eroded
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What is the 'bubble' on BOAC's 747-100s?

Sun Feb 17, 2019 6:09 pm

Hi,

Looking at photos of BOAC's 747-100s (in the context of the next retro-livery emerging tomorrow), I note that there is a 'bubble' behind the Upper Deck, not seen on other 747-100s (Pan Am, etc):

Image

Anyone know what it was for?

Thanks,
 
ikramerica
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Re: What is the 'bubble' on BOAC's 747-100s?

Sun Feb 17, 2019 6:30 pm

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Of all the things to worry about... the Wookie has no pants.
 
codc10
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Re: What is the 'bubble' on BOAC's 747-100s?

Sun Feb 17, 2019 6:31 pm

I believe this fairing housed an antenna for a very early iteration of a satcom system, which did not prove to be useful in service and subsequently removed.

You'll see them on early TW 747s as well.
 
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Finn350
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Re: What is the 'bubble' on BOAC's 747-100s?

Sun Feb 17, 2019 6:37 pm

I would say that is just a feature of the original 747-100 with 3 pairs of windows on the upper deck.

Image
 
by738
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Re: What is the 'bubble' on BOAC's 747-100s?

Sun Feb 17, 2019 6:41 pm

Its not just a normal 747-100 feature, it is as stated earlier a primitive satcom antenna, didnt feature on all 747-100's starting after some produced.
Lots of old threads about it ...
Last edited by by738 on Sun Feb 17, 2019 6:51 pm, edited 1 time in total.
 
na
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Re: What is the 'bubble' on BOAC's 747-100s?

Sun Feb 17, 2019 6:50 pm

Not just BOACs 747-100 did have this bubble, but so did all very early 747s until 1973, and some until 1974, and certainly also Pan Ams. It was abolished around ln.230-250. On the majority of these planes it was removed during their first D-check, however.
 
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TurboJet707
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Re: What is the 'bubble' on BOAC's 747-100s?

Sun Feb 17, 2019 6:52 pm

Some of KLM's 747-206s had this too:



BTW, this is the ill-fated PH-BUF that was involved in the Tenerife disaster. It was part of KL's first batch of 747 with PW engines.
I vaguely remember that this 'bubble' housed some kind of additional antenna but I don't rember what its function was.

Edit: posters by738 and na beat me to this, it's indeed not exclusive to the 741.

na wrote:
On the majority of these planes it was removed during their first D-check, however.


Correct, it was indeed removed from KLM's 742s later on, as we can see on PH-BUB here:

 
Aptivaboy
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Re: What is the 'bubble' on BOAC's 747-100s?

Sun Feb 17, 2019 7:03 pm

I believe codc10 is right, although I'm personally not sure of the exact type of antenna. It makes sense that it was only on 3 window per side 741s since their upper decks were often lounges, so any extra space at the end of the upper deck needed for the new installation wouldn't really be missed much. They could "tap into" the rear of the upper deck for that antenna bubble and really not impact lounge operations. When they started using the upper deck for regular seating it went away, either because it didn't work well, wasn't needed, or the airlines decided that they wanted whatever space was being occupied by the installation for one or two last rows of seats. Anyway, that's my interpretation worth exactly a plug nickel in inflation adjusted dollars!
 
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TurboJet707
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Re: What is the 'bubble' on BOAC's 747-100s?

Sun Feb 17, 2019 8:07 pm

Here is a picture of three of the very earliest 747s, being prepared for testing in September 1969. On the first one, the 'bubble' is not yet installed, but it seems there is an opening in the fuselage in the place where it is going to be. It looks like the satcom equipment is about to be built in and covered, I can't image that they will let a brand-new 747 stand out in the open for too long with that hole in the roof..

Fascinating picture by the way, hard to image that it was taken almost 50 years ago.

 
pgcnewyork
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Re: What is the 'bubble' on BOAC's 747-100s?

Mon Feb 18, 2019 1:01 pm

Lots of -100 and -200 series 747s had this 'bubble'

Take a look at the photos of any of the -200s in this collection:
http://www.aussieairliners.org/b-747/aust747index.html

These are all Qantas, but pretty representative. Interestingly, the -SPs did not appear to sport the 'bubble'.
 
Max Q
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Re: What is the 'bubble' on BOAC's 747-100s?

Mon Feb 18, 2019 1:23 pm

Aptivaboy wrote:
I believe codc10 is right, although I'm personally not sure of the exact type of antenna. It makes sense that it was only on 3 window per side 741s since their upper decks were often lounges, so any extra space at the end of the upper deck needed for the new installation wouldn't really be missed much. They could "tap into" the rear of the upper deck for that antenna bubble and really not impact lounge operations. When they started using the upper deck for regular seating it went away, either because it didn't work well, wasn't needed, or the airlines decided that they wanted whatever space was being occupied by the installation for one or two last rows of seats. Anyway, that's my interpretation worth exactly a plug nickel in inflation adjusted dollars!




Three windows on the upper deck doesn’t always denote a -100


There were -200 series built with three windows, most had more windows added later as did some 100’s
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mmo
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Re: What is the 'bubble' on BOAC's 747-100s?

Mon Feb 18, 2019 4:49 pm

IIRC, that small structure is a holdover from the original military proposal. It was originally designed to hold an Astrotracker which was used for navigation as a navigator was proposed in the original military design.
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