The International Cessna^® 170 Association

Like most 170s, I'm sure, 56D is a day VFR airplane. 99% of the time that the airplane is out of the hangar, I'm either flying it, or I'm flying the owner around in it (or with her in it). Prospective tailwheel students have dried up, so the only time that the primary instructor gets in it is to do his night currency. Occasionally I'll have the airplane out after dark, but it's rare.

That said, the light pollution inside the airplane is terrible. The biggest culprit is the dimmer rheostat having become an on/off switch, but there is a lot of light that spills out from behind the false panel and shines on the windscreen. This doesn't bother me nearly as much as it does Dave, but it does make adjusting my eyes to the outside more difficult. It's been bothering Dave, so he asked the owner if we could do some things to combat the light pollution inside the cockpit, and she agreed.

First, I would like to know if this is a common issue with the piano key-style panel, and if it is, are there some missing parts that this airplane doesn't have? The ability to accurately photograph what I'm talking about is above my abilities behind a camera, but there is sufficient gap over and in front of the shock panel and the panel cover that light spills out over the top. Since the light needs to radiate from the bulb, simply fabricating some sort of shield would doubtfully be successful. My thought is to line the top of the shock panel with some 1/4" wide adhesive-backed foam rubber (similar to wing saddle tape for model airplanes) in an effort to create a flexible seal to block light from shining on the windscreen. Has anyone done similar? This is exacerbated by the lack of ability to dim the lights, but it was a problem for him even when we could crank the lights down.

The second area of interest are the bulbs that illuminate the four 2" gauges on the fixed panel (ammeter, clock, oil pressure/temperature)...they appear to be too long for the sockets into which they're inserted. There is probably 1/2" of exposed bulb that illuminates the floor underneath the panel. There is so much light that I thought that perhaps the missing post light on the far right-hand side of the panel had fallen down (more on that later), but examination showed that it was those smaller post lights. It appears as though the exposed portion had been painted/tinted red at some point...presumably this was to tone the light down. Are the lights supposed to be like this to create some ambient light in the cabin, or does it sound like we have the wrong bulbs installed? Whatever they are, they've been there a long time.

In that same vein, we're missing a post light on the far right-hand side. I thought perhaps the bulb had simply burned out, and pulled the panel cover to check the type to get a replacement and found that the socket itself was missing. Not wanting to dig too deep into it until it's time to turn wrenches, I am not sure how they're even installed - I presume that the wires for each socket are run individually to the dimmer rheostat? Are the sockets hard to come by? I haven't pulled the shock panel, but I'm going on pretty good guess that the entire socket is missing after looking under the panel, but it could very well be simply bundled with some wires and forgotten. Assuming the wiring is missing, what sort of bill of materials am I looking at to add the missing post light? It's the far right one, so it's only affecting the VSI and tach, but it's still a pain.

This is probably foolish, and is not related, but I would like to replace the piano switch grommets as the one for the master switch is completely missing (and creates a problem for people thinking that they've turned off the master when they really haven't). Since I may have to fiddle with the post lights for the fixed panel, I figure this would be an opportune time to address this as it's been bothering me for a long time.

The main qualifiers for this project are that it has to be simple and (relatively) inexpensive. I want to fix what's there, not replace an entire system when it's not necessary. While I'd really like to abandon the post light system altogether and change to electroluminescent bezels, today is not the day for that, nor will it be any time soon. Once I actually own the airplane, I would love to zero time the airframe, but for right now, we're enjoying what we have. I'm flying the airplane between 10-15 hours per month (and I'm knocking out a bunch of hood work and cross country time for far less than it would have cost me to do a dry lease on a friend's 150), and loving life.

Any input or suggestions are appreciated. I believe that there was a pretty lengthy thread about dimmer rheostats on here in the not-so-distant past, so I will refer to that for that portion of the repair, but I welcome input for the other topics/questions posed.

Best regards,

Ryan

Ryan, As you can see Cessna calls for felt along the top of the panel (#14,15, and 16). I think you're on the right track with some sort of self-adhesive foam rubber or weatherstripping. Another idea would be to place a bead of RTV along the top of the panel, let it skin over, and then place the false panel in position to mold the RTV down into a light-blocking strip. Might want to lay a strip of masking tape on the top inside of the false panel where it will contact the RTV in case the "skin" breaks--the goal is not to glue the panel to the false panel. Congratulations on all the flying you're doing! I'm envious.

I'm always amazed at your knowledge of how these things are put together, Gary! I guess if I cracked an IPC, I'd be ahead of the game.

I've got two hardcopies and one on the computer. My father gave me one several years ago, and happened upon another one a few days ago. My mother and father have a decrepit sharecropper's cabin on their property that they use for a storage building. My mom needed to go out there to look for an old train set of mine that she wanted to put around the base of their Christmas tree this year, and while we were rummaging, I found two boxes marked "Airplane". They were quickly whisked away to the car and I tore into them upon getting home. Jackpot! All of my grandfather's records of 56D were in there, including several bills of sale, work invoices back tin 1975, some vintage TIC170A memorabilia that I had not seen before, and my grandfather's copy of the IPC from the 1950s. The one I have is pretty old, but is not in the Cessna binding like this one is. In addition to that, I found a mountain of paperwork for our old Bonanza back to 1947, and a small bundle of paperwork for my dad's 1958 172. I even have my dad's temporary airman certificate from when he passed his private back in 1987. I have both his and my grandfather's logbooks...I'm going to give his back after I get my CFI and shame him into getting a medical and doing a flight review with him in the 170.

I'm glad to know that I wasn't too far off base with blocking the light on the top of the panel. Looking forward to what becomes of the post light situation.

Thanks again!

Ryan, along the line of felt, at the local hardware will be a felt like product made by Frost King, used ton insulate around doors and windows. It's pretty cheap. It is about 1-1/4" wide by 1/4"thick. I'd use some contact cement like 3M or Weldwood and glue a strip to the back of the panel Gary pictured.

The felt: My idea (hope you appreciate the Photo shop drawing ): Hard to tell what you call a post light. They come in a few flavors. In this picture on the right is a normal short post light attached to a L bracket. The bulb in the lens. The white wire sticks through the "post" with a small plastic insulator and a small flat blob of solder. This is the center post and can be manufacture from scrap stuff if your handy and I know you are Ryan. The rest of the socket is the "post" The silver colored socket is an brand new replacement for the original Cessna used in the panel. These where available cheap until a few years ago at Newark Electronics. I only have two a friend bought a gave to me. If this is the post light type your talking about, it is very similar to the other post light, The barrel is the outside of the socket and the inside is nothing but the wire sticking through a small phenolic button with a flat blob os solder. BTW the failure for these types of sockets is in the grounding. They rely on the spring tension and clean contact of the mount to the panel. I make all of mine work by simply running a ground wire to the base of each of them.

As for the rheostat, we have a few posts identifying replacements. But there is very little that can go wrong with these that can't be fixed unless the resistant wire winding is burnt out. I'd remove it the rheostat and carefully clean the wire windings where the contact contacts them and also the contact itself. Test with a ohm meter before reinstall to be sure you fixed it.

I found the same problem with my panel and temporarily put some tape across the gap behind the stand off panel. What you quickly discover is that even with this gap covered you still get a light glare on the windscreen coming from the front of the panel because of the tilt of the panel. I ended up making an aluminum panel top cover which overhangs the front by about 1.5 or 2" to block the light. I had an apholstry shop glue some 1/8" foam to the top of my aluminum and then cover it with black vinyl. Turned out really nice all for about $60. I'm out of the country and don't have access to pictures.

Thanks for the replies, guys. Richard, I'll be interested in seeing how much the felt helps...I have to imagine that I'll end up in a similar situation. The issue is that right now the airplane isn't mine, so I can only do so much...but I'll see how it looks when we can block some light and dim what's left.

I did a little digging on the airplane today. After finally finding the correct size socket (I fiddled for over an hour yesterday and after several trips back to the maintenance hangar yielding incorrect sizes, I finally gave up) to take the shock panel loose, I was successful in pulling the panel out just a bit to look behind and survey the situation better. Good thing I did - I found two broken shock mounts. I'll replace all of them as well as the remaining ones are pretty hard and grungy.

There are two missing lamp sockets...my dad knew that one was missing because he took it out. He gave it to me, but it's pretty ratty looking, so I think I will opt to replace it, along with the rest of the others. Even at their current price that is 200% inflated over what they were back in 2008, they're still relatively inexpensive. Newark no longer has them, but www.tedss.com does...same part made by SPC Technologies. https://www.tedss.com/2099000931

With that, I have a couple of questions.

1. Because the airplane has the venturis on the left-hand side, I am inclined to believe that the vacuum system wasn't installed at the factory (or Yuengling, which I understand actually did a lot of these installs), so the airplane likely had the compass originally located in the shock panel. When we got the airplane, the compass hung from the center strap of the windshield. Dad installed a vertical card compass in the airplane when the windscreen was replaced with a strapless one, but he never hooked up the light to the panel lights. I got tired of looking at the wires bundled on top of the compass, so after some investigation, I discovered a hole through which I could pass the wires underneath/behind the panel. When I re-do the panel lights, I want to light the compass as well. I can tie the wiring in pretty well to the top center lamp in the panel, but I would like a way to disconnect it so that I don't have to unsolder the compass lights when/if the shock panel needs to be removed for service in the future. Is there any sort of connector that I can install inline to disconnect the compass light from the rest of the panel lights to make working on the airplane easier? In the modeling world, we use a lot of connectors from JST...do they manufacture anything that would be suitable/FAA approved? Any other suggestions? I'd prefer not to use model airplane parts on this one, not out of specific consideration for regs, but because I would prefer to do a quality job on the work I do on the airplane.

2. I recall a post from George where he gave the specific wire gauges and lengths to rewire an entire airplane, but I'd rather not leave this somewhat open-ended question open for mis-interpretation on my part. What gauge Tefzel would I need for this job? The original wire appears to be 18AWG or so, and the IPC appears to corroborate this.

3. As the shock mount dampers have star washers underneath the nuts, do I need to put any anti-sieze on the threads of the bolts to prevent them from breaking? I thought that perhaps a gorilla broke the two in the airplane, but I was reminded that they could have sheared when they were loosened.

4. Related to the shock mounts - the shock panel in this airplane seems to be almost flush with the panel in the center and there is about 1/4" gap behind it on the ends. Is there something out of alignment or bent? I would expect a pretty even reveal behind the shock panel to the main panel across the entire span.

5. Has anyone been successful with LED lamps in this application? The panel lights aren't so bad, but the landing light is a big drain on the generator. Still, anything to reduce load is welcomed.

6. Related to my desire to replace the the grommets on the piano key switches - it would appear as though the plexi panel needs to be removed to gain access to some of the screws that hold the piano key assembly in place...is this correct? It looks like there are two screws at the bottom corners of the plexi panels that retain it, and the control cables retain it towards the top. I'm betting that it has never been removed, so were they bonded along the top edge with anything? I've never tried to pry behind there (for good reason) and I really don't want to break the plexi panel trying to remove it; I'd rather have the missing grommets on the switches for now.

I'm still trying to decide on what to do with the rheostat. I'm at a bit of a loss with the different resistance values. Ohmite still manufactures a 25W rheostat that Aircraft Spruce sells, but it only goes up to 18Ω. There is a NOS Ohmite Model 'H' 25W/75Ω for sale on eBay, but that's as close as it gets. The rest of the rheostats that I have found are either 5Ω or something crazy like 1500Ω or 5000Ω. Would a lower ohm value mean more finite adjustment of the light, or would it simply prevent the lights from being fully shut off? I'm a little surprised that the panel lights aren't wired in conjunction with the nav lights in that the rheostat is the only thing that keeps the lights off. Doesn't that generate a lot of heat, or does it act like a switch at the far extreme of its rotation?

Please be gentle, I'm not trying to be dense, but I was really to young to be of much help when dad restored the airplane, and I wasn't really asked to help with anything when I got older. Just trying to do the right thing and have a safe, airworthy finished product.

Good find on those sockets.

You don't need anti-seize on the shock dampers.

I would not go through the trouble it is to remove the plexi in order to replace the grommet.

The dimmer rheostat should have an off position that the wiper does not make contact.

For the wire, you would first determine the continuous amps. To do this find the amp draw of each bulb then add them together. Measure the length of the wire run. Then look on a table in 43.13 to determine the wire size and then use a fuse big enough to protect the wire.

Cessna used 18 ga. If you are only wiring the original lights and no new, 18 ga should be good.

It is very common to find knife disconnects covered with shrink wrap in lines going to things like the compass. https://www.aircraftspruce.com/catalog/ ... fedisc.php. There are other methods of course like a Molex connector. http://www.molex.com/molex/products/fam ... troduction

Can't find it at the moment but Gary pointed out that in the instrument equipped planes there is suppose to be two more shock dampers. Maybe this is why your floating panel is bent as you seen to indicate.

Bruce Fenstermacher wrote:Good find on those sockets.

You don't need anti-seize on the shock dampers.

I would not go through the trouble it is to remove the plexi in order to replace the grommet.

The dimmer rheostat should have an off position that the wiper does not make contact.

For the wire, you would first determine the continuous amps. To do this find the amp draw of each bulb then add them together. Measure the length of the wire run. Then look on a table in 43.13 to determine the wire size and then use a fuse big enough to protect the wire.

Cessna used 18 ga. If you are only wiring the original lights and no new 18 ga should be good.

It is very common to find knife disconnects covered with shrink wrap in lines going to things like the compass. https://www.aircraftspruce.com/catalog/ ... fedisc.php. There are other methods of course like a Molex connector. http://www.molex.com/molex/products/fam ... troduction

Can't find it at the moment but Gary pointed out that in the instrument equipped planes there is suppose to be two more shock dampers. Maybe this is why your floating panel is bent as you seen to indicate.

Thanks Bruce! I was wondering what the two large holes were this evening, but looking at the IPC and recalling the discussions that Gary and I had when I was drawing up the shock panels, I see what they are now. I imagine that these mounts are probably kind of hard to come by, but I also believe that they cost less to make than they do to buy. Gary, do you happen to have a dimension for the backset of those brackets so that I may fabricate a pair? I've got all seven holes in the panel filled, and while the instruments that are in there are undoubtedly lighter than the old AN gyros that would have been installed in the 1950s, it's still a heavy load and I think it would be prudent to have the additional mounting points added.

I will ask about the control cable removal, but I have a feeling that it will be outside the scope of this project for now. The airplane has been flying like this for greater than the last 30 years...I think it can wait a little while longer.

Dumb question - I see that Spruce sells two different kinds of Tefzel for each size. I'm assuming the difference is the number of wires inside...much like a CAT 5e/CAT 6 data cable in that it has two individual wires shielded inside a single sheath? The airplane appears to currently be wired with a single separate hot and ground wire. If the new Tefzel wire has two separate wires inside, I only need a single run of wire between my contact points, correct (ensuring maintenance of continuity, of course)?

Rest assured, I'm not striking into this blindly, I'll have close supervision here while I'm doing it under the A&P/IA that works on the airplane, but I have to ensure proper dispersion of my stupid questions before anyone begins to doubt my ability to be around anything that can hurt me.

You don't need shielded wire. This would be used for installations where shielding is required such as audio. This is what you want: https://www.aircraftspruce.com/catalog/ ... dlwire.php

Airplanes, like cars use the fuselage or body for ground requiring only a positive lead for each device. This saved on wire and weight. These are negative grounded vehicles. There are positive ground vehicles as well meaning the body is positively charged and all wires run to the ground side of the power source. Positive ground vehicles ran out of favor in the late 40 early 50s.

Now I can tell you that by this age with these lights sockets and your panel, relying on a good ground is just not going to happen. That is why I ran a separate ground wire soldered directly to each socket frame and then to ground. Your compass, being remotely located, may not have a path to ground. For convenience and looks it wouldn't be wrong to run a single pair of wire in a sheath to the compass. Problem is finding such wire acceptable for aircraft that is not also shielded. In this case I'd just use a piece of shielded cable. Now some might use a single shielded wire and use the shield as the ground. This will work and work fine in this application but I'm not sure how accepted the practice would be.

You can also run two unshielded wires to the compass light but they must be twisted together to keep from creating a magnetic field which will affect the compass.

There are a myriad of ways to do it. Including using those JST plugs. 43.13 calls for wiring and terminals to be of "aircraft quality" or "suitable for aircraft installation". In most cases what I've found is what is considered to be "aircraft quality" or "suitable for aircraft installation" is what the A&P thinks is "aircraft quality" or "suitable for aircraft installation". This is based on his experience, what he last saw or sees all the time in aircraft installations. New fangled stuff is not well received unless it can be shown to meet some standard of AN, MIL, ANSI or other applicable standard that would be good for "aircraft quality" or "suitable for aircraft installation".

Present your A&P with the JST plug which may be perfectly suitable and watch him roll his eyes cause he's never seen that in an aircraft before.

Ryan Smith wrote:
5. Has anyone been successful with LED lamps in this application? The panel lights aren't so bad, but the landing light is a big drain on the generator. Still, anything to reduce load is welcomed.

For the panel lights, you want to google "BA9S 3-SMD 5050 LED"
http://www.amazon.com/Jtech-5050-SMD-Wh ... B00B0I5YM0
They will almost fit - require opening the light hole in the floating panel a touch.

For landing/taxi lights - look for PAR36 LED replacement bulbs. I installed one for my taxi light and never turn the thing off.

Nav Lights are just as easy and there are plenty of sources for replacement LEDs. Get them in the color you need as the white ones don't come out right under red or green lenses.

Ryan Smith wrote:Gary, do you happen to have a dimension for the backset of those brackets so that I may fabricate a pair?

0.25" but you might consider making a slightly deeper hat section and then use washers on the mounts to shim it to a level which matches the panel.

Just an FYI, the correct light bulb, per the Cessna IPC is an 1826 and I found only one source for them at a place called Bulb Town, http://www.bulbtown.com/, they also sell what I call bulb condoms or bulb hoods in different colors as well, as far as the rheostat, mine was shot and I bought a replacement from Aircraft Spruce p/n RHS8RO 0-8 ohm, rated at 25 watts, http://www.aircraftspruce.com/catalog/e ... key=352405, more than enough to handle those lights and is built better than the original I pulled all of my sockets out, found two bad ones and I was able to buy two originals for $50, as I was unable to locate a source for them, now I see that you have and appreciate you sharing that with folks, I did away with all the cloth covered wire, replaced it with more modern wire, ran a ground to each socket and tied it all in with a common ground, its all set to re-install, not looking forward to it, but its a project in the works......good idea you have for the top of the panel to keep stray light, but a better idea would be rubber weather striping that has a wide flange on it, like what is used at wing roots in some other types of aircraft.....

Here's what those switch grommets look like