Tachometer

[OR75]

My A&P compared the prop RPM and compared with what the tachometer indicated on my J.  The difference is about 100rpm (depending on RPM range).

Anyone had same experience ?. My tach needle also tend to vary although I cannot detect an RPM change based on sound.

Anyone had the same experience ? Any recommendation ? change tachometer ?

 

 

[N33GG]

Only 100 rpm error? You should be grateful! The mechanical instruments can be off by much more than that, and not be unusual.

Several years ago, I bought one of the small electronic handheld optical units (PropTach I believe) and carry it with me when I fly either my aircraft or others.  It is amazing how many tachs are off, by how much, and to the surprise of the owner.  Errors I see are often on the order of 200 to 300 rpm.

The tach in my Mooney completely died last year, and I purchased an electronic tach made by EI.  It is digital, and I miss the plain needle tach that has been so familiar to me for so many years.  But the new tach is digital and clearly more accurate than analog mechanical tachs.

If you want absolute accuracy, consider a digital electronic tach, such as the units made by Horizon or EI.  Another option is to get your mechanical instrument calibrated (a previous aircraft I owned had a tach that was way off, and after I had it calibrated, it was amazing how accurate it was after calibration).  Or, purchase a handheld unit such as the PropTach, and get an idea where your tach is off, and by how much (kind of like a compass card for your tach).

Only off by 100 rpm, maybe you should be grateful. :-)

[davbert]

Here is a down and dirty tach accuracy check. it only works at night.

When operating in the presence of hangar or ramp lighting (other than incandescent lighting), the prop will strobe at a multiple of 60 Hz in North America, 50 Hz in Europe.  if your prop doesn't strobe at 1200 RPM you should investigate your tach accuracy usnig.

 

Dave

[pjsny78]

I’m not a mechanic but I just had my mechanical Tach checked just a few days ago and it was only off by 25rpm. The technician said it’s very good to be off by that much. I’m not sure if this helps you at all but just wanted to give you an idea.

[OR75]

Thank you all for the input. I prefer the needle (analog) tach. It looks like it is not too expensive to replace but I wonder if the issue maybe with the cables or the tach unit.

[jetdriven]

Our AC tach ws off by ~150 RPM we discovered when we bought it. The seller had it overhauled at the annual/sale but it still is off by 50 RPM.  ther eis another thread that discusses the fact that it also counts off time faster than it should.  We are replacing it this annual.

[gregwatts]

I recently had my tach checked to find out that it was reading ~80 rpms high. The tech....at a reputable prop shop at LNA.....told me that it is not necessary to replace the tach. Apparently, most tachs have an error.

If it bothers you and money is no object, replace it....but otherwise......just manage your power accordingly.

My opinion only!

[DaV8or]

Here is a tachometer option most over look when dealing with a wonky tach. Most either have their original tach overhauled or worked on, or they get some digital tach like the EI one with digital read out. However, If you like the analog needle look and function of your original tach, but would like electronic reliability and accuracy, UMA makes an electronic, analog needle display tach that is TSO'd and legal with our planes.

UMA Electronic Tach

[KSMooniac]

My tach is also high, and I had it overhauled a couple years ago with no improvement.  I haven't replaced the cable but am thinking about it.  I too like the analog display (instead of the EI or Horizon variants) but might just upgrade my engine monitor to include MP and RPM and forget the original tach.

When I had a windows smartphone, there was a great app that measured RPM from the exhaust sounds, and it was exceedingly accurate when compared to an optical tach I used at the same time.  There isn't an Android app with the same functionality that I can find, unfortunately.

[Ncbosshoss]

We have our JPI set to display RPM full time and it is about 50 off our analog tach.

[OR75]

Anyone has all the part numbers for tach system for a '78J ?