I have a Tower Hobbies Digital Tach and trying to tach a G-38 Engine with 18 x 10 Wooden Prop. I am getting a reading of 10,300 and that does not sound correct. The figure keep changing by large amounts. I changed the battries in the tach and tested it by aiming the tach at a light bulb. The figure on the tach was correct with the light bulb, 3,600.

If I paint a couple bands on the prop, will the tach pick up better?

thanks,

Ed

sometimes pointing the plane into the sun and taching it works better. Also it's importatnt to always put the tach in the same spot when taking readings. IE, I always tach my engines from behind the plane, on the right side right where my cowl and fuselage come together.

Be sure to not move the tach around when you're taking the reading. For a G-38 with an 18-inch prop, that might be a correct reading. Be sure the tach is in two-blade mode, not 3-blade.

Dr.1

No G38 ever made will turn a 18-10 at anything close to 10,000...
You might get 9000+ with an 18-6

A G-38 with an 18-10 woodie should be turning in the low to mid 7s...Your numbers are an unrealistic figure for that size engine...

EMF has thrown my tack off. I have an electronic ignition. I would think a magneto might be worse???

Like Bubba said, keep the sun on the opposite side of the prop from the tach. No matter if you are reading it from the front or back. These little tachs need the light behind the prop to read properly.

Well I fought this unstable/is it correct? tach problem for awhile and got really tired of it with stuff that was sensitive to where the sun was or shadows interfering with readings.

Then Fromeco started building TNC tachs again and that solved my problem... [8D]

http://www.fromeco.org/shop/atnc%20tach.htm

You can buy them direct, or there are several other vendors that stock them. They are a little more money but pretty much eliminate the problems you've noted. Those tachs were very well thought of around here from what I was able to find, but had gone out of production until Fromeco got the rights to build them again. Try it, you'll like it!

I use a Stihl electronic tachometer, which reads the pulse to the plug rather than the light through the prop. Any Stihl saw dealer could show you how these tacks work.