Why does Boeing use the number 7 on its aircraft?

7-7 designation has come signify boeing's line of commercial passenger jets chosen purely marketing purposes, story of 707 interesting one, nonetheless. boeing, other aircraft manufacturers, has used internal numbering system identify various designs since company founded in 1917. company's first design b&w biplane, named after co-designers william boeing , g. c. westervelt. aircraft referred boeing model 1.

during 1930s , 1940s, company model numbers 200s , 300s. famous b-17 flying fortress known internally boeing model 299. other well-known designs of period included model 314 clipper, flying boat ushered in age of airline travel, , model 345, better known b-29 superfortress.

start of jet age, boeing had progressed 400s. of better known designs included b-47 stratojet (model 450) , b-52 stratofortress (model 464). these 2 aircraft made boeing nationally-recognized leader in design , construction of large, jet-powered aircraft. wealth of experience prove vital in producing country's first commercial jetliner.

during 1930s , 1940s, company model numbers 200s , 300s. famous b-17 flying fortress known internally boeing model 299. other well-known designs of period included model 314 clipper, flying boat ushered in age of airline travel, , model 345, better known b-29 superfortress.

start of jet age, boeing had progressed 400s. of better known designs included b-47 stratojet (model 450) , b-52 stratofortress (model 464). these 2 aircraft made boeing nationally-recognized leader in design , construction of large, jet-powered aircraft. wealth of experience prove vital in producing country's first commercial jetliner.

effort began when boeing initiated study of turbojet-powered version of kc-97 stratofreighter. known internally model 367, kc-97 piston-engined derivative of b-29 developed in-flight refueling tanker b-47 , b-52. same design had been adapted model 377 stratocruiser commercial airliner. although boeing eager develop jet-powered airliner replace model 377, company knew airlines not commit enormous development costs required. instead hoped air force fund development of jet-powered variant of kc-97, , final product adapted civilian spin-off.

unfortunately, air force showed no interest in proposal, , rejected in 1951. boeing instead decided commit on $15 million of company funds develop turbojet-powered transport, convinced usaf buy anyway. owing legacy derivative of model 367 , in effort maintain secrecy, new project dubbed model 367-80, popularly known "dash-80" boeing employees. however, dash-80 evolved far beyond initial concept. design became larger, longer, wider, , more streamlined fuselage able hold 130 passengers. overall "figure-8" fuselage shape derived kc-97 , stratoliner, faired on improve aerodynamics. otherwise, design largely inspired b-47, having borrowed bomber's 35° swept-wing , mounting of turbojet engines on underwing pylons.

time dash-80 made first flight in 1954, air force had changed mind project , ordered 29 kc-135 tanker/transports. airline interest slow in coming, however, boeing officials looked give project new, more memorable name. model 367-80 had never been intended more internal designation. models in 500s had been reserved gas turbine engines , 600 series missiles. 700 series again intended aircraft, company board decided officially christen dash-80 model 707.

indeed, many of boeing's successful products on years had had connection number 7. these included model 75--hundreds of used trainers during world war ii, model 77--one of first carrier-based fighters, model 247--considered prototype of modern airliner, b-17 flying fortress--of 13,000 built use during world war ii, , model 314 clipper--greatest of passenger flying boats. other notable aircraft included b-29 superfortress (i.e. 9-2=7) saw great success in pacific theater of world war ii , developed number of derivatives, including model 367 , model 377, b-47 stratojet , b-52 stratofortress (5+2=7).

on 1,000 built time production closed in 1991, 707 proved such huge success boeing decided retain same naming convention of future jetliners. 1 exception model 717 given military version of 707, better known kc-135. however, designation did not last , later briefly given different commercial derivative of 707. later, applied md-95 after boeing had acquired former rival mcdonnell douglas. mcdonnell douglas production line remain open long after merger boeing, md-95 re-christened 717 in 1997. other unusual case model 720, shorter range version of 707 developed domestic use. 720 began life 707-020 , later briefly known 717-020 before model 720 became official.

otherwise, boeing has retained 7-7 convention past fifty years, having applied entire family of commercial jetliners:

* 727 (1,831 built)
* 737 (over 4,300 built date)
* 747 (over 1,300 built date)
* 757 (over 1,000 built date)
* 767 (over 880 built date)
* 777 (over 400 built date)

latest member of family 787, formerly known 7e7 because of use of "super-efficient" technologies.

plane started all, dash-80 still holds honored place in aviation history. prototype workhorse 18 years, serving boeing flying test laboratory new technologies. on course of career, aircraft heavily modified test aerodynamic , structural changes advanced features incorporated later planes. among these modifications new wing planform , leading edge shapes, airfoil designs, leading-edge , trailing-edge wing flap concepts, , new engines. dash-80 carried fifth engine in aft-mounted pod evaluate concept 727. historic aircraft retired in 1972 when donated national air & space museum. however, dash-80 remained stored @ davis-monthan air force base desert storage facility until 1990. @ time, smithsonian agreed return prototype boeing's facilities in seattle full restoration original form. there model 367-80 has remained, being displayed @ boeing field. transferred national air & space museum steven f. udvar-hazy center in fall of 2003.

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