HILLER  XH-44

 Stanley Hiller Jr., era solo un adolescente cuando abrió la cuarta compañía americana de helicópteros y comenzó a construir estas máquinas en 1948. El preludio a este hito en el desarrollo del vuelo vertical fue el primer helicóptero de Hiller, el XH-44 (XH por “Experimental Hiller” y 44 por el año 1944, año en el que la aeronave voló por primera vez). Hiller diseñó la aeronave con dos rotores contrarrotativos eliminando de este modo el torque. Un helicóptero de este tipo era único entre los diseños de la época, proveyéndole a Hiller una fuente de valiosos datos. Le demostró también a este joven inventor a donde no apuntar con el desarrollo de helicópteros, sus modelos posteriores utilizaron una configuración de rotor convencional.

El interés de Hiller en los helicópteros comenzó en 1941 a la edad de 16 años. A esta edad ya fabricaba coches potenciados por pequeños motores a gasolina. Después de que los Estados Unidos declarara la guerra a Alemania y a Japón, Hiller convierte su línea de producción para la construcción de ventanillas para los Douglas C-47 Dakota, pero continúa refinando sus ideas sobre los helicópteros. Para 1942, sus avances son lo suficientemente grandes como para crear una organización para la construcción de aeronaves y forma la Hiller Aircraft. Trabajando con un pequeño grupo de ingenieros y artesanos, comienza la fabricación de un helicóptero compacto con un fuselaje de tubos recubierto con tela en diciembre de 1942.

Los esfuerzos de la nación en soportar la guerra causan una escasez de materiales y equipamiento que retrasan al helicóptero de Hiller al igual que al desarrollo de Piasecki, el PV-2. El equipo de Hiller tiene que construir o pedir prestadas la mayoría de los componentes. El motor era un ítem crítico, para esto, Hiller eligió un Franklin de 90 HP reducido a 65HP. Debido a la falta de fondos, apeló a varias agencias de gobierno para obtenerlo. El entusiasmo de este muchacho de 18 años convenció a Grover Loening, consultor jefe de la Producción de Guerra por ese entonces, que le proveyó el motor.

El XH-44 constaba de una configuración coaxial, diferente de los otros helicópteros de la época, pero Hiller eligió esta configuración por varias razones. Los franceses Louis Bréguet y René Dorand habían probado este concepto durante los vuelos del Bréguet-Dorand Laboratory Gyroplane en 1935. El mecanismo que permitía a los rotores contrarrotar en el mismo mástil era algo complejo, pero tenía varios beneficios: no genera torque, el motor no gasta potencia en manejar un rotor de cola y se omite el cono de cola, caja de cola, etc, reduciendo el peso total de la aeronave. Así también la configuración coaxial tiene algunos problemas como el pobre control direccional en vuelo hacia delante y el control de guiñada en la autorrotación.

Para el control direccional en una aeronave coaxial, el piloto utiliza los mismos controles que en un helicóptero convencional. Solo el método del control de guiñada es diferente. En lugar de manejar el rotor de cola, los pedales controlan las palas del rotor principal.

Hiller eligió el desarrollo coaxial debido también a su olfato comercial. Se dio cuenta que competir con Sikorsky y otras firmas especializadas en desarrollos estándares era imposible. Ellos ya disfrutaban de su marketing y su apoyo financiero. Hiller esperaba que su novedad atrajera la atención de inversores. Aparte de la novedad, uno de los puntos fuertes del XH-44 era la ausencia del rotor de cola como posible fuente de accidentes.

Las pruebas en tierra comenzaron en 1944 y a los pocos días comenzaron las pruebas de vuelo pero amarrado, debido a la poca experiencia de Hiller, aprendiendo sobre la marcha los rudimentos del vuelo. Los vuelos se desarrollaron primeramente en el camino de entrada de la residencia Hiller y posteriormente se llevaron a cabo en el estadio de fútbol de la Universidad de California en Berkeley. El 4 de julio de 1944, Hiller voló la aeronave amarilla por primera vez, libre completamente de sus amarres, y dos meses después, el 30 de agosto de 1944, realizó demostraciones públicas, en San Francisco. Estas demostraciones atrajeron inversiones, principalmente de Henry Kaiser, un rico constructor de barcos.

Con estos fondos pudo rediseñar las palas del rotor y el mástil. También le instaló un motor mas potente, un Lycoming O-290 CP de 125HP. A fines de 1945, Hiller juzgo que el XH-44 se lo había rediseñado lo suficiente y procedió a construir un nuevo modelo, el X-2-235. Con este diseño esperaba conseguir ordenes de producción. Cuando esto no sucedió, preparó otra versión, el UH-4, una aeronave personal, pero también faltó interés en el mercado.

 Stanley Hiller, Jr., was only a teenager when he opened the fourth American helicopter company and began mass-producing helicopters in 1948. The prelude to this milestone in vertical flight development was the design, construction, and flight of the first Hiller helicopter, the XH-44 (XH stands for 'Experimental Hiller, 1944 refers to the year the aircraft first flew). Hiller designed this rotorcraft to fly beneath twin rotors that counter-rotated about the same mast so there was no need for a tail rotor to control main rotor torque. A helicopter with coaxial rotors was unique among the American designs of that day and the XH-44 flew well enough to provide Hiller invaluable data. It also demonstrated to the young inventor where not to go with helicopter design, his follow-on production models used a single main rotor configuration.

Hiller's interest in helicopters began in 1941 at age sixteen. At that time, this young man was already running a successful enterprise manufacturing model cars powered by small gasoline engines. After the United States declared war on Germany and Japan, Hiller converted his production line to build window frames for Douglas C-47 Dakota transports but he continued to refine his ideas about helicopters. By 1942, his thinking had advanced enough to warrant creating an organization to build the aircraft and he formed the Hiller Aircraft Company. Working with a small group of experienced engineers and craftsmen, he started fabricating a compact helicopter with a steel-tube fuselage covered with fabric in December 1942.

The nation's all-out efforts to support the war effort caused shortages of materials and equipment that delayed development of Hiller's helicopter, just as it affected Frank Piasecki's efforts to build his first helicopter, the PV-2. Hiller's staff had to scrounge or manufacture almost all their own components. The power plant was a critical item that no small firm could fabricate and Hiller selected a Franklin 90 horsepower engine, de-rated to 65 horsepower. Hiller could not buy the engine commercially so he appealed to several government agencies before he obtained one. The enthusiastic eighteen year-old convinced Grover Loening, then chief aircraft consultant to the War Production Board, that his helicopter was worth supporting with a small, reciprocating engine. Workers installed the unit in late 1943 and testing began immediately.

The XH-44 coaxial configuration differed dramatically from other helicopters developed during this period but Hiller chose the layout for sound reasons. Frenchmen Louis Bréguet and René Dorand had already proven the concept during flights of their Bréguet-Dorand Laboratory Gyroplane that began in 1935. The mechanism that allowed the rotors to counter-rotate on the same mast was somewhat complex but this feature had considerable benefits. Because a coax' did not generate torque, no engine power was wasted driving a tail rotor that produced no lift or forward thrust. Doing away with the tail boom, tail rotor drive shaft, gearbox, and other accoutrements also saved considerable weight and reduced drag. The coaxial configuration did have several drawbacks. The coaxial helicopters exhibited weak directional control in forward flight and yaw control forces reversed during autorotations.

To control the direction of a coaxial rotorcraft, a pilot used the same set of controls that guided single main rotor helicopters: collective and cyclic levers, and yaw pedals. Only the method of yaw axis control differed between the two types. Instead of feathering the blades of a tail rotor to pivot a helicopter about its yaw axis, the pedals at the feet of the pilot of a coax' alternately feathered the blades on both main rotors to yaw the helicopter left or right.

Hiller also chose to develop coaxial helicopters because it made good business sense. He realized that competing with Sikorsky, and other firms that specialized in single rotor helicopters, was nearly impossible. They already enjoyed a head start in rotorcraft marketing, and they were far richer in material and financial assets than Hiller's fledgling company. He hoped that the sheer novelty of the coaxial design might attract enough attention and investors to offset the popularity of single rotor aircraft. Apart from novelty, one of the XH-44's great selling points as a home-based commuter aircraft was the absence of the inefficient and potentially dangerous tail rotor.

Ground tests began 1944 with the roar of 65 horsepower and broken glass when the first engine run-up inside the Hiller workshop sucked the skylights from the ceiling. Test flying started a few days later but slowed nearly to a crawl because Hiller had no prior flight experience. He taught himself to fly the XH-44 as the test flight schedule evolved. During these early hops, the Hiller team securely tethered the XH-44 to preserve the pilot and their hand-crafted machine. Accidents did occur. On the first flight test, made from the driveway of Hiller's family residence, someone did not adjust the tether properly and the helicopter tipped over with minor damage. Subsequent tests took place in the football stadium at the University of California at Berkeley. On July 4 1944, Hiller flew the bright yellow aircraft free from its tether for the first time in the stadium. A public demonstration followed less than two months later on August 30, 1944, in San Francisco. These events attracted outside investment, primarily from Henry Kaiser, a wealthy Seattle ship builder. Kaiser infused the project with enough capital to allow Hiller to further refine the XH-44.

His most important improvement was a redesign of the rotor blades and mast to allow each two-blade set to teeter freely. The new arrangement resembled the teetering rotor developed by Arthur Young and flown on all Bell helicopters for decades. The XH-44 now handled much more smoothly in calm air or turbulence. Hiller also installed a more powerful Lycoming O-290 CP engine on December 1, 1945. By late 1945, Hiller judged the XH-44 test bed refined enough that he could proceed with construction of a new model, the X-2-235. The designer hoped that this helicopter would lead to a production order. When it did not, Hiller prepared another version, the UH-4, for production as a personal commuter aircraft and it too failed to win outside interest. The problem was not of Hiller making but rather the result of faulty social forecasting. During World War II, many captains of the aviation industry forecast a massive shift of thousands of pilots from the cockpits of military aircraft to the cabins of personal, commuter aircraft as soon as the war ended. This boom failed to occur, dooming hundreds of promising light fixed- and rotor-wing aircraft including the Hiller designs. Stanley Hiller shifted his sights to the market for commercial and business helicopters.

THANKS TO SMITHSONIAN NATIONAL AIR &SPACE MUSEUM

Characteristics
Características

Information
Información

Characteristics
Características

Information
Información

1944

1 FRANKLIN

1

90 HP
Derated 65 HP

1244 Lb

Ft

Lb

Ft

Kts

Ft

Kts

NM

Dimensions / Dimensiones

13,45 ft
4,1 m

25,0 ft
7,6 m

8,85 ft
2,7 m

NA