Pan Am Clippers from southern California

The Boeing 314, Martin M-130, and Sikorsky S-40 and S-42 flying boats, nicknamed "Clippers" by Pan American World Airways after the clipper merchant ships of the mid-1800s, epitomized the romance of US air travel in the 1930s by providing passengers with a unprecedented level of luxury during long-distance transoceanic flights. However, as noted in a handful of publications, near the end of the 1930s, Pan Am articulated plans to field even larger passenger aircraft in the 1940s that could utilize a new generation of piston engines far more powerful than those used on the Boeing 314, Martin M-130, and Sikorsky S-40 and S-42, namely the Wright R-3350 Duplex Cyclone and Allison V-3420. No aircraft manufacturer from southern California was ever given the chance to build a large passenger aircraft for Pan Am in the late 1930s, so I'm dedicating this post to "Clipper" airliner designs conceived in southern California during this timeframe.

An artist's rendering (left) and cutaway interior view (right) of the Consolidated Trans-Oceanic Flying Boat from the project documents.

Months before the first flight of its new PB2Y Coronado patrol flying boat, Consolidated Aircraft in July-August 1937 conceived a passenger flying boat design that was similar in size and seating capacity to the Boeing 314 despite the fact that Pan Am had selected the Boeing 314 among design submissions for the 1936 flying boat requirement for full-scale development. Officially dubbed the Trans-Oceanic Flying Boat by Consolidated, this design had a rounded nose section faired into the fuselage hull lines, a single vertical stabilizer, seating capacity for 54 passengers in stateroom-type accommodations on two decks, a wingspan of 185 feet (56.39 meters), a wing area of 2,911 ft² (270.44 m²), and a gross weight of 110,000 lb (49,895 kg). Power was provided by four radial piston engines (probably Wright R-3350 Duplex Cyclones or Pratt & Whitney R-2800 Double Wasps), and the top speed of the Trans-Oceanic Flying Boat was estimated at 226 mph (363 km/h). Given that the Trans-Oceanic Flying Boat had a single vertical stabilizer as in the initial Model 30 ("XPB3Y-1") design conceived in early 1937 and a similar wingspan, it is plausible that this project was an evolutionary derivative of the initial Model 30 flying boat design.

Artist's concepts of Consolidated's pusher engine 100 passenger floatplane (left) and 100 passenger flying boat (right) designed in early 1938 for the December 1937 requirement by Pan Am for a new long-range passenger aircraft. The latter design was chosen by Consolidated for eventual submission to the Pan Am requirement.

On December 9, 1937, Pan Am announced a requirement for a long-range airliner with seating capacity for 100 passengers, a range of 5,000 miles (8,046 km), a 25,000 lb (11,340 kg) payload, and a cruising speed of 200 mph (321 km/h), and invitations were sent out to eight companies. Consolidated worked out two proposals in January 1938, one being a gigantic floatplane and the other a conventional flying boat. The floatplane iteration was powered by four 2,600 hp (1,938 KW) liquid-cooled piston engines buried in the wing in pusher arrangement, and it had twin vertical stabilizers, a wingspan of 220 feet (67 meters), a wing area of 4,850 ft² (450.58 m²), an elliptical widebody fuselage, and a gross weight of 200,000 lb (90,718 kg). The flying boat design also had twin vertical stabilizers but arranged the liquid-cooled piston engines in tractor position, and it was 120 feet 9 in (36.80 meters) long with a wingspan of 200 feet (61 meters), a wing area of 4,000 ft² (371.6 m²), a gross weight of 170,000 lb (77,112 kg), and a top speed of 261 mph (420 km/h). Consolidated judged the floatplane design to be slower and heavier than the conventional 100-passenger flying boat design, so it selected the flying boat proposal for eventual submission to Pan Am. The 100-passenger flying boat proposal was subsequently tweaked to have a shorter hull truncated at the water line and a more upswept aft fuselage that supported the tail empennage (similar to that seen in the P4Y Corregidor), a more streamlined and shorter nose, and a broader fuselage to better accommodate the interior arrangement. With these refinements, Consolidated submitted the flying boat iteration to Pan Am by the March 1938 deadline for design submissions.

A front view of and seating maps for the 1938 Douglas land-based airliner submission for the December 1937 Pan Am requirement for a new-generation transoceanic airliner (from a 1954 issue of Interavia)

While Consolidated tinkered with passenger flying boat proposals roughly rivaling the Model 30/PB3Y  designs in length and wingspan, the Santa Monica division of the Douglas Aircraft Company apparently responded to the December 1937 specification by Pan Am by submitting a design for a slightly scaled-up version of the DC-4E airliner powered by six radial piston engines and with greater seating capacity sometime in the first half of 1938. The exact company designation for this proposal is unknown and any other technical data for this project are uncertain, but the the tail empennage design and slight dihedral of the wings could indicate a potential relationship of the design to the Douglas XB-19 prototype heavy bomber.

Although the Consolidated and Douglas design submissions for the Pan American's December 1937 requirement for a new-generation long-range airliner would, like other proposals for this competition, have provided a greater level of luxury than the Boeing 314, Martin M-130, and Sikorsky S-42, the outbreak of war in Europe in 1939 caused Pan Am to shelve its grandiose plans for a new generation of long-range flying boats, and neither the Consolidated 100 passenger flying boat nor the Douglas design were ever built.

References:

Bradley, R., 2010. Convair Advanced Designs: Secret Projects from San Diego 1923-1962. North Branch, MN: Specialty Press.