Venturi Vacuum

Fearless Tower

Fearless Tower

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Fearless Tower
Not terribly familiar with this type of system, but understand that in some of the early GA airplanes, the engines were not designed for engine driven vacuum pumps and therefore vacuum for the AI and DG was provided by externally mounted venturis - how well do those systems work?

Are they reliable enough for IFR ops?
 
On the one hand, there's no pump to break. On the other hand, they do not start creating said vacuum until you start flying and they collect ice efficiently.
 
Ken Ibold said:
On the one hand, there's no pump to break. On the other hand, they do not start creating said vacuum until you start flying and they collect ice efficiently.
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In other words, you have no idea if your vacuum instruments are working until you are actually committed to flight?

Sounds less than favorable for an instrument departure, but might be useful to make an approach through the SoCal marine layer.
 
Fearless Tower said:
Not terribly familiar with this type of system, but understand that in some of the early GA airplanes, the engines were not designed for engine driven vacuum pumps and therefore vacuum for the AI and DG was provided by externally mounted venturis - how well do those systems work?

Are they reliable enough for IFR ops?
Click to expand...

They were replaced by vacuum pumps for some very good reasons, a couple already mentioned. No good for serious IFR.

Dan
 
Fearless Tower said:
In other words, you have no idea if your vacuum instruments are working until you are actually committed to flight?
Click to expand...
That's about the size of it.

Sounds less than favorable for an instrument departure, but might be useful to make an approach through the SoCal marine layer.
Click to expand...
I'd agree with that, since you'd know if things are working before you punch into the actual instrument conditions.
 
Ken Ibold said:
On the one hand, there's no pump to break. On the other hand, they do not start creating said vacuum until you start flying and they collect ice efficiently.
Click to expand...
I've seen a couple that would make sufficient airflow to operate a gyro from the prop blast at runnup RPM so it should be possible to launch into IMC with one. But the ice issue is kind of a deal killer unless you never venture into below freezing clouds. And more often than not, the kinds of airplanes equipped with a venturi aren't what I'd want to fly in any significant weather anyway.
 
As a backup system (having seen all the Motor-driven stuff out there) I would love to see is a venturi or set of venturi's nessleled right up next to the exhaust system (for ice) with an automatic door and regulation as a backup to vaccum pumps...

Once the airplane is in motion why do you need a motor to drive another vaccum pump? Could it be that Burt Rutan is right...sometime Engineers overlook the most simple solution so they can engineer something?


JMPO

Chris
 
Hiperbiper said:
As a backup system (having seen all the Motor-driven stuff out there) I would love to see is a venturi or set of venturi's nessleled right up next to the exhaust system (for ice) with an automatic door and regulation as a backup to vaccum pumps...

Once the airplane is in motion why do you need a motor to drive another vaccum pump? Could it be that Burt Rutan is right...sometime Engineers overlook the most simple solution so they can engineer something?
Click to expand...

Tony will have to help me on this, but IIRC the Arrow I that I flew at Green Castle had a backup vacuum system that used the intake manifold. If you lost the vacuum pump, you throttled back to a pre-determined maximum manifold pressure based on your altitude, and the lower pressure inside the intake manifold functioned as your vacuum. Really elegant solution, since it didn't leave you with any additional drag on the outside of the airplane either!
 
A good many Pilots flew a great many hours on ventures, If you are thinking they ice up any faster than the rest of the aircraft you are mistaken, this is one of the things that are good in theory, but not in practical life. Icing will occur on the wing just as fast as the venturi, because the same thing is happening there as in the venturi.

the 11 inch venturi will spin up the old AN 1 Gyros on the prop blast, simply because the old style gyro requires a lot less vac pressure. That is why you saw the old pilots go full power for 1 full minute before take off.

BTDT and never had a vac pump failure.
 
Fearless Tower said:
Not terribly familiar with this type of system, but understand that in some of the early GA airplanes, the engines were not designed for engine driven vacuum pumps and therefore vacuum for the AI and DG was provided by externally mounted venturis - how well do those systems work?

Are they reliable enough for IFR ops?
Click to expand...

If you have the big old AN gyros they were meant to work with, they work pretty good. If you have newer style gyros they take a bit more flow to spool up since they have smaller hamster wheels. I found with the old gyros they'd start spooling at about 40 on taxi and even on a high power runnup. With new style gyros it starts stabilizing about 1000' down the runway and by the time you make 100' it's pretty solid. Obviously you don't want to fly into icing conditions.

There's been a heck of a lot of hours of IFR ops flown on them in days gone by, and I've done a few of them....
 
flyingcheesehead said:
Tony will have to help me on this, but IIRC the Arrow I that I flew at Green Castle had a backup vacuum system that used the intake manifold. If you lost the vacuum pump, you throttled back to a pre-determined maximum manifold pressure based on your altitude, and the lower pressure inside the intake manifold functioned as your vacuum. Really elegant solution, since it didn't leave you with any additional drag on the outside of the airplane either!
Click to expand...


I think it's a considerably less than optimal solution myself since it limits your power and basically creates an induction leak. Never really liked them myself. You don't much want to be having to go missed in a plane carrying weight in it.
 
Has anyone ever seen a heated venturi system that would be reliable? That would be an interesting solution...

Ryan
 
My 1957 c172 with 180hp cs prop

It has 2 venturis that we left on during rebuild and engine conversion.
We used a Presice Flight back up system converted it to use the venturi's, done on a Field approval

I did lose a dry pump with about 100hrs snew on a vfr flight, Low vac. light came on pulled the Presice flight alternate vacumn on, a few seconds shazam! the light went out gyros were normal.

I do fly actuall in this c172

I do not know about Ice on the Venturi's and hope not to find out.
 
Ken Ibold said:
another interesting solution is electronic gyros and a backup battery and/or deployable air-driven generator.
Click to expand...

You mean like this ?
 

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weirdjim said:
If your venturi vacuum starts to ice up, you are about to have way more problems than lack of vacuum.

Jim :idea:
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I haven't personally ever had a venturi "ice up" but I suspect that while it wouldn't be likely to collect ice any faster than the flying surfaces, it probably takes a lot less ice to kill the vacuum than it does to prevent the plane from flying.
 
weirdjim said:
If your venturi vacuum starts to ice up, you are about to have way more problems than lack of vacuum.

Jim :idea:
Click to expand...

That's kind of what I was thinking. At any rate, thanks for the info everyone. The plane I am looking at right now has all of the required IFR instruments with the exception of OBS indicators - has two Collins Nav radios, but the OBS's were removed. I'm looking at it as more of a VFR, tailwheel timebuilder, but if I can get it to pass a pitot static check and pick up a couple of refurb OBS's, it may increase my use of the plane for x-countries around here knowing that I can get back into San Diego through the marine layer if need be. Most of my IFR flights here in the southwest seem to consist of .1 and .2 actual IMC logged.
 
Fearless Tower said:
I can get back into San Diego through the marine layer if need be.
Click to expand...

I had an IFR C-120 (!) with venturis that I used when based at Montgomery. HOwever, I generally got under the layer at VFR Gillespie, hung a left around S-Mountain, and got a S-VFR into Montgomery.

Jim
 
Seems like I have seen heated Venturi's, but could name one specifically.

I have also heard that they sometimes mounted them underneath the airplane so that the air outlets from the engine would keep warm air on the venturi and prevent them from icing.

Brian
 
Henning said:
I think it's a considerably less than optimal solution myself since it limits your power and basically creates an induction leak. Never really liked them myself. You don't much want to be having to go missed in a plane carrying weight in it.
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At higher altitudes, no, but IIRC at the lower altitudes (<3000') the power setting was still 24" MP, which is plenty. It's definitely a flatland feature in that case, but it's better than nothing.
 
flyingcheesehead said:
At higher altitudes, no, but IIRC at the lower altitudes (<3000') the power setting was still 24" MP, which is plenty. It's definitely a flatland feature in that case, but it's better than nothing.
Click to expand...
I had such a system in a Bonanza and I made a test flight with the vacuum pump disconnected to see how effective it was. If you could accept a lower than normal cruise speed it would work fine up to six or eight thousand feet. Above that or if you wanted to cruise faster there was an option to close the throttle for 10 seconds every couple minutes to keep the gyros spinning and while inconvenient, that also worked OK. In the worst case flatland scenario (losing the vacuum pump on the takeoff roll into low clouds) my plan was to climb straight ahead using the ASI and TC until I reached an adequate altitude for an approach then reducing power and flying an approach with all the gyros.
 
flyingcheesehead said:
At higher altitudes, no, but IIRC at the lower altitudes (<3000') the power setting was still 24" MP, which is plenty. It's definitely a flatland feature in that case, but it's better than nothing.
Click to expand...

Not to me, I'm quite comfortable partial panel. During my IR training I had vacuum gyros for about 2 hours. The rest was all needle, ball and airspeed with the luxury of an altimeter most of the time. I'd much rather have my performance available and not have an induction leak.
 
Henning said:
Not to me, I'm quite comfortable partial panel. During my IR training I had vacuum gyros for about 2 hours. The rest was all needle, ball and airspeed with the luxury of an altimeter most of the time. I'd much rather have my performance available and not have an induction leak.
Click to expand...

Plus the fact that this system has a huge AD to comply with.
 
Fearless Tower said:
AD for the Venturi???
Click to expand...
Nope. The PreciseFlight Standby Vacuum system has an AD that came out quite a while ago. IIRC the valve that switches from pump to intake manifold had a problem with leaks or something.
 
gismo said:
Nope. The PreciseFlight Standby Vacuum system has an AD that came out quite a while ago. IIRC the valve that switches from pump to intake manifold had a problem with leaks or something.
Click to expand...

Got it, thanks for clearing that up
 
Rotor&Wing said:
Too bad GA has not gone to FOG (Fiber Optic Gyros). Do away with mechanical gyros and vacuum pumps all together.
Click to expand...

Too bad the FAA does not consider the electric gyro a suitable replacement for the vac gyro.
 
Rotor&Wing said:
Sure. Send the Form 337 and all the data and request a field approval. :wink2:
Click to expand...

Were they an authorized replacement parts none of that paper work would be needed.

As it stands, the removal of the vac system is a major alteration, plus the aircraft no longer meets the redundancy requirements of the equipment for IFR ops.
 
Tom-D said:
Too bad the FAA does not consider the electric gyro a suitable replacement for the vac gyro.
Click to expand...

"Electric" or "Fiber Optic"?

The DA40 is all electric - The G1000 uses an electronic AHRS (obviously) and the backup instruments are electric. So the FAA doesn't have it in for electric gyros entirely.

I think they don't want people to replace their vacuum gyros with electric gyros unless there is sufficient redundancy in the electrical system. In the event of an alternator failure in the DA40, there is an "Essential Bus" switch that can be turned on that automatically sheds load down to the essentials, running one G1000 screen in reversionary mode. With the essential bus on, you're guaranteed to get at least an hour from the essentials with the aircraft battery. Should you need more than that, there's a second "Emergency" switch that powers the backup AI and glareshield lighting for at least 1/2 hour off of a separate battery - When you flip the "Emergency" switch, those components are disconnected from the remainder of the electrical system.

IIRC, Cirrus does something similar with the two-bus setup, but uses a second alternator and doesn't have the emergency battery setup.

Now, if you take your average brand C, P, or B bird from the steam-gauge era, it's not set up that way - You would need to re-wire a helluva lot of stuff, and add another battery/alternator. Just simply replacing gyros with electric leaves you no redundancy.
 
flyingcheesehead said:
"Electric" or "Fiber Optic"?

The DA40 is all electric - The G1000 uses an electronic AHRS (obviously) and the backup instruments are electric. So the FAA doesn't have it in for electric gyros entirely.

I think they don't want people to replace their vacuum gyros with electric gyros unless there is sufficient redundancy in the electrical system. In the event of an alternator failure in the DA40, there is an "Essential Bus" switch that can be turned on that automatically sheds load down to the essentials, running one G1000 screen in reversionary mode. With the essential bus on, you're guaranteed to get at least an hour from the essentials with the aircraft battery. Should you need more than that, there's a second "Emergency" switch that powers the backup AI and glareshield lighting for at least 1/2 hour off of a separate battery - When you flip the "Emergency" switch, those components are disconnected from the remainder of the electrical system.

IIRC, Cirrus does something similar with the two-bus setup, but uses a second alternator and doesn't have the emergency battery setup.

Now, if you take your average brand C, P, or B bird from the steam-gauge era, it's not set up that way - You would need to re-wire a helluva lot of stuff, and add another battery/alternator. Just simply replacing gyros with electric leaves you no redundancy.
Click to expand...

Yup. The FAA doesn't care whether your gyros are electric, air, or nuclear powered, the regs simply require that some of the gyros are powered from an independent/different source. IOW having multiple gyros provides needed redundancy but for true redundancy requires a redundant power source. For an all electric airplane the redundant source could be a second alternator (possibly mounted to the vacuum pump pad on the engine), an extra battery with charging system, or a radioisotope thermoelectric generator (might be some hazmat issues with that one) among other things.
 
Hiperbiper said:
As a backup system (having seen all the Motor-driven stuff out there) I would love to see is a venturi or set of venturi's nessleled right up next to the exhaust system (for ice) with an automatic door and regulation as a backup to vaccum pumps...

Once the airplane is in motion why do you need a motor to drive another vaccum pump? Could it be that Burt Rutan is right...sometime Engineers overlook the most simple solution so they can engineer something?


JMPO

Chris
Click to expand...

Or just use the exhaust system for the source of the vacuum... It is simple,,,, works any time the engine is running..

http://www.jegs.com/i/Mr-Gasket/720/6002/10002/-1?parentProductId=745564
 
gismo said:
Yup. The FAA doesn't care whether your gyros are electric, air, or nuclear powered, the regs simply require that some of the gyros are powered from an independent/different source. IOW having multiple gyros provides needed redundancy but for true redundancy requires a redundant power source. For an all electric airplane the redundant source could be a second alternator (possibly mounted to the vacuum pump pad on the engine), an extra battery with charging system, or a radioisotope thermoelectric generator (might be some hazmat issues with that one) among other things.
Click to expand...


My obvious choice for power:

mr_fusion.jpg
 
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