|The Boeing 737-100 prototype
Reading aviation history books is one thing but to read about aviation history from one of the view point of someone who played a vital role can sometimes be more enjoyable. One of those books is Joe Sutter's book 747: Creating the World's First Jumbo Jet and Other Adventures from a Life in Aviation from Smithsonian Books. Long employed by Boeing, Sutter led the team of engineers that developed the Boeing 747. But before the 747 came along, Sutter was tapped by his boss, Jack Steiner, to assist with the development of the Boeing 737. The 707 was well on to insuring its place in aviation history and Steiner was flush with success with the creation and introduction of the Boeing 727. It was Steiner who realized that Boeing could create a family of airliners across sizes that could span different market segments in the growing airline industry. By 1964 many of Boeing's competitors were well ahead in the short-haul jet market with the Sud Aviation Caravelle in France having been in service since 1959, the BAC One-Eleven was in flight test in the UK and Boeing's main US rival Douglas was two years head on the development of the DC-9. At a heated and divisive 1964 meeting, half of those present wanted to proceed with the 737 and the other half felt that Boeing's energies were better focused elsewhere given the state of progress of the competition in the short haul market. According to Sutter, the decision was deferred and Jack Steiner was told to keep refining the concept in the interim.
But that wasn't enough to Steiner. He felt that Boeing should build the 737 and he went around Boeing CEO Bill Allen and personally lobbied each of the members of the corporate board of directors. Bill Allen supported the 737 project but Steiner's determination to get the 737 built didn't win him any points with Bill Allen. But the 737 project was given the go-ahead for launch in 1965. But getting a refined project to launch wasn't easy. Conventional wisdom pointed to a rear-engined T-tail design with five abreast seating which was what the competition used as their respective configurations (though to be fair, the Caravelle's tailplane was mounted halfway down the vertical fin). With Joe Sutter assisting him, the 737's initial designs had a very similar layout. But Steiner's ideas of a family of Boeing jetliners led to divergence- the first of which was the fuselage cross-section. By using a 707 fuselage cross section, they could cut development time, but give airlines six-abreast seating which offered more capacity and operating efficiencies not possible with similarly-sized aircraft with five-abreast seating.
But going with the 707's fuselage cross section and nose meant the 737 got a bit portly in shape and this led Steiner and Sutter to abandon rear-mounted engines for the 737. Because of the short wide fuselage, aft mounted engines would have to mounted further way from the fuselage to allow for smooth airflow into the planned Pratt and Whitney JT8D engines. This resulted in the need for more structure and more weight, which ended up offsetting the efficiencies of six-abreast seating. Sutter recalled in his book taking drawings of the 737 up to his office and cutting the engines out with scissors and moving them around to see if there was a better place for them. The most obvious alternative to Sutter was to mount them on the wings, but to use a 707-style engine pylon meant that the 737 would need a tall landing gear to sit higher off the ground. Sutter's dealing with airlines indicated that ease of loading/unloading and servicing meant that having the 737 low to the ground would be a major selling point for the planned short haul market. Having the jet lower to ground meant it could be loaded, unloaded, and serviced faster without specialized vehicles, platforms or even ladders for engine work.
Sutter was stumped. Aft mounted engines were out. Pylon mounted wing engines were out. It donned on him there was a third solution as he moved the engine drawing cut outs around on his desk. Why not snuggle up the engines right under the wings? The key concern was safety and this was solved by putting the hot section of the JT8D behind the aft spar of the wings which meant it was behind the main wing fuel tanks in the event of an uncontained turbine failure. Sutter recalled presenting his solution to the intrigued Steiner, so they decided to do a paper "fly off"- Steiner and an assistant would work up a series of numbers on the performance and costs of a rear-mounted 737 design as the "Red Team" and Sutter and an assistant did the same with his 737 configuration as the "Blue Team". Although they gave themselves two months for the study, the answer was obvious after two weeks- mounting the JT8Ds right under the wings meant six more passengers could be carried for the given configuration. With six-abreast seating, this meant Sutter's configuration for the 737 was the clear choice and the design was locked in late 1964 in preparation for the eventual go-ahead given a few months later by the Boeing board and CEO Bill Allen. This was the design Steiner passionately believed in so much that he was willing do end runs around Bill Allen!
Both Jack Steiner and Joe Sutter shared the patent for the layout of the 737 and the design has gone on to be not just the best-selling jetliner in Boeing's product line, but as the most-produced jet airliner in history- as of April of this year, 7,147 Boeing 737s have rolled off the Renton, Washington, production line since 1967 when the prototype 737-100 rolled out.
More pictures that show the unique engine mounting of the Boeing 737-100/200 family:
On Flickr someone has posted an NAC 737-200 undergoing maintenance with an interesting shot of a "naked" JT8D still mounted on the wing.
On JetPhotos there is a similar shot of a Malev 737-200's JT8D engine.
Source: 747: Creating the World's First Jumbo Jet and Other Adventures from a Life in Aviation by Joe Sutter with Jay Spenser. Smithsonian Books, 2006, p74-79.