Takeaways from visit to Western Museum of Flight, January 2020, part 1: desktop models of exotic SoCal aircraft

While visiting the Western Museum of Flight in Torrance, I had finished discussing with the museum staff my previous blog posts on advanced 1950s Northrop flying wing bomber designs and Northrop cargo transport projects, as well as the recent maiden launch of the Boeing CST-100 Starliner last year, and eventually I was touring the museum's main building when a trio of desktop models of planes developed in Southern California caught my eye while touring the museum's displays. Although the glass case displays at the museum contain notable Northrop products like the YF-23 Black Widow II/Grey Ghost prototype stealth fighter that lost to the F-22 Raptor as well as the Northrop YF-17 Cobra prototype lightweight fighter and 1940s flying wings, but also desktop models of the North American X-15 and Douglas C-124 Globemaster II heavy airlifter, the three desktop models I came across had never been displayed in a glass case before during my previous visits of the Western Museum of Flight. 

Left: Desktop model of the North American F-107 prototype fighter-bomber (donated to WMoF by Donald Spaulding)

Bottom: First F-107 prototype (serial number 55-5118) in flight over the Mojave Desert, southern California 

The first of the three desktop models that caught my eye while visiting the Western Museum of Flight worth discussing is a 1/40 scale desktop model of the North American F-107 prototype fighter-bomber donated by Donald Spaulding. While gazing at a glass case containing memorabilia and artifacts concerning the history of aviation development in Southern California, I happened to notice an F-107 desktop model inside a glass case containing photos of the U-2 Dragon Lady and SR-71 Blackbird spyplanes but also a copy of a memoir by Ben Rich (1925-1995) detailing his years as head of the Lockheed Skunk Works from 1975-1991. The F-107 is a plane that most military aviation gurus don't think about too much, but it was one of the most advanced US combat planes built by North American Aviation apart from the B-70 Valkyrie trisonic heavy bomber. North American Aviation made its mark on US military aviation history with the WW2-era P-51 Mustang that escorted vast armadas of B-17 and B-24 bombers over Nazi-occupied Europe, the F-86 Sabre swept-wing jet fighter of Korean War fame, and the first US supersonic jet fighter, the F-100 Super Sabre. The F-107 began life as an advanced variant of the F-100, the F-100B (company designation NA-212) in response to a USAF requirement for supersonic fighter-bomber to replace the F-84F Thunderstreak. Although supersonic like the F-100, the F-100B differed in having an engine intake atop the fuselage and pointed nose for housing the  interception radar, leading the USAF to redesignate the F-100B as the F-107. Three prototypes were built, the first one taking to the skies on September 10, 1956. The F-107 performed well in flight tests, but the USAF selected the Republic F-105 Thunderchief over the F-107 as the next American fighter-bomber in 1957. Fortunately, two of the three F-107 prototypes survived the breaker's torch and are now in museums in the US, with 55-5118 displayed at the Pima Air & Space Museum in Arizona, and 55-5119 on display at the National USAF Museum near Wright-Patterson Air Force Base in Dayton, Ohio. North American pitched a carrier-based derivative of the F-107 to the US Navy in 1955, unofficially dubbed "FJ-5" and "Improved FJ-4" by the company, but this proposal did not materialize.

Top: Northrop X-21 desktop model at Western Museum of Flight.

Bottom: Northrop X-21 serial number 55-0408 in flight over the Mojave Desert.

Another desktop model of a plane built in southern California that was worth getting my attention at the Western Museum of flight is of the Northrop X-21 experimental aircraft. The X-21 was basically a technology demonstrator for a large transport aircraft equipped featuring long-span wings with laminar flow control surfaces, being based on the airframe of the Douglas WB-66D Destroyer. Northrop believed that a large aircraft sporting a wing with laminar flow control properties could have better fuel efficiency, greater range, and higher endurance, pointing out that an 80 percent laminar wing might reduce overall drag by 25 percent. Therefore, two WB-66Ds (serial numbers 55-0408 and 55-0410) were modified by Northrop to feature a new wing with laminar flow control systems spanning 93 feet 6 inches (28.51 meters) and the underwing Allison J71 turbojets removed and replaced by two General Electric J79 turbojets mounted on the sides of the rear fuselage underneath the horizontal stabilizer, thus being designated X-21. The first flight of the X-21 took place on April 18, 1963, but experience from flight testing suggested that the laminar flow control system were prone to damage from ice, rain, dirt, and dust. Consequently, the US Air Force and NASA decided that application of the laminar flow wing to civil and military transport aircraft was impractical. Both X-21s survive in a derelict state at Edwards Air Force Base, but neither has been restored for display at air museums in southern California.

Desktop model of the McDonnell Douglas MD-91 propfan airliner project

The third and final desktop model worthy of discussion that caught my eye while I was at the Western Museum of Flight is of the McDonnell Douglas MD-91, a proposed propfan airliner design of the 1980s. Given the high price of oil in the 1980s, the McDonnell Douglas company, capitalizing on the MD-80 twin-jet airliner, envisaged derivatives of the MD-80 series with two propfan engines (either General Electric GE36 or Pratt & Whitney/Allison 578) under the designations MD-91 and MD-92. Propfan technology (turbofans with swept-blade propellers) was seen by the aeronautical community as offering the benefits of both turbofans and turboprops, combining the fuel economy of turboprop engines with the speed and performance of turbofans in order to offer better fuel economy than turbofan engines. The MD-91 design was to seat 110-120 passengers, while the 157 foot long MD-92 would have seated 165 passengers. An all-new McDonnell Douglas propfan-powered airliner, the MD-94, was similar in size to the MD-92 and could seat 160-180 passengers. Entry into airline service for the MD-91, MD-92, and MD-94 was planned for 1991, 1992, and 1994 respectively. There was also a project for a maritime patrol version of the MD-91 (informally called "P-9D") as a successor to the Lockheed P-3 Orion, but that proposal lost out to the Lockheed P-7 Orion II for the P-3 replacement contract, even though the P-7 would later be cancelled in July 1990 due to cost overruns. McDonnell Douglas modified a number of MD-80s as testbeds for the propfan engines planned for the MD-91, MD-92, and MD-94, and tests were conducted in 1988. Tests with the General Electric GE36 and Pratt & Whitney/Allison 578 seemed to validate the suggested benefits of propfans, but falling oil prices in 1989 caused the airline industry to lose interest in propfan airliners, leading to the axing of the MD-91, MD-92, and MD-94 projects. For these same reasons, another US propfan airliner project, the Boeing 7J7 (J standing for Japan) was cancelled without reaching the hardware phase.

[EDIT: It came to my attention recently that North American proposed a navalized version of the F-107 under the company labels "Improved FJ-4" and "FJ-5", thanks to a detailed monograph on this project by Zichek (2011).]

References:

Zichek, J.A., 2011. North American FJ-5 Fighter: A Navalized Derivative of the F-107A (American Aerospace Archive Number 2). La Jolla, CA: American Aerospace Archive.

Little-known Northrop flying wings of 1940s-early 1950s, part 3: commercial and military transport designs

For over four decades, US aerospace companies like Boeing, Lockheed Martin, and Northrop Grumman (in concert with NASA) have tinkered with the notion of blended wing body (BWB) aircraft that could be used as airliners, air freighters, or airlifters, recognizing that a BWB design could offer greater carrying capacity and better fuel efficiency than conventional American long-range airliners like the Boeing 747, 777, and 787. However, the notion of adapting a flying wing or blended wing body design for use as a commercial airliner, cargo carrier, or airlifter is not a recent phenomenon; in the late 1940s and early 1950s, the Northrop Corporation investigated the possibility of using flying wings to carry passengers and cargo, producing the first designs for commercial flying wings.

*McDonnell Douglas (absorbed by Boeing in August 1997) tinkered with studies for flying wing/BWB designs that could carry hundreds of passengers or freight loads beginning in the late 1970s. Boeing took stewardship of design studies into passenger and commercial freight BWB aircraft that McDonnell Douglas had conceived beginning in 1988 after acquiring McDD in 1997, so I've omitted mention of McDonnell Douglas in the first paragraph of the post for convenience.

Rising Cold War tensions and the aftershocks of the Berlin Airlift prompted the United States Air Force to stress the importance of strategic heavy airlift in overseas US military operations, considering that World War II had seen American troops ferried to Europe and the Pacific via troopship. The Douglas C-74 Globemaster I and Boeing C-97 Stratofreighter designed in the WW2 era came too late for the war, but the USAF learned the hard way when dealing with the question of hauling large loads of troops and military equipment to faraway war zones in a short space of time. Meanwhile, mass air freight was very much in its infancy, with air freight being carried out largely by mail planes, and the technology of the jet airliner had just come into being with the first flight of the de Havilland D.H.106 Comet in 1949. Perhaps sensing the growing importance of heavy airlift in the post-WW2 era and the vastly enhanced carrying capacity offered by a flying wing/BWB design, Northrop decided to look into adapting its flying wing designs for use as airliners, air freighters, and airlifters.

Left: Cutaway view of the interior of the airliner version of the Northrop YB-49 flying wing jet bomber
Right: Interior of the mock-up of the airliner version of the YB-49

Beginning in the late 1940s, Jack Northrop investigated adapting the YB-49 flying wing jet bomber for use as a jet airliner. His company hired a Hollywood film studio to make a film touting the benefits of a jet airliner based on the YB-49, including the creation of a full-size mockup complete with rolling food carts and beautifully dressed actors posing as passengers. The airliner version of the B-49 would have had accommodated 50-80 passengers. However, the proposed flying wing airliner wasn't taken seriously by the airline industry in light of longitudinal instability experienced by the YB-49 during flight testing, so it never went beyond the drawing board. If Northrop had managed to get its airliner derivative of the B-49 into the hardware phase, it would have been the first US jetliner rather than Boeing 707, considering that the YB-49 derived flying wing airliner was envisaged around the time that Boeing proposed America's first design for a jetliner, the Model 473.

Left: Northrop cargo pod-carrying flying wing transport design study, 1949
Right: Three-drawing of a Northrop flying wing transport with four Allison T40 turboprops, April 1950

As I mentioned in the post about the EB-35B, Northrop had conceived a transport version of the XB-35 under the N-10 designation, but that project never came to fruition. However, by 1949, thanks to the Berlin airlift having highlighted the importance of strategic heavy airlift, Northrop returned to adapting the N-9 series for used as strategic airlifters, this time proposing a spree of flying wing airlifter designs powered by turboprop engines. One Northrop flying wing airlifter design dated April 27, 1949 had the same wingspan and outer wing panels as the B-35 and B-49 but was powered by two Allison T40 turboprops and had a raised center section housing a 75-foot long cargo pod that could accommodate either 84 combat troops or a bombardment crew and nuclear weapons (drawings in Chong, p. 69, and Cox & Kaston, p. 174). An alternative airlifter design, powered by two Northrop XT37 turboprops, retained the flat wing profile and wingspan of the N-9 development lineage and was to carry two cargo pods outboard of the T37 turboprops. Northrop's designs for cargo flying wings for the commercial market were basically based on the N-31 medium bomber design in terms of a forward fuselage section protruding from the wing and came in two iterations, one powered by four Allison T40s and another with two T37s. The Northrop commercial flying wing freighters dispensed with the external pods for cargo carriage and instead relied on hauling transit vans and they both had a cruising speed of 380-400 mph (612-644 km/h) as well as a higher aspect ratio wing to deliver greater fuel economy and range (Cox and Kaston, pp. 175-176). The T40-powered flying wing freighter was 102 feet 9 inches (31.32 meters) long with a wingspan of 184 feet 2 inches (56.11 meters), a wing area of 5,018 square feet (466.68 sq. meters), and a payload of 70,000 pounds (31,751.5 kg). The Turbodyne-powered proposal would have had the same wingspan as the B-35 and B-49 but with a slightly longer fuselage measuring 80 feet 2 inches (24.43 meters) in length, and it was to carry a payload of 66,000 pounds (29,940 kg).

Despite a marketing blitz by the Northrop Corporation trumpeting the advantages of its commercial and military cargo flying wing designs, unsurprisingly, neither the US Air Force nor the civil aviation industry had any genuine interest in these flying wing projects. And if minimal customer interest weren't enough, the Allison T40 turboprop that would have powered the four-engine Northrop flying wing transport proposals was beset by teething troubles and proved to be a complete engineering failure when it came to usage on several aircraft it powered, including the Convair P5Y and R3Y Tradewind flying boats, Douglas A2D Skyshark attack aircraft, Republic XF-84H Thunderscreech, and North American XA2J Super Savage prototype carrier-based strategic bomber. Nevertheless, the design philosophy embodied by Northrop commercial flying wing freighter designs of 1949-1950 lives on in the many designs for flying wing and blended wing body designs that have been worked on (and continue to be investigated) since the late 1970s by Boeing, Lockheed Martin, McDonnell Douglas, and Northrop Grumman.

References:

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

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

Little-known Northrop flying wings of 1940s-early 1950s, part 2: N-31 medium bomber and N-55 patrol flying wing designs

In the first part of a trio of posts discussing little-known Northrop designs for large flying wing aircraft, I discussed in detail Northrop's scheme to convert a YB-35 airframe under construction into a testbed for the Northrop XT37-NA-3 turboprop engine under the designation EB-35B, considering how Northrop touted the EB-35B as potentially leading to a fuel-efficient gas turbine-powered B-35 derivative with greater range than the jet-powered B-49. However, even though the United States Air Force cancelled the B-49 program in 1949, the Northrop Corporation continued to look into designs for advanced flying wing bombers in hopes of remedying the shortcomings of the jet-powered YB-49.

The first advanced Northrop combat flying wing from the 1940s-early 1950s interval that is worthy of discussion is the N-31 medium bomber. Even before the second YB-49 crashed over Muroc Dry Lake in June 1948, Northrop was starting to realize that it would have to start anew with novel flying wing bomber designs that could theoretically correct problems inherent in earlier Northrop flying wings like the B-35 and B-49 if it hoped to convince the US Air Force of the viability of flying wing bombers. With the Soviet Union having detonated its first nuclear weapon in present-day Kazakhstan in August 1949, Northrop was eager to develop a flying wing bomber with a bomb bay big enough to carry America's available nuclear weapons and ultimately the in-development hydrogen bomb. Multiple flying wing bomber and reconnaissance designs with either turbojet or turboprop engines were investigated under the N-31 company designation with two, four, or six engines.

3-view drawing of the Westinghouse J40-powered N-31, with accompanying specification at the top right corner

The first flying wing bomber design studied under the N-31 label was a strategic bomber powered by six Westinghouse J40-WE-6 turbojets (each with 7,500 pounds of thrust), conceived in February 1947. It was similar to the YB-49, YRB-49A, RB-49, and EB-35B in featuring vertical stabilizers on the trailing edge of the wing, but differed in having a blended wing body layout with a forward fuselage section reminiscent of the delta-wing Avro Vulcan bomber. The arrangement of the turbojets in the turbojet-powered N-31 design iteration was quite unorthodox; four of the J40s were buried between the center section of the aircraft and the vertical stabilizers, but the other two were placed on the wingtips. The jet N-31 design had a wingspan of 128 feet 4 inches (39.11 meters) and a length of 74 feet 11 inches (22.83 meters), with a crew of five and provisions for twin 20 mm cannons (0.50 caliber) in nose and tail barrel turrets. It was intended to have a combat radius of 2,022 miles (3,254 km) with a 10,000-pound bomb load, a cruising speed of 502 mph (808 km/h), and a top speed of 608 mph (978 km/h).

3-view drawing from Northrop company documents of N-31A design with two Allison T40 turboprop engines. Note the absence of upright vertical stabilizers.

The N-31A design (envisaged January 1948) had the same wingspan, length, armament, gross weight, and wing sweep and baseline N-31, but returned to some aspects of the design layout of the XB-35, especially the lack of vertical stabilizers, and it was powered by two 7,500 hp Allison T40 turboprops, possessing an operational range of 2,600 miles (4,441 km) with a 10,000-pound bomb load. The N-31B, would have been similar to the baseline N-31 but with an all-wing configuration and just the four wing-mounted turbojets, while the N-31C proposed in late April 1948 would have had two Turbodyne T37s, and the N-31F was to be a a photo-reconnaissance derivative of the N-31B (see Buttler 2010, pp. 19-20, for more details). In May 1950, two additional N-31A proposals were conceived, one with two 10,000 hp Turbodyne T37 turboprops each driving six-bladed counter-rotating propellers, a cruising speed of 500 mph (804 km/h), a top speed of 518 mph (833 km/h), a range of 2,760 miles (4,441 km) when unrefueled or 5,580 miles (8,980 km) when refueled, an empty weight of 161,540 pounds (73,227 kg), a gross weight of 222,710 pounds (101,019 kg), and a maximum altitude of 43,000 feet (13,106 meters), and another with four T40s each driving six-bladed counter-rotating propellers, an empty weight of 175,400 pounds (79,560 kg), a gross weight of 212,000 pounds (96,206 kg), a cruising speed of 506 mph (814 km/h), and an altitude of 37,000 feet (11,277 meters) (Rose 2010, p. 84). The combat radius of the T40-powered design when unrefueled was similar to that of the T37-powered proposal but had lower range with in-flight refueling were lower (4,027 miles for Allison-powered version vs. 5,580 miles for T37-powered design). 

Northrop N-55 (left) and N-55A (right) design studies for a long-range patrol flying wing

Northrop's study of advanced combat flying wings in the 1940s and early 1950s was not confined to bomber aircraft. Prior to the cancellation of the RB-49, Northrop looked at the potential of the flying wing to be used for long-range patrol missions. With the US Air Force promulgating an across-the-board scheme to improve American air defense systems, which partly led to the WS-201 (aka 1954 Interceptor) requirement that resulted in development of the delta-winged Convair F-102 Delta Dagger and F-106 Delta Dart as well as the trisonic Republic XF-103 Thunderwarrior, the Northrop company adapted the YB-49 airframe into a design for a patrol plane under the designation N-55. The wingspan of the N-55 would be same as that the B-35 and B-49, but the fuselage design would mirror that of the N-31 flying wing designs in utilizing fore and aft crew nacelle extensions, giving the plane a length of 61.8 feet (18.8 meters). The N-55 concept was basically not just intended for long-range patrol missions but also would serve to function as an airborne radar picket ship that could fire air-to-air missiles against enemy planes that intruded into North American airspace. As noted by Chong (p. 66), search radars operating in the X-band or S-band ranges would be internally accommodated in the nose and tail of the N-55. Two N-55 variants were studied, the baseline N-55 powered by two Northrop XT37-NA-3 turboprops each delivering 10,000 hp and armed with 44 AAM-N-2 (later GAR-1/2/3/4/5/6/9 and finally AIM-4) Falcon air-to-air missiles (of which a dozen would be fired from leading edge tubes with eyelid covers, the rest being housed in two weapons bays), and the N-55A using six Westinghouse J40 turbojets. The turboprop-powered N-55 looked like a cross between the baseline N-31 and later N-31A versions because it had two T37 turboprop engines and a pair of vertical stabilizers, while the engine arrangement of the N-55A resembled that of the YB-49, with the jet engines buried between two pairs of vertical stabilizers on the wing's trailing edge.

But the N-31 and N-55 flying wing studies were all for naught, despite offering potential remedies to the stability and range problems that made the YB-49 unsuitable as a bombing platform and ineligible to carry large nuclear and thermonuclear weapons. Continued concerns about longitudinal instability of flying wings combined with evolving air defense priorities meant that the N-31 and N-55 were never green-lighted for full-scale development by the US Air Force, so they remained paper projects only.
   

References:

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

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

Rose, B., 2010. Secret Projects: Flying Wings and Tailless Aircraft. Hersham, UK: Ian Allan Publishing.

   

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.