To: All
Here is a theory that will really get you to thinking. Assuming the pressure differential between the cliff side of the rotor and the opposite side of the rotor. If there is a differential of pressure between the sides of the disc there is a differential of pressure on the fuselage and the greater pressure is on the side of the fuselage away from the cliff. Nature being what it is, the pressure differential acting on the fuselage will push the helicopter towards the cliff in order to compensate for the differential. The closer to the cliff the greater the differential and the greater the sidward force.
Don’t laugh or, I’ll have to use rocket science. If you have ever seen a large liquid propellant rocket engine you will have noticed circumferential rings around the nozzle. These rings give stiffness to the bell and help maintain the shape of the engine. Sometimes, during the start of the combustion at sea level the gasses can’t fully expand which creates a pressure differential between the inside and the outside of the bell. This is called Jet Separation, This pressure gradient can be so strong as to shift the engine sideways and force the control servos up into the structure or, it could cause the nozzle to collapse. The rings increase the resistance to collapse by altering the hoop stresses on the nozzle. I am not sure but the Space Shuttle Lox / Hydrogen engines may have a two stage hydraulic system to allow the engine movement but the force is attenuated by a spongy servo. Next time they show a closeup of the engines you can see them move at ignition start.
The same is true for aircraft wings on aircraft flying in close formation and the wings overlap. The air between the wing tips increases in speed due to the venturi effect and causes a low pressure. The result is that the wings “lock”. These illustrations prove that pressure acting over a large surface can generate a great deal of force and in this case move the helicopter, which is a free body in space into the cliff.
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The Cat
[This message has been edited by Lu Zuckerman (edited 23 January 2001).]
[This message has been edited by Lu Zuckerman (edited 23 January 2001).]