The International Cessna^® 170 Association

Decided to bite the bullet and install some gyros. Any suggestions on the venturi installation - should they be parallel to the longitudinal axis of the airplane or slightly nose down to parallel to the relative wind (at approach speed?). Also when tying two venturis together, what is the best connection so as not to restrict airflow.

The IPC shows the factory installation (which should be followed if you wish to have the benefits of IFR approvals based upon the type certificate.)

They should be parallel to the fuselage, and plumbed in parallel to each other. Use aeroquip fittings whenever possible.

Here's the installation for 1953 and later. (SN35373 and on)

Thanks George. I had seen this but it is hard to tell from the diagram if the venturis are parallel with the fuselage or slightly nose down. I guess it probably is not that crucial either way. I also see no air filter installation - do the old AN gyros just have screens?

The majority of your flight will occur with a relative wind parallel to the lower wing surface and that's what your venturis will "see" also. Don't forget that your prop-stream will also be influencing the venturiis with a slight downwash. In other words, make them parallel to the longitudinal axis.

Yes, if you install two standard venturiis, connect them in "parallel" also. Older AN gyros only had screens, however they can be connected to a gyro filter also (as mine are.)

Now, ...here's a consideration for you: You can install two std venturiis.... or one SUPER venturi t o accomplish the same task. The actual size differences are insignificant, in my opinion. If it were me making a new installation, I'd install only one super-venturi.

gahorn wrote: Now, ...here's a consideration for you: You can install two std venturiis.... or one SUPER venturi t o accomplish the same task. The actual size differences are insignificant, in my opinion. If it were me making a new installation, I'd install only one super-venturi.

I actually have one super venturi and 2 8" venturis. I was thinking of going with the two 8" venturis as they are AN hardware while the super venturi has no approval. I will be using newer gyros and a regulator rather than the old "relief valve".

According to the mfr of the super ventuir it is a "minor" alteration and needs no further approval. I have a copy of the FAA letter which approves it's use. I'll try to scan it and post it (just as soon as I clean up my office and find it!)

George if memory serves me right I believe some time ago we at the forum (you probably) found that the super venturi (sold by Spruce I believe) is made to an AN standard and that is the line for the basis of approval for it's use.

That is correct. The letter I'm searching for is from FAA who states that since it is made in accordance with AN drwgs it is a STANDARD part, and needs no further approval.