Second Artificial Horizon Project

[GAHorn]

In another message thread, I revealed my plans to improve the "light-IFR" capability of my instrument panel.

N146YSPanel.JPG

"One of my next expenditures will be to UN-original my panel by moving the T&B to one of my blank places and install a back-up, modern, pictorial AH in it's place. I'll likely do that by replacing my standard venturiis with "super" venturiis to provide sufficient vacuum to run all three vac-driven gyro's ..dual AH's plus DG... rather than spend money on a pricey elect AH which, as a group/type, happen to suffer miserable failure rates."

Besides the decidedly-odd location of the original AN gryo-horizon, ... those AN gyro's are a bit more susceptible to "upset" or "tumbling" than modern 3-1/8" pictorial horizons, which have greater gimbal-limits. So I have gone ahead with this project, and intend to write a detailed article for The 170 News on it .

The first thing I"ve done is to order additional hose (Aeroquip 306) and super-venturiis, from Aircraft Spruce. I've rec'd those materials and am searching for the appropriate vacuum-horizon for the installation.
Since venturiis are unlikely to produce sufficient vacuum on take-off roll to fully erect the gyros before lift-off...I've decided to install a gyro-horizon which is "cageable"...for purposes of fast-erect after lift-off. (I've found that my standard AN gyros are fully spooled-up by 300' AGL, and I don't plan to fly a single-engined airplane in weather lower than about 500' anyway.) Addendum: Now it's several years later and I've found it completely unnecessary to pay the extra for a "cageable" modern horizon. This new Sigma Tek unit is fully erect and functional by the time I'm over the departure end of my 3500' grass runway. It has never "tumbled" ...despite some rather, err... "mild".... departures from normal flight attitudes.

Something which caught my eye in a recent Trade A Plane Advert was one by Sigma Tek, which offered a NEW 5000B Attitude Horizon for $495 plus a rebuildable core. I have such a core and contacted them and discussed my plans with their salesman.
He agreed to investigate and provide a quote for the gyro I want, hoping to be able to do so at a similar price.

But that has so-far proven a disappointment in that he did not call me back. After one week, I contacted Sigma Tek again, and left a voice msg. No response.
Another week and I sent an email. No response.
Another week and I left another voice mail, fairly explicit in tone, to the effect of how my disappointment in lack of response was being received. Three days later I rec'd a voice mail on my cell phone from them.
I called and talked again to the same salesman, who apologized, and promised to have a quote to me by the following Wednesday. That was TWO Wednesdays ago.

I am now searching for another supplier who is interested in selling their product, knowlegeable that I plan to write an article on the subject, which will be on the World Wide Web, and in our Quarterly Magazine.

I don't know why Sigma Tek spends money on advertisements, yet doesn't seem interested in selling the product they advertise to someone who is willing to share his experience with many others who are also prospective purchasers.

I'll keep you posted.

George

[Bruce Fenstermacher]

George I'm assuming since you are calling this modern gyro a backup that you are also planning on keeping the original AN gyro(s) working. So you will have equipment that calls for 3 1/2" of vacuum and equipment that calls for between 4 1/2" and 5 1/2".

You say you have bought two super venturis which pull 8" of vacuum each by themselves or 8" tied together.

Are you going to run two vacuum regulators with two separate lines to the appropriate gauges and have two vacuum gauges?

You could run one super venturi with the regulator to the modern gyro and one of the original 4" venturis to the AN gauges unregulated. You still need two vacuum gauges to monitor each system or assume one is working if the other is showing sufficient vacuum.

What are your plans here?

[GAHorn]

I plan to remove both OEM venturiis, and replace them with a pair of super-venturiis. I will simply add the new horizon to the entire system.
My working reference is "Aircraft Instruments" by George Ellis Irvin, President of Irvin-Aircraft Instrument Schools, published by McGraw-Hill in 1941. It is exceptionally detailed and intended for instrument technicians for installation and repair of all types instruments, and includes a chapter on new installations of both pump and venturi powered systems. (It even has diagrams for a selectable system using both sources.)

Since my T&B is electric, it will not be in the diagram I'm scanning into this message. Imagine the new gryo to replace the T&B depicted in the diagram, with a central air filter added to supply all instruments.

gyro project.jpg

The instrument specifications section states that, once spooled, the old AN style gyros operate with a minium of 3.5 in Hg, Modern gyros operate at 3.5 to 5.5 in Hg. Most vacuum relief regulators are pre-set to 5.5 in Hg, and should properly power both types of instruments. (Vacuum exceeding minimum values is not harmful operationally, but vacuum exceeding 5.5 in Hg leads to excessive wear and precession.)

It's my intent to place the relief valve in series, between the paired venturiis and all gyros. The two original AN gyros will remain exactly as already installed, and the new gyro horizon will be plumbed directly to the relief valve which has two inlet ports and one exit port (leading to the venturii pair.)

A gyro air filter with dual exit ports will have one port feeding existing gyro's and one port feeding the new gyro.

[Bruce Fenstermacher]

I thought running the AN gyros up at 5.5 would cause them harm and maybe change their operating characteristics. If it is easy, for you to do it would be interesting to find out if one super venturi would run the whole boat load for those with only one venturi installed. (Or for cheap skates like me who only want to buy one.)

[GAHorn]

To be completely forthright (as I know almost everyone except bluEldr and Ol'Gar expects of me) ...
I am thinking of the times that those with modern pictorial gyro's have complained of low vacuum for those gyros during approach...and since I'm in there doing all this work...what the hey!... the only additional cost is $69.75 for the second super venturi.
That's such a small additional amount considering the project, that I'd rather have a relief valve that works 100% of the time...in order to guarantee that I have gyros that work 100% of the flight. (Suction, in most endeavors, is like engines, anchors, bilge pumps, and certain anatomical parts... the bigger the better.)

I'll soon have two ORIGINAL, unpainted natural-aluminum, flight-proven, guarannteed-to-work venturiis for sale at HALF-PRICE, for anyone interested.)

(I also plan to take measurements at various airspeeds to make a comparison between the two systems WITHOUT the relief valve, just for our mutual edification.)

[wingnut]

"....unlikely to produce sufficient vacuum on take-off roll to fully erect the gyros before lift-off...I've decided to install a gyro-horizon which is "cageable"...for purposes of fast-erect after lift-off.... "

[cessna170bdriver]

George,

You sure started down a slippery slope when you installed that right-wing (pun intended ) landing light and baggage door!!

[DaveF]

For what it's worth, I'm currently running "modern" AI and DG with one super venturi, which is mounted on the right hand side.

I get 5" at 120mph IAS, 4" at 100, and about 3 at 80. It's good enough for now, but I have a suction regulator on the shelf for the day I install a second venturi.

[Bruce Fenstermacher]

(I also plan to take measurements at various airspeeds to make a comparison between the two systems WITHOUT the relief valve, just for our mutual edification.)

Blocking one venturi with duct tape for a test wouldn't be hard. Pretty please, for us more frugal owners.



Yes sir Miles you hit it right one the head. When George decides to cover the red with fast green we'll know he's gone over the deep end.

[mekstrand]

George,

Since you are going down the path anyway....

If you plan on keeping the antique horizon anyway, have you considered installing a Dynon D-6? It would fit in the same size hole, provide completely redundant air data, and probably be cheaper. (You could utilize the “flush mount” option and cut out a cover for ground use so no one would ever know you went modern.) You would not need to modify anything on your aircraft, and the "experimental" status would not be an issue, as the standard horizon would be still installed. I installed a D-10 several years ago in my aerobatic plane (Interavia E-3) and it performed very well in a harsh environment. (+10 –6 G’s) The gyro would get confused when the roll rate exceeded about 300° per second, but that shouldn’t be a problem in a 170.

This would be the way I might go about solving the problem if I were in your situation.

http://www.dynonavionics.com/docs/D6_intro.html

[GAHorn]

That is an interesting instrument (the D-6), and it certainly does a lot, but it will cost about $1800 plus incidentals for installation, while adding a second gyro is probably less than $1K.(In a pinch, it could be done for about $700.)
Also while the D-6 claims to "fit in a 3-1/8" hole"...in fact it does not when the false-panel/overlay is considered. It would only fit a 3-1/8" hole if no overlay panel is installed. The D-6 would also require mounting a non-standard Pitot tube. (If I still had my Baron, I would DEFINITELY consider the D-6, however. I really like the display-similarity to the EFIS systems I fly at the day-job.)

If I were building a new panel, from scratch, no overlay, and wanted a modern EFIS appearance... that would certainly be my choice!

[mekstrand]

Also while the D-6 claims to "fit in a 3-1/8" hole"...in fact it does not when the false-panel/overlay is considered. It would only fit a 3-1/8" hole if no overlay panel is installed. The D-6 would also require mounting a non-standard Pitot tube.

I was thinking the D-6 could be semi-flush mounted in the structural panel and a cover could be installed in the overlay to keep the appearance of the original panel. (It would not be difficult to build a flush cover and install the face of an old instrument for ground use) Also, the Dynon Pitot tube is only required IF you want to utilize the AOA feature. I elected to use the standard Russian "baseball bat" pitot tube on my plane.

If you like the D-6 you should check out some of their other products!

[lowNslow]

I have the two super venturi setup running a "modern" DG and AI. I am actually getting just below 6" suction in cruise (yeah, a little high) and get 5" down to 80mph and then it slowly starts to drop below 80 mph, but the gyros are fully operable to touchdown. My gyros are operable between 100-200' AGL on T/O. I was surprised how fast these come up to speed, but still use a 500' ceiling for minimums for T/O.

[cessna170bdriver]

(I also plan to take measurements at various airspeeds to make a comparison between the two systems WITHOUT the relief valve, just for our mutual edification.)

Blocking one venturi with duct tape for a test wouldn't be hard. Pretty please, for us more frugal owners.

I don't think just blocking the face of the venturi without blocking the vacuum port would work. In that case, the working venturi would be sucking air through the inop one, placing an undue load on the system. A more appropriate test would be to disconnect the second venturi and cap the line.

I have the two super venturi setup running a "modern" DG and AI. I am actually getting just below 6" suction in cruise (yeah, a little high) and get 5" down to 80mph and then it slowly starts to drop below 80 mph, but the gyros are fully operable to touchdown. My gyros are operable between 100-200' AGL on T/O. I was surprised how fast these come up to speed, but still use a 500' ceiling for minimums for T/O.

Karl, are both of your venturis on the same side, per the IPC? I also have two "super" venturi's but they are on opposite sides of the airplane. (The "originals" were installed that way when I bought the airplane, and there's no evidence of ever having both on one side.) I've done some tests, and the one on the right by itself seems to work just about as well as both together. I suspect it has something to do with the angles of the rotating slipstream being different from one side to the other, and the one on the left isn't seeing as much relative wind as the one on the right.

[lowNslow]

Both my venturis are on the right side of the aircraft.