<VV>Mo Fan

[Padgett]

>Sorry Padgett, but this is just not correct. When you block the output
>cooling air, the fan has much less work to do and the required horsepower 
>goes DOWN,
>not up.

Guys: the fan loss (hp required) has nothing to do with the amount of air 
moved but rather the power required to turn the fan. The power required to 
turn the fan at maximum air movement (unblocked inlet and outlet) is 
actually a middle value. Block the inlet and the fan is turning in a 
partial vacuum of its own creation and the power required for a constant 
rpm goes down (in the tank vacuum example or a turbosupercharger, the rpm 
will increase). Block the outlet and the air density in the plenum goes up, 
increasing the drag on the impeller. This increases the power required to 
turn the fan and the temperature of the air in the plenum goes up slightly.

Now if you want to get heat quickly and increase the heater air flow in 
cold weather, this makes sense since the change in drag is not a whole lot 
for the engine driven cooling fan in a Corvair but in a turbo, particularly 
one making a lot of boost, it is a serious issue.

Padgett