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Date: Fri, 05 Aug 2011 09:46:48 -0700
From: Cedric Gould <nghthwk@bellsouth.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Impellor Rotation Direction
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Jeff,

To give the short answer, Mazda is turning the impeller in the correct 
direction (namely in the direction correlating to the increasing scroll 
volume, as depicted in your "Water Pump Pulley 03.jpg").

The long answer is that the impeller blades, oriented as they are, is a 
stable, wide operating band style impeller.  To use an aircraft analogy, 
this pump has a positive static margin.

Something that's interesting about pumps such as this is that they can 
squeeze more efficiency out of the impeller by rotating the blade on the 
impeller.  The downside to increasing the efficiency in this manner is 
that the operating range is reduced and, similar to reducing the static 
margin in an airplane, is that you pay for it in stability.  If a pump 
of this design were "flying" at its neutral point, the blades would be 
oriented radially from the axis of rotation.  Continuing with the 
airplane analogy, if the pump were "flying" with negative static margin, 
but also at its most potentially efficient, but also most likely to 
cavitate and go unstable, the blades would be mirror-imaged from the 
orientation they're in now, but still rotating in the same direction.

I'm sure what I've explained is clear as mud, yes?

Anyway, hope it helps.

Regards,

Cedric Gould


On 8/5/2011 5:13 AM, Jeff Whaley wrote:
> Why do I get the feeling these impellors are being turned in the wrong
> direction?
>
> Image 1 is a scan of a test engine … from my cockpit the prop turns
> clockwise and so does the e-shaft with an RD1-C - as referenced to this
> scanned image.
>
> Now look at these water pump impellors … if I wanted to move water I’d
> cup my hand and scoop it, not use the back of my hand.
>
> Has Mazda got this wrong? Or am I missing something?
>
> It looks like I’ll have to change the water pump, as the flange may be
> warped and the thread bosses are definitely burred.
>
> **
>
> *Jeff Whaley*
>
>
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