Bill Freeman wrote:

Ken Powell wrote:

I would just like to remind everyone of the failure mode that Jeff
Spitzer (and others) mentioned recently.  When you are running 2 belts
side by side and 1 breaks, there is a good chance that the broken belt
will get between the good belt and the pulley and break the good belt
also.  Jeff mentioned that he will be building a shield between the
belts to prevent this.  Thanks to everyone who has mentioned this for
the reminder.

I am building a Day VFR only RV-4 and I plan to tap manifold vacuum to
run at least an attitude indicator.  I realize that the throttle will
have to be partially closed to generate a vacuum (cannot run WOT) but
this is an acceptable tradeoff for me.  If I really need an Attitude
Indicator then I already have big problems in a day VFR only bird so
slowing down should not be a problem.  I would guess that I will need
both a vacuum regulator and a vacuum accumulator (to smooth the intake
pulses) to make this work.  However, I am still years away from having
the plane to this point of construction.

Thanks,
Ken Powell

Ken,

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

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