REFLECTOR: updraft cooling

Scott Derrick scott at tnstaafl.net
Sat Feb 17 14:57:56 CST 2007


Doug,

I had updraft on my IO360 and it worked fine. I had to run LOP in the
summer(I did all the time anyway)  to keep the engine cool enough.  There
were times when I stopped for gas and during the following departure
climbout I would have to level off at an intermediate altitude for awhile
to get the oil temps back down below 230.

Installing my 520 I conferred with Velocity(ScottB and Brendon) and was
advised I would need to use downdraft as they had never successfully seen
an  updraft system work for the big six cylinder engines.  So I did the
conversion.

I thought that using NACA intakes would "theoretically" be more drag
effecient ?

Scott


> I can understand why Burt Rutan and Nat Puffer are proponents of updraft
> cooling. From an engineering point of view, it has a lot going for it. You
> need more cooling when the airplane is climbing. If the cooling intake is
> below the wing, the pressure is higher during a climb so you automatically
> get more cooling during a climb. Similarly, it would be nice if cooling
> was minimized during descent. The pressure is reduced under the wing
> during descent, and so there is less cooling to the engine. Also, you've
> got convection working with you instead of against you with an updraft
> system.
>
> That all adds up to more drag with down draft cooling, because the NACA
> scoops have to be large enough so that there is adequate cooling during
> climb out, when the pressure at the NACAs is at its minimum.
>
> But the down draft is a lot simpler to implement, and that's probably
> going to be the deciding factor for me.
>
> Doug Holub_______________________________________________
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