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Boeing 707/Boeing 720 double build


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As part of a group build on another forum, I've decided to have a go at a double build of two members of the 707 family. The kits in question are the Airfix 707-436 and the Roden 720.

 

 I thought it would be an interesting comparison between these 707 family members as there are quite a few significant differences between the two types.

The Airfix kit dates back to the mid 1960s and is rather crude in many ways. However, as is often the case with Airfix, they got the overall shape fairly correct. They chose a 420 series aircraft because this was the initial version chosen by BOAC back in the late 1950s. This was a very controversial decision at the time because it was supposed to be part of BOAC's "brief" that they should prioritise British designs wherever possible. The candidate that they were expected to chose was the new Vickers 1000.

However, BOAC were pretty pragmatic and recognised that the 707, which was already flying in its initial versions, was a better bet. The one concession they made was that their 707s would be fitted with Rolls Royce Conway low bypass turbofans, as opposed to the regular fit on the original 707s of Pratt & Whitney JT3C or JT4 turbojets. They also stipulated a taller tail fin and a large ventral fin.
These modifications were actually retro fitted to earlier versions of the 707.

The edition of the Airfix kit I have is the 1993 release which came in gold trimmed boxes and were issued in their "Classic Airliners" range. It came with British Airways markings, which were the last colours worn by these aircraft when in service with the national carrier.

The kit was released more recently in BOAC colours - which I prefer. I may try and source a set of BOAC decals. In the meantime, I do have a set of BEA Airtours decals for a 707-436. BOAC transferred some 707-436s to BEA Airtours in the early 70s as by then the 436 model was becoming less economic on routes which were now being served by turbofan equipped 707-336s and 747s. The BEA Airtours colours are interesting because the 707s they used also had the famous BEA Red Wings which is rather unique for 707s, most of which had wings in bare metal/grey anti-corrosion paint colours.

The 720 is the much more recent Roden kit. As far as I am aware, it is the first injection moulded kit of a 720 ever released. The only other 1/144 720 I am familiar with is the vacform from Welsh Models.
The 720 was designed to operate medium range routes and was launched in order to compete with Convair's upcoming 880. The 720s differed in many ways from the 707. It had a shorter fuselage (although there were short fuselage 707s too). It had a strengthened wing - to cope with increased take-offs and landings. It also had an angled leading edge wing shape between the inner pair of engines and the fuselage. This was to improve short field performance. The undercarriage was beefed up too.

Like the 707, initial versions of the 720 had straight turbojets rather than turbofans. This particular kit comes with the turbofans which I will not be using as I have a set of Welsh Model resin turbojet replacements. Roden do have a pure turbojet version in their range as well but it is commonly held that they made their turbojet nacelles too big. So alternatives are recommended.

The reason why I chose their 720B version is that the 720 I wanted to model, whilst a pure turbojet version, also featured the distinctive fin mounted HF aerial. Roden's turbojet 720 kit does not feature this because the original 720s that were delivered to United Airlines were not fitted with this "spike".

My plan is to finish the 720 in the colours of Aerlínte Éireann/Irish International Airlines. Note that this is not Aer Lingus. Aerlínte Éireann had been set up in 1948 alongside Aer Lingus in order to start trans-Atlantic operations. A change of government in 1948 saw this plan shelved but it was revived in 1958 and three 720s were ordered to fulfill this objective. For two years (1958-60) the routes were flown using leased Super Constellations. These were swapped for the 720s when they arrived later in 1960.
In order not to confuse American passengers, the English name "Irish International Airlines" was used on the 720 rather than the Gaelic version of the name.

 

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I've included this last image because it shows the differences between the fuselage of a 707-420 and a 720 -

 

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Mods - I realised that I've posted this in the wrong area. Would it be possible to move it to the Aircraft Work in Progress forum?

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It's quite a while since I last built a 1/144 airliner so I have no idea how it will turn out. The old Airfix kit is pretty crude but it looks like a 707-436. I'm leaning towards finishing it in the BEA Airtours scheme.

 

My favourite choice would be the 1960 delivery scheme used by BOAC (the two white stripes on the fin scheme) but I can't see anyone doing decals for that in 1/144. If anybody knows if such a sheet is available, please let me know.

 

 

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7 hours ago, Eric Mc said:

 

My favourite choice would be the 1960 delivery scheme used by BOAC (the two white stripes on the fin scheme) but I can't see anyone doing decals for that in 1/144. If anybody knows if such a sheet is available, please let me know.

Looks like you're in luck Eric!

https://www.f-dcal.fr/decals/index.php?id_product=429&controller=product&id_lang=1

Cheers,

Ian

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14 hours ago, Eric Mc said:

It also had an angled leading edge wing shape between the inner pair of engines and the fuselage. This was to improve short field performance.

 

Great project!  Looking forward to seeing this unfold.  

 

Regarding your comment, above:

This low-load-bearing "glove" was to designed to lower the thickness-to-chord ratio on the wing, and raise the cruise mach number by .02 to compete with Convair's designs.  It may have had a secondary effect of increasing lift, too, but the primary purpose was mach-number related.  As it was relatively easy to retrofit  (it was basically bolted to the outside of the load-bearing wing structure, including the skin) Boeing later fitted this "glove" to its fan-powered 707-100s.  Also, the entire 720 structure was lightened in comparison with the 707-100, to include the landing gear.  The main gear were unique in having wheels of smaller diameter than those on the nose.  In 1/144, this is almost imperceptible, but the wheels on both the nose and mains should measure about 1/4" diameter.  

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4 hours ago, Turbofan said:

Sadly they don't appear to be available in 1/144 scale.  F-DCAL did produce a set for this scheme a few years ago but they were laser printed. 

Chris.

 

PS. I have a set of the latter if you can't find a suitable alternative.

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8 hours ago, stringbag said:

Sadly they don't appear to be available in 1/144 scale.  F-DCAL did produce a set for this scheme a few years ago but they were laser printed. 

Chris.

 

PS. I have a set of the latter if you can't find a suitable alternative.

Yes - I did have a look at F-DCAL and the BOAC set seemed to be only available in 1/72. I'll keep looking.

 

I quite like the BEA Airtours scheme but I did finish the Airfix Comet 4 in a BEA Airtours scheme not too long ago and it would be nice to try something different.

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On 2/3/2021 at 3:24 PM, TheyJammedKenny! said:

 

Great project!  Looking forward to seeing this unfold.  

 

Regarding your comment, above:

This low-load-bearing "glove" was to designed to lower the thickness-to-chord ratio on the wing, and raise the cruise mach number by .02 to compete with Convair's designs.  It may have had a secondary effect of increasing lift, too, but the primary purpose was mach-number related.  As it was relatively easy to retrofit  (it was basically bolted to the outside of the load-bearing wing structure, including the skin) Boeing later fitted this "glove" to its fan-powered 707-100s.  Also, the entire 720 structure was lightened in comparison with the 707-100, to include the landing gear.  The main gear were unique in having wheels of smaller diameter than those on the nose.  In 1/144, this is almost imperceptible, but the wheels on both the nose and mains should measure about 1/4" diameter.  

i wonder if the wing glove fairing was actually tried on the American 707s, before it became a fixture on the 720? i'm not sure about the chronology. However, totally agree the purpose of the glove was primarily to allow for a higher Mach number.

 

-d-

Edited by David H
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2 hours ago, David H said:

i wonder if the wing glove fairing was actually tried on the American 707s, before it became a fixture on the 720? i'm not sure about the chronology. However, totally agree the purpose of the glove was primarily to allow for a higher Mach number.

 

-d-

All interesting stuff. I expect that Boeing were still tweaking the design through the early versions as they learned of the characteristics of these new fangled jets.

 

Edited by Eric Mc
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I've just looked up the 720 in this book.

Boeing707.jpg

Got to say that I've yet to be able to spot that wing-root glove in a photo.

Originally planned to be called the 707/020,  renamed to 720 at the request of William A. Paterson,  president of United Airlines (lead customer), who didn't want to backtrack his committment to DC-8s by purchasing 707s.

 

And best of luck with the builds.

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One of Aviation Week's 1960 issues contained a detailed article on the 720 of which I may still have a xerox copy.  It clearly shows the glove in the wing cross-section on the plant floor.  The glove fits over the wing, back to about mid-chord, and creates a second aerodynamic shape over the wing, until it gradually curves to wrap around the leading edge of the wing, and is bolted to the outside of the existing wing structure.  You can see it in delivery photos of the aircraft when the aircraft is photographed in mid-air while in a bank. 

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On 2/4/2021 at 11:45 PM, David H said:

i wonder if the wing glove fairing was actually tried on the American 707s, before it became a fixture on the 720? i'm not sure about the chronology. However, totally agree the purpose of the glove was primarily to allow for a higher Mach number.

 

-d-

No.  The 720 was built from the outset---and type-approved--with the glove in June 1960, whereas the fan-powered -100B received its type approval in March 1961.  All fan-powered -100s had the glove, which is why it is difficult to modify the -135 wing (for example) in 1/72 to suit a fan-powered 707-100.  Some straight-pipe (turbojet) 707-100s were retrofitted with the fans and glove, including Australia's 707-138s, which became -138Bs.  The -320/-400 did not need the glove because they were designed from the outset with a wider chord wing, and the economics of Transatlantic/Pacific travel did not necessarily dictate high Mach numbers.  

 

I don't know whether the 720 was approved for runways shorter than 10,000 feet.  

 

Alex

Edited by TheyJammedKenny!
word order, revised dates
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Monarch Airlines used Boeing 720's out of Luton Airport,UK  regularly with a 6,500 foot runway.

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4 hours ago, theplasticsurgeon said:

I've just looked up the 720 in this book.

Boeing707.jpg

Got to say that I've yet to be able to spot that wing-root glove in a photo.

Originally planned to be called the 707/020,  renamed to 720 at the request of William A. Paterson,  president of United Airlines (lead customer), who didn't want to backtrack his committment to DC-8s by purchasing 707s.

 

And best of luck with the builds.

Pounds are expensive to my dollar no matter what, 6 from 25 is a great sale.

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20 hours ago, busnproplinerfan said:

Pounds are expensive to my dollar no matter what, 6 from 25 is a great sale.

The £25 is very misleading.   It's unlikely that any of this range of books has ever been sold in TheWorks for that price.

£6, makes them VERY attractive as reference for modellers - I've got loads of them.

 

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3 minutes ago, theplasticsurgeon said:

The £25 is very misleading.   It's unlikely that any of this range of books has ever been sold in TheWorks for that price.

£6, makes them VERY attractive as reference for modellers - I've got loads of them.

 

Can never have enough references.

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There is a very good article with lots of scale drawing in the January 1968 IPMS(UK) Magazine by Bill Matthews explaining the various versions of the Boeing 707/720 family - the scale drawings show the various wing forms, fuselages, tailplanes, etc.  I can scan it if of interest - PM me if wanted.

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I knew the glove was incorporated into the 720 from the get-go, but i thought it may have been tested first on American Airlines' 707-100 series planes that were retrofitted with the JT-3D. i guess i have it backwards, the glove being offered as a retrofit option. Some airlines like QANTAS and American upgraded with better engines, whereas other carriers like TWA and maybe Pan Am did not.

 

Up until recently i thought the glove was strictly a 720 thing. Clearly this is not the case.

 

-d-

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4 hours ago, David H said:

Up until recently i thought the glove was strictly a 720 thing. Clearly this is not the case

See my revised dates in an earlier posting.  The 720 was type approved June '60, 707-100B March '61.  TWA upgraded some of its fleet of 100B's with JT-3Ds/wing glove, and these served until the early 80s (I think), but Pan Am sold its short-bodied jets without first re-engining them.  

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Been making decent progress on both the 707 and the 720.

As expected, the Airfix 707 requires quite a bit of fettling and filling. The slots in the fuselage for accepting the wings were way too tight and needed a fair bit of opening up to allow the wing locating tabs to slot in. Once in place and glued, the resultant gaps needed filling with a combination of plastic card slivers and Humbrol filler. The fuselage went together quite well and the tailplanes slotted into place with little fuss. They just needed a bit of filler and sanding for an acceptable look.

The engine pylons just didn't fit into the slots provided in the wings. So, I had to open the slots up a bit to allow the pylons to be located properly. Indeed, when test fitting, I managed to snap one of the pylons. It's fixable so not as big an emergency as it could have been. You can see from the pictures that the engines aren't in place yet. I'd normally prefer to paint the engines and pylons separately but because of the poor fit and gaps, I'll have to glue them in place first, fill the gaps etc before I can paint the wings, pylons and engines all in one go.

The 707 is primed but after the engines are attached to the wings and the pylons properly blended in, it will need to be primed again.
I've been kindly given a set of BOAC decals for the 707 so it will, hopefully, look resplendent in the original livery adopted by BOAC when first put into service.


The 720 is also coming along - slightly behind in the assemble and painting process. It's obviously a more modern moulding but, as it is a short run kit, fit is not "Tamiya Quality". The fuselage went together pretty well but the wings are not that great a fit. However, once the gaps have been filled (again with plastic card and Humbrol filler) it should be OK. You can see below that this is where the 720 build has got to.

The big problem with the Roden 720 is their rendition of the Pratt and Whitney JT3C engines. Basically, they are too big in diameter. I thought I had sorted the problem by buying some Welsh Models JT3C replacements (originally designed for their own vacform 720). However, even though they look better, the pylons are not long enough and therefore look wrong when offered up to the wing. So, I am reverting to the original kit offerings as neither situation is correct. I will try to rehsape the cowlings as best I can to and make them look less hefty as they appear.

 

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