Vacuum, Venturi's, pumps, & wing leveling.

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U2Hoog
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Vacuum, Venturi's, pumps, & wing leveling.

Post by U2Hoog »

THanks! I'll keep a jug of distilled water down at the hangar and check after each flight. I may have the A&P adjust the output volts down just a little to 14 or 13.7 -- just as an experiment.

Since I have your ear, one more question. I'm currently using "dual venturi" as my source of vacuum. As I slowly migrate my mighty 1948 C-170 towards an emergency IFR capable machine, what do you recommend for use as vacuum air? I still have the stock engine.
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GAHorn
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Vacuum source, Venturi's OK?

Post by GAHorn »

I have the dual venturi's on my airplane as well, and I'm comfortable with them as a source of vacuum. I have a vacuum guage and monitor it when I'm in clouds. Venturi's work just fine as long as you're not in ice (and even if you were in ice, in only a short while you won't be whether you like it or not :cry: ) and as long as you're not trying to climb at very slow speeds at very high altitudes. (like 55 mph/ 11,000 ft) In such cases do whatever it takes to increase airspeed to get your vacuum where you need it. My dual installation gives me 3.5" at 9,000 ft, at 75 mph IAS, enough to keep my two vacuum driven AN-style gyros spinning properly. Newer 3 1/8" gyros need more air than original AN ones do.
I don't intend on changing my venturi system except to add a vacuum regulator as per the IPC (illustrated parts catalog. I had made a trade to acquire one, and I sent my part in the deal, but the wrong regulator was sent to me, which I returned, but I haven't heard back from the guy since. :? )
One thing about venturi's, ...despite the fact that their vacuum levels must be monitored (so what's different about that?),...at least they don't conk out on you 8O unexpectedly. If you're flying, you're vacuuming. The most serious drawback I can see is launching. The gyro's don't work until you're flying for at least one minute to ensure that they've spun up to speed. No problem for me in a single engined airplane! I don't intend on being IFR single-engine with ceilings less than 1,000 feet anyway and it takes that long to get up into the clouds!
Last edited by GAHorn on Wed Apr 24, 2002 6:12 pm, edited 1 time in total.
N7155A

Post by N7155A »

>IFR capable machine, what do you recommend for use as vacuum air?

I have a '57 172 with dual venturis. We upgraded radios, did Pitot/Static cert. I then did the Instrument rating in it and have a few hours of actual.

The venturis are good (172 has a vacuum regulator). If I wanted to add backup, I'd put in a precise flight vacuum system off the intake manifold (instead of a vacuum pump).

The stock venturis won't work well with newer style gyros - not enough flow. Stick with AN style gyros and you will be fine.

Mitch
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GAHorn
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AN style gyros...

Post by GAHorn »

A little more insight to the older AN style gyros vs the newer ones..
The older gyros are physically larger than modern gyros. (The D.G. may look smaller, but behind the panel it's actually a larger device.)
This allows the actual gyro, the spinning wheel, to be larger and more massive. That larger, more massive wheel spins more steadily, and with less air because it's size means it weighs more, and it's size means it's outside circumference is more respondent to the air-jet. (Not only does it have a larger surface area, it's vanes are larger, and it has more leverage to act upon the central axis and impart spin.) The end result is that it will operate with less air mass and less air velocity, i.e., less vacuum.
There are drawbacks to these older designs as well. The most noticeable is their displays are fairly plain, and most folks like colorful instruments. (I personally think the larger AN horizon is actually better for viewing. Most airliners have instruments with larger faces as well, which is generally seen as an advantage.) But the AN Horizon usually has only a black background and some pilots worry about "upsets" that get them upside down and they worry that they'll not quickly see the difference between the "sky" and the "ground". Most modern gyros have blue sky's, sometimes with pitch-angles depicted, and brown or black ground's with "section" lines drawn upon them. That display is certainly more readable in a glance.
In defense of the AN horizon, I'll point (pun) out that the bank-angle pointer will point opposite to the actual direction of bank. (This further causes confusion to pilots who learned to fly with modern instruments, because the modern group of instrument almost always has their bank-angle pointer move in the same direction as the direction of roll or bank.) But with the old AN style horizon, think of the pointer as always pointing UP at the SKY! If you're rolled onto your right side,...the pointer is pointing out your amount of bank on the upper LEFT side of the instrument,....the direction of UP! (therefore the direction you want to correct to,...LEFT bank is called for!)
Another major but little known difference between the gyro types are the internal limits of those instruments. AN style horizons may "tumble" if banks of more than 90-degrees or pitch angles of more than 60-degrees are exceeded. This is due to the internal limits of the gimbals. Repeated excursions beyond those limits will cause excessive wear, and that is why the instrument has a "cage" position for acrobatic flight. (Not all "cage" features are pilot accessible, unless the "Cage" knob is installed, but regardless, the feature is designed into all AN horizons and can be operated with the small pinion gear on the side of the instrument case.)
(All D.G.'s are natrually cageable by pushing in on the Hdg. knob. AN style gyro's will allow the pilot to leave the knob in the "caged" position, while modern gyros do not.)
Modern horizons have somewhat greater limits designed internally, usually on the order of 90-degrees pitch, and 110-degrees bank. While some folks consider this a deficiency of the AN gyros, I do not. Anyone in IFR conditions that let the aircraft get beyond 60 degrees pitch, and 90 degrees bank is already way out of their league, and if you get into turbulence that great it's most likely the modern gyros will be tumbled as well. At least with the AN gryo's you can cage and reset them quickly, something impossible with modern style air-driven gyros. There are modern gyros that are fully acrobatic, but they are not usually found in light aircraft, are usually not air-driven, and are very expensive to buy and maintain.
Modern gyros do have a typically longer life, but this is mostly due to better air-filtration. Installing a modern central air filter (I did) in your aircraft should give the same life to AN gyros.
As a further note of helpfulness, ...a major reason "modern" pilots prefer vertical card compass D.G.s is because it's easier to interpret turn directions with them, and also there is not mental arithmetic involved to turn to a heading that is out of view when useing an AN D.G. Here's my helpful hint: If you want the numbers in the AN D.G. to move to the right, then make a right turn. Example: Flying a heading of due west (270) you are told to fly new heading of 290. Your view of the instrument looks like this:
[290 | 280 >270< 260 | 250]
So all you have to do is move the 290 to the right by turning right. Simple.
Last edited by GAHorn on Wed Apr 24, 2002 8:29 pm, edited 1 time in total.
dalemed
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Post by dalemed »

I and my plane are both IFR certified (in fact, I just passed my IPC yesterday). I've flown with the new style DG and AI for 8 years with no problems. I have one 8" venturi mounted on the passenger side. (For those that don't already know, the 8" refers to the amount of vacuum, not the physical size of the venturi).

I have a regulator set for 6" and, at density altitudes below 5000 feet, I can usually pull that much in cruise.

Both instruments are stable before I reach the end of the runway. I can set the DG to the runway heading as I start my takeoff roll and trust it to be pretty accurate by the time I'm in the air.

I think venturis are great! The only drawback is that instructors will have you spend an inordinate amount of time under the hood practising 'No Gyro' manuvers and approaches. But that aint all bad!!
Dale
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U2Hoog
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Regulator of Venturi suction

Post by U2Hoog »

Thanks for the inputs! I did notice yesterday on the first flight out of the barn (read very expensive annual) that my venturi suction seemed lower. I just this year put in a new DG and Artificial Horizon. I quickly noticed that the DG was quick to wander, and the off flag in the Artificial Horizon was on. So the question now is, it seems like you're recommending 6" as a pretty good setting? I don't do much "high altitude flying" in the 170 (usually 8500 is the max for me). So it sounds like if I set up for 6" at 5000 & below, I shouldn't have any problems?
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GAHorn
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Re: Regulator of Venturi suction

Post by GAHorn »

U2Hoog wrote:Thanks for the inputs! I did notice yesterday on the first flight out of the barn (read very expensive annual) that my venturi suction seemed lower. I just this year put in a new DG and Artificial Horizon. I quickly noticed that the DG was quick to wander, and the off flag in the Artificial Horizon was on. So the question now is, it seems like you're recommending 6" as a pretty good setting? I don't do much "high altitude flying" in the 170 (usually 8500 is the max for me). So it sounds like if I set up for 6" at 5000 & below, I shouldn't have any problems?
What you really should desire is a regulated 4.5 inches. Did you read my post on older vs newer gyros? When you say you just installed new gyros,...which did you install? And did you install new hoses? and filter? ALL this stuff has to be correct to work properly. You'd be surprised how many of our 50 year old airplanes have original vacuum hoses, cracked, and leaking.
U2Hoog
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Gyros

Post by U2Hoog »

I just recently (2 weeks ago) had installed, an RC Allen Artifical Horizon 22-7F (vacuum driven with off flag) and RC Allen DG 11-D7 (vacuum driven with hdg bug). The "plumbing" is all brand new. The A&P replaced all my old hoses with tubing. I guess I made the assumption that everything would pretty much be the same as far as vacuum requirements. I'm surprised that the older ones require less vacuum, according to your post.

So 4.5" ? The only thing I had to go on was that my vacuum guage read lower than it did before, and the DG was wandering, and the Artificial Horizon had an OFF flag in view except at around 110 MPH.

Thoughts?
dalemed
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Post by dalemed »

What are you using for venturi(s)?
U2Hoog
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Venturi's

Post by U2Hoog »

I'm not sure I understand your question. There are two venturi's mounted on the left hand side of the aircraft, which I believe were original equipment. Is that what you're asking?
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GAHorn
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venturis

Post by GAHorn »

It's possible that your venturis are internally blocked by insects, etc. Disconnect your vacuum system from them and blow them out with compressend air in all directions. Connect your vacuum system to a shop vacuum source and test the system in the shop for proprer vacuum, then reconnect the system to the venturis and go test fly.
U2Hoog
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Joined: Tue Apr 23, 2002 4:27 am

Shop Vacuum Source

Post by U2Hoog »

Known vacuum source! Great idea! I Don't know why that didn't occur to me before you said it. I'll do that this week. Hopefully once the system is cleared out / cleaned out, and the vacuum re-regulated at 4.5", I'll have a full up flying machine. Thanks again.
zero.one.victor
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vacuum for new venturi's

Post by zero.one.victor »

Hoog,maybe just your regulator needs adjustment.
BTW,looks like you fly outa pearson? What's the local scuttlebutt down around Vancouver/Portland about this year's Evergreen Fly-in? I understand that Evergreen Field is still for sale,so last year's rumored "done-deal" sale was just that. Does it still look like maybe Scappoose?

Eric
U2Hoog
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Regulator and Evergreen

Post by U2Hoog »

Eric,

I'm hoping that you're right on the vacuum.

Last I heard, Evergreen was still up for the highest bidder. No words yet on the summer fly in. I'll ask around.

Pearson has established a group to try and keep our airport from being taken over by those who want the land. PAGA (Pearson Advocates of General Aviation) is working with the locals at the Mayor's office, and in the community to try and generate more interest in flying locally. We're having a gathering on 18th of May (Armed Forces Day) and having a BLACKHAWK HELICOPTER fly in for the day. Lots of general aviation guys showing off their planes. We're hoping the events will help. Thoughts?

Hoog
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GAHorn
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vacuum regulator maintenance

Post by GAHorn »

Vacuum regulators do get dirty and act up. Most of the types in 170's are the Garwin style with small screens the size of a quarter on their bottoms, held in by a circlip. These screens should be removed, soaked in solvent, and scrubbed clean with a toothbrush. The valve itself can be removed, safety-wire clipped, and the adjustment lock-nut removed, so that the internal spring, piston, and valve-body/seat cleaned. Reassembling them, and readjusting them, safetying them, etc, is an easy job. I've had them become new regulators with this treatment. They are a simple device, easy to understand, and easy to put back into first-class operation.
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