Gyros Summary

  • Last updated on November 10, 2022

An aircraft that, during most of its flight, derives a substantial part of its lift force from a free-spinning rotor system not provided with any form of direct power drive.

Terminology

As recognized by the Federal Aviation Administration (FAA), “gyroplane” is the correct generic term for a type of aircraft that, during most of its flight, derives a substantial part of its lift force from a free-spinning rotor system not provided with any form of direct power drive. The term “gyrocopter” is actually a proprietary name originally used by Bensen Aircraft Corporation to designate its B8-M Gyrocopter. The B8-M was the predecessor of most amateur-built sport gyroplanes. “Autogyro” is an older term, often used for this type of aircraft, but it, too, is actually a proprietary name used by the Autogyro Company of America, which built some of the first gyroplanes. “Gyro” is a nickname applied to all these types of aircraft.

Features

The gyroplane is any type of aircraft that relies primarily on an unpowered, freewheeling (or autorotating) rotor as the main source of lifting force and has a separate propeller and engine combination providing forward thrust. Modern gyroplanes look much like helicopters with conventional-appearing tail surfaces. An example of a gyroplane is the Air and Space 18-A, which has these typical characteristics.

The gyroplane was invented by Juan de la Cierva, an early twentieth century civil engineer born in Spain. Cierva’s first successful flight was made near Madrid, Spain, on January 9, 1923. The first gyroplane to be certified by the FAA in the United States was the Pitcairn PCA-2 gyroplane, which, at that time, was called an autogyro. Early gyroplanes looked much like double-wing aircraft with the top wing removed and replaced with a rotor. They had a conventional engine and propeller in front for forward thrust, a small lower wing for auxiliary lift and control, and conventional-looking tail surfaces, with a large rotor on top of the fuselage for primary lift.

The performance features of gyroplanes are a combination of those of helicopters and fixed-wing aircraft. The rotor is usually in autorotation, turned by the wind, much like the blades of a windmill that has been turned edgewise to the wind. There must be airflow through the rotor to keep it turning, and thus the gyroplane requires separate forward propulsion to keep it moving through the air. For this reason, gyroplanes cannot hover or take off and climb vertically like a helicopter. Although they can make fully controlled vertical descents, the speed is somewhat high, and landings are not performed in this manner. A gyroplane can fly very slowly and has a very short landing roll. Most gyroplanes temporarily use the engine to spin up the rotor before the takeoff run, thus allowing a very short takeoff roll. Engine power is removed from the rotor just before takeoff. A few gyroplanes also have a jump-takeoff capability. In a jump takeoff, the rotor is oversped with the rotor blades in a low pitch setting while the gyroplane is sitting on the ground. Power is then removed from the rotor and transferred to the forward propulsion system. The blade pitch is then rapidly increased to the normal cruise flight setting, and the gyroplane literally jumps off the ground, perhaps 10 to 15 feet into the air before transitioning to forward flight.

Amateur-built sport gyroplanes are often single-seat, open-cockpit aircraft that look much like flying lawn chairs, with a rotor on top and engine, propeller, and tail surfaces in the rear. An example of this type of gyroplane is the Brock KB-2.

Rotor Systems

A gyroplane’s rotor “disk” is the tip path plane swept out by the individual rotor blades as they spin. The rotor disk is approximately perpendicular to the rotor shaft. A fundamental difference between the rotor disks of helicopters and gyroplanes is that a gyroplane rotor disk is tilted slightly rearward when viewed from the side. This angle provides both upward lift and rearward drag that must be overcome by the forward propulsion system. The individual rotor blades of a gyroplane are set at a low-pitch angle, which allows them to operate in autorotation. In a helicopter, the rotor disk is tilted slightly forward, providing upward lift as well as a component of the forward thrust for propulsion. The helicopter’s engine spins the rotor and must provide the torque necessary to turn the rotor. Because the rotor blades of a helicopter have a higher pitch angle than those of a gyroplane, they require a power input in order to rotate.

A number of different rotor systems are in use in gyroplanes. All gyroplanes must have hinges on the blades where they attach to the rotor hub. In forward flight, the blade moving into the wind (advancing blade) would create more lift than the blade moving away from the wind (retreating blade). Without hinges, this would cause a dissymmetry of lift that would tend to roll the gyroplane over. This was the source of many problems in early attempts at rotary wing flight. Hinging the individual rotor blades allows them to flap up and down slightly as they move into the wind and away from the wind. This equalizes the lift and allows controlled flight.

Smaller gyroplanes usually have a rotor system that consists of two blades rigidly attached together. The two blades are hinged to the rotor shaft at their center, much like the pivot on a seesaw, and allow the blades to flap as a unit to equalize the lift. In larger gyroplanes, with three or more rotor blades, each blade is individually hinged to the rotor hub, so the blades can flap up and down slightly as they rotate. Flapping stops designed into the rotor hub prevent the flapping motion from becoming excessive and keep the blades from drooping excessively when the gyroplane is on the ground and the rotor is not turning.

Propulsion

The forward propulsion in gyroplanes is usually provided by a conventional reciprocating engine turning a pusher propeller located behind the rotor mast and ahead of the tail surfaces. The pusher propeller arrangement has three advantages over an arrangement with the engine and propeller mounted in front, known as a tractor arrangement. First, the pusher propellor system allows for a more balanced gyroplane design, with cabin and crew weight in front of the rotor mast and the engine weight behind the rotor mast. Second, it provides better forward visibility for the pilot. Third, in the pusher propeller arrangement, the propeller slipstream hitting the tail surfaces provides better directional control and stability. Most early gyroplanes of the 1930’s vintage had propellers pulling from the front. Some gyroplanes have rotary Wankel-type engines, and one, the Groen Brothers Hawk 4 Gyroplane has a gas-turbine engine driving a three-bladed propeller.

Tail Surfaces

The tail surfaces, or empennage, on a gyroplane are used more for stability than for control purposes. As do fixed-wing aircraft, gyroplanes display a wide variety of tail surface designs. Conventional tail designs, as well as V-tail, H-tail, and triple-tail designs can be found. Vertical stabilizers usually have rudders on them that can be deflected to cause the nose of the gyroplane to yaw to the left or right. Large rudder surface areas are usually used to take advantage of the propeller slipstream to provide yaw control at low forward speeds. Unlike in an airplane, the horizontal tail surfaces of a gyroplane are not usually movable, but rather are fixed surfaces provided for stability. Because a gyroplane can fly very slowly, relatively large tail surfaces are usually necessary for stability at low speeds. For this reason, it is not uncommon to see double or even triple rudders on a gyroplane, used to increase the total surface area without having a single, excessively large tail. Occasionally a large single vertical fin is used if it is centrally placed in the propeller slipstream.

Control Systems

The main flight controls of a gyroplane consist of a joystick, rudder pedals, and a throttle. Variations of these do occur. The throttle controls the engine power output and thus the forward thrust of the propeller, much as in a conventional fixed-wing aircraft. This arrangement is different from that of a helicopter, in which the throttle controls the engine power input to the main rotor, usually operating at a constant rate of revolutions per minute.

A gyroplane’s joystick, also called a cyclic stick, controls the tilt of the rotor disk either by tilting the rotor shaft or by individually changing the pitch of the blades as they cyclically rotate (hence the term cyclic pitch). Tilting the stick to the left effectively causes the rotor disk to tilt to the left, causing a sideward component of rotor thrust that makes the gyroplane turn and bank to the left. Tilting the stick to the right does just the opposite. Pulling back on the cyclic stick tilts the rotor disk more rearward, causing an increase in rotor thrust due to the increased angle of attack to the airflow. This makes the gyroplane climb, assuming that sufficient thrust is produced by the propeller. Pushing forward on the cyclic stick tilts the rotor disk more forward, causing a decrease in rotor thrust and making the gyroplane descend. In essence, the cyclic stick controls the mechanical operation of the main rotor much the same as it would in a helicopter, but because the rotor is unpowered, it causes the gyroplane to respond much like an airplane to similar control stick inputs. Some gyroplanes have an overhead stick that requires movement in directions just the opposite of a joystick to control the rotor.

Rudder pedals operate the rudder as they would in an airplane, causing a yawing motion from right to left. In a helicopter, the rudder pedals are used to control yawing of the helicopter by changing the tail rotor blade pitch.

The gyroplane does not use a collective pitch lever in the same way a helicopter does. Instead, the collective pitch of the gyroplane’s rotor blades is factory preset at an optimum angle for normal flight operation. Gyroplanes that have a rotor prespin or jump-takeoff capabilities will usually have a two-position collective pitch control. One position, with the blades in flat pitch, is used for rotor spinup while on the ground. The other position, for normal flight, is engaged just before starting the takeoff roll or making a jump takeoff. In a helicopter, a collective pitch lever is provided to manually change the pitch of all the rotor blades simultaneously, thus changing the rotor thrust as needed.

Typical Gyroplanes

The following gyroplanes designed for production have been developed in the United States or Canada: Kellet, Pitcairn, Umbaugh (later designated the Air and Space 18-A), the Canadian Avian, McCulloch J-2, and the Groen Brothers Aviation Hawk 4 Gyroplane.

Amateur-built sport gyroplanes can be licensed with the FAA in the experimental category if the aircraft is at least 51 percent amateur-built. A number of companies—including Air Command International, Joe Souza Gyroplanes, Barnett Rotorcraft, Ken Brock Manufacturing, Rotor Flight Dynamics, Rotor Hawk Industries, and Rotary Air Force—have developed sport gyroplane kits, which can be assembled in various combinations to suit the homebuilder’s ability. The number of companies in the amateur-built field has proliferated so much that one must use care to select a well-proven and time-tested design.

Bibliography
  • Gablehouse, Charles. Helicopters and Autogiros. Philadelphia: J. B. Lippincott, 1967. A chronicle of rotary-wing aircraft, written in layperson’s language and illustrated with a number of photographs, with coverage of gyroplane history, designs, predictions for the future, helicopter airlines, and some technical descriptions of control systems and rotor mechanisms.
  • Jackson, P., ed. Jane’s All the World’s Aircraft. Alexandria, Va.: Jane’s Information Group, 1996. An excellent summary of most types of aircraft in the world, with photographs and descriptions in easy-to-read form. Gyroplanes appear in various editions from early to the present.
  • McCormick, Barnes W., Jr. Aerodynamics of V/STOL Flight. New York: Academic Press, 1967. Suitable primarily as a textbook for engineering students, this book discusses many principles applicable to gyroplanes as well as helicopters and describes the concept of autorotation.
  • U.S. Flight Standards Service. Rotorcraft Flying Handbook. Washington, D.C.: U. S. Department of Transportation, Federal Aviation Administration, Flight Standards Service, 2000. A well-illustrated technical manual for applicants seeking various levels of pilot ratings in helicopters or gyroplanes, with descriptions of how to fly gyroplanes and how gyroplane systems work.

Airplanes

Helicopters

Propellers

Propulsion

Rotorcraft

Rudders

Tail designs

Performance Specifications for Two Gyroplane Models

Air & Space 18-ABrock KB-2Number of rotor blades32Rotor diameter35 feet22 feetOverall length19.8 feet12 feetOverall height9.7 feet6.6 feetSeating capacity21Engine horsepower180 @ 2,700 rpm90 @ 4,100 rpmGross weight1,800 pounds600 poundsEmpty weight1,280 pounds230 poundsFuel capacity28.4 gallons10 gallonsTakeoff run50 feet, run or jump300 feetLanding rollShort roll or full stop0 to 10 feetMinimum level speed20 miles per hour20 miles per hourMaximum speed100 miles per hour95 miles per hourCruising speed95 miles per hour70 miles per hourMaximum rate of climb700 feet per minute1,000 feet per minuteEndurance3 hours at 65 percent power2 hours at 65 percent powerService ceiling12,000 feet13,500 feet

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