🚀 go-pugleaf

In article <9md4k6$hb0$1@bugstomper.ihug.com.au>, "Roidy" 
<roidy23@ihug.com.au> wrote:

> "Kevin Lowe" <serpentriver@yahoo.com> wrote as such message
> 
> > There'll be extra downward forces of short duration from the birds
> > taking off and landing.  There'll be some lessening of the downward
> > force the birds exert on the plane while they are flying, since the
> > downward force exerted by their wingbeats will experience some losses
> > due to turbulence and general entropy before it reaches the floor of 
> > the plane.  (But also partially because they are "borrowing" against the
> > take-off and landing forces).  I don't know how to work out if these
> > changes in the downward force would be significant, but I'd guess it
> > would have a lot to do with the size of the space they are flying 
> > around in.  Small space, little loss.  Big space, more scope for the 
> > shockwaves in the air to lose energy.
> 
> 
> ahh, i see your point, the "elastic properties of air pressure".
> a better way to get the point across would be to imagine a plane that's
> cargohold is about 500metres high (ie: from the bottom to the top of the
> cargohold is 500metres), there would be enough air for the pressure 
> changes to degrade before they hit the bottom of the cargohold. what WOULD happen 
> to the downward force though? i guess the energy lost would be converted 
> into air friction (sound and heat) right?

I'm no expert, I'm making this up as I go along.

But yeah, I'd guess that there would be a transfer of energy into heat 
and non-directed air movement.  And I'd further guess that the net 
effect would be pretty small unless it was a very big cargo hold.

My gut feeling is that air is a pretty inefficient way to transfer 
energy.  A wingbeat that sent, say, 1 kilojoule of energy downwards 
wouldn't transfer all that energy to the floor below - the air would hit 
the bottom and scoot sideways, retaining plenty of energy as it did so.

I guess that's why you don't get crushed if you stand directly under a 
helicopter - the air isn't very efficient at carrying the force, so even 
though the force exerted by the rotor blades is enough to bear the 
weight of the helicopter all that force doesn't fall on someone below 
and squish them.

Kevin Lowe,
Brisbane, Australia.

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