31 July 2015

The USAAF Looks for Something Better than a C-47

Loading a Jeep into this RAAF C-47 shows it wasn't ideal for large or bulky loads.
During the interwar period of the 1920s, US military air transport was modest at best and consisted primarily of "off the shelf" civilian designs that were modestly modified with things like reinforced cabin floors and wider doors but were essentially airliners without seats. Until 1934, for example, the US Navy and Marine Corps relied on Ford Trimotors for transport! The arrival of the Douglas DC-2 offered a big improvement in capability for the US military. With war clouds looming in Europe and Asia in the 1930s, the US Army Air Corps went about looking for something better than adapted DC-2s. Bids were requested and Douglas offered an attractive proposal for upgraded DC-2 aircraft better tailored to military transport operations. Not long after, General Henry "Hap" Arnold became head of the USAAC (which later became the USAAF) and being a personal friend of Donald Douglas, was well aware of a DC-2 upgrade in the works that was the result of a marathon telephone conversation between Donald Douglas and the head of American Airlines, C.R. Smith. That aircraft was a leap in performance and capability over the DC-2 and at the time was called the Douglas Sleeper Transport (DST). In due time, of course, the DST became the DC-3 but General Arnold saw the DST's design and performance as an ideal basis for a transport. Army officials met with the designer of the DST, Arthur Raymond, and the C-47 was born. When the war finally broke out with the German invasion of Poland in September 1939, the C-47 wasn't yet in production and suddenly the branches of the US military needed air transport aircraft. The C-47 Skytrain (Dakota in RAF service) made its first flight on 23 December 1941 as Douglas embarked on a major facility expansion to meet the demand for the C-47. At production peak in May 1944, the company was building just under 19 C-47 aircraft each day! Despite the massive expansion and number of C-47s needed, the Army did have several issues with the C-47 but it was the best aircraft available at the time. There were three main issues the Army had- the first was that the tailwheel configuration and side cargo door made it difficult to load large items. Secondly, the maximum payload was too light as it was based on the maximum civilian load for the DC-3, and thirdly, the Army felt that as it was a DC-1/DC-2 derivative, it was old technology. With the United States now in the war, the Army thought that aluminum production was best used for armed combat aircraft and that cargo aircraft which operated in support roles ought to use non-strategic materials. While there was never a formal competition for a C-47 replacement but rather a series of issued requirements, quite a bit of money was spent over the course of the war to develop a transport that was better than the C-47. 

Budd C-93/RB-1 Conestoga
At the outbreak of war, several aircraft made out of the non-strategic materials made the first attempt at replacing the C-47. The first came from the E.G. Budd Company of Philadelphia- they had developed the shotweld technique for joining two pieces of metal- it used a short burst of electrical current to bond two pieces of metal. Invented in 1932 by a Budd engineer, shotwelding was used on the products Budd was known for- railroad cars and road vehicle bodies made of stainless steel. In discussions with the US Navy, Budd hired an aeronautical engineering staff to design a shotwelded (therefore no rivets) transport that would be made of readily available stainless steel. The Navy ordered 300 to be designated the RB-1 and the Army ordered 600 to be designated the C-93. Though made primarily of thin-gauge stainless steel, the wing aft of the spar and the moving surfaces of the tail were fabric covered to offset the weight of the steel. 

The design of the Conestoga was radical for the day and set the pattern for an efficient military transport even to this day. A high mounted wing allowed for an unobstructed main deck with a tricycle landing gear to keep the main deck level and low to the ground to ease loading. An aft loading ramp/door allowed rolling stock to be driven on/off of the aircraft. The flight deck sat up above the main cargo deck to maximize the cargo volume of the fuselage. In addition, there was an integrated hoist in the cargo deck to ease loading an locations that lacked ground equipment. The first flight was on 31 October 1943 and three prototypes conducted the flight test program. Using the same engines as the C-47, the Conestoga was underpowered and possessed sluggish handling- pilots joked that for a plane made by a railroad car company, it sure handled like one! By time time cost overruns and construction delays were resolved at the Budd factory, aluminum production had vastly increased in the United States and the need for an aircraft made of non-strategic materials diminished. The Army canceled its order for the C-93 and the Navy reduced its order from 300 to just 25. Just 17 RB-1s were delivered to the Navy by March 1944 and that small number served primarily as hacks for naval air stations. With such a small number in the fleet, the Navy found the RB-1s uneconomical and sold them off as surplus in early 1945 before the war even ended. Twelve Conestogas were purchased by a new cargo operation, National Skyways, that was founded by a group of pilots that had once served with the American Volunteer Group in China. National Skyways would later change their name to Flying Tigers- but that's a story for future blog article!

Curtiss C-76 Caravan
Another aircraft from the Army's concerns in 1941 that was a contemporary of the Budd C-93/RB-1 Conestoga was the Curtiss C-76 Caravan. The company was engaged by the Army that year to build a transport aircraft that like the Conestoga, would not only be made out of non-strategic materials but also exceed the performance and utility of the C-47. The Caravan was designed by the chief designer at Curtiss, George Page, who was also responsible for the C-46 Commando. While the Conestoga would be made of stainless steel, Page elected to use wood for the Caravan but interestingly, the only high performance aircraft at the time in production made from wood, the De Havilland Mosquito, wasn't used as a source of expertise. De Havilland used a layered plywood construction using a lightweight balsa wood core that made the Mosquito strong but light. Curtiss engineers instead favored mahogany in layers- being a much denser wood than what was used on the Mosquito, the Caravan soared in weight. Despite this, the Army helped Curtiss secure large stocks of mahogany and a number of furniture manufacturers were set up as component subcontractors with final assembly at Curtiss's new plant in Louisville, Kentucky. 

Much like the layout of the Conestoga, the C-76 Caravan featured a retractable tricycle landing gear to keep the main deck level. It also had a high wing layout for an unobstructed main deck hold and also put the flight deck above the main deck. Instead of an aft loading door and ramp, the Caravan had a swing nose that opened to the side ahead of the flight deck. The prototypes were built at existing Curtiss facilities in St. Louis as well as the new Louisville plant with the first flight on 3 May 1943. The flight test program was a disaster. The aircraft, using the same engines as the C-47 but made of dense mahogany, was woefully underpowered with a cargo payload not much more than the C-47. On the first flight, the aircraft vibrated so badly the flight test crew made a hasty return to the St. Louis Lambert Field. On the second test flight, the prototype literally shook itself apart with the loss of the pilots. In addition, when empty, the Caravan had to be ballasted to maintain its center of gravity- amusingly, the ballast needed to maintain an empty load CoG was more than the maximum payload! The control surfaces suffered from buffet and even shook while the plane was on the ground if it was windy. The wing spar failed load testing eight times, only holding up to 40% of the predicted maximum load. The Army wasn't pleased and was more than happy to cancel their order for 175 C-76s, particularly as aluminum production had vastly increased as the war progressed. Only 14 aircraft were built and most spent their days as ground instructional airframes. 

Wind tunnel model of the Waco C-62
There was a third aircraft that stemmed from the Army's 1941 call for something better than the C-47, but it never flew. Waco Aircraft had been building both training and assault gliders for the military and they tendered a design that received the designation C-62. Like the Curtiss C-76 Caravan, the Waco design was made out of wood and featured a high wing and rear loading door/ramp. The tadpole-shaped aircraft had the empennage cantilevered over the aft ramp on a boom. The undercarriage was fixed as well. Using the same engines as the C-47, the Army placed orders for 13 pre-production examples and 240 production aircraft. However, again, like the Conestoga and Caravan, the anticipated shortage of aluminum never occurred and the C-62 was canceled. Allegedly the first aircraft was nearing completion at the time of the cancellation, but this hasn't been confirmed. 

Fairchild C-82 Packet at the National Museum of the USAF
The last aircraft that sprang from the 1941 call was the Fairchild C-82 Packet. Designed by Fairchild's chief designer, Armand J. Thieboldt, the original plans were for the C-82 to be made of wood. Like the other three aircraft, the Packet had a high wing and tricycle landing gear to allow for a level main cargo deck that was unobstructed. The flight deck was raised above the cargo deck and a twin boom layout was chosen to leave the tail area completely clear for straight though loading and unloading. With the fortunes of war shifting in favor of the Allies in the summer of 1942 after the Battle of Midway and an expansion of domestic aluminum production eased shortage concerns, the USAAF requested that Fairchild abandon wood for the C-82 and go with aluminum. Of four aircraft designs for a C-47 replacement, the decision to switch to aluminum more than likely contributed to the reasons why the Packet did get to production and service. Being the last submission probably saved the design as it was also redesigned to take a more powerful engine, the Pratt & Whitney R-2800 Double Wasp instead of using the same engines as the C-47. As a result, the C-82 had the highest cargo payload of the four designs. 

First flight took place on 10 September 1944 at Fairchild's plant in Hagerstown, Maryland. The first series of flights were so encouraging that the USAAF ordered 100 C-82s just 18 days after the first flight. With an eye towards the coming invasion of Japan, North American's Dallas plant was planned for an additional 1000 C-82s on top of an additional 100 from Fairchild for a total of 200 from the Hagerstown plant. The first C-82s were delivered to the USAAF in June 1945 but the sudden end of the war with the Japanese surrender in September 1945 resulted in the cancelation of the North American production run at Dallas with only just three Dallas-built C-82s being built. Despite the drawdown in US military forces, the C-82 Packet was the C-47 replacement the USAAF wanted and the 200-aircraft order from the Fairchild plant in Maryland stood to fulfill postwar airlift requirements. Five C-82s participated in the Berlin Airlift, bringing in heavy equipment and vehicles that couldn't be accommodated onto the Douglas C-54 Skymasters. Operational use of the C-82 revealed several shortcomings, the most concerning of which was that with a full load, a C-82 with one engine out couldn't maintain level flight. Thieboldt and his team at Fairchild went about improving the C-82 design first by incorporating more powerful engines in the form of the Pratt & Whitney R-4360 Wasp Major as well as a host of other improvements to satisfy the newly-independent US Air Force's concerns. Originally designated XC-82B, the changes were so significant that a new designation was assigned to the upgrade which became the C-119 Flying Boxcar. The first flight was made on 17 December 1947. As C-119s were delivered to USAF units, the C-82s were retired. A total of 220 Packets were built. Quite a few Packets had long civilian careers, but that's a story for future blog article! 

Source: The Legacy of the DC-3 by Henry M. Holden. Wind Canyon Publishing, 1996, pp 141-148. Information also from National Museum of the USAF, Wikipedia and www.c82packet.com. Photos: Wikipedia, Australian War Memorial, National Museum of the USAF. C-62 wind tunnel model from R/C Groups forum.

1 comment:

  1. Thank you for another engaging read. I hope you cover the civilian Flying Tigers and the Boxcar in future articles.