Formation of elastic-mass characteristics BLADE HB
Formation of elastic-mass characteristics BLADE HB




When designing the helicopter units should strive for the greatest possible reduction in their weight. This requirement is of particular importance for the blade HB because of its weight acting on it depends on the centrifugal force and, as a consequence, the weight of the sleeve. However, there are limits determined by the minimum feasible konstruktivno- technological weight of the blade.

The level of operating voltage and variable vane existing stocks in certain types of buckling (swing-Makhov, chordal and stall flutter, divergence, etc.) Depend on the characteristics of the mass of the blade u0:

This is explained by the desire to reduce operating blade spar AC voltage decreases with decreasing 70, and that is more effective more

limitation - constructive and technological. This limitation is due to the minimum allowable wall thicknesses of the blade parts. The thicknesses of the side member walls must not be reduced below certain limits, based on technological limitations, permissible torsional deformations, bending of the side member belts under the action of aerodynamic forces, and also to exclude the loss of stability of the lower side member belt when the blade hits the stopper when the propeller stops. Due to operational, technological and strength considerations, it is not possible to reduce the thickness of the frame parts. These and a number of other limitations of a constructive and technological nature lead to a relative increase in the mass of small blades. Therefore, the value of k turns out to be usually large for small blades (R = 4 m, / w> 12, y0 = 4,5) and

smaller for large (R> 16 m, / w = 5,5, y0 = 7). In this regard, it is convenient to introduce the concepts of the structural and technological mass of the blade and the mass required to ensure the normal operation of the NV.

Improving the design and manufacturing technology of the blade, the appearance of new, stronger materials and hardening processing processes make it possible to reduce its structural and technological mass, providing the necessary strength at large alternating stresses, arising, in particular, with increasing mass characteristics of 0. However, this reduction in weight is hampered by the difficulties in ensuring the proper operation of the HB. The experience of creating blades shows that most of the phenomena preventing the normal operation of HBs can be easily eliminated with relatively heavy blades, when the mass characteristic of the blade is not more than y0 = 4-5, and is much more difficult with relatively lighter blades when 0 = 6- 7. On the other hand, the reduction of the constructive-technological mass is more successful for large blades and easily leads to the creation of blades with large mass characteristics, but it does not allow to obtain the same results for small blades.

As a result, to reduce the mass of small-diameter blades, it is necessary to solve mainly structural and technological problems, and a decrease in the mass of large-diameter blades is associated with solving the problem of ensuring the normal operation of NV with blades having a mass characteristic y0> 7.

For different sizes HB optimal in terms of minimum practicable mass determined by the technological possibilities and the requirements of the static strength can be different types of construction of the blades.

The application of new technical solutions will reduce the weight of the minimum workable in some modern structures of blades or extend the scope of a design. The need to comply with other conditions may significantly affect these conclusions, although out of the situation need not be very costly mass.

Among the many conditions dictated by the strength of the blade are required to perform two very important requirements of the static strength:

Plot inboard weighting blades may appear in blades HB particularly large diameter and blades with unusually high elongation. With the increase in cross-sectional dimensions of the spar (while maintaining the thickness of its walls unchanged) the critical buckling stress when bending in the direction of the force of its own weight of the blade is significantly falling. Weight tip from existing serial blades HB is usually from 10 17% to the mass of the blade.