The International Cessna 170 Association

All,

Any seen this before: tach is bouncing high rpm, much like the indication of a cable problem. Tach needle then drops to zero. Tach still counts hours.

Mitchell is quoting 1 month + for getting out a marked tach. Really tempting to just put a blank/unmarked tach in there.

There are only so many times I can wash and wax it in lieu of flying.

I'm referring to washing and waxing the plane. For clarity.

This is not a paid advertsment for EI instruments but they have a very good tacho that doesnt have drive cables to break or leak and is totally electronic . Yes it has to be set up correctly due to different mags fitted to our aircraft but its not rocket science . Plus it has many additional features that you will love . Your issue with your tacho could be a worn or partially bad drive cable or internal bearings worn. Compare the cost of overhaul of steam gauges and the cost of electronic gauges , the gap is closing.

I still prefer the mechanical tach to the EI tach with the ring of led lights, and they are still about $200 cheaper. My old one wasn't as bad as the OP's but it still had about a +/- 50-75 RPM waver in it. I put a new one in at the last overhaul, and haven't regretted it one bit. VERY smooth and accurate. The custom markings only added about $25 to the price. IRRC, this is a Mitchell brand.

I installed a new Mitchell with custom markings and hours preset. Great product, but 4 or 5 week delivery. I bought it through Spruce.

Here is a very good source for instrument repair. They even repair antique instruments for vehicles.
http://keystoneinstruments.com/

John

Just so everyone knows I am sort of for the electronic tachometers. I have an old school Hartzell prop rpm checker and most steam gauge tachometers are off by at least 75 rpm and many lots more that go into 150 rpm plus. I have guys wanting their props or governors adjusted and I first do a tach check in cruise and find them to be reading low so they already are at the rpm they are supposed to be and on a few occasions higher.

I wouldn’t trust an electronic tach either until I’d checked it against a known instrument. Many people think that digital is automatically more accurate, but that just isn’t the case. Im not against electronic tachs per se, as I made my living working with electronic instrumentation. I just don’t care for the presentation on the EI.

Most turbine aircraft have electronic instrumentation and EI has features on it like time of this flight and a digitial numerical read out of RPM however mine has a green outer ring of lights with red leds for over speed. Checked it out with 2 digitial strobe tachos and all 3 were with in 7 rpm. [we had problem with a prop gov on the super decathlon also and the mechanical tacho wasnt accurate enough in that aircraft plus it was a good opporunity to play with the strobe tacho,s]

epeter786 wrote:All,

Any seen this before: tach is bouncing high rpm, much like the indication of a cable problem. Tach needle then drops to zero. Tach still counts hours.

Mitchell is quoting 1 month + for getting out a marked tach. Really tempting to just put a blank/unmarked tach in there.

There are only so many times I can wash and wax it in lieu of flying.

Aircraft Spruce says they only need a 14-day lead time to set custom inst. markings as well as set the displayed tach-time.

ghostflyer wrote:Most turbine aircraft have electronic instrumentation and EI has features on it like time of this flight and a digitial numerical read out of RPM however mine has a green outer ring of lights with red leds for over speed. Checked it out with 2 digitial strobe tachos and all 3 were with in 7 rpm. [we had problem with a prop gov on the super decathlon also and the mechanical tacho wasnt accurate enough in that aircraft plus it was a good opporunity to play with the strobe tacho,s]

Most of the turbine equipment I've flown had electronic instrumentation.... for installation simplicity...but the presentation has an analog display.... because trend is easier to notice by a pilot than the constant "dance" of digits which become a meaningless distraction.

I tried a digital EGT gauge in my 206 and subsequently removed it and gave it away because the constant dance of digits, while perhaps exact, were useless.

I'll stick with original analog tachometer in my airplane.

I'm guessing the 14 days through Aircraft Spruce is a standard time. I ordered through them, and the invoice even quoted that lead time. It was only after I got to 14 days and called that they told me about the extended time.

No big deal - I should have just called to verify when ordering.

Anyway. New Mitchell tach is in. The response is amazing. With the original, I would set a moderate MP, and then wait for the tach to catch up... in time. Not a bad, gentle approach to flying the plane, but the difference is really noticeable in the instrumentation.

Did you stick with the old cable or install a new one?

When I replaced mine i used the existing cable. Offhand I don't know how old it is. FWIW, I replaced the tach because I needed to re-mark the ranges for my new prop, not because the old one malfunctioned, and it cost about as much for a new tach as to have a shop repaint and certify the old one.