Curtiss-Wright C-76 Caravan

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.^[1] 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.^[2]

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.^[1][3]

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,^[4] rejected this approach, insisting instead on a ply construction of dense mahogany, which greatly increased the plane's weight.^[5] 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.^[5][2]

A radial engine was mounted on each wing, and the aircraft was capable of carrying 23 personnel or a cargo payload. The Caravan had a nose section that swung out to the right so out-size loading could be done, including a jeep or small artillery pieces.^[6]

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.^[3] 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][2][7]. To keep the plywood flexible during construction the factory was kept hot and damp.^[8] The prototype YC-76 first flew on May 1, 1943.^[3]

Only five production aircraft were completed in 1943: three from Curtiss-Wright's St. Louis Division, and two from a new plant at Louisville, Kentucky, which was finished in May 1942.^[2][3][8] The Higgins Aircraft Co. contract was cancelled by the Army on August 3, 1943 before the Higgins factory in New Orleans had been completed, and Higgins was awarded another contract to produce the C-46 Commando.^[7]

Operational history

The first flight of the YC-76 prototype took place on May 3, 1943.^[2] 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 Curtiss 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.^[5]

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.^[9] 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.^[5][9] At any speed, or in any gusting wind, the C-76's elevators would flap back and forth violently.^[9] The wing structure failed in eight separate static tests, sometimes with a load as low as 40% of the wing's rated capacity.^[10] The wing failures were attributed by some sources to the failure of the fasteners used to secure the wood components of the aircraft.^[9][11] 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.^[9]

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.^[11] 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 Okolona, Kentucky, killing three Curtiss test crew, pilot Ed Schubinger, co-pilot John L. "Duke" Trowbridge, and engineer Robert G. Scudder.^[12][2]</ref>^[13] As war priority measures designed to increase aluminum production proved successful, the feared shortage of light alloys never materialized.^[2] 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.^[5] The War Department cancelled its orders for the C-76 on 3 August 1943^[12][14], 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.^[12] In the interim, the Curtiss-Wright plants at Buffalo, New York and Louisville, Kentucky went over to full production of the C-46 Commando.^[15][16][2] 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.^[5]

Variants

YC-76

Prototypes, 11 built.^[17]

C-76A

Production aircraft built at St Louis, five built.^[17]

YC-76A

Production variant, nine built.^[17]

C-76A

Production variant, order for 175 cancelled, non-built.^[17]

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: 2 × Pratt & Whitney R-1830-92 Twin Wasp radial piston engines, 1200 hp (895 kW) each

Performance

• Maximum speed: 192 mph (309 km/h)
• Cruise speed: 160 mph (260 km/h)
• Range: 750 mi (1207 km)
• Service ceiling: 22,600 ft (6,888 m)

See also

Related lists

• List of military aircraft of the United States
  

References

1. ^ ^{a b} Dreher, Carl, Wood Is A War Weapon, Popular Science, Vol. 141 No.3 (September 1942), pp. 48-74
2. ^ ^{a b c d e f g h} Kleber, John E., The Encyclopedia of Louisville, University Press of Kentucky (2001) ISBN 0-8131-2100-0, 9780813121000, pp. xxvii, 235-236
3. ^ ^{a b c d e} Dorrell, David (ed.), Curtiss Caravan, Air Pictorial: Journal of the Air League, Air League of the British Empire, Volume 35, No. 7 (July 1973), p. 69
4. ^ 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." Forest Products Laboratory: supporting the nation's armed forces with valuable wood research for 90 years
5. ^ ^{a b c d e f} Sessums, Col. J.W., Design and Engineering Problems of Aircraft Production {Restricted}, May 14, 1946, pp. 6-8 National Defense University Archives
6. ^ "Army In Long Pants" Popular Mechanics, July 1944 - bottom of page 21 photo showing front nose opened for loading
7. ^ ^{a b} Burck, Gilbert, Mr. Higgins and His Wonderful Boats, Life Magazine, 16 August 1943, p. 112
8. ^ ^{a b} Curtiss C-76 Caravan http://aeroweb.brooklyn.cuny.edu/specs/curtiss/c-76.htm
9. ^ ^{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
10. ^ Curtiss-Wright Corporate Records, Static Tests of Curtiss-Wright C-76 Wings, ENG-51-C359-10, 7/24/43
11. ^ ^{a b} Aviation Enthusiast Corner, Curtiss C-76 Caravan http://aeroweb.brooklyn.cuny.edu/specs/curtiss/c-76.htm
12. ^ ^{a b c} Boyne, Walt, "C-46 [sic]: 'The Basketcase Bummer' " Airpower, Granada Hills, California, May 1974, Volume 4, Number 3, page 64.
13. ^ Army Air Forces in World War II, Vol. VII,http://www.ibiblio.org/hyperwar/AAF/VII/AAF-VII-1.html
14. ^ News Article, New York Times, August 4, 1943, October 17, 1943
15. ^ Curtiss C-46 Commando http://www.faqs.org/docs/air/avc46.html
16. ^ News Article, New York Times, August 11, 1944
17. ^ ^{a b c d} Andrade 1979, p. 80

Bibliography

• Andrade, John (1979). U.S.Military Aircraft Designations and Serials since 1909. Midland Counties Publications. ISBN 0 904597 22 9. 
• The Illustrated Encyclopedia of Aircraft (Part Work 1982-1985). Orbis Publishing.