Venturi location

[Alwine00775]

Since I started looking for a 170 I have seen all sorts of Venturi configurations 1 on each side, 1 on the left or the right , in Hesperia Ca there is one that has 2 on the right. None of them were rag wings though. Makes you wonder if there was truely a specific location.

[counsellj]

I have also seen them mounted on the belly.

[Bruce Fenstermacher]

Very nice looking '48. The large registration numbers on the side are not original. As for the venturi they were an option and many planes were delivered without any. Cessna's placement was one or two but they were always on the right. You will see them almost any place as they were added by many different people.

[cessna170bdriver]

Re Venturis: I have one on each side; bought it that way. I've always seemed to have lower vacuum than some, and in an effort to find out why, I blocked them off one at a time with the result that the left one by itself wouldn't operate the system at all. The right one by itself worked almost as well as both together. The IPC shows two on the right for my s/n 1955 B-model. I ended up cheating and installed a manifold "backup" vacuum system and left the ventruis where they were.

[Bruce Fenstermacher]

Sorry I meant right side. (i corrected my earlier post)

[minton]

Cessna originally had them on the right. Moving them to the left means you have to move the static port too.

http://cessna170.org/forums/viewtopic.p ... uri#p78987

Could you explian the rational of you having to move the static port (as well) as you say? The factory positioning is on the left boot cowl. The Cessna service kit you reference does'nt mention it as it only addresses adding an additional venturi (AK 7053-14) but certainly does outline where the venturi(s) is (are) to be placed on the right side of the boot cowl.

Seems to me that Cessna engineering got involved at some point and have some reasoning as to where these components were origanally positioned (venturi(s) and static port). If the aircraft is to be 1) Certified for IFR operations and 2) Any alterations are made to the certificated aircraft (Ref: Venturi, static port positioning) there "could be issues" in several areas.

When installing these components research is in order before hand (Cessna IPC's, service kits offered, Cessna service manuals, even 43.13 has things to say on the subject). Shooting from the hip and placing them where ever you please is not in the picture from my perspective as a AI and any found to be out of the ordinary would not get my signature unless data existed in the aircraft records to support their new locations.

Again, just my opinion.

[minton]

No need to get testie. I'm not chiming in to pick a fight or ground your aircraft. It was a valid question more than anything given the stuff I read here sometimes gives me pause. When a reference is presented (AK 7053-14) and referencing relocation of the static ports and venturi's using that reference ( And, oh by the way, does'nt mention static ports or relocation of venturi's) I get a big question mark over my head as to what Data was used to support such a statement. If there is valid Data to support such please give reference to such for us upfront thus not getting anyones blood pressure up. It's all meant to educate, right?

Thats all that I ask, present the data to support your statements. You will get better responces when giving the background for us all to better understand the issue.

As I presented it, Cessna has done their homework. Has anyone going their own way done theirs? And as presented, there is plenty of reson for me me wonder. Reference material out there is in support of Cessna's positioning. Speculation gets us all chasing our tails and when placement of critical components is left up to? Remember if there is no material out to support those modifications you are on your own as you are the last in line of responcibility (Or first) to take the fall.

If we were talking experimental I'd have no questions for you.

Please have a good day.

[lowNslow]

I can also provide anecdotal info to support putting the venturis on the right side. I have two 8" venturis on the right and get 3 inches of vacuum at run up which is enough to spin up the gyros on the ground. I hold a consistent 5 inches or slightly more in flight down to touch down speeds.

[minton]

Dude,

Have a good day.

[minton]

minton, first of all you are giving yourself more credit than you deserve. You couldn't ground my plane if you tried.

Second, you asked me a question in a public forum and get defensive when I actually reply? I apologize...I'll try and learn to just go ahead and let you spread your gospel unchallenged from now on. It may take me awhile to adjust though, so please have some patience.

You asked me to explain the rational of having to move the static port to the opposite side that the venturi was located on. So...do you agree that the Cessna Acc Kit document shows the venturi and static port on opposite sides of the fuselage? Mine sure is. I think there are a few other 170s (regardless of which side the venturi is on) that have their static ports on opposite sides from their venturis too. (Hint: there is the background for my statement).

In case you missed it, my only declaration was/is don't have your static port on the same side as the venturi. I think you're fishing for me to declare that it's OK to put your venturis anywhere you want, but I've never/and won't say that.

I've always enjoyed your input on this board, think you're a good guy, and you're probably a heck of an AI A&P, but you're having issues seeing the forest for the trees here. I forgive you though, as there seems to be a lot of times on this board that some really smart folks forget that their opinions of what is/is not approved on these old airplanes is much less meaningful than an airworthy airplane signed off by an AI, and in compliance with their local FSDO. My aircraft happens to be one (of many others) that have the venturi on the left...don't lose too much sleep over it OK?

According to some other folks that have venturis on both sides (GASP!!!!) the left side ones don't work as good...that should make you feel better, right?

Absolutley not fishing for anything. Sure wish that I was though. This winter has been the pits!!

I don't get upset by this stuff just enjoy the back and forth towards the goal. I would never ground an airplane. George sez I can't

[russfarris]

Both my 170 and my current '57 172 have the venturi mounted on the left side, added years after manufacture on a 337. Static port is still on the left, and both aircraft are/have been IFR certified. Both work very well. I'm not following what the issue is supposed to be.

Russ Farris

[Bruce Fenstermacher]

Russ, there may or may not be an issue with the venturi on the same side as the static port.

From memory we had a forum member who had a venturi on both sides and he discovered that the left venturi didn't seem to work as well. He asked if we might know why. I don't recall anyone could explain it but in the conversation of course we pointed out the Cessna installation and it's relationship to the static port. Some thought was that the venturi may on the same side may effect the static port. I don't recall anything but speculation came out of that discussion.

[cowboy]

FWIW, my 1950 'A' model came from Wichita with one 2" Venturi on the left side and the static port on the right. It has since been upgraded, first with an additional 4" Venturi above the original 2" in the early '60s and then the 2" replaced with an additional 4" about 5 years ago. While taxiing I see 0.5 to 0.7 inches with 1000 rpm and around 4.4 inches in flight.

A therory about higher vacuum with the venturi on the right side than the left, at least while on the ground. Given the three point attitude and the pitch of the prop blade, the blade on the left side is acceding and taking a relatively small bite of air, where the blade on the right side is taking a much bigger bite. If my therory is correct the amount of air moved through the venturi would be notably higher on the right side, thus making the venturi on the right more effective.

[GAHorn]

FWIW...
A therory about higher vacuum with the venturi on the right side than the left, at least while on the ground. Given the three point attitude and the pitch of the prop blade, the blade on the left side is acceding and taking a relatively small bite of air, where the blade on the right side is taking a much bigger bite. If my therory is correct the amount of air moved through the venturi would be notably higher on the right side, thus making the venturi on the right more effective.

The same is true of aircraft in high power, low speed climb....when vacuum would otherwise be
low, as descending aircraft would presumably have plenty of speed and vacuum.
I believe that is why Cessna mounted/illustrates them on the right.
(Just because an airplane " left wichita" with one mounted on the left...doesn't mean Cessna did
it....Yingling did lots of alterations for new owners prior to delivery in accordance with custom
orders.

[minton]

I Emailed my brother in law in hopes of him pulling the rabbit (Or a pooring written paper) out of the hat as he is a aeronautical engineer.

Questions presented:

1) What factors come into play when determining the optimum positioning/location of a gyro instrument drive venturi on a single engine aircraft.

2) When subjected to prop wash. (Direction of rotation, RPM, airspeed, angle of attack, etc.

3) What comes into play if a static port is near by.

Who knows we might get the some useful information from him