Panel lights and other questions/observations.

[rframe]

Hi all,

New owner of a '46 Cessna 140 here. I'm loving the airplane, but being that it's new-to-me I have several projects to fix/improve as well as "make it my own".

One small change is I really dislike the bubbly instrument panel overlays on early Cessna's. I removed this one to expose the flat aluminum and plan to refinish that. However I ran into a question...

I found three plastic rear mounted light bulbs that had been covered by the overlay (middle one circled in green). What are they for?

I expected at least one to be a generator warning light, but found they all light up all the time and are wired to each other.

Perhaps some intent to serve as instrument spill lighting, but not at all effective if that's the idea.

Also, while I intend to pull that panel and refinish it, I might get a new panel cut in the future. I think there are plenty of CAD-based online fabrication shops that will cut and ship a blank to my specs easy enough, but wondering if anybody has specific sources they can recommend?

Finally, the ammeter is on the load side at all times, so that even if the generator is running it's showing the total load on the system via discharge reading. This seems odd to me but is it normal in these airplanes?

I do have a cigarette lighter USB charger with a digital voltage readout, so I can see when the generator kicks in thanks to the voltage spike, but I'm thinking I want to rewire the ammeter in line with the battery so I can see if it's being discharged or charged.

[6277]

I found three plastic rear mounted light bulbs that had been covered by the overlay (middle one circled in green). What are they for?

I was curious and looked at the parts catalog. They are instrument lights (Grimes) designed I guess to reflect light off the back of the cover.

My 1947 140 has the same system only with six Grimes lights controlled by a rheostat.

[6277]

Here's a link to the parts catalog.

https://cessna120140.com/wp-content/upl ... 120140.pdf

[rframe]

Here's a link to the parts catalog.

https://cessna120140.com/wp-content/upl ... 120140.pdf

Awesome, thank you!

[edidin]

Hi all,

New owner of a '46 Cessna 140 here. I'm loving the airplane, but being that it's new-to-me I have several projects to fix/improve as well as "make it my own".

One small change is I really dislike the bubbly instrument panel overlays on early Cessna's. I removed this one to expose the flat aluminum and plan to refinish that. However I ran into a question...

I found three plastic rear mounted light bulbs that had been covered by the overlay (middle one circled in green). What are they for?

I expected at least one to be a generator warning light, but found they all light up all the time and are wired to each other.

Perhaps some intent to serve as instrument spill lighting, but not at all effective if that's the idea.

Also, while I intend to pull that panel and refinish it, I might get a new panel cut in the future. I think there are plenty of CAD-based online fabrication shops that will cut and ship a blank to my specs easy enough, but wondering if anybody has specific sources they can recommend?

Finally, the ammeter is on the load side at all times, so that even if the generator is running it's showing the total load on the system via discharge reading. This seems odd to me but is it normal in these airplanes?

I do have a cigarette lighter USB charger with a digital voltage readout, so I can see when the generator kicks in thanks to the voltage spike, but I'm thinking I want to rewire the ammeter in line with the battery so I can see if it's being discharged or charged.

The three bulbs reflect light off the interior of the cover plate (which you suggest is not to your liking). Mine work very well and come on with the NAV lights, and like yours all light up at once.

The ammeter in my plane works as you describe, which I call "Piper" style since they wire their ammeters thusly and not to show discharge/charge as Cessna typically does. Personally I prefer it that way as can see the total load at any time. For example, after a start, the load will briefly spike to maybe 20 amps as the battery recharges. My plane has the alternator conversion though. Voltage is seen on the EFIS AI so both can be monitored at once.

[simonlowther]

Your ammeter appears to be wired as a load-meter (piper do this) but is not correct for a Cessna. Piper ammeters have a 0 on the left and show total alternator output. Cessna ammeters have the 0 in the center with a - and + either side showing battery charge or discharge.

I guess its personal preference as to which is superior but I note that my little generator can have a positive output with the battery still discharging, the piper style would never show this but the Cessna type do.

Kindest
Si

[8474]

I also use a cigarette lighter USB charger with a digital voltage readout to confirm my gen is doing its thing. My ammeter just bounces around all the time....

[6643]

The ammeter is supposed to show current into and out of the battery. (Except starter motor current). If not, why would you have a zero center meter? Yours is wired incorrectly. It could be as simple as the generator wire being on the wrong (battery) side of the shunt.