Douglas DC-7D/DC-7T Turboprop


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25 July 2007
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Greetings Folks,

I'm looking for help filling in some blanks in our Piston-to-Turboprop conversion listings.

The aircraft in question is an unbuilt turboprop evolution of the Douglas DC-7. I came across the an image (attached) of the DC-7D with R-R Tynes or Allison turboprops.

Boxkite was good enough to send me details of the DC-7T also with Tynes (3-view attached and details below). Obviously, the DC-7T and DC-7D are closely-related aircraft.

Can anyone shed any light on turboprop DC-7 developments and their designations?

Any idea on the Allison engine proposed for the DC-7D? The timing is right for the 501-D13A but it is a lot less powerful than a Tyne. Timing is right for the T40 too but that seems an improbably-complex engine for an airliner.

Thanks in advance.

Info from: Les avions de ligne américains, 1913-2008, Alain Pelletier, Larivière (éditions).

To meet the needs of United Airlines, Douglas studied a turboprop version of its DC-7. The turbine engines envisaged were the Rolls-Royce Tyne Mk. I or Mk. II. Depending upon configuration, the DC-7T would have been able to transport from 82 to 135 passengers from Los Angeles to Honolulu.

Span: 38.86m, Length: 37.98m, Height: 9.74m, Max Weight: 64,865 kg, Max Speed: 708 km/h, Ceiling: 7620m.


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Wow, a real looker :)

Too bad they didn't go through with this (or the Turbo-Connie, either). I can tell you at least they're not the same model as what's on the C-130/Electra/Hawkeye as I don't think they'd be able to fit it into a nacelle that thin.
Thanks Ray.

Yeah, that swept tail really makes a difference. You can see the beginnings of DC-8 styling in these DC-7 studies.

I'm guessing that the painting illustrates a Tyne-powered version but I'm not sure.

You're right about engine sizes, the Allison 501 is a bit chunkier that the R-R Tyne. The numbers I have are: Tyne 43.2 inches, 501 44.6 inches (I think that's width rather than diameter).
The early successors of DC-7 were to be a couple of planes sharing the fuselage, one with swept-wing and jets, the other with straight wing and turboprop. They were called DC-8 and DC-9.
I don't suppose it would be fair to say that that DC-8 led to the "real" DC-8? It would've at least provided a point to start with and then realize it would be best to go with an entirely new-from-scratch design, in much the same way as the 707 is "derived" from the B-47/Model 337.
Skybolt: Are you saying that this 'ur-DC-9' is the same thing as (or a direct descendant of) the DC-7D/DC-7T?
Umm, no, actually is, as usual, much more complicated than that.. The "designation" DC-9 emerged for the first time in 1947 as the classical "DC-3 replacement", a twin engined project (TS1119) in the same vein of the various Convair 240s and Martin 2-0-2, as large of the Convair but seating less people (28 versus 40). No interest was forthcoming, so the project was abandoned and the Super DC-3 effort started (with little success). The turboprop DC-9 I was referring to is a parallel effort of the first "DC-8" iteration (see dedicated topic somewhere in the forum), in 1953. It used the same double-bubble fuselage of the four-jets DC-8 but with a straight wing and four turboprops. So it was a rather large aircraft. The idea was to produce something similar to the Lockheed Electra, with a military derivative in sight: the Navy was starting to ask a long-range turboprop patrol plane (like Lockheed did with Orion, same specification). Since the parallel military contracts went to Boeing for the 4-jets spec (KC-135), Douglas had to choose, not having enough money to develop the two in parallel. Donald Douglas wisely decided to bet the company on the DC-8, so the turboprop DC-9 was shelved. BTW, the DC-7T could be seen as a low development cost substitute for this DC-9.... It would be interesting to look at the competitors of the long range patrol plane for the Navy that originated the Orion...
BTW, all 50's turboprop derivatives of piston liners (DC-7T and the various proposals for the Constellation and Super Constellation family) were caught in the middle between the exceptional fuel efficiency of late-model 3350 Turbo Compounds and the up-and-coming jets. The Britons, for their part, wasted their lead in engine development first in giant planes (Bristol Brabazon and Saro Princess) trying to scale up to 100 passengers the amenities sought-after in pre-war 40-passengers long range liners, and then embarking in the extremely delayed Britannia development. As Mr. Miles rightly thought, the Brabazon Committee would have chosen a smaller and faster aircraft as a transatlantic liner.
Skybolt: thanks for the clarification.

DC-8 original model 1954 ?,4415.0.html

Paul also posted the Model 1856 (Big_Douglas_Bomber2.jpg) which also looks a bit DC-7-ish (albeit with jet engines and a bombardier's position!).,3825.0
Skybolt pretty much covered it as thoroughly as anyone could. It's interesting to note that the "final" DC-9 was also a brand-new, from the ground up design sharing nothing with the DC-8 despite a strong "family resemblance" which in hindsight may have been a mistake; if Douglas had used the same fuselage for the DC-8 (as Boeing did with the 707/727/737, with appropriate tweaks of course) they would've had a wider cross-section that would've been more competitive with the Boeing offerings. As Skybolt said they even did this with the "original" turboprop version.
Theoretically you're right, Ray, but in the "original final" DC-9, so to speak, they were striving to stay under the weight limit that at the time the Civil Aviation Administration posed as the maximum allowed for two-crew cockpits. Using the fuselage of the DC-8 wouldn't be compatible with this goal.
Apo, the Douglas bomber projects of late '40s-early50s are a big mistery, with only some flashes of light. No-one really knows the genealogy yet. For example, the B-52 contender illustrated in another part of this forum, has a totally different wing, to someone reminiscent of the later C-132.
And, for not keeping talking about thin air, the two original DC-8 and DC-9 couple.
And, Ray, the "almost final DC-9", Model 2076, the mini-DC-8 with four engines, used the same cockpit section of the "final" DC-8 but the fuselage section was the bilobate one of the 1953 DC-8 (upper lobe 132 inches) , because they planned to use the same Douglas' patented seating system called Palomar. DC-8 production fuselage dia. is 147 inches.


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Great stuff, thanks Skybolt!

Any idea what engine type was planned for this "DC-9"?
" the maximum allowed for two-crew cockpits"

In Flugwelt 11/1959, the crew for the "mini DC-8" was still given as
three ( "Besatzung").


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Yes, that's why they changed direction and went for a smaller one. One of the reasons for abandoning the SE Caravelle option was the same: weight.
According to Mr. Harry Gann in the fine volume; Airliner Tech No. 4; Douglas DC-6 and DC-7, the only two engine proposals for the DC-7D/T were the Rolls Royce RB-109 (DC-7D) and the Rolls Royce Tyne (DC-7T).

However, Mr. Gann mentions a series of very interesting earlier turboprop proposals centered around the DC-6/C-118A/R6D aircraft. The earliest of these (Model 1134-C from 1951) called for the C-118A/R6D aircraft to be powered by four Allison T38-8 turboprops with 3,750 s.h.p. each. These aircraft, if approved, would have provided the Air Force and Navy, respectively, with substantially higher performance aircraft than the conventional R-2800 powered aircraft. They would have been used for "cargo and personnel aircraft", etc.

Another study, under the Douglas Specification 1867 (1954), involved a series of variants. The highest performance model of this group was the 1867-H variant (using the DC-6B as a starting point, but reducing the length of the fuselage back down 60 in. to the length of the DC-6). This model would have been powered by four Allison T-56-D8's rated at 4,030 s.h.p. each in an airframe modified for the expected higher performance. This model was, also, to be equipped with a new thinner airfoil (15% thickness, as opposed to the earlier 16%) Douglas wing.
Factory model of Douglas DC-7D (Douglas Model DS-1848) from the Douglas model shop in Santa Monica.


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Skybolt said:
........., because they planned to use the same Douglas' patented seating system called Palomar. DC-8 production fuselage dia. is 147 inches.

What was the "Palomar" seating system?
TG: Skybolt may have more but the Palomar system was Douglas' wall-mounted passenger seats with vents, fluorescent light, and stewardess call-button built into the headrests. IIRC, they were only used on early series DC-8s.

Flight 23 Jan 1964: Douglas, however, has been developing seats since DC-2 days, a programme which reached a peak in 1957 with the Palomar seat for the DC-8. This was something of a revolution in seat design, as it accommodated the passenger utilities: each triple seat contains its own passenger service unit incorporating oxygen masks, reading lights, stewardess call-light, tray lights, trays and cold-air outlets. These services are connected to the sidewall utilities duct through an umbilical attachment."
Douglas DC-7 turboprop manufacturer model, from the Douglas in-house model shop in Santa Monica. This later variant is marked as Model 1867C (Dymo label -- nothing official). A proposal for American Airlines.

Forward positioning of lighter turboprop engines (for CG balance) is noteworthy.


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CORRECTION: The Douglas proposal model for American Airlines, posted above, is actually a Model 1867J. All 1867 variants are listed as a DC-6 upgrades, as opposed to DC-7s.

This 1954 proposal would have been equipped with Allison T56-D8 engines. It was also supposed to have a DC-7 fuselage and a 12.5-ft wingspan extension, which is how I got confused (still am, probably always will be).

This revelation came from the AirlinerTech book on Douglas propliners by Harry Gann, who was the Douglas company historian.
American Airlines Douglas 1867J (turboprop DC-6) and Douglas 1848 (DC-7D), both from the Douglas in-house model shop at Santa Monica. The lengthened fuselage and swept fin of the 1848 would have made it the ultimate Douglas propliner.

The numbering sequence makes me wonder if the Douglas 1867 proposals weren't offered later, to upgrade existing airframes, as opposed to all-new airplanes like the DC-7D/T.

The often-confusing designation system at Douglas came in large part from the assignment of blocks of numbers to specific plants (El Segundo, Santa Monica, Long Beach, etc.) or to a family of related studies. Many of those simply never got used. In addition, when some projects got reassigned to a different plant, they inherited a new number, but sometimes not. Sometimes that depended on how far along the study was completed, but other times it didn't.

Clearly, these people did not care at all about us SPF members.


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And if you look at Air International May 1989 pg 213, Snow Aviation proposed a turboprop powered DC-4/C-54. Does someone has any illustration of this proposal?

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