On 23/08/2019 18:53, The Natural PhiThe lift with zero rpm is still
zero.losopher wrote:
On 23/08/2019 13:17, Robin wrote:
On 23/08/2019 11:17, The Natural Philosopher wrote:
On 23/08/2019 10:34, Mike Clarke wrote:
On 23/08/2019 08:14, The Natural Philosopher wrote:

All force, no distance
An infintely large infinitely strongÂ* helicopter could hover with
no power input.

Not so. It's having to generate lift with the rotating rotor blades.
The work is proportional to the torque on the rotor shaft and the
number of revolutions.

An infintely large rotor turns at zero RPM

There are no revolutions.



if it is also an infinitely heavy helicopter I'd like to see the proof

if it isn't infinitely heavy why bother with rotors when you could
just use cavorite?


The point is that it takes no energy to hover since no potentialÂ* energy
is lost or gained.

ItÂ* takes energy to accelerate an air mass downwards to generate the
momentum change that provides the lift.

But energy is 1/2mV^2 whereas momentum is mV so as m tends to infinity V
tends to zero for the same lift

That is, an infinitely large rotor.

Consider a helicopter with rotors with radius r=10m turning at 0 rpm.
Lift generated is zero. OK?

Double the radius to 20m. Lift generated is still zero. OK?

Let the radius r tend to infinity. The lift if rpm is zero is still
zero. Oh dear!

--
Robin
reply-to address is (intended to be) valid