What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Checking the tachometer for accuracy

AN23

Well Known Member
My plane, a IO-360/CS equipped RV-8, had me questioning the accuracy of the tach. Before I did my panel upgrade, the old round dial, first generation, Westach electronic tach would show just below 2700 rom on takeoff. After installing the Dynon, it showed 2540 rpm max rpm. Ok, which is correct? I was going to have a friend bring his prop balancing equipment and get him to check it even though I HATE doing full power run ups on the ground. The thought occurred to me that perhaps there's an app that can do it. Well, there is! It's called Video Tachometer and it works perfectly. What I did was set the app to 2540 (max rpm observed on Dynon with prop control full forward) then took off and once at altitude, I pushed the prop control full forward. The Dynon showed 2540 rpm. I then held the iphone up to the windscreen and the prop was stationary on the iphone screen meaning the rpm set on the app exactly matched the rpm shown on the Dynon! Now, I know that the Dynon is correct and I avoided the full power ground run. Next up, governor adjustment!
 

Attachments

  • C84875AC-A995-4BE3-99BC-A971001CE395.jpeg
    C84875AC-A995-4BE3-99BC-A971001CE395.jpeg
    1.1 MB · Views: 214
Nice get. This probably means more capable apps will follow soon. Can't wait to play with it.

You can be off by by some multiple/order but should be fine for a lot of applications. You can check cal @ 60 Hz via the power grid. Cool.
 

Attachments

  • 60Hz pic.png
    60Hz pic.png
    433.3 KB · Views: 112
Last edited:
I have an iPhone app I use that is a strobe. I use it for RPM's on HVAC blowers and it is very good at exact RPM but needs to be dark enough to see the strobing phone flashlight. This looks like a good app for my application as well.
 
I checked the tach on my old RV-4 by running it at night under (I think) sodium vapor lights, which were in effect a 60Hz strobe. Something like that..
 
Tachs

Be careful using apps that are not calibrated. Back it up with a second source.

Trust but Verify!
 
Back
Top