Herrick HV-2A Vertaplane

Manufacturer

Gerard P. Herrick

Physical Description

Fabric-covered; tubular steel frame; with low wing and Kinner B-5 engine.

Summary

Herrick HV-2A Vertaplane

During the 1950s a number of aircraft manufacturers experimented with convertiplane designs. These Vertical Takeoff and Landing (VTOL) aircraft were equipped with both a helicopter rotor system and conventional airplane wings to achieve some of the speed advantages of an airplane in addition to the vertical takeoff capabilities of the helicopter. The first successful convertiplane experiments began before the advent of the practical helicopter Gerard P. Herrick and his HV-2A in the 1930s. He combined an innovative autogyro rotor system with a conventional airplane resulting in an aircraft capable of autogyro-style short takeoffs and near-vertical landings, but with the greater cruising speed of a typical biplane. Herrick perfected the aircraft for over a decade, but like later convertiplanes, its remarkable performance did not justify production as the weight penalties imposed by carrying both rotary and fixed wing structures eliminated its commercial advantage over conventional airplanes.

Before the helicopter developed into a practical production aircraft in the 1940s, the autogyro, pioneered by the Spaniard, Juan de la Cierva, was the only type of rotary-winged aircraft that had demonstrated any degree of commercial promise. Autogyros differed from helicopters in that they depended on unpowered, free-wheeling rotors for lift. Once a continuous airflow was established over an autogyro's rotor blades, the resulting pressure distribution developed a lifting force that pulled them forwards as well as upwards in a state of autorotation. Most autogyros depended on a tractor or pusher propeller to move them through the air with sufficient airspeed to maintain rotorblade autorotation. This meant that while autogyros could make near vertical descents, with sufficient airflow to keep the blades spinning above their stall-speed, they could not hover or take off vertically.

In 1927, Gerard, a cousin of a Myron T. Herrick, the U.S. Ambassador who greeted Charles Lindbergh upon his arrival in Paris, began to theorize about the possibility of constructing a convertiplane, which he referred to as the vertaplane. A novel symmetrically cambered wing that could produce lift while either fixed or rotating formed the heart of the design. He enlisted the advice of the respected engineer Alexander Klemin for the wing design, and with the help of Ralph McClarren from the Franklin Institute, he designed a flying prototype vertaplane, designated HV-1. Herrick's basic design consisted of a low-wing monoplane, built by Heath Aircraft, with a rigid, highly tapered wing attached to an autogyro rotor mast. This upper wing, with a span of 7.32 m (24 ft), locked into position for cruise, which allowed the aircraft to operate as a biplane, otherwise it rotated freely as a autogyro rotor. Though the wing itself did not hinge like typical autogyro rotor blades, it attached to a hinged mount, using standard ball bearings, which tilted to compensate for the lift differential between the advancing and retreating sides. The aircraft could take off and land with the upper wing either fixed for higher-speed flight or rotating for short take-off and landing operations, but at the cost of a reduced cruise speed. The aircraft could convert in flight from fixed-wing to autogyro mode, but not vice-versa.

Heath Aircraft quickly completed the HV-1, powered by a 48-hp engine. On November 6, 1931, it completed its first flight. After further testing, Herrick's test pilot attempted a transition from fixed-wing to autogyro mode. At an altitude of 1,220 m (4,000 ft) he began a glide and at 1067 m (3,500 ft) he unlocked the upper wing, which rotated for a few turns and then slowed down, resulting in a complete loss of control. A post-crash examination revealed that, when the upper wing unlocked, it teetered hard against its bearings, broke them and contacted the propeller. The pilot attempted to bail out, but his parachute failed to open properly, resulting in his death.

Herrick was largely unfazed by the tragedy and began work on an improved vertaplane. The new HV-2A design, also constructed by Heath Aircraft to Herrick's specifications, came close to the HV-1 in external appearance, but it incorporated some significant changes. It utilized a much more powerful 125 hp Kinner B-5 radial engine. The HV-2A incorporated an improved rotor system with rubber teeter stops instead of the earlier ball bearings, which dampened the seesaw action of the HV-1's rotor, and would have prevented the earlier accident.

By September 1933, the completed HV-2A had emerged, but the construction of the aircraft depleted Herrick's finances and he could not begin sustained flight tests until 1936. George Townson, a young and enthusiastic test pilot, flew the aircraft throughout its test program. He later became a test pilot for Kellett's XO/YO-60 (see NASM collection) and the Piasecki PV-2 and XHRP-X helicopters (see NASM collection for both). The HV-2A's new rotor system proved to be much safer than the one installed on the HV-1. Townson made the first conversion from fixed-wing to autogyro mode on July 30, 1937 at the Boulevard Airport in Philadelphia. By the end of the year, he had made more than 100 conversions in the aircraft. On one flight, Townson experienced heavy vibration after converting into autogyro mode and set down in someone's backyard. After making a few adjustments, he took off again, remaining in autogyro mode for the rest of the flight.

The HV-2A cruised at 161 kph (100 mph) in fixed-wing mode and 105 kph (65 mph) in autogyro mode. During an autogyro takeoff, a mechanical starter brought the rotor up to autorotation speed. Autogyro take-offs were possible with only 18 m (60 ft) of runway, and the HV-2A could land at a mere 19 kph (12 mph) stop within a few yards of its touchdown point. While in autogyro mode, the HV-2A could also complete safe power-off autorotations safely to the ground. Unfortunately, the gross weight of the aircraft was 91 kg (200 lb) heavier than initially intended. Although Herrick designed the cockpit with side-by-side seating for two, the test pilot and a small amount of fuel overburdened it. This was a problem endemic to most contemporary autogyros, and was a principle reason that autogyros did not see more commercial or military service.

In 1937, Herrick again ran low on resources, and had to give up the HV-2A's development program. In 1943, he used the aircraft to drum up enthusiasm for his newest variant, the HV-3. This model was a coaxial helicopter version that did not come to fruition. In 1949, Herrick proposed a convertiplane with rotor-mounted ramjets, but this proposal also did not attract any investors.

In the early 1950s the convertiplane appeared to come of age as a number of manufacturers developed Vertical Takeoff and Landing (VTOL) projects, such as the McDonnell XV-1 (see NASM collection). While the HV-2A was an innovative and advanced design for its day, it was, like the other convertiplane projects, ultimately abandoned because other types of VTOL aircraft proved to be more efficient. In 1958, Herrick's children donated the HV-2A to the Smithsonian Institution, which accepted it as one of the earliest examples of VTOL technology.

Rotor Diameter: 7.32 m (24 ft)

Wingspan: 8.53 m (28 ft)

Length: 6.45 m (21 ft 2 in)

Height: 3.12 m (10 ft 3 in)

Weight: Gross, 771 kg (1,700 lb)

Engine: Kinner B-5, 125 hp

References and Further Reading:

Brooks, Peter W. Cierva Autogiros: The Development of Rotary Wing Flight. Washington DC: Smithsonian Institution Press, 1988.

Labermont, Paul. Helicopters and Autogyros of the World. Cranbury, NJ: Cassell & Company Ltd., 1970.

R. D. Connor

Long Description