Bill Freeman wrote:

Chris Gentry wrote:

Is it possible to tap into the vacuum side of the turbocharger to get a
vacuum for the gyros?  Could a short intake stack be used for the tap point
for a venturi effect.  I'm sure there is a lot of sucking going on at the
input of the turbo pump.
Best Regards,  Chris Gentry

Grumman Cheetah, Glasair(Rotary) & Dragonfly

The pressure drop across the air filter is on the order of one to two inches
of Hg. (Mercury)  One inch of Hg is about .5 psi. What the instruments need is
ten times that amount or 5 psi as I recall. Another way of looking at it is
sea level is 30 inches of Hg or 15 psi. So you would need 10 inches of Hg
to operate the instruments which would severely restrict the power to
about 2/3 of normal. Did I make a mistake here?

No way for me to know for sure without trying it but I suspect if you had a

big

enough venturi in the exhaust for cruise vacuum you would also restrict
the takeoff power.

Paul Lamar

I don't know what is meant by "the vacuum side of the turbo"  - as I understand
it you have ambient at the inlet (less losses thru filter and piping, say 1
inch Hg)
and pressure at the outlet.  Doesn't leave any place for vacuum.

My vacuum gauges are marked in inches of Hg, and you need about 5 in Hg for
normal gyro performance.  

I was wrong there. It is 5 HG and not 5 psi. Thanks for correcting me 
on that Bill. That would be only about 2.5 psi. PL

This will cost significant power, but most aircraft
can fly OK with the throttle pulled back to provide adequate emergency gyro
capability.  My Dad has this type of emergency system in his Mooney and it
leaves enough to get somewhere, slower and potentially more importantly
LOWER - bad news if over mtns of Colorado in IMC.

Why not a venturi mounted on a piece of fuselage skin which is on a fore-aft
pivot.  When the venturi is rotated to the interior, a smooth skin surface
is visible.
At the pull of a handle, the venturi rotates out 180 deg into the airstream,
bringing SIMPLE & RELIABLE vacuum on line.  Put it on the belly of a
conventional A/C (engine waste heat mixed with some exhaust) and it
probably won't even ice until your prop and wings are too far gone
for loss of vacuum to be the primary cause of the accident.

Bill

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