Little-known Northrop flying wings of 1940s-early 1950s, part 1: Northrop EB-35B turboprop testbed flying wing

What a better way to start the new year with a blog post about the development of the original flying wing bombers designed by Jack Northrop in the 1940s and early 1950s?  

The story of the original flying bombers designed and built by the Northrop company in the 1940s is well-documented in literature on flying wings and US military aviation in World War 2 and the Cold War, as highlighted by the Northrop XP-79 prototype flying wing fighter and the Northrop B-35 and B-49 flying wing bombers. However, lost in talk regarding the development of the B-35/B-49 flying wing bomber development lineage and large Northrop flying wings in general is the fact that Jack Northrop considered modifying one B-35 airframe for testing his company's homegrown design for a turboprop engine (designation EB-35B) but also flying wing bombers more advanced than B-35 and B-49 as well as passenger/cargo flying wing projects. Tony Chong's recently published book Flying Wings & Radical Things: Northrop's Secret Aerospace Projects & Concepts 1939-1994 (Specialty Press, 2016) has helped to illuminate these little-noticed Northrop flying wings by providing a wealth of previously published and unpublished This post will be the first part of a three-part blog post series about unbuilt Northrop flying wing projects, and intends to touch upon the Northrop B-35 testbed for the Turbodyne XT37 turboprop, the EB-35B.

Beginning in 1939, the newly formed Northrop Corporation in Hawthorne, California, began a private venture aimed at developing a turboprop engine, and in 1941 the company was awarded a joint US Army/US Navy contract for design, analysis, and fabrication of a prototype turboprop engine, the Turbodyne I (company designation: N-10). (The contract was eventually amended to cover the construction of two turboprop prototypes.) The Turbodyne I Given its lack of experience in making aircraft engines with its nascent financial resources, Northrop formed a joint venture with the Joshua Hendy Iron Works of Sunnyvale, California, the Northrop-Hendy Corporation, to manufacture the Turbodyne I prototypes. The Turbodyne I prototype turboprops were completed on schedule and the engine began test runs in 1944. However, both prototypes failed during test runs and the Navy withdrew from the Turbodyne program in early 1945. Meanwhile, the US Army Air Force awarded Northrop a contract to build a more advanced version of the Turbodyne I under Wright Field Air Material Command designation MX 562, which was to have an output of 4,000 hp at 500 miles per hour. This turboprop engine design, given the company designation N-19 by Northrop, became known by its official designation XT37. The XT37-NA-3 was intended to deliver 10,000 shp.*

*Since this post is only intended to be a systematic treatment of the Northrop EB-35B, I have opted to only give some brief details on the powerplant intended for the Northrop (Turbodyne) XT37 turboprop.

The Northrop (Turbodyne) XT37 turboprop, which was intended to power the EB-35B.

In the late 1940s, with the XB-35 flying wing bomber design already made obsolete by the Jet Age thanks to its use of piston engines, and the jet-powered YB-49 having a lower operating range with a decent bombload than the B-35, Northrop investigated proposals for equipping the B-35 airframe with turboprop propulsion in hopes of combining the range of the B-35 with the speed of the B-49. Given that test runs of the latest version of the XT37 found the engine to approach the expected 10,000 shp output, the United States Air Force saw the XT37-NA-3 as a potentially fuel-efficient alternative to the turbojet, so on November 1, 1948, a contract was issued authorizing conversion of the first XB-35 prototype to a testbed for the XT37 under the designation ERB-35B (company designation: N-45) (note: the letter "E" stood for "Exempt", not "Electronic"). The proposed conversion of the first XB-35 to ERB-35B configuration entailed replacing four of the eight buried Allison J35s with two XT37s and placing two of the eight J35s in pods under the wings; the propellers for the XT37s would be mounted in pusher configuration, and the engine inlets were to protrude from the leading edge of the center section of the aircraft. After the Air Force cancelled its production contract for the RB-49 photo-reconnaissance version of the YB-49 on January 14, 1949, the November 1948 contract was emended whereby the XB-35 was to be salvaged, the ERB-35B was redesignated EB-35B, and the last YB-35 airframe (serial number 42-102378) was earmarked for conversion to the EB-35B. Northrop planned to have the EB-35B conduct the first 30 hours of its flight testing with one XT37 installed, with a later scheme to have the EB-35B fitted with both XT37s during the next 30 flight testing hours (Chong, p. 60).

The EB-35B was not the only iteration of the B-35/B-49 development lineage that was contemplated by Northrop to be fitted with Turbodyne turboprops. One design iteration of the planned RB-49, the RB-49C (company designation: N-37B), was to have two XT-37-NA-3 turboprops alongside two General Electric J47 turbojets, and Northrop envisaged additional variants of the RB-49 using the XT37-NA-3 turboprop under the company designations N-46 and N-47. However, none of these studies progressed beyond the design phase.

Top: 3-view drawing of the Northrop EB-35B testbed for the Northrop XT37 turboprop engine.
 Bottom left: Northrop EB-35B under construction at Northrop plant in Hawthorne, California, October 27, 1949.
Bottom right: Desktop model of the Northrop EB-35B at the Planes of Fame Museum, Chino, California.

Unfortunately, the EB-35B, despite potentially offering the promise of a gas turbine powered derivative of the B-35 with greater range than the B-49, was not to be. On March 30, 1950, the EB-35B was nearing completion at the Northrop plant in Hawthorne when the USAF ordered the EB-35B to be scrapped, presumably concerned that the EB-35B might be plagued by the same vibration troubles with the long propeller shafts that had bedeviled the XB-35 during flights. Despite offers from Northrop employees to have the EB-35B completed just for the sake of testing the XT37 in flight, Jack Northrop declined that suggestion because he knew the Air Force would not be happy if the EB-35B were not broken for scrap. Consequently, the EB-35B was destroyed by the breaker's torch without ever having had the chance to fly. As the EB-35B was consigned to California aviation history's dustbin, so was the Turbodyne, for in September 1950 Northrop sold the designs and patents for the Turbodyne engine to General Electric.

In an interesting footnote to this post, Chong (2016, pp. 27-28) notes that the N-10 designation allocated to the Turbodyne I turboprop was also used for a Northrop design for a cargo flying wing looking like a scaled down XB-35 with a wingspan of 114 feet and a crew of four (pilot, co-pilot, navigator, loadmaster). The N-10 flying wing project had flaps running the full length of the wing from the outboard of the propeller shaft nacelles to the wingtips, and cargo bay doors might have slid or dropped open to allow for cargo to be loaded into or unloaded from the cargo bay of the aircraft. It is unclear why the N-10 designation was re-used for Northrop's cargo flying wing proposal; Chong (p. 28) suggests that Northrop conceived this design for the 1941 USAAC/USAAF transport competition but never submitted it as a bid and instead supplanted it with the Navy Turbodyne contract.

References:

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