So I'm trying to picture a scenario here. (Not a homework scenario, just a hypothetical I thought of years ago that came back to mind recently.) A bunch of people need to be rescued from a fire, but there isn't enough room in the helicopter, and the only thing attached to the helicopter they can grab onto is a spring. As they all leap onto the spring, the helicopter begins oscillating vertically; as in, they rise when the helicopter falls, the helicopter rises when they fall, etc.

 

Presuming they didn't otherwise exceed the helicopter's weight load limit, would the vertical motion prevent the helicopter from achieving the kind of lift it would need to achieve in order to move forward without falling to the ground?

Edited November 22, 20205 yr by ScienceNostalgia101

It could. The spring force is -kx, and could exceed mg if the people were falling when they grabbed it, so the force on the helicopter would likewise exceed mg. If the mass was at the limit, then this force would exceed that. It’s possible the ‘copter could be pulled down and not recover. But the load goes away when the people touch down, so one might expect crashing to be limited to some specific range of solutions. (e.g stiff spring so the load isn’t removed until you are close to the ground, people falling far enough so the excess force is large)

I wasn't referring to the weight load, but to whether or not vertical oscillation hampers the way in which helicopters generate lift.

It could certainly initiate stall of the rotor blades if there is too great an angle of attack.

That could reduce lift quite abruptly but this should not happen close to the weight limit, or essentially safe lifting force limit. The design should include appropriate safety factors. Turbulence would create similar challenges

Edited November 22, 20205 yr by J.C.MacSwell