The International Cessna^® 170 Association

Hi,

I have a 52 170B with one 4" venturi (10" long) with adjustable regulator running an old AN DG. I added an RC Allen AI. I still will get 4.75-5.25in Vacuum in cruse with both units hooked up. I am going to replace the old AN DG with RC Allen DG. I have seen a lot of 170s with two venturi I don not want to add a second venturi. Has anyone used an 9" (11.25" long) #15052 venturi to run two modern gyros?

Thanks

Collin

I'm running a single venturi (I forget if it is 8" or 9") feeding two "modern" gyros - AH & DG. No problems pulling 4.5" - 5.5" vacuum. I don't have my paperwork in front of me at the moment, but I can check the specifics of the venturi tonight (it was on the plane when I bought it).

My 170 had two venturies that were independent of each other. The IPC appears to show two linked. Any thoughts? Sincerely, Luke Walker

Collin,

I was in the same boat a couple months ago and swapped out my 4" venturi for an Aircraft Spruce 9" venturi. These are made by Spruce by their ACS products division. This 9" venturi does run my two new Sigmatek gyros just fine.

Bruce

The Instrument Flight equipped 170B had two venturi's interconnected, just as depicted in the IPC. Those wanting to change the system, might wish to consider their basis of approval, not only for an unapproved change in design, but also for certification approval (PMA) for the venturi's. The original venturi's were AN5807 specification. What are "super" venturi basis of approval? And where is their parts manufacturing authority? And by what approval are they installed if they are not approved parts? Just some thoughts.

The venturis supplied by Wag-Aero meet the definition of "Standard Parts" in AC20-62D. They have 2", 4" and 8" venturis available that meet AN standards. The 9" supplied by Spruce does not. I got one of these from a friend hoping it would be usable but decided against it. Now the question is, would it be legal to use any other configuration other than the one shown in IPC, i.e. two 8" venturis in parallel, or one 8"?

Karl how do you know the Wag-Aero venturis meet AC20-62D? What part of it do they meet?

It's a venturi for !@$%&@ sake. No moving parts. It's well made, can't really tell its any different than the original except a little longer. My IA recommended this procedure and has installed many of these exact 9" venturis on 170's for the reason to keep things simple and clean with only one venturi. I examined my original 4" venturi and didn't see any FAA PMA sticker or part number either. I think this one is really a minor technicality. It's not like we installed a Holly 4 barrel carb on the engine or something.

My two cents, Bruce

Hi Collin,

A little of topic but seeing your name reminded me that I was going to send you some paperwork on the oil filter (seen you at the Flying "M"). Do you still need it? Let me know. Joe from Longview.

N9149A wrote:Karl how do you know the Wag-Aero venturis meet AC20-62D? What part of it do they meet?

AC20-62D "Standard Part. Is a part manufactured in complete compliance with an established U.S. Government
or industry-accepted specification which includes design, manufacturing, and uniform identification requirements.
The specification must include all information necessary to produce and conform the part. The specification
must be published so that any party may manufacture the part. Examples include, but are not limited
to, National Aerospace Standards (NAS), Air Force-Navy Aeronautical Standard (AN), Society of Automotive
Engineers (SAE), SAE Aerospace Standard (AS), Military Standard (MS), etc."

Wag-Aero list their venturis as "Code 5". If you go to the back of their catalog it list Code 5 it says "These items meet AN, MS, NAS or other Military specifications or may be identified as Standard Parts as defined by the FAA."

N3243A wrote:It's a venturi for !@$%&@ sake. No moving parts. It's well made, can't really tell its any different than the original except a little longer.

I hear ya Bruce, your preaching to the choir here. I would love to strap that big puppy on there, but our Feds out here in CA are not so forgiving, and neither is my IA.

Your right - it is a pretty simple device (that is the beauty of it in my mind). It seems that Spruce could get the super venturi approved under a "AN" classification easily enough.

Thanks Karl,

I'm all for using FAA PMA parts on critical stuff but I draw a line in the sand on a few things and venturis are good example. I really don't think the Feds (up here anyway) would be all that concerned and that my IA installed the venturi testifies somewhat to this fact.

Bruce

N3243A wrote:It's a venturi for !@$%&@ sake. No moving parts. It's well made, can't really tell its any different than the original except a little longer. My IA recommended this procedure and has installed many of these exact 9" venturis on 170's for the reason to keep things simple and clean with only one venturi. I examined my original 4" venturi and didn't see any FAA PMA sticker or part number either. I think this one is really a minor technicality. It's not like we installed a Holly 4 barrel carb on the engine or something.

My two cents, Bruce

Ha! I know what you mean, Bruce. It's irritating when life really should be simpler.
But to address your observation, just for discussion's sake ...
".. can't really tell its any different than the original except a little longer..." it's different size is the proof that it doesn't conform to the original "approved" design. If I was an inspector it'd stand out like a sore thumb.
"...didn't see any FAA PMA sticker or part number ..." -The part number is listed in the IPC as AN5807-1,...a standard, approved specification. Any other requires additional approval.
"It's a venturi for !@$%&@ sake..." Ha! Yes, but there are those who would argue that's why it's important that it be approved! It's the sole-source power for critical instruments.
"It's not like we installed a Holly 4 barrel carb ..." A single barrel carburetor is a pretty simple thing too! Except that the two-piece venturi in it can cause loss of engine power, so an AD note was issued.
Is the "super" venturi's throat machine-fit/swaged or is it one-piece cast and machine-finished like the AN5807 spec.? Vibration might make that an important distinction up there in the clouds. Those are the sort of questions answered by such things as AN specifications.
BTW, I have a copy of the AN5807 specs posted at the old site if anyone was curious about them. Bruce is right, it's dirt-simple. I love it. Hate dry-pumps.

George,

Well I would bet $100 that the average FAA FSDO inspector could not tell the difference at glance between a 4" and a 9" venturi. You have lots of type specific experience that allows you to tell the difference but does not reflect the experience of most ASI's.
I agree that there is a Part Number listed for the 4" venturi in the IPC bit I don't see the PN stamped on my old venturi, so how do I know Cessna or someone else put the proper AN5807-1 on in the first place? My point is that that these aren't all that well documented anyway.
If you use your airplane IFR maybe you have a point about powering your critical gyro instruments with the "approved setup". I use mine for VFR only so if the venturi fell off because Spruce made it from paper mache' it would be no big deal to me. But I'm just not to worried about the quality of the part. The throat looked nicely machined to me. This is probably not the time to mention that I also have a Spruce ACS products mixture control either (also installed and documented by my mech.)

On a related issue, the famous F. Atlee Dodge here in Anchorage sells generic Bowden cables (solid wire in wound casing) for carb heat, cabin heat, cabin air, etc. complete with nicely labled knobs. No where do the cables have an FAA PMA sticker yet they are found in many Supercubs and Cessnas across Alaska. No one seems to get too upset about this type of minor stuff up here (A&P's or FAA). In fact much of Atlee's stuff doesn't have PMA stickers yet his name and products are so well regarded that it appears to be overlooked by the FSDO in my opinion. Another reason why Alaska is a great place to live and fly!!

Bruce

N3243A wrote:It's a venturi for !@$%&@ sake. No moving parts........................... It's not like we installed a Holly 4 barrel carb on the engine or something.

My two cents, Bruce

You mean that Holley 4-barrel I put on back in '99 isn't legal?

Eric