Electronic Engine RPM Tachs -Thoughts

Very reliable. Solid state with a photo cell pickup. They are usually accurate within 100 RPM. Good if you care about your engines, especially 4 strokes, which can't be leaned by sound alone. Dr.1 Driver "There's a Hun in the sun!"

On 12/23/2003 8:40 PM Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:

If you have a 4 stroke, you need one. Tuning a 4 stroke PROPERLY without one is impossible. I would also highly recommend using them on ANY engine for tuning.

Dr1Driver opined

You can check the accuracy using a florescent light. Lights turn 3600 rpm.

-ash for assistance dial MYCROFTXXX

Hangar 9 has a sweet little micro electronic tach for under $30. Good deal...

Its almost imp[ossible to make a frequency counter/rpm meter that isn't crystal controlled - they woould be SO innacurate and crystals are cheap.

Its like watches. Digital ones are cheap as chips and a hundered times more accurate.

If you measure line frequency and it shows off, its more likely the line frequency itself is slightly off than the tach is innacurate, frankly.

Four strokes can easily be leanded by sound alone. I have been racing them for over ten years and adjusting by ear. Of course, if you cant tell the difference between lean and rich, maybe you need some help.

Thanx, I picked up the Hangar 9 version ---now to build either a test stand or just mount the engine in the plane.....

thanx again....

I agree Paul, some of the manufacturers instructions to drop off the max rpm's by 200-300 using a tach just won't get it right(especially

91AC's), but you can tune them fine by ear if you have a little experience and an eye for exhaust vapors. Of course, I've known guitar players that couldn't tune without a digital tuner too. My advice to newbies is to spend their $39 on something more useful. I know that with your experience you have noticed that the "engine tweakers" (usually with tach in hand), are guys that seem to have the most engine trouble. Tachs and gauges are fine but every engine takes on a new set of running perameters whenever its application changes and having worked for a long time in a race engine performance shop it never ceases to amaze me how a small load characteristic change can produce remarkable dyno and exhaust temp variations. This stuff was never evident until we started to use chassis dynos which show you the whole picture. Prop, fuel, drag, and atmospheric variatons produce the same variations in model airplane engines and for a flyer to rely on a tach reading to say that the engine is tuned right, is tunnel vision.

Phil AMA609

Only 2-bladed lights turn 3600 RPM. 3-bladed lights turn 2400. 8-)

You mean three phase lights :-)

50 or 60hz? Depends on the country.