Re: To hover, a reaction-motor pushes on the earth?

[John Denker <jsd@MONMOUTH.COM>]

At 02:02 AM 8/18/99 -0700, William Beaty wrote:
> On Sat, 14 Aug 1999, John Denker wrote:
> > billb wrote:
> > > How can any aircraft remain suspended above the ground (or
> > > remain in level flight)?
> > >
> > > It can either push upon the earth, or it can employ action/reaction in the
> > > way a rocket does.  A helium balloon pushes indirectly upon the earth.  So
> > > does an aircraft in "ground effect" flight.
/jsd/ So does *everything*.
/jsd/ Gravity is a force between the earth and the aircraft;
/jsd/ the only way to counteract it is a force (indirect or otherwise)
/jsd/ between earth and aircraft.
/jsd/ The only question is how indirect it is going to be.
> Everything flys by pushing against the earth?  I strongly disagree.

I stand by my assertion that in a closed system, the wing pushes indirectly
against the earth.  The only question is how indirect it is going to be.
My assertion is a simple consequence of Newton's laws.  If we can't agree
on this, we have nothing further to say to each other.

> Another point.  Whenever a rocket hovers near a massive object, there is
> no requirement that the rocket's exhaust strikes the object.

In a closed system there is.

This thread started as a discussion of aircraft.  The analogies to
deep-space rocketry are misleading.

> I believe that the controversy between the "Bernoulli-ist" and the
> "Newtonist" explanations of flight definitely revolve around the above
> concepts.

This is crazy.  Bernoulli's principle is consistent with, and indeed a
consequence of, Newton's laws.  How could there possibly be a conflict
between them?