C120 Avionics Upgrades

hamer

hamer

Pre-takeoff checklist
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hamer
I'm a new owner of a 1946 C120. I'll hopefully be doing an alternator conversion soon, and after that I'd like to do some avionics upgrades. I'm a new private pilot (115hrs TT, 50hrs TW). I'll be starting my IFR training soon (not in a huge rush at the moment) and it would be nice to do some of the training in my airplane. I never intend to take it into IFR conditions, but I think it's good training to be prepared for unintended IFR.

Anyways, my mission is mainly day and night VFR flight, weekend XCs (cruise is 130mph). I'd like the updated panel to give me a little more confidence at night and more convenience during the day. I plan to keep the airplane 3-5+ years. I know I won't get all my money back, but I don't mind if I get enjoyment out of it. I also don't want to digitize too much, I'd like to keep the spirit of the airplane.

I have a basic 6 pack (in an unconventional pattern) along with 1 nav/com and 1 ADF. Photo attached. My current attitude indicator occasionally tumbles, so I'm using it as an excuse to replace it.

My goal is to plan out all the wiring diagrams and have it reviewed by my installer. I'm not an A&P/IA, but I do enjoy understanding what goes on under the hood.

Current instruments:
Airspeed Indicator
Attitude Indicator
Vertical Speed Indicator
Altimeter
Heading Indicator
Magnetic Compass
Turn Coordinator
NARCO MK12E Nav/Com w/Glideslope
KR 85 ADF w/Indicator
Sigtronics 2-place intercom
Garmin GTX327

Planned upgrade:
Remove:
Attitude Indicator, KR85 ADF, Intercom

Add:
Garmin G5 w/magnometer, GPS antenna
Garmin GTR200

Maybe:
Replace GTX 327 w/335 or TailBeacon install

The Narco Nav/com works great, however the com isn't very clear due to the sigtronics intercom, so my intent was to use the GTR200 as the primary com/intercom and only use the nav half of the narco. I really don't need the second radio, and I don't want to complicate the install with a second antenna and audio panel to manage the two. This is a priority for me since I fly in busy airspace and clear coms are important. I'm also having issues with the sigtronics squelch and I'm hoping the GTR200 will fix that. I'd also like to move the headset plugs to behind the seats to keep the cords out of the way. Tempted to add a Bose lemo connector as well, but that is still up in the air.

The G5 is where most of my new capability will come from. With the magnometer and GPS antenna I'll get just about everything I need out of it for VFR flight. It will also give me a decent platform to do some IFR work.

Anyways, I think this gives me a solid upgrade in capability and convenience without breaking the bank. I also feel like I'm maintaining the spirit of the airplane and adding some value to it when it comes time to sell. I'm happy to hear any suggestions based on what I've chosen. I'll also be posting my wiring diagrams for review when I finish them.
Panel.PNG
 
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GeorgeC said:
Congrats on the bird! I'm happy with the GTR225 and GTX335 I put in my 140.
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Thanks George! Any photos of your panel? How did you wire the 225? Did you relocate the plugs? Or leave them in the panel?
 
I left the plugs in the panel and just used the builtin intercom:
img_0411-jpg.65180
 
I’d just toss in a HSI (maybe that new round style glass one) and 430
 
James331 said:
I’d just toss in a HSI (maybe that new round style glass one) and 430
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I’ve been contemplating a 430 instead of the GTR200 and completely replacing the narco. But for $5k i don’t know if it’s giving me enough capability over the G5 w/GPS and ForeFlight.
 
Well I fly in some major weather with GNS series, it’s still the working plane standard
 
Man I thought I was really upping the avionics in my 140 when I bought the really nice suction cup mount for my iphone to run foreflight on! lol.

Congrats on the 120, you will love it. I'm not much advice on avionics but couldn't resist a little banter and panel pic swapping with another 120/140 guy. IMG_2535.JPG
 
If you could replace or DG with one of these, it would make for a easy swap and clean look with a GNS replacing your existing radio, I’d think that would be all you’d need right there

https://aerovonics.com/av-30
 
Leave that beautiful instrument panel alone. It is half the value of your aircraft. cut it see how difficult it will be to sell.
 
GeorgeC said:
Thanks. It's on the yoke, above the N number.

Oh, and wait until after your first annual before you start upgrading avionics...
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Because of the unknown costs of it?

Tom-D said:
Leave that beautiful instrument panel alone. It is half the value of your aircraft. cut it see how difficult it will be to sell.
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There is no cutting in my plan, everything is a swap out.
 
hamer said:
I’ve been contemplating a 430 instead of the GTR200 and completely replacing the narco. But for $5k i don’t know if it’s giving me enough capability over the G5 w/GPS and ForeFlight.
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Dump the NARCO, and install a talcum 2000, and update the transponder to ADSB compliant
 
Tom-D said:
VAL-COM 2000
damn auto correct
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That's a nice unit, but for more than the garmin I'm not sure what it's getting me. And I don't want to ditch the NARCO completely because I use the VOR. The ADF on the other hand I'm happy to sell.
 
I test fit the G5 the other day, I think it looks pretty good. It's running off the backup battery here. I'll have it installed after my alternator conversion which is hopefully happening next week.
G5.JPG

I did run into a question about the PTT circuit on the GTR200. Per the wiring diagram, there is a 3rd wire that goes to the mic jack that the PTT switch operates. I plan to put the plugs in the back behind the seat. This means I need to run a separate wire all the way to the back, then to the yoke for the switch? I can't just get a 3 conductor cable and use that? I'm not sure if having that PTT wire in the same shielding will cause audio issues?
PTT.PNG
 
hamer said:
I test fit the G5 the other day, I think it looks pretty good. It's running off the backup battery here. I'll have it installed after my alternator conversion which is hopefully happening next week.
View attachment 71665

I did run into a question about the PTT circuit on the GTR200. Per the wiring diagram, there is a 3rd wire that goes to the mic jack that the PTT switch operates. I plan to put the plugs in the back behind the seat. This means I need to run a separate wire all the way to the back, then to the yoke for the switch? I can't just get a 3 conductor cable and use that? I'm not sure if having that PTT wire in the same shielding will cause audio issues?
View attachment 71666
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Bottom line is that if you pull pin 35 (PTT) to ground it will transmit.

PTT is really a discrete but has been wired to the jack for decades because you can plug an in-line PTT switch into the mic jack make make it work.

The same thing is happening on Biz jets, the oxygen mask has its own PTT button. Some headsets have their PTT button too. So if that isn't wired to the jack those built in PTT buttons won't work.
 
bnt83 said:
Bottom line is that if you pull pin 35 (PTT) to ground it will transmit.

PTT is really a discrete but has been wired to the jack for decades because you can plug an in-line PTT switch into the mic jack make make it work.

The same thing is happening on Biz jets, the oxygen mask has its own PTT button. Some headsets have their PTT button too. So it that isn't wire to the jack those built in PTT buttons won't work.
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Ahh I see. So if I don't wire it to the jack that just means an inline PTT switch plugged into the jack won't work?
 
Making some progress here. I took the headliner home and mounted new jacks with a bose lemo on each side. Will be running the wires up to the radio this weekend.
jacks-01.JPG jacks-02.JPG jacks-03.JPG
 
Love the plugs behind you- in our tiny cockpits that bit of clutter gone is nice. I want mine moved to back as well...
 
Can you really get 130 mph out of a C120?

Does the metal skin eliminate the issues of a fabric plane of that vintage? I was looking st Champs for LSA but if I clear Basic Med, a 120/140 is interesting.
 
Terry M - 3CK (Chicago) said:
Can you really get 130 mph out of a C120?

Does the metal skin eliminate the issues of a fabric plane of that vintage? I was looking st Champs for LSA but if I clear Basic Med, a 120/140 is interesting.
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Its just a matter of which issues you wish to deal with. Corrosion or deterioration.
Fabric you can change.
 
Hey guys... please get some of these pictures and discussion over on the Cessna 120-140 forum. The group will really benefit from it.
 
Huckster79 said:
Love the plugs behind you- in our tiny cockpits that bit of clutter gone is nice. I want mine moved to back as well...
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I’m excited to have the headset cords over my shoulder and out of the way! I’d definitely recommend it!

Terry M - 3CK (Chicago) said:
Can you really get 130 mph out of a C120?

Does the metal skin eliminate the issues of a fabric plane of that vintage? I was looking st Champs for LSA but if I clear Basic Med, a 120/140 is interesting.
Click to expand...

I’ve seen as high as 140mph but I have an O290D and a huge prop, I think most cruise in the 105 range

Rob58 said:
Hey guys... please get some of these pictures and discussion over on the Cessna 120-140 forum. The group will really benefit from it.
Click to expand...

I’ve been meaning to make a build thread over there, been doing a lot of work on mine since I got it in November.
 
7D257B31-FE70-43CB-AD03-F9A4BB6B846B.jpeg 4D6A02E2-4016-42DA-9845-A055103BA2AE.jpeg 84D2628F-BACC-4233-9EA1-78B0EDF0EF65.jpeg
Well since we’re posting pictures of our 120/140 panels.....

To the OP, it would REALLY be good to train with a conventional six pack, but I fully understand that there are times in life when you just do what you have to do.
 
Terry M - 3CK (Chicago) said:
Can you really get 130 mph out of a C120?

Does the metal skin eliminate the issues of a fabric plane of that vintage? I was looking st Champs for LSA but if I clear Basic Med, a 120/140 is interesting.
Click to expand...

With a strong engine and the right prop, I can easily see that 130 indicated could be in reach. Mine comes short of that, but she is heavy with a 46 pitch prop, with a tired O200A, but she gives over 110MPH indicated with no effort. A strong O200 with a 48 or 50 should deliver that kind of speed no problem.

With modern synthetic materials, the fabric will last for decades if kept hangared. Mine was recovered in 1980 and is still in perfect shape. If not recovering yourself, but rather buying a used plane, the trick is knowing if it has been kept hangared.
 
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MBDiagMan said:
With a strong engine and the right prop, I can easily see that 130 indicated could be in reach. Mine comes short of that, but she is heavy with a 46 pitch prop, with a tired O200A, but she gives over 110MPH indicated with no effort. A strong O200 with a 48 or 50 should deliver that kind of speed no problem.

With modern synthetic materials, the fabric will last for decades if kept hangared. Mine was recovered in 1980 and is still in perfect shape. If not recovering yourself, but rather buying a used plane, the trick is knowing if it has been kept hangared.
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The real trick is, knowing what system was put on, and what to expect from that system.
 
@MBDiagMan @Tom-D what spooked me on the Champs was the fabric. I can’t do the fabric work and I read to recover well exceeds the cost of the plane.

Tom - I first watched you on the AOPA board refurbishing planes. If I had to pay someone to recover (and fix ribs etc) would that exceed $30k?
 
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