Rotorcraft Structural Dynamics and Aeroelasticity

Course Outline

Day One

• Introduction: overview of rotorcraft structural dynamic problems and solutions
• Mathematical tools: linear systems, Fourier analysis, damping, multiple-degree-of-freedom systems, natural modes, resonance, stability
• Rotational dynamics and gyroscopics: simplified gyroscope equation, precessional characteristics of rotors
• Dynamics of rotating slender beams: hinged rigid blades, effects of elastic restraints about the hinges, the Euler beam and basic DEQ for transverse bending, rotor speed characteristics and fan plots, out-of-plane vs. inplane bending, Yntema charts and numerical methods for bending modes, the two-bladed rotor, torsional dynamics, coupling issues, experimental verification and tracking and balancing, blade section properties, the SECT_PRT computer code, blade natural frequencies, the BLAD_FREQ computer code
• Problem session

Day Two

• Transverse vibration characteristics: the Jeffcott rotor model, subcritical and supercritical operation, pseudo-gyroscopic effects, whirl speeds and modes, and rotor instabilities
• Basic balancing techniques
• Torsional natural frequencies of shafting systems: element equivalences, basic natural frequency calculations, branched gear systems, drive system for a typical rotorcraft, drive system natural frequencies, the TORS_HDS computer code, problem session
• Fuselage vibrations basic issues: forced response and vibrations, the rotor as an excitation source and filter, rotor-fuselage interaction, 1P vibrations, the two-bladed rotor
• Full-scale vibration testing of real systems: suspension and excitation techniques, instrumentation, typical shake-test results for helicopters, operational modal analysis

Day Three

• Fuselage vibrations (continued): modal identification, techniques for achieving response modification, antiresonance theory, methods for vibration alleviation, elastomeric devices, vibration testing applied to material characterization
• Linear stability analysis methods: constant coefficient systems, force phasing matrices, Floquet theory, frequency-domain methods
• Blade aeromechanical instabilities: air mass dynamics, quasi-steady aerodynamics, pitch-flap-lag and flap-lag instabilities
• Software for blade aeromechanical stability analysis
• Linear unsteady aerodynamics: general frequency domain theories, finite state formulations
• Problem session

Day Four

• Bending-torsion flutter: basic flutter theory, bending-torsion of rotor blades, general analysis methods
• Nonlinear aeroelastic stability analyses: nonlinear unsteady aerodynamics, stall flutter, BOOT and SHOT
• Rotor-fuselage coupled instabilities: propeller-nacelle whirl flutter, ground resonance, air resonance
• Software for ground resonance calculations
• Testing for dynamics at model and full scales: model scaling law, instrumentation and test procedures, methods for instability quenching
• Methods for quantifying stability
• Problem session

Day Five

• Special topics: aeroelastic optimization, composite blade design, drive system compatibility with engine/fuel control systems-analysis techniques, stabilization
• Summary and future trends
• Course evaluation