Standard Aircraft Clock

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Mike21380

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Mike
I’m not sure where to post this one- it’s kind of arcane, so here it goes: Today while riding in my flight schools 1973 Cherokee 140 while it was towed to the pumps I started playing with the clock. In all my time flying I admit having never looked at, nor bothered to tinker with the original clock installed on the instrument panel of any plane I flew, it was truly an after thought. I either used the timer built into the Garmin transponder, the GPS, or a good, ol’ fashion wristwatch. So, is the clock electrically powered in an old Cherokee? And if so, does it draw current even when the master switch is off? The Cherokee Cruiser POH didn’t say a thing about it, and the electrical system diagram doesn’t have every circuit posted, so I didn’t see it there either. Curiously, the knob on the clock seemed to click, like I was winding a spring, when I turned it (it turned out you had to pull the knob out to set the time). So is it an old fashion mechanical clock? I did wind it up and the second hand started ticking. Either way, the time I set while sitting in the plane with the master switch off held as I flew, which was actually more convenient than I ever thought. So, how does the standard-issue, panel-mounted clock work on the garden variety Cessna or Piper?
 
The wind up ones are usually Waltham 8 day movements.
never wind them fully.
 
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Thanks! Seems I remember the clocks in the 1960s/1970s era Cessnas I’ve flown having the word “electric” printed on the front, like the Borg images I found online- and yep, the clock in the Cherokee functioned exactly like the instructions on the Waltham website... so I’m guessing it really was a mechanical clock. Kinda cool, add “Clock: SET/WOUND” to my pre-start checklist! Now, let’s go fly some holds and procedure turns ;-)
 
Mike21380 said:
Thanks! Seems I remember the clocks in the 1960s/1970s era Cessnas I’ve flown having the word “electric” printed on the front, like the Borg images I found online- and yep, the clock in the Cherokee functioned exactly like the instructions on the Waltham website... so I’m guessing it really was a mechanical clock. Kinda cool, add “Clock: SET/WOUND” to my pre-start checklist! Now, let’s go fly some holds and procedure turns ;-)
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183593368237
 
My '63 C172D came with a windup 8 day clock in the panel, Cessna p/n CM2629N1. I replaced it with a Davtron LC-2 battery operated quartz chronometer in 1999, but still have the mechanical clock somewhere.
 
Dana said:
Why? How do you know when to stop?
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If I remember, it no so much about not winding fully as overwinding. You stop at the first sign of resistance. Use a light touch and you will feel it (like using a light touch on a stick or yoke).
 
My '60 SAAB automobile had an 8 day wind up clock.
 
Can't remember who, but someone in another thread said they have an 8 day clock and their goal was to fly often enough that they'd never have to reset the time.
 
The original cherokee's came with the Wakmann wind-up clock. Wakmann went out of business decades ago, and there are no parts. I had mine repaired by a superb watchmaker about 15 yrs ago... He was delighted to see a masterpiece of watchmaking. He cleaned it up, and it ran beautifully for about 10 yrs. Then it just gave up. With no parts, I pulled it out and installed an electric clock.
 
Doug Reid said:
This thread really makes me feel old. We have the initial post somehow reminding me of an archeological dig where they find a sundial....how does it work...how do we set it ..do we wind it or is it battery powered ? Sorry, I just couldn’t resist. I was told recently that they are removing all the wall clocks in our schools...the kids were not taught how to tell time..go figure.
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My wife solved that when she was teaching. She covered the digital clock on the wall with an analog one (that I gave her and all the numbers were equations). This was a 6th grade class (later a 5th grade one). She forced them to learn to read a real clock. :D
 
At least some of the "Cessna" clocks were a hybrid of electrical and spring mechanisms. Just like automobile clocks in the 60'3, 70's. As the spring un-winds it eventually gets to a point where a "tang" closes an electrical circuit that actuates a cheap solenoid that winds the spring with a single shot movement thus opening the contacts. The process continues until the contacts become so pitted and oxidized that they no longer complete the electrical circuit thus resulting in the spring un-winding totally and the clock stops. I have repaired such a clock multiple times simply by opening the case and using a small file to "brighten up" the electrical contacts. Also, a 0.01 mfd disk capacitor across the points helps reduce the usual "spark" as the contacts open just like a condenser on an automobile distributor. BTW, these clocks do obviously require a constant source of battery voltage even when the a/c master is off. On my old Skyhawk this circuit had a small fuse in the line to the battery.
 
My plane has an Elgin 8 day clock. But it's a homebuilt, almost certainly a used instrument from another aircraft.

It's flaky, won't keep running if the engine isn't running and even they I have to tap it to get it moving at first.
 
Doug Reid said:
My old clock did the same thing until I got it repaired. It needed cleaning and lubrication. There is a local clock repair guy who knows his stuff.
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What did that cost you?
 
I had a Wakeman 8 day in my plane. Supposedly ran 8 days without winding, longer if you wound it. The only problem is that it didn't work in the plane. I took it out and set it on my desk and it started running. Figuring I had jarred something loose I put it back in the plane where it promptly failed to run. I took it out (it's still on the bookshelf) and replaced it with one of those cheap Ashteck digital things. The only problem with the latter is when the battery starts to go dead in the thing, it stops keeping good time. I had fun on my instrument training as the timed turns weren't working and the instructor noted I was taking way too long according to his watch. Sure enough I switched to another timer (they seem to build timers into every modern piece of avionics now) and gave up on the ashtech which was losing 20 seconds or so a minute.
 
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