Simple Question to do with TORQUE on a helicopter

[06mangro]

Homework Statement

If the force pushing the helicopter blades from the pivot point surely r is 0... therefore T (torque) is 0 also...

Homework Equations

r is the Length from pivot point to force
F is force
τ= r × F ×sin(θ)

The Attempt at a Solution

 

[tiny-tim]

welcome to pf!

hi 06mangro! welcome to pf!

If the force pushing the helicopter blades from the pivot point surely r is 0... therefore T (torque) is 0 also...

ah, but the force actually comes from the outside of a shaft …

so r is the radius of that shaft ​

 

[06mangro]

hi 06mangro! welcome to pf! ah, but the force actually comes from the outside of a shaft …

so r is the radius of that shaft ​

would it be possible to elaborate on what you mean... and where this shaft would be on the chopper

 

[tiny-tim]

i'm not knowledgeable on helicopter construction,

but clearly the engine is attached to a cylindrical shaft that goes up to the centre of the blades …

exactly like the axle going to the centre of a wheel​

the outside of the shaft turns the blades, in the same way that the outside of the axle turns the wheel

 

[06mangro]

thank you very much :)

 

[06mangro]

one more thing...
so does that mean the blades do not create torque...
only the shaft does?

or does it mean that that the torque is transferred into the blades in a sense...?

 

[tiny-tim]

one more thing...
so does that mean the blades do not create torque...
only the shaft does?

the shaft creates a torque on the blades

by good ol' Newton's third law, there's an equal and opposite reaction …

the blades create an equal and opposite torque on the shaft ​

 

[CWatters]

For your purposes you can probably treat the rotor like the spokes on a rigid wheel.

The blades on some helicopters are (in effect) rigidly connected to the shaft. Others have a lead-lag hinge that allows the blade to swing back and forth (normally only a little) for quite technical reasons.

Even if it had a big floppy hinge the hinge is outboard from the shaft so it's a bit like swinging buckets around your head. Having a hinged handle on the bucket isn't a problem.