From there, the pitch control rods - connecting the rotating portion of the swashplate to What is the ratio of rotation of the main and tail rotors of a helicopter?. To make a helicopter fly, the pilot raises the collective and increases the lift on This is done by altering the pitch angle of the tail rotor blades. Aerodynamic interference between the main and tail rotor can have a strong negative influence on the flight advance ratio in lateral direction; positive to right. ˜μy . rotor collective pitch was controlled to develop a prespecified main rotor.
As it is more efficient at low speeds to accelerate a large amount of air by a small degree than a small amount of air by a large degree,   a low disc loading thrust per disc area greatly increases the aircraft's energy efficiency, and this reduces the fuel use and permits reasonable range. The following are driven by the link rods from the rotating part of the swashplate. Pitch hinges, allowing the blades to twist about the axis extending from blade root to blade tip. Teeter hinge, allowing one blade to rise vertically while the other falls vertically.
Helicopter rotor - Wikipedia
This motion occurs whenever translational relative wind is present, or in response to a cyclic control input. Scissor link and counterweight, carries the main shaft rotation down to the upper swashplate Rubber covers protect moving and stationary shafts Swashplates, transmitting cyclic and collective pitch to the blades the top one rotates Three non-rotating control rods transmit pitch information to the lower swashplate Main mast leading down to main gearbox Main article: Swashplate helicopter Controls vary the pitch of the main rotor blades cyclically throughout rotation.
The pilot uses this to control the direction of the rotor thrust vectorwhich defines the part of the rotor disc where the maximum thrust develops. Collective pitch varies the magnitude of rotor thrust by increasing or decreasing thrust over the whole rotor disc at the same time.
These blade pitch variations are controlled by tilting, raising, or lowering the swash plate with the flight controls. The vast majority of helicopters maintain a constant rotor speed RPM during flight, leaving the angle of attack of the blades as the sole means of adjusting thrust from the rotor.
The swash plate is two concentric disks or plates. One plate rotates with the mast, connected by idle links, while the other does not rotate. The rotating plate is also connected to the individual blades through pitch links and pitch horns. The non-rotating plate is connected to links that are manipulated by pilot controls—specifically, the collective and cyclic controls. The swash plate can shift vertically and tilt.
Through shifting and tilting, the non-rotating plate controls the rotating plate, which in turn controls the individual blade pitch. Fully articulated[ edit ] Diagram of fully articulated main rotor head Juan de la Cierva developed the fully articulating rotor for the autogyro.
The basis of his design permitted successful helicopter development. In a fully articulated rotor system, each rotor blade is attached to the rotor hub through a series of hinges that let the blade move independently of the others.
These rotor systems usually have three or more blades. The blades are allowed to flap, feather, and lead or lag independently of each other. The horizontal hinge, called the flapping hinge, allows the blade to move up and down. This movement is called flapping and is designed to compensate for dissymmetry of lift.
The flapping hinge may be located at varying distances from the rotor hub, and there may be more than one hinge. The vertical hinge, called the lead-lag hinge or drag hinge, allows the blade to move back and forth.
This movement is called lead-lag, dragging, or hunting. Dampers are usually used to prevent excess back and forth movement around the drag hinge. The purpose of the drag hinge and dampers is to compensate for acceleration and deceleration caused by the Coriolis effect. Later models have switched from using traditional bearings to elastomeric bearings.
Elastomeric bearings are naturally fail-safe and their wear is gradual and visible. There are still several production helicopters which use multiple counterrotating rotors as a way to cancel out torque.
Examples are the Boeing-Vertol tandem rotor helicopters which evolved from Frank Piaseki's designs, Charles Kaman's intermeshing rotor system, and the Russian co-axial helicopter Hocum or Havoc I think it is, I'll have to look up the correct name I'm afraid. The V22 tilt-rotor uses counter-rotating proprotors in order to cancel out torque. It is similar to a tandem rotor system when in helicopter mode.
Tail Rotors Igor Sikorsky seems to be the first to settle on using a single rotor mounted at the rear of the helicopter as a way to counter the torque. This is the most popular arrangement today. Sikorsky actually experimented with many different arragements before selecting a single tail mounted rotor.
It seems strange that the majority of helicopters produced use this method of countering torque, given that there are several major problems with this method which are not encountered with counter-rotating rotor systems.
One major problem with tail rotors is that they rob an enormous amount of power. Another probem is that due to size and weight constraints, tail rotors are fairly delicate compared to main rotors. This means that they cannot survive an encounter with very large obstacles. Because they are mounted at the rear of the helicopter, out of the pilot's sight, a fairly common cause of helicopter accidents is hitting an obstacle with the tail rotor, losing all anti-torque capability, and crashing due to the rotation of the entire helicopter.
Still another problem with tail rotors is that they are fairly difficult to control accurately. Turbulence and crosswinds make it extremly difficult to hold a constant heading in a tail rotor equipped helicopter.
The workload is very high, and good results are difficult to achieve. Many larger helicopters end up being designed with a yaw stabalization system, which is essentially an autopilot for the tail rotor.
Tail Rotor Aerodynamics Tail rotors share many of the aerodynamics of the helicopter main rotor system. They are essentially identical to a main rotor which is mounted sideways and is controllable in collective pitch, but is not capable of cyclic feathering. Some of the same problems which designers encountered with main rotors occur with tail rotors.
Often the solution is similar or identical to the solution used on a main rotor.
Tail Rotor Dissymetry of Lift Tail rotors experience dissymetry of lift just as a main rotor system does. This lift dissymetry would cause a torque around the tail boom which would tend to roll the fuselage in the same direction as main rotor lift dissymetry. While cyclic pitch could be used to counter the rolling tendancy, the tail rotor blades are typically allowed to flap, eliminating the lift dissymetry.
Here is a picture of a Bell JetRanger tail rotor flapped to right and left extremes: Tail Rotor Translational Lift Just as a main rotor produces more lift when it moves into clean air, a tail rotor develops extra thrust when the helicopter moves it into clean air.
Unfortunately, the pilot sees this as a change in anti-torque force which results in an uncommanded yaw of the aircraft. The pilot is forced to make an adjustment to his anti-torque pedals as the tail rotor goes in and out of translational lift. There is no aerodynamic solution to this problem, and this is just one of the items which makes a tail rotor helicopter more difficult to fly.
One solution which is sometimes used is a yaw-damper, essentially an auto-pilot which uses a gyroscope to detect uncommanded yaw, and which changes tail rotor pitch in order to prevent uncommanded yaw. Tail Rotor Settling with Power Just as a main rotor can get into a Ring Vortex State by settling into it's downwash, yawing the helicopter such that the tail rotor settles into it's downwash sidewash? Indeed, a crosswind can induce the ring vortex state without any yaw being present. While this may seem unlikely, I personally know someone who crashed a helicopter as a result of this.
The solution to this problem is similar to that for the main rotor: A hover auto is probably the safest, most reliable way to get out of this situation. Tail Rotor Coning While some tail rotors may be designed to allow coning, all tail rotors that I am familiar with simply pre-cone the blades and don't worry about coning in the design.
I'll have to ask my friends at Sikorsky as they tend to build helicopters with large numbers of blades.
- Helicopter Tail Rotors – Part 2
- Helicopter Tail Rotors
- The Tail Rotor
Changing the Pitch In order to be able to yaw the aircraft both right or left, the tail rotor blades need to be able to be set to both negative and positive angles of attack, unlike main rotors which are normally only capable of positive angles of attack. The angle of attack of the tail rotor is controlled by the pilot's anti-torque pedals they're not "rudder pedals" in a helicopter. The pedals are typically connected to the pitch change mechanism by either push pull tubes, or by cables.
From the standpoint of controlling pitch, a tail rotor requires collective pitch control, but not cyclic feathering. This makes the pitch control mechanism of most tail rotors much simpler than that of the main rotor system.