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C-76 Caravan
Role Medium transport
National origin United States
Manufacturer Curtiss-Wright
First flight 1 January 1943
Status Cancelled
Primary user United States Army Air Force
Number built 14 (5 production C-76, 9 revised YC-76A)

The Curtiss-Wright C-76 Caravan (company designation CW-27) was an all-wood military transport aircraft. The C-76 was intended as a substitute standard aircraft in the event of expected wartime shortages of light alloys. However, both prototype and production aircraft failed several critical flight and static tests, and after U.S. aluminum production proved sufficient for wartime defense requirements, orders for the C-76 were cancelled and production terminated.

Contents

Design and development

In 1941, Curtiss-Wright was contracted by the United States Army Air Force to design and construct an all-wood military transport aircraft, with performance specifications meeting or exceeding that of the C-47 Skytrain then in service.

The Curtiss-Wright CW-27 was designed by Curtiss-Wright's chief designer George A. Page, Jr. as a high-wing, twin-engine, cargo transport aircraft, utilizing plywood construction with a tricycle undercarriage. Though the British de Havilland Mosquito had successfully employed a ply construction using a balsa wood core and birch hardwood exterior, Curtiss-Wright engineers, using research provided by Forest Products Laboratory,[1] rejected this approach, insisting instead on a ply construction of dense mahogany, which greatly increased the plane's weight.[2] At Curtiss' request, Army Materiel Command laid in large supplies of mahogany, and a number of furniture manufacturers, including the Baldwin Piano Company, were subcontracted to build components for the plane, which would be assembled at Curtiss-Wright's new defense plant in Louisville, Kentucky.[2]

A radial engine was mounted on each wing, and the aircraft was capable of carrying 23 personnel or a cargo payload. The original contract called for 11 YC-76 pre-production aircraft, and the first aircraft would be built and tested at Curtiss-Wright's St. Louis, Missouri Division plant. Subsequently, orders for five C-76 production aircraft and nine revised YC-76A were placed by the USAAF, with line production to commence at the Curtiss-Wright plant in Louisville as well as a Higgins Aircraft factory in New Orleans, Louisiana.[3][4] To keep the plywood flexible during construction the factory was kept hot and damp.[5] The prototype YC-76 first flew on January 1, 1943.

Only five production aircraft were completed in 1943: three from Curtiss-Wright's St. Louis Division, and two from the Louisville, Kentucky plant (the Higgins Aircraft complex in New Orleans had not been completed at the time of the contract's cancellation).[4]

Operational history

The C-76 proved severely underpowered from the start, with a cruise speed of 160 mph, a service ceiling of 22,600 feet, a range of only 750 miles, and a cargo capacity of under 8,000 lbs. Colonel J.W. Sessums, a USAAF officer at the Air Materiel Command at Wright Field, later related:

'The first flight [of the C-76] was made and the airplane was very heavy. It developed some serious vibrations. In fact, the pilot was awful glad to make a quick circuit to get back on the ground ... two of the Curtis test pilots took it out on a flight and the Army requested that our project officer on the airplane be allowed to fly along on this trip. The Curtiss Company refused. We were very glad that they refused because on this second flight, it [the C-76] flew apart and the pilots were lost and so was the plane.[2]

Compared to other cargo aircraft then coming into service, the C-76 was already obsolescent, even allowing for its 'war-priority' method of construction. In addition, the C-76 failed a number of critical flight tests.[6] It was discovered in testing that the C-76 was unstable when not carrying a cargo load; in order to obtain a stable center of gravity, the plane had to be ballasted beyond its maximum permissible gross takeoff weight.[2][6] At any speed, or in any gusting wind, the C-76's elevators would flap back and forth violently.[6] The wing structure failed in eight separate static tests, sometimes with a load as low as 40% of the wing's rated capacity.[7] The wing failures were attributed by some sources to the failure of the fasteners used to secure the wood components of the aircraft.[6][8] Numerous additional fasteners, metal stirrups, and wood ply reinforcements were added to the structure in an effort to strengthen it, thereby increasing the plane's overall weight.[6]

At the Louisville plant, Curtiss line workers would later recall two C-76 production planes that were kept for some time in the assembly building, with one plane cannibalized to keep the other in flyable condition.[8] On 10 May 1943, the first YC-76 constructed at the Louisville, Kentucky plant, 43-86918, lost its tail unit at 1729 hrs. due to lack of "forgotten" securing bolts during test flight, crashing at Okalona, Kentucky, killing three Curtiss test crew, pilot Ed Schubinger, co-pilot John L. "Duke" Trowbridge, and engineer Robert G. Scudder.[9][10][11] As war priority measures designed to increase aluminum production proved successful, the feared shortage of light alloys never materialized. Moreover, USAAF Training Command had begun to forward widespread complaints of insufficient service life on their wooden-winged Fairchild PT-19 primary trainers when exposed to high heat in training bases located in Texas and Florida.[2] The War Department cancelled its orders for the C-76 on 3 August 1943[4][9][12], and the remaining prototype aircraft were recalled from testing and active service. Only five production and nine pre-production aircraft had been completed by the time of the project's cancellation, with two aircraft lost in crashes, and other airframes cannibalized for parts. The remaining flyable aircraft were all grounded by 12 September 1944. Four C-76s at the St. Louis, Missouri plant were granted one-time flight clearance and flown directly to Air Training Command bases for use as instructional airframes.[9] In the interim, the Curtiss-Wright plants at Buffalo, New York and Louisville, Kentucky went over to full production of the C-46 Commando.[13][14] USAAF Materiel Command later estimated the entire C-76 project cost the U.S. government $400 million dollars and several months in lost production time.[2]

Specification

General characteristics

  • Crew: 1-2
  • Capacity: 23 total
  • Length: 68.33 ft (20.83 m)
  • Wingspan: 108.17 ft (32.97 m)
  • Height: 27.25 ft (8.31 m)
  • Wing area: 1560.05 ft² (144.93 m²)
  • Empty weight: 18262 lb (8301 kg)
  • Max takeoff weight: 28000 lb (12701 kg)
  • Powerplant:Pratt & Whitney R-1830-92 Twin Wasp radial piston engines, 1200 hp (895 kW) each

Performance

See also

Related lists

References

  1. ^ Forest Products Journal, January 1, 2007: "G.A. Page, chief engineer of the Curtiss-Wright Division at St. Louis, Mo., wrote, "It [the Design Handbook] has expedited and facilitated our work in connection with the design of the C-76 airplane to a degree that is hard to estimate." http://goliath.ecnext.com/coms2/gi_0199-6309544/Forest-Products-Laboratory-supporting-
  2. ^ a b c d e f Sessums, Col. J.W., Design and Engineering Problems of Aircraft Production {Restricted}, May 14, 1946, pp. 6-8 http://www.ndu.edu/library/ic1/L46-084.pdf
  3. ^ Kleber, John E., The Encyclopedia of Louisville, University Press of Kentucky (2001) ISBN 0-8131-2100-0, 9780813121000
  4. ^ a b c Freeman, Paul, Abandoned & Little Known Airfields: Louisiana: Eastern New Orleans area, http://members.tripod.com/airfields_freeman/LA/Airfields_LA_NewOrleans_E.html
  5. ^ Curtiss C-76 Caravan http://aeroweb.brooklyn.cuny.edu/specs/curtiss/c-76.htm
  6. ^ a b c d e Mansfield, Howard, Skylark: The Life, Lies, and Inventions of Harry Atwood, UPNE (1999) ISBN 0-87451-891-1, 9780874518917, pp. 204-205
  7. ^ Curtiss-Wright Corporate Records, Static Tests of Curtiss-Wright C-76 Wings, ENG-51-C359-10, 7/24/43
  8. ^ a b Aviation Enthusiast Corner, Curtiss C-76 Caravan http://aeroweb.brooklyn.cuny.edu/specs/curtiss/c-76.htm
  9. ^ a b c Boyne, Walt, "C-46 [sic]: 'The Basketcase Bummer' " Airpower, Granada Hills, California, May 1974, Volume 4, Number 3, page 64.
  10. ^ Kleber, John E., The Encyclopedia of Louisville, University Press of Kentucky (2001) ISBN 0-8131-2100-0, 9780813121000, p. xxvii
  11. ^ Army Air Forces in World War II, Vol. VII,http://www.ibiblio.org/hyperwar/AAF/VII/AAF-VII-1.html
  12. ^ News Article, New York Times, August 4, 1943, October 17, 1943
  13. ^ Curtiss C-46 Commando http://www.faqs.org/docs/air/avc46.html
  14. ^ News Article, New York Times, August 11, 1944
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