Vacuum systems

Bill Hart · Post by **Bill Hart** » Fri Nov 04, 2005 8:19 pm

Hi Guyâ€™s

I am looking at a 51â€™ A model and need some advice. The airplane has no vacuum system on it at all and if I get this airplane I will need to put some type of vacuum on it to drive an attitude indicator and DG. What is the preferred method of doing that? I have seen some airplanes with belt driven pumps on them is that a good system and how much are we talking about for the system. Or would it be better or more cost effective to put a ventrui on it? By the way it has a C-145 on it.

I guess in short I need an airplane with an AI and DG should I be looking at on with out or is it easy to convert the airplane?

doug8082a · Post by **doug8082a** » Fri Nov 04, 2005 8:35 pm

The venturi would certainly be the most cost effective and least hassle. The 170 came standard from the factory with venturis so that method is already approved. The C-145 has no provision for a vacuum pump, so you'd have to buy the STC to install the belt drive pump. The belt drive pump would require modifying the nose bowl to allow for the prescence of the pump and the belt. Most people end up replacing the nose bowl to accomodate this with one from an early '60's 172.

I have a super venturi on mine and drive an AH & DG with no problem at all.

Bill Hart · Post by **Bill Hart** » Fri Nov 04, 2005 9:37 pm

If the Airplane never had a venturi is it still an eazy thing to add a new one?

BH

doug8082a · Post by **doug8082a** » Sat Nov 05, 2005 12:51 am

I can't see that it would be that big a deal. The only critical thing would be to get it oriented correctly into the slipstream. Once mounted, your A&P should be able to plumb it to the instruments as required.

Post by **GAHorn** » Mon Nov 07, 2005 2:42 am

The illustrated parts catalog shows the installation.

zero.one.victor · Post by **zero.one.victor** » Mon Nov 07, 2005 6:25 am

Bill, I'm curious why you want or need to add a DG & AH along with the required vacuum system? Is it for IFR use? Since the airplane doesn't have IFR instrumentation I assume it probably doesn't have IFR radio gear either.
Unless you're planning IFR flight I would recommend not bothering with the instruments-- just stay out of the clouds! Without a DG & especially an AH you won't be tempted, you'll be more careful to maintain VFR conditions than if you had them.
My 2 cents worth...

Eric

Bill Hart · Post by **Bill Hart** » Mon Nov 07, 2005 1:39 pm

Eric

Yes I would use the airplane for light IFR use, mainly just for filing and getting in the system. With that being said I already have the avionics that will go in the airplane so I am looking for a solid airframe with junk radios. However I am finding that most of the nicer airframes someone has already installed more radios than I want.

I have found an airplane that has low time on it and the engine but has only a com radio and that is it. So I am now trying to decide how much time and money it will take to get it to my standard. The airframe looks to be in great shape but getting home would be a challenge at best, and with no transponder I could not bring it to my home airport as it is in class C airspace.

Oh the problems with trying to find the perfect airplane.

Bill

Post by **GAHorn** » Mon Nov 07, 2005 2:58 pm

Bill, here at the forums, we almost never have a difference of opinions. It's really rare.

But I fly my 170 in "light" IFR about 5% of the flights I put on it involves at least some IFR, usually just a climb or descent thru clouds, but it adds considerably to the usefulness of the airplane for me.
My airplane has the original AN type gyros and dual-venturi system as illustrated in the B-model IPC and it works just fine. But be aware that modern "pictorial" type gyros sometimes complain about being sluggish. They require 4.5" of vacuum generally....about a full inch more than the origninal AN type gyros. My dual venturis give me 5-6 inches depending upon altitude and cruise speed. During climb to 7500' indicating 80 mph the other day I only had 4.5".
The gyros are up and running just fine after takeoff by around 300-500 feet, and as long as 70-75 mph is maintained on approach there's been no problem with holding 4" or so, plenty for gyros already spooled up.
Another solution for consideration would be to have only a vacuum T&B (operable with the smaller 2" venturi) and DG, ...and electric horizon. The rule only requires that the T&B/Turn coordinator and the horizon be of different power sources. The horizon doesn't have to be vacuum as long as a different power source is available for the TB. (But be aware that electric horizons don't enjoy the longevity of vacuum gyros, and they cost about $1500 or more.)
Also be aware that there are cheap import gyros being sold these days. I wouldn't trust them in my airplane being used for IFR.

Bill Hart · Post by **Bill Hart** » Mon Nov 07, 2005 6:15 pm

Thanks a lot for the imput, I have just about decided to ditch this effort and start looking for a different airplane.

BH

doug8082a · Post by **doug8082a** » Mon Nov 07, 2005 6:29 pm

Another 170, we hope!

zero.one.victor · Post by **zero.one.victor** » Tue Nov 08, 2005 4:37 am

Bill, I'm not aware that txp/mode C is legally required in Class C airspace. It is required within the mode C veil of (some) Class B airspaces. I have heard negative-transponder aircraft talking to Navy controllers & getting clearance into & thru Class C airspace at NAS Whidbey in western Washington, didn't sound like a big deal- especially if you were just getting the airplane home & weren't going to make a habit of it. If nothing else, a pre-arrival phone call to explain the situation would probably get you cleared in to get home.
If the airplane is a good one and the price is right, I wouldn't let it stop me.

Eric

lowNslow · Post by **lowNslow** » Tue Nov 08, 2005 4:54 pm

zero.one.victor wrote:Bill, I'm not aware that txp/mode C is legally required in Class C airspace. Eric

Per FAA:
"Two-way radio communications and operational transponder are normally required for operations within Class C airspace, but operations without radio communications or transponder can be conducted by LOA, facility directive, or special arrangement with Class C airspace controlling facility." (LOA = letter of agreement)

Walker · Post by **Walker** » Tue Nov 29, 2005 8:40 pm

In regards to getting the venturi oriented in the slipstream, putting a big wet smear of dirty engine oil forward of the intended location and flying the plane will leave streak lines that show the direction of the air flow.