And what country can preserve its liberties if their rulers are not warned from time to time that their people preserve the spirit of resistance? Let them take arms. The remedy is to set them right as to facts, pardon and pacify them. What signify a few lives lost in a century or two? The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants.
once you have ground resonance, there is only one sure way to survive it intact and that is to get off the ground. this Hook was chained to the ground. it is a shame.
crew survived in the cockpit. the rear rotor went into resonance. note the landing gear dancing as the rotor vibration came into frequency of the airframe harmonic frequency. usually, we find the shock struts on the landing to be under serviced in some manner; the landing gear usually dampens the vibration which is always there at some level. sometimes it is caused by lead lag dampner failure, a blade flying lower than the others could be a lot of things together.
From Wikipedia: "Ground resonance is an imbalance in the rotation of a helicopter rotor when the blades become bunched up on one side of their rotational plane and cause an oscillation in phase with the frequency of the rocking of the helicopter on its landing gear. The effect is similar to the behavior of a washing machine when the clothes are concentrated in one place during the spin cycle. It occurs when the landing gear is prevented from freely moving about on the horizontal plane, typically when the aircraft is on the ground. Articulated rotor systems with drag hinges allow each individual blade to advance or lag in its rotation to compensate for stress on the blade caused by the acceleration and deceleration of the rotor hub (due to momentum conservation). When the spacing of the blades becomes irregular, it shifts the rotor's center of gravity from the axis of rotation, which causes an oscillation. When the airframe begins to rock back and forth from the oscillation, the oscillations can reinforce each other and cause the rotor's center of gravity to spiral away from the axis of rotation to a point beyond the compensating ability of the damping system."
There is other u-tube video showing this problem. Pilot has to react quickly to get it airborne before the forces disable the crew, or cause airframe or power system damage that would make a takeoff attempt more hazardous than the guaranteed self-destruction of the aircraft. The result of this is a 100% total loss of the aircraft. Stresses involved make salvage attempts inadvisable.
once you have ground resonance, there is only one sure way to survive it intact and that is to get off the ground. this Hook was chained to the ground. it is a shame.
ReplyDeleteCapt, what was the reason to chain down a choppa? If there was any men aboard it didn't really look survivable.
DeleteHeres the story on this Helicopter with additional video
Deletehttps://chinook-helicopter.com/history/aircraft/D_Models/84-24156/84-24156.html
crew survived in the cockpit. the rear rotor went into resonance. note the landing gear dancing as the rotor vibration came into frequency of the airframe harmonic frequency. usually, we find the shock struts on the landing to be under serviced in some manner; the landing gear usually dampens the vibration which is always there at some level. sometimes it is caused by lead lag dampner failure, a blade flying lower than the others could be a lot of things together.
Deletelooks like it was straight outta a Harry Potter series:
ReplyDeleteole Huffa Chuffa
ReplyDeleteWhat is ground resonance?
From Wikipedia: "Ground resonance is an imbalance in the rotation of a helicopter rotor when the blades become bunched up on one side of their rotational plane and cause an oscillation in phase with the frequency of the rocking of the helicopter on its landing gear. The effect is similar to the behavior of a washing machine when the clothes are concentrated in one place during the spin cycle. It occurs when the landing gear is prevented from freely moving about on the horizontal plane, typically when the aircraft is on the ground. Articulated rotor systems with drag hinges allow each individual blade to advance or lag in its rotation to compensate for stress on the blade caused by the acceleration and deceleration of the rotor hub (due to momentum conservation). When the spacing of the blades becomes irregular, it shifts the rotor's center of gravity from the axis of rotation, which causes an oscillation. When the airframe begins to rock back and forth from the oscillation, the oscillations can reinforce each other and cause the rotor's center of gravity to spiral away from the axis of rotation to a point beyond the compensating ability of the damping system."
DeleteExcellent response, thanks!
DeleteThere is other u-tube video showing this problem. Pilot has to react quickly to get it airborne before the forces disable the crew, or cause airframe or power system damage that would make a takeoff attempt more hazardous than the guaranteed self-destruction of the aircraft. The result of this is a 100% total loss of the aircraft. Stresses involved make salvage attempts inadvisable.
ReplyDeleteThis was a test, but I don't recall the story.