Autogyro
An autogyro, gyroplane or gyrocopter, is a class of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. A gyroplane "means a rotorcraft whose rotors are not engine-driven, except for initial starting, but are made to rotate by action of the air when the rotorcraft is moving; and whose means of propulsion, consisting usually of conventional propellers, is independent of the rotor system." While similar to a helicopter rotor in appearance, the autogyro's unpowered rotor disc must have air flowing upward across it to make it rotate. Forward thrust is provided independently, by an engine-driven propeller.
It was originally named the autogiro by its Spanish inventor and engineer, Juan de la Cierva, in his attempt to create an aircraft that could fly safely at low speeds. He first flew one on January 1923, at Cuatro Vientos Airport in Madrid. The aircraft resembled the fixed-wing aircraft of the day, with a front-mounted engine and propeller. The term became trademarked by the Cierva Autogiro Company. De la Cierva's Autogiro is considered the predecessor of the modern helicopter. The term "gyrocopter" was used by E.Burke Wilford, who developed the Reiseler-Kreiser feathering-rotor-equipped in the first half of the twentieth century. Gyroplane was later adopted as a trademark by Bensen Aircraft.
The success of the Autogiro garnered the interest of industrialists and under license from de la Cierva in the 1920s and 1930s, the Pitcairn & Kellett companies made further innovations. Late-model autogyros patterned after Etienne Dormoy's Buhl A-1 Autogyro and Igor Bensen's designs feature a rear-mounted engine and propeller in a pusher configuration.
Principle of operation
An autogyro is characterized by a free-spinning rotor that turns because of the passage of air through the rotor from below. The downward component of the total aerodynamic reaction of the rotor gives lift to the vehicle, sustaining it in the air. A separate propeller provides forward thrust and can be placed in a puller configuration, with the engine and propeller at the front of the fuselage, or in a pusher configuration, with the engine and propeller at the rear of the fuselage.Whereas a helicopter works by forcing the rotor blades through the air, drawing air from above, the autogyro rotor blade generates lift in the same way as a glider's wing, by changing the angle of the air as the air moves upward and backward relative to the rotor blade. The free-spinning blades turn by autorotation; the rotor blades are angled so that they not only give lift, but the angle of the blades causes the lift to accelerate the blades' rotation rate until the rotor turns at a stable speed with the drag force and the thrust force in balance.
Because the craft must be moving forward with respect to the surrounding air to force air through the overhead rotor, autogyros are generally not capable of vertical takeoff. A few types such as the Air & Space 18A have shown short takeoff or landing.
Pitch control is achieved by tilting the rotor fore and aft, and roll control is by tilting the rotor laterally. The tilt of the rotor can be effected by utilizing a tilting hub, a swashplate, or servo-flaps. A rudder provides yaw control. On pusher configuration autogyros, the rudder is typically placed in the propeller slipstream to maximize yaw control at low airspeed.
Flight controls
There are three primary flight controls: control stick, rudder pedals, and throttle. Typically, the control stick is termed the cyclic and tilts the rotor in the desired direction to provide pitch and roll control. The rudder pedals provide yaw control, and the throttle controls engine power.Secondary flight controls include the rotor transmission clutch, also known as a pre-rotator, which when engaged drives the rotor to start it spinning before takeoff, and collective pitch to reduce blade pitch before driving the rotor. Collective pitch controls are not usually fitted to autogyros but can be found on the Air & Space 18A, McCulloch J-2 and the Westermayer Tragschrauber, and can provide near VTOL performance.
Pusher vs tractor configuration
Modern autogyros typically follow one of two basic configurations. The most common design is the pusher configuration, where the engine and propeller are located behind the pilot and rotor mast, such as in the Bensen "Gyrocopter". Its main advantages are the simplicity and lightness of its construction and the unobstructed visibility. It was developed by Igor Bensen in the decades following World War II, who also founded the Popular Rotorcraft Association to help it become more widespread.Less common today is the tractor configuration. In this version, the engine and propeller are located at the front of the aircraft, ahead of the pilot and rotor mast. This was the primary configuration in early autogyros but became less common. Nonetheless, the tractor configuration has some advantages compared to a pusher, namely greater yaw stability, and greater ease in aligning the center of thrust with the center of mass to prevent "bunting".
History
was a Spanish engineer, pilot, and aeronautical enthusiast. In 1921, he participated in a design competition to develop a bomber for the Spanish military. Cierva designed a three-engined aircraft, but during an early test flight, the bomber stalled and crashed. Cierva was troubled by the stall phenomenon and vowed to develop an aircraft that could fly safely at low airspeeds. The result was the first successful rotorcraft, which he named autogiro in 1923. Cierva's autogiro used an airplane fuselage with a forward-mounted propeller and engine, an un-powered rotor mounted on a mast, and a horizontal and vertical stabilizer. His aircraft became the predecessor of the modern helicopter.Early development
It took four years of experimentation for Cierva to invent the first practical rotorcraft, the autogyro, in 1923. His first three designs were unstable because of aerodynamic and structural deficiencies in their rotors. His fourth design, the C.4, made the first documented flight of an autogyro on 17January 1923, piloted by Alejandro Gomez Spencer at Cuatro Vientos airfield near Madrid, Spain.The first tests of the C.4 model, built in 1922 according to principles that Cierva had worked out for rotor flight, were unsuccessful. To find a solution, Cierva conducted a complete series of tests in the closed-circuit wind tunnel at Cuatro Vientos Aerodrome, at that time the best in Europe. The new, modified aircraft was successfully tested on January 9, 1923, at Getafe Aerodrome, piloted by Lieutenant Alejandro Gómez Spencer. Although this flight consisted only of a 183 m jump, it demonstrated the validity of the concept. At the end of the month, the C.4 completed a 4 km closed circuit at Cuatro Vientos Aerodrome in four minutes, at an altitude of about 30 m. The C.4's powerplant was a 110 hp Le Rhône 9Ja engine. In July 1923, the same engine was used in the C.5, which flew at Getafe. From that moment on, La Cierva, who had financed his previous experiments at his own expense, relied on a grant from the Spanish government for his work.
Cierva had fitted the rotor of the C.4 with flapping hinges to attach each rotor blade to the hub. The flapping hinges allowed each rotor blade to flap, or move up and down, to compensate for dissymmetry of lift, the difference in lift produced between the right and left sides of the rotor as the autogyro moves forward. Three days later, the engine failed shortly after takeoff and the aircraft descended steeply but slowly to a safe landing, validating de la Cierva's efforts to produce an aircraft that could be flown safely at low airspeeds.
Cierva developed his C.6 model with the assistance of Spain's Military Aviation establishment, having expended all his funds on the development and construction of the first five prototypes. The C.6 first flew in February 1925, piloted by Captain Joaquín Loriga, including a flight of from Cuatro Vientos airfield to Getafe airfield in about eight minutes, a significant accomplishment for any rotorcraft of the time. Shortly after Cierva's success with the C.6, he accepted an offer from Scottish industrialist JamesG. Weir to establish the Cierva Autogiro Company in the UK, following a demonstration of the C.6 before the British Air Ministry at RAE Farnborough, on 20October 1925. Britain had become the world centre of autogyro development.
A crash in February 1926, caused by blade root failure, led to an improvement in rotor hub design. A drag hinge was added in conjunction with the flapping hinge to allow each blade to move fore and aft and relieve in-plane stresses, generated as a byproduct of the flapping motion. This development led to the Cierva C.8, which, on 18September 1928, made the first rotorcraft crossing of the English Channel followed by a tour of Europe.
United States industrialist Harold Frederick Pitcairn, on learning of the successful flights of the autogyro, visited de la Cierva in Spain. In 1928, he visited him again, in England, after taking a C.8 L.IV test flight piloted by Arthur H.C.A. Rawson. Being particularly impressed with the autogyro's safe vertical descent capability, Pitcairn purchased a C.8 L.IV with a Wright Whirlwind engine. Arriving in the United States on 11December 1928 accompanied by Rawson, this autogyro was redesignated C.8W. Subsequently, production of autogyros was licensed to several manufacturers, including the Pitcairn Autogiro Company in the United States and Focke-Wulf of Germany.
File:Bundesarchiv Bild 102-00996A, Hubschrauber Focke-Wulf C 19 "Heuschrecke".jpg|thumb|A Focke-Wulf-built Cierva C.19 Mk.IV Autogiro
In 1927, German engineer Engelbert Zaschka invented a combined helicopter and autogyro. The principal advantage of the Zaschka machine is its ability to remain motionless in the air for any length of time and to descend in a vertical line so that a landing could be accomplished on the flat roof of a large house. In appearance, the machine does not differ much from the ordinary monoplane, but the carrying wings revolve around the body.
Development of the autogyro continued in the search for a means to accelerate the rotor before takeoff. Rotor drives initially took the form of a rope wrapped around the rotor axle and then pulled by a team of men to accelerate the rotorthis was followed by a long taxi to bring the rotor up to speed sufficient for takeoff. The next innovation was flaps on the tail to redirect the propeller slipstream into the rotor while on the ground. This design was first tested on a C.19 in 1929. Efforts in 1930 had shown that the development of a light and efficient mechanical transmission was not a trivial undertaking. In 1932 the Pitcairn-Cierva Autogiro Company of Willow Grove, Pennsylvania, United States solved this problem with a transmission driven by the engine.
Buhl Aircraft Company produced its Buhl A-1, the first autogyro with a propulsive rear motor, designed by Etienne Dormoy and meant for aerial observation. It had its maiden flight on 15December 1931.
De la Cierva's early autogyros were fitted with fixed rotor hubs, small fixed wings, and control surfaces like those of a fixed-wing aircraft. At low airspeeds, the control surfaces became ineffective and could readily lead to loss of control, particularly during landing. In response, de la Cierva developed a direct control rotor hub, which could be tilted in any direction by the pilot. De la Cierva's direct control was first developed on the Cierva C.19 Mk.V and saw the production on the Cierva C.30 series of 1934. In March 1934, this type of autogyro became the first rotorcraft to take off and land on the deck of a ship, when a C.30 performed trials on board the Spanish navy seaplane tender Dédalo off Valencia.
Later that year, during the leftist Asturias revolt in October, an autogyro made a reconnaissance flight for the loyal troops, marking the first military employment of a rotorcraft.
When improvements in helicopters made them practical, autogyros became largely neglected. Also, they were susceptible to ground resonance. They were, however, used in the 1930s by major newspapers, and by the United States Postal Service for the mail service between cities in the northeast.