The helicopter term comes from Greek Helix (propeller) and Pteron (wing). In fact the big propeller that surmounts the pilotage cabin is compound from two or plus shovels, shaped as the wings of a plane. The lift to win the force of gravity, is produced by the rotation of the shovels, mounted on the rotor shaft (called head rotor either horizontal rotor or principal rotor) and attached to an engine.
This rotation solves a problem but it creates another: For effect of the third principle of the dynamics (for every action, there is an equal and opposite reaction) the helicopter nacelle starts to rotate in sense adverse to that of shovels. To avoid this behaviour, it's necessary to apply a strength opposite to the rotation, gauged to offset the phenomenon. Used methods are generally two:
    1- A little propeller on the tail of helicopter (the tail vertical rotor), mounted in vertical position, on an arm being far from the head rotor.
    2- Another rotor in axis with the head rotor, of the same dimension, which rotates in oppsite direction.

The first solution is more used in the practice because offers a big readiness in the commands, and a simpler realization. The disadvantages are a greater trend to instability and a greater waste of energy.
The second system has a better stability of flight, a better use of the engines power, a more compact form due to the absence of the tail rotor. Disadvantages are a more less readiness in the commands, a more less speed of cruise, a high noisiness.
The coaxial rotor solution can be realized also with two rotors placed to the extreme points of helicopter (tandem rotors), as in the case of the famous Chinook CH 47, a giant long 30 meters (included shovels).

But once in air, how does it moves our helicopter? Several system are used, but everything must produce a strength opposed the direction of the movement. The better method is to incline the principal rotor so it pushes the air in the wanted direction: if for istance it inclines forward (back pushing), the helicopter will move ahead. Inclination can happen in the four directions: ahead, back, left, right. For this reason the helicopter succeeds to move also in reverse and slip of side, how we see in the saving or vigilance operations.
To finish, we can exploit the natural tendency of the helicopter to rotate on itself to our advantage, and obtain a further movement. Is sufficient to increase or decrease forces it that offsets the self-rotation, to turn in a sense or in the opposite sense. The system with tail rotor, uses the greater or minor push of vertical propeller; the coaxial system uses the thrust difference between the two rotors.
 

EVERYTHING HERE?
I simplified the concept of helicopter, to make you understand the principles of base that raise these wonderful aircraft from the ground. Actually the flight theory is much more complex, for the realization of the rotors, for the technique and the physics that regulates rotating wing aerodynamics, for the pilotage. To this we have to add the interaction with the ground and near objects, the autorotation mechanism and the gyroscopic systems. I apologize for this extreme simplification, but if you will want it I will publish a more complete article on the basis of your curiosities. Write!
 

The helicopter tested uses the system of the coaxial double rotor, with an original variation. The back-forward thrust is obtained with a little "horizontal" tail rotor which can turn clockwise or anticlockwise. In practice the tail comes pushed up or down from the airflow produced: if the thrust is toward down, the helicopter go forward; if the thrust is toward up it countermarches. The two head rotors, change their speed of rotation in an independent but coordinated way: this way the helicopter can rotate clockwise or anticlockwise about its axis.

From keen on technology, I wanted to look at the structure of this helicopter closely. Begin from the coaxial rotors. They are of four shovels kind, inclined to produce the right lift, fixed to a plastic ring that protects them by the accidental crashes. Shovels are connected to the rotor tree with balancing hinges, in pairs of two. This precaution is fundamental for the "passive compensation" of the aerodynamic turbulences.
The result, covered by international patent, is a remarkable stability of rotation with few parts in motion.
 

After removing the nacelle, made of very light plastic, we can access the mechanical and electronic components that drives the rotors. The rechargeable Lithium Polymers rechargeable battery is placed in vertical in the front. Alongside, always in vertical, finds place the electronic board. It is aprinted circuit double-sided with the functions of receiver, engine control, regulation and battery charging. The receiving antenna is constituted by the support skates (shaped to V inside-out) of the helicopter.

Between battery and board, finds place the rotor tree with the gears group, on the top. The two engines are mounted vertically and everybody drives a different shaft, connected to the relative group of shovels.
 

The tail rotor is constituted by a micro motor with the propeller protected from a plastic ring. Rings surrounding the propellers have the dual function to avoid carving (to the aircraft and to the people) and make more soft reactions to the movements.

The helicopter is an RTF (Ready To Fly). Inside the box we find Blade Runner, the remote control with the antenna, the charger and an instructions manual essential but well done. We will have to melt the strings of packing that fix the skates and the tail rotor, with delicacy, free the two coaxial rotors and remove the protections in tissue paper.

After extracting all the pieces, obtain a 9 volt battery (not included) for the radio control, insert it with the right polarity, screw the telescopic antenna and extract it completely. We are already ready to the first flight!
The radio control serves also to charge the battery of the model with an ingenious system: connect the power supply to the radio control; extract the small energy cable from the compartment near the 9 volt battery; insert the small cable in the connector under the helicopter (insertion only takes place in one way, use delicacy and not force). When charging, both the radio control and the helicopter must be off.

The radio control has two levers (stick) to control the flight. The lever to left moves up or down (high and low), that to right can move in the four directions (ahead, back, left, right). In addition, a slider to sledge (trim) is used to balance the rotation of the two head rotors.
 

Now we can turn on the radio control and the helicopter from the respective switches (position ON). After verifying that the flight area is free from obstacles, start up the principal rotor. Bring the altitude stick all down to activate the rotors, and with a settled movement move it to half run (up). The helicopter lifts up and we can observe if it rotates itself: in this case acting on the trim of the principal rotor, in the opposite direction of the rotation is necessary. Try to rise and get down of altitude, then begin to try left rotation (left), right rotation (right) and at last the directions ahead (fwd) and back (rev).
A perfect landing is obtained by taking the altitude stick gradually down and raising it slightly before touching the ground. Just touched earth, take the stick to zero (all down) to avoid dierty movements of the aircraft. The action field of the radio control is about 20 meters.


 

A toy of this kind would have been unthinkable until some year ago. The flight of a helicopter is very difficult to manage, in particular when the model has reduced dimensions (41 centimetres of length and 29 centimetres of width). With Blade Runner the pilotage complexity is subdued from the innovative system of coaxial propulsion and from the control electronics. If you want to approach yourselves to the charming world of the radio-controlled helicopters, this aircraft will not disappoint you.

I thank Nicoshop for having turned my house into a flying field and give you the direct link for Blade Runner:
http://www.nicoshop.it/cat102.html