Venturi Vacuum System

[Jeff Palmer]

Alright folks. Leaks in the casing and around any of the seams of the instrument will cause it to go crazy. After two test flights and many steep turns my AH works perfectly. It is more responsative than the old one. Rock solid. I have a line running directly to it from the right venturi, with a tee to the DG, which tees over to the left venturi. I get 4 1/2" of vacuum at 130 mpg IAS and 5" at 160. So all I can say is BINGO!

[zero.one.victor]

Hey Bingo, I want to hear more about seeing 160 IAS. I've never seen over about 145 or so on mine,and that was on a pretty hot low pass-- you musta been going straight down!

Eric

[Jeff Palmer]

On a decent of 500 FPM at red line. I just wanted to see if I could over do it with the vacuum. I don't ever do that as a practice. I do know that my airspeed indicator will go well above VNE. When I was taking my check ride and he did that unusual attitude recovery thing, that I don't like, I actually saw the air speed go around and past zero. We both had to empty our pants that day. At least there is a wide margine of safety built into these airplanes. Another time this guy who flies everything and wanted to go up with me to show me what the 170 will do (You let people fly your airplane when you are just taking lessons and figure everybody knows more than you) wanted to show me how nicely it rolls. Well, when we got inverted, it fell out and went way past zero again. That's a good way to loose altitude by the way. For some reason I don't think it bothered me as much that time, with him flying. I haven't let anybody fly my airplane since then, except my wife. I have checked my airspeed indicator against the GPS and it's accurate.

[Bruce Fenstermacher]

On a decent of 500 FPM at red line. I just wanted to see if I could over do it with the vacuum. I don't ever do that as a practice. I do know that my airspeed indicator will go well above VNE. When I was taking my check ride and he did that unusual attitude recovery thing, that I don't like, I actually saw the air speed go around and past zero. ......Another time this guy who flies everything and wanted to go up with me to show me what the 170 will do (You let people fly your airplane when you are just taking lessons and figure everybody knows more than you) wanted to show me how nicely it rolls. Well, when we got inverted, it fell out and went way past zero again.

Sorry Jeff I just couldn't get my curser off that emoticon.

I must confess I to have exceeded a few limitations in some aircraft I've flown or at least consented to ride in while a maneuver was performed. I'll bet more that a few of us here have. But holy cow past 0 Jeff?

[zero.one.victor]

Going thru VNE & past zero ain't the , it's the recovery from it that's the
(darn it, we need an emoticon that looks like the wide-eyed face, only stretched out to a peanut shape from the 12 G's it's pulling )

[Jeff Palmer]

[img]c:\Documents%20and%20Settings\Jeff%20Palmer\My%20Documents\Emoticons\Smiles_Wacky_Prv.gif[/img] I am trying to put a picture in here.

[Bruce Fenstermacher]

Like this


(Jeff nice try but the photo needs to be in a spot with an internet address and not blocked by a fire wall. Stuff in your computers documents folder aren''t available over the internet or at least they shouldn't be. See the thread on posting pictures>)

[Jeff Palmer]

Too much work. I'd rather polish my airplane.

[N8249A]

Jeff, Any luck with your vacuum system? My aircraft was partially restored when I bought it. Everthing behind the instrument panel was redone. I have two modern gyros, a DG and A/H. My turn and bank is electric. The plumbing is alum tube and rubber hose. An older cessna regulator and new filter are installed. I can't get more that 4.0 from this system and my DG constantly precesses. below cruise speed the dg is worthless. I have finally found something that is "rocket science"! I would appreciate any suggestions you may have. Thanks

[Jeff Palmer]

OK folks, I have found out that 4” venturis are not measured as 4” in any dimension. They are designed to create 4” of vacuum at 100 MPH. So if you have 52, 4” vinturis on your airplane all connected together, all you will get from them is 4” of vacuum at 100 MPG. The more venturis you have, the more volume of air they will move. But they cannot produce more vacuum. The faster you go the more vacuum you’ll get. I got up to 5.5” at 140, but in a dive, was not able to exceed 5.5”. I put my regulator back in though just to save my instruments. The problem I was having with my AH was completely the fact that they did a lousy job of sealing it. Or should I say, they mayde very little attempt to seal it. Air was blowing in from various places causing the AH to take on very strange attitudes. So I would seal the inlet on your DG and draw a vacuum on it. There shouldn’t be any leaks. I put my DG in the sink and blew pressure into it to find my leaks. Good old RTV did the trick. It shouldn’t be necessary with new stuff though. Also remember to allow 3 minutes for your stuff to spool up.