Caracas, 11/05/2010, Learning Aeroblog .- to fly a helicopter is a challenge. If you fly an airplane can be likened to riding a bike, fly a helicopter is more like juggling riding a unicycle.
helicopters are
helicopters are
so difficult to drive, because they are unstable in itself. While an aircraft can "focus" and then let it fly almost alone, if given freedom to a helicopter, it will start up and could end up crashing. Avoid giving these oscillations is part of pilot work, but it is a task that can fray the nerves of a beginner.
Students often need an average of between 10 and 15 hours to control the basics of how to fly a real helicopter. Pilots using Flight Simulator typically need an average of 6 hours to master the basics in a Robinson R22 Beta II or a Bell 206B JetRanger III by simulation. The first few hours can be frustrating, but do not throw in the towel. Indeed, these characteristics make flying a helicopter into a challenge so do a lot of fun. And once you've mastered the subtleties of rotary flight, there is nothing that can compare.
rotors are the wings
To understand the aerodynamics of the helicopter, remember that the main rotor system of the device serves as the wings. The rotors are profiles of the wing and, therefore, generate a lift similar to those of aircraft wings and react to changes in the angle of attack and loss-enter-just as the wings.
In an airplane, the wings are responsible for the lift, while the propeller provides traction. In a helicopter, the same component generates lift as much traction: the main rotor blades. The circular area defined by the rotation of the blades is called "disk rotor. In short, the rotor disc pushes air down and the helicopter rises. If you tilt the disc rotor, the helicopter will move in the direction of tilt. If the main rotor rotates, a force equal and opposite spin to the fuselage the helicopter in the opposite direction. The tail rotor compensates for this couple.
SPECIAL EFFECTS SPEED
operational characteristics of helicopters create special aerodynamic conditions that the pilot must understand perfectly. Among the most important may be mentioned:
- Ground Effect
refieree The ground effect is a reduction in induced drag when a plane flies near the ground. In a helicopter, ground effect is defined as an increase in performance when the device is at a distance from ground equivalent to the size of its rotor. This effect is more obvious when the main rotor disk is half the distance from the rotor to the ground. As in an aircraft, ground effect occurs when the soil interferes with the vortices produced at the ends of the main wing profile, in this case, vortices of the rotor tip. In addition, the soil reduces the induced flow acceleration (air is pushed down and through the rotor disk). The slowing down of the induced flow makes any angle of pitch is more effective in generating lift. When you are under the ground effect, the helicopter requires less power to maintain the hover.
- travel trend (cyclical stiffening)
helicopters tend to result in the same direction as the tail rotor drive. For example, helicopters built in the U.S. tend to drift to the right in a hover. Manufacturers compensate this effect by tilting the main rotor mast slightly to the left or cyclic stretching step slightly to the left. However, it is possible that the pilot should apply light pressure cyclic step to the left to compensate, especially when operating at a high rate power, for example, during a hover or a promotion.
- effective translational lift (ETL)
- Effect of crossflow
Reduction of lift on the rear disc rotor that occurs during forward flight or in a hover into the wind. At low speeds, the air passing through the rear disc rotor speeds for longer and more vertically moving air from the front of the disc. When this accelerated air flows through the back of the disc, reduce the angle of attack of rotor blades, reducing the lift generated by the rear disc rotor. Dissymmetry
The dissymmetry lift is a situation in which the main rotor does not generate the same level of support throughout the disc rotor. The dissymmetry of lift is more evident during a blade loss, which left half of the rotor disk (top view) stalls due to high feed rate, high gross weight, high density altitude and low rotor rpm as well as turbulence, abrupt use of controls and steep turns. This effect occurs only when the helicopter is flying forward or in a hover into the wind. Designers can compensate for dissymmetry of lift making the fins or blades are put into flag. FLIGHT CONTROL
- Step cyclic Accelerator
anti-torque pedals Helicopters are much more sensitive to movement controls of any aircraft. To fly a helicopter in a smooth and precise, it is necessary to coordinate the use of all flight control and power. Remember these basics:
- Apply gentle pressure to the controls, always refraining from sudden or exaggerated movements, since they cause increasing oscillations greater than can quickly lead to a loss of absolute control. Almost just about what to do and the helicopter will: so mild pressure should be applied to the controls.
- must anticipate what will happen when you move a control and what should be the corresponding movements of the other controls. For example, if the power increases by increasing the general step, you must also drive the left anti-torque pedal to compensate for the tendency of the helicopter to turn right.
- sure you fully understand the effects of special aerodynamic characteristics of helicopters and settings control necessary to compensate. Must be able to anticipate these effects, not just reacting to them. If you expect to notice the effect to react and have trouble controlling the device.
- Under no circumstances remove the hand of the cyclical passage while the main rotor is spinning.
- After landing, make sure the helicopter is firmly seated and that the general step is completely down prior to engine shutdown. Keep the cyclical passage in neutral until the main rotor stops.
The general step
The general step (or "control the pitch of the general step) is used as the primary way to control the altitude and the power of a helicopter. This step varies the lift produced by the main rotor system to increase or decrease simultaneously or jointly pitch of all main rotor blades. Basically, the general step determines the thrust vector.
In a real helicopter, you use the left arm to raise and lower the general step, moving a long lever mounted on the cabin floor.
By raising the general step simultaneously increases the pitch (and therefore the angle of attack) of all the blades, increasing the lift generated by the main rotor system. Lowering the general way, simultaneously decreasing the pitch (angle of attack) of all the blades, reducing the lift generated by the main rotor system.
Raising the collective pitch, rotor blades produce more lift. However, the higher angle of attack of the blades also generates a higher resistance, so you must increase power to maintain rotor rpm. This increase in power results in an equal and opposite reaction by increasing torque. Therefore, when you increase the collective pitch must also tread left anti-torque pedal. Reducing the general step, reduce lift and drag, less power is needed to maintain rotor RPM and therefore, the torque decreases. To achieve a coordinated flight, must step on the right pedal when you reduce the general step. Remember to predict what will happen. If you wait to feel the effect of a control movement to react and have trouble controlling the device.
acceleration accelerator is mounted on the end of the general step.
The most important rule for flying a helicopter is this: keep constant the number of rotor revolutions per minute!
If the main rotor and tail do not turn fast enough, will not generate sufficient lift, which could have fatal consequences. Without the lift of the main rotor, a helicopter can not stay in the air, without the lift of the tail rotor, the pilot can maintain control of yaw.
The cyclical passage
During the flight, the step cycle (or step control cyclic pitch) controls pitch attitude and tilt of a helicopter, that is, performs the same function as the control lever that controls the rudder and ailerons on an airplane. The cyclical passage is the main control airspeed during flight. By applying the cyclic step forward, airspeed increases, if applied back is reduced.
The direction of the force generated by the rotor disk is controlled by tilting the same for cyclic and step through a series of mechanical devices. The cyclical passage of the rotor disk tilts, and during a hover, controls the direction and speed of movement of the helicopter on the ground. Moving the cyclic step forward, the helicopter flies forward. To move to the left, the helicopter moves (ie moves in the field) to the left, and so on. The general position of the step determines the thrust vector. The cyclic pitch position determines the angle (or direction) of the thrust vector.
The degree of pressure applied on the cyclical passage will determine how fast the helicopter will move in a specific direction. To move the step cyclical adjustments are usually due to other flight controls over general and anti-torque pedals. For example:
- In a normal cruise flight, when it is cyclic step forward, the nose of the helicopter also leans forward. Airspeed increases and the helicopter drops below an increase in the general way to increase lift produced by the main rotor and increase power.
- Moving back the cyclic, the nose of the helicopter rises. Airspeed decreases and the helicopter rises, unless a reduction in the general way to decrease the power.
- When you move the general step, the pair change, so also must tread left or right anti-torque pedal to maintain coordinated flight.
anti-torque pedals
The torque produced by the main rotor is compensated by the anti-torque pedals. Increasing the step generally increases the torque, if you reduce the collective pitch is reduced to par. You must use the pedals, or end up turning without control.
By increasing the general way to increase power, you walked on the left pedal to prevent the helicopter turn to the right. Similarly, by reducing the general way to decrease the power, you walked on the right pedal to compensate for the reduction in torque. (Note that this contradicts the trends turn left onto an airplane at high power.)
In forward flight, a helicopter tour as an airplane is tilted. In a hover, use the pedals to keep track of the helicopter, that is, the direction you point the nose. During the hover, you can also use the left or right pedal rotate the helicopter. This type of rotation is often called "turn of foot."
During cruise flight and the normal ups and downs, use the pedals to maintain coordinated flight, ie for the helicopter to keep focused. Do not use the pedals for turns, except during hovering. Use the cyclical passage to tilt and turn the helicopter and to stay the course of the unit. You can determine if the helicopter is not centered or watching the ball inclinometer or needle turn. If the ball is on the left of center, step on the pedal. If the ball is on the right of center, push the right pedal. Power divided
engine helicopter rotor drives both the main and tail rotor tail. If you need a high power setting to maintain a hover or to make a hover in strong crosswind conditions may cause the tail rotor is not able to generate enough momentum to counteract the torque provided by the main rotor or the tendency of the helicopter to spin in the wind.
DNA / Aeroblog
Source: MAFUSO.NET
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