The Boeing KC-135 is making an appearance in the static park at the Paris air show this year, bringing a reminder of the legacy of the US manufacturer's jet product line, as well as a link to the origins of the modern era of international air transport.
The KC-135 – which marks six decades in service this month - was the military offspring from Boeing's private venture into jet transport production. This began in t1954 with its jet transport prototype 367-80 – or "Dash 80" (pictured above with KC-135). Powered by four Pratt & Whitney J-57 turbojets (civil designation: JT3), this aircraft was effectively a proof-of-concept design for its future civil product line as well as its jet tanker series. It spawned the ubiquitous "model 707 Stratoliner" for the airlines and the "model 717 Stratotanker/Stratolifter" – designated KC-135/C-135 – for the military.
The origins of the decision to build the Dash 80 go back to 1952, when Boeing's then president William "Bill" Allen is said to have “ bet the company” on his management team's jet vision when the board approved the investment of $16 million in the project. Boeing says at the time that represented a huge amount investment, equating to nearly all its profits since the end of the Second World War.
Although both the commercial 707 and the military KC-135 shared the basic design of the Dash 80, they are very different aircraft and not derivatives of each other. A key differentiator is the cabin width. To counter the threat of the six-abreast Douglas DC-8, Boeing was forced to make the 707 fuselage 10cm (4in) wider than the KC-135 to allow it to match its rival's seating arrangement. Boeing points out that while the exteriors of the 707 and the DC-8 were almost identical, "the 707 wing had more sweepback, so it could fly about 20mph (32kmh) faster".
The C-135 was the lead jet project, making its first flight in August 1956 with deliveries to the USAF beginning in June 1957, initially to Castle Air Force Base, California.
Boeing secured its first customer for the 707 in October 1955, when Pan Am signed for 20, and the prototype took to the air in December 1957. Ten months later Pan Am inaugurated 707 services, on 26 October 1958, between New York and Rome via Paris.
To counter competition from the Convair 880 jet, Boeing created a short- to medium-range derivative, dubbed the 720, which was 2.7m shorter. Boeing built 154 720s between 1959 and 1967.
Production of all the Dash 80 offspring was undertaken Boeing's Renton plant where the 737 is built today. The KC-135 line closed in 1965 after 820 had been delivered, while production of the 707 continued until 1994 with 856 units built. Later production was purely of military versions, but 725 were produced for commercial use through to 1978.
While Flight Fleets Analyzer shows that the 707 fleet has diminished to just over 100 aircraft (all with military and non-commercial operators), the C-135 variants have proved extremely sustainable with over 450 of the 820 aircraft built remaining in operation.
All in all, that Boeing "company bet" to build the Dash 80 resulted in the sale of 1,830 four-engined narrowbody jets for the airlines and the military, not a bad endorsement for Bill Allen's jet vision.
Source: Flight Daily News