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Piasecki — The Dogship and the Flying Banana

Frank Piasecki

Although helicopters had not been produced in large numbers during World War II (only a few hundred had been built compared to hundreds of thousands of bombers and fighters), they had demonstrated their utility for a variety of military tasks. By 1947, there were dozens of companies in the United States developing helicopters, but only a few of them would actually produce successful aircraft that were built in large numbers. One of the early successes was Piasecki Aircraft.

Frank Piasecki was born in Philadelphia in 1919, the son of an immigrant Polish tailor. He earned degrees in aeronautical and mechanical engineering by the age of 20 and in 1940, he gained the support of a few friends and started a small aeronautical company. He built a single-person, single-rotor helicopter designated the PV-2 and test-flew it by 1943. Piasecki realized that Sikorsky was the favoured helicopter manufacturer for the U.S. Army, so he made an appeal to the U.S. Navy with his PV-2. Navy leaders initially showed little interest in helicopters, but soon changed their minds. Piasecki also had an idea for a much larger helicopter capable of fulfilling various naval missions, such as rescuing sailors at sea. On January 1, 1944, he received a Navy contract for a single new heavy-duty transport helicopter.

Before developing the tandem helicopters for which he is known, Frank Piasecki built and flew the PV-2 single-rotor craft in 1943. A result of three years' research by his company, the P-V Engineering Forum. It had a three-bladed, 25-foot (7.6-meter) rotor and was 22 feet (6.7 meters) long.

Piasecki decided to build a helicopter that had two rotors, one at each end of a long, somewhat cylindrical fuselage. The two rotors were easier to manufacture and control than a single large rotor, and the long fuselage could be loaded with cargo or people, without much concern for even weight distribution. Piasecki also simply did not like the idea of a tail rotor, which had given Igor Sikorsky problems with his VS-300 and which looked like a circular saw mounted right at head-chopping level—and robbed valuable horsepower from the lifting rotor. The new tandem two-rotor craft was designated the PV-3 and made its first flight in March 1945. The Navy designated it the XHRP-X, but Piasecki employees referred to it affectionately as the Dogship.

The Dogship weighed 5,000 pounds (2,268 kilograms) empty and less than 7,000 pounds (3,175 kilograms) fully loaded. Its fuselage had an enormous 400 cubic feet (11.3 cubic meters) of space. The fuselage was constructed of tubular steel filled with wooden ribs and covered with fabric. A 450-horsepower (336-kilowatt) Continental R-975 radial engine was housed amidships with shafts angling forward and aft to the rotors. Automotive gears were used in its transmission.

During the first test flight, the Dogship flew without its fabric covering, looking like a skeletal praying mantis. Soon after, during another early test, the craft rose off the ground and pitched up suddenly, its rear rotor coming alarmingly close to the ground. During a later test flight, the helicopter's transmission grew dangerously hot. Piasecki did not want to perform repairs at the Navy field and let Navy personnel see that he was having problems with his aircraft, so he sent his flight engineer to buy ice and soda pop, which they then poured over the transmission to cool it. After a harrowing low-level flight back to the factory outside Philadelphia, the Dogship landed and its rotors came to an unusually abrupt halt. The engineers opened the transmission and realized in horror that all the gears had been stripped nearly clean. They had to redesign the transmission using parts much more tough than the automotive parts they had started with—learning a lesson that aircraft required more robust designs and parts than automobiles.

The U.S. Coast Guard and Navy have used the Piasecki "Dogship" (PV-3/HRP-1) as a rescue craft. It has ten seats and is powered by a 600 hp Pratt & Whitney R-1340 engine.

Despite these early problems, the tandem-rotor configuration soon proved itself highly capable. After the war, Piasecki received a contract to build a military prototype called the XHRP-1, which was similar to the Dogship. The Navy then ordered several more to use as rescue craft, since they could retrieve more than one person at a time. The craft could carry ten men in addition to the pilot and copilot. Navy leaders still had little interest in helicopters at this stage and passed most of the HRP-1s onto the Marines and Coast Guard.

To ensure that the rotors did not hit each other, the rear end of the fuselage curved upwards so the rear rotor was higher than the forward rotor. Because of this odd shape, the craft soon acquired the nickname Flying Banana. This nickname would also be applied to later Piasecki craft, such as the HRP-2 and the highly successful H-21, which entered service in the 1950s and which was used by the U.S. Navy, Air Force, Army and many foreign militaries. All had the same tandem-rotor configuration pioneered by the Dogship.

The Piasecki "Flying Banana" entered service in the 1950s.

Piasecki eventually became Vertol and was later acquired by Boeing. The Dogship and later the Flying Banana would serve as the forerunners to a number of tandem-rotor craft ultimately produced in the hundreds, such as the Navy/Marines CH-46 Sea Knight and the Army's heavy-duty workhorse CH-47 Chinook. Both types saw extensive use in Vietnam and later. The CH-46 was still in naval use in 2000 for "Vertical Replenishment" or "VERTREP" at sea, where a helicopter is used to lift cargo from one ship to another.

The Marines also still use the Sea Knight, but hope to replace it with the V-22 Osprey. The CH-47 was also in use carrying jeeps, artillery, and other supplies slung under its fuselage on cables. Special Operations versions, equipped with refuelling probes and night vision equipment, are used to place troops deep behind enemy lines. The Chinook has been exported to a number of countries where it has been highly successful and serves in a number of foreign militaries including Argentina, Egypt, Greece, Iran, Italy, Japan, Morocco, Netherlands, Singapore, South Korea, Spain, Taiwan, and the United Kingdom. Both the CH-46 and CH-47 were produced in civilian versions, although not in large numbers. In the civilian role, they are often used as heavy-lift "skycranes."

The CH-47 Chinook helicopter is the U.S. Army's only medium-lift helicopter. It is a twin-engine, tandem rotor, cargo helicopter.   Beginning in 1975, it was modernized to include new fibreglass rotor blades, transmission and drive systems, modularized hydraulics, electrical systems, advanced flight controls, triple hook cargo system, and an auxiliary power unit.

One other helicopter manufacturer, the British firm Bristol, copied the basic tandem-rotor layout. Bristol produced the Belvedere in the early 1960s. The Belvedere, which looked like a baguette with rotors on either end, saw service in Borneo. The Soviet Union design firm Yakovlev manufactured a tandem-rotor craft starting in the 1950s known as the Yak-24. But by far the most successful helicopter of this type is the Chinook, which has also been produced under license in Italy by Agusta and in Japan. Over a thousand have been built.