Airframe structural dynamic considerations in rotor design optimization

Original publisher: Hampton, Va. : National Aeronautics and Space Administration, Langley Research Center, [1989] OCLC Number: (OCoLC)25394179 Subject: Rotors (Helicopters) -- Design and construction. Excerpt: ... and rotor mode frequencies ( all expressed with respect to a fixed coordi-nate system ) vary with rotational speed for both hingeless and articulated rotors. For simplicity, the uncoupled rotor and airframe frequencies are shown in figure 10. The open circles denote points of frequency coales-cence between the critical rotor modes and an airframe frequency and are regions of potential instability. The amount of structural or viscoelastic damping present determines whether the system responds excessively at resonance and goes unstable. The rotor design requirement is to insure that, within the operating speed range of the rotor, there are no coinci-dences of the frequency of the critical rotor mode with an airframe mode and that sufficient damping is present. CONCLUDING REMARKS An overview and discussion has been presented of those aspects of air-frame structural dynamics that have a strong influence on rotor design op-timization. Primary emphasis was placed on vibration requirements. The vibration problem was described, the key vibratory forces were identified, the role of airframe response in rotor design was summarized, and the types of constraints which need to be imposed on rotor design due to air-frame dynamics were discussed. Some considerations of the influence of ground and air resonance on rotor design were also discussed. REFERENCES. Adelman, H.M.; and Mantay, W.R.: Integrated Multidisciplinary Optimization of Rotorcraft: A Plan for Development. NASA TM 101617 ( AVSCOM TM 89-B-004 ), May 1989.. Kvaternik, R.G.; Bartlett, F.D., Jr.; and Cline, J.H.: A Summary of Recent NASA / Army Contributions to Rotorcraft Vibrations and Structural Dynamics Technology. Proceedings of the1987 NASA / Army Rotorcraft Technology Conference, NASA CP 2495, pp. 7...