Lockheed L-133 jet fighter and L-1000 jet engine

The story of early American jet fighters has been well-documented in the literature, starting with the debut of the Bell P-59A Airacomet and Lockheed P-80/F-80 Shooting Star (Jenkins and Landis 2008; Norton 2008; Pace 1991). However, thanks to project documents in the National Archives and Lockheed Martin company archival records, it is clear that American aircraft designers were tinkering with a design for a jet fighter and turbojet engine technology long before the Japanese attack on Pearl Harbor, the Lockheed L-133.

The Englishman Sir Frank Whittle had set in motion the trajectory of future aviation development when he successfully conducted test runs of the world's first jet engine, the Power Jets WU, on April 12, 1937, yet Nazi Germany beat the United Kingdom to the punch in the race to develop the world's first jet airplane when on August 27, 1939 the Heinkel He 178 took to the skies for the first time. However, the benefits of the turbojet engine with regards to the performance of aircraft were not lost on US engineers during the 1930s. In 1933, Nathan Price, an engineer at Doble Steam Motors, began work on an exotic steam turbine design that featured a centrifugal compressor that fed air to a combustion chamber, which would feed steam into a turbine before exiting via a nozzle, powering both the compressor and propeller. This experimental steam turbine was fitted to a test aircraft in early 1934, and tests showed performance on par with existing piston engines, although the engine had difficulty maintaining power at high altitudes. The US aerospace industry and US Army expressed little interest in Price's steam turbine design, and work was halted in 1936.

Top: A side view of the Lockheed L-1000 turbojet 

Bottom left: Prototype of the Lockheed L-1000 (XJ37) turbojet at the Planes of Fame Museum, Chino, California (courtesy of author)

Bottom right: Hall Hibbard (l) and Nathan Price (r) examining an L-1000 (XJ37) turbojet

Although his Doble Steam Motors design did not attract serious interest from the military or the aerospace industry, Price continued work on centrifugal engine designs. In 1938, he conceived the first design for an American turbojet engine, which featured low-compression axial compressor stages that fed a high-compression reciprocating compressor. Price was eventually hired by the Lockheed Aircraft Corporation in Burbank, California, to evaluate General Electric superchargers being fitted to the Lockheed XP-49 prototype long-range fighter (itself a derivative of the P-38 Lightning). Clarence "Kelly" Johnson, the future head of the Lockheed Skunk Works, recognizing the problem of compressibility experienced by the P-38 Lightning, expressed interest in Price's turbojet design, so the jet engine conceived by Price was given the company designation L-1000 (Kay 2007, pp. 71-73).

Top left: Two desktop models of the Lockheed L-133 early jet fighter design at the Planes of Fame Museum, Chino, California (courtesy of author)

Top right: Interior of the L-133, including the crew compartment and jet engine (courtesy of Lockheed Martin)

Bottom: Three-view drawing of the Lockheed L-133 jet fighter (courtesy of Lockheed Martin)

With Price having devised the first design for an American jet engine, Kelly Johnson teamed up with Lockheed engineers Hall Hibbard and Willis Hawkins to devise the first design for a US jet fighter, the L-133, powered by two L-1000s. The layout of the L-133 was quite futuristic in many respects, including the use of canards, a blended wing body planform, and the turbojets buried in a very low-drag integral fuselage section. Length was to be 48 feet 4 inches (14.73 meters), the wingspan was to be 46 feet 8 in (14.22 m), and top speed was estimated at 625 mph (985 km/h). Four 20 mm cannons were mounted internally in the front nose section (Francillon 1982, p. 468; Norton 2008, p. 221). Remarkably, the jet engine intended to power the L-133 was the first jet engine design to use an afterburner, considering that early British and German jet engine designs had no afterburner.

In April 1941, General Henry "Hap" Arnold, head of the US Army Air Force (later US Army Air Force) witnessed test flights of the first British jet aircraft, the Gloster G.40 Pioneer (aka E.28/39), and he successfully persuaded the Power Jets company to export examples of the W.1 turbojet as well as drawings for the improved W.2B/23 design to the US, leading to General Electric being awarded a contract in September to license-build the W.2B/23 as the General Electric I-A/J31. On March 30, 1942, Lockheed submitted the L-133 and L-1000 designs to the USAAF for consideration. The Army Air Force, however, decided that the L-133 was too advanced for its time to be a practical weapon, so the L-133 remained a paper project (Norton 2008, p. 221). Instead, the Bell Aircraft Corporation in Buffalo, New York, would get the chance to build the first US jet fighter, the Bell P-59A Airacomet, which first flew on October 1, 1942 and used two J31 turbojets. Nonetheless, Lockheed would later use experience gained in designing the L-133 to develop a jet fighter of less radical design than the L-133, the P-80 (later F-80) Shooting Star, whose first flight occurred on January 8, 1944. Meanwhile, Nathan Price in May 1943 redesigned the L-1000 as a simpler design consisting of two 16-stage axial compressors; in July the USAAF awarded Lockheed a contract to build the L-1000 jet engine under the military designation XJ37. Three L-1000s were built, with the first example beginning test runs in 1946 (Kay 2007, p. 74). 

Although the L-133 never left the drawing board, the timing of its design along with that of the L-1000 jet engine envisaged by Nathan Price highlight the fact that American engineers were coming up their own schemes for jet engine and jet planes technology around the same time as those by Frank Whittle and Hans von Ohain. In retrospect, every American jet fighter built since World War II basically owes their existence thanks to the aerodynamic properties and jet engine technology first developed for the L-133, namely the afterburner and maneuverability in combat.

References:

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

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

Kay, A., 2007. Turbojet: History and Development 1930–1960, Vol. 2. Ramsbury: Crowood Press. 

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

Pace, S., 1991. X-Fighters: USAF Experimental and Prototype Fighters, XP-59 to YF-23. St. Paul, MN: Motorbooks International.

Electra's grandson: The Lockheed Model 18 Lodestar

The Lockheed Model 10 Electra twin-engine aircraft is best known as the aircraft used by Amelia Earhart in her ill-fated bid to circumnavigate the globe in 1937. However, it also spawned a number of descendants, including the Model 12 Electra Junior, the Wright Cyclone-powered Model 14 Super Electra, and the Hudson patrol bomber. One long-term derivative of the Electra that some aviation historians tend to overlook at times is the Model 18 Lodestar. During my April 2019 visit to the Planes of Fame Museum in Chino, California, I happened to notice two Model 18 Lodestars in a location for unrestored planes and armored vehicles, one of which was undergoing renovation. Therefore, I thought it might be worth writing a summary of the Lockheed Model 18 Lodestar, with some emphasis on the Lodestars I saw at the Planes of Fame Museum.

Top: Lockheed Model 18 Lodestar prototype (NX17385)

Bottom: National Airlines Model 18 Lodestar (civil registration NC18199)

Due to a poor sales record of the Lockheed Model 14 Super Electra, owing to the fact that the Super Electra was more expensive to operate than the Douglas DC-3. In order to improve the economics of the Model 14, Lockheed proposed the Model 18 Lodestar which differed from its predecessor in having a fuselage stretched by 5 feet 6 inches, and two more rows of seats (for a total seating capacity of 18 passengers) (Francillon 1982, pp. 185-186). The fourth Super Electra (returned to Lockheed by Northwest Airlines after a number of crashes involving the Super Electra) was selected by the Lockheed company to be converted to the Model 18 prototype, making its first flight in this forum on September 21, 1939. Two more Model 18 prototypes were produced from conversions of additional Super Electras, while the first new build Lodestar flew on February 2, 1940. Entry into service with Mid-Continent Airlines took place in March 1940, and the extra seats satisfied Lockheed's expectations for cheaper operating costs by putting the Lodestar's seat-mile costs to a similar level to that of the DC-3. Despite a minimal sales record of the Lodestar to US airlines due to the American airline industry being largely committed to the DC-3, the Model 18 received huge orders from foreign airlines, including South African Airways, Trans-Canada Airlines, and BOAC.

Left: Lockheed C-60 Lodestar in flight

Right: A Lockheed R5O-1, staff transport for the Secretary of the Navy, San Francisco, August 4, 1941

With the US building up its military aviation strength in 1940-1941, many Lodestars were impressed into service as the C-56, while many new-build Lodestars were designated C-60 by the US Army Air Force and R5O by the US Navy and US Marine Corps.* Ten Lodestars powered by two Pratt & Whitney R-1690 Hornets were designated C-59 and delivered to the Royal Air Force, while the C-57 designation was allocated to several Lodestar airframes fitted with the Pratt & Whitney R-1830 Twin Wasp engines (three were converted C-60s). Other foreign customers of the military Lodestars included New Zealand, Norway, Australia, Brazil, Canada, Haiti, Israel, Mexico, Netherlands, and South Africa; one Lodestar delivered to Brazil had been designated C-66 by the US Army Air Force and would later serve as the presidential transport of Brazilian President Getúlio Vargas (Francillon 1982). Meanwhile, the Lodestar would eventually spawn the a dedicated patrol bomber for the US Navy, the PV-1 Harpoon, which was used by the USAAF as the B-34 Lexington and B-37, as well as the armed forces of British Commonwealth countries. A revised version of the PV-1, the PV-2 Harpoon, had an increased wing area, bigger bombload, and provisions for eight 5-inch HVAR rockets under the wings. In all, 625 Model 18 Lodestars were constructed.

*A 21-seat troop transport version of C-60 was planned as the C-104 (later C-60C), of which 691 aircraft were ordered (serial numbers 43-16467/17123) (Andrade 1979, p. 78). However, the C-60C/C-104 never reached the hardware phase.

Side view of Lockheed C-60A Lodestar s/n 42-32181 painted in Royal Air Force colors at the Planes of Fame Museum, Chino, California.

The first Lodestar that I saw at the Planes of Fame Museum boneyard, C-60A serial number 42-32181, was part of a batch of 52 Lodestars originally earmarked for delivery to the Royal Air Force as FK261/FK312, but that order was canceled and planes on order instead delivered to the US Army Air Force in 1942. Later, 42-32181 was sold to Aerovías Coahuila and registered XB-BOC (later XA-GUH), before being sold to American Aircraft Corporation and registered N4652V in 1954. The aircraft was eventually transferred to Arthur Struble and registered N3779G; on April 17, 1969, N3779G suffered an engine failure while flying from Seattle, Washington to the Annette Islands in Alaska, so was forced to make an emergency landing at Port Hardy Airport in Port Hardy, British Columbia. In 1988 this Lodestar was donated to the Planes of Fame Museum in Chino, being painted in RAF colors with the bogus serial AG711 so as to reflect its originally intended customer.

Lockheed C-60A Lodestar s/n 43-16462 (later registered NC44899, then NC1000B/N1000B) undergoing restoration at the Planes of Fame, Chino, California.

The other Lodestar on display in the boneyard at the Planes of Fame Museum, which is undergoing restoration, was built as a C-60A and delivered to the USAAF with the serial number 43-16462 in December 1943. After World War II, 43-16462 was sold to Aero Services on August 19, 1945, and assigned the civil registration NC44899. Nearly two years later, on March 28, 1947, the aircraft was acquired by Edwin W. Pauley and given the registration NC1000B (later changed to N1000B in 1981). In November 1985, N1000B was donated to the Planes of Fame Museum, and the civil registration for this aircraft was cancelled in December 2014. At the current time of writing, 43-16462/N1000B is undergoing restoration to static display.

The Model 18 Lodestar may be somewhat overlooked by experts on US civil/military transport planes, but this final descendant of the Lockheed Model 10 Electra would find a niche in the US Navy as a land-based maritime patrol bomber, breaking the USAAF monopoly on land-based bombers.

References:

Andrade, J. M., 1979. US Military and Aircraft Designations and Serials since 1909. Leicester, UK: Midland Counties Publications.

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

Convair's last propeller-engine flying boats: the P5Y/R3Y Tradewind and P6Y

The Convair company in San Diego, California is best known for building some of the finest American flying boats of World War II, namely the PBY Catalina and PB2Y Coronado. While visiting the Planes of Fame Museum in January 2018, I happened to notice a model of the Convair R3Y Tradewind, a turboprop-powered flying boat that most people don't think about too much, with the exception of the most talented US naval aviation historians. The R3Y, nevertheless, seemed quite interesting because it offers a window into a time when turboprop-powered flying boats promised to give the US Navy an advantage in new-generation anti-submarine and maritime patrol technologies, including minelaying, sonobuoys, and dipping sonar, only to be overtaken by ballistic missile submarines and the submarine-launched ballistic missile.

On December 20, 1944, the US Navy's Bureau of Aeronautics initiated a requirement for a maritime patrol flying boat powered by four Pratt & Whitney R-2800 Double Wasp radial piston engines and carrying 4,000 lb (1,814 kg) of bombs, which would be used for anti-submarine warfare, anti-shipping missions, and search-and-rescue. Convair, Hughes, and Martin submitted bids in early 1945, and the Convair design proposed in January 1945 had four 2,100 hp (1,544 kW) Pratt & Whitney R-2800C-14 radial piston engines, a gross weight of 105,000 lb (47,628 kg), and a crew of seven (pilot, co-pilot, navigator/bombardier, radar operator, radio operator, flight engineer, and countermeasures operator). An alternate design was proposed with four 5,000 shp (3,677 kW) Wright turboprop engines and a gross weight of 140,000 lb (63,502 kg). Both designs had a wing area of 2,625 ft² (243.87 m²) and armament for these designs comprised eight .50 caliber machine guns in four turrets (one nose turret, two waist turrets, and one tail turret) and either four 1,000 lb (453 kg) bombs, two 2,000 lb (907 kg) bombs, four 400 lb (181 kg) bombs, twelve 325 lb (147 kg) depth charges, or six 657 lb (298 kg) depth charges in internal weapons bays in the wings.

Top: A desktop model of the R3Y-1 Tradewind at the Planes of Fame Museum, photographed by me in January 2018.
Bottom left: The first XP5Y-1 prototype (BuNo 121455) taking off for its first flight on April 15, 1950.
Bottom right: An R3Y-1 Tradewind flying low over San Francisco Bay near Alameda NAS

As 1945 progressed, the BuAer decided that the performance parameters jotted out in the December 1944 specification for a new four-engine patrol flying boat only offered marginal improvement over that of the Consolidated PB2Y and Martin PB2M/JRM Mars, so the idea of a brand new flying boat with R-2800s was instantly abandoned and Convair's design solicitations were not proceeded with. and However, the Navy still wanted a new flying boat able to perform the operational roles specified in the December 1944 requirement, and on December 27, 1945, the Navy's Bureau of Aeronautics (BuAer) issued a specification for a new-generation maritime patrol flying boat designed to use gas turbine engines. Convair, Hughes, and Martin submitted bids for turboprop flying boat designs, and the Navy selected Convair's Model 117 design, assigning it the designation XP5Y-1. Technical details of the P5Y and its transport derivative, the R3Y Tradewind, have been covered in Bradley (2010, pp. 65-68, pp. 82-85), so will not be wastefully replicated here, except to say that the  P5Y/R3Y series used four Allison T40 turboprops driving counter-rotating propellers. Two XP5Y-1 prototypes were ordered on May 27, 1946, and the first prototype flew on April 18, 1950 (the second prototype never flew). However, by the time of the P5Y's first flight the Navy gave up on turboprop-powered patrol flying boats and ordered Convair to rework the P5Y design as a transport aircraft to replace the Martin JRM Mars, leading to the R3Y Tradewind (designated Model 3 by Convair), the first flight of which occurred on February 22, 1954. Eleven R3Ys were built, with the baseline R3Y-1 version retaining the nose of the XP5Y-1 and the the R3Y-2 version with a lifting nose similar to that of the Lockheed C-5 Galaxy. Unfortunately, the T40 used on the Tradewind suffered teething troubles, and when one R3Y-1 was lost en route to Alameda, California on January 24, 1958, the Navy ordered all R3Ys removed from active service and sold for scrap.  

Left: 3-view drawing of the Convair P6Y dunking sonar ASW flying boat from the Convair project documents

Right: A company scale model of the Convair P6Y 

The last Convair flying boat design to receive a US Navy designation was the Convair Model 24, designated P6Y. Aware of the pitfalls of its traditional anti-submarine warfare capabilities, Convair beginning in October 1953 explored the notion of an ASW flying boat with the capability to use dunking sonar, even constructing a large free-flight model nicknamed the "Dunker", tested in late 1955 and early 1956 (Bradley 2010, p. 99). On May 21, 1956 the US Navy issued a Request for Proposals for an ASW flying boat able to use dunking sonar to track enemy submarines. Convair responded with the Model 24, a high-wing seaplane with three Wright R-3350 Duplex Cyclones (two outboard, one above the fuselage), a boundary layer control system powered by two General Electric J85 turbojets situated behind the outboard piston engines, a wingspan of 127 feet 6 inches, a gross weight of 107,648 pounds, and a crew of 10 (Buttler 2010, pp. 152-153). (Grumman and Martin's submissions for the Class VP requirement were the G-132 and Martin Model 313/P7M respectively.) Despite falling short of the performance parameters in the requirement, the Model 24 was judged by the Navy to be superior to the Grumman and Martin designs, and in November 1956 the Navy selected the Convair design and allocated it the designation XP6Y-1. Two prototypes were ordered in February 1957, but members of the US Navy top brass who had experience with flying seaplanes were not too enthusiastic about the P6Y, viewing the operational environment of  the dunking sonar seaplane concept fairly dangerous and highly uncomfortable. As a result of this criticism, the P6Y program was canceled before any of the prototypes were built (Bradley 2010, p. 102).

References:

Bradley, R., 2010. Convair Advanced Designs: Secret Projects from San Diego 1923-1962. North Branch, MN: Specialty Press.

Buttler, T., 2010. American Secret Projects: Bombers, Attack, and Anti-Submarine Aircraft 1945-1974. Hersham, UK: Ian Allan Publishing.

Douglas transport gliders

The Douglas Aircraft Company based in Santa Monica, California (later Long Beach) is famous in the annals of US aviation history for producing a plethora of civil and military transports, including the DC-1, DC-2 (military designations: C-32, C-33, C-34, C-38, C-39, C-41, C-42, R2D), DC-3 (military designations: C-41A, C-47 Skytrain, C-48, C-49, C-50, C-51, C-52, C-53 Skytrooper, C-68, C-84, C-117, C-129, R4D, CC-129), DC-4 (military designations: C-54 Skymaster, C-114, C-116, C-117, R5D), DC-5 (military designations: C-110, R3D), DC-6 (military designations: C-112, C-118 Lifmaster, R6D), DC-7, DC-8, DC-9, C-74 Globemaster I, C-124 Globemaster II, and C-133 Cargomaster. However, one aspect of the Douglas company's design and development of transport planes that is largely overlooked by most military aviation historians is the fact that in the 1940s, Douglas itself tinkered with cargo gliders for the US Army Air Force (later US Air Force). During a visit to the Planes of Fame Museum in Chino, California in April 2019, I happened to notice a subscale plastic model of the Douglas XCG-17 prototype transport glider in the Foreign Hangar building of the museum, and it may quite surprise some historians that Douglas developed transport glider designs of its own because the vast majority of American transport gliders built in World War II were made by the Waco Aircraft Company. Therefore, I thought it would prudent to discuss the Douglas company's design and development of transport gliders.

Left: Desktop model of the Douglas XCG-17 transport glider at the Planes of Fame Museum.

Right: Douglas XCG-17 transport glider being towed during flight testing, 1944.

Following the introduction of the Douglas C-54 Skymaster military transport version of the DC-4 airliner, the US Army Air Force, facing the challenge of hauling troops and war material over the Himalayas from India to China, realized that its existing transport gliders would be unsuitable for towing over the "Hump" because of altitude, turbulence and additional payload. Therefore, it felt that a larger transport glider based on an existing powered transport plane was better suited to be towed by a C-54 over the Himalayas at higher speeds because it had much higher wing loading, and therefore withstand mountain turbulence. At the behest of Lieutenant Colonel Chet Decker, the USAAF suggested converting a C-47 Skytrain to glider configuration (Norton 2012, p. 176). One C-47 (serial number 41-18496; originally built as a Northwest Airlines DC-3 with the civil registration N69030) was earmarked by Douglas for modification to a transport glider in April 1944 and given the designation XCG-17. Conversion of the aircraft, completed on June 12, involved removing the engines and covering the engine nacelles with hemispherical domes, but also removing the radio operator and navigator spaces as well as bulkheads and wiring. The XCG-17 had a towing speed of 290 mph, a glide speed of 190 mph, with a capacity of 42 troops or 15,000 pounds (three jeeps and a 4x4 truck), carrying 3.75 times the payload capacity of the Waco CG-4. The first flight of the XCG-17 took place on June 14, 1944, and flight testing continued through the remainder of 1944. Despite satisfactory results of the flight test program, the XCG-17 was not ordered into production because the aircraft did not meet the USAAF requirement that it prove its ability to land on unimproved airfields. In any case, the war situation in Asia reached the point that the need for a large transport glider like the XCG-17 was obviated. The sole XCG-17 was sent to the boneyard at Davis-Monthan Air Force Base in August 1946, and it was eventually modified back to DC-3 configuration and sold to Mexico, where it remained in service until 1980.

Douglas C-47 "Nez Perce" (serial number 43-16229) after being converted to a transport glider, January 1946

The XCG-17 was not the only conversion of a C-47 airframe to transport glider configuration, however. In January 1946, a C-47 with the serial number 43-16229 was ferried to Nichols Field in Manila, the Philippines, for conversion to a glider transport; as with the XCG-17, the engines were removed and fairings mounted on the nacelles, but the nacelle fairings were octagonally shaped rather than hemispherical. An auxiliary power unit was taken from a B-24 Liberator to enable the operation of a radio and other electrical equipment. The converted C-47, christened "Nez Perce", flew on June 17, 1946, towed by a C-54 transport. Flight tests of the "Nez Perce" proved stellar, and later in June, the aircraft was towed by C-54 from Luzon to Tachikawa Airfield, Tokyo, with an overflight stay in Okinawa Airfield. The flight, which covered a distance of 1,800 miles, suggested that the "aerial freight train" concept of using large gliders for regular transport might be viable, but that concept never really caught on. In August, the "Nez Perce" had its piston engines reinstalled and converted back to C-47 configuration.   

Three-view drawing of the Douglas XCG-19 transport glider (after Mrazek 1977)

Douglas Aircraft's next foray into transport glider design when the USAAF's Air Service Technical Command on January 31, 1946 announced a requirement for two new assault gliders, a light glider able to carry an 8,000 pound payload and a heavy glider with a payload capacity of 16,000 pounds. The proposed gliders were to be of steel tube and monocoque construction, with provisions for loading men and military equipment into the aircraft via a ramp at the rear of the fuselage, as well as cargo space 35 feet long, 8 feet 8 inches wide, and 7 feet 11 inches high (10.67x2.64x2.41 meters) (Cox and Kaston 2019, p. 67). Douglas responded to this requirement with two designs, the Model 1028 light glider and Model 1029 heavy glider. Both proposals were similar in having a shoulder-mounted wing and an upswept rear fuselage rectangular in cross-section. The Model 1028's rear fuselage was hinged to swing sideways, while the Model 1029 had clamshell doors, each with triangular folding panels for ground clearance together with an integral ramp. Besides being intended to carry an 8,000 pound payload, the Model 1028 would be 61 feet long, with an 85 foot wingspan and gross weight of 14,200 pounds; the Model 1029, on the other hand, not only would carry a 16,000 pound payload but also have a length of 76 feet and five inches, a wingspan of 107 feet 3 inches, and a gross weight of 28,500 pounds (Cox and Kaston 2019, p. 69). The Douglas Model 1029 lost the heavy glider contract to Chase's MS-3 (designated XCG-20, later XG-20), but the Model 1028 and Chase's MS-7 won the light glider competition, receiving the designations XCG-19 and XCG-18 respectively. A mockup of the XCG-19 was inspected by USAAF officials in March 1947, but budget restrictions imposed later that year forced the USAAF to cancel the XCG-19 in favor of Chase's XCG-18, since the Chase XCG-18 prototypes were nearing completion (Mrazek 1977, p. 143).*    

Although somewhat outside the scope of this post, it should be noted that two other aircraft manufacturers in southern California issued their own proposals in response to the ASTC requirement. Hughes submitted its Model 31 and Model 32 designs, the former with an upward-swinging rear fuselage and the latter having a full-width loading ramp that formed the lower surface of the rear fuselage. North American, for its part, proposed the RD-1413 heavy glider which was unusual for having a detachable fuselage 'egg' for accommodating troops and cargo hanging from a rack under the glider (Cox and Kaston 2019, pp. 72-73). Of course, like the Douglas designs, the Hughes and North American glider proposals remained paper projects only. 

The Douglas transport glider designs represent a seldom-noticed footnote in the history of the Douglas Aircraft Company, but they also were a reminder that in the post-World War II era, the notion of large gliders designed to haul men and war materials to the battlefield was becoming a thing of the past due to the advent of helicopters and powered tactical transports.

*Although the XCG-19 and Model 1029 never reached the hardware stage and large transport gliders were rendered obsolete by powered tactical airlifters and helicopters, Douglas proposed powered derivatives of the XCG-19 and Model 1029 as the Model 1044 and Model 1072 respectively, both of them powered by Ranger XV-770 inline piston engines (Cox and Kaston 2019, p. 74). Like the XCG-19 and Model 1029, however, the Model 1044 and Model 1072 never left the drawing board.

References:

Cox, G., and Kaston, C., 2019. American Secret Projects 2: U.S. Airlifters 1941 to 1961. Manchester, UK: Crécy Publishing.

Mrazek, J., 1977. Fighting Gliders of World War II. London, UK: St. Martin's Press.

Norton, W. J., 2012. American Military Gliders of World War II: Development, Training, Experimentation, and Tactics of All Aircraft Types. Atglen, PA: Schiffer Publishing.   

Northrop YA-9 and little-known design studies for the A-X program from the Southern California aviation industry

Much has been written about the late 1960s-early 1970s A-X program by the US Air Force for a dedicated ground attack aircraft, with emphasis on the two competing aircraft involved in the A-X competition, the Fairchild-Republic A-10 Thunderbolt II and the Northrop YA-9, of which the former was declared the winner of the A-X contest. For the most part, the fly-off between the YA-9 and A-10 as part of the A-X competition was one aspect of the 'fly-before-buy' method concocted by the USAF at times whereby two or more designs for an aircraft competition were selected for prototyping, and the Pentagon could evaluate those designs to decide on which aircraft should be selected for production. During my first visit to the March Field Air Museum in Riverside, California, I got the chance to see the YA-9 for the first time in person back in December 2018, marveling at the placement of the YA-9's engines and the sleek fuselage. Thanks to project documents in the archives of southern California aircraft manufacturers contained in the books American Secret Projects: Bombers, Attack, and Anti-Submarine Aircraft 1945 to 1974 (Midland Publishing, 2010) and Convair Advanced Designs II: Secret Fighters, Attack Aircraft, and Unique Concepts 1929-1973 (Crecy Publishing, 2013), it is apparent that Northrop wasn't the only aircraft manufacturer in southern California to submit a design bid for the A-X program.

In the first two decades of the Cold War, the US Air Force viewed long-range combat aviation, strategic mobile airlift, and air defense as paramount priorities for US military aviation, putting ground attack aviation on the back burner. However, combat experience the Vietnam War involving the Douglas A-1 Skyraider highlighted pitfalls in the USAF's ground attack capabilities, so beginning in mid-1966, the Air Force launched the A-X program to begin shopping for an aircraft exclusively designed for close air support missions, including taking out Warsaw Pact armored vehicles stationed in Eastern Europe. The initial A-X requirements, which called for long loiter time, extreme survivability, and massive cannon firepower, requested that any design submission rely on use of turboprop engines. However, by May 1969, the Air Force tweaked the A-X design parameters to require that ground attack aircraft design bids be powered by turbofans (Jesse and Engbrecht 1994, p. 58).

                                                           

Unrealized A-X designs by the southern California aerospace industry: Northrop N-308 V-tailed pusher turboprop design study (top); three-view drawing of the General Dynamics (Convair) Model 70 high-wing attack aircraft (bottom left); three-view drawing of the Lockheed CL-1400-1 attack aircraft with underwing nacelles.  

No fewer than half a dozen aircraft companies submitted design bids as part of the A-X competition (see Buttler 2010, pp. 175-181). Of these companies, four of them (Convair-San Diego division of General Dynamics, Lockheed, North American, Northrop) were based on southern California. Northrop's first design studies for the A-X competition, under the N-308 designation, ranged from tractor turboprop attack aircraft designs to a V-tail attack aircraft with a Lycoming T55 turboprop in pusher configuration (Chong 2016, pp. 177-179). The Northrop YA-9 (company designation N-320) has been described extensively by Wagner (2004) and Chong (2016), but it can be readily summarized as a design with Lycoming F102 turbofan engines buried in the wing roots (similar to Russia's Sukhoi Su-25 ground attack aircraft), a single vertical stabilizer, and underwing pylons for anti-tank weapons, and prior to design of the N-320, Northrop proposed two jet-powered A-X designs, one with rear fuselage mounted turbofans and another with F102s buried in the wing roots, the latter closely resembling the YA-9 (Chong 2016, p. 185). Convair's A-X study, the Model 70, was a high-wing design powered by two General Electric TF34 turbofans slung under the wings, and it had six underwing weapons pylons with provisions for carrying bombs under the wings on the fuselage corners (Bradley 2013, pp. 261-266). Lockheed's A-X design study, the CL-1400, was quite similar to Lockheed U-2 spy plane in having engines buried in the wing roots and a pair of wing nacelles, and it had ten underwing pylons for air-to-surface weapons, two situated between the air intakes and wing nacelles, and eight outside the undercarriage (Buttler 2010, p. 180; see drawing on p. 182). Lastly, the North American NA-339 design (for which only an artist's conception exists) was apparently similar to the N-312 in having turbofans on the upper sides of the rear fuselage, and armament comprised a guns under the nose, bombs mounted under the inner wing sections and fuselage, and (unusually) wingtip-mounted rocket pods (Buttler 2010, p. 177).

Selected photos of the Northrop YA-9, losing competitor to the A-10 Thunderbolt II: second YA-9 prototype (serial number 71-1368) at the March Field Air Museum in Riverside, California; first YA-9 prototype (serial number 71-1367) in flight.

By December 18, 1970, the Northrop N-320 and Farchild Republic proposals were selected by the USAF for prototyping and a subsequent fly-off. The Northrop and Fairchild Republic designs were designated A-9 and A-10 respectively, and the first flight of the YA-9 took place on May 30, 1972 with Northrop test pilot Lew Nelson at the controls. From October 10 to December 9, the A-9 and A-10 prototypes entered a fly-off competition, and on January 10, 1973, the A-10 was declared the winner of the A-X competition. The engine arrangement probably played a role in the USAF's decision to chose the Fairchild Republic design over the Northrop design, because the Air Force top brass was concerned about the wing root-mounted engines of the A-9 being vulnerable to anti-aircraft artillery during combat missions, whereas the location of the A-10's TF34 engines on the rear fuselages were very likely to give the A-10 greater survivability in wartime conditions. Also, the F102 powerplant for the A-9 was still in the testing phase, while the TF34 used to power the A-10 had recently passed test runs, being cleared for production (Jesse and Engbrecht, 1994, p. 59).

The story of the Northrop YA-9 can be seen as one of rigorous and painstaking evaluation of various designs for jet-powered attack aircraft from southern California aircraft companies by the USAF, considering the diversity of engine layouts for the different A-X proposals conceiving by Northrop, Lockheed, North American, and General Dynamics. However, the engine layout of the YA-9 ensured that the Pentagon would deny Northrop the chance to build America's first production attack aircraft since World War II.

References:

Bradley, R., 2013. Convair Advanced Designs II: Secret Fighters, Attack Aircraft, and Unique Concepts 1929-1973.. Manchester, UK: Crécy Publishing.

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

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

Jesse, W., and Engbrecht, B., 1994. Not Quite Ten: Northrop's A-9, A-X runner-up. Air Enthusiast

64 (July–August): 57–59.

Genesis of the Lockheed C-141 Starlifter: designs for the SOR-182 competition from California

The Lockheed C-141 Starlifter earned its place in military aviation history as the first US jet-powered strategic airlifter, representing a quantum leap in US transport technology in the post-World War II era in terms of combining jet power with the strategic range and payload capacity of the propeller-driven Douglas C-124 Globemaster II and C-133 Cargomaster. I finally had the chance to see the C-141 Starlifter in person when I saw one C-141 at the March Field Air Museum in Riverside, California, especially when bearing in mind that the C-141 would serve half of the USAF's strategic airlift needs from the 1960s until 2006, when it was supplanted by the C-17 Globemaster III. However, very little emphasis has been paid to unbuilt competitors to the C-141 in most publications on strategic military aviation, including designed in southern California. Thanks to a copy of the book American Secret Projects 2: US Airlifters 1941-1961 that I received last year, I am now able to discuss strategic airlifter designs by aircraft manufacturers in southern California for the Air Force's SOR-182 requirement of 1960.

The Lockheed C-141 Starlifter (serial number 65-0257 Spirit of the Inland Empire, photographed by me in the outdoor section of the March Field Air Museum in Riverside, California), winner of the SOR-182 competition.

By the end of the late 1950s, the Military Air Transport Service (MATS) of the US Air Force saw the need for a new-generation airlifter powered by jet engines to supplant its fleet of C-124 Globemaster II piston-engine airlifters. The Boeing C-135 Stratolifter transport version of the KC-135 Stratotanker provided the USAF with an interim solution to some airlift requirements outlined by MATS, with 48 aircraft built, but it wasn't enough to truly satisfy the logistical demands issued by the Air Force in its search for a dedicated jet-powered airlifter. Therefore, two companies based in southern California with experience in building commercial and military transports, Convair and Douglas, decided to tinker with designs for dedicated strategic airlifter designs in the late 1950s. The San Diego division of Convair unveiled the 'Model 105' airlifter design with two podded pairs of Pratt & Whitney JT3D turbofans, and Douglas conceived the jet-powered Model 1467-79 and Model 2204 derivatives of the Douglas DC-8 jet airliner as well as the turboprop powered Model 1467-55. None of these proposals moved beyond the design phase, but they at least gave America's leading builders of large transport planes, especially Douglas, a starting point from which to plan for the USAF's transition to a wholly jet-powered airlifter force.

Left: A display model of the Convair (San Diego) Model 63
Right: A desktop model of the Douglas (Santa Monica) Model 2085

In May 4, 1960, the US Air Force issued its formal requirement for a jet-powered strategic airlifter able to carry the load of the C-124 Globemaster II, the SOR-182 specification. This specification stipulated that the aircraft conduct airlift missions over a distance of 4,600 miles (6,440 km) with a maximum payload of 70,000 pounds (31,780 kg), and that the new airlifter accommodate troops and battlefield vehicles within 6,000 cubic feet (170 cubic meters) of usable space within a rectangular fuselage measuring 70 feet long, 10 feet wide, and 9 feet high (21.35 m x 3.03 m x 2.75 m). Convair, Douglas, and Lockheed responded with the Model 63, Model 2085, and the GL-207-45 Super Hercules designs respectively. The Convair Model 63, like the earlier 'Model 105', had jet engines mounted in podded pairs under the wings, but differed in having the main undercarriage retracting into large fairings extending beyond the trailing edges of the wings. The Douglas Model 2085, on the other hand, departed from earlier Douglas jet strategic airlifter studies in its double-lobe, double-deck fuselage, whose flight deck was positioned above the cargo compartment in a manner similar to that of the cancelled XC-132 heavy turboprop-powered airlifter. Lockheed submitted a new design for the GL-207-45 Super Hercules with four Pratt & Whitney JT3D turbofans and a T-tail configuration*, the latter feature contrasting with the placement of the horizontal stabilizers below the base of the vertical stabilizer in the Douglas and Convair proposals. Convair built a mock-up of the Model 63 for the purpose of carrying out loading tests for military payloads, including Army vehicles.

After evaluating all proposals for the SOR-182 specification, the US Air Force picked Lockheed's design to be the successor to the C-124 Globemaster II, and five development aircraft were ordered under the designation C-141A. Production orders were placed for 132 aircraft (later increased to 248 units), and the first flight of the C-141 Starlifter occurred on December 17, 1963, the 60th anniversary of the Wright brothers' historic flight at Kitty Hawk, North Carolina. Deliveries of the Starlifter commenced in October 1964, with entry into service in April 1965. Over the course its service life, the C-141 Starlifter would eventually be deployed abroad to war zones in Southeast Asia, the Middle East, and the Hindu Kush during the Vietnam War, Operation Nickel Glass, Operation Desert Shield/Desert Storm, Operation Enduring Freedom, and Operational Iraqi Freedom. In one interesting chapter of its late operation career, in September 2005 it was used by the US Air Force to evacuate thousands of people seeking refuge from Hurricane Katrina. With the deployment of the McDonnell Douglas/Boeing C-17 Globemaster III picking up the pace, the C-141 itself was phased out of Air Force service in May 2006.

*The T-tail design trait seen in the C-141 Starlifter has become the tail empennage design philosophy for all American jet-powered strategic airlifters, while the tail empennage configuration of the Douglas Model 2085 and Convair Model 63 is similar to that of the Antonov An-124 Ruslan.

[EDIT: Since I wrote this post, project documents pertaining to the Convair Model 63 and photos of the Model 63 mockup came to my attention via the Secret Projects Forum and Flickr websites. My many thanks to the San Diego Air and Space Museum for alerting me to this.]

References:

Cox, G., and Kaston, C., 2019. American Secret Projects 2: U.S. Airlifters 1941 to 1961. Manchester, UK: Crécy Publishing.