George

Everyone seems to have forgotten about one of the cheapest and most
reliable vacuum sources out there --  the venturi.  These are kinda

clunky

looking and certainly cost some drag, but they can be mounted on the

belly

where they are less visible, and the drag can't be all that serious.  The

only

problem is icing, and if it is in the path of the exhaust, I would expect

that

icing would be less of a problem with the venturi than the wings and

prop.

Cheap, light, absolutely reliable - pretty good for a day VFR bird.

Probably

cost you about 2-3 kts in cruise or less.  The primary disadvantage is

that

they are not too stylish.

Bill

George Lendich wrote:

Bill,

Someone mentioned that a venturi can be mounted inside the cowl, provided
there is an
opening in the cowl (with tube/ baffle) to feed it - could probably put it
near the exhaust  pipe, if concerned with icing.

I really like this idea.
It will still cause drag unless a butterfly valve is placed somewhere in
the duct feeding the venturi. When the butterfly valve is closed air will be 
diverted around the cowl opening with little or no measurably increase in drag. 

BTW that new SCEET silicone impregnated fiber glass two ply ducting is very 
smooth inside for less aerodynamic losses. Page 123 in the new AC Spruce catalog. 
I have installed all new ducting in my C182 using that great stuff.

Paul Lamar

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