In the last few hours, a video of a video has been going viral online helicopter Bell 222SP that suddenly loses control near the Californian seafront of Huntington Beach on the occasion of the annual event Cars ‘n Coptersstarting to rotate on itself until crash to the ground. Fortunately, the accident, which occurred on 11 October, did not cause any casualties: the five passengers of the vehicle and three people on the ground were injured, including a child. According to what was reported by various local media, it seems that the pilot Eric Nixon he used to perform acrobatic maneuvers with these vehicles for work, although analyzing the video it does not seem at the moment that this can be directly linked to the accident.
The causes of the accident are still unknown, but we can still analyze what happened from one point of view technical-scientific based on captured videos, such as the one attached to this article, in which we clearly see the helicopter LOSE the tail rotor as it rotates on itself.
The most plausible hypothesis at the moment seems to be the loss of control of the tail rotor following a mechanical failure. In fact, the tail rotor is used precisely to prevent helicopters from rotating like tops during flight. In fact, helicopters fly thanks to main rotorthat is, what we commonly call “helicopter blades” and which is in fact a system of rotating wings. Their rotation moves a large amount of air downwards, generating the lift (i.e. the aerodynamic thrust perpendicular to the direction of motion) necessary for vertical take-off – typical of helicopters – and for actual flight.
Now, in physics there is a law called conservation of angular momentum which, put simply, says that the “total rotation amount” of a system tends to remain constant over time. Now let’s try to apply it to a helicopter. Before the rotor turns on, the total rotation of the helicopter system is zero: the vehicle is stationary, so there is no rotational motion. When the rotor starts to spin, however, an important rotational motion appears “out of nowhere”. But the law of conservation of angular momentum dictates that the “total amount of rotation” of the helicopter remains zero overall, as it was before the rotor was turned on. To achieve zero angular momentum, the only thing the helicopter can do is counter-rotate in the opposite direction to that of the rotorto compensate for the rotation of the rotor itself.
The tail rotor is really there for avoid counter-rotation of the helicopter body: pushes air in the opposite direction to that in which the aircraft would like to rotate to compensate for this effect and keep the helicopter pointed straight in the direction of motion. What we see in the video of the Huntington Beach helicopter is just that: it’s what happens when a helicopter is missing its tail rotor. We are essentially seeing the law of conservation of angular momentum in action.
Obviously we don’t know what the causes of the probable tail rotor failure are and it is precisely this that the competent authorities will have to clarify in the coming weeks.
