<VV>Mo Mo Fan

[JVHRoberts at aol.com]

Well, since I have been known to be wrong on VERY rare occasions, I ducked  
into the garage and fired up the shop vac. And sure enough, the motor speeds up 
 no matter which port, inlet or exhaust, is plugged. Less so when the outlet 
is  plugged, only because some of the air exhausts out the top of the motor, 
and I  don't have enough hands to block that path off. Although sitting on it 
seemed to  speed it up some. OK, let the sit on it jokes commence.. <G>
 
John
 
In a message dated 7/14/2005 5:49:27 P.M. Eastern Standard Time,  pp2 at 6007.us 
writes:

Can  ontly think of one way to tell and since I do not have a Corvair yet  
(hoped I would find one over the weekend, didn't) all I have is my shop  
vac.  Blocked the inlet and could hear the motor speed up. Blocked  the 
outlet and really could not hear any difference. Unfortunately the low  
range on my clamp-on ac-ammeter is 200 amps which only gives one decimal  
point of resolution but my small shop vac (big one does not have a blower  
connection) read 5.5A(occasionally 5.4A) running open, 5.3A with the  intake 
blocked and 5.6A with the outlet blocked (repeatable).

Agree  that the more air moved, the more power it takes but that does not 
mean  that the system needs to have an output, the air could just be moving  
around in the plenum. If the power is going down when the doors are closed  
then some other effect is taking place which may include reversion around  
the fan (in a gas turbine engine if the first stage goes sonic, you can  get 
exhaust reversion through the bypass ducts which will stall the  engine. Not 
good on takeoff.)

Yes air has weight but it is also  compressible. This means that a given 
volume will weigh more at a higher  pressure than a lower. If you block the 
outlet, the internal pressure is  going to rise which means the fan is 
moving in a denser medium.

Now  obviously empirical data is showing a fan loss drop if the doors are 
shut.  To me this means that something more complex is going on than just  
blocking the outlet.

Padgett