in 2 cabins with a spacious lounge in between. Actually, to allow for the weight of mail and light cargo, as well as a generous supply of reserve fuel, only 12 passengers were carried on trans-Pacific flights. A passenger on one of these flights once referred to rattling around in the spacious accommodations. The captain, first officer, radio operator, flight engineer, and steward comprised the usual crew of five.
 
Each of the Martin Clippers met a violent end. While on a flight from Guam to Manila in July 1938, the Hawaiian Clipper simply vanished. No trace of wreckage, no oil slick, nothing was ever found, and radio transmissions from the aircraft had given no hint of trouble. Even today, over 40 years later, speculation on the disaster continues, just as it does on the disappearance of Amelia Earhart in 1937. In January 1943, the Philippine Clipper was destroyed, along with everyone aboard, while on a flight from Hawaii to San Francisco. At the time of arrival in the San Francisco area, bad weather prevailed and the captain elected to fly a holding pattern until conditions improved. Unfortunately, a navigational error caused the aircraft to fly into a mountain east of San Francisco. According to some accounts, bits of the Philippine Clipper can still be found on the lonely mountainside where it crashed so many years ago. Finally, after flying millions of miles over a 10-year period, the famous China Clipper was lost while attempting a night landing at Trinidad in January 1945. All 25 persons aboard perished.
 
[198] The last, the largest, and the most advanced of the flying clippers was the Boeing 314, which first flew in June 1938. Twelve of these flying boats were built, and they gave fast, comfortable, and reliable service for many years. Both Atlantic and Pacific routes were served by the Boeing 314. On June 28, 1939, the first regular, nonstop, trans-Atlantic service was inaugurated by the Dixie Clipper with a flight from New York City to Lisbon, Portugal. Several of the Boeing Clippers were transferred to the British Overseas Airways Corporation during the war, and one of these was used by British Prime Minister Winston Churchill on a round-trip flight from the British Isles to the United States in 1942. Photographs of the aircraft and of Churchill taking a turn at the controls were released after the flight, and the Boeing 314 became familiar to millions of people all over the world.
 
The interior of the Boeing Clipper was designed to accommodate 74 day passengers and a crew of 10. With this number of people aboard, the maximum range was estimated (by the author) to have been about 1900 miles. A range of 3685 miles is often found in specifications for the aircraft, but this range could only be achieved with a much-reduced passenger load. In an arrangement reminiscent of the Do X, crawlways in the wings connected the crew quarters in the hull to the engine nacelles, thus allowing simple engine repairs to be made in flight.
 
Because they were no longer competitive with high-performance, long-range land-planes, such as the Douglas DC-4, DC-6, and Lockheed Constellation, Pan American terminated operation of the Boeing 314 flying boats in 1946. Several of these aircraft were later used in nonscheduled operations. In forced landings at sea due to fuel starvation (poor flight planning), two of these aircraft demonstrated their seaworthiness when all passengers and crew members survived the open-sea landings unhurt and were later rescued by surface ships. All Boeing 314 operations ceased in 1950. So ended the colorful and pioneering era of the flying clippers.
 
The Flying Boat and General Aviation
 
Military and commercial operations are usually thought of as the principal arena of the flying boat. Yet almost from the beginning, flying boats have been operated by private individuals for sport, pleasure, and personal transportation and by small operators for short-range, commuter-type, passenger-carrying use. As early as 1913, versions of the Curtiss F boat were sold to private individuals, and in the early 1920's, the Loening air yacht was offered for both personal and commuter airline [199] use. Later in the 1920's, a number of small flying boats and amphibians were produced. The single-engine Ireland amphibian and Eastman flying boat, both biplanes, as well as the civil version of the previously described Loening amphibian, appeared in this period. Described next are three general-aviation-type flying boats, actually amphibians, that appeared in the 1930's.
 
At a time when contemporary engineering practice called for a multitude of struts for support of flying-boat wings and engines, the Douglas Dolphin, shown in figure 8.17, clearly broke with tradition. This eight-place, twin-engine monoplane had a full cantilever wing located at the top of the hull, with the two radial engines strut mounted above the wing. Unlike the Loening amphibian, the landing gear did not retract into the hull for water operation but pivoted outward and upward at the juncture of the two lower struts with the side of the hull. A telescoping motion of the single long strut attached at the top of the hull permitted this action. The modified vee bottom hull had a single transverse step and a tapered afterbody that terminated in a sharp, vertical stern post. Structurally, the cantilever wing was of all-wood construction including the plywood covering, and the hull was all metal.
 
The aerodynamic cleanness of the Dolphin was somewhat marred by the strut-mounted engine installation and the exposed landing gear.
 
 
ground view of a Douglas Dolphin
 
Figure 8.17 - Douglas Dolphin twin-engine utility amphibian; 1930. [mfr via Martin Copp]
 
[200] Consequently, the CD,0 and (L/D) max values of 0.0430 and 8.82, respectively, are somewhat disappointing. A maximum speed of 153 miles per hour, however, gave the 9387-pound amphibian an attractive performance, and the aircraft was certainly a long step ahead of contemporaneous flying boats such as the Martin PM-1. Although intended primarily for the civil market, most Dolphins were operated by the military services for various purposes. They continued to give good service as utility and search-and-rescue vehicles well into World War II. One Dolphin, in the hands of an antique airplane collector, is still flying today.
 
What must be regarded as one of the most long-lived flying boats ever produced was introduced by the Grumman Aircraft Engineering Corporation in 1937. Affectionately known as the Goose, the twinengine Grumman G-21 is illustrated in figure 8.18. With the two cowled, 450-horsepower, radial, air-cooled engines mounted in the leading edge, the cantilever wing was located at the top of the hull. Lateral stabilization on the water was provided by tip-mounted floats, and the landing gear retracted neatly into the sides of the hull. Split trailing-edge flaps were incorporated in the wings, and power and efficiency were enhanced by controllable-pitch propellers. The aircraft was of all-metal construction except for the rear portion of the wing, which was covered with fabric. Depending on the interior arrangement, accommodations were provided in this 8000-pound aircraft for a crew of...
 
 
ground view of a Grumman G-21
 
 Figure 8.18 - Grumman model G-21 Goose twin-engine utility amphibian, 1937. [NASA]
 

[201] ...two or three and four to seven passengers. The data in table IV indicate a maximum speed of approximately 200 miles per hour and values of CD,O and (L/D)max. of 0.0325 and 10.5, respectively -a good performance even today for such a versatile aircraft.

 
The Goose has been used by private owners, airlines, charter operators, and the military services. Even today, 45 years after its introduction, at least two short-haul airlines utilizing water and land facilities employ the Grumman Goose in daily operation.
 
Serving as the first of a series of amphibian flying boats of similar configuration but different size, the Goose was followed in 1939 by the 4525-pound Widgeon, the 12 750-pound Mallard in 1946, and the 32 000-pound Albatros in 1947. Extensively used by the U.S. Navy, Coast Guard, and Air Force, the last Navy Albatros was retired in 1976 although the Coast Guard retained a few of these aircraft in active service for a while longer. Today, a completely remanufactured Albatros is being offered by Grumman for civil use by short-haul airlines employing water-and land-based facilities.
 
Intended strictly for the private owner, the four-place, single-engine Fleetwings F-5 Seabird amphibian is shown in figure 8.19. The monoplane wing was mounted on top of the hull and braced with wires that ran from the side of the hull to the wing and from the wing to the strut-mounted engine nacelle above the wing. For operation on the water, the landing gear was retracted in such a way that the wheels projected horizontally from the sides of the hull, well above the waterline, and all struts were buried either in the wing or sides of the hull. In the photograph, the tail wheel and water rudder are clearly visible behind the stern post of the single step hull. Lateral stabilizing floats were located near the wingtips.
 
The Fleetwings Seabird illustrates a basic problem that faces the designer of a single-engine flying boat. Most single-engine landplanes have the engine mounted in the nose. Obviously, this solution is not available to the flying-boat designer except for some restricted types of configuration such as the Loening amphibian. Many single-engine amphibians have employed pusher or tractor engine arrangements similar in concept to that of the Seabird. Struts and, sometimes, single streamlined pylons have been used to support the engine nacelle. In addition to considerations of center-of-gravity location, thrust line position, and spray avoidance, the engine must be located so that the rotating propeller poses no threat to persons leaving or entering the aircraft, or in case of blade failure, to persons sitting in the cabin. These various constraints frequently lead to a pusher configuration.
 
 
ground view of a F-5 Seabird
 
[202] Figure 8.19 - Fleetwings model F-5 Seabird four-place single-engine amphibian; circa 1937. [Peter C. Boisseau]
 
To avoid the corrosion problem inherent in the operating environment of flying boats, extensive use was made of stainless steel in the structure of the Seabird. Both the internal structure and the covering of the hull of the aircraft were of stainless steel. The internal framework of the wings and tail surfaces were also formed of stainless steel, but these surfaces were covered with fabric. Wrinkles are evident in the skin of the hull (fig. 8.19), which indicates the extreme thinness of the metal covering. According to reference 81, the engine-turned pattern of the metal skin was intended to disguise the wrinkles.
 
With a 285 Jacobs radial air-cooled engine, the 3750-pound Seabird had a maximum speed of 150 miles per hour and a landing speed of 53 miles per hour. The aircraft thus offered good performance and operational flexibility for the private owner, without an alarmingly high landing speed and with a modest amount of power that promised relatively low hourly fuel consumption. The Seabird first flew sometime in the late 1930's. The total number built is not known, but at least one is still flying today in the hands of an antique airplane collector.
 
 
PreviousIndexNext