zoggavia

Douglas DC-7

History of the Douglas DC-7

Project of a civil C-74


HP-385, ex 42-65409, Douglas C-74 Globemaster  named Heracles,
of Air Systems Panama 
at London Heathrow in 1963.  This C-74 crashed
later at Marseilles, France, on 9 October 1963. Zoggavia Collection

The original project of the Douglas DC-7 was a civil version of the military transport C-74 'Globemaster 1' but never reached the market introduction despite a first order of 26 aircraft from Pan American World Airlines. As the limited military production run increased the cost per civilian aircraft Pan American canceled its order. Douglas then dropped the DC-7 project. The DC-7 designation was later used for a completely different civilian airliner project in the early 1950s, having no relationship to the C-74.

DC-7



N6305C DC-7United Airlines equipped with radar nose, seen at New York
Idlewild in 1957, Zoggavia Collection


After much persuasion of the President of American Airlines, C.R. Smith, Douglas decided to modify the DC-6B around the new Curtiss-Wright R-3350 turbo-compound engine available for civil use late in 1951. This new power plant developed 3'250 hp for take-off and the increased power brought the speed up to 360 mph (560km/h), which also gave an improved range allowing transcontinental operations the first time. The DC-7 differed further from the DC-6B in having a 40inch  (1,02m) stretch in fuselage length, and four bladed propellers.



Magnificent view of the mighty Curtiss Wright R-3350 988TC-DA-2 turbo compound radials each delivering 3250 hp.
Flying American Airlines DC-7B from Chicago to Los Angeles in 1959. Zoggavia Collection


The first flight was on 18 May 1953, and American Airlines introduced the first of totally 25 ordered new airliner on the daily non-stop New York - Los Angeles service on 29 November 1953, reducing the coast to coast flying time to 8hrs 45min westbound and 8hrs eastbound. The DC-7 was not as economical per seat mile as the DC-6B and the market was limited to four major U.S. airlines; American (24), National (4), Delta (10) and United (57 in total), resulting in a total production of 105 aircraft.

DC-7B


The DC-7B was basically designed as a long range version of the DC-7, which included greater fuel capacity the nacelles to from saddle tanks and an increased all-up weight. Many of the aircraft delivered did not incorporate these arrangements.




N777PA DC-7B of Pan American World Airways on a test flight over California,
April 1955, Clinton H Groves Collection



As an interim measure to compete with the Super Constellations Pan American World Airways introduced DC-7B's on its transatlantic service from New York to London 13 June 1955, though they were later transferred to more suitable routes owing to the inadequacy of their range on these transatlantic routes.


DC-7C




N70C, the Douglas DC-7C prototype during one of the its test flight along the Californian coast.
This version was called Seven Seas as it was capable to cross every sea due to its increased range.
This aircraft was later sold to Panair do Brasil as PP-PDO. Zoggavia Collection


When the development of the DC-7B was under way, Douglas realized the potential of the  new 3 '400 hp version of the Wright R-3350 engine in manufacturing an even longer version of the DC-7 capable of flying the most important transatlantic routes non-stop in both directions and in all but the most adverse weather conditions. This ability was later used under the synonym 'Seven Seas', meaning all seas could be crossed non-stop.


Douglas DC-7C HB-IBK of Swissair seen air to air in November 1956.
This DC-7 was later the only type used in military service as F-ZBCA operated
by the l'Armee de l'Air, French Air Force,  in 1963. Zoggavia Collection

The fuel capacity was increased by an additional 5 foot (1,5 ) wing section inserted between the inboard engine and the wing root, thus giving the DC-7C an extra 10 foot (3m) wing span. This gave an additional capacity of 1'000 gallons (4'450 l) resulting in a range of 5'600 miles (9'000 km). A further 42 inch (1,06 m) fuselage ahead of the wings, and a taller fin and rudder to cope with the greater power and weight. The DC-7C's managed the a considerable share of the passenger traffic across the North Atlantic until the Boeing 707 and DC-8 jetliners were introduced in 1959 and 1960. Plans for a turboprop version, designated DC-7D, with Rolls Royce Tyne engines never materialized. All DC-7 built; 338 of all series.

DC-7A and DC-7C/F



American Airlines converted several DC-7B aircraft into freighters.
Here N345AA is seen receiving its load in 1963, Clinton H. Grove  Collection




PH-DSG DC-7C/F KLM pictured together with a sister ship in the cargo area of
 the airport of Amsterdam in 1965, Zoggavia  Collection


There were no all-freighter aircraft as such, built by Douglas, with the sole purpose of use for cargo operations only. All conversions made by Douglas involved standard series DC-7 aircraft, with the installation of two large freight doors and a stronger cabin floor plus other modifications based on specifications of the individual airline were made.



N6344C Douglas DC-7A in United Airlines colors with its forward
 freight door open. San Francisco in 1965. Zoggavia Collection




Same aircraft showing the rear cargo door. San Francisco in 1965.
Zoggavia Collection
The first DC-7A went in service with American Airlines in September 1959. Conversion orders were placed by American Airlines, 15 DC-7B, United 6 DC-7B, Panagra one DC-7B, KLM two DC-7C, Alitalia two DC-7C, BOAC two DC-7C, Japan Air Lines two DC-7C and Riddle three DC-7C (plus seven more on option).

Other DC-7 series conversions were carried out by other companies and airlines. These conversions merely had the letter 'F' added to the original designation. The DC-7 freighters replaced the Douglas C-54 / DC-4 and Douglas DC-6 freighters until the introduction of DC-8F and Boeing B707C on the major long haul routes.
Summary and technical data
   Versions
C-74
DC-6B
DC-7
DC-7B DC-7C DC-7C/F
Dimensions
Length (m)
37,58 32,50 29,53 33,98 34,21 34,21
   Wingspan (m)
52,81
35,80 34,98 34,98 
38,86  38,86
   Height (m)
13,34 8,78
 8,75
8,75
9,70
9,70
  Wing Area (m2)
233 188,3
188,3 197,04
197,04
191,30
Weight
Take off (t)
78
 48,5 57,2
57,2 57,2
57,2
  Fuel capacity (l)
 27'300 20'865
17'413
20'366
24'662  24'662
  Max Payload (t)
 21,3 9,1
 9,1 9,8
 10,4  15,9
 Propulsion Powerplant
 Pratt & Whitney
R-4360-49 Wasp Major Radial

Pratt & Whitney
R-2800-CB17 Radial

 Wright R-3350
988TC-DA-2
Turbo compound radial

Wright R-3350
988TC-DA-4
Turbo compound radial
Wright R-3350
988TC-EA-4
Turbo compound radial
Wright R-3350
988TC-EA-4
Turbo compound radial

  Horsepower
(hp)
(kW)

3'250
2'424

 2'500
1'864

3'250
2'424
 
3'250
2'424

3'400
2'535


3'400
2'535
 Performance  Speed (km/h)
 528  507 503
504
 563
563 
  Range (km)
 8'350
-
12'550
 4'200
-
8'014
41'00
-
6'067
4'587
-
6'880
6'437
-
7'890
6'437
-
7'890

   Passengers 125
54-89
60-95
60-95 60-100 71-119
 First Flight
Date 5.9.45
 2.2.51 18.5.53
21.4.54  20.12.55  27.6.1959
 First Service
Date
10.45
 11.4.51 18.5.53
 24.5.55 15.5.56
 9.59
Engines of the DC-7

The Wright model TC18EA
series engine is a turbo-compound 18 cylinder, air cooled, radial, reciprocating power plant. This engine incorporates  three blow-down turbines for exhaust power recovery. All in all 12'000 units were produced for the TC Super Connie/Starliner, DC-7, PV-2, and Canadair Argus variants. Developing up to 3'500 hp, this was one of the most powerful serial piston engined produced.

Operators

Alitalia
Boac
Braniff
Caledonian
Continental
Dan-Air London
Delta
Eastern Air Lines
Japan Air Lines
KLM
Madair
Mexicana
Modern Air
National Airlines
Northwest Orient
Overseas National
Panagra
Pan American World Airways
Panair do Brasil
Sabena
SAS
Saturn
Shannon Air
South African Airways
Spantax
Swissair
TAE
TAI
Tassa
Teca
Trans Europa
United
United States Overseas

Military
French Air Force

DC-7 photo gallery - click the photo to enlarge



Douglas DC-7C/F 'Irish Sea' of KLM
, Kenneth Munson,
Civil Airliners, OF 1967


click on the drawings to enlarge





DC-7C cut away drawing, Flight International