Elastic-mass characteristics of HB blades
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Elastic-mass characteristics of HB blades

Elastic-mass characteristics of HB blades

 

  • 1. Based on the data of the technical assignment for the design of the helicopter HB blade, the blade KCC is formed.

  • 2. A static calculation of the blade is carried out, and the conditions are checked

If any of the conditions are not met, then the calculated adjustment for an increase in moment of inertia and the recalculation of force elements of the blade sections.

Determined by the thickness of structural elements for the sections of the entire length of the blade. We calculate all geometrical, mass and centering blades features: the moment of inertia in the planes of the largest and smallest stiffness; the position of the principal axes of the cross sections; the mass of the blade; its center of gravity, etc. In parallel, the calculated torsional stiffness of the cross sections and identifies the critical buckling stresses bottom panel member.

  • 3. The effective centering of the blade is determined and, if it turns out to be greater than the specified one, the required mass of the counterweight is calculated, which is distributed in the front part of the profile.

  • 4. Frequencies and forms of natural oscillations of the blade in the planes of the highest and lowest stiffness are determined and, if the frequencies do not satisfy the conditions for detuning from the harmonics of the external load by a given value, data are generated for the program of redistribution of concentrated masses and moments of inertia along the blade radius. The use of CM makes it possible to form the bending and torsional stiffness of the blade with the corresponding orientation of the reinforcement without changing the weight of the blade.

  • 5. Corrections to the distribution of the stiffness of the blade and the mass along the length of the blade are found, and thereby the tuning from resonances is carried out. In this case, the variations in the moments of inertia required to correct the oscillation frequencies of the blade in the thrust plane are realized directly in the change in the section thickness of the load-bearing elements. Variations in the moments of inertia required to change the vibration frequencies in the plane of rotation are obtained both due to changes in the position of the front and rear walls of the spar along the chord of the blade, as well as the width of the stringer and small additives in the thicknesses of the bow and tail shell. Thus, independent tuning of the oscillation frequencies of the blade in the thrust plane and in the plane of rotation is provided. An increase or decrease in only the mass of the blade without changing the stiffness, which is required to adjust the vibration frequencies both in one and in the other plane, is achieved by means of a counterweight.

  • 6. Corrections are found for the width and position of the spar along the chord, the thicknesses of the nose fittings and the tail plating, necessary to ensure an acceptable level of compression stress in the lower panel of the spar and the torsional stiffness of the section.

  • 7. All integral characteristics of the blade are determined after several iterations. After that, the process of forming the blade parameters based on static calculations ends.

  • 8. The calculation of the "ground" resonance of the helicopter is carried out and, if necessary, the frequency of the first tone of the natural oscillations of the blade in the plane of rotation is corrected.

  • 9. The calculation of the blade for torsion-fly flutter is carried out. The necessary margin for effective centering at a given flight speed is provided by adjusting the counterweight mass. If the calculated stresses exceed the permissible ones, the moments of inertia of the blade section are corrected,

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