Re: helicopter not equal rocket

[John Denker <jsd@MONMOUTH.COM>]

At 01:14 PM 8/19/99 -0400, Michael Edmiston wrote:
> Okay, John, I was not aware of this power difference between hovering
> and translating.

OK.

> But now that you have told me about it, I think it
> does make sense in the reaction-engine view...

I don't see it; see below.

> and this partly comes
> from the information you told us about how a slow airplane makes worse
> vortex wake than a faster plane.

> A translating helicopter is visiting/affecting much more air than a
> hovering helicopter.

True, but irrelevant to a reaction engine.

>  It doesn't need to "jerk the air downward" as
> violently in translation as it does in hovering because when it
> translates it affects a much larger quantity of air.

True, but irrelevant to a reaction engine.

> I believe this is
> essentially the same type of reasoning you used to explain the
> tremendous wake behind a slow plane.  This type of argument is a
> reaction-engine (F = dp/dt) type of argument.

It's a dP/dt type of argument.  It is not a reaction-engine argument.

> Worse, a hovering helicopter partially experiences the same air over
> and over.  To the extent that the air just goes down, out, up, in, and
> back down in a continuously circulating "smoke ring," we aren't
> throwing significant net amount of air downward.

Exactly the point.  Again irrelevant to a reaction engine.

> Away from ground
> effect, this mechanism could be significant and I can imagine the
> difficulty in hovering.

Good.  You are agreeing that translational lift is a real phenomenon.

> Interaction between the vortex ring and the
> ground would interfere with this recirculation... it would spread out
> the downward moving air along the ground and result in a greater
> quantity of "new air" being brought into the blades.

Ground effect is not nearly that simple.

> I think this type
> of reasoning is also consistent with a reaction engine view.

I don't see it at all.

> As you have stated, the Bernoulli, circulation, etc. views/analyses
> have to be consistent with the Newtonian (F = dp/dt) views.

Right.

> You
> understand a way to view "translational lift" using the traditional
> aeronautical engineering views of Bernoulli, et.al.  But there also
> must exist an F = dp/dt way of viewing this.

Of course.  I discuss this in some detail in
  http://www.monmouth.com/~jsd/how/htm/airfoils.html#sec_stream_line_curvature

>  I think what I said above does that.

Yes, it expresses a dP/dt view.  No, it does not come close to explaining
why a reaction engine should exhibit translational lift.

Consider the counterargument:  Reaction engines, according to the
definitions everybody else is using, don't exhibit translational lift!
Certainly Bill B.'s machine gun (which started this thread) doesn't.
Bottom line: there is a fundamental difference between the *observable*
behaviors of helicopters and reaction engines.

You haven't come even 1% of the way to convincing me that the physics is
the same when the observed behavior is so different.