Boeing 707, 727 and 737 fuselage cross-sections.

[Mooncrest]

For the 707, Boeing employed what looks like (head-on) an oval shape cross-section. The 727 used an apparently perfectly circular section. The 737 saw a reversion to the 707 style. Does anybody know why Boeing didn't stick to one design for its narrowbodies ?

Thankyou.

[DaveReidUK]

Does anybody know why Boeing didn't stick to one design for its narrowbodies ?

They did.

[MechEngr]

It's a double bubble - top and bottom are cylinders of different radii with a floor to take up the difference in load - picture a round section pulled inward by the floor. It allows more width at the shoulder height of the passengers which allows more seats across the width. It probably requires a small weight increase over a circular section. For a large enough diameter it is less useful.

[Mooncrest]

Thankyou Mech, that's what I thought. I work extensively with 737s and have noticed the double bubble. It just seems strange that Boeing abandoned that particular design for the 727 and then took it up again for the 737.

[tdracer]

It just seems strange that Boeing abandoned that particular design for the 727 and then took it up again for the 737.

They didn't - where did you see that the 727 had a circular cross-section? The 747 was the first commercial jetliner that used a circular cross-section.

[DaveReidUK]

Thankyou Mech, that's what I thought. I work extensively with 737s and have noticed the double bubble. It just seems strange that Boeing abandoned that particular design for the 727 and then took it up again for the 737.

Read my earlier post. The 727 fuselage is the same double-bubble as the 707/737. It's not circular.

[The Flying Stool]

As has been said above, the forward fuselage of the 707, 727 and the 737 is the same.

[DaveReidUK]

The 747 was the first commercial jetliner that used a circular cross-section.

No, not by a long chalk - it was the first Boeing with a circular section fuselage.

[HOVIS]

It's a double bubble - top and bottom are cylinders of different radii with a floor to take up the difference in load - picture a round section pulled inward by the floor. It allows more width at the shoulder height of the passengers which allows more seats across the width. It probably requires a small weight increase over a circular section. For a large enough diameter it is less useful.
In my dim and distant past I remember it being called a 'crease beam'. I think.

[Allan Lupton]

They didn't - where did you see that the 727 had a circular cross-section? The 747 was the first commercial jetliner that used a circular cross-section.
No, not by a long chalk - it was the first Boeing with a circular section fuselage.
and for extra emphasis I can point out that the first commercial jetliner (i.e. the de Havilland Comet) used a circular cross-section

[Mooncrest]

Diagrams I have seen from various spotter books over the decades. I can't reproduce them here but the head-on view of the 707 and 737 are identical, i.e. double bubble or oval shaped and the 727 is a perfect circular section. Either the books are wrong or I am.

[treadigraph]

The Stratocruiser also had the double bubble and in fact design studies to develop it into a swept wing jet transport led to the 367-80 "707" prototype, which retained the same diameter upper bubble as the Stratocruiser. The upper bubble width was increased for the C-135 and again for the 707 so there was space for six abreast seating.

Sad that I never flew on a 707/720.

[DIBO]

https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/512x768/cross_section_of_boeing_727_in_syracuse_airport_ii_491735764 42__f52566ba5d9cc79d8c52114c99c6e57cec70824f.jpgCross Section of Boeing 727 in Syracuse Airportfrom: commons.wikimedia.org

[dixi188]

The DH Comet was circular.
I think the Boeing 757 has the same section as the 707/727/737. It started life as a stretched 727 with a Tee tail and two rear mounted engines, then morphed into the aircraft we know today.

[DaveReidUK]

Diagrams I have seen from various spotter books over the decades. I can't reproduce them here but the head-on view of the 707 and 737 are identical, i.e. double bubble or oval shaped and the 727 is a perfect circular section. Either the books are wrong or I am.

You are, I'm afraid.

All the Boeing civil narrow bodies have a fuselage 148" wide and 158" high.

But don't take my word for it, take Boeing's:

https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/1420x2000/727_ga_annotated_650de00a25eb18ed9a561f9a6b7aa3b75df8d8af.jp g

[DaveReidUK]

The upper bubble width was increased for the C-135 and again for the 707 so there was space for six abreast seating.

Actually, the C-135 has a circular cross-section, just to be awkward. :O

[DaveReidUK]

and for extra emphasis I can point out that the first commercial jetliner (i.e. the de Havilland Comet) used a circular cross-section

Followed by the circular Caravelle, Trident and One-Eleven.

[tdracer]

No, not by a long chalk - it was the first Boeing with a circular section fuselage.

Yea, I stand corrected - I meant to write the first Boeing with a circular cross section. I guess I had a senior moment because I honestly thought that's what I wrote until I came back to this :rolleyes:.
As for the KC-135 - it wasn't commercial...

[treadigraph]

As for the KC-135 - it wasn't commercial...

No, but it was something of a step between the 367-80 and the 707, though I'd never noticed it doesn't have the double bubble.

DC-8 and DC-9 also are double bubbled though I believe the 9 has a smaller cross section.

[DaveReidUK]

As for the KC-135 - it wasn't commercial...

Indeed it wasn't - hence my careful choice of words:

All the Boeing civil narrow bodies have a fuselage 148" wide and 158" high.

:O

[nonsense]

Followed by the circular Caravelle, Trident and One-Eleven.
Doesn't the Caravelle share the cockpit structure with the Comet?

[washoutt]

Wasn't the Boeing Stratoliner (1938) not also circular in cross section? That would precede the Comet.

[oxenos]

I had long believed that Boeings had a machine that extruded an endless tube of fuselage, with different lengths being cut off for the various types.

[DHfan]

Doesn't the Caravelle share the cockpit structure with the Comet?

Sud-Aviation licenced the Comet cockpit design from de Havilland for the Caravelle.

[DHfan]

Wasn't the Boeing Stratoliner (1938) not also circular in cross section? That would precede the Comet.

Not a jetliner...

[HOVIS]

Sud-Aviation licenced the Comet cockpit design from de Havilland for the Caravelle.
They reciprocated with the engine stub wing design for the BAC 1-11. Or so I was told when I noticed the Sud Aviation data plate during an engine change.

[Alan Baker]

The 707 fuselage lower lobe was deeper than the forward fuselage lower lobe of the 727 (thus the double bubble effect was less noticeable on the 727). The rear fuselage of the 727 was deeper than the forward section (a feature perpetuated on the 757). The 737 used the 727's forward fuselage section throughout its length. The C-135 was not circular, it just didn't have a crease line, which reappeared when the 707 upper lobe was widened for 6 abreast seating.

[DuncanDoenitz]

I had long believed that Boeings had a machine that extruded an endless tube of fuselage, with different lengths being cut off for the various types.
Still available in larger branches of B&Q. (Please ask a colleague for assistance).

[Self loading bear]

Still available in larger branches of B&Q. (Please ask a colleague for assistance).

When properly terminated with sausage end clips it can be inflated to widebody when still warm from the extruder.

[Mooncrest]

The 707 fuselage lower lobe was deeper than the forward fuselage lower lobe of the 727 (thus the double bubble effect was less noticeable on the 727). The rear fuselage of the 727 was deeper than the forward section (a feature perpetuated on the 757). The 737 used the 727's forward fuselage section throughout its length. The C-135 was not circular, it just didn't have a crease line, which reappeared when the 707 upper lobe was widened for 6 abreast seating.
Thankyou Alan. This makes everything much clearer.

[Mooncrest]

Thankyou everyone for your replies. I consider myself enlightened and educated.

Speaking of 707s, I've just been looking at pictures of the cockpit of John Travolta's old 707. It's remarkably tidy and neat for its vintage and I guess set the template for the 727, 737 and 747 cockpits, although bearing in mind there was never an FE station on the production 737s.

[DaveReidUK]

The 707 fuselage lower lobe was deeper than the forward fuselage lower lobe of the 727 (thus the double bubble effect was less noticeable on the 727). The rear fuselage of the 727 was deeper than the forward section (a feature perpetuated on the 757). The 737 used the 727's forward fuselage section throughout its length. The C-135 was not circular, it just didn't have a crease line, which reappeared when the 707 upper lobe was widened for 6 abreast seating.

Excellent summary. (note to self) change adjective applied to C-135 from "circular" to "egg-shaped" :O

This might be of interest - there are several versions on the Net, this one includes the DC-8 for comparison:

https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/802x243/fuselage_cross_sections_f86c60487495d452b31c9a1f56d8f83528e6 8f27.jpg

[ATNotts]

I had long believed that Boeings had a machine that extruded an endless tube of fuselage, with different lengths being cut off for the various types.
I remember reading or hearing similar, I think in the 1970s, but obviously an urban myth.

[Sue Vêtements]

Time for a new thread maybe? . . . "What cross section?"

and then there's Egg Shaped . . .

https://i.imgur.com/ElxcWt8.jpg

Building something like that has to be an interesting job though - better than a career IT at least :(


Sorry for the interruption. Back to the original thread

[dixi188]

How come the B707 and DC-8 arrived on the scene at almost the same time with almost the same dimensions?
Obviously sized to the available engines, but who was spying on whom?

[Jhieminga]

The way I remember from reading about the two designs is that the 707's fuselage shape was widened in response to the DC-8 going for six-abreast seating. At that point Boeing realised that they needed the same on the 707 and widened the upper part of the double bubble, but leaving them with two different fuselages for the C-135 and 707 families.

This image doesn't show the full fuselage shape for these types, but it is a nice comparison.
https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/2000x1099/fuselage_width_diagrams_fb96412797227640749005c4ba0540f8e6bf a9c8.jpg

[tdracer]

How come the B707 and DC-8 arrived on the scene at almost the same time with almost the same dimensions?
Obviously sized to the available engines, but who was spying on whom?
My understanding was that Boeing originally planned to use the KC-135 fuselage cross-section for the 707, but potential customer airlines quickly pointed out that the DC-8 cross-section allowed more seating and hence was more desirable.
So it's far from a coincidence that the 707 and DC-8 fuselage cross-sections are so similar.

[treadigraph]

Of course, Pan Am hedged their bets a bit by also ordering some 20 DC-8s which they flew between 1961 and '68 before flogging them on to Delta, United and one or two other airlines...

Looking at the cross section of the KC-135, if drawn accurately the inner skin looks to be double bubbled and the outer skin smoothed over the crease? Is that right?
,

[dixi188]

There is no inner skin, I think it is the shape of the frames that are beefed up at the floor attachment.

[treadigraph]

Ah, gotcha, thanks!

[WHBM]

Sud-Aviation licenced the Comet cockpit design from de Havilland for the Caravelle.
More so, I read (in French, so it must be right) the first Caravelle forward sections on the prototypes and initial production were actually built by De Havilland at Hatfield under subcontract, and shipped over. As the Rolls-Royce engines and some of the instrumentation etc were from the UK as well, the Caravelle, a bit like Airbus, had more UK content than sometimes realised.

Unkind commentators said De Havilland had cut the forward fuselages off the abandoned Comet 1 fleet, by the mid-1950s laying around behind various hangars in the UK !.

When the Caravelle was sold to United in the USA, the FAA refused the cockpit design as they said the pilots' visibility was not good enough, hence the design for the Caravelle 6R and subsequent variants is notably different, with a more bulbous window arrangement.

Sorry, back to Boeing.

[washoutt]

Ah, this post concerns jetliners. I hadn't seen that from the post title. Apologies.

[oxenos]

When the Caravelle was sold to United in the USA, the FAA refused the cockpit design as they said the pilots' visibility was not good enough
Interesting, since the Comet morphed into the Nimrod. The only additional cockpit windows the Nimrod had were the "eyebrow windows" which were certainly useful in steep turns. The visibility from the cockpit was good, particularly after the Mk 2 and 3 Shackletons, which had the gunners position in front of the cockpit. Perhaps there was an element of protectionism in the FAA's ruling.

[DH106]

Interesting, since the Comet morphed into the Nimrod. The only additional cockpit windows the Nimrod had were the "eyebrow windows" which were certainly useful in steep turns. The visibility from the cockpit was good, particularly after the Mk 2 and 3 Shackletons, which had the gunners position in front of the cockpit. Perhaps there was an element of protectionism in the FAA's ruling.

The Bristol Britannia suffered from a similar problem when Canadair tried to certify their CL-44 derrivative with the FAA. An alternative set of windshields had to be adapted (some sources say from the Convair 880/990 jets).

[Liffy 1M]

Interesting, since the Comet morphed into the Nimrod. The only additional cockpit windows the Nimrod had were the "eyebrow windows" which were certainly useful in steep turns. The visibility from the cockpit was good, particularly after the Mk 2 and 3 Shackletons, which had the gunners position in front of the cockpit. Perhaps there was an element of protectionism in the FAA's ruling.

There were at least a couple of jet/propliner mid-airs in the US the early 1960s and, even today, the US does rely quite a lot on visual separation between IFR and indeed VFR traffic in the airport environment, so perhaps it was a prudent approach. The 707, 727, 737-100 to -500 and the DC-8 and DC-9 all had eyebrow cockpit windows, supposedly to assist when manoeuvering and with traffic avoidance.

[DaveReidUK]

A couple of hundred or so early 737NGs were also built with eyebrow windows.

[EXDAC]

Flight test B-717 had eyebrow windows just like the DC-9 and all the earlier derivatives. Sometime early in the test program they were permanenty blocked by sunshields presumably to evaluate if they were really needed. Made me cringe as I preferred the crew to look outside in a turn. I don't know when in the production run they were deleted.

[megan]

In 2005 Boeing said re eliminating the eyebrows on the 737 “The design change reduces airplane weight by 20 pounds and eliminates approximately 300 hours of periodic inspections per airplane.”

[EXDAC]

In 2005 Boeing said re eliminating the eyebrows on the 737 “The design change reduces airplane weight by 20 pounds and eliminates approximately 300 hours of periodic inspections per airplane.”

Imagine what the savings would be if all the forward windows were eliminated. Not a joke. NASA studied elimination of all forward looking windows in the HSR/XVS program. https://en.wikipedia.org/wiki/External_vision_system.

[stilton]

I flew the 727 for six years, as an FO I found the eyebrow windows very useful in a visual left hand circuit turning from downwind and base leg to final, in that left turn i could look across through that eyebrow window and see how we were positioned very well

[Dr Jekyll]

My understanding was that Boeing originally planned to use the KC-135 fuselage cross-section for the 707, but potential customer airlines quickly pointed out that the DC-8 cross-section allowed more seating and hence was more desirable.
So it's far from a coincidence that the 707 and DC-8 fuselage cross-sections are so similar.
Wasn't the V1000 also planned to seat six abreast or was that decision made later?

[DaveReidUK]

Wasn't the V1000 also planned to seat six abreast or was that decision made later?

Wikipedia quotes a 150" fuselage for the VC7, so if built it would have been a tad wider than both the 707 and DC-8

[Jhieminga]

Wasn't the V1000 also planned to seat six abreast or was that decision made later?
It was, as well as the HP.111 and at least one version of the Avro type 722 Atlantic. Wikipedia also states that the US companies moved from a 2+2 or 2+3 fuselage to a 3+3 version in response to airlines rejecting their proposals in favour of the Vickers 1000/VC7 but I have not read that anywhere else (and there is no supporting evidence on Wiki). It is pretty clear that Boeing followed Douglas' lead, but whether Douglas was influenced by the Vickers/HP/Avro/de Havilland projects being discussed across the Atlantic is another question. It may well have been one of the influences, but even then, it was still a bold move from the DC-8 team to go for the 3+3 option. We need a Douglas/McD-D researcher to shed some light on that part of the story.

[Mikelman]

If I remember right, in the 80s Boeing considered using the 757 nose section (first flight 1982) for the "new" 737-400 (first flight 1988). It would have been a very nice ergonomic improvment for the cramped 737 flightdeck.
And also a real chance to make a common flight deck layout standard for the 737 / 757 / 767 family. Saddly, money was talking and the "old" 737 cockpit structure remained for the 737-400 and follow on models.

[tdracer]

If I remember right, in the 80s Boeing considered using the 757 nose section (first flight 1982) for the "new" 737-400 (first flight 1988). It would have been a very nice ergonomic improvment for the cramped 737 flightdeck.
And also a real chance to make a common flight deck layout standard for the 737 / 757 / 767 family. Saddly, money was talking and the "old" 737 cockpit structure remained for the 737-400 and follow on models.
Remember that the 757 nose section structure ("Section 42" in Boeing parlance) is common with the 767 - that's why there is that step down into the 757 flight deck to make it fit (same structure also used on the 777).
I'd not heard that the 757/767 nose was considered for the 737-3/4/500 series (to be fair, I wasn't involved in the development of the that series, being quite busy with the reengining for the 767 and development of the 747-400 that was going on at the same time). However I'd be a little surprised if that was more than just a casual suggestion and never really seriously considered - there was a great deal of emphasis on 'minimum change' during the 737-300 development.

[condor17]

Hovis , in 12 yrs of doing walk rounds on Tridents ; I saw the licence plate many times . Sud Aviation licenced Dh/ HS the Caravelle engine stub pylon for the Trident .
TD , also first I've heard of '75 cockpit on '73s . Perhaps there was a look at it as when first 733s hit Europe , they had round dial cockpits . The first generation EICAS/glass avionic boxes for the A/H and HSI were too long to fit from instrument panel to to nose just under the windscreen .. Then avionic makers [ Honeywell ? ] decreased the length allowing them to fit in the space available .
All according to a Boeing training pilot on our B733 differences course .
If the avionic boxes could not be made smaller , then a '75 nose might have been the only way to upgrade '73s to glass cockpits ..
Not sure if it would have been higher or lower ... It was always a guess as to whether you stepped up or down ........When barely awake at 0Dark30 you stepped into a cold dark cockpit ; depending on which way you stumbled woke up the brain as to whether you were on a '75 or '76 today ..

rgds condor