Supersonic research aircraft from El Segundo: The Skystreak and Skyrocket

The story of Charles E. "Chuck" Yeager's historic flight over the Mojave Desert in southern California on October 14, 1947 in the Bell X-1 supersonic research aircraft remains one of the most pivotal milestones in the history of not just post-World War II aviation, but also that of aviation development in southern California. However, the United States Air Force that sponsored development of the X-1 was not alone in encouraging the construction of experimental aircraft to investigate flight at transonic/supersonic speeds. Around the time that the Air Force commenced development of the Bell X-1, the US Navy launched their own program for a supersonic research aircraft in the late 1940s. During my visit to the Planes of Fame Museum in Chino, California, on April 13, 2019, I happened to come upon one of the three airframes of the Douglas D-558-2 Skyrocket supersonic rocket-powered research aircraft. Given that the US Navy's own supersonic research aircraft never received Navy designations, and they are at times overshadowed in the public eye by the X-1 and X-15, I though it would be very convenient to discuss in-depth the Navy's efforts in production research aircraft to investigate flight in the supersonic flight regime.

    Douglas D-558-1 Skystreak

In the mid-1940s, around the time that Bell was working on the XS-1 (later X-1) supersonic research aircraft, the US Navy and National Advisory Committee for Aeronautics (NACA) jointly initiated a research program to investigate the aerodynamic challenges of transonic and supersonic flight. This scheme, designated D-558 by Douglas, was originally to proceed in three phases: (1) a jet-powered transonic/supersonic research aircraft; (2) mixed rocket/jet-powered design; and (3) design of a combat plane. The first phase of this program was designated D-558-1 (christened Skystreak), and six aircraft were ordered by the Navy (to be fitted with nose and side air inlets and varying wing airfoil sections), while the second phase was called D-558-2 (christened Skyrocket). However, on January 27, 1947, the original D-558 blueprint was revised whereby the D-558-1 order was reduced to three aircraft (BuNos 37970/37972) with a single nose inlet, and the D-558-2 design conceived as a sleek, airplane with backswept wings. Three D-558-2 aircraft (BuNos 37973/37975) were ordered as substitutes for the final three D-558-1s that had been canceled. Construction of the first D-558-1 Skystreak began in 1946 and was finished in January 1947, with the first flight taking place on April 14. The Skystreak set a world speed air record of 641 miles per hour (1,031 km/h) on August 20, which was broken five days later by the second D-558-1, which had made its first flight that month. The design of the Skystreak featured a streamlined fuselage with a nose inlet (made from magnesium) and straight wings (made of aluminum), and power was supplied by Allison J35 turbojet. The first Skystreak made a total of 101 flights before being handed over to the NACA flight test unit at Edwards Air Force in April 1949. The second D-558-1 flew a total of 46 flights (27 by Douglas and the Navy, 19 by NACA) before it crashed on takeoff on May 3, 1948, due to compressor disintegration, killing test pilot Howard Lilly. The third D-558-3 began flying in 1949 and conducted a total of 81 flights until June 10, 1953, when it was retired by NACA. Like the X-1, the Skystreak was instrumental in providing a library of data on the fundamentals of transonic and near-supersonic flight, taking the US Navy closer to entering the supersonic age.

   

Top: Douglas D-558-2 Skyrocket (BuNo 39374) at the Planes of Fame Museum
Bottom: Third Douglas D-558-2 Skyrocket (BuNo 39375) at Edwards Air Force Base

Even while tests flights of the Skystreak were ongoing, the El Segundo Division of Douglas proceeded in earnest with development of the D-558-2 Skyrocket, which had a sleek, streamlined fuselage with a pointed nose and backswept wings and horizontal stabilizers. Like the Skystreak, the fuselage of the Skyrocket was made of magnesium and the wings and tail empennage were constructed from aluminum alloys. Although the Skyrocket was initially configured with a flush cockpit canopy, it was clear that visibility from this cockpit design was poor, so it was reconfigured with a raised cockpit with conventional angled windows. The first flight of the D-558-2 took place on February 4, 1948, with test pilot John F. Martin at the controls, and the first and second Skyrocket airframes initially flew using a single Westinghouse J34 turbojet only, but were later modified to include a Reaction Motors LR-8 four-chambered liquid-fuel rocket engine, while the third D-558-2 was completed with both the turbojet and rocket motor. A total of 313 flights were made by the Skyrocket (123 by BuNo 37973, 103 by BuNo 37974, and 87 by BuNo 37975), and the first Skyrocket was modified with air-launch capability and pure rocket power in 1955. One Boeing P2B-1S (patrol version of the B-29 Superfortress), christened Fertile Myrtle (BuNo 84029, previously USAAF serial number 45-21787), was modified to serve as the mothership for the Skyrocket, and the first aerial launch of the D-558-2 from the P2B-1S took place on September 8, 1950. On November 20, 1953 (nearly a month before the 50th anniversary of the Wright brothers' historic flight at Kitty Hawk in 1903), the Skyrocket became the first aircraft to reach Mach 2 when NACA pilot Scott Crossfield took the second D-558-2 into a dive to attain a top speed of Mach 2.005 (1,291 miles per hour, 2,078 km/h). The last flight of the Skyrocket occurred on December 20, 1956, and the three Skyrocket aircraft now reside in air museums, with BuNo 37973 (photographed by me in 2019) now displayed at the Planes of Fame Museum in Chino, California, BuNo 37974 (the only Skyrocket to reach Mach 2) on display at the National Air and Space Museum in Washington, D.C., and BuNo 37975 displayed on a pylon on the grounds of Antelope Valley College in Lancaster, California.

Left: Douglas Model 674; Right: Douglas Model 684

As an important footnote, in 1954, Douglas proposed a high-altitude hypersonic research aircraft, the Model 674, after the US Navy's Office of Naval Research awarded a preliminary contract for Douglas to look into a new-generation high-speed research aircraft. The Model 671 combined the straight wings of the Skystreak with the fuselage and tail empennage of the Skyrocket and was designed to reach an altitude of 1,000,000 feet and a speed of Mach 7. However, the performance benchmarks laid out for the Model 671 were rather too ambitious, and when the US Air Force, US Navy, and NACA announced a competition in December 1954 for a hypersonic research aircraft able to reach Mach 6.7 and 250,000 feet, Douglas unveiled a less ambitious but more radical proposal, the Model 684, which had stubby wings and the horizontal stabilizers and vertical fins arranged in a cruciform manner. The Model 684 was submitted in May 1955 along with the Republic AP-76, Bell D-171, and the North American design, and on September 30, North American's design was declared the winner and designated X-15. Some sources refer to the Model 671 and Model 684 projects as "D-558-3" or "Skyflash", but there is no evidence from Douglas company documents that either of these design was designated as much or given a company name.

Although overshadowed by the Bell X-1 in the public imagination, the Douglas D-558-1 Skystreak and D-558-2 Skyrocket played a role in helping the US Navy enter the supersonic age by providing a huge wealth of data on flight in the transonic and supersonic areas.     

 

Northrop's lost fighter jets: the YF-17 Cobra, F-20 Tigershark, and YF-23 Black Widow II/Spider/Grey Ghost

Everyone is familiar with the F-15 Eagle, F-16 Fighting Falcon, and F-22 Raptor jet fighters for the US Air Force and the F-18 Hornet strike fighter for the US Navy. (The Lockheed F-35 Lightning II was given an out-of-sequence designation after winning the Joint Strike fighter contest in October 2001 because the X-35 was Lockheed Martin's technology demonstrator for the JSF competition, but that's another story.) But whatever happened to the F-17 slot between F-16 and F-18? While Northrop aced a couple of success stories in combat jet development with the F-89 Scorpion all-weather fighter and F-5 lightweight fighter to make up for the cancellation of its flying wing bomber programs, it also produced a handful of jet fighter designs that are less well-known to most people, the YF-17 Cobra and F-20 Tigershark lightweight jet fighters and the YF-23 Black Widow II/Grey Ghost prototype stealth fighter jet. Therefore, I thought it'd be convenient to give an overview of all three "lost" jet fighters created by the Northrop Corporation in the 1970s and 1980s, because these designs remained at the prototype stage only.

Left: Desktop model of the Northrop YF-17 at the Western Museum of Flight
Right: Northrop YF-17 during flight testing, 1974

The first "lost" Northrop jet fighter design that is worth discussing is the Northrop YF-17 Cobra. In the late 1960s, the US Air Force initiated the Lightweight Fighter (LWF) competition for a lightweight jet fighter to replace the F-5 Freedom Fighter/Tiger II, at the behest of the so-called "Fighter Mafia" led by Pierre Sprey, Everest Riccioni, and John Boyd. Boeing, General Dynamics, Lockheed, Northrop, and Vought responded with proposals for the LWF competition. Since 1965 Northrop had initiated design studies for advanced versions of the F-5E Tiger II, including the N-300 proposal with a longer fuselage, two General Electric GE15-J1A1 turbojets each delivering 9,000 pounds (40 kN) of thrust, small leading-edge root extensions (LERXs), and a slightly elevated wing. and the N-530 proposal with a greater wing area, two GE 15-J1A5 turbojets delivering 13,000 pounds (58 kN) of thrust, a trapezoidal wing planform and nose section, and LERXs that tapered into the fuselage under the cockpit and enabled maneuvering at angles of attack exceeding 50° by providing about 50% additional lift. By January 1971, Northrop conceived a revised version of the P-530 design with cannons mounted on the upper part of the fuselage, designated P-600, to meet the LWF requirement parameters. The P-600 had two General Electric YJ101 turbojets each delivering 14,400 pounds (64 kN) of thrust, two rudders with a 45° cant, and a fly-by-wire electronic control augmentation system (ECAS) that utilized ailerons, rudders, and stabilators for primary flight control. The General Dynamics and Northrop designs were selected for prototyping by the Defense Department and designated YF-16 and YF-17 respectively. The design of the P-600's LERXs resembled a cobra, hence the YF-17's unofficial name, Cobra. The YF-17 made its first flight on June 9, 1974, nearly five months after the F-16, and two prototypes were built (serial numbers 72-1569/1570). After a fly-off contest between the F-16 and YF-17, on January 13, 1975, Air Force Secretary John L. McLucas declared the F-16 the winner of the LWF competition, citing low operating costs, greater range, and higher maneuver performance in the supersonic flight regime. Despite losing the LWF competition, Northrop would later team with the St. Louis division of McDonnell Douglas to use the YF-17 Cobra design as the basis for a new-generation lightweight jet fighter for the US Navy, the F-18 Hornet, which flew in 1978, and the first prototype YF-17 was sent to NASA Dryden Research Center (now Neil Armstrong Flight Research Center) for base drag studies in May-July 1976. The first and second YF-17 prototypes are now preserved at the Western Museum of Flight in Torrance, California, and Battleship Memorial Park in Mobile, Alabama, respectively.

Left: Sole remaining F-20 prototype (serial number 82-0064) at the California Science Center, Los Angeles

Right: F-20 prototype (serial number 82-0062) in flight

Years after losing the LWF competition to General Dynamics, Northrop began work on an advanced version of the F-5E Tiger II with one General Electric F404 turbofan engine under the designation F-5G in response to the FX program initiated in the late 1970s for a new fighter jet for export that could outperform the F-5E. After a series of back-and-forth moves by the Defense Department to support and then defer the FX program, the F-5G was cleared for full-scale development and four prototypes (serial numbers 82-0062/0065) were ordered. The first F-5G prototype made its first flight on August 30, 1982, and recognizing the advanced nature of the F-5G compared to past F-5 variants, Northrop requested that the F-5G be redesignated F-20, and this request was approved by the Defense Department in late 1982 (Northrop initially wanted the F-5G to be redesignated F-19, but it later changed its mind and requested that F-19 be skipped in favor of F-20 due to possible confusion with the Mikoyan-Gurevich MiG-19 fighter). In March 1983, the F-20 was officially named Tigershark and a number of countries, including Bahrain and South Korea, expressed customer interest in the F-20. With Northrop looking at incorporating avionics upgrades, an expanded fuel tank, and fiberglass composite materials into the planned production F-20, plans were made to have the fourth Tigershark prototype built to include fully operational equipment. Although the Tigershark performed well during test flights, Northrop's hopes for securing production orders for the F-20 from foreign customers were stymied by several US allies in Europe, East Asia, and the Middle East buying the F-16 but also a Congressional investigation in 1984 on the merits of the F-20 compared to the F-16, and the fact that European countries were offering combat jet designs of their own to foreign customers. Meanwhile, the first and second F-20 prototypes crashed during flight testing, with the first aircraft being lost during a demonstration flight in South Korea on October 10, 1984, and the second prototype crashing at Goose Bay in Labrador, Canada, in May 1985; both crashes were found to have been caused by the pilots losing consciousness due to excessive g-forces. By late 1986, Northrop canceled the F-20 program without any orders from foreign customers, and the fourth F-20 prototype (serial number 82-0065) was only half-complete when the Tigershark program was terminated. The third F-20 prototype (the only one to survive the flight test program) is now on display at the California Science Center at Exposition Park in Los Angeles.

Left: Second YF-23 prototype (serial number 87-8701) at the Western Museum of Flight in Torrance, California

Right: The first YF-23 prototype (serial number 87-8700) in flight over the Mojave Desert, California 

 

The third and final "lost" Northrop jet fighter to be discussed is the Northrop/McDonnell Douglas YF-23 stealth air superiority fighter. In 1981, the US Air Force initiated the Advanced Tactical Fighter program for a stealthy air superiority fighter to replace the F-15 Eagle in response to the Soviet Union's new MiG-29 and Su-27 jet fighters. The ATF requirement called for supercruise capability (sustained supersonic flight without the need for afterburners), survivability, and ease of maintenance, and several aerospace companies, including Lockheed, Boeing, General Dynamics, McDonnell Douglas, Northrop, Grumman and Rockwell International, submitted bids for the new aircraft by July 1986. Lockheed later decided to form a team with Boeing and General Dynamics to develop whichever of their proposed designs was selected, while Northrop followed suit by forming a team with McDonnell Douglas should its design be chosen. In October 1986, under the "fly-before-buy" principle, the USAF selected the Lockheed/Boeing/General Dynamics and Northrop/McDonnell Douglas designs for prototyping, and these designs were designated YF-22 and YF-23 respectively. The YF-23, like the F-22, had chines along the nose, but utilized diamond-shaped wings as well as vertical stabilizers angled 50 degrees from vertical position. S-duct engine air intakes were provided to allow air to flow into the jet engines. The two YF-23 prototypes were painted in different colors, the first prototype (serial number 87-8700) being painted in charcoal gray and nicknamed "Black Widow II" in honor of the Northrop P-61 Black Widow night fighter of World War II, while the second prototype (serial number 87-8701) was painted in two shades of gray and nicknamed "Spider" and "Grey Ghost".* The first YF-23 had two Pratt & Whitney F119s, while the second YF-23 used two General Electric F120s. The first flight of the YF-23 took place on August 27, 1990, piloted by Alfred "Paul" Metz (who later became the test pilot for the first service test F-22 Raptor in 1997), while the second prototype flew on October 1990. A fly-off contest between the YF-22 and YF-23 continued into late 1990, and on April 23, 1991, the Air Force declared the YF-22 the winner of the ATF competition. The YF-23 was faster and stealthier, while the YF-22 was more maneuverable, but development experience played the final role in the outcome of the ATF contest; the Northrop company was busy with development of B-2 Spirit stealth bomber, and McDonnell Douglas was reeling from the cancellation of the A-12 Avenger II carrier-based stealth attack aircraft. Lockheed, by contrast, had built the F-117 Nighthawk under budget and on time, so the USAF must have decided that the YF-22 offered lower technical risks (Jenkins and Landis 2008; Miller 2005). The YF-23 prototypes were transferred to NASA Dryden Flight Research Center (now NASA Armstrong Flight Research Center) at Edwards AFB with their engines removed. One of the aircraft was to be used by NASA for studying techniques for the calibration of predicted loads to measured flight results, but those plans never materialized, and the first YF-23 prototype is now on display at the US Air Force Museum in Dayton, Ohio, while the second YF-23 is now displayed at the Western Museum of Flight in Torrance, California.

*The different names applied to the YF-23 prototypes reflected the different naming conventions by the YF-23 manufacturers for their jet fighters. Northrop named its fighters after arachnids and other deadly animals, while the St. Louis division of McDonnell Douglas named its fighters after evil spirits.

 

In an interesting footnote, McDonnell Douglas submitted a design for a lightweight stealth fighter based on the YF-23 for the Joint Strike Fighter competition of the 1990s. It was similar to the YF-23 in the tail empennage design but differed in a having wings reminiscent of the McDonnell F-101 Voodoo escort fighter, and utilized a reheated turbofan, with a remote gas-driven fan to augment lift in STOVL mode. However, the McDonnell Douglas proposal was rejected in favor of the Boeing and Lockheed Martin designs for JSF prototyping by the Pentagon in late 1996, and the Boeing and Lockheed Martin technology demonstrators for the JSF became X-32 and X-35 respectively, flying in late 2000 (the Lockheed Martin design won the JSF contest on October 26, 2001, and subsequently developed into the F-35 Lightning II, but that's another story). Northrop Grumman in the early 2000s conceived a long-range fighter-bomber version of the YF-23 (internally known as "FB-23") as an interim stopgap design pending the arrival of a planned replacement for the B-52H and B-1B (now called the B-21 Raider), but this design remained on the drawing board.

Although Northrop had accomplished something to make up for the cancellation of its jet flying wing bomber programs in the late 1940s by producing the F-89 Scorpion and F-5 Freedom Fighter/Tiger II, the 1970s to early 1990s sapped away Northrop's fortunes in the fighter jet business, either because of technical and aerodynamic considerations or fierce competition from other aircraft for the export market. Nevertheless, the YF-17, F-20, and YF-23 constitute Northrop's willingness to adapt to leaps and bounds in aviation technology during the late Cold War as well as geopolitical circumstances, and the design philosophy of the YF-17 is still prevalent in the F-18 Hornet naval strike fighter. 

References:

Chong, T., 2016. Flying Wings & Radical Things: Northrop's Secret Aerospace Projects & Concepts 1939-1994. Forest Lake, MN: Specialty Press.

Jenkins, D.R. and Landis, T.R., 2008. Experimental & Prototype U.S. Air Force Jet Fighters. North Branch, Minnesota: Specialty Press.

Miller, J., 2005. Lockheed Martin F/A-22 Raptor, Stealth Fighter. Hinckley, UK: Midland Publishing. 

The US Navy's airborne whale of a whale: Douglas A-3 Skywarrior

The United States Navy in the Cold War years deployed its significant share of carrier-based tactical warplanes, the most recognizable of which were the F3H Demon, F-8 Crusader, F9F Panther/Cougar series, F-4 Phantom II, A-4 Skyhawk, A-1 Skyraider, A-7 Corsair II, and A-6 Intruder. However, the early years of the Cold War bore witness to one unsung hero of carrier-based jet aviation: the Douglas A3D/A-3 Skywarrior. Although not as well-known as the B-47 Stratojet or B-52 Stratofortress, the Skywarrior was the chief airborne warrior queen of the US Navy from 1956 until the deployment of ballistic missile-armed nuclear submarines, and gave the Navy the ability to launch nuclear strikes on enemy territory from large carriers over long distances.

In the late 1940s, the US Navy feared that the US Air Force would control the American nuclear weapons stockpile. To address this concern of, the Navy decided to build a nuclear-armed strategic bomber of its own, the North American AJ/A-2 Savage twin-engine strategic bomber. However, the Savage was a piston-engine warplane, and gas turbine engines made it obsolete by the time it reached service in 1950. With General Curtiss Lemay, the head of Strategic Air Command (SAC), engaged in a lobbying blitz to have Congress divert funds for nuclear weapons delivery systems to US Air Force strategic bombers, the US Navy in January 1948 issued its OS-111 requirement for a jet-powered strategic bomber to operate from the planned USS United States aircraft carrier that could carry either a 10,000 lb (4,500 kg) bomb load or a nuclear weapon. Because the United States would allow the Navy to conduct nuclear strikes on large parts of the globe that the USAF could not reach with its existing bomber fleet, it was crucial to prevent the US Navy from being finished as a major service in case the Air Force got a hold on all US nuclear weaponry. A total of seven companies from submitted bids for the OS-111 requirement: Convair, Curtiss-Wright, Douglas, Fairchild, Lockheed, North American, and Republic (Zichek 2009 is consulted for details of these submissions). Of these proposals, the Convair proposal had three Westinghouse J40 turbojets (two under the wings and third buried in the rear fuselage), while the Douglas (El Segundo) D-593 had two underwing Westinghouse J40 turbojets and the Douglas (Santa Monica) Model 1181 was powered by three J40 tubojets (two in the wing roots and a third in the rear fuselage), whereas the Lockheed L-187 encompassed various designs ranging from swept-wing jet- and turboprop-powered aircraft to a jet-powered flying wing, and North American's RD-4554 was studied in conventional and flying wing layouts (Butler 2010, 2021). (A number of alternate layouts for the Convair design and the Model 1181 were worked out without the third turbojet in the rear fuselage, and one alternate Convair design for the OS-111 had two J40s buried in the wing roots.) The Curtiss-Wright P-558 and Douglas D-593 were picked for further study in late 1948, and by the spring of 1949 a few modifications were made to the D-593 and P-558 designs, and the D-593 was considered the most favorable design by the Navy.

Douglas A3D Skywarrior (BuNo 135422) at Naval Air Station Jacksonville, Florida, mid-1950s

On April 23, 1949, the USS United States was cancelled by US Defense Secretary Louis Johnson due to budget cuts. Although the Navy top brass was disappointed at the cancellation of the United States-class carriers, the US Navy continued with the OS-111 competition, issued a new weight requirement to make a winning design able to operate from the Midway-class carriers. Douglas came out with a lighter version of the D-593 design, the D-593-8, and by July the Navy declared the D-593-8 the winner of the OS-111 competition. The Douglas design, officially named Skywarrior by the Navy, was designated XA3D-1 and a contract for two prototypes (BuNos 125412/125413) was signed. The first flight of the Skywarrior took place on October 28, 1952, and the aircraft was cleared for service on March 31, 1956. In the meantime, the Westinghouse J40 engines used on the A3D prototypes were to prove unreliable, and Douglas selected the more powerful Pratt & Whitney J57 turbojet to power all service test and production A3Ds. A total of 282 Skywarriors were built, and production of the A3D continued until 1961. As a strategic bomber, the Skywarrior could carry 12,800 lb (5,800 kg) of free-fall conventional bombs and mines, including one free-fall nuclear weapon. Navy crews dubbed the Skywarrior the "Whale" because of its size and less-than-slender appearance. On September 18, 1962, the A3D was redesignated A-3 under the new Tri-Service aircraft designation system. By the end of the 1950s, the strategic bomber role of the Skywarrior was rendered obsolete due to the introduction of the Polaris submarine-launched ballistic missile and the ballistic missile submarines designed to carry them. However, many A-3s would be modified to serve tactical reconnaissance, electronic warfare, and tanker roles. The Skywarrior also happened to form the basis of the Douglas B-66/RB-66 Destroyer medium bomber for the US Air Force, which first flew in June 1954 and of which 294 were built. Like the Skywarrior, the B-66 served as both a bomber, reconnaissance platform, and EW platform during its operational career, but it differed in having ejection seats.

Top: Douglas EKA-3B Skywarrior (BuNo 142251) on display at the USS Midway Museum, San Diego
Bottom: Douglas EKA-3B (BuNo 147663) in flight, 1971

Although the A-3 Skywarrior's career as a nuclear-armed strategic bomber was rather brief given the introduction of SLBMs, it represented a quantum leap forward in the US Navy's efforts to acquire a long-range airborne nuclear weapons delivery system for use from large carriers. Even in situations where the Americans did not use a carrier-based plane to drop a nuclear weapon in anger, the A-3's airframe gave it operational flexibility to be used for electronic warfare, reconnaissance, and tanker missions during the Vietnam War and Operation Desert Storm. 

Now all this brings me to discussing one A-3 Skywarrior I saw on the deck of the USS Midway during my visit to the USS Midway Museum in April 2017. Although the A-3 Skywarrior fell out of use as a nuclear-armed strategic bomber after the Polaris SLBM was introduced, the Vietnam War paved the way for the Skywarrior to be used as a tanker aircraft (KA-3B), reconnaissance aircraft (RA-3B), and electronic warfare aircraft (EA-3B, EKA-3B, ERA-3B). The KA-3B had all bombing equipment replaced by a probe-and-drogue system for refueling aircraft, while the EA-3B featured a pressurized compartment in the former weapon bay for one Electronic Warfare Officer and three ESM operators. The RA-3B, on the other hand, had the weapons bay modified to accommodate 12 cameras plus photoflash bombs, and increased pressurization enabled the camera operator to enter the weapons bay to check the cameras. The EKA-3B version that I saw at the USS Midway Museum was designed for a dual tanker/EW role, with the tail turret replaced by a tail fairing with electronic countermeasures (ECM) equipment. A total of 85 A-3Bs were converted to KA-3B iteration, and 34 of them were modified to EKA-3B standard. During the Vietnam War, EA-3Bs and EKA-3Bs were used to jam North Vietnamese radars, as well as refuel tactical aircraft operating over Vietnamese airspace. After the Vietnam War, most of the EKA-3Bs were converted back to KA-3B configuration, and the EKA-3B was replaced in active service by the Grumman KA-6D Intruder (tanker version of the A-6 attack aircraft). The EA-3B was also used during the Cold War for electronic intelligence against Warsaw Pact member states in Eastern Europe, and it served long enough to take part in Operation Desert Storm in early 1991, before being retired from service on September 27 of that year.

References:

Buttler, T., 2010. American Secret Projects: Bombers, Attack, and Anti-Submarine Aircraft 1945 to 1974. Hinckley, UK: Midland Publishing.

Buttler, T., 2021. American Secret Projects 4: Bombers, Attack, and Anti-Submarine Aircraft 1945 to 1974. Manchester, UK: Crécy Publishing.

Francillon, R. J., 1979 McDonnell Douglas Aircraft since 1920, Volume I. Annapolis, MD: Naval Institute Press. ISBN 0-370-00050-1.

Gunston, B., and Gilchrist, P., 1993. Jet Bombers: From the Messerschmitt Me 262 to the Stealth B-2. Oxford, UK: Osprey Publishing. ISBN 1-85532-258-7.

Heinemann, E., 1987. "A Whale of an Airplane." Naval Aviation News 70 (November/December 1987): 18–21.

Zichek, J.A., 2009. The Incredible Attack Aircraft of the USS United States, 1948–1949. Atglen, PA: Schiffer Publishing. ISBN 978-0-7643-3229-6.

Experimental warplanes from the Los Angeles basin, part 3: Lockheed and North American penetration fighter designs

The early years of the Cold War saw the US develop a wide variety of jet fighters for a plethora of officially delineated combat missions, including air superiority, long-range interception, escort, and all-weather/night operations. Some, like the F-84, F-86, F-89, and F-94, entered production and operational service, but others remained at the prototype stage only. During my recent visit to the Planes of Fame Museum, I surprisingly happened to notice desktop models of two seldom-known US jet fighter designs of the early Cold War, the Lockheed XF-90 and North American F-93 penetration fighters. Therefore, I have devoted the third post of my multi-post series on prototype warplanes created in the Los Angeles to discussing in detail the XF-90 and F-93.

On August 28, 1945, a few days before the Japanese surrender aboard the USS Missouri, the US Army Air Force issued a requirement for a new-generation penetration fighter able to escort heavy bombers to enemy targets. Intended as a successor to escort versions of the P-51 Mustang that were used to escort B-17s and B-24s over Nazi Germany in World War II, the new jet-powered penetration fighter was to have a combat radius of 900 miles (1,450 km) and high combat performance. Several companies submitted bids to the jet penetration fighter contest, including Convair, Curtiss, Goodyear, Lockheed, McDonnell, Northrop, and North American. Technical details regarding the Convair and Northrop penetration fighter designs are discussed Buttler (2013) and will not be replicated here, although it should be stressed that the Northrop design was a derivative of the XP-79B flying wing fighter. The USAAF selected the McDonnell Model 36 and Lockheed L-167/Model 90, and North American NA-167 designs for prototyping, designating them XP-88, XP-90, and P-86C respectively. After the Air Force became independent of the US Army in September 1947 and adopted the policy of classifying fighter planes as fighters rather than pursuit planes, these designs were redesignated XF-88, XF-90, and F-86C (later YF-93A) in June 1948.

Left: Desktop model of the Lockheed XF-90 at the Planes of Fame Museum

Right: First XF-90 prototype (serial number 46-687) in flight over Edwards Air Force Base, California

Now this brings me to describing the two US penetration jet fighter designs from the Los Angeles basin, of which I will discuss the XF-90 first. The Lockheed XP-90/XF-90 was a sleek jet fighter with a pointed nose and engine intakes similar to that of Lockheed's earlier P-80/F-80 Shooting Star, as well as two 3,000 lb (13.3 kN) thrust Westinghouse J34 turbojets. Armament provisions included six 0.79 inch cannons, eight 5 in (127 mm) HVAR rockets, and 2,000 lb (907 kg) of bombs. The original design of the XP-90 featured a delta-wing, T-tailed configuration, but the US Air Material Command judged the delta wing configuration to produce high drag at lower speeds, so Lockheed reworked its fighter design into a backswept wing machine with a tail empennage like that of the F-86 Sabre. After a mock-up inspection in December 1947, two XF-90 prototypes (serial numbers 46-687/688) were ordered and the first of these flew on June 3, 1949, with the second prototype following suit on April 12, 1950. The XF-90 broke the speed of sound in a dive on May 17, 1950, reaching a speed of Mach 1.2. However, the XF-90 was too big and heavy for the available thrust generated by the Westinghouse turbojets, and RATO boosters were used for most of the takeoffs.

Left: Desktop models of the North American YF-93 at the Planes of Fame Museum

Right: First YF-93 prototype (serial number 48-317) in flight over Edwards Air Force Base, California

The other penetration jet fighter from the Los Angeles area that took flight was the North American YF-93. It was a derivative of the F-86 Sabre that had the air intakes moved to the fuselage sides to  allow the nose to accommodate the radar scanner. Due to its size difference compared to the F-86, the F-93 was powered by one Pratt & Whitney J48 turbojet delivering 6,000 lb (27 kN) of thrust, and it featured a dual-wheel main landing gear and increased wing area. Although originally designated P-86C/F-86C, in September 1948 the Air Force judged the NA-157 design sufficiently distinct to be allocated the new designation YF-93A. Two prototypes (serial numbers 48-317/318) were ordered in June 1948, along with 118 production F-93As (serial numbers 49-001/048, 49-059/068, 49-392/421, 49-1966/1995). The production order was cancelled in February 1949 due to budget cuts, work on the two prototypes continued apace, with the first aircraft flying on January 25, 1950.

The USAF staged a fly-off of the XF-88, XF-90, and YF-93A in June-July 1950, and the XF-88 was declared the winner of the penetration fighter contest in late July. The McDonnell design was judged superior to the Lockheed and North American designs in terms of handling, maneuverability, and high-speed characteristics, as well as armament stability and ability to operate from existing runways (see Buttler 2013, pp. 75-76). However, the euphoria at the McDonnell Aircraft Corporation over the outcome of the penetration fighter competition was all for naught. On August 22, 1950, just as the XF-88 was about to be cleared for production, the US Air Force gave up on the penetration fighter concept due to changing priorities and a tight defense budget. However, experience gained during the Korean War prompted the USAF to revive the notion of the penetration fighter, leading to General Operational Requirement (GOR) 101 being issued in February 1951 for a long-range escort fighter. McDonnell eventually developed an enlarged version of the XF-88, the F-101 Voodoo, which made its first flight in late September 1954.

References:

Buttler, T., 2013. Early US Jet Fighters: Proposals, Projects, and Prototypes. Manchester, UK: Hikoki Publications. 

Experimental warplanes from the Los Angeles basin, part 2: the Lockheed XP-49 and XP-58 Chain Lightning

The Lockheed P-38 Lightning was one of the outstanding US fighters of World War II, one of only two American twin-engine fighter planes for the US Army Air Force to enter production (the other being the Northrop P-61 Black Widow night fighter). In particular, one of the most famous P-38 missions of the war involved the shootdown of a G4M bomber flown by Admiral Isoroku Yamamoto, the architect of the Japanese attack on Pearl Harbor, and one P-38 pilot, Richard Bong, was the top American fighter ace of World War II, shooting down forty Japanese warplanes. However, with the exception of highly experienced military aviation historians, most people don't think highly often of the fact that Lockheed made two abortive attempts to develop an modernized P-38, the XP-49 and the XP-58 Chain Lightning. During my visits to the Planes of Fame Museum in January 2018 and again in June 2020, I saw a desktop model of the XP-58 inside a glass display cabinet at the museum's Foreign Hangar. My first post in an overview of experimental warplanes built in the Los Angeles basin drawing upon my photos of desktop models taken at air museums in Southern California dealt with the Hughes XF-11 spyplane and its secret D-2 predecessor; thus, the second post of this series will focus on the XP-49 and XP-58 Chain Lightning derivatives of the P-38.

Front angular view of the sole Lockheed XP-49 prototype (serial number 40-3055)

In March 1939, the US Army Air Corps issued Circular Proposal 39-775 and Specification XC-615 for a twin-engine escort fighter with two Pratt & Whitney Twin-Wasp radial engines and fitted with conventional undercarriage. Bell, Bellanca, Brewster, Curtiss, Grumman, Lockheed, and Vought submitted bids for the new fighter design, and Army Air Corps selected the Lockheed L-106 and Grumman G-41/G-45 designs for prototyping, designating them XP-49 and XP-50 respectively. The XP-49 was similar to the P-38 Lightning but differed in having a pressurized cockpit, as well as new nacelles and booms for different engines. It was 40 ft 1 in (12.22 m) long, with a wingspan of 52 feet (15.85 m), a gross weight of 19,948.5 lb (9,049 kg), a maximum take-off weight of 22,000 lb (9,979 kg), and a service ceiling of 37,500 feet (11,430 m). The XP-49 was originally intended to use two either two 2,000 hp (1,491 kW) Pratt & Whitney X-1800 H-block inline engines or two Wright R-2160 Tornado radial engines, but the X-1800 showed disappointing performance during bench tests in 1940 and was cancelled after just one example had been built, while the R-2160 ran into development problems, forcing Lockheed to substitute two 1,600 hp (1,193 kW) Continental XIV-1430 V-cylinder inline engines. Technical problems plaguing the Continental engines meant that the sole XP-49 prototype (serial number 40-3055) did not fly until November 14, 1942, by which time the introduction of P-38 variants with new versions of the Allison V-1710 engine made the XP-49 redundant. Not surprisingly, the low power output of the IV-1430 compared to the X-1800 meant that the XP-49 had dismal speed (406 mph at 15,000 ft) despite good maneuverability and handling, relegating the aircraft to being a mere testbed for the XIV-1430. The XP-49 continued to be tested at Wright Field, Ohio, and was scrapped in 1946.

Left: Desktop model of the Lockheed XP-58 Chain Lightning at the Planes of Fame Museum, Chino, California
Right: The first (and only completed) Lockheed XP-58 prototype (41-2670) in flight over Los Angeles County en route to Muroc Army Air Field. 

Now it should be possible to discuss the one P-38 derivative of which I saw a desktop model at the Planes of Fame Museum, the XP-58 Chain Lightning. In April 1940, Lockheed began work on an advanced version of the Lightning (company designation L-121 in return for the US Army Air Corps allowing for the export of the P-38 Lightning to France and the UK. The initial L-121 proposal was to use two Continental IV-1430 V-cylinder inline engines, and it was offered in single- and two-seat versions, the former with the P-38's armament and the latter armed with two tail boom-mounted 0.50-inch machine guns. The two-seat version was chosen for further development and designated XP-58, but concerns about the viability of the IV-1430 prompted Lockheed to re-engine the XP-58 design with two Continental X-1800 (H-2600) engines. The Model 20-14 design of September 1940 had a second forward-firing 20-mm cannon and the tail boom guns were replaced by a remote-controlled dorsal turret with two 0.50-inch machine guns. One XP-58 prototype was ordered with the serial 41-2670. Extensive details about redesign of the XP-58 are discussed in Angelucci & Bowers (1987), Francilion (1982), and Norton (2008), so thus not need repeating here. Lockheed explored the Pratt & Whitney XH-2470, Continental XH-2860, and Pratt & Whitney R-2800 Double Wasp as possible powerplants for the Chain Lightning after Pratt & Whitney shelved development of the H-2600 due to disappointing performance during test runs. The R-2800 was seen as a perfect choice by Lockheed, but the USAAC judged the XP-58's performance estimates with the R-2800 inadequate, suggesting that the Wright R-2160 Tornado be substituted for the Twin Wasp; Lockheed agreed to this recommendation and also revised the rear-firing armament of the XP-58 to include one ventral turret with a 0.50-inch machine gun. A second prototype was ordered by the Army Air Force in May 1942 with extra fuel capacity. Throughout the first two years of US involvement in World War II, the USAAF mission requirements for the Chain Lightning became superfluous, with the escort fighter role of the XP-58 being reworked into a ground attack machine and finally a bomber destroyer. With the Chain Lightning redesigned as a bomber destroyer, Lockheed proposed that the first prototype use four forward-firing 37-mm cannons, with the second having a 75-mm cannon and two 0.50-inch machine guns. When the R-2160 ran into development problems and was cancelled in February 1943, the XP-58 was equipped with two Allison V-3420 V-cylinder liquid-cooled engines. Only the first XP-58 prototype was finished, but without any armament and fitted with dummy dorsal and ventral turrets, and it first flew on June 6, 1944 (the same day as the D-Day invasion). By now, the need for a bomber destroyer had vanished, and the sole XP-58 became relegated to a non-flying instructional airframe in early 1945.

As a side note, in 1942 Lockheed proposed a redesigned version of the XP-58, under the designation L-134. Unlike the Chain Lightning, the L-134 lacked tail booms and instead had a conventional twin-tail empennage, and it had two piston engines inside the fuselage between the pilot and rearward-facing gunner driving counter-rotating pusher propellers. The nose was armed with six machine guns in three pairs, and the dorsal and ventral rearward-firing gun turrets were retained (Buttler and Griffith 2015, p. 68). There was also a version of the L-134 that would have had canards, judging from Lockheed documents. However, the L-134 was destined to remain a paper project only.      

References:

Angelucci, E., and Bowers, P.M., 1987. The American Fighter. Sparkford, UK: Haynes Publishing.

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

 

Francillon, R.J., 1982. Lockheed Aircraft since 1913. London, UK: Putnam & Company.

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

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.