The Alcor Duo-4 was a high wing cabin aircraft, unusually powered by a pair of four cylinder straight engines mounted horizontally either side of the nose. After an accident it was rebuilt with six cylinder engines, becoming the Alcor Duo-6. The name Alcor derived from ''A''llan ''L''ockheed ''Co''rporation.

Design and development

Apart from their engine cowlings the Duo-4 and the rebuilt Duo-6 had identical structures. They had ply-covered cantilever

high wing A monoplane is a fixed-wing aircraft configuration with a single mainplane, in contrast to a biplane or other types of multiplanes, which have multiple planes. A monoplane has inherently the highest efficiency and lowest drag of any wing confi ...

s which tapered outwards both in plan and thickness, built around two box spars. Their

aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around ...

s were inset. Both were powered by air-cooled Menasco engines within carefully streamlined cowlings. The Menascos were mounted horizontally, head to head, on the nose of the fuselage so their propeller shafts were much closer together than on most conventional twin-engined aircraft, producing handling generally nearer to that of a single-engined design. On the Duo-4 the tips of the two-bladed propellers could be as little as apart. The Duo-4 had

Menasco C-4 The Menasco Pirate series were four-cylinder, air-cooled, in-line, inverted aero-engines, built by the Menasco Motors Company of Burbank, California, for use in light general and sport aircraft during the 1930s and 1940s. The Menasco engines c ...

and the Duo-6 ,

supercharged In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement. The current categorisation is that a supercharger is a form of forced induct ...

Menasco C-6S engines. The rectangular cross-section, ply-covered fuselage had a Cr/Mo structure. On the Duo-6 pilot and co-pilot sat side by side in an enclosed cockpit under the wing leading edge and the passenger cabin behind them, with two windows on each side, could be configured to hold four or six seats. Two separate baggage compartments provided a combined volume of . Entry was via a port side door. There is less detail about the lower-powered Duo-4 but it is recorded as a five place aircraft. The fuselage tapered to a conventional tail of rounded profile and plan. Like the wing the tail had wooden structure and ply covering. Its tailplane, mounted at mid-fuselage, was in-flight adjustable for trim. The Duos had conventional, fixed, split axle landing gear with axles and drag struts mounted on the fuselage centreline. On each side a long, near-vertical leg, equipped with a hydraulic shock absorber, joined the outer end of the axle to the forward spar. The wheels, fitted with brakes, were enclosed under spats. The first flight of the Duo-4 was in 1930, piloted by Frank Clarke, though there is some uncertainty about the Menasco sub-type used. By 18 March 1931 Menasco C-4s were fitted when it was flown from

Muroc Dry Lake Rogers Dry Lake is an endorheic desert salt pan in the Mojave Desert of Kern County, California. The lake derives its name from the Anglicization from the Spanish name, Rodriguez Dry Lake. It is the central part of Edwards Air Force Base as its ...

by E.L. Remelin. Later that month it was damaged by a wind gust and, though damage was slight, funding problems slowed the rebuild. Lockheed used the three year delay to fit C-6S engines which almost doubled the engine power. The first flight of the Duo-6 was in March 1934, piloted by Frank Clarke at Alhambra airport. Soon after, test flights were made with one propeller removed. The Duo-6 took off from an extended run, climbed at then performed a series of right- and left-handed wingovers, handling much like a single-engined aircraft despite the power asymmetry. In October 1934 U.S. regulations limited commercial use of single-engined passenger aircraft, offering the Duo-6 a market opportunity but it was damaged again in 1935 and Alcor concentrated on a new, low wing design with a similar engine layout, the

Alcor C-6-1 Junior The Alcor Junior was a small, six passenger, twin-engined airliner built in the U.S. and flown in 1938. As on Alcor's earlier Duo-4 and Duo-6, its inline engines were mounted horizontally to minimize their separation and drag. Only one was bu ...

Specifications (Duo-6)

References

{{reflist, refs= {{cite journal , title=Test "Olympic" Twin-engined Cabin 250 horsepower Monoplane , journal=Aero Digest, date= April 1931, volume=18, issue=4 , page=214 , url=https://archive.org/details/aerodigest1819unse/page/214/mode/1up {{cite journal , title=New Alcor successfully flown, journal=Aero Digest, date= April 1934, volume=24, issue=4 , page=42 , url=https://archive.org/details/aerodigest2419unse/page/n293/mode/1up {{cite journal , title=Allan Lockheed's Twin-motored ''Alcor'', journal=Aero Digest, date= June 1934, volume=24, issue=6 , page=42-3 , url=https://archive.org/details/aerodigest2419unse/page/42/mode/1up {{cite journal , title=Alcor Duo-6, journal=Aero Digest, date= April 1935, volume=26, issue=4, page=50, url=https://archive.org/details/aerodigest2619unse/page/n317/mode/1up {{cite web , url=http://www.aerofiles.com/_al.html, title=Aerofiles, author= , date= , publisher= , accessdate=18 September 2020 {{cite web , url=https://oldmachinepress.com/2013/10/18/alcor-duo-4-duo-6-and-c-6-1-transports/, title=Old Machine Press - Alcor Duo-4, Duo-6, and C-6-1 Transports, author=William Pearce , date=18 October 2013 , publisher= , accessdate=18 September 2020 Twin piston-engined tractor aircraft High-wing aircraft 1930s United States airliners

Duo Duo may refer to: Places *Duo, West Virginia, an unincorporated community and coal town in Greenbrier County, West Virginia *Duo, Tampere, a shopping centre in Hervanta, Tampere, Finland * DUO, a twin-tower development in Singapore Arts, enterta ...

Aircraft first flown in 1931