Helicopter flight controls
Encyclopedia
A helicopter
pilot
manipulates the helicopter flight controls in order to achieve controlled aerodynamic flight
. The changes made to the flight controls are transmitted mechanically to the rotor, producing aerodynamic effects on the helicopter's rotor blades which allow the helicopter to be controlled. For tilting forward and back (pitch), or tilting sideways (roll), the angle of attack
of the main rotor blades is altered cyclically during rotation, creating differing amounts of lift at different points in the cycle. For increasing or decreasing overall lift, the angle of attack for all blades is collectively altered by equal amounts at the same time resulting in ascents, descents, acceleration and deceleration.
A typical helicopter has three separate flight control inputs. These are the cyclic stick, the collective lever, and the anti-torque pedals. Depending on the complexity of the helicopter, the cyclic and collective may be linked together by a mixing unit, a mechanical or hydraulic device that combines the inputs from both and then sends along the "mixed" input to the control surfaces to achieve the desired result. The manual throttle may also be considered a flight control because it is needed to maintain rotor speed on smaller helicopters without governors.
and Robinson R44
have a unique teetering bar cyclic control system and a few early helicopters have had a cyclic control that descended into the cockpit from overhead, one example being the HC-2 "Heli Baby", HC-102.
The control is called the cyclic because it changes the pitch
angle of the rotor blades cyclically. That is, the pitch or feathering angle of the rotor blades changes depending upon their position as they rotate around the hub so that all blades will change their angle the same amount at the same point in the cycle. The change in cyclic pitch has the effect of changing the angle of attack
and thus the lift generated by a single blade as it moves around the rotor disk. This in turn causes the blades to fly up or down in sequence, depending on the changes in lift affecting each individual blade.
The result is to tilt the rotor disk in a particular direction, resulting in the helicopter moving in that direction. If the pilot pushes the cyclic forward, the rotor disk tilts forward, and the rotor produces a thrust vector in the forward direction. If the pilot pushes the cyclic to the right, the rotor disk tilts to the right and produces thrust in that direction, causing the helicopter to move sideways in a hover or to roll into a right turn during forward flight, much as in a conventional aircraft.
On any rotor system there is a delay between the point in rotation where a change in pitch is introduced by the flight controls and the point where the desired change is manifest in the rotor blade's flight. While often discussed as gyroscopic precession for ease of teaching, this phase lag varies with the geometry of the rotor system and is the angular difference between the point of application of a cyclic pitch change and the point where the effect of that pitch change reaches maximum amplitude. This lag is an example of a dynamic system in resonance but is never more than ninety degrees.
pedals in an airplane, and serve a similar purpose, namely to control the direction in which the nose of the aircraft is pointed. Application of the pedal in a given direction changes the pitch of the tail rotor blades, increasing or reducing the thrust produced by the tail rotor and causing the nose to yaw
in the direction of the applied pedal. The pedals mechanically change the pitch of the tail rotor altering the amount of thrust produced.
In many piston engine-powered helicopters, the pilot manipulates the throttle to maintain rotor speed. Turbine engine helicopters, and some piston helicopters, use governors or other electro-mechanical control systems to maintain rotor speed and relieve the pilot of routine responsibility for that task. (There is normally also a manual reversion available in the event of a governor failure.)
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. It is the interaction of these controls that makes hovering difficult, since an adjustment in any one control requires an adjustment of the other two, creating a cycle of constant correction.
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Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...
pilot
Aviator
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...
manipulates the helicopter flight controls in order to achieve controlled aerodynamic flight
Flight
Flight is the process by which an object moves either through an atmosphere or beyond it by generating lift or propulsive thrust, or aerostatically using buoyancy, or by simple ballistic movement....
. The changes made to the flight controls are transmitted mechanically to the rotor, producing aerodynamic effects on the helicopter's rotor blades which allow the helicopter to be controlled. For tilting forward and back (pitch), or tilting sideways (roll), the angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
of the main rotor blades is altered cyclically during rotation, creating differing amounts of lift at different points in the cycle. For increasing or decreasing overall lift, the angle of attack for all blades is collectively altered by equal amounts at the same time resulting in ascents, descents, acceleration and deceleration.
A typical helicopter has three separate flight control inputs. These are the cyclic stick, the collective lever, and the anti-torque pedals. Depending on the complexity of the helicopter, the cyclic and collective may be linked together by a mixing unit, a mechanical or hydraulic device that combines the inputs from both and then sends along the "mixed" input to the control surfaces to achieve the desired result. The manual throttle may also be considered a flight control because it is needed to maintain rotor speed on smaller helicopters without governors.
Cyclic
The cyclic control is usually located between the pilot's legs and is commonly called the cyclic stick or just cyclic. On most helicopters, the cyclic is similar in appearance to a joystick in a conventional aircraft. By contrast, the Robinson R22Robinson R22
The Robinson R22 is a two-bladed, single-engine light utility helicopter manufactured by Robinson Helicopter. The two-seat R22 was designed in 1973 by Frank Robinson and has been in production since 1979.-Development:...
and Robinson R44
Robinson R44
|-See also:-External links:* * * * * *...
have a unique teetering bar cyclic control system and a few early helicopters have had a cyclic control that descended into the cockpit from overhead, one example being the HC-2 "Heli Baby", HC-102.
The control is called the cyclic because it changes the pitch
Blade pitch
Blade pitch or simply pitch refers to turning the angle of attack of the blades of a propeller or helicopter rotor into or out of the wind to control the production or absorption of power. Wind turbines use this to adjust the rotation speed and the generated power...
angle of the rotor blades cyclically. That is, the pitch or feathering angle of the rotor blades changes depending upon their position as they rotate around the hub so that all blades will change their angle the same amount at the same point in the cycle. The change in cyclic pitch has the effect of changing the angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
and thus the lift generated by a single blade as it moves around the rotor disk. This in turn causes the blades to fly up or down in sequence, depending on the changes in lift affecting each individual blade.
The result is to tilt the rotor disk in a particular direction, resulting in the helicopter moving in that direction. If the pilot pushes the cyclic forward, the rotor disk tilts forward, and the rotor produces a thrust vector in the forward direction. If the pilot pushes the cyclic to the right, the rotor disk tilts to the right and produces thrust in that direction, causing the helicopter to move sideways in a hover or to roll into a right turn during forward flight, much as in a conventional aircraft.
On any rotor system there is a delay between the point in rotation where a change in pitch is introduced by the flight controls and the point where the desired change is manifest in the rotor blade's flight. While often discussed as gyroscopic precession for ease of teaching, this phase lag varies with the geometry of the rotor system and is the angular difference between the point of application of a cyclic pitch change and the point where the effect of that pitch change reaches maximum amplitude. This lag is an example of a dynamic system in resonance but is never more than ninety degrees.
Collective
The collective pitch control, or collective lever, is normally located on the left side of the pilot's seat with an adjustable friction control to prevent inadvertent movement. The collective changes the pitch angle of all the main rotor blades collectively (i.e., all at the same time) and independent of their position. Therefore, if a collective input is made, all the blades change equally, and the result is the helicopter increases or decreases its total lift derived from the rotor. In level flight this would cause a climb or descent, while with the helicopter pitched forward an increase in total lift would produce an acceleration together with a given amount of ascent.Anti-torque pedals
The anti-torque pedals are located in the same position as the rudderRudder
A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...
pedals in an airplane, and serve a similar purpose, namely to control the direction in which the nose of the aircraft is pointed. Application of the pedal in a given direction changes the pitch of the tail rotor blades, increasing or reducing the thrust produced by the tail rotor and causing the nose to yaw
Flight dynamics
Flight dynamics is the science of air vehicle orientation and control in three dimensions. The three critical flight dynamics parameters are the angles of rotation in three dimensions about the vehicle's center of mass, known as pitch, roll and yaw .Aerospace engineers develop control systems for...
in the direction of the applied pedal. The pedals mechanically change the pitch of the tail rotor altering the amount of thrust produced.
Throttle
Helicopter rotors are designed to operate at a specific rotational speed. The throttle controls the power produced by the engine, which is connected to the rotor by a transmission. The purpose of the throttle is to maintain enough engine power to keep the rotor speed within allowable limits in order to keep the rotor producing enough lift for flight. In many helicopters, the throttle control is a single or dual motorcycle-style twist grip mounted on the collective control (rotation is opposite of a motorcycle throttle), while some multi-engine helicopters have power levers.In many piston engine-powered helicopters, the pilot manipulates the throttle to maintain rotor speed. Turbine engine helicopters, and some piston helicopters, use governors or other electro-mechanical control systems to maintain rotor speed and relieve the pilot of routine responsibility for that task. (There is normally also a manual reversion available in the event of a governor failure.)
| Name | Directly controls | Primary effect | Secondary effect | Used in forward flight | Used in hover flight |
|---|---|---|---|---|---|
| Cyclic (lateral) |
Varies main rotor blade pitch with left and right movement | Tilts main rotor disk left and right through the swashplate Swashplate (helicopter) A swashplate is a device that translates input via the helicopter flight controls into motion of the main rotor blades. Because the main rotor blades are spinning, the swashplate is used to transmit three of the pilot's commands from the non-rotating fuselage to the rotating rotor hub and... |
Induces roll in direction moved | To turn the aircraft | To move sideways |
| Cyclic (longitudinal) |
Varies main rotor blade pitch with fore and aft movement | Tilts main rotor disk forward and back via the swashplate Swashplate (helicopter) A swashplate is a device that translates input via the helicopter flight controls into motion of the main rotor blades. Because the main rotor blades are spinning, the swashplate is used to transmit three of the pilot's commands from the non-rotating fuselage to the rotating rotor hub and... |
Induces pitch nose down or up | To control altitude | To move forwards/backwards |
| Collective | Collective angle of attack Angle of attack Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving... for the rotor main blades via the swashplate Swashplate (helicopter) A swashplate is a device that translates input via the helicopter flight controls into motion of the main rotor blades. Because the main rotor blades are spinning, the swashplate is used to transmit three of the pilot's commands from the non-rotating fuselage to the rotating rotor hub and... |
Increase/decrease pitch angle of all main rotor blades equally, causing the aircraft to ascend/descend | Increase/decrease torque. Note: in some helicopters the throttle control(s) is a part of the collective stick. Rotor speed is kept basically constant throughout the flight. | To adjust power through rotor blade pitch setting | To adjust skid height/vertical speed |
| Anti-torque pedals | Collective pitch supplied to tail rotor Tail rotor The tail rotor, or anti-torque rotor, is a smaller rotor mounted so that it rotates vertically or near-vertically at the end of the tail of a traditional single-rotor helicopter. The tail rotor's position and distance from the center of gravity allow it to develop thrust in the same direction as... blades |
Yaw rate | Increase/decrease torque and engine speed (less than collective) | To adjust sideslip angle Sideslip angle Sideslip angle, also called angle of sideslip , is a term used in fluid dynamics and aerodynamics and aviation. It relates to the rotation of the aircraft centerline from the relative wind... |
To control yaw rate/heading |
Flight conditions
There are two basic flight conditions for a helicopter; hover and forward flightFlight
Flight is the process by which an object moves either through an atmosphere or beyond it by generating lift or propulsive thrust, or aerostatically using buoyancy, or by simple ballistic movement....
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Hover
Hovering is the most challenging part of flying a helicopter. This is because a helicopter is dynamically unstable. The end result is constant control inputs and corrections by the pilot to keep the helicopter where it is required to be. Despite the complexity of the task, the control inputs in a hover are simple. The cyclic is used to eliminate drift in the horizontal plane, that is to control forward and back, right and left. The collective is used to maintain altitude. The pedals are used to control nose direction or headingCourse (navigation)
In navigation, a vehicle's course is the angle that the intended path of the vehicle makes with a fixed reference object . Typically course is measured in degrees from 0° clockwise to 360° in compass convention . Course is customarily expressed in three digits, using preliminary zeros if needed,...
. It is the interaction of these controls that makes hovering difficult, since an adjustment in any one control requires an adjustment of the other two, creating a cycle of constant correction.
Forward flight
In forward flight a helicopter's flight controls behave more like those in a fixed-wing aircraft. Displacing the cyclic forward will cause the nose to pitch down, with a resultant increase in airspeed and loss of altitude. Aft cyclic will cause the nose to pitch up, slowing the helicopter and causing it to climb. Increasing collective (power) while maintaining a constant airspeed will induce a climb while decreasing collective will cause a descent. Coordinating these two inputs, down collective plus aft cyclic or up collective plus forward cyclic, will result in airspeed changes while maintaining a constant altitude. The pedals serve the same function in both a helicopter and an airplane, to maintain balanced flight. This is done by applying a pedal input in whichever direction is necessary to center the ball in the turn and bank indicatorTurn and bank indicator
In aviation, the turn and bank indicator shows the rate of turn and the coordination of the turn. The rate of turn is indicated from a rate gyroscopically and the coordination of the turn is shown by either a pendulum or a heavy ball mounted in a curved sealed glass tube. No pitch information is...
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