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H-21 Shawnee / HRP Rescuer / Flying Banana

In 1945 Frank Piasecki built the first successful tandem rotor helicopter for the U.S. Navy [Piasecki Helicopter Corporation later became part of Boeing]. The HRP-1 Rescuer was nicknamed the Flying Banana because of its long, curved shape. The unique "Flying Banana," had a fabric covered fuselage. It was powered by a single Pratt & Whitney R-1840-AN-1 engine that drove both rotors. The U.S. Coast Guard and Navy have used the Piasecki "Dogship" (PV-3/HRP-1) as a rescue craft.

All the small Sikorsky helicopters and the Piasecki PV-2 had lacked the lifting capacity necessary to perform a rescue mission involving the carrying of more than one person, but more lifting ability and passenger space meant a larger helicopter. One method of obtaining a larger design, was to take a "proven" configuration and multiply it by 1 1/2 or 2 times its original size. At this time, however, the Navy's Bureau of Aeronautics (BuAer) wanted to stay within the scope of existing component development and eliminate as many unknown areas of design and construction as possible. Therefore, BuAer decided to approve the design of a helicopter with two smaller lift rotors, each approximately 40 feet in diameter rather than attempt construction of a larger rotor system (60 to 70 feet in diameter) which was still in the early design stage.

In May 1943, prior to the flight of the PV-2, Piasecki had discussed with BuAer a design for a helicopter with two main rotors in tandem, one forward and one aft. The power plant would drive the two 37-foot diameter rotors through reduction gearing and shafting. It would carry a useful load of about 1,800 pounds, by far the best lifting capability of any helicopter to that date. Useful load is defined as the difference between the empty weight of the aircraft and the overall gross (maximum) weight at take-off. Useful load includes th e weight of the pilot, fuel, oil, any other special equipment, and the payload. Payload, however, is quite variable. It is not only a function of distance but also of many other factors including altitude of operation, fuel load, temperature, humidity, and wind conditions.

Piasecki's May 1943 proposal conformed somewhat to BuAer's desire, although there was considerable doubt as to whether a tandem machine could be made to fly-mainly because of the interference of the air-flow to the rear rotor and th e problem of longitudinal control. After almost a year of negotiations and study, BuAer awarded Piasecki a contract in early 1944 for the tandem rotored machine, the XHRP-X . This was the Navy's first experimental helicopter, a design arrangement which never received serious attention by any of the leading helicopter manufacturers except Piasecki.

Development of the XHRP-X into a final design acceptable for Navy use was slow. The policy of BuAer required the contractor to produce a full-sized flying model without Navy inspection or interference, with the idea that the contract would be cancelled if the model did not prove successfu1. The plan also required the test aircraft, XHRP-X, or " Dogship," to be flown by the contractor prior to commencing construction of the first production type HRP-1.


The "flying banana, " as the HRP-1 was later nicknamed, and also referred to as the "sagging sausage, " was designed to be powered by a 600-horsepower engine driving the two 41-foot rotors. With a full fuel load and a crew of two, it was to carry 900 pounds and cruise at 75 miles per hour. The cargo space could accommodate seats for 10 passengers and would measure 14 feet long and 5 feet wide.

Within one year after receiving the contract, Piasecki built and successfully flew the PV-3 (XHRP-X) . The March 1945 flight of the "Dog-ship" paved the way for design and construction of the 6,400-pound gross weight HRP-1. Unfortunately, the first production aircraft would not be delivered to the Navy for almost two years after BuAer approved the contract.


In June 1948 the U.S. Navy ordered five examples of the much-developed PV-17 with the designation HRP-2. This had a considerably longer, redesigned fuselage with an all-metal skin (the HRP-1's front half was fabric-covered), a more roomy crew cabin with side-by-side seats, and modified rotor heads. This version formed the basis of the later PD-22 model which became the highly successful military Vertol H-21 series.

By 1949 the Marine Corps was interested in a 3,000-pound payload transport helicopter. Such a helicopter appeared to be the most feasible model for operating from escort aircraft carriers. Modifying an existing helicopter was one course of action suggested while making a model based upon "proven " and existing configurations was the alternate proposal. It was considered that extensive expenditures of funds for research and development would not be necessary in the "growth" version since a large part of the basic design and engineering was already completed. None of the current models would be of sufficient improvement over the Piasecki HRP-1 to justify procurement, nor would they even approximate the Marine's assumed required general specifications.

Further investigation disclosed that only one - the YH-21 Air Force Arctic Rescue model - had the potential of closely approximating the desired specifications. The main variation, though, existing between Air Force and Marine Corps requirements, was that the former had a greater range demand where the latter had a requirement for larger troop capacity. It appeared that the most effective means of obtaining money would be to select an existing type helicopter which could be modified with production funds - since the availability of research and development funds was extremely critical.


The H-21 cargo helicopter with tandem rotors was designed for the US. Army during the 1950s and it was used in substantial numbers during the initial phase of the Vietnam war. The H-21 Shawnee was the fourth of a line of tandem rotor helicopters designed by Piasecki. Although the overall dimensions of the YH-21 and the HRP were almost identical and somewhat similar in appearance, the YH-21 weighed twice as much empty (9,148 pounds), and had three times the horsepower (1,425) and useful load carrying capability (5,556 pounds), while retaining approximately the same air speed. The Piasecki Helicopter Corporation, its new name since 1946, developed the YH-21 as an Arctic rescue helicopter for the Air Force.

The Boeing Vertol (formerly Piasecki) H-21 was a multi-mission helicopter, utilizing wheels, skis, or floats. It was used for Artic rescue because it performed so well at low temperatures.

The CH-21 also served with the U.S. Air Force (as the "Workhorse"), the French Navy, the Royal Canadian Air Force and the West German Air Force. The French used an armed version of the CH-21 in Algeria, mounting guns in the door ways and on the skids.

The CH-21B assault helicopter could carry 22 fully-equipped troops, or 12 stretchers, plus space for two medical attendants, in the MedEvac role. The CH-21B was first deployed to Vietnam in December 1961 with the Army's 8th and 57th Transportation Companies, in support of ARVN (Army Vietnam) troops. The CH-21B/CH-21C Shawnee could be armed with 7.62mm or 12.7mm door guns. Some Shawnees were armed with flex guns under the nose. An interesting experimental version was tested stateside with a Boeing B-29 Superfortress ball-turret mounted beneath the nose.

The CH-21 was relatively slow. It's cables and fuel lines were so vulnerable to small arms fire it was even rumored that a CH-21 had been downed by a Viet Cong spear. The Shawnee was the "Workhorse" of Vietnam until 1964 when it was replaced with the fielding of the UH-1 "Huey" in 1963, and the later fielding of the CH-47 Chinook in the mid-1960s. The Shawnee had two tandem fully-articulated three-bladed counter-rotating rotors. The CH-21 was powered by one Curtis-Wright R1820-103 Cyclone supercharged 1150 hp piston engine. The CH-21B was equipped with an uprated 1425 shp engine. The CH-21 had a speed of 128 mph (111 knots).

The Coast Guard acquired three HRP-1 twin-rotor helicopters beginning in November 1948 from the Navy. All three helicopters were stationed at Coast Guard Air Station Elizabeth City along the North Carolina coast. At least one was assigned to the Rotary Wing Development Unit based out of Elizabeth City. Here they participated in numerous experiments, including on-the-water landings with newly invented flotation gear and the testing of various types of hoists, rescue baskets, and rescue harnesses. Most of this equipment was developed by then-CDR Frank Erickson and his men. He also tested helicopter landings on board the USCGC Mackinaw in Buffalo, New York, including landing an HRP on the icebreaker's stern after first flying the helicopter to Buffalo from Elizabeth City. Erickson also participated in flood relief experiments in the Second Coast Guard District in 1949 as well, using HRP CG-111826. The experiments included testing various hoisting methods and equipment at various points along the Mississippi River, beginning in St. Louis, Missouri. The first recorded search and rescue mission carried out by a Coast Guard HRP occurred on 31 December 1948. The SAR Office at Elizabeth City received a request to transport a fourteen-month-old baby girl, who was suffering from pneumonia, from Cape Hatteras, North Carolina, to the hospital at Elizabeth City.

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Page last modified: 07-07-2011 02:32:29 ZULU