Transcribed from the National Air and Space Museum website:

The father-and-son team of Emile and Henry Berliner became the first Americans to make any significant progress towards the creation of a practical helicopter. Before 1926, they pioneered a number of experimental helicopters with only moderate success. However, the Berliners' final versions displayed the best performance of any American helicopter project until Igor I. Sikorsky unveiled his VS-300 fifteen years later.

Emile, a German immigrant living in Washington D.C., was already a prodigious inventor when he began to dabble in aviation. He received a number of notable patents for substantial improvements he made to the design of gramophones, phonographs, and telephone transmitters. In 1903, he became fascinated with powered flight and experimented with a large rocket-powered model airplane.

Even after the success of the Wright brothers' first powered flight became widely known, Emile continued to pursue helicopter development in a quest for an aircraft that could operate from any location. In 1907, he began work on a helicopter with a tandem intermeshing-rotor system.

Emile Berliner realized that his design required a light engine and decided on a rotary model instead of the heavier in-line engines used previously in aircraft. Berliner worked with the Adams-Farwell Company to develop a 36-hp rotary engine for his helicopter. Remarkably, this was the first application in aviation of the rotary engine, which became quite popular during the following decade because of its weight advantages. A short time later, Berliner founded the Gyro Motor Company to further the development of rotary engines in aviation. In 1913, the company donated Emile's historic first engine to the Smithsonian Institution.

On July 11, 1908, Berliner's first "test-rig" helicopter design demonstrated that it had the potential to lift twice its own empty weight. Emile then constructed a larger version with a 55-hp motor, which he dubbed the Aeromobile. Simultaneously, Berliner cooperated with J. Newton Williams on a coaxial design. Neither effort progressed very far as the demands of operating the Gyro Motor Company distracted Emile's attention. However, this did not prevent him from conceiving new approaches to the problem of vertical flight. In 1910, Berliner began to consider the use of a vertically mounted tail rotor to counteract torque on his single main rotor design. This configuration later played a pivotal role in the development of practical helicopters during the 1940s.

For the next nine years, Emile's business concerns and deteriorating health prevented him from pursuing improved designs. However, his son Henry, was also a superb engineer and wanted to continue his father's work. In 1919, after a short stint in the Army Air Service as an aerial photographer, Henry moved to Washington D.C. to construct a helicopter under his father's guidance.

Henry's first effort was a coaxial design mounted on a two-wheeled test stand. He soon transformed this model into a manned version, powered by an 80 hp Le Rhône engine. It was able to lift Henry, and make the transition from a hover to forward flight, but its control was so poor that assistants running alongside had to steady it. Henry decided to take a new approach and adapt his experience with conventional airplanes to the control problem.

In 1922, Henry ordered a surplus Nieuport 23 fighter fuselage and mounted a Bentley 220 hp engine to the front. He attached a spar mid-way up the fuselage to form the bottom of a truss extending from the sides of the aircraft. The trusses each supported one of the two contra-rotating lifting rotors, which the engine powered through a series of geared shafts. The two rotors could tilt slightly in opposite directions to control yaw.

A variable-pitch tail rotor, 76 cm (30 in) in diameter, mounted horizontally in front of the vertical stabilizer, maintained pitch control while hovering. To initiate forward flight, the pilot pushed forward on the stick to increase the pitch of the horizontal tail rotor, which dropped the nose and inclined the lifting propellers slightly to initiate forward flight. The flight controls also connected to elevators and an enlarged rudder on the tail of the fuselage, which helped maintain control at higher forward speeds. Two sets of five 91 cm (36 in) x 20 cm (8 in) louvers, located below each rotor, opened and closed differentially to provide roll control by presenting a flat surface, which reacted against the rotor downwash.

In the fall of 1923, Henry decided to mount a set of triplane wings onto the aircraft to allow for a safe glide in case of an engine failure. With the new design, he found he could marginally control the helicopter in a hover and in forward flight at speeds up to 64 kph (40 mph). However, Henry discovered that the helicopter did not have adequate thrust to climb out of ground effect. The roll-control louvers were the weak-point of the control system and lateral handling was poor. On February 23, 1924, the helicopter recorded its best performance when it reached a height of 4.57 m (15 ft) during a one minute, thirty-five second flight. Many observers felt that the airframe was simply too heavy, including an Army engineer sent to observe the tests from McCook Field.

Henry and his father then decided to build a new, lighter helicopter to improve the thrust-to-weight ratio. Completed in 1925, the new design bore a superficial resemblance to the previous model, but it utilized a more efficient biplane configuration. The lower wing relied on a high angle of incidence and large camber to generate some lift from the rotor downwash. The Berliners also enlarged the rotors and added a novel differential collective pitch control system to replace the ineffective louvers.

However, even with the reduced weight and aerodynamic alterations, the 1925 model showed only a marginal increase in performance over the triplane version. Frustrated, Henry abandoned his helicopter experiments and became disillusioned with the potential of the helicopter. He went on to establish the Berliner Aircraft Company, and played an important role in the development of the innovative Erco Ercoupe.

Henry Berliner's reluctance to adopt a cyclic control system and a dependence on relatively small high-load lifting rotors incapable of autorotation ultimately prevented him from constructing a practical helicopter. While Emile and Henry struggled with their designs, the Spaniard, Raul Pateras Pescara demonstrated a helicopter with effective cyclic and collective pitch controls. However, his underpowered machine also could not climb out of ground effect and more than a decade passed before Louis Breguet improved on Pescara's approach. In 1935, with the cooperation of René Dorand, Breguet completed the Gyroplane Laboratoire, which was the first helicopter to meet the aviation industry's control and performance expectations for a practical design.

After Emile and Henry completed the testing of their triplane model, the younger Berliner offered it to the Smithsonian Institution. This aircraft is the oldest intact helicopter in the world and is currently on loan to the College Park Aviation Museum, appropriately located on the site of the Berliner's original testing ground.

Wingspan: 11.58 m (38 ft)
Rotor Diameter: 4.57 m (15 ft)
Length: 5.49 m (18 ft)
Height: 2.06 m (6 ft 9 in)
Weight:
     Empty, 748 kg (1,650 lb)
     Gross, 870 kg (1,918 lb)
Engine: Bentley BR-2 Rotary, 220 hp