REFLECTOR:Cooling a canard

[John Dibble]

Chuck Jensen wrote:

> John, your right about that.  My engine operates at a temp way lower than
> 190F and I get thirsty several times a day.
>
> There is one other dynamic at play here, related to moisture evaporation,
> that I'm unsure of the impact (if any).  Clearly, water has a higher vapor
> pressure than oil, so it'll evaporate off more readily.  However, in the
> engine, any condensation that collects in the crankcase is going to be
> covered by a thick blanket of oil which may reduce/prevent evaporation.

Yes, the blanket will slow evaporation.  However water does have a small solubility
(~10 ppm) in oil so it can slowly migrate through the oil and evaporate.

John

>
> Nonetheless, by long experience in aircraft ops, it seems that any engine
> oil temps in the +190F range is effective at driving off unwanted moisture
> and that temps of +212F is not required.
>
> The only other advantage of running higher oil temps is it implies a hotter
> engine.  Some basic physics taught us a hotter engine is more efficient (up
> to the point that you start melting components).  In addition, the high temp
> implies less cooling and less associated drag.  By my calculations, if you
> run the oil at 212F instead of 190F, considering the improved engine
> efficiency and reduced cooling drag, your overall operations will be 0.0197%
> more efficient.  Of course, the speed gain of 0.101 mph from the increased
> energy conversion efficiency will require you to recalculate the timing of
> your descent so you don't overshoot the airport.  Caution: Your calculations
> may vary.
>
> Chuck Jensen
> Diversified Technologies
> 2680 Westcott Blvd
> Knoxville, TN  37931
> Phn:     865-539-9000 x25
> Cell:     865-406-9001
> Fax:     865-539-9001
> cjensen@dts9000.com