Snipped....

For my currently flying duct2, if the exit pressure (p4) is sea level
standard 14.70 psi, the pressure just aft of the fan plane (p3) is 14.51
psi and the pressure just in front of the fan plane (p2) is 14.35 psi.
This is all theoretical. Not very large "vacuums" there. This is with a
cruise speed of 115 knots and an airspeed of 156 knots in the fanplane.

But because of the location of my rad exit near the duct inlet, I get
the suction you are talking about through my rad, it eliminates any
ground cooling issues for me.

Perry

That answers the issue!  :)
I thought the pressure might be lower after the fan, as the speed should be
higher there and if the duct outlet is smaller than the inlet, Mr.'s Venturi
and/or Bernoulli might be at work somewhere!

A cooling duct outlet in ringform all the way around the fan might pull a
lot of air. Obviously this might be neutralized by the quite big inner
surface area of such a duct.

Knowing now, that you have the lowest pressure in front of the fan, there
might be chance for a bigger volume rimg duct dumping the cooling air in
front of the fan (as it does now, but) all around the duct.

Though you say, you don't get "a very large vacuum", you would have it in a
"very large" area. This large area pulling on a rather small area after the
radiator might produce a substancial flow (allowing reduction of the intake
area).

How far away from the fan is your cooling outlet now? What kind of vacuum
are you pulling at this station?

Thomas J.

 
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