Deviation from the flutter of blades

Physics is similar to HB flutter phenomena observed in flexural-torsional and flexural electronic flutter of wings.

When the bending blade flutter in the plane of stroke varies according to the form close to any one tone characteristic oscillations blade bending and twisted shape close to the shape of the first tone own torsional oscillations.

Vane HB, unlike wing is hinged to the sleeve in the horizontal and vertical plane and the hinge axis about which it rotates.

The axial bearing loaded by the centrifugal force when rotating blade friction occurs. In addition to the centrifugal force at the time of friction in the axial joint affects the value of pre-tightening of the thrust bearing. Seals axial hinge provide significant friction torque, independent of the value of the centrifugal force.

The friction in the axial bearing increases the critical speed of flutter. The effectiveness of the friction of friction decreases with increasing angular velocity of the relative movement in the axial hinge when forced oscillations of the blade. Therefore, the critical speed of flutter in the air decreases as with increasing flight speed relative movements in the axial hinge generally increase.

Flapping blade, the presence of the compensator stroke and forced cyclical change the angles of the blades are largely complicate the calculation of the critical speed of flutter NV.

Improved flutter characteristics rotor blade is achieved by moving the leading edge of its center of gravity and a decrease in stroke compensator. The position of the focus may be more posterior.

Thus, when designing a blade, it is necessary to correctly set its lateral centering. The usual way to create the necessary lateral alignment is the rational distribution of the spar material along the chord of the blade, the maximum allowable lightening of its tail section. Correction of the centering of the blade is carried out by installing a counterweight in its nose - a balancing weight on the outer part of the blade along the radius. The experience of operating helicopters shows that a satisfactory value is the centering of the blade with a radius of r> 0,6 to 7 = 1,0 on the order of 23-24% of the blade chord (counting from the leading edge). In some cases, this value can change significantly.

Very important parameter strongly affects the critical speed of flutter, a torsional rigidity and stiffness of the blade angle control its setting - Supra (2.3.9).

When designing the mechanical elements of the power management system (swash, rocking control of hinge joints, attachment points boosters) should strive to increase their rigidity and eliminating backlash-free in the hinge sites.

Main and tail rotor must be checked flutter. To ensure the security of the flutter is necessary that in all modes of flight critical speed of flutter Ufl was no less than 20% higher than the maximum permissible speed of flight in these conditions, and the critical speed in the vial should be not less than 20% exceed the maximum permissible speed screws during operation in each flight mode.

Ufl and n fl shall be determined by calculation flutter, full-scale ground tests propellers flutter. In some cases, the test results should be used to dynamically similar models in wind tunnels in all flight modes. The test results of models and calculations flutter refined on the basis of specific frequency testing of full-scale helicopter.

When full-scale ground tests necessary to check the availability of an adequate supply of the transverse alignment of the blade. Thus flutter, must not occur throughout the range of operating frequencies of the propeller up to n so when mounted on

HB blades provoking freight, strengthened on the back edge of the blade moves back and the effective cross-alignment of the blades. The load to be selected so as to compensate an adverse effect on the flight conditions of safety against flutter throughout the speed range, and the maximum spread in transverse alignment due to tolerances adopted in manufacture of the blade.

If the value of n depends substantially on changes in ambient temperature, type of lubricant et al., It is necessary to increase the weight for provoking account of these factors.

The value of the stock on the effective cross-checking alignment for ground blades flutter for each type of helicopter is established performer.

The lack of in-flight flutter needs to be validated during the flight test by measuring characteristic of the parameters on flutter speed ravnoy- 1DUgpah, but no more

Ymax + 30 km / h. This may be a flight with the reduction.

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