Beyond the Rainbow: Republic Turboprop and Jet Airliners

boxkite

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This Republic "Rainbow" development with a 35° swept wing was published in a German aviation magazine in the 1950s (no idea which one). Is anybody able to identify the type and to give further information?
 

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Antonio

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Many Thanks Boxkite!

It is a very interesting project. Republic derivative from its fine Rainbow was designated RC-2. This is clearly a step beyond, intended to get access to the jet airliner market in the 50's. A probable manufacturer designation could be RC-4 (the RC-3 was the Seabee from 1945).

What do you think Lark?
 

lark

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There was a step inbetween.A turboprop development of the Rainbow.I have it
in an old French magazine of the late fifties but I have to dig (very) deep.
As far as I remember the article gives no info of designations.
 

devi

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Hi Boxkite.
In what number and in what to page it is told about Republic Rainbow (jet engined version).
 

boxkite

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Sorry, but I cannot give a satisfying answer. I've got the Republic image as a Xerox copy from a friend a few years ago. Unfortunately he is too lazy to make notices of the source. My further inquiry wasn't successfully. He only remembers, that 'it was published in a German magazine in the 1950s'. :(

[So SPF members please don't forget the source of your knowledge to help for further study. Thanks a lot.]
 

lark

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This illustration -with the " Rainbow" and the turboprop version -
appeared in "L' Echo des Ailes" of 10 June 1950.
It was part of the illustrations in an article about the future
of air transport.The turboprop version should have a less sleek
wing and almost the same fuselage.The all jet retained only the basics
of the fuselage. no info was given about the designation.It seems that these illustrations are highly speculative...
 

Antonio

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Dear Friends Boxkite and Lark.

My especulative RC-4 designation for this project it's not correct. My friend David from The Nederlands sent me a photocopy with the real RC-4 which corresponds to an aircraft with a layout very close to the Fokker F.27. This design dates back from the 60's so now I think that the "jet RC-2" could have retained the RC-2 designation.
 

elmayerle

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lark said:
This illustration -with the " Rainbow" and the turboprop version -
appeared in "L' Echo des Ailes" of 10 June 1950.
It was part of the illustrations in an article about the future
of air transport.The turboprop version should have a less sleek
wing and almost the same fuselage.The all jet retained only the basics
of the fuselage. no info was given about the designation.It seems that these illustrations are highly speculative...
If you can find it, a scan of the illustration of the turboprop version would good to see. I'm just wondering what turboprops were proposed? IMHO, the use of Darts, Tynes, or similar engines rather than the Allison 501/T56 would suit the aesthetics better, but I'd be most interested in seeing any info available.
 

Sentinel Chicken

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Are you sure they were going to use turboprops on the evolved Rainbow versions or VDTs? There was quite a bit of work on variable discharge turbines in those days- there was even a version of the B-36 (I think it was the B-36C) that was to have used VDTs.
 

elmayerle

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Sentinel Chicken said:
Are you sure they were going to use turboprops on the evolved Rainbow versions or VDTs? There was quite a bit of work on variable discharge turbines in those days- there was even a version of the B-36 (I think it was the B-36C) that was to have used VDTs.
The basic Rainbow already used VDTs, that's one reason for the exhaust at the rear of the nacelle.

And, yes, the B-36C was a proposal for using VDTs on the B-36 in a tractor propeller configuration.
 

Sentinel Chicken

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elmayerle said:
Sentinel Chicken said:
Are you sure they were going to use turboprops on the evolved Rainbow versions or VDTs? There was quite a bit of work on variable discharge turbines in those days- there was even a version of the B-36 (I think it was the B-36C) that was to have used VDTs.
The basic Rainbow already used VDTs, that's one reason for the exhaust at the rear of the nacelle.

And, yes, the B-36C was a proposal for using VDTs on the B-36 in a tractor propeller configuration.
The VDT (Variable Discharge Turbine) engine was a Pratt & Whitney R-4260-51 Wasp Major where the exhaust gases drove a GE CMH-2 turbosupercharger that had a clamshell nozzle that could modulate the thrust by varying the opening of the nozzle- hence the term VDT.*

The Republic XF-12/XR-12 Rainbow did have turbosupercharger exhaust that was used to add forward thrust but it wasn't a VDT- it had a slightly different Wasp Major model (the -31) and the exhaust drove two GE BM-4-5 turbosupercharger units (at lower speeds only one unit was engaged) which then exhausted via a fixed oval nozzle at the rear of the nacelle.**

*"Magnesium Overcast: The Story of the Convair B-36" by Dennis Jenkins, Chapter 3, p.54
**"Republic XF-12 Rainbow: All the Fours" from Wings of Fame Volume 3, p.29
 

devi

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Hi lark.

What number this magazine?("L' Echo des Ailes" of 10 June 1950)

In what pages about the Republic "Rainbow"?

And if it is possible, the name of article.
 

lark

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Since I only have a part of the magazine , I cant give
you the issue number.

Title :" L'Amerique découvre l' Europe"
(America discovers Europe)

pages :25-26-27 of 10 June 1950
 

boxkite

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Did we have an artwork of the turboprop Rainbow yet?

SOURCE: aero magazine 1958 (page 127)
 

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elmayerle

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boxkite said:
Did we have an artwork of the turboprop Rainbow yet?

SOURCE: aero magazine 1958 (page 127)
Going by the appearance of the engine nacelles, I'd say it's powered by Allison 501/T56 engines.
 

circle-5

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An early jet development of the Republic Rainbow, probably from the late 1940s. Four engines in stacked pairs will re-appear on Republic's UTX proposal (see photos here and here). Between the V-tail surfaces is a large door, probably the upper half of a clamshell rear loading ramp.

Photos courtesy Tony Buttler.
 

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nugo

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Hi All and personally circle-5!
Thank you very much my friend circle-5!
It is a very interesting development of the XF-12/Rainbow.
Model designation maybe---AP-3? or AP-4? and maybe transport (primarily for personnel and also cargo) aircraft proposal for USAF purpose.
 

hesham

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Excellent work Circle-5,


and I agree with you my dear Jemiba.
 

circle-5

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Another jet variant of the Republic Rainbow, with a conventional tail. The 4 jet engines are still in pairs, but are now arranged side-by-side. Rear loading doors are still present under the tail. I suppose these doors (and the high wing arrangement) were in response to a long-forgotten USAF logistics requirement. The prominent fairing between the intakes is for the main landing gear.

I don't know which variant came first: the V-tail shown above, or this one.

Photos courtesy Tony Buttler.
 

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Jemiba

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circle-5 said:
...The prominent fairing between the intakes is for the main landing gear.
The V-tail variant then had it in the fuselage, I assume ? Or a bicycle type with outriggers ?
 

circle-5

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Jemiba said:
circle-5 said:
...The prominent fairing between the intakes is for the main landing gear.
The V-tail variant then had it in the fuselage, I assume ? Or a bicycle type with outriggers ?
I don't know, but the main gear could also be in the stacked engine pod, below the bottom engine. That would also keep the landing gear legs reasonably short.
 

circle-5

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This beauty was likely the last civilian project of any kind from Republic Aviation. An all-new, purely commercial medium passenger aircraft, it boasted low swept wings, a T-tail, podded engines and a streamlined cockpit reminiscent of the defunct Rainbow.

Based on the spurious registration number, this might be the elusive Republic Advanced Project No. 25 (AP-25). Of course, this is barely an educated guess -- if I'm wrong, please have your people talk to my people.

Photos courtesy Tony Buttler.
 

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nugo

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Hi All and personally circle-5!
Thanks, thanks, thanks...
Can not be that this project would have designation of AP-25;
My two arguments:
1) AP---is the designation of the military projects.
2) AP-25---is the designation of the military draft mid-1940s years, and this project with swept surfaces(wing of the Thunderstreak and fin of the XF-84H), the development of the 1950s years.
 

circle-5

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Okey Dokey. Thank you for the clarification. AP-25 was just a guess. If anybody has more info on these Republic airliner designs, this is a good place to enlighten the masses.
 

hesham

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Marvelous work Circle-5.
 

Stargazer2006

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OMIGOD. I can't begin to express how thrilled I am at the contents of this thread... You've made my day, circle-5!!! Thank you so much, and I also extend my utmost gratitude to Tony Buttler for sharing these with you.
I totally agree with nugo that the designation AP-25 was much too early to apply to the third project, and went back to 1945 or about (AP-24 was the YOA-15 Seabee). However, and though he is correct in asserting that "AP-" was used for military projects, it's not entirely true. It was used for ARMY projects (Navy projects, which were few, carried the NP- prefix). There is a likelihood that at some point in the 1950s the prefix simply was used for all projects and might have read as "Advanced Project" but there is no confirmation of this.
Anyway, considering the beauty of these models and designs, and the tragic loss of the Republic archives (because of the idiotic handling of Fairchild's executive management), it is an absolute thrill when such projects by Republic suddenly resurface from other sources!
 

Jemiba

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A long, long time ago, in a forum not far away .... I said, I'll make a drawing of the jet transport derivative of the Rainbow.
As already well known in Germany for airports, railway stations or other big projects, it took a little bit longer ... but here at
least the costs remained the same ! ;)

I started with the assumption, that as many components of the original Rainbow as possible would have been used, at least
in modified form. The forward fuselage seems to have a somewhat different glazing but more or less remained unchanged, but
the rear part got a completely new, wider shape for incorporarting the loading ramp, the tail was modified, too, accordingly. The
wing was moved from the middle to the shoulder position, but planform seems to be identical, changes (hinge lines for ailerons
and flaps) probably were a result of the underslung single nacelle on each side, contrary to the former two with the wingn running
through.
A more difficult point was the landing gear, not shown on the model. In order not to need too long main gear legs, the nose gear
would have been to be shortened considerable, but that not impossible, I think. Asuming, that the main legs would have been
attached to the main spar, as in the Rainbow, length was determined then by the length of the protruding nacelle. Single wheeled
main gear would be unsuitable then, so I switched to legs with twin (smaller) wheels, fortunately allowing for sufficient tail clearance
during take-off rotation. For the drawing without landing gear, I would claim source grade 3, as I could rely on Rainbow drawings,
with landing gear 2, at best. Clues and critics welcome.
BTW, I checked several drawings of the Rainbow and found considerable discrepencies ! Anybody an idea, what's the best ?

I hope, to present something more colourful soon, and the V-tail variant, too. Just have a look at the development of the new
Berlin BER airport for estimating the probable waiting time ...
 

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circle-5

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The Jet Rainbow landing gear is probably not far from the truth. If somebody from the Cradle of Aviation Museum is reading this, please do not hesitate to help!

Thank you Jens.
 

hesham

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Great work my dear Jemiba.
 

foiling

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Thanks Jemiba, another very impressive work of art from you. Much appreciated.
 

MaxLegroom

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elmayerle said:
boxkite said:
Did we have an artwork of the turboprop Rainbow yet?

SOURCE: aero magazine 1958 (page 127)
Going by the appearance of the engine nacelles, I'd say it's powered by Allison 501/T56 engines.
According to World's Fastest Four-Engine Piston-Powered Aircraft: Republic XR-12 Rainbow, the engines, despite the similar nacelle shapes, were to be either Rolls-Royce Darts or General Electric T64s.

The proposal was also said to have dated from 1955, though even as the first 707s were about to enter service, they were still trying to sell this to the airlines. The real tragedy was that the RC-2 never was built nor entered service. The jet powered Rainbow proposals look like they'd have been good competition for the C-102.
 

Jemiba

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Still in b/w only, here's the V-tailed jet transport. Principally quite similar to the other one, its rear fuselage
is somewhat wider and taper begins further aft, so the cargo bay would have been bigger. It's not only fitted
with a rear loading ramp, but with an upper hatch, too. Reason may be, that this arrangement allows using the
full height of the cargo bay, whereas in the variant with the conventional tail, loads certainly would have to be
somewhat lower (see first sketch). Those clamshell doors on the other hand would demand a considerable different
structure of the rear fuselage, actually turning it into a kind of twin boom aircraft.
Nevertheless my main problem here was the main landing gear again (Sorry for bothering again and again with this
component, I know, it's kind of a kink of mine, but to my opinion, without a landing gear such an aircraft would be
pretty useless. So, if such a model was built, I expect, that some of those masters of aircraft design had had some
thoughts about it. It's just not always obvious for us ordinary mortal, to follow those thoughts).
As it certainly had to fit into those nacelles. I assumed, that a likely choice for an engine could have been the GE/Allison
J35 or J47, or the Wright J65. Without reheat all of them would have had a length of about 3,500 mm (140 inch)and a
diameter of about 1,000 to 1,200 mm (38 to 47 inch. The size of the nacelles can be determined relativey easy on
the model, my problem was just to squeeze those two engines and the landing gear into them. Made a sketch, that
shall show, what the internal arrangement maybe could look like and by placing the engines in the aft part of the nacelles,
there is some space left for the wheels and even sufficient room for the inlet of the lower engine, I think. Another
difference between the two variants is the bigger area of flaps and ailerons on the V-tail version,at least on the model
they clearly have a wider chord.
 

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Jemiba

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As already announced, here's some colour. Thinking about a paint schem, I had the idea of a presidential
transport (not sure, if the term "Airforce One" was already in use in the '50s/early '60s ?). May have
been used instead of the Boeing 707, so a similar livery seemd plausible to me. Doubts about an
aircraft with a rear loading ramp for that purpose, I could appease for myself with the explanation,
that it could have not only carried the president, but his sedan as well.
 

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hesham

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Wow,excellent my dear Jemiba.
 

MaxLegroom

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Very nice work indeed, but that plane would have been around a long time for it to wear those colors. These proposals were old enough that some of them have a suffix after the N on the registration number, which was phased out about 1949 (?). How would it have looked with the C118 Independence colors on it?
 
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