Mailing List flyrotary@lancaironline.net Message #11771
From: Russell Duffy <13brv3@bellsouth.net>
Subject: RE: [FlyRotary] Re: Oil viscosity
Date: Sun, 26 Sep 2004 10:00:50 -0500
To: 'Rotary motors in aircraft' <flyrotary@lancaironline.net>
Message

Well, no; but. The specific heat is the same and the flow rate around the loop is (roughly) the same.  The lower viscosity will result in more flow through the bearings and rotors (less bypassing through the pressure control valve) providing more effective cooling of the rotors.

Well that's actually a bonus that I wasn't considering.

  But it has little effect on the heat rejection (other than slightly better heat transfer coefficient), so, one might expect the oil to heat up at the same rate, or a bit faster.

I've always read that it was difficult to cool oil because it tends to cling to the surface.  Specifically, when the subject of cooling oil in the pan comes up, someone always points out that oil clings to the cooler pan surface, and gets a little thicker, allowing other hot oil to just flow over the top of that film of thicker oil.  In other words, the oil flows past without making any real contact with the relatively cool pan surface.  I always figured this same thing happened to some extent in the tubes of oil coolers as well.  So go ahead, shatter my mental reality and tell me this is all BS :-) 
 
Unless there is something major I’m missing.
 
In a couple weeks, we'll see if there's any real difference in temps.  If not, you aren't missing anything major :-)
 
Thanks,
Rusty (@$*^& Earl's fittings)
 


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