Its unusual shape made it known as “the flying banana”. And designed for a purpose.
Since World War II, new military doctrine emphasizes flexibility on the battlefield, helicopters have been developed as a multi-role combat vehicle that can operate in complex terrain. The H-21 was fairly early tandem-rotor helicopter from the 1950s. Its unusual shape made it known as “the flying banana”. And designed for a purpose.
The banana shape came from Piasecki’s attempts to streamline the helicopter for better cruising performance. While resting on the ground, the nose and cabin are inclined with a nose-up attitude. And the engine and main gear are located where the helicopter is bent at an incline to the rear. The rotors are nearly at the same height and orientation with this arrangement so the helicopter will hover with this attitude.
In forward flight, the helicopter must nose down to transform some of its vertical lift into horizontal thrust. Now thanks to the banana shape, the cabin is much more level with the ground for streamlining and comfort during long cruises. The aft rotor also rises higher than the front rotor to avoid its turbulent rotor wash.
Vertical tail fins were situated outboard of the rear main rotor position. Internally, the H-21 was crewed by two in the cockpit and held space for up to 20 fully-laden combat troops or up to twelve medical litters with accompanying medical staff. Performance included a maximum speed over 130 miles per hour and a range out to 400 miles.
Production of H-21s spanned from 1952 until 1959 and their operational service ran into 1967. Beyond the United States and Canada, global operators included France, West Germany, Japan, and Sweden. The French pressed their H-21C models into combat service during the Algerian War in the gunship role, armed with rockets and machine guns. Nevertheless the helicopter continued on in its given transport roles through to the end of the French commitment.
American H-21s were deployed during the Vietnam War from December 1961 on, and these were typically armed through trainable machine guns of 7.62mm and 12.7mm caliber for defensive purposes. However, their service in the conflict was relatively short-lived as the line was superseded in its over-battlefield roles by the new Bell UH-1 “Huey” and Boeing CH-47 “Chinook” series helicopters. The war showcased several deficiencies in the H-21 design – slow performance and susceptibility to ground fire as well as below average hot weather operation. Their services in the war was greatly reduced from 1964 on.
More study and development of tandem-rotor helicopters led to the changes that are present in today’s tandems, like the famous CH-47 Chinook. It still hovers with a nose-high attitude, but the banana shape has been eliminated since the cabin runs the length of the helicopter and since the engines are mounted externally in the rear. And the vertical rotor separation is achieved by making the fore and aft rotor masts different heights.
