Second Artificial Horizon Project

[GAHorn]

The location illustrated in the IPC is that used by the factory, perhaps for efficiency reasons. At least one of our members (a certain, sodden, auctioneer) has his mounted on the belly, aft of the cowling exits, perhaps as a method of heating them, although I doubt that hot air provides the most vacuum, nor is that a clean area. I suspect they suffer from efficiency losses also due to grime buildup.
I am a bit puzzled/amused over the concerns some owners have about venturi "icing" up, since the airplane is not approved for flight in icing conditions, and that is why another source of power for backup gyro is usually required in IFR aircraft. (My electric T&B, for example.... although I don't have a heated pitot and "needle, ball, and airspeed" isn't necessarily guaranteed to be available.)
I actually will keep in mind my Garmin's simulated instrument panel, if such an unlikely event should occur.

[GAHorn]

Update:
The Sigma-Tek horizon arrived this week (4-weeks after ordering as they stated). It looks good and is the model with the caging feature I wanted. The caging knob exits the stationary panel thru the 5-o'clock hole ordinarily used for a gyro mounting screw. I will have to bore a hole thru my false-panel to accomodate that. (The knob is attached to it's shaft with an allen screw, so that should make it easier to keep the false panel's looks in better condition, avoiding the need to relieve the 3-18" instrument-hole.)
I have ordered the additional installation parts I'll need from Aircraft Spruce and hope to have them all this upcoming week. (Hose, tubing, and assorted hardware to modify the vacuum system to accomodate the additional gyro horizon. I'll post a parts-listing when I write the complete article.

I removed the elect. T&B and placed the new horizon in the panel to check for fitment

MVC-001S.JPG

and discovered that the control column "T" and aileron control chains slightly interfere with the new horizon when the elevator is held full up/yoke full aft. To be sure, the control column "T" (right side tube) had contacted the (original) OEM AN-Gyro horizon at the point of full up-elevator previously, but it did not prevent full control movement or offer any real hazard to operations...it was just as if the rear of that horizon acted as an additional "stop" for up elevator. I didn't like it...but wasn't sufficiently motivated to do anything about it. However the new horizon does limit movement by about 1/8-1/4 inch and the chains actually rub the caging feature.

Now that another reason to address this issue has arisen...I've undertaken to see what can be done about it.

Now, I'd already determined that the previous contact between the original AN-gyro and the control "T" wasn't limiting or hazarding anything, and I'd already found the elevator makes the correct/full deflection angles in accordance with the TCDS/rigging instructions. The control cables and lengths, as well as all the pulley's and bearings were new when the airplane was restored ten years ago. And the instrument panel had not been altered from factory original in any leading particulars.
The simple solution, in order to gain more clearance, appears to be to relocate the floating panel farther aft (about .25 to .50 inch seems necessary.)

How would one accomplish that task without extensive modifications (which I don't want to do, not only for expense, but also for appearance?) Hmmmn....

I'm certain that everyone is familiar with the rubber shock-mounts Cessna used to mount the floating panel. Notice the "set" which this one has developed from ten years of instrument-panel weight hanging on it. When I re-install the rubber mount, I will re-orient it to 180-degrees opposite it's previous position to relieve that offset.

MVC-031S.JPG

(By the way, these are available also from Aircraft Spruce.)

They are about .75 inches long with 8-32 threaded phosphor-bronze studs (which use brass nuts to avoid magnetism) vulcanized to the rubber shocks. To my mind, I need some that were .50 inch longer, but that is not available. So my solution was to lengthen their reach by adding .50 inch nylon bushings, thru which pass aluminum (for anti-magnetic properties since they will be near my compass) "binding posts", (also known as "screw posts") which are commonly available at hardware stores. They are already made in the correct length and already machined at one end with male, and the other female, 8-32 threads. The nylon bushings had .171 holes thru them, which I enlarged using a 13/64" drill bit. Notice the 1/2" binding-post extension, the nylon bushing (also from the hdwr store), and the bushing/mount relationship prior to insertion of the aluminum extension. (You can also see two of the extensions partially mated to each other to demonstrate that each one has both male and female ends.)

MVC-027S.JPG

MVC-029S.JPG

The nylon bushings came in two diameters...3/8" and 1/2". I chose to use only the 1/2" diameter bushings in order to provide the maximum amount of support in the panel.

Notice also that there are grounding straps which "jumper" across the mount bushings which assure an electrial "ground" across the assembled nylon/mounts. "Star" or "lock" washers are also used beneath the nuts to prevent looseness and provide good grounds. Use only non-magnetic stainless washers if you wish to avoid affecting the magnetic compass. Here's a pic of the mounts prior to the work, and after the new mounts are assembled, prior to re-mounting the floating panel.

MVC-030S.JPG

MVC-034S.JPG

MVC-033S.JPG

Temporarily bolted up to check clearances.

MVC-002S.JPG

When the false cover-panel is replaced over the black basic panel, it will reacquire it's original look.

The most difficult part so far has been to hold the nuts/washers behind the metal panel with one finger while removing the rubber mount and installing the new bushing/extension-threads into the nut, all while attempting to prevent the nut/washer from shifting or dropping down into the panel. (I used small ignition-wrenches to loosen and then tighten those nuts because they offered greater freedom in such a tight place. The downside was finding that small ignition wrench when I once dropped it.)

Why didn't I simply place the nylon bushings in between the floating panel and the rubber mounts?, one might ask, as it would have avoided the difficulty of removing/replacing the nuts/washers behind the metal stationary panel.
Answer: Because that would have doubled the ARM of the floating-panel upon those rubber mounts and increased the MOMENT of panel, increasing the load the rubber shock mounts would have to carry. This would likely introduce a higher failure rate of those rubber mounts. (I already found one such mount failed, seperated from it's stud that passed thru the stationary mount, and had to replace it. Surprisingly, it was the one at the bottom of the panel, in the very middle, just above the cabin-heat knob. That mount supports very little actual weight, but quite a bit of longitudinal "pull" due to stance of the airplane imparting a "pull" on the lower area of the floating panel as it tends to return to a vertical position during rest. Keep in-mind that the C/G of all those instruments lie BEHIND the floating panel and imparts an outward twist to the lower edge out towards the cockpit.)

I remounted the floating panel and re-checked control "T" movement for interference and ...PROBLEM SOLVED!
No more interference, full movement available, and the finished, remounted floating panel will be virtually undetectable to the discerning eye.

The beauty of this portion of the job is that it required no disconnection of any instruments from the panel or their power sources for such a small relocation of the entire panel. (Suggestion: Standard shop practice before undertaking any kind of work which exposes open wiring is to disconnect the negative terminal/ground-cable of the main ship's battery.)

At the same time, I am removing my GPS-196 (see the velcro-mounting pad on top of the panel?) and installing the Aera 510 in the same location. Those are the power-leads which pass thru the hand-grip on the top panel.

More when the vacuum system modification parts arrive this week.

[170C]

Mentioning the Cessna rubber panel mounts refreshes a subject/question. I have it on pretty good authority that these rubber/shock mounts are no longer needed with today's instruments, etc. The source said we could hard mount the old floating panel and everything would be OK. Do you share this opinion?

[GAHorn]

Mentioning the Cessna rubber panel mounts refreshes a subject/question. I have it on pretty good authority that these rubber/shock mounts are no longer needed with today's instruments, etc. The source said we could hard mount the old floating panel and everything would be OK. Do you share this opinion?

No.

If your panel included them as original equipment, they should be maintained.

The reason some "modern" mechanics talk that way about "modern" instruments is because most of them work on "modern" turbine, and/or pressurized equipment that already has ample isolation of the entire airframe and panel from much-reduced vibration of turbine and better shock-mounted engines,....and haven't witnessed them on modern designs.... so they leap to a wrong conclusion.

(Keep in mind also that many "modern" panels have dispensed with intricate/delicate instrumentation in favor of "glass" and "LCD" instrumentation.)

[n2582d]

When I re-install the rubber mount, I will re-orient it to 180-degrees opposite it's previous position to relieve that offset. (By the way, these are available also from Aircraft Spruce.)

George, you're a man after my own heart: Cheap. Sacramento Sky Ranch Lists P/N 6984-1 for $2.75 ea. As I researched these lil' buggers things got pretty confusing. First, the part number in our IPC is 0411059-1. When I ordered the "round shock mount as used on Cessna aircraft", p/n 10-14700, from Aircraft Spruce they sent mounts that were 3/8" diameter. They matched the old ones I took off (which also were severely sagging like yours). Yours appear to be at least 1/2" diameter and if I'm reading correctly are p/n J6984-8. According to Wag-Aero, Lord p/n J6984-8 is Cessna's p/n 0411059-3 and Lord p/n J6984-1 is Cessna's p/n 0411059-1. Wag-Aero's catalog disagrees with Sacramento Sky Ranch's as to which shock mount is the larger diamenter. Sacramento Sky Ranch says that the J6984-1 is "the large one" and J6984-8 is "the small one". I contacted Lord and they said that J6984-1 hasn't been manufactured in a long time. I asked for a cross reference to a current Lord p/n but they just referred me to Aviall who apparently stock J6984-8 and J6984-64. Here's Lord's spec. sheet on Flex-bolt Sandwich Mounts. Notice that to get a larger diameter than .38" it would require having 1/4 X 20 studs. My wimpy 3/8" dia. mounts don't appear up to the job of holding up at least 13 lbs. of panel and instruments. The panel will accommodate 3/4" dia. shock mounts without interfering with the instruments. So to those thinking of replacing these shock mounts I would suggest that you confirm that the mounts are at least 1/2" diameter when you order them. In addition to the above links they are available at SkyGeek and Chief.

[blueldr]

Most of the mechanics that I'm acquainted with buy their little rubber shock mounts from Grainger Industrial Supply.
About $1.50 each.

[GAHorn]

[...According to Wag-Aero, Lord p/n J6984-8 is Cessna's p/n 0411059-3 and Lord p/n J6984-1 is Cessna's p/n 0411059-1. Wag-Aero's catalog disagrees with Sacramento Sky Ranch's as to which shock mount is the larger diamenter. Sacramento Sky Ranch says that the J6984-1 is "the large one" and J6984-8 is "the small one". ...

I purchased my 0411059-1 from a Cessna distributor (Lubbock Aero) while I was awaiting pax. They are 1/2" diameter, so Sacramento's catalog is correct. (Cessna's official price is $12 ea. but discounts are available for 170 Assoc'n members from Cessna distributor Hill Aircraft.

[n2582d]

George,
What's the p/n on your shock mount? In the picture it looks like there is a "-8".

[GAHorn]

George,
What's the p/n on your shock mount? In the picture it looks like there is a "-8".

[...
I purchased my 0411059-1 from a Cessna distributor ....

I did indeed picture a -8 (1st pic on a paper towel) for illustration of "sagging" purposes. The ones pictured assembled on the nylon spacers are -1's.

(My panel actually had a mix of the two PNs when I disassembled it, with -1's on the uppers and -8's on the lowers. I recommend the -1 (1/2 inch dia).