REFLECTOR: Low CHTs

John Dibble aminetech at bluefrog.com
Wed Jan 17 14:00:00 CST 2007



Ron Brown wrote:

> Hi John,
>
> I think that is a GREAT idea - using bimetallic springs.  I have been
> thinking about adding butterfly valves in the NACA down ducts, but didn't
> want to run actuating cables.  However, the bimetallics would be a great
> approach.  Two thoughts, build the valves so that they can't close
> completely off, i.e. they can only close part of the air flow off.

I agree.  I was thinking of making the valve smaller than the duct (50-75% of the
duct).

>  Second,
> the airflow should try to open the valves, the bimetallic would close the
> valve with cold OAT.

 I agree.  I assume the back (relative to the axis it rotates on) end of the valve
should be a bit longer than the front to achieve this.  Any idea how much longer?
Also I think posts/stops to limit valve travel to nearly full open and to full closed
might be helpful to prevent flutter, if that can happen.  Also the stops would be
necessary since it may be difficult to adjust the spring to stop at these points.


>  However, the bimetallic springs in carb chokes
> operates off of either exhaust heat or an electric coil - I've seen both
> used.

I think the electric coil is more likely to fail, at least in my experience.

>
>
> My cabin heat is working good down to about 30 degrees or so - as some one
> suggested earlier, closing off the damper valve completely restricts the
> amount of cooling of the oil, and therefore causes the engine to run warmer,
> hence warmer oil and vernatherm opens.  (did that make any sense???)  But my
> heads are running around 310 degrees which is a bit cool.

If I had 310 F at 30 OAT, I wouldn't even bother with the valve.  I have very good
cooling and at 30 OAT, my CHTs run 160 F.

John

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