Profile – Boeing Stratocruiser

As the B-29 was being developed, Boeing engineers were also working on a military transport aircraft known as the Model 367. By July 20, 1942, an engineering summary had been completed and accepted and in December the company received an order from the US Army Air Force (USAAF) for three prototypes under the designation XC-97. The first prototype, No 43-27470, received the name Stratofreighter and made its maiden flight at Seattle on November 15, 1944. It was basically a B-29 with an enormous whale-like fuselage. Boeing had pioneered the use of the perfectly circular fuselage with its Model 299, B-17 Flying Fortress and used it on the Model 307 Stratoliner. The same circular design had been employed on the B-29 but the Model 367 Stratofreighter made use of a double cylindrical shape so that its cross-section looked like an inverted figure ‘8’ – it became known as the ‘double-bubble’.

The larger diameter circle of 11 feet (3. 35m) at the top was the passenger section, while the lower part was actually the lower portion of a B-29 fuselage with cargo/baggage holds instead of bomb bays. According to Boeing, the Stratofreighter offered in all 6,140 cubic feet (173. 5 cubic metres) of usable cargo space, more than twice the volume available in any transport aircraft then in operation and the large clamshell cargo doors opening beneath the tail had an integral ramp and hoist system with 78ft (24m) rails running the full length of the hold which provided easy access and permitted the simple loading of such large objects as standard 2½ ton trucks. Power was supplied by four 2,200hp (1641kW) Wright R- 3350-23 engines but these were soon replaced by R-3350-57A engines rated at 2,325hp (1734kW). The aircraft’s handling characteristics were described as being as good as or even better than those of a B-29 and it gave an impressive demonstration of its capabilities on January 9, 1945, when it made a non-stop flight from Seattle to Washington DC in six hours and four minutes while carrying a 20,000lb (9,072kg) payload. The Stratofreighter flew at 30,000 feet (9,150m) taking advantage of favourable tailwinds for the entire trip and by doing so averaged 383mph (616km/hr), some 20mph (32km/hr) faster than the top speed of a B-29 Superfortress and faster than some piston engined fighters then in service!

The USAAF ordered six YC-97s, basically the same as the three XC-97 prototypes plus four° more powerful variants: three designated YC-97A and one YC-97B. The first of the six YC-97s flew on March 11, 1947 and these machines were the last to be fitted with the Wright engines. Four 28-cylinder Pratt & Whitney R-4360 Wasp Major Engines initially rated at 3,000hp (2,237kW) fitted in slimmer cowlings with nacelles of different outlines, powered the YC-97As.

They incorporated new four-bladed propellers fitted with broad square-tip paddle blades formed by welding together thin steel sheets. A taller vertical tail by 5 feet (1. 5m), as used on the new B-50 Superfortress was added to improve the capability of holding a straight and level course should an outer engine stop in flight, with provision for folding to fit existing hangar spaces. Some fears were held, however, that the new engines and their twin, newly designed, General Electric turbochargers might prove unreliable. By utilising the new 75ST alloy for the structure of the wings and a refined internal design, although the ‘117’ aerofoil of the B-29 was retained, they weighed 6501b (295kg) less than those of the B-29/XC-97 while being 16% stronger and 26% more efficient. Complete thermal de-icing was also added. Accommodated in a new fuel system with 35 bladder cells, 3 in the centre section and 16 in each outer wing, a total of 5,867 Imp gal (26,6701) of fuel could be carried. The outside dimensions and basic loading facilities remained the same as the original XC-97 configuration. A load of 41,000lb (18,598kg) of cargo could be carried or, if used as a troop carrier, 134 seats could be installed or 83 stretchers and 4 seats for medical attendants carried. Boeing engineers meanwhile hoped that the lone YC-97B (45-

59596) fitted out as a VIP transport would be useful as the prototype of a commercial airliner version.

Military Acceptance

In September 1947, the US Department of the Air Force came into being within the US Department of Defense and was created equal in status with the Army and the Navy – thus, the US Air Force (USAF). The combining on June 1, 1948, of the Air Transport Command and the Naval Air Transport Service to form the Military Air Transport Service (MATS) created a global air transport system tor the Department of Defense and other authorised government agencies. MATS began operations in August that year with a miscellaneous assortment of aircraft mainly transports of World War Two vintage including Douglas C-47’s and C-54’s. Recognising the limitations of these machines, the USAF immediately began a replacement and modernisation programme. Among others, an order tor 27 Stratofreighters was placed with Boeing and this was increased to 50 shortly afterwards.

Used for the long-range transport of bulky cargo at high speeds, C-97A Stratofreighters became the mainstay of MATS’

Pacific operations fly mainly between Travis Air Force Base (AFB) on the mainland and Hickam AFB in Hawaii. Fourteen

C-97C Stratofreighters, featuring a strengthened cargo floor and extra equipment, were later added.

At the end of World War Two, the German capital Berlin virtually became an island completely surrounded by the Russian Zone of Occupation. By agreement, the US, Britain and France took over West Berlin leaving East Berlin to the Russians. The

Western powers were guaranteed access to the city through the Russian Zone and free use of three 20 mile (32km) wide air Corridors leading directly into the city from the British and US Zones but, beginning early in June 1948, the Russians imposed more and more restrictions on travel by rail and road through their zone finally completely choking off all surface traffic into West Berlin. This left the Western powers with the choice of either supplying their forces and a populace of over two million in the capital by air or withdrawing altogether and abandoning the city to the Soviets. So began a joint enterprise called “Operation Vittles” by the Americans and “Operation Plainfare” by the British and which became known to the world as the “Berlin Airlift”.

The success of the airlift is now history. By the time the Russian blockade ended on May 12, 1949, many new lessons had been learned especially in the area of air transportation.

Among other things, it underlined the importance and proved the feasibility of sustained around-the-clock mass movement of cargo by air and gave valuable experience in operational techniques, air traffic control and the maintenance and reconditioning of aircraft. It also showed that the future of military air transport lay in bigger planes. The bakbone of the airlift had been the sturdy and reliable Douglas C 4 Skymasters, initially designed to carry a 9,000Ib (4,082kg) payload but many had been stripped to increase capacity by 2,000Ib (1,134kg) tor coal carrying operations. By comparison, the first YC-97A Stratofreighters, which flew in the Airlift at an average daily utilisation of between nine and twelve hours, demonstrated the obvious advantages of their 41,000lb (18,598kg) payload capacity. One C-97 made a total of 27 flights carrying a record one million pounds (453,590kg) of cargo as diverse as coal, steam boilers, baby food, iron pipe and dehydrated potatoes. Had there been more Boeings available, much more cargo could have been shifted in tar fewer flights. Meanwhile, fears that the Pratt & Whitney Wasp Major engines and their turbochargers would prove unreliable were dissipated. There was clearly a future tor the C-97. In US planning the need for an intercontinental bomber force had been recognised even before WW2 and concept development of the Convair B-36 had begun in 1941. The Strategic Air Command (SAC) had been established on March 21, 1946, however, up to 1949 it had to rely almost entirely on the now obsolescent B-29 which could not reach targets in Europe or Asia from the US mainland. To increase the combat radius of its bombers SAC turned to developing the techniques of aerial refuelling. In 1948 as part of a programme to make all of its bombers capable of in-flight refuelling, SAC organised its first two aerial refuelling squadrons and began flying practice missions. A Boeing B-50A, the Lucky Lady II, made the first nonstop around-the-world flight between February 26 and March 2, 1949, covering 23,452 miles (37,742km) in 94 hours 1 minute. The plane had been refuelled in the air four times by B-29 tankers from the Azores, Saudi Arabia, the Philippines and Hawaii. The C-97 was selected by SAC as the most suitable type of aircraft for conversion to the role of tanker to support its new B-4 7 Stratojets and B-52 Stratofortresses. Boeing converted three C- 97A’s (Nos. 49-2591, 2592 and 2596) for tanker tests and designated them KC-97A. The new ‘flying boom’ system developed by Boeing was utilised. Meanwhile, in June 1950, war broke out in Korea and Boeing was suddenly flooded with orders for C-97’s, B-47’s and B-52’s. To cope, the entire C-97/Stratocruiser programme was transferred to the company’s Renton plant so that those at Seattle and Wichita could concentrate on newer projects.

The initial production batch of sixty Stratofreighter tankers were designated KC-97E and the first (No. 51-0183) was delivered to the 306th Air Refuelling Squadron (ARS) at MacDill AFB, Florida, on July 14, 1951-it was the first machine for the formation of two squadrons that year with twenty tankers each. These featured large above-floor fuel tanks and the flying boom refuelling system which was considered an improvement over the British-developed ‘dangling hose’ system. They were followed by an order for 159 KC-97F’s which had more powerful Pratt & Whitney 3,800hp (2,834kW) R-4360-59B engines. One KC-97F (51-322) was outfitted with the probe/drogue refuelling system for evaluation.

By removing the fuselage tanks, boom and operation station, the early KC-97 versions could be quickly converted back into transports but the KC-97G could operate effectively as a transport while retaining its refuelling equipment because it carried two fixed underwing refuelling tanks and modified boom and delivery tanks. A total of 592 of the ‘G’ model were produced making it the most numerous version. One hundred and thirty-five of these later had the in-flight refuelling gear removed completely and served as C-97G transports. Three others were designated EC-97G and outfitted for special electronic duties. About thirty more were later designated HC-97G and converted for interim search and rescue operations.

Two KC-97G’s (52-2693 and 2762) from the production line in 1953 were modified at the USAF’s request to act as testbeds for a new Pratt & Whitney turboprop engine. They were initially given the designation YC-137, then YC-97H but ended up with YC-97J. Powered by their 5,700hp (4,250kW) T34-5A turboprop engines, these planes were test flown by MATS operating from Kelly AFB, Texas but, although they showed promise, production was not achieved because of the faster and more promising jet aircraft coming into the picture. Other conversions consisted of the C- 97K of which 27 were made as SAC mission transports to carry passengers, although the interior refuelling boom was retained and the KC-97L of which there were 82, all converted by Hayes Aircraft which replaced the underwing tanks with J47-25A boos- ter jet pods.

In operational service it was found that the KC-97s could match the minimum speed of B-47 Stratojets giving them the capability of being intercontinental bombers. By 1952, SAC had 139 KC-97s in service and a year later the total had risen to 359 in twenty squadrons. The first B-47 ninety day deployment exercise to England took place in June 1953, when the 306th Bomb Wing brought its forty-five Stratojets and supporting KC-97 tankers to RAF bases Fairford and Mildenhall. In August 1953, in “Operation Longstride” the first mass nonstop flight across the Atlantic was carried out by eight F-84 Thunderjets of the 31st Strategic Fighter Wing. These left Turner AFB, Georgia and were refuelled in the air three times on their way to North Africa, twice by KC-97s of the 305th ARS from Bermuda and once by KC-97s of 26th ARS from Lajes AFB in the Azores. After 10 hours 20 minutes, they landed at Nouasseur in French Morocco. Another flight of twenty F-84s which left at the same time reached RAF Lakenheath 11 hours 20 minutes later also with the aid of three inflight refuellings. Operation Power Flite in January 1957, saw three B-52B Stratofortresses fly around the world nonstop for the first time, a distance of 24,325 miles (39,146km) in 45 hours 19 minutes making an average speed of 534mph (859km/hr). KC- 97 tankers were utilised five times during the flight. The SAC’s commander, General Curtis Le May stated that: “. . . This flight demonstrated SAC’s capabilities to strike any target on the face of the earth. ”

But the C-97s days as the SAC’s exclusive tanker were numbered. The use of a piston-engined tanker with jet bombers made refuelling difficult and reduced the overall performance of the bomber because it had to descend, reduce speed and afterwards climb back again to its operating altitude. Clearly a jet tanker was necessary and as early as 1953 the USAF initiated a design competition for a new aircraft- the winner was Boeing’s KC-135 Stratotanker and the rest is history! The last KC-97G (No. 53-3816) was delivered to the 98th ARS at Lincoln AFB, Nebraska, on November 16, 1956. It was the 888th of the Stratofreighter line. In 1958, with the arrival of new KC-135 Stratotankers, KC-97s began to be phased out of SAC service. The Air National Guard (ANG) began receiving these in 1960 as they came into second-line service. Eventually, 28 squadrons of the ANG used the type, 18 with transports and 10 with tankers, for a total period of 18 years. The ANG retired its last KC-97, a machine of the 181st ARS Texas ANG, in 1978.

Enter the Starcruiser

In the first full year of peace after WW2, eighteen million passengers were carried by the scheduled services of the world’s airlines. By 1949 the total for the year was up to twenty-seven million and while passenger services were growing tonn- age carried grew at an even faster rate. To Mr William M. Allen, the new president of Boeing, taking over at a time when military orders had been drastically cut back, it was obviously desirable to re-enter the commercial airliner business, a field already dominated by Douglas with its DC-4 and larger DC-6 and Lockheed with its Constellation.

As already mentioned, the lone YC-97B (45-59596) had been designed as a VIP transport and for this purpose it had upper deck seating for 80 (arranged 3+2), a galley and a spiral stair-case to a lower deck lounge. It had rows of circular windows and the rear door and ramp was not fitted, nevertheless, it could still carry 17,000lb (7,711kg) of cargo or baggage in the lower deck holds. Delivery of the YC-97B was made to the Air Transport Command (later MATS) on January 31, 1949, for flights by the Pacific Division between California and Hawaii. The essentially Similar civil prototype (9X90700) was labelled the Model 377. Faced with no firm orders, Allen decided to gamble Boeing’s own money on this plane and ordered 50 to be built on spec. The first Stratocruiser was the very next aircraft on the assembly line after the YC-97B. It made its first flight on July 8, 1947.

Meanwhile, Bill Allen’s gamble began to pay off when, on November 28, 1945, Pan American Airways placed an order for 20 Stratocruisers at a price of $24,500. 000 (PanAm were to become famous for launching Boeing airliner programmes as they did likewise with the 707 and 747 aircraft), reputedly the largest contract for civil airliners up to that time. Other orders soon followed: Scandinavian Airlines System (SAS) ordered four; American Overseas Airlines (AOA) eight; Northwest Airlines (NWA) ten; British Overseas Airways Corporation (BOAC) six and United Airlines (UAL) seven.

Passenger reaction to the Stratocruiser with all its luxuries was good. It was the largest civil airliner in use and the interior could be altered and outfitted to suit the needs of the purchaser. The model 377-10-26 supplied to PanAm featured rounded windows, had 61 day seats and 18 Pullman-style night berths to sleep 27, the beds swinging down from sides of the high ceiling which followed the curve of the fuselage.

The four Model 377-10-28 aircraft built for SAS were taken over by BOAC which increased its number of Stratocruisers to ten. These featured 55 day seats and 17 night berths to sleep 26 plus 20 seated. There were also two upper-deck staterooms.

Model 377-10-29s supplied to AOA featured 60 day seats, 30-night berths to sleep 45 plus 25 seated. These six Stratocruisers were taken over by PanAm when AOA was absorbed into that Company in 1950. The PanAm fleet eventually increased to 27 with the addition of these and the first prototype machine the Model 377-10-19. NWA’s Model 377-10-30’s had square windows, 61 day seats, 16 night berths to sleep 24 plus 29 seated.

Model 377-10-32 aircraft of BOAC had 60 main deck seats plus twelve lower deck lounges, 16 night berths to sleep 24 and 28 seated. The four SAS machines brought the British fleet up to ten and later, because of the teething troubles that caused delays to the introduction of the de Havilland Comet, BOAC bought six more from UAL, these being Model 377-10-34 which featured square windows, 55 day seats plus a rear stateroom, 17 night berths to sleep 26 and either 20 or 28 seated. The BOAC fleet finally increased to a total of 17 when one more Stratocruiser was obtained from PanAm. These remained in service until 1958-59 when they were superseded by jets.

Altogether, Boeing built a total of 55 Stratocruisers, the last of which was delivered to BOAC in May 1950.

In general, Stratocruisers enjoyed a satisfactory safety record but during their ten years of first-line service six were involved in fatal accidents or disappearances and there were a number of non-fatal incidents. The causes were discovered to be mostly related to engine problems or propeller failures. One dramatic incident occurred when PanAm’s Clipper Sovereign of the Skies, piloted by Captain Richard Ogg had to ditch into the sea during a flight from Hawaii to San Francisco. He brought the plane down lightly on the surface of the water next to a US Coast Guard weather ship and all crew members and passengers, totalling 22, were rescued before it sank. PanAm lost two other Stratocruisers: The Good Hope which came down somewhere in the Brazilian jungle and the Clipper Romance of the Skies which disappeared somewhere over the Pacific.

Retirement

The rapid development and introduction of jet aircraft swiftly cut short the Stratocruiser’s career as a first-class international airliner. Together with the DC-6s and Constellations, they disappeared from the scene. By 1960, fourteen Stratocruisers, purchased in 1958 from BOAC by a small airline based at Oakland, California, which later went broke, were auctioned off for a mere $105,000. Ten others, bought by a Venezuelan-based cargo airline that also went broke, were just left abandoned at Miami airport to rot. They became an eyesore so the authorities burned them.

Meanwhile, the first batch of six KC-97’s arrived for storage at the 2704th Air Force Aircraft Storage and Disposition Group (AFASDG) at Davis Monthan AFB, Arizona, in late 1959 and this was followed by a further 43 in 1960. During “Operation Fast Fly” the AFASDG received KC-97s at the rate of two per day from late 1965 until 118 more were stored. The final phase-out was completed when Stratofreighter 53-0282 of the 100th ARS flew in from Pease AFB, New Hampshire, on December 12, 1965. At the same time as it landed, stored early model C-97s were being stripped of useful parts and sold for scrap.

A small number ended up in other air forces. Israel obtained about fifteen former C-97s and Stratocruisers and rebuilt them for their own use. Three KC-97Ls of the ANG were used by the Spanish Air Force, where they were designated TK-1, to support their F-4C Phantoms based at Torrejon until they were scrapped in 1976.

One single aircraft of interest was the C-97E Stratofreighter (51-0224) which was converted to an airborne command post and operated by the 137th Military Airlift Wing, Oklahoma ANG. It began service in 1961 and was under the USAFHQ’s direct control, ready to be sent anywhere in the world where emergency communications were needed.

Undoubtedly many would consider the best use ever made of Stratofreighters occurred in 1969-70 when three C-97G’s were leased to the International Red Cross and four others to joint Church Aid for relief operations to Biafra.

Only a few Stratofreighters now remain in USAF storage and these are non-flyable because they have been stripped for parts. Some are still on the American Civil Register and one of these was converted into a fully equipped, computerised 3,000 gal (13,6501) capacity aerial fire fighting tanker which went into service in Alaska in 1984. This machine could still utilise its upper deck for cargo work.

The US Air Force Heritage Programme began while there were still some relatively intact KC-97’s in storage and an adequate number have been preserved and placed into various museums across the USA. One KC-97G Stratofreighter (No. 52- 2736) is held in preservation by the Hatzerim Museum, Israel. But the Boeing Stratocruiser/Stratofreighter story does not end here. The final chapter rests with the Guppy family of conversions and this will be outlined in the next issue.