Balance of forces in level flight
When the helicopter is in level flight with respect to the speed axis system, the forces acting on the helicopter are mainly the rotor pull T, the gravity of the whole aircraft G, the waste resistance of the fuselage X body and tail rotor thrust T tail. The principle of selecting the speed axis system in forward flight is: X uranium points to the direction of flight speed V; Y axis is perpendicular to the X axis upward as positive, and the 2 axes are determined according to the right-hand rule. Equilibrium condition of force to keep the helicopter in level flight with equal speed and straight line
Equilibrium of force in level flight
Where Tl, T2, T3 are the components of rotor pull force in X, Y, Z directions respectively. For single rotor helicopter with tail rotor, because the tail rotor axis is usually not in the rotor rotation plane, in order to keep the lateral moment balance, the helicopter is slightly with a slope angle r, so the tail rotor thrust and the horizontal plane between the angle of y, T tail and T3 direction is not exactly the same as the angle of y is very small, i.e., the cosr is equal to about 1, so the Z force using the approximation of the equal sign.
Power demand in level flight and its change with speed
When level flight, the vertical component of flight speed Vv=0, the rotor has no displacement in gravity direction and Z direction, and no work is done by the component force in these two directions, at this time, the rotor's demanded power consists of three parts: the type resistance power - P type; the induction power - P induction; the waste resistance power - P induction; the power of the rotor. --P induced power; waste resistance power - P waste. The third one is the power consumed by the rotor pulling force to overcome the fuselage resistance.
From the figure above, it can be seen that the second component of the rotor pull, T2, balances the fuselage drag, X-body. For the rotor, its component force T2 is displaced in the X-axis direction by a velocity V. The rotor must do work, P2, in the direction of the X-axis. Obviously the rotor must do work, P = T2V or P waste = X body V, and the fuselage waste resistance X body in the fuselage attitude changes relative to the horizontal plane is not too much, its value is approximately proportional to the square of V, so the waste resistance work
Leveling the change in the power required with the speed
Rate of change of power with speed
Rate of change of power with speed
Can be approximated as being directly proportional to the third power of the leveling speed
leveling the power of the induced The induced power is P=TV, where T is the rotor pull and vl is the induced speed. When the flight weight is unchanged, it is approximated that the rotor pull is unchanged, and the induced speed 271 decreases with the increase of the leveling speed V. Therefore, the change of the leveling induced power P with the leveling speed V is as shown in the thin solid line ② in the above figure.
The level-flying type of resistance power corpse type is related to the average angle of the paddle blade. With the increase of the level flight speed of the average angle of attraction does not change much. So the P-type with the flight speed V does not change much, as shown in the figure of the dotted line ①.
The solid line ④ in the figure is the sum of the above three items, i.e., the total power required for leveling P is changing with the change of leveling speed. It is a saddle-shaped curve: small speed level flight, the waste resistance power is very small, but this time the induced power is very large, so the total power required to fly is still very large. But it is smaller than when hovering. Within a certain speed range, as the leveling speed increases, the induced power decreases sharply, while the increment of the reject power is not large, so the total leveling power requirement decreases with the increase of the leveling speed, but this decreasing trend slows down with the increase of V. If the speed continues to increase, the induced power decreases sharply, while the reject power increases little, so the total leveling power requirement decreases with the increase of the leveling speed. However, if the speed continues to increase, the power dissipation increases sharply with the leveling speed. The leveling power requirement increases with V after reaching the lowest point of the leveling power requirement; the total leveling power requirement increases with V and becomes more and more obvious.
Backward flight of helicopter
Relative airflow asymmetry, caused by the swing and blade angle changes
Side flight of helicopter
Side flight is another unique helicopter flight state, which is indispensable to the implementation of some special operations, along with the hovering, vertical flight at small speeds and backward flight. Generally speaking, side flight is a flight state implemented on the basis of hovering. It is characterized by the need to pay more attention to the change and balance of lateral forces. Due to the large lateral projection area of the helicopter fuselage, the aerodynamic resistance of the fuselage is particularly large when flying sideways, so the helicopter's speed in sideways flight is usually very small. Since the lateral forces in a single rotor helicopter with tail rotor are asymmetric, the forces are different for left and right side flight. When the sideways force is balanced, the horizontal component of the rotor pull is equal to the sum of the tail rotor thrust and aerodynamic drag, and the helicopter can maintain the same speed to the side of the backward blade. When the forward blade side flight, the horizontal component of the rotor pull force is less than the tail rotor thrust, under the effect of the remaining tail rotor thrust, the helicopter to the direction of the civil propeller thrust a case of movement, aerodynamic drag and tail rotor thrust reversal, when the side force balance, to maintain the same speed to the forward blade side flight.