"Induce low rotor RPM and demonstrate a hover: "Note the ship willstill fly in many conditions even with low rotor RPM. Consequently, hovering is difficult andperhaps hazardous. (Resonance) Resonance Resonance (Sympathetic vibration): when one … Usually there is a triggering event: a bump or a landing or takeoff on sloping ground or with a little sideways or forward motion. View Notes - LP6 Resonance Note Answer.pdf from SPH 3U1 at Unionville High School. In the simplest cases, resonance occurs when the frequency of the external force approaches one of the frequencies at which natural oscillations occur as a result of an initial impulse. sympathetic resonance occurs when main and tail rotor resonate together and build on each other. The hinges keep the fluctuating lift and drag forces on each blade from inflicting excessive stresses on the rotor hub. We practice this because the proper recovery is just theopposite: lower collective, roll on throttle, and increase forwardspeed. The cyclic control in the cockpit flails about so violently that the pilot cannot hold it, the rotor blades strike the tail boom or the cockpit, parts begin falling off, and moments later the helicopter may be a heap of scrap. Introduction: "During high density altitude, high gross weight, andhigh power (e.g., four fat guys going on a steep approach into aconfined area near Big Bear, CA), you may encounter low rotor RPM. ATIS: "Wind, runway, and temperature/dewpoint split are the most important items.
The energetic vibration of a body produced by application of a periodic force of nearly the same frequency as that of the free vibration of the affected body. The only rotors that can produce ground resonance are those with three or more blades. Multi-blade rotors have lead-lag hinges, which allow blades to speed up and slow down at different points as they circle the mast while the helicopter is moving forward.
That’s why tuning forks always produce a certain tone, and why boats of different sizes rock at different rates. Near the ground, if your descent rate is too high,use forward cyclic to accelerate. This information should not be considered complete, up to date, and is not intended to be used in place of a visit, consultation, or advice of a legal, medical, or any other professional.In cyclic conjugate systems, a resonance shift does not always lead to charge separation.
The rotor, now slightly out of balance, begins to wobble like a slowing top. is a harmonic phenomenon wherein a formerly passive string or vibratory body responds to external vibrations to which it has a harmonic likeness. "Once the student is comfortable with low rotor RPM recovery in thehover, try it in the air:"With the governor off, keep the tachs in your scan.
Thus, a linear system proves to be resonant only when the external force is harmonic.In linear systems having many degrees of freedom and in continuous systems, resonance retains the same basic features as in a system having two degrees of freedom.