Which one do I have?

[108pc]

How do I know what size venturi I have? Outside dimentions are 10 1/8" long and the hole is 3 3/16". Today just wasn't a good customer service day for aircraft parts suppliers...eternal hold....trying to make up information...etc! But I know my shortwingers can come to the rescue! Thanks, Wayne

[JohnW]

Hard to know without a really GOOD picture, or info off a data tag. There are "plain tube" models, and there are different "turbulators" that have been used over the years. There are many "variations on design", and these effect the efficiency. But I'll take a shot anyway, FWIW. You've just about fer sure got either a "eight inch" or a "nine inch" venturi there. The "two inch" is noticeably shorter and only around an inch in diameter opening to about 1 1/2"). All the "nine inchers" I have seen (keep it clean, boyz) say "9 inch venturi" cast into the base, the throat or on a datatag. The older model "bigger" venturii like were stock on most Pipers of "our era" did not say anything on them (except in some cases they carried a MIL Spec number cast in), and were rated "eight inch". The "-inch" size tells you what "number of inches of mercury" the venturi would "draw" at some defined airspeed (which I do not recall precisely, but MAY HAVE BEEN 100mph... but don't hold me to that), it has NOTHING to do [directly] with the length of the tube itself. You have to size your venturi according to what instruments you want to run. An eight inch will not reliably "power" two gyros requiring "four inches of suction" at any less than upper-high-end cruise speeds. Yet an AN type T&B requires only TWO INCHES of suction, and if coupled with ONE gyro needing 4" on an 8 or 9 inch venturi, must include a "regulator" before the T&B to only draw about 2.3" max on it, or the gyro inside it will overspeed. This makes the T&B "hypersensitive" and worse, it DRASTICALLY reduces it's life span. A nine inch will [marginally] run a DG and a Horizon together, but not a DG, AH AND a T&B. All three will suffer from underspeed. For the "advanced panel" Pipers that came from the factory, you would routinely see one 4" and one 8" venturi. Almost as often, you would see "field modified" "IFR equipped" airplanes with too little (or too much!) vacuum being supplied. Some later airplanes from Piper would have one 4" and TWO 8" suckers on 'em. A single instrument requiring 4" will run fine all by itself on an 8" or 9" venturi without a regulator.

[108pc]

Thanks John. I knew I could count on you to come to the rescue! There are no data tags or number stamps to be found on the venturi itself so I'm attaching a couple of pictures that might give a better idea of what I have (yes that's Dan Stewart in the driver's seat!). I read the thread you posted on a while bag regarding the topic and am hoping I have a nine incher (since apperantly size does matter!). My intent is not to be IFR, but I'm somehow stuck on this "if you have it, you might as well use it" kick, and I have a AI and figure that since I'm re-doing the panel now is the time to throw it in! If it's not do-able then I'll leave it out.

Wayne

[JohnW]

I regret that despite your best efforts, the pics really don't allow any better determination (for me, anyways) as to "what you got". I can say that I LEAN towards what I see there as your having an "original eight inch venturi" consistent with what Piper could have had available Post War. Since the Clipper had NO gyro instruments "stock from the Factory", it didn't actually HAVE a "correct venturi" at all, per the Production Drawings. More likely, it was probably an "add-on" a couple -or more- years later, making it what I would label as a "period piece" rather than "stock from the Factory" one. This alone would LIKELY mean that it's an 8". Then too, it COULD BE a 9" (but they didn't "come along" until the Clipper had aged past it's Majority!). There is really very little difference in actual operation. The question becomes..."do you NEED to add another gyro to your airplane?". Seems kind "odd" to me if all you wanna do is "use up " whatever excess vacuum you might have available! If all you HAVE is a T&B, then I would GET RID OF that draggy venturi and DOWNSIZE to a smaller model. You'll go faster, save fuel, and you'll be able to fly more! I dunno what you mean exactly when you say you are going to "re-do the panel", but did you know that Clyde Smith sells PA-16 panels with the original holes cut out, or with NONE OF THE HOLES cut out? He'll even "custom make" a panel for you, and his pricing is fair and reasonable. Find him on the Web at http://www.cubdoctor.com/

The best and easiest way to lose weight in our airplanes is for the Occupant(s) to STOP EATING SO DAMN MUCH. The second best way is to KEEP IT LIGHT, and generally speaking that means "leave off what you do not actually NEED". They're more fun to fly (depending on your Mission, of course) the lighter they are. Now, if you NEED a gyro for something, then discuss with your IA what you can or can't do.

[108pc]

John,

I hope you didn't think I was ignoring you or your replies to my questions. I wouldn't want you to get your feelers hurt! The reality is that I've been thinking long and hard about what you've said and have come to the conclusion to not put the AI int the airplane right now. It is a VFR bird with no plans for IFR. The "boy scout" approach (be prepared) doesn't really make sense. And with the questionable ability of my venturi to run all three instruments it makes more sense to leave it out.

As far as weight savings goes, the AI doesn't weight that much! And I haven't been "eating too damn much". 173lbs to be exact! I will, however, be pulling the back seat out of that puppy so I can fit more camping and hunting gear in it!!!

Thanks again for your thoughts on the matter.

Wayne