The Doak VZ-4 (or Doak Model 16) was an American prototype

Vertical Takeoff and Landing A vertical take-off and landing (VTOL) aircraft is one that can take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust-vectoring fixed-win ...

(VTOL) aircraft built in the 1950s for service in the

United States Army The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cla ...

. Only a single prototype was built, and the U.S. Army withdrew it from active trials in 1963.

Development

Edmund R. Doak, Jr., a self-taught engineer and vice president of

Douglas Aircraft Company The Douglas Aircraft Company was an American aerospace manufacturer based in Southern California. It was founded in 1921 by Donald Wills Douglas Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas; it then operated as ...

, founded Doak Aircraft Company in Torrance,

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

, in 1940. The company grew to 4,000 employees during World War II, with subcontracts from every major American aircraft manufacturer. These included molded plywood fuselages for trainers such as the AT-6 and

Vultee BT-13 The Vultee Aircraft Corporation became an independent company in 1939 in Los Angeles County, California. It had limited success before merging with the Consolidated Aircraft Corporation in 1943, to form the Consolidated Vultee Aircraft Corporat ...

, and doors, hatches and gun turrets for a multitude of aircraft. Doak proposed a VTOL aircraft to the U.S. Armys Army Transportation and Research and Engineering Command at

Fort Eustis Fort Eustis is a United States Army installation in Newport News, Virginia. In 2010, it was combined with nearby Langley Air Force Base to form Joint Base Langley–Eustis. The post is the home to the United States Army Training and Doctrine Co ...

Newport News Newport News () is an independent city in the U.S. state of Virginia. At the 2020 census, the population was 186,247. Located in the Hampton Roads region, it is the 5th most populous city in Virginia and 140th most populous city in the Uni ...

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...

, in 1950. He touted the aircraft as able to take off and land in a small area, hover and loiter over a target area, and fly backwards like a

helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...

without the noise and vibration of a helicopter, while also having the horizontal cruising ability, high speed, wing-mounted weapons, and mission flexibility of a conventional

fixed-wing A fixed-wing aircraft is a heavier-than-air flying machine, such as an airplane, which is capable of flight using wings that generate lift caused by the aircraft's forward airspeed and the shape of the wings. Fixed-wing aircraft are distinct ...

fighter aircraft Fighter aircraft are fixed-wing military aircraft designed primarily for air-to-air combat. In military conflict, the role of fighter aircraft is to establish air superiority of the battlespace. Domination of the airspace above a battlefield ...

. Knowing that a

Soviet The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...

attack on airbases would interdict takeoffs and landings by conventional aircraft, the Army found Doaks proposal attractive, and on 10 April 1956, it awarded Doak a contract to produce a single prototype for use as a research aircraft. The aircraft, designated the Doak Model 16 by the Doak company and assigned the serial number 56-9642, was originally powered by an Lycoming YT53

turboprop A turboprop is a turbine engine that drives an aircraft propeller. A turboprop consists of an intake, reduction gearbox, compressor, combustor, turbine, and a propelling nozzle. Air enters the intake and is compressed by the compressor. Fuel ...

engine mounted in the

fuselage The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraft t ...

, later replaced by a Lycoming T53-L-1

turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...

.Harding 1990. The engine drove two wingtip-mounted

fiberglass Fiberglass (American English) or fibreglass (Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass cloth ...

tilting

ducted fan In aeronautics, a ducted fan is a thrust-generating mechanical fan or propeller mounted within a cylindrical duct or shroud. Other terms include ducted propeller or shrouded propeller. When used in vertical takeoff and landing (VTOL) applicatio ...

propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...

s through a "T" box on the engine that transmitted power to the propellers via a 4-inch (102-mm)

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...

tubular shaft and two smaller shafts. Each propeller was 48-inch (1.22-meter) in diameter and the duct outer diameter was 60-inches (1.52-meter)). The fans were positioned vertically for takeoff and landing – with a rotation speed of 4,800

rpm Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...

required for liftoff – and rotated to a horizontal orientation for horizontal flight, the first time this VTOL propulsion concept was tested successfully. The aircraft had metal wings and a metal

tail The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, r ...

. To save weight, the aircraft originally was constructed of uncovered welded

steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...

tubing, but after it was found that the open frame interfered with forward-speed tests, molded fiberglass was installed over its nose section and thin

sheeting over its aft

. It accommodated a two-person crew, with a pilot and observer seated in tandem in the

cockpit A cockpit or flight deck is the area, usually near the front of an aircraft or spacecraft, from which a Pilot in command, pilot controls the aircraft. The cockpit of an aircraft contains flight instruments on an instrument panel, and the ...

. The pilot used a standard stick and rudder to control the aircraft. Its landing gear were taken from a

Cessna 182 Skylane The Cessna 182 Skylane is an American four-seat, single-engined light airplane built by Cessna of Wichita, Kansas. It has the option of adding two child seats in the baggage area. Introduced in 1956, the 182 has been produced in a ...

, its seats from a

North American P-51 Mustang The North American Aviation P-51 Mustang is an American long-range, single-seat fighter aircraft, fighter and fighter-bomber used during World War II and the Korean War, among other conflicts. The Mustang was designed in April 1940 by a team ...

, and its duct actuators from a

Lockheed T-33 Shooting Star The Lockheed T-33 Shooting Star (or T-Bird) is an American subsonic jet trainer. It was produced by Lockheed and made its first flight in 1948. The T-33 was developed from the Lockheed P-80/F-80 starting as TP-80C/TF-80C in development, then d ...

.Stevenson 2014, pp. 14–15. Flight testing began at

Torrance Municipal Airport Torrance, also spelled Torrence, is an originally Scottish surname. Torrance may also refer to: Places *Torrance, California, United States * Torrance, East Dunbartonshire, Scotland **Torrance railway station *Torrance, Ontario, Canada *Torrance, ...

, and Doak completed several tests by 1958. The Model 16 hovered for the first time on 25 February 1958, and the first transition from vertical to horizontal flight (and back again) took place on 5 May 1958. Although the prototype generally was successful, its short takeoff and landing performance was less than hoped for and it displayed a tendency to nose up while making the transition from vertical to horizontal flight.Stevenson 2014, p. 15. Doaks engineers believed that they could solve the prototypes problems, and after taxiing testing, 32 hours of flight testing in a test stand, and 18 hours of tethered hovering, the aircraft was transferred to

Edwards Air Force Base Edwards Air Force Base (AFB) is a United States Air Force installation in California. Most of the base sits in Kern County, but its eastern end is in San Bernardino County and a southern arm is in Los Angeles County. The hub of the base is E ...

, California, in October 1958. It underwent another 50 hours of testing, in which it proved capable with the turbine engine of achieving a maximum speed of 230 mph (370 km.hr), a cruise speed of 175 mph (282 km/hr), a range of 250 miles (403 km), an endurance of one hours, and a service ceiling of 12,000 feet (3,658 meters).

Operational history

The U.S. Army accepted the prototype in September 1959, designated it the Doak VZ-4DA, and passed it to the NASA

Langley Research Center The Langley Research Center (LaRC or NASA Langley), located in Hampton, Virginia, United States of America, is the oldest of NASA's field centers. It directly borders Langley Air Force Base and the Back River on the Chesapeake Bay. LaRC has fo ...

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, Virginia, for further testing. When Doak laid off 90 percent of his employees late in 1960 due to a recession in the aircraft industry,

Douglas Aircraft The Douglas Aircraft Company was an American aerospace manufacturer based in Southern California. It was founded in 1921 by Donald Wills Douglas Sr. and later merged with McDonnell Aircraft in 1967 to form McDonnell Douglas; it then operated as ...

took over the project, purchased its

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...

rights and engineering files, and hired four engineers from Doak to continue work on the VZ-4DA. Work continued on the VZ-4DA until 1963, when the U.S. Army decided that the helicopter would meet its VTOL requirements, shifted funding away from the design and testing of unconventional VTOL aircraft to the design and procurement of helicopters, and discontinued trials of the VZ-4DA. The

National Aeronautics and Space Administration The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding th ...

(NASA), later acquired the aircraft. In 1973, it was transferred to Fort Eustis and placed in storage.

Preservation

The VZ-4DA was eventually donated to the U.S. Army Transportation Museum at Fort Eustis, Virginia, where it is on public display with other aircraft in the museum's outdoor Aviation Pavilion. Other Doak artifacts are preserved at the

Western Museum of Flight The Western Museum of Flight (WMOF) is an aviation museum located at Zamperini Field, the municipal airport in Torrance, California. WMOF is operated by the Southern California Historical Aviation Foundation. It houses not only historic aircraft, ...

in Torrance, California.

Operators

;USA *

(NASA) *

Specifications

References

Bibliography

* ''The Illustrated Encyclopedia of Aircraft'' (Part Work 1982–1985). London: Orbis Publishing, 1985. * Harding, Stephen. ''U.S. Army Aircraft Since 1947''. Shrewsbury, UK: Airlife Publishing, Ltd., 1990. . * Lobb, Charles. ''Torrance Airport''. Charleston, South Carolina: Arcadia Publishing, 2006. . * Parker, Dana T. ''Building Victory: Aircraft Manufacturing in the Los Angeles Area in World War II'' . Cypress, California: Dana T. Parker Books, 2013. . * Stevenson, Roy, "Doak's One-Off," ''Aviation History'', July 2014, pp. 14–15. * Swanborough, F.G. and Peter M. Bowers. ''United States Military Aircraft since 1909''. London: Putnam, 1963.