Steady flight. Unsteady flight.
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Steady flight. Unsteady flight.

Steady flight. Unsteady flight.

 

 

To review and coordinate forces take for example a single-rotor helicopter with tail rotor.

The flight of the helicopter may be steady or unsteady. In a steady flight, the speed of the helicopter is constant or zero. In other words, we can say that there is no acceleration in the steady flight. From the first law of mechanics it is known that every body is in a state of rest or uniform rectilinear motion in the case when the resultant of all forces acting on the body is zero. If this condition is not met, then under the influence of an unbalanced force, the speed of movement of the body changes its magnitude or direction, or both simultaneously, that is, there is an acceleration.

In the presence of an unbalanced force, and hence the acceleration of the helicopter flight will be unsteady, which will cause the appearance of additional inertial forces.

Steady modes of flight are the main modes, whereas transients are transition from one steady state to another.

Consider the simplest case of steady flight.

We know that the plane of rotation of the rotor of the helicopter is called a plane passing through the hub of the rotor perpendicular to its axis.

However, during flight the rotor blades do not rotate in this plane, but to describe the surface of a cone whose axis is generally not coincident with the axis of the screw.

Draw a plane through the ends of the blades. The angle formed between the plane of the propeller blades and is called the average angle of taper. In practice, this angle is of the order 6 °.

The axis of the cone formed by rotating blades at © generally rejected (filled up) of the rotor axis in the longitudinal and in the transverse plane. The pro

longitudinal plane of the dam axis of the cone angle is denoted by. The blockage is caused by the presence of cone screw blower speed in the plane of rotation.

In the transverse plane angle of the dam axis of the cone is denoted by. Blockage of the cone to the side due to different speed blow coming and retreating blades.

We can assume that the total aerodynamic force of the rotor R is along the axis of the cone formed by the blades. Thus, the total aerodynamic force of the screw is generally off-axis passing through the propeller hub.

To understand the impact of the provisions of the forces R on the helicopter elect reference system, coordinate system consists of three mutually perpendicular axes X, Y and Z.

Thus the X-axis is directed along the flight (forward), the Y axis - a vertical plane perpendicular to the axis X, and Z-axis goes to the right, perpendicular to the plane of the figure. We expand the force R on the three components of the three axes of the coordinate system chosen by us.

As a result of the expansion of the force R in the general case, when the axis of rotation is deviated from the vertical axis, we obtain three forces. The force Y turned out as the projection of the force R onto the axis of rotation of this screw.

The strength of the H turned as the projection of force R on the plane of rotation of the screw along the X axis of the helicopter. This force is called the longitudinal strength of the screw.

The power of S is obtained as a projection of force R on the plane of rotation of the rotor of the helicopter along the transverse axis Z. This force is called lateral force resulting from flapping.

We have found that by the main rotor on the helicopter, there are three forces along each of the coordinate axes.

However, the screw, in addition to forces, also creates moments around each of these axes.

Due to the difference in operating conditions of the individual rotor blades, the blades develop a different lift at any given moment. Therefore, different components of the force R act on the horizontal hinges of the screw sleeve. Since the horizontal hinges are usually spaced by some distance 1G. w from the axis of rotation, then a moment is created on the sleeve from the difference in the lifting forces of the blades. This moment can be decomposed into two moments: one acting around the longitudinal axis, Mx, and the other around the transverse axis, Mg. Moment Mg tends to cause a dive or pitching of the helicopter, and Mx - its roll.

Since the rotor receives torque from the engine, located in the fuselage, propeller inevitably transmits to the fuselage back, reactive time, aspiring to rotate the fuselage of the helicopter in the direction opposite to the rotation of the screw.

In addition, we know that the force of the helicopter tail rotor thrust and weight force, and in forward flight, and also the power of parasitic drag all parts of the helicopter.

To perform steady flight is necessary that the sum of forces acting along each axis, and the sum of the moments of forces acting with respect to each axis of the coordinate system chosen by us is equal to zero, ie. E.

These modes of operation as hovering, vertical ascent, climbing straight path, horizontal flight, planning, and vertical descent flight mode on autorotation, are special cases of steady flight.

These cases can be divided into three basic modes of flight, fundamentally different from each other:

  • 1. Attack angle rotor A = ± 90 °. In this case, the air flow coming to the plane of rotation of the screw along the axis of its top or bottom. This regime corresponds to hover, climb vertical - vertical lift and a vertical descent.

  • 2. Angle of attack of the main rotor A <0. In this case, the air flow approaches the plane of rotation of the rotor at a certain angle and passes it from top to bottom. This mode corresponds to horizontal flight, climb along an inclined trajectory and a gliding gentle descent with a running engine (motor).

  • 3. Angle of attack of the main rotor A> 0. Here, the air flow approaches the plane of rotation of the screw also obliquely and passes through the surface swept by the screw from bottom to top. This mode corresponds to non-motorized autorotting gliding.

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