Ok, the new guy with more questions.
Is there any kind of STC based add on vacumm pump for the O-300-B (the pumpless wonder)? My venturis work Ok, but wondering if the little wheels will spin up as I enter the clouds...
Not looking for backup here, I can use the venturis for that..
sj
O-300-B Vacuum
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
O-300-B Vacuum
1952 170B
Steve Johnson
Lake Waukomis, MO
Email: Steve (at) Supercub (dot) Org
There are only two that I am aware of, one attaches to the front of the engine (sticks out the front of the cowling a bit actually) which is belt driven by a pully attached to the front of the crankshaft. Ugly!!
The other, which I have never actually seen, is an alternator with a vacuum pump pad on the back of it. There is someone on the forum who has one these who might be able to give the name of the STC holder.
The other, which I have never actually seen, is an alternator with a vacuum pump pad on the back of it. There is someone on the forum who has one these who might be able to give the name of the STC holder.
The Association can provide paperwork copies of the Universal Tow All (352/666-2929) alternator/vacuum pump conversion. Its a 45 AMP alternator with an Airborne 211CC dry vacuum pump piggy-backed onto it.
It seems like a step backwards to me however, if you're looking for increased reliability, to go to a quirky, little-known alternator on a common drive with a failure-prone dry vacuum pump. As often as the vacuum pumps fail and break their drives, ...I'm thinking how that might overload the alternator drive and cause it to fail at the same time,...OR...the loss of the alternator from a failed bearing would shear the alternator drive shaft causing simultaneous loss of the vacuum pump. (The very reason we have some gyro's electrically driven and some vacuum driven is to avoid simultaneous outages!) Imagine what it'd be like to lose both electrics and vacuum simultaneously.
It seems like a step backwards to me however, if you're looking for increased reliability, to go to a quirky, little-known alternator on a common drive with a failure-prone dry vacuum pump. As often as the vacuum pumps fail and break their drives, ...I'm thinking how that might overload the alternator drive and cause it to fail at the same time,...OR...the loss of the alternator from a failed bearing would shear the alternator drive shaft causing simultaneous loss of the vacuum pump. (The very reason we have some gyro's electrically driven and some vacuum driven is to avoid simultaneous outages!) Imagine what it'd be like to lose both electrics and vacuum simultaneously.
Last edited by GAHorn on Tue Dec 03, 2002 7:40 pm, edited 1 time in total.
My thoughts exactly, THANKS!
There is some info on the guy and the install in a Stinson...
http://www.hangar9aeroworks.com/Alterna ... nator.html
sj
There is some info on the guy and the install in a Stinson...
http://www.hangar9aeroworks.com/Alterna ... nator.html
sj
1952 170B
Steve Johnson
Lake Waukomis, MO
Email: Steve (at) Supercub (dot) Org
Re: O-300-B Vacuum
I have a belt driven on mine it is a Airborne STC and is still available. Call Aviall for details.sj wrote:Ok, the new guy with more questions.
Is there any kind of STC based add on vacumm pump for the O-300-B (the pumpless wonder)? My venturis work Ok, but wondering if the little wheels will spin up as I enter the clouds...
Not looking for backup here, I can use the venturis for that..
sj
Last edited by mit on Thu Dec 05, 2002 2:04 am, edited 1 time in total.
Tim
One of our members called me tonight and we discussed this thing some of us have about not trusting venturis. We kinda both came to the same conclusion. (I think.) 
(Here's the summary of what we discussed.)
The folks who seem most worried about venturis usually don't have much experience with them, so it could just be a matter of distrust or lack of confidence in them. Venturis are really simple devices and they just do not fail. (It's far more likely that your gyro or your hoses will fail, but not that venturi.) If you're moving forward in flight the venturi will produce vacuum. If you don't have enough vacuum on your gauge but your hoses/filters, etc, are all good, then you need a dual venturi setup. If you don't have a vacuum gauge then you should get one. (The 170 had dual venturis in the IFR certified model. My own has dual venturis and I observe about 6 inches Hg in cruise and 4.5 inches at 75 mph, plenty for approaches, etc. The older AN style gyros require less vacuum (3.5 inches) than the 4.5 inches for the 3 1/8" pictorial types.) If your pictorial gyros are not happy with a dual venturi setup which is producing the correct vacuum, then the central filter and the hoses should first be checked, and then the gyros themselves would be suspect. Overhauls or exchanges might be in order. A clogged central filter or individual filter would reduce the gyro's perceived vacuum. (And don't forget to inspect for and get rid of Eastman hoses that are notorious for failure and have an AD note out against them. Look on the outside of the hoses for the name. Fresh, pliable hoses are cheap from Aircraft Spruce and others.)
Another worry some have is whether or not the gyros will be spooled up before entering the clouds after takeoff. First of all, takeoff in a single engined airplane in very low ceiling conditions is a questionable practice at best. I'd worry a lot more about an engine failure with insufficient ceiling/visibility/time to select a landing spot than I would worry about venturis. Your venturis are far more reliable than your engine is. They also will beat your electrical system for reliability. And your radios. Second, ...after takeoff I simply look at my vacuum gauge to confirm adequate vacuum exists, then I uncage my AN gyros, which have spooled up during takeoff and initial climb,...doing this all well before entering clouds. If you don't have cageable gyros then it's a simple matter to initiate a shallow climb and confirm they are erect before entering the clouds. In any case, you have an electric T&B to confirm your attitude in poor visibility while the gyros spool up.
Yet another worry is icing. Some people really sweat their venturis icing up in flight. In case no one's noticed, Cessna 170's have absolutely no business flying in icing conditions. As soon as you detect inadvertent ice you'd better take aggressive actions to get out of it. Your most serious problems are not the venturis at that point. Venturis will produce vacuum long after the airframe is in trouble due to icing. (And heated venturis are an option if you are just plain psychotic about this.)
A far more reasonable thing to worry about, I think, is vacuum pump failure. You want to worry about an unreliable piece of expensive equipment,...just think about current technology dry vacuum pumps!
(Here's the summary of what we discussed.)The folks who seem most worried about venturis usually don't have much experience with them, so it could just be a matter of distrust or lack of confidence in them. Venturis are really simple devices and they just do not fail. (It's far more likely that your gyro or your hoses will fail, but not that venturi.) If you're moving forward in flight the venturi will produce vacuum. If you don't have enough vacuum on your gauge but your hoses/filters, etc, are all good, then you need a dual venturi setup. If you don't have a vacuum gauge then you should get one. (The 170 had dual venturis in the IFR certified model. My own has dual venturis and I observe about 6 inches Hg in cruise and 4.5 inches at 75 mph, plenty for approaches, etc. The older AN style gyros require less vacuum (3.5 inches) than the 4.5 inches for the 3 1/8" pictorial types.) If your pictorial gyros are not happy with a dual venturi setup which is producing the correct vacuum, then the central filter and the hoses should first be checked, and then the gyros themselves would be suspect. Overhauls or exchanges might be in order. A clogged central filter or individual filter would reduce the gyro's perceived vacuum. (And don't forget to inspect for and get rid of Eastman hoses that are notorious for failure and have an AD note out against them. Look on the outside of the hoses for the name. Fresh, pliable hoses are cheap from Aircraft Spruce and others.)
Another worry some have is whether or not the gyros will be spooled up before entering the clouds after takeoff. First of all, takeoff in a single engined airplane in very low ceiling conditions is a questionable practice at best. I'd worry a lot more about an engine failure with insufficient ceiling/visibility/time to select a landing spot than I would worry about venturis. Your venturis are far more reliable than your engine is. They also will beat your electrical system for reliability. And your radios. Second, ...after takeoff I simply look at my vacuum gauge to confirm adequate vacuum exists, then I uncage my AN gyros, which have spooled up during takeoff and initial climb,...doing this all well before entering clouds. If you don't have cageable gyros then it's a simple matter to initiate a shallow climb and confirm they are erect before entering the clouds. In any case, you have an electric T&B to confirm your attitude in poor visibility while the gyros spool up.
Yet another worry is icing. Some people really sweat their venturis icing up in flight. In case no one's noticed, Cessna 170's have absolutely no business flying in icing conditions. As soon as you detect inadvertent ice you'd better take aggressive actions to get out of it. Your most serious problems are not the venturis at that point. Venturis will produce vacuum long after the airframe is in trouble due to icing. (And heated venturis are an option if you are just plain psychotic about this.)
A far more reasonable thing to worry about, I think, is vacuum pump failure. You want to worry about an unreliable piece of expensive equipment,...just think about current technology dry vacuum pumps!
-
russfarris
- Posts: 476
- Joined: Wed May 15, 2002 2:25 am
Everything George says about venturi driven gyros I agree with 100%.
I fly my 170 IFR, probably more than most guys, with a single super (nine inch) venturi. GA hit the nail on the head with his statement about people not being comfortable with older technology.
Some upgrades and mods are worth their weight in gold...GPS, strobes, and an alternator are a few my airplane has. Shoulder harnesses, too.
I wouldn't trade my venturi for a vacuum pump...KISS! Russ Farris
I fly my 170 IFR, probably more than most guys, with a single super (nine inch) venturi. GA hit the nail on the head with his statement about people not being comfortable with older technology.
Some upgrades and mods are worth their weight in gold...GPS, strobes, and an alternator are a few my airplane has. Shoulder harnesses, too.
I wouldn't trade my venturi for a vacuum pump...KISS! Russ Farris
All glory is fleeting...
-
Bruce Fenstermacher
- Posts: 10327
- Joined: Tue Apr 23, 2002 11:24 am
George
You mention your set up with 2 venturis pulling about 6 inches. Are they the standard venturis? Do you have a regulator?
I have a single venturi which only pulls about 4.5 inches max. I'm running like new 3 1/3 picturial type gyros which seem to work OK. Would like to improve the vacuum cause I think the vacuum with one venturi is probably marginal. Though I needed to go to a super venturi but your setup seems to indicate just adding another standard venturi would work. I can get the standard venturi for FREE. What migh you do in my situation?
You mention your set up with 2 venturis pulling about 6 inches. Are they the standard venturis? Do you have a regulator?
I have a single venturi which only pulls about 4.5 inches max. I'm running like new 3 1/3 picturial type gyros which seem to work OK. Would like to improve the vacuum cause I think the vacuum with one venturi is probably marginal. Though I needed to go to a super venturi but your setup seems to indicate just adding another standard venturi would work. I can get the standard venturi for FREE. What migh you do in my situation?
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
First off, in total agreement with the above statements on the reliability of a venturi system. But, like any system that you are going to trust your life with, it is important to know and understand any limitations. The difference of having spun up gyros on the ground vs fully spun up gyros only after achieving a certain airspeed for a given amount of time has the potential of chasing a false AH if not managed properly. Untill fully spun up for "x" amount of time the AH will show wings not level. If a person not aware of this was to accidently enter the clouds, the potential for relying on the AH while it was indicating a false attitude could be fatal. My point is that it is a very manageable limitation, but it should be part of transition training if someone was moving from a plane with a pump to one with a venturi, as an example.
Joe
51 C170A
Grand Prairie, TX
51 C170A
Grand Prairie, TX
I acquired one of the "super venturis" from a friend who no longer had a need for it and was thinking of finally setting up my 170 with some gyros. My IA says I would need a field approval to install this venturi since it is not the original setup. The originals were AN5801s (sperry) which I don't think are available any longer. Russ did you file a 337 for your installation?? (Don't mean to put you on the spot)
If this is true, does this also apply to the the gyros, which are also AN in the parts manual? What about the relief valve?
If this is true, does this also apply to the the gyros, which are also AN in the parts manual? What about the relief valve?
My airplane was/is originally equipped with dual 4-inch venturis. (4-inch is the design vacuum level, ...they are about 10" long). They are connected to the gyros in parallel, and should be equipped with a regulator, as depicted in the Cessna 170B Illustrated Parts Catalog. (IPC)
Since mine produces too much vacuum, I investigated and found the regulator missing, so I've acquired one and will install it during this annual inspection (in January). The only problem I've noticed with too much vacuum is that my DG precesses a bit (a common symptom of excessive vacuum. My DG precesses about 5-degrees every 15 minutes when the vacuum is above 5.5". At higher cruise altitudes the vacuum drops to about 5" and the precession goes away.) The Artificial Horizon (also the name of my big-band-era Swing Band
) is not affected by excessive vacuum except of course, it causes a bit more wear on gyros because it spins them too fast.
Re: Initiating flight with gyros not yet up to speed: It is highly desireable that aircraft equipped with venturis have cageable gyros. The old AN gyros were equipped with provisions for Caging knobs, but some have had them removed. This is an error in my opinion, and the caging knobs should be re-installed. The AN 5736 horizon specs call for 6 minutes of 3.5 inches vacuum to come up to the correct indication from an un-caged position. A gyro that is caged will start out at the straight/level indication and so is much faster to get into action. Similar behavior is applicable to the AN 5735 DG.
Newer-style gyros are only rarely cageable because they have different operating limits. While the AN 5736 horizon has gimbal limits of 60-degrees pitch and 90-degrees bank (as did the early pictorial styles), most newer pictorial gyros do not. What this means is that with AN gyros when the limits are exceeded (such as during aerobatics) the gyros will either "tumble" or precess to an unuseable indication, requiring re-setting them with the caging knob. (They will self-erect after about a 10-minute recovery. Hmmmn. That sounds familiar.
)
Exceeding the limits on all gyros, both AN and pictorial, places excessive wear on the bearings. That is why AN's are equipped with and should be caged with their caging knobs before aerobatics (and why aerobatics should not be performed with non-aerobatic model pictorials.) The same is true of cageable gyros before and after fight. They should be caged until after takeoff, and should be caged after landing and arriving at the chocks. This applys to both 5736 horizons and 5735 DG's.
Since mine produces too much vacuum, I investigated and found the regulator missing, so I've acquired one and will install it during this annual inspection (in January). The only problem I've noticed with too much vacuum is that my DG precesses a bit (a common symptom of excessive vacuum. My DG precesses about 5-degrees every 15 minutes when the vacuum is above 5.5". At higher cruise altitudes the vacuum drops to about 5" and the precession goes away.) The Artificial Horizon (also the name of my big-band-era Swing Band
) is not affected by excessive vacuum except of course, it causes a bit more wear on gyros because it spins them too fast.Re: Initiating flight with gyros not yet up to speed: It is highly desireable that aircraft equipped with venturis have cageable gyros. The old AN gyros were equipped with provisions for Caging knobs, but some have had them removed. This is an error in my opinion, and the caging knobs should be re-installed. The AN 5736 horizon specs call for 6 minutes of 3.5 inches vacuum to come up to the correct indication from an un-caged position. A gyro that is caged will start out at the straight/level indication and so is much faster to get into action. Similar behavior is applicable to the AN 5735 DG.
Newer-style gyros are only rarely cageable because they have different operating limits. While the AN 5736 horizon has gimbal limits of 60-degrees pitch and 90-degrees bank (as did the early pictorial styles), most newer pictorial gyros do not. What this means is that with AN gyros when the limits are exceeded (such as during aerobatics) the gyros will either "tumble" or precess to an unuseable indication, requiring re-setting them with the caging knob. (They will self-erect after about a 10-minute recovery. Hmmmn. That sounds familiar.
)Exceeding the limits on all gyros, both AN and pictorial, places excessive wear on the bearings. That is why AN's are equipped with and should be caged with their caging knobs before aerobatics (and why aerobatics should not be performed with non-aerobatic model pictorials.) The same is true of cageable gyros before and after fight. They should be caged until after takeoff, and should be caged after landing and arriving at the chocks. This applys to both 5736 horizons and 5735 DG's.
-
russfarris
- Posts: 476
- Joined: Wed May 15, 2002 2:25 am
Well, the guy that owned it before installed the super venturi, and no 337 was filed. Interestingly, my airplane had only the VFR panel (electric Turn and bank) until 1990.lowNslow wrote:I acquired one of the "super venturis" from a friend who no longer had a need for it and was thinking of finally setting up my 170 with some gyros. My IA says I would need a field approval to install this venturi since it is not the original setup. The originals were AN5801s (sperry) which I don't think are available any longer. Russ did you file a 337 for your installation?? (Don't mean to put you on the spot)
If this is true, does this also apply to the the gyros, which are also AN in the parts manual? What about the relief valve?
For some reason they installed it on the left side of the fuselage. From the factory, venturis were on the right side. Although I have had good luck with my setup, I think I would install two smaller venturis if I started from scratch.
Sounds like your IA is a little anal-retentive, but these days CYA is the order of the day. I would hardly think a 337 is required for installing a modern gyro. George Horn has more insight into this. Russ Farris
All glory is fleeting...
Your IA is technically correct. I talked to Aircraft Spruce who couldn't answer about their approval basis, so I contacted the manufacturer, ACS. The original venturis are AN 5807-1's and are mfd by ACS in accordance with the original Air Force-Navy Aeronautical Standard, DWG # FSC 6610, Procurement Specification AN-T-10, and sold by Aircraft Spruce as their PN 15050 for $44.95 each. Since they are a standard AN part they meet the IPC specification. The "super venturi" is a later Mil-spec.lowNslow wrote:I acquired one of the "super venturis" from a friend who no longer had a need for it and was thinking of finally setting up my 170 with some gyros. My IA says I would need a field approval to install this venturi since it is not the original setup. The originals were AN5801s (sperry) which I don't think are available any longer. Russ did you file a 337 for your installation?? (Don't mean to put you on the spot)
If this is true, does this also apply to the the gyros, which are also AN in the parts manual? What about the relief valve?
George,gahorn wrote: Since mine produces too much vacuum, I investigated and found the regulator missing, so I've acquired one and will install it during this annual inspection (in January). The only problem I've noticed with too much vacuum is that my DG precesses a bit (a common symptom of excessive vacuum. My DG precesses about 5-degrees every 15 minutes when the vacuum is above 5.5". At higher cruise altitudes the vacuum drops to about 5" and the precession goes away.) The Artificial Horizon (also the name of my big-band-era Swing Band
What model of vacuum regulator are you going to install (or recommend)with a Venturi driven system? There are about 4 or 5 different Airborne models plus other brands. The one that seems the most common would be the Airborne 2H3-12 which has 2-3/8" outlet ports (one for each gyro). The other Airborne models typically have 1 inlet and 1 outlet. The Airborne web site does a very poor job explaining the differences between the models. I have been floundering around on this subject for a week and no one in my peer group seems to have a solid answer.
Bruce
Whenever in doubt about such things, it's a good idea to consult the Illustrated Parts Catalog for your aircraft.
The 170B IPC, pgs 130/131, Figure 77, item 13, pn 0511059 is likely a Garwin unit, which can be purchased from most salvage yards. If you wish to buy new, then I suggeest one with one inlet and one outlet, installed betwixt the gyros and the venturis (as depicted in the above Figure 77).
Keep in mind that this is actually a vacuum relief valve. It will open up a regulated "leak" into the vacuum line coming from the venturis, to relieve excess vacuum from being applied to the gyros.
The 2H3-12 has only two fittings, one an inlet, the other an outlet. They are one a 5/8" and the other a 3/8" fitting at an angle. You probably want the 2H3-6 with two 5/8" straight fittings. Although not being used on a vacuum pump and therefore not critical to prevent pump failure, the "garter" filters must nonetheless be changed annually to prevent damage to the regulator valve itself. They are cheap insurance.
The 170B IPC, pgs 130/131, Figure 77, item 13, pn 0511059 is likely a Garwin unit, which can be purchased from most salvage yards. If you wish to buy new, then I suggeest one with one inlet and one outlet, installed betwixt the gyros and the venturis (as depicted in the above Figure 77).
Keep in mind that this is actually a vacuum relief valve. It will open up a regulated "leak" into the vacuum line coming from the venturis, to relieve excess vacuum from being applied to the gyros.
The 2H3-12 has only two fittings, one an inlet, the other an outlet. They are one a 5/8" and the other a 3/8" fitting at an angle. You probably want the 2H3-6 with two 5/8" straight fittings. Although not being used on a vacuum pump and therefore not critical to prevent pump failure, the "garter" filters must nonetheless be changed annually to prevent damage to the regulator valve itself. They are cheap insurance.