Experimental warplanes from the Los Angeles basin, part 1: the Hughes D-2 and XF-11

Howard Hughes (1905-1976), the wealthy yet reclusive and eccentric aviator who would capture the public's imagination when he starred in the 2004 film The Aviator, is forever remembered for building the H-1 that set a new landplane speed record (352 mph) in September 1935 as well as the largest-ever flying boat, the 320-foot span the H-4 Hercules (popularly called the Spruce Goose), that had the biggest wingspan of any airplane until the 385-foot span Scaled Composites Stratolaunch space launch platform took to the skies in April 2019. Hughes also served as head of TWA from the late 1930s until 1966. During my visits to the Planes of Fame Museum in January 2018 and June 2020, I saw a model of the Hughes XF-11 prototype photo-reconnaissance aircraft in a glass display cabinet at the Jet & Air Racers Hangar, but I also happened to notice a desktop model of the XF-11's top-secret and seldom-known ancestor, the D-2 prototype attack/fighter aircraft. Given that the Hughes D-2 is one of the most enigmatic US warplane designs of the World War II era, but also the fact that the XF-11 shared much of its heritage with the D-2, I thought it would make sense to devote the first post out of a number of planned blog posts on prototype warplanes from the Los Angeles area to the D-2 and XF-11.

Left: Hughes company artwork showing notional Hughes A-37 attack aircraft bombing a German factory

Right: Artist's rendering of the proposed A-37 attack version of the D-2

The story of the mysterious D-2 goes back to 1937 when Howard Hughes envisaged a design for a twin-engine, twin-boom interceptor in response to the X-608 specification by the US Army Air Coprs for a twin-engine fighter plane. The design, which was similar in layout to the Lockheed P-38 Lightning that won the X-608 competition, was stated by Hughes himself in a 1947 testimony before the US Senate to have been stolen by Lockheed, although many others refute this claim. Although the Hughes design lost to the P-38 Lightning, beginning in the summer of 1939 the Hughes Aircraft Corporation began work on a new aircraft design, the D-2 (aka DX-2), which was to be made of Duramold, a plastic-bonded plywood molded under heat and pressure. The D-2 design was floated by Hughes personnel as having the potential to be used as either a light bomber or heavy fighter. The D-2 design was initially to have a tailwheel but the landing gear arrangement was changed to a tricycle undercarriage as in the P-38, with the main wheels retracting into the tail booms and a nose wheel retracting and folding 90 degrees into the nose. The originally intended powerplant for the D-2 was to have consisted of two Wright R-2160 Tornado liquid-cooled radial piston engines, but developmental problems with the Tornado caused Hughes to substitute two Pratt & Whitney R-2800 Double Wasp radials. By March 1941, the D-2 design was relegated to its role as a convoy protector with a 2,600 mile (4,284 km) range, 450 mph (724 km/h) top speed, and seven .50-cal machine guns. In response to an August 1941 Army Air Force requirement for a convoy protector able to escort bombers for distances of up to 2,000 miles (3,218 km), Hughes proposed the D-3 with two four-gun turrets, design estimates of which were submitted to the Air Material Division on January 13, 1942. Power was supplied by two Allison V-3420 V-cylinder inline piston engines, and four variants of the D-3 were under consideration: the D-3 bomber convoy-protector, D-3F fighter, D-3H interceptor, and D-3R bomber convoy-destroyer (Buttler and Griffith 2015, pp. 59-60).

Top: Hughes D-2 under construction at the Hughes factory in Culver City, late 1942

Bottom: The completed D-2 at Harper Dry Lake in front (left) and side (right) views

 

Although Duramold was a potential remedy for shortages of strategic metals, it was difficult to work with, so the US Army Air Force judged Duramold to be insufficiently robust, rejecting the D-2 for use as a fighter plane in November. However, in early 1942, the AAF reversed course and decided that the Duramold construction of the D-2 could be suited for high aerodynamic performance, so Hughes was given the go ahead to build one D-2 prototype. The D-2 was 57.8 feet (17.6 meters) long, with a wingspan of 60 feet (18.3 meters), a gross weight of 31,672 pounds (14,366 kg), a top speed of 433 mph (697 km/h) at 25,000 ft (7,620 m), a cruising speed of 274 mph (441 km/h), and a service celling of 36,000 ft (10,973 m). Armament included 2,200 lb (998 kg) of bombs and ten .50-cal machine guns (six on the nose, four positioned above each other in a turret in the rear of the fuselage nacelle). In June 1942, the USAAF reserved the XP-73 designation for the D-2 fighter version, but in July, it envisioned the D-2 more in its role as an attack aircraft, so recommended designating it XA-37 (Norton 2008, p. 192). (Neither designation was officially used for the D-2.) Construction of the D-2 commenced in secret and even though the USAAF wanted to spend $500,000 on the D-2's construction, Hughes turned down the offer, instead investing $3 million to build the D-2 with his fortune. Still lacking a definite role, the D-2 was completed at a facility in Harper Dry Lake near Barstow, California, and after a few modifications to the control surfaces following some technical problems in ground tests, it made it first flight on June 20, 1943, with Hughes himself at the controls. The D-2 accumulated nine hours of flight testing, but issues with control surfaces prompted Hughes to propose an improved version of the D-2 with a new wing spanning 92 feet (28 meters) and larger bomb bay, the D-5. However, many in the USAAF remained disinterested in the D-2 and D-5, largely due to Hughes' erratic behavior and a collective feeling that his company didn't have the capacity to undertake series aircraft production, so on August 13, the AAF decided not to take any further action regarding the D-2 or D-5. On November 11, 1943, the D-2 was being modified to D-5 standard at its hangar in Harper Dry Lake when the hangar housing it was destroyed by a lightning strike (some claim Hughes deliberately burned the aircraft and hangar).

Desktop models of the Hughes D-2 (left) and XF-11 prototype reconnaissance aircraft (right) in a glass display cabinet at the Planes of Fame Museum, Chino. The differences between the two in size and rearward extent of the fuselage nacelle are evident.

Even before the D-2 was destroyed by fire, in early August 1943, President Franklin D. Roosevelt's son, Colonel Elliot Roosevelt, toured the Los Angeles area conversing with US aircraft companies to develop a dedicated photo-reconnaissance aircraft. He was greeted by Hughes, who took him on a tour of the D-2. Roosevelt was so impressed by the D-2 design that the White House asked USAAF General Henry "Hap" Arnold to approve full-scale development of a reconnaissance version of the D-5 design. To address concerns about duramold construction by the US Army Air Force, the design was revised so that the wings and tail booms would be of all-metal construction, with only the fuselage being of duramold construction (Hansen 2012, p. 541). On October 6, 1943, the USAAF issued a letter of intent to purchase 100 of the D-5 reconnaissance version under the designation F-11, and a contract was signed on May 5, 1944, for two prototypes (serial numbers 44-70155/70156) and 98 production machines (44-70157/70254). (Prior to 1948, all reconnaissance aircraft were designated with the letter F, but after the USAAF became the US Air Force, F was used to denote fighters and the Air Force substituted R for F when denoting reconnaissance planes.) The XF-11 was 65 ft 5 in (19.9 m) long, with a wingspan of 101 ft 4 in (30.9 m), a height of 23 ft 3 (7.09 m), a top speed of 450 mph (725 km/h), and a service ceiling of 42,000 ft (12,802 m). The aircraft had an empty weight of 39,278 lb (17,816 kg), a maximum weight of 58,315 lb (26,451 kg), and a 5,000 mile (8,047 km) maximum range with 2,105 gallons (7,968 L) internal fuel. Besides having a bigger wingspan and using metal in construction of the wings and tail booms, it also differed from the D-2 in that the fuselage nacelle only extended to the middle of the wing's center section, and power was supplied by two Pratt & Whitney R-4360 Wasp Major radials. The front of the fuselage and left tail boom contained photographic equipment, and one of the crew members could serve as a photographer by crawling past the pilot and into the aircraft's nose to service the cameras in flight.

Left: The first XF-11 prototype (44-70155) takes off for its ill-fated first flight, which nearly cost Howard Hughes his life

Right: Top view of the second XF-11 prototype (44-70156) with single rotation propellers

The first XF-11 was originally scheduled for November 1944 with production plans for 10 aircraft a month. However, delays were encountered almost immediately, supporting the USAAF's belief that the Hughes Aircraft Corporation wasn't up to series aircraft production. By mid-1945, the XF-11 had not yet flown, and with World War II winding down, the F-11 production contract was canceled on May 26, 1945, but construction of the two prototypes continued. The first prototype, completed in April 1946, featured Hamilton Standard counter-rotating propellers. After receiving minor damage during taxi testing, it took off for its maiden flight on July 7, 1946. One hour and 15 minutes into the flight (contravening the USAAF's requirement that the first flight last 45 minutes), the rear set of propellers went into reverse pitch, and the aircraft lost altitude, crashing into a golf course in Beverly Hills. Hughes himself escaped the burning wreckage, but suffered severe burns, a displaced heart, a punctured lung, and broken ribs, so he was hospitalized for several months. The second XF-11 prototype (44-70156) was subsequently completed with single rotation Curtiss Electric propellers (legend has it that Hughes masterminded these modifications from his hospital bed). It first flew on April 4, 1947, with Hughes himself at the controls; the first flight of the second prototype was smooth and flawless, and in November the aircraft was delivered to Wright Field, Ohio. Test flights at Eglin Air Force Base in Florida lasted from December 1947 to July 1949, and even though the second XF-11 displayed good performance, in-flight access of the camera equipment was difficult and some of the aircraft's systems were unreliable. After the Air Force became independent of the Army in 1947, it changed the designation lettering for reconnaissance aircraft from F to R, meaning that XF-11 became XR-11. By now, however, the intended operation role of the XF-11 was taken up by B-29s and B-50s modified for reconnaissance, so the XF-11 became irrelevant. The second XF-11 was flown to Sheppard Air Force Base in Wichita Falls, Kansas, on July 26, 1949, serving as a ground training aid. It was finally stricken off the USAF inventory in November and eventually scrapped.

As a side note, it is astounding to note that the XF-11 became a political football long after reaching the hardware phase. Technical and managerial problems during development of the XF-11 but also the H-4 flying boat prompted the Truman Committee and Brewster Committee to investigate the XF-11 and H-4 programs in 1946-1948, precipitating the Hughes-Roosevelt hearings of August 1947 (Hansen 2012, pp. 530-536). Senator Owen Brewster claimed that Howard Hughes received $40 million from the War Department without delivering any of the F-11s on contract, but Hughes insisted that Brewster had been motivated by his connections to Pan American World Airways, the rival to Hughes' TWA. Despite making counter-claims, Brewster's reputation suffering as a result of the hearing, and he resigned from the Senate at the end of 1952.

The story of the D-2 and its big descendant the XF-11 is a reminder the promising military applications offered by the Hughes Aircraft Corporation's novel aircraft designs, yet it duly reflects the eccentric nature of Howard Hughes himself, considering that the reclusive aviator felt he could finance construction of the D-2 and XF-11 with his own money with little financial input from the US military top brass.

References:

Buttler, T., and Griffith, A., 2015. American Secret Projects 1: Fighters, Bombers, and Attack Aircraft, 1937 to 1945. Manchester, UK: Crecy Publishing.

Hansen, C., 2012. Enfant Terrible: The Times and Schemes of General Elliott Roosevelt. Tucson, AZ: Able Baker Press.

Norton, W., 2008. U.S. Experimental & Prototype Aircraft Projects: Fighters 1939–1945. North Branch, MN: Specialty Press.

Yenne, B., 1990. The World's Worst Aircraft. New York: Barnes & Noble Books.