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Control

BAsics

A helicopter is controlled with three different controls. The joystick, also called cyclic, is used in hover to move the helicopter left, right, front or back. In forward flight, the Cyclic initiates the turns or the ascent and descent. With the pedals, the helicopter can be rotated around the vertical axis in place, and with the Collective, the pilot controls the ascent and descent in hover, and together with the Cyclic the speed in forward flight.

For each helicopter, the joystick is operated with the right hand and the collective with the left. The feet are needed to control the tail rotor via the pedals. Because of the instability of a helicopter, the Cyclic must not be released in flight, unless the helicopter is equipped with an automatic stabilization system.

With the control organs (Cyclic, Collective and Pedals) the setting angle to the Hauptrotor- resp. Tail rotor blades mechanically adjusted. The setting angle is the angle between a defined line on the helicopter and the employment of the rotor blade profile. The angle of attack, on the other hand, is the angle between the rotor blade profile and the incoming air. This means that with the adjustment of the adjustment angle via the control system, the angle of attack and thus the lift are also changed.

Grundlagen Helikopterflug

As soon as the pilot pulls up on the collective, the setting angle (and thus the angle of attack) of all rotor blades is increased by the same amount. As a result, the overall lift increases and the helicopter begins to rise. By analogy, the setting angle decreases as the pilot pushes the collective down.

When the Cyclic is pushed forward, the pitch of the rotor blades changes continuously during one revolution. Due to the different buoyancy, the rotor blade plane is tilted forward. Of course, the plane tilts back as soon as the pilot pulls the Cyclic backwards.

The same as described above happens when the pilot pushes the cyclic either to the right or to the left.

 

With the pedals the adjustment angle of all tail rotor blades is adjusted by the same amount (similar to the collective blade adjustment on the main rotor). This increases or decreases the tail rotor thrust.

 

The whole thing with the controller has only a small catch. As soon as the pilot changes something on one of the three rudders, he also has to correct the other two. As we know, the pilot has to pull at the collective if he wants to climb up in hover. This now causes the torque increases due to the larger angle of attack of the rotor blades (and thus increased air resistance). As a result, the helicopter begins to turn around the vertical axis, which can only be prevented with a correction to the tail rotor. Now that the tail rotor provides a greater lateral thrust, the lateral displacement of the helicopter is also increased, which in turn can only be compensated with a correction on the Cyclic. One might think that the helicopter is now in a stable hover. This is unfortunately not the case!! Due to the external influences (especially wind) and the non-constant turbulence around the helicopter, the pilot must always correct at all controls in order to keep a stable hover. The big difficulty is to properly coordinate all these little corrections. Only when a pilot student no longer has to study which control they should now correct, they can keep the helicopter in a more or less stable hover. To train this automatism, it takes some time (and some sweat drops).

Technology

The control of a helicopter is ensured by control rods on the swashplate (or tail rotor) via control rods, reversing levers and control cables.

 

The most important element of helicopter control is the swashplate. It lies on the rotor axis, directly under the main rotor and is responsible for the transmission of the control impulses to the individual rotor blades.

 

Basically, the swash plate consists of two parts, the fixed and the rotating part. The fixed or lower part is connected via control rods and lever with the joystick and the rotating or upper part with each individual rotor blade. If the swashplate is tilted forwards or sideways with the control stick, the setting angle of each rotor blade changes during one revolution (cyclic pitch adjustment). When the pilot pulls up on the collective, the swashplate moves up as a whole and the pitch of all blades increases simultaneously (collective pitch). This principle works regardless of the number of rotor blades of the helicopter.

The control is usually supported on smaller helicopters with hydraulic servomotors to reduce the effort of the pilot. In medium and large helicopters occur on the swash plate so large forces that a purely mechanical control (only with control rods and lever) is no longer possible, and the control can be ensured only with hydraulic assistance.

 

 

 

 

 

 

The control of the tail rotor works basically the same. The main difference is that only the collective blade adjustment is needed. The pedals in the cockpit are connected to the so-called spider via control rods, bellcrank and control cables. The spider transmits the control pulses to the individual tail rotor blades, similar to the swash plate on the main rotor. Again, the larger the helicopter, the greater the control forces on the tail rotor and the more the control must be supported with hydraulic aids.

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