A rare VTOL bird demonstrated some promising flight characteristics, until it was sunk by the rise of the helicopter.
The U.S. Army Transportation Museum at Fort Eustis, Virginia, might seem like an unlikely place to find a stable of bizarre flying machines, but some of the aircraft on display there defy imagination, especially when you consider how long ago they were built. In addition to a Piasecki VZ-8 Airgeep, Avro Canada VZ-9 “flying saucer” and de Lackner HZ-1 Aerocycle, the collection includes the prototype of a one-of-a-kind vertical takeoff and landing aircraft, the Doak VZ-4DA.
During the Cold War, the U.S. Army was open to considering most every type of aviation technology that could possibly provide an advantage over the expanding threat of the Soviet Union. Fort Eustis’ VZ-4DA, also known as the Model 16, was one result of this era.
Edmond R. Doak, president of Doak Aircraft Company in Torrance, Calif., had been experimenting with ducted fans and similar air-moving concepts since 1935, and he proposed a VTOL aircraft to the U.S. military as early as 1950. Doak convinced the Army Transportation Research and Engineering Command at Fort Eustis that his VTOL craft could combine the advantages of a conventional fixed-wing fighter (horizontal cruising ability, high speed, wing-mounted weapons, mission flexibility and lower noise and vibration than helicopters) with the helicopter’s ability to take off and land in a small area. Since the Army knew allied air bases and runways would be targeted by Soviet first strikes, it considered the latter capability vital. VTOLs, like helicopters, could also loiter longer over a target, hover and even fly backward. In short, the Doak Model 16 seemed like an ideal utility and observation platform, with potential for delivering fire to ground targets as well.
On April 10, 1956, the Army awarded Doak a contract for a single research vehicle. Only one prototype, serial no. 56-9642, would ever be built and tested. The Doak 16’s two 5-foot-diameter, ducted fiberglass fans were located on its wingtips. Positioned vertically for takeoff and landing, they were rotated into a horizontal attitude for normal forward flight—the first time this concept was successfully employed. A rotation speed of 4,800 rpm was required to achieve lift. To keep weight down, the fuselage was built of uncovered welded steel tubing—later covered with molded fiber glass at the nose and thin aluminum sheeting on the aft fuselage, once it was found the open frame hampered forward- speed trials. The wings and tail were metal.
Doak showed considerable ingenuity in his efforts to cut costs, pirating the aircraft’s landing gear from a Cessna 182, seats from a North American F-51 and duct actuators from Lockheed T-33 electric flap motors. The two-place tandem cockpit accommodated a pilot and observer, with the pilot controlling the aircraft via standard stick and rudder. Its empty weight was 2,400 pounds, and gross weight was 3,300 pounds. The aircraft had a wing span of 25 feet 7 inches, measured 32 feet long and stood 10 feet 1 inch high.
By 1958, the Doak 16 had undergone several test flights at Torrance Municipal Airport. Its first hovering flight took place on February 25, 1958, and on May 5, 1959, the prototype made its first conversion from vertical to horizontal flight, and vice-versa. Soon the Doak 16 had completed 50 hours of flight-testing, including 32 hours in a test stand and 18 hours of tethered hovering, plus taxiing. In the process a few undesirable flight characteristics came to light, such as a tendency of the aircraft to nose-up during transition from hovering to forward flight, and short takeoff and landing performance that was below expectations. But engineers believed those problems were all solvable.
Transferred to Edwards Air Force Base in October 1958, the Doak 16 underwent another 50 hours of testing, in the course of which it logged some promising performances. The VTOL’s single 825-hp Ly – coming T53-L-1 turbine power plant gave it a maximum speed of 230 mph, a cruising speed of 175 mph and range of 250 miles. A “T” box on the engine transmitted power to the ducted fans via a 4-inch tubular aluminum shaft and two smaller steel shafts. The aircraft’s service ceiling was 12,000 feet, and its flight endurance was one hour—performance that warranted its acceptance by the Army in September 1959. Officially designated the VZ-4DA, the prototype was passed on to NASA Langley Research Center in Hampton, Va., for further testing.
Late in 1960, a recession in the aerospace industry forced Edmond Doak to lay off 90 percent of his employees. For a time Doug las Aircraft took over the VZ-4DA project, purchasing the patent rights and engineering files. Douglas also hired four of the Doak engineers to continue their work at El Segundo. They installed a larger engine and made some structural improvements.
After three more years of testing, however, the Army withdrew the VZ-4DA from active trials. NASA subsequently acquired it. In 1973 it was transferred to Fort Eustis, where it languished in storage for a time. What led to the demise of the VZ-4DA as a viable Army aircraft? During the Doak 16’s development, the helicopter had emerged as the Army’s preferred mode of transport. As a result, it concentrated on funding rotor craft at the expense of the unconventional prototypes it had previously considered putting into production.
Numerous black and white photographs of the Doak 16 VZ-4DA show it was given two different paint schemes during testing. Today, at the U.S. Army Transportation Museum, the aircraft has acquired yet another. Now sheltered from the elements in the covered outdoor Aviation Pavilion, the Doak one-off sports a bright orange nose and dark green fuselage, with white duct cowlings. Its paintwork may be chipped and its fuselage dented—reminders of its hard life at the hands of engineers and test pilots—but otherwise this unusual bird still looks as ready for a quick takeoff as it did more than five decades ago.
Originally published in the July 2014 issue of Aviation History. To subscribe, click here.
