FORE-AND-AFT ON THE HELICOPTER

Repeated attempts to rework expense of building a traditional model helicopters RC, as it was with model airplanes and gliders, were unsuccessful. This is because model helicopters, free flight, built according to a single-ended or coaxial circuits with rotating engines, do not have what is called a case. Simply put, they have neither the nose nor tail. Therefore, any movement for them, all except “up” and “down” is the direction forward. And control of the direction of motion of the model helicopter without orientated in space of body and the speed control of the movement, is impossible without swashplate. His on free-flying and so-called timer helicopters and no.

 

The lack of information about such models hinders the development of this class. As a result, unfortunately, we must note a big gap in it of our athletes.

 

Fig. 1.

 

 

Fig. 2.

 

Fig. 3.

 

There were many attempts to raise in the air RC model helicopter, but to overcome the psychological barrier — fear to break this difficult technique — was only the model aircraft at the Moscow aviation Institute Makeeva Vitaly and Igor Cibizova who established the first all-Union record duration flight with a landing at the take-off location is 6 min 20 s. In another flight, their model flew 2,700 m and landed at the prearranged site.

 

The study of the piloting of the model without serious breakdowns. Therefore, the possibility of trouble-free development of new technology should be considered proven. It is even held the opinion that learning to fly a model helicopter from easier than to relearn after piloting the model airplane. But before you start building the model, you need to get acquainted with the peculiarities of the schematic design and the principle popeta helicopter. Let’s start with the terminology that will facilitate our understanding.

 

Helicopter — a flying machine heavier than air, still able to hang and move in the air at any angle to the horizon. Lift and thrust he created one or several rotors driven in rotation by the motor.

Single-rotor helicopter (Fig. 1) with one (main) main rotor and tail rotor to compensate for the reactive moment. The tail rotor is also used to control the rate.

 

Coaxial helicopter (26, Fig. 2) with two rotors arranged on the same axis and rotating in opposite directions.

 

Helicopter transverse scheme (Fig. 3) with two rotors located on each side of the fuselage and rotating in opposite directions.

 

The helicopter of the longitudinal scheme (Fig. 4) with two rotors located at the ends of the fuselage and rotating in opposite directions.

 

 

Fig. 5. Automatic-bias:

 

1 — rotor shaft, 2 — thrust, 3 — axis flybarless, 4 — machine-skewed, 5 — pull roll control, 6 — pull longitudinal control 7 — lever upravlennya collective pitch.

 

 

Fig. 6. Diagram of a single-rotor helicopter:

 

1 — desire, 2 — vertical thrust, a 3 — set horizontal pull, 4 — weight 5 — drag.

 

The rotor (main) bolt that is used to create a lifting force.

 

The machine-skewed (Fig. 5) is a mechanism that serves to cyclic changes of the mounting angle (pitch) of the blades of the rotor.

 

Bushing rotor unit serving for connection of the blades with the drive shaft.

 

A horizontal hinge — part rotor hub, providing the ability of the flapping motion of the blades.

 

Axle joint part of the rotor hub, allowing you to change the mounting angle (pitch) of the blades.

 

The taper of the rotor surface described by the blades of the rotor.

 

The plane of rotation of the rotor , a plane passing through the hub of the rotor perpendicular to its axis.

 

Sway angle is the angle between the axis of the blades and the plane of rotation of the rotor.

 

The mounting angle is the angle between the chord of the profile to get there and the plane of rotation of the rotor.

 

The change in the total step is a simultaneous, identical change in the angle of installation of all the blades of all rotors of the helicopter.

 

Hovering — fixed the position of the helicopter in the air when his vertical and horizontal speed relative to the surrounding air is zero.

 

Autorotation mode of operation of the rotor without supplying power from the motor. The rotor in autorotation rotates under the influence of the incident (bottom or side) of air flow, creating lift and thrust. The term is applied to the helicopter in the chain.

 

The most prevalent modeling for design reasons got single-rotor model helicopters.

 

On the rotor need to know the following.

 

The smaller the number of blades, the greater its effectiveness.

During hovering and at vertical lift rotor of the helicopter works like a propeller. In forward flight its axis of rotation is tilted forward, and he is working on a new blasting. When the blades rotate, the lifting force causes them to climb, while the centrifugal force prevents their excessive-ing up, so the rotor disk has the conical shape.

 

From the shape of the blade is theoretically independent of the aerodynamic characteristics of the helicopter. However, even the practice tests did not reveal this influence as to be able to make any certain conclusions. But the improvement of the surface of the blade enables a significant reduction in required for popeta engine power. Negative twist to get there at 8-10° gives an increase of thrust by 3-4%.

 

The speed of movement of the blade relative to the air varies. It is less axis rotation and more at the end and, in addition, varies from state to tend towards the direction of flight.

 

Thus, when the screw rotation speed to get there, moving forward, is composed of the velocities of rotation and translational motion of the helicopter. For the blades, moving backwards, the speed will be determined by the difference between the velocity of the translational motion of the entire machine and its speed of rotation.

 

Due to the lower speed to get there, moving back, there will be less and the lift, or rather, would have been less if in this case did not increase its angle of attack to maintain balance. But too to increase this angle too.

 

Limit the maximum flight speed is determined by the value of the true angle of attack of the stragglers to get there. The increase in the number of revolutions of the rotor with a corresponding decrease of its diameter leads to deterioration of characteristics of hovering. Significant improvements can be achieved by applying a profile with a large value of the critical angle of attack, if it does not lead to a significant increase in resistance.

 

Fig. 7. Schedule of required power for horizontal flight.

 

 

Fig. 8. Chart safe heights for event authorityrules landing.

 

The proximity of land and the so-called “earth pillow” significantly affect the aerodynamic characteristics of the rotor. But at a distance equal to the diameter of the rotor, this effect can already be neglected. For a hovering helicopter with no forward speed on required power 30% greater than in horizontal flight at the optimum speed.

 

The same phenomenon is observed during climb. Dynamic ceiling (translational velocity) is always greater than the static (hovering). When you stop the motor, the helicopter becomes a gyroplane. In this case, the rotor is rotated without supply of power due to aerodynamic forces. The latter provide the required thrust of the rotor and support its rotation. But this transformation depends on many factors. The main of them — the direction of airflow of the rotor air flow.

 

During motor flight the air flow incident on the rotor of the helicopter on top of the autorotation — bottom. To enable autorotation requires a certain flow rate (direct or oblique), that is, the helicopter should move relative to it. So, for avtomotornaya safe landing from hover, the apparatus must have a clearance of not less than 150 m or in horizontal flight, the forward speed at least 120 km/h, otherwise an accident is inevitable.

 

These are brief information about the helicopter that you need to know the model airplanes.