What is this?

[jesse]

Any idea what this is?

 

[HPNPilot1200]

A venturi...I'll post a link later

Used prior to pitot tubes to measure airspeed I believe (correct me if I'm wrong)...I believe it created some sort of vacuum to find the differ in airpressure.

 

[jesse]

I am pretty sure this airplane has a pitot tube. I feel like an idiot since I've flown the thing... Maybe it doesn't though.

I just was looking at pictures and seen that and was a bit confused.

 

[mgkdrgn]

Venturi - possibly (high probability)

Measure airspeed? Don't think so. Venturi's were used to drive vacuum driven instruments prior to the days of vacuum pumps. Meaning your AH didn't work worth snot until you got some airspeed up for a while.

A venturi...I'll post a link later

Used prior to pitot tubes to measure airspeed I believe (correct me if I'm wrong)...I believe it created some sort of vacuum to find the differ in airpressure.

 

[HPNPilot1200]

Venturi - possibly (high probability)

Measure airspeed? Don't think so. Venturi's were used to drive vacuum driven instruments prior to the days of vacuum pumps. Meaning your AH didn't work worth snot until you got some airspeed up for a while.

At least I had the vacuum part right. Airspeed part wasn't.

 

[jesse]

the plane has airspeed, altimeter, VSI.. and that is it for instruments other then oil pressure / temp and a compass.

No DG.. no AI... Maybe it's there just incase you wanted such things?

 

[Fast n' Furious]

Well, it's a venturi alright but it wasn't used to determine airspeed. Back in the day, before pressure pumps or vaccuum pumps they were used to "make" the suction that was required to make instruments like the AI (if you had one) and the DG (same thing) spin so that they would function as a gyroscope. Some airplanes also were adapted to use the venturi like an airhorn for use in uncontrolled airports where cows and dogs were known to congragate on the runway.

 

[Everskyward]

Caution. If you see something that looks like that on the bottom of the fuselage it's the outlet for a relief tube.

 

[Henning]

the plane has airspeed, altimeter, VSI.. and that is it for instruments other then oil pressure / temp and a compass.

No DG.. no AI... Maybe it's there just incase you wanted such things?

Well, you can hook up a "relief tube" to it if you want, but usually those are on the belly of the plane. In origional context, that was at one point used to drive vaccuum instruments.

 

[trombair]

hey jesse!

the particular item in the photo is a 2" venturi which means it will draw 2" of water in suction. there are 4" and 9" (super venturi) that are fairly common on vintage aircraft.

the 2" is typically used to run a vacuum turn and back (not turn coordinator). the 4" are used to run A/H or D/G (1 each). a 9" venturi will run both A/H and D/G if positioned and plumbed properly.

the cool thing about them is that they never fail, unlike dry vacuum pumps. the down side is that they are draggy and will ice up . mostly they are positioned somewhere near the cowling exit air (warm) to prevent the icing problem.

i did my IR back in 1995 in a 1948 stinson 108-3 with a single 9" venturi running the A/H and D/G. the T/C was electric. the only down side was the A/H would not always be fully erect on initial takeoff roll. so i got very good at partial panel departures. otherwise, it was completely trouble free. (the stinson is no speed wagon, so drag was not a big deal.)

hope this helps!

 

[SCCutler]

...this topic brings up an idle thought: I wonder if anyone ever built a "pop-out" venturi as a backup emergency vacuum source? Seems like it'd be a useful gadget in the event of vacuum failure related to engine failure, a circumstance where the electric backups would be of marginal utility with no alternator action.

Just a thought. Waiting now for Henning or Tom to explain to me just how boneheaded my idea is, for reasons which make compelling sense.

 

[Bill]

...Just a thought. Waiting now for Henning or Tom to explain to me just how boneheaded my idea is, for reasons which make compelling sense.

When are you most likely to need the venturi to actually work? When in real IFR conditions. When is a venturi most likely to ice up? When in real IFR conditions.

That would be my reason why not.

 

[mgkdrgn]

I do believe I have seen something -like- that, but rather than being a venturi it was a unit with a little propeller on it that dropped into the airstream and provided a vacuum source.

...this topic brings up an idle thought: I wonder if anyone ever built a "pop-out" venturi as a backup emergency vacuum source? Seems like it'd be a useful gadget in the event of vacuum failure related to engine failure, a circumstance where the electric backups would be of marginal utility with no alternator action.

Just a thought. Waiting now for Henning or Tom to explain to me just how boneheaded my idea is, for reasons which make compelling sense.

 

[jesse]

I do believe I have seen something -like- that, but rather than being a venturi it was a unit with a little propeller on it that dropped into the airstream and provided a vacuum source.

Sounds like the device that comes out of hte belly of airliners to provide hydraulics during a dead stick scenario.

 

[MSmith]

Does it play "Dixie" when you press the right button?

 

[Skip Miller]

I do believe I have seen something -like- that, but rather than being a venturi it was a unit with a little propeller on it that dropped into the airstream and provided a vacuum source.

I've flown behind a wind driven alternator that tipped out of the forward baggage compartment of a PA-32. Never needed it in flight, though.

The unit is similar to this one at Aircraft Spruce.

http://www.aircraftspruce.com/catalog/eppages/turboalt.php

-Skip

 

[Bill]

Does it play "Dixie" when you press the right button?

And yankee doodle dandy when you press the left...

 

[MSmith]

And yankee doodle dandy when you press the left...

I meant "Correct" rather than "Right Wing", but I like your version better!