View Full Version : Boeing - Why 7 series?

6th Aug 2002, 11:45
Can any enlighten me as to why Boeing aircraft families are all 7XX series? Ie. 747, 707, 737, 777 etc.

Is there some historical logic to this or was it an arbitrary choice?

6th Aug 2002, 13:14
Remember hearing somewhere the following explanation - the sweep of the wing on the a/c was 45degrees, sine of that is 0.707...hence B707. rest just followed.

Captain Stable
6th Aug 2002, 13:34
Possible, but unlikely. I can't find specs on the wing sweep, but on the Dash 80, which was the prototype for the 707 series, the sweep was only 35 deg. It's possible that by the time it went into production the wing had completely changed, but I doubt it.


Clare Blacklock
6th Aug 2002, 17:13
Sorry guys - nothing as technical as wing sweep!

Numbers in the 400 series had been used up, the 500 and 600 series were being reserved for missiles, pilotless aircraft and gas turbines, hence new aircraft types would start afresh in the 700 series.

The 707 should really have been called the 700 but Boeing felt that 7 was a lucky number and having two 7s in the designation would mean twice the luck. The head of Boeing public relations, Carl Cleveland, agreed that Model 707 sounded better and the rest they say is history...

Hope that clears up the mystery! Wonder if the proposed Sonic Cruiser will be given an all-new designation?

6th Aug 2002, 18:45
i hate to rain on someones parade, but the 707 started out as the 367- 60. so i reckon there were a few numbers left!

6th Aug 2002, 18:48
Well, actually it was the 367-80, but that doesn't have quite the ring of "707", does it? :)

6th Aug 2002, 20:57
The 367 was the C-97 Stratofrieghter/tanker. The 367-80 was the 80th design study stemming from the basic project. Of course after 80 rehashes it didn't look anything like a C-97 :)


Clare Blacklock
6th Aug 2002, 23:20
Very true!

I suggest taking a look at "Legend and Legacy" by Robert J. Serling and "Boeing Aircraft since 1916" by Peter M. Bowers for the full lowdown on the Boeing method of airplane numbering.

7th Aug 2002, 09:16
Interesting stuff.

Thanks to all for your thoughts/comments.

(787 for the proposed Sonic Cruiser?)

7th Aug 2002, 12:03
I suspect that the marketing department's idea of what sounds good is often the major factor...

Similar things happen with car model numbers. I read that when Porsche were developing a certain well-known rear-engined, air-cooled sports car, they wanted to call it the 901, only to find the Peugeot had trade-marked all three-digit numbers with a zero in the middle (I guess it only applied to cars!) so they called it the 911 instead.


Golf Charlie Charlie
7th Aug 2002, 12:50
Classic Aviator

If I recall well, the Boeing 720 was originally designated the 707-020, but they wanted to make something of the short-haul features of the type and gave it a separate number.

As for the 367-80, again if I'm right, it was given this designation, ie. the Dash-80, as a kind of cover story to allow the competition think it was just another version of the basic 367 Stratocruiser.

Clare Blacklock
7th Aug 2002, 13:53
Also, the 720 launch customer, United Airlines, did not approve of the designation 707-020 and pushed for a new designation number, hence 720. This was to show their customers that the plane was not just another 707 version, but American Airlines actually marketed their 720s as 707s.

Boeing first launched the aircraft as Model 717 (Boeing News - July 25th 1957) but was renamed in the November of that year.

The consensus was the aircraft was not different enough to warrant a whole new designation (727), so 720 became the compromise.

Interestingly, 717 was Boeing's commercial designation for the C-135 tanker/transport until superseded by the renamed MD-95.

Golf Charlie Charlie
7th Aug 2002, 14:31
I would be surprised to learn that the 'first' model was the 717, which was re-named the 707. I thought Boeing launched two models almost simulataneously, ie. the civilian 707 and the military 717, which became the (K)C-135 series. The 717 military type had a slightly narrower fuselage, did it not, than the civil 707 ?

7th Aug 2002, 16:09
Yes, the 707 has a larger cross-section than the Air Force version (C-135/KC-135 etc. etc.) The whole family started as a project to produce a jet version of the C-97/KC-97 Stratotanker, and originally had the same cross-section dimensions as the KC-97 except that the 'crease' at the cabin floor was smoothed over.

The USAF made Boeing enlarge the cross section, and then the airlines required an even larger section. So, the 367-80 has the smallest section , then the KC-135 is larger, and the 707/720 is yet larger again.

FWIW, the KC-97 was essentially a B-29 design (tubular fuselage) with another, larger tube grafted on top.

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