Mar 31 2021 - Mar 31 2021

Sikorsky Flying Boats


The First Clipper Ships: The Sikorsky Flying Boats

Why the Flying Boat?
During the early 1930s, at the time when Juan Trippe was spinning his globe and dreaming of a Pan American world network, there was still much controversy in the aviation world as to which was the best kind of aircraft for long-distance trans-ocean flying. Should it, for example, be a lighter-than-air vehicle (i.e. the airship) or heavier-than-air craft, i.e. airplanes, and should these latter be biplanes or monoplanes? Airships certainly had their supporters, notably in Germany, where the great Deutsche Zeppelin-Reederei persevered with its Graf Zeppelin and Hindenburg to establish the world's first trans-Atlantic passenger air services ó until the disaster of 1937 destroyed all faith in airships. However, for a while, the advantages of long-range capability, measured in thousands of miles, compared with the hundreds of miles by airplanes, outweighed the disadvantages of enormous ground installations, ponderous ground handling, and a complement of crew who customarily outnumbered the passenger load.

Land-planes were not seriously considered as a trans-ocean solution until way into the mid-1930s, when the French and Germans began to operate four-engined monoplanes like the Farman 2200 and the Focke-Wulf Condor. In the United States, the land-plane was not developed until Boeing bomber development opened the technical path, and the big airlines sponsored large land-plane design in the late 1930s. The big problem was the establishment of suitable airports with concrete or hard runways capable of supporting the heavy machines. Such airports were very few - Detroit's Dearborn and New York's Floyd Bennett Field were exceptions to the rule in the United States. In Europe the first hard runways were built not to support large aircraft, but to combat the frost-melt in the spring which turned the grass and earth strips at Stockholm, Helsinki, Stavanger, and Amsterdam into quagmires.

Flying boats had problems of passenger convenience. Transferring from a small launch on to a Clipper Ship or an Empire Boat could be quite an adventure in choppy water. And the provision of such necessary services were expensive. But the advantages of being able to alight on a cleared waterway, whatever the size and weight of the flying boat, outweighed such considerations. There was also the matter of safety. Popular, and even specialist opinion, favored the view that a flying boat could at least alight on water in an emergency, and stood an outside chance of remaining afloat until help arrived. And the availability of large stretches of water was inestimably greater than the availability of suitable landing strips, especially in Asia, Africa, and Latin America. As a matter of geographical coincidence, almost all the great cities of the world, especially those on the routes of Europe's colonial powers, and the United States, in its overseas territories and its Latin American sphere of influence, were either on the coast or on or near large waterways.

Juan Trippe's choice for ambitious development in the 1930s was the flying boat. Pan American led the world in sponsoring its development, and larger land-planes did not enter extensive service until after World War II.
Trippe, losing no time, restlessly moved on to bigger and better things. Turning to Igor Sikorsky, on 20 December 1929 he had ordered three S-40 flying boats. They carried a crew of 6 and 38 passengers - almost twice as many as the Commodore, and almost three times as many as the Ford. The Sikorsky S-40 was easily the largest U.S. civil aircraft of the era, the first S-40, piloted by Charles Lindbergh, took off from Miami on November 19th, 1931 to the Canal Zone. This aircraft, the American Clipper, was the first to carry the famous Clipper name, which was subsequently registered as a trademark by Pan American, to become the epitome of air travel excellence, and to represent a standard to which all competitors aspired, for the next half century.

The Sikorsky S-40

In general appearance, the S-40 seemed to be a double-sized S-38, plus a few refinements. It had the same twin booms, the same-shaped wings, floats, and tail. Only the fuselage was differently designed, effectively so. The S-40 could carry 38 passengers against the S-38's eight. Weighing seventeen tons, it was easily the largest commercial aircraft of its time. Only three were built, all for Pan American, which operated them in Latin America until they were scrapped during World War II.

Sikorsky S-38

Sikorsky S-40

The Sikorsky S-42

An Airliner Before Its Time: Luxury Aloft
Before this aircraft was designed, its predecessors could carry full payloads on flights of only a few hundred miles. The S-42 could carry its full payload of 32 passengers over a range of 750 miles. This was more than adequate for the nonstop trans-Caribbean route to Colombia, and permitted the omission of several en route points on the long east coast route to Brazil and Argentina, where the Commodores or the S-40s had to refuel, even though traffic was sparse.
The S-42 made its first flight on 30 March 1934 and incorporated many technical refinements such as large wing flaps, extensive flush riveting, engine synchronization indicators (also on the S-40), propeller brakes, and automatic carburetors. Its wing loading was higher than that of any previous airliner and was not exceeded by any other type until 1942, eight years after it went into service. Had it been a land-plane, concrete runways would have been needed at airports (then normally grass, gravel, or cinder strips) to support the wheel loads. Fully equipped, including engines, propellers, instruments, and radio, the S-42 cost $242,000, equivalent to perhaps $3,500,000 in today's currency.
The great Douglas DC-3 was arguably the first commercial aircraft to which the term airliner could be applied without fear of deception. It was derived directly from the DC-2 which went into service in 1934. Too often forgotten, however, is another airliner that also went into service at the same time, and whose effects and influence on the world of air transport were more immediate. This aircraft was the Sikorsky S-42 flying boat.

Pan American placed an order for ten aircraft on 1 October 1932. Juan Trippe wanted a luxury airliner that could fly faster and farther than the Sikorsky S-40 (the original Clipper) and which would incorporate all the technical refinements that were then revolutionizing the aircraft manufacturing industry. Trippe got exactly what he wanted.

Sikorsky S-42

The S-42s could carry almost twice as many passengers at least as fast and twice as far as the DC-3. Introduced on the Miami-Rio de Janeiro route on 16 August 1934 (only three months after the DC-2's inaugural) its superiority gave Pan American a clearcut preeminence over rival airlines the world over.

Pacific Duties
When Soviet intransigence over the northern Great Circle route to the Orient forced Juan Trippe to turn to the central Pacific, the S-42 (NC 823M) was selected to perform the arduous survey flights across the vast over-water inter-island segments. The Martin M-130s were not due for delivery until the end of 1935 and Trippe was impatient. Accordingly, one of the two S-42s was modified for this special assignment. Stripped of all passenger accommodation and fitted with extra fuel tanks, it had an endurance of 21 1/2 hours and a range of almost 3000 miles.

On 16 April 1935 it flew to Honolulu, returning on the 22nd. On 12 June it surveyed the Honolulu-Midway Island segment, and on 9 August and 5 October it performed the same mission on Midway-Wake and Wake-Guam, respectively. Such a methodical approach was typical of the efficient organization that Pan American had nurtured, especially in the high standards demanded of its flying crews. On the day that the S-42 arrived back in San Francisco, 24 October 1935, the U.S. Post Office awarded Pan American the trans-Pacific air mail contract (FAM-14) at $2.00 per mile.

The S-42A

This was a modified S-42, with improved aerodynamics and a slightly longer wing span. Uprated Hornet engines permitted a higher gross weight and thus more tankage to give greater range. All the S-42A's were used in the Caribbean and South America.

The Long-Range S42B
Later, the further improved S-42B made survey flights to New Zealand in 1937 and began South Pacific service on 23 December of that year. Sadly, on 11 January 1938, on the second scheduled flight, a disastrous fire at Pago Pago caused the death of the famous Captain Musick and his crew and the service was temporarily suspended.

The Atlantic Survey
In the Atlantic, the problems with the British were finally resolved, and a S-42B, the Bermuda Clipper, started service to the British islands of that name on 18 June 1937, alternating with the Short S-23 Cavalier of Imperial Airways. During the same year, the S-42B Pan American Clipper III made five round trip survey flights in preparation for the Atlantic service. The first went as far as Shediac, the next to Botwood, the next two to Southampton, by the northern route, and finally to Southampton via the Central Atlantic.

The Sikorsky S-43 "Baby Clipper"

Feederline Flying Boat
In South America, in the 1930s, the large S-42 flying boats needed a smaller aircraft to back them up, to handle the traffic to the smaller cities where average loads did not justify the large Clipper operations. The Commodores inherited from NYRBA were reliable but were rather slow. Just as the Boeing 247 and the DC-2 had swept aside the Ford Tri-Motor, mainly by an incremental speed of about 65%, so the Commodore had to give way to a flying boat roughly equal in size, but with more zip.
Once again Sikorsky came up with the answer. The S-43 was a scaled-down S-42 with two engines instead of four and which inevitably earned the title of "Baby Clipper." A total of thirteen of these ships (which were actually amphibians) went into service with Pan American. Ordered on 10 September 1937, the first were delivered in an amazingly short time in January 1936. Seven were allocated to Panair do Brasil and two to PANAGRA. The others flew for Pan Am in the Caribbean.

A Big Baby
References to the "Baby Clipper" should be seen clearly in perspective. The S-43's all-up weight was 20,000 lb, or ten tons. This was more than the DC-2's by about 10%. The DC-3 which went into service a few months later was only 20% heavier. The Baby Clipper's 18 seats was only three short of the DC-3's and its range was not a great deal less.

Sikorsky S-43 "Baby Clipper"

Postscript to the Jelling Expedition
Charles Lindbergh's remarkable circumnavigation of the North Atlantic in 1933 had led to serious exploration by Pan American to fashion an air route to Europe, following the route taken by the Lone Eagle via Greenland, Iceland, and making landfall in the Eastern Hemisphere somewhere in Scandinavia. A common point in the scheme was Iceland, where Pan Am constructed, staffed, and operated an experimental radio station in 1936 and 1937.

One plan was to start a service from Copenhagen, Denmark, to Reykjavik, Iceland, by the summer of 1936, and gradually extend westwards, with the objective of full service from Denmark to the U.S. by July 1938. A cooperative agreement was made with the Danish airline Det Danske Luftfartselskab (D.D.L.) but in parallel with this, another was made with the Norwegian airline Det Norske Luftfartselskap (D.N.L.) for operations to the strategically situated airfield at Stavanger which was one of the first to have a paved runway.

D.N.L. actually ordered a Sikorsky S-43 early in 1936 for a proposed amphibian service from Stavanger to Reykjavik, via the Shetland and Faroe Islands, but the idea never materialized, as for a number of reasons, Pan American's interest in the northerly route to Europe waned. But for this change of plan, the "Baby Clipper" may not have had to take second place to its big brother in Pan Am's chronicle of transocean achievement.
  • Mar 31 2021 - Mar 31 2021

  • Flying Boats

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