bobgoodman
New member
today i finished installing, temporarily, a cheap digital tachometer i ordered on the internet. it only cost a couple of bucks, and they are pretty accurate so far as i can tell. i made a bracket that fit on the left side of the motor where a palnut holds the front air scoop in place, and bolted the bracket over it. i put a bicycle computer magnet on the spinner back plate. i put the display in an empty instrument hole.
i just wanted to see how accurate my tachometer is. here is the verdict. at low speeds, the analog tach (the original) runs several hundred rpm low, as compared to the digital. for example, at very slow idle the digital reads about 450 rpm but the analog reads 8-900. at normal speeds they seem pretty close, with the analog only about 100 rpm low at 2000 rpm. from there the analog reads higher again where at 2500 on the digital the analog shows 27-2800.
in essence, i have been running it way too slow. at 2500 on the analog, i was really running 22-2300. i figured it was low, but now i know how much.
no telling how fast it's going to be now. i wanted an accurate reading because of all the interest in counterweight pins wearing out.
you know theres a way to calibrate your tack by timing how many seconds it takes to turn over .1 hour on the tach, but i forget the details. you could find it on the internet if you are interested. as i recall there are 2 kinds of gears in there, depending on the tach, one is set to run off an hour on time at 2500 rpm and one set to run off an hour at 2300. or something like that. in other words, if you have a 2500 rpm tach and you set the prop at 2500, you should tick over .1 hours every 6 minutes. if it takes longer, your tach is reading proportionally low. i forget the exact rpms though. maybe 2550. the needle is driven by a magnet but the odometer is gear driven.
but i'm glad i went ahead and tried the digital tach because the difference isn't constant, it's off more at low rpms and at high rpms.
bobg. it was a very nice day to fly here at last.
i just wanted to see how accurate my tachometer is. here is the verdict. at low speeds, the analog tach (the original) runs several hundred rpm low, as compared to the digital. for example, at very slow idle the digital reads about 450 rpm but the analog reads 8-900. at normal speeds they seem pretty close, with the analog only about 100 rpm low at 2000 rpm. from there the analog reads higher again where at 2500 on the digital the analog shows 27-2800.
in essence, i have been running it way too slow. at 2500 on the analog, i was really running 22-2300. i figured it was low, but now i know how much.
no telling how fast it's going to be now. i wanted an accurate reading because of all the interest in counterweight pins wearing out.
you know theres a way to calibrate your tack by timing how many seconds it takes to turn over .1 hour on the tach, but i forget the details. you could find it on the internet if you are interested. as i recall there are 2 kinds of gears in there, depending on the tach, one is set to run off an hour on time at 2500 rpm and one set to run off an hour at 2300. or something like that. in other words, if you have a 2500 rpm tach and you set the prop at 2500, you should tick over .1 hours every 6 minutes. if it takes longer, your tach is reading proportionally low. i forget the exact rpms though. maybe 2550. the needle is driven by a magnet but the odometer is gear driven.
but i'm glad i went ahead and tried the digital tach because the difference isn't constant, it's off more at low rpms and at high rpms.
bobg. it was a very nice day to fly here at last.
