WEIGHT necessary to eliminate aeroelastic EFFECTS HELICOPTER
WEIGHT necessary to eliminate aeroelastic EFFECTS HELICOPTER

WEIGHT necessary to eliminate aeroelastic EFFECTS HELICOPTER


Main and tail rotors and auxiliary lifting surfaces (wing) and plumage should be tested for flutter. There are three types of physical connections, interacting with the flutter: elasticity, aerodynamic and inertial forces.

The critical velocity (Ukr) depends on the proximity of the vibration frequencies that correspond to the degrees of freedom that form a given form of flutter. The closer to unity the ratio of natural vibration modes interacting during flutter, the lower Yt. Typical dependence of Y flutter on the ratio of natural frequencies in two system (flexural-torsional) flutter is shown in 1.2.1. It can be seen that there is some similarity with the phenomenon of resonance, since at equal frequencies or near this point, Y is minimal.

Enlarge Y can be due to changes in one of the natural oscillation frequencies, forming a flutter while maintaining constant a different frequency, and variable frequency does not necessarily increase. At the V flutter are strongly influenced by the inertial and aerodynamic connection. Particularly adversely affects the inertial connection when the center of gravity (CG) is located behind (by flow rate) of the center of rigidity (CF).

Moving forward on the axis of the CG relative to the axis of SF V significantly increases the flutter. This effect is based weight-balancing action (protivoflatterny load) being used on wings of feathers and blades. Approximate FKp dependence on the degree of imbalance between the axes of the CG and SF also shows

by 1.2.2.

The result of the influence on F of the useful inertial coupling (balancing) depends on the ratio of the frequencies of the flutter-forming vibration modes. When the partial natural frequencies are close, the effect of inertial coupling is more effective than when they differ. This effect is illustrated in 1.2.3, when a smaller balancing weight is required to increase the FK flutter at close frequencies.

Elastic ties are determined by the coefficient of anisotropy of the whole structure or structural material. The effect of elastic anisotropy can be created using a special material having these properties, or to reinforce the longitudinal trim set at an angle to the axis of the building.

Flutter phenomenon occurs with a large number of interacting modes of vibration. Most often possible to distinguish two principal degrees of freedom in every form of the observed flutter; the others play a supporting role. Therefore the form of flutter is usually characterized by two main degrees of freedom, such as "bending the wing" - "Twist wing", "wings bend" - "bending the fuselage," etc. When the flexural bending-torsion flutter of the wing shape, which leads to changes in the angle of attack is due to the bending of the fuselage.

On JIA may occur several forms flutter. If due to some structural measures possible to increase One of the forms of the flutter, in which this rate was lowest, it begins to show another form of flutter.

For example, in 1.2.4 it is shown that with an increase in the torsional rigidity of the wing, the flexural-torsional form 1 of the flutter can change into a flexible form 2. This circumstance significantly complicates the solution of the problem of optimizing the structure according to the flutter conditions.



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