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Pioneering Convertiplane

By Jon Guttman
7/15/2017 • Aviation History Magazine

Gerard Herrick tried to have the best of both worlds—fixed-wing and rotary-wing—with his HV-2A.

The concept of rotary-winged aircraft goes all the way back—on paper, at least—to Leonardo da Vinci, but even after the Wright brothers achieved  controlled flight in 1903, rotary-winged flight remained elusive. In 1919 Spanish inventor Juan de la Cierva came up with a hybrid compromise, the autogiro, which derived lift primarily from an unpowered rotor (see “Autogiro Genius,” September 2012 issue). First demonstrated successfully on January 23, 1923, it could not fly vertically, but its takeoff and landing runs were much shorter than those of a conventional airplane.

Airplanes, autogiros and experimental attempts to produce a true helicopter coexisted throughout the 1920s and 1930s, with occasional ventures in between their respective concepts. One such attempt to attain the best of both worlds was the Herrick HV-2A, which combined rotary and conventional flight not just in the same aircraft, but in the same wing.

Inspired by Cierva’s experiments, Gerard Post Herrick—a cousin of Myron T. Herrick, the U.S. ambassador who greeted Charles Lindbergh upon his arrival in Paris in 1927— decided to take them to a whole new plane…literally. Instead of the four hinged blades that provided Cierva’s autogiro with lift, he produced, with the help of engineer Alexander Klemin, one highly tapered, symmetrically cambered wing that would confer lift whether fixed or rotating. He then collaborated with Ralph H. McClarren from the Franklin Institute to design a prototype that he called the HV-1, the initials standing for Herrick Vertaplane. Both the aircraft and the airfoil were patented on February 10, 1931.

Built by Heath Aircraft, the HV-1 was a low-wing monoplane with an additional rotatable wing pivoting atop a gyroplane mast. Although not hinged like Cierva’s rotor blades—or those commonly seen on modern helicopters—the HV-1’s wing sat on a hinged mount, utilizing ball bearings, which teetered to compensate for the lift differential between the advancing and retreating sides. The wing could either remain fixed, making the aircraft a conventional biplane, or rotate for short takeoffs and landings. Once aloft, the wing could be converted from fixed-wing to gyroplane mode, but not vice versa.

Powered by a 48-hp Poyer 3-cylinder engine, the HV-1 required the upper rotor to be spun at nearly autorotational speed in order to take off like an autogiro. To achieve this, it had to be taxied around the airfield perimeter, or a long rope was wound around the rotor and then pulled by a group of running men to start it spinning—much like one would start a lawn mower.

The HV-1 was ready for its first flight on November 6, 1931. After some conventional test hops in the biplane configuration, Merrill Lambert entered a glide at 4,000 feet altitude and at 3,500 feet unlocked the upper wing. After a few turns, however, the wing slowed down, resulting in a complete loss of control. As the aircraft gyrated wildly and then plunged straight toward the ground, Lambert bailed out, but his parachute failed to open properly and he was killed. Analysis of the wreckage revealed that the unlocked wing had teetered hard against its bearings, shattering them and then striking the propeller.

Undaunted, Herrick resumed his work. Heath produced the improved HV-2A, whose rotor system used rubber teeter stops rather than ball bearings, which dampened the rotor’s seesaw action. It also had a more powerful 125-hp Kinner B-5 radial engine.

Instead of relying on a ground crew pulling a rope to start the rotor in gyroplane mode, the HV-2A had an internal bungee cord in its pylon. Two volunteers slipped ropes over the rotor and wound it backward two turns, after which it was released, achieving an initial rotation of 60 rpm. Using this method, similar to the way a model airplane is launched, and gunning the engine, the HV-2A could take off in 60 feet. It could also land at 12 mph, stopping just a few feet from where it touched down. An electric “prerotor” motor allegedly served as a backup, but only the bungee cord was found when the Smithsonian Institution acquired the aircraft.

Although the HV-2A was completed in September 1933, Herrick had so depleted his finances that he could not test fly it until late 1936. On July 25, 1937, George Townson put the aircraft through several successful inflight conversions from conventional to gyroplane operation, after which he gave its first public demonstration at Philadelphia’s Boulevard Airport on the 30th. By year’s end Townson had logged more than 100 such flights, proving the safety of the modified rotor system. Although the HV-2A tended to veer to one side due to the spinning wing’s gyroscopic forces, its conventional controls allowed the pilot to compensate for it. On one flight Townson experienced heavy vibrations, compelling him to land in a backyard, but after making a few adjustments he took off and flew home without further incident. Even with the engine off, the HV-2A performed safe landings by autorotation, which could reach as much as 250 rpm at the gyroplane’s maximum speed of 65 mph. Cruising speed in fixed-wing mode was 100 mph.

Promising though these flights were, Herrick’s “convertiplane” suffered from the same weakness as most of its overweight rotary-winged contemporaries: Its gross weight of 1,700 pounds was 200 pounds more than originally intended. Moreover, the aircraft displayed an inordinate amount of drag, even in fixed biplane configuration. Consequently, although its cockpit was designed to accommodate two people side by side, the aircraft performed as if it was overloaded when carrying just the pilot and a little fuel. That deficiency made it too impractical for civilian or military purposes.

Having again exhausted his financial resources, Herrick curtailed further development of the HV-2A. In 1943, however, he brought it out of mothballs for an unsuccessful attempt to drum up interest in his latest concept, a coaxial helicopter called the HV-3. In 1949 he proposed a convertiplane with rotor-mounted ramjets, but that too failed to attract investors.

Though Herrick remained a lifelong advocate of vertical takeoff and landing, earning a reputation as the “dean of convertible aircraft designers,” a new generation of jet age experiments had left his ideas in the dust when he died at age 83 in September 1955. Three years later, his children donated the HV-2A to the Smithsonian’s National Air and Space Museum, which accepted it for what it was: an overweight, underpowered pioneer of VTOL technology that had been ahead of its time. It is currently stored at the Paul Garber facility in Suitland, Md., waiting for its turn in the Udvar-Hazy Center’s new Mary Baker Engen Restoration Hangar.

 

Originally published in the May 2013 issue of Aviation History Magazine. To subscribe, click here.

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