<VV>Mo Mo Fan

[Ron]

My shop vac speeds up when blocking the exit.  For the low pressures seen 
here, incompressible flow correlations will be reasonably accurate.
RonH

----- Original Message ----- 
From: "Padgett" <pp2 at 6007.us>
To: <BobHelt at aol.com>; <ronh at owt.com>; <virtualvairs at corvair.org>
Sent: Thursday, July 14, 2005 2:48 PM
Subject: Re: <VV>Mo Mo Fan


> 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
>
>
>>I hope that Padgett would run this test. But to me it's just so obvious 
>>that air has weight, and it takes power to move that air. So the more air 
>>that is moved, the more power it is going to take. Blocking the damper 
>>doors closed reduces or eliminates the air movement, so the power required 
>>goes way down.
>>Regards,
>>Bob Helt
>
>