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.