Hi Steven;

As far as I know, there is a minimum equiment list for IFR flight, and as long as your airplane systems can support this equipment, you can fly it IFR.  Basically, the only two required instruments that run off of the vacuum system are the Attitude Indicator and the Directional Gyro.  There are electric AI and DG instruments that could be installed in your airplane.

The only downside to this is in a partial panel situation after losing your electrical system.  The Turn Coordinator is sort of a backup for the two vacuum instruments in that it indirectly indicates bank attitude and can be used (along with the compass) for timed turns to headings.  In this scenario you will lose all indications of bank on your instrument panel (except for your compass).

There is probably a placard in your C-172 indicating it is not certified for IFR flight because it was not equipped for it when Cessna delivered it from the factory.  However, FAR 91.205 Subpart C--Equipment, Instrument, and Certificate Requirements lists all the required equipment for IFR operations.  It makes no mention of a vacuum system, but does require an electrical system and the instruments, gauges, lighting, communications, and navigation equipment necessary for IFR flight.  Therefore, I would think that you could equip your airplane for IFR flight if you installed all the required equipment.

I hope this information is helpful.

Jon

i have a 56 skyhawk with the venturis. i had them removed after i had issues with attitude not spooling up in the bank etc. I had a dg and a attitude indicator installed electric. they are stc / pma approved. in addition i installed a new alternator to carry the new loads. according to the avionics mechanic who installed the devices and after reviewing the regs it does meet min ifr, although personally i would not do HEAVY ifr as if the alternator failed you would be on battery alone. another option i suppose would be to install the attitude indicators with battery back up installed. - hope this helps..

A few years ago I had a 1959 172 with Venturi's and I was visiting a airport and saw a early 172 wih no venturi's so I checked it out.  It had a mod that had a pulley mounted behind the prop and a belt going to a vacuum pump mounted in the right airscoop, it had to be an STC item.  There is a company who has a STC on a alternate (emergency vacuum) system that takes suction off the intake manafold to run your vacuum instruments when your other suction systems die.  Venturi's are at least reliable until they get iced up. I've alway wondered if you mount them so they were right behind the exhaust pipes the heat could keep icing from ever forming.

I'm a&p IA and I agree with the other A&P as I am also a 8353 hour ATP and you are not required to have a heated pitot to fly in visible moisture.   It makes sense but it is not a requirement.

Visible moisture and 10 degrees celcius is considered by most to be known icing conditions.  That is only 50 deg F.

So if you knowingly take the aircraft into  visible moisture at 10 and below it is a bad thing.

I fly my 56 C-172 regularly in visible mosture going back and forth to work to allow me to climb above the MVA min vectoring alt direct between my corporate job and my home to not have to worry about the scud

I have two venturi systems with one vaccum dg and two vacuum horizons and a Garmin 296 for reference only

So with the venturis which I would take any day over dry air pumps and even a wet pump which I would like to have I simply can't take off with so little vis that I would not be spooled up before the clouds.

Putting the venturis behind the exhaust is a novel idea.

As an emergency using the manifold intake vacuum is good but you wouldn't want to use it all the time because even though it is vacuum and nothing from the engine is being brought into your instruments I watched a 172 configured this way eat amny instruments after it was installed. Probably because f the beat of the drum of the valves opening and closing even though it was a O-300.

Beside what if the engine quits then you got nothing.  Oh yeah that's the same for a wet pump and a dry pump.

I also have a digital KR87 ADF and a Narco late model digital ILS receiver with GS

I don't have a DME other than the 296 so if I did a non precision I would have to be at an altitude that would have me be in radar environment at the FAF (you have to be at or above the alt on the chart as long as the controller knows what you are doing ahead of time for other aircraft) and have the controller call the fix before descending to MDA  Not very good so I am loking to put in a DME receiver

I also installed an alt static port

I have the regualr pitot and cessna furnished the aircraft with an OAT probe in a vent that must be open to sense the OAT

I think the Garmin 430 and 530 Garmin would be nice but compared to antiquated airline simple dme dme fms they suck

I do keep my approach speed up for venturi but I have never ever seen a problem in turns or any attitude with the venturis and vaccum horizons either of them

This also goes for my Navion with venturi vacuum