Hi Guys,
It is sometimes easyer to tach a engine from behide the prop will adjusting the hsnv, is this as accurate as taching from in front or not?
thanks,
Frank

just as accurate, even with a crappy tach.




dave

It's safer.

Most tachs use a photo cell so as long as it can "see" a contrast between the prop and the background it should be accurate.

On saturday I was breaking in an engine on a stand reading the tach behind the prop. I moved to the front just to see if it changed - no difference in the reading.

The only place you should be standing doing a tach check or any other time your bring the motor upto full poweris behind the prop. I had a buddy of mine shread a 28" carbon fiber prop when doing a run up and it would of done some serious injury had ther been anybody to the side or in front of the prop at the time.

well said stay in the back jack

Yes, from the back of the prop - the only really safe place.

I have foud that checking with the sun behind you can affect the reading. Dont go in front if this happens, turn the plane around.

Hi!
Why wouldn't it be the same....?? Same prop ! Same rpm!

I think it's a good thing to point out that you should not have ANYONE or ANY part of your body in front of a prop when you bring an engine above an idle.

Taching in front of an engine??? does anybody do that??? SCARY!!!!!

those with the antiquated direct contact tachs still do, i'm sure. at mile square park in the mid eighties i remember seeing one get caught in the prop of a .60....nobody got hurt but it sure did scare the crap out of everyone around.



dave

I got the Fromeco TNC tach and it doesn't matter much where the sun is. You can run up the engine standing and holding it at the stabilzer, and get a reading. No more holding the tach an inch from a prop at wide open throttle. I never liked that while the tach readings bounced around.

Fellows: I have been having trouble taching my engines in low light situations especially when running an engine on the test stand during the break-in run. Even using a flashlight has not worked. I am using a Thunder Tiger ventage tach. What is the story on this Fromeco TNC tach, and who sells them? Think it would be a good idea to upgrade this important tool.

Rich S.

Rich,


The biggest difference between the Fromeco TNC and the GlowBee/Hobbico/Tower is that the latter can be had for 'a twenty', while the former will require one of those deeply scrutinized $100 bills.

They work pretty much the same and neither will work in the dark (you shouldn't be running an engine with a spinning prop in the dark either...).

You get more accurate readings from the TNC over the Hobbico level tachs. It is easier to get a lock on RPMs with the TNC and from a greater distance. I've seen the original TNC tach a prop from behind the engine (about 6 feet away). I have the newer one, and it always reads fast from 2-4 feet away, as when I'm holding the plane with the other hand. It is far easier to get readings without bothering where the sun is. I've never had to position a model to get readings like you have to do with the Hobbico. I don't know about low light levels with the TNC. I had my test stand under a covered deck before I bought the TNC. I would use a large flashlight then.

Is it worth the extra money? I would have to say that it is once you actually have it and get to use it some. It is different. I happened to have the extra $$$ at the time, and was tired of cleaning the lens and hoping that my readings were right. Bottom line is that it is more reliable and far safer to use. This is a personal opinion.

Thanks Dar for the price difference on the tach units. No, No, I am not running an engine in the dark, but just next to the 10' shop open door. Probably should have said shade. With the engine exhausting towards the open door 6' away, my tach does not work very well from behind the rotating prop. Probably need to paint the tips white to make it easier for the tach to read which is a good idea in the first place for safety reasons.

Thanks for the reply.

Rich S.

i could def use a tach that will reach from a distance. sometimes i would like to tach my 40% and its just not possilbe when you do not have help. so i will get me one of those tach this year, or when i am standing back like this pic of my 30% Ultimate .

I avoid taching from in front of the prop of any engine but will not under any circumstances do it with a four-stroke engine. I saw an innocuous early OS FS .40 toss its prop at full rpm the other day. Luckily, the prop was "fielded" by a safety fence. The prop nut and washer teleported themselves into another metaphysical plane and were lost forever. I shudder to think of what would have happened to the frail old owner had he been in front of his model at the time.

I do a lot of taching of guys' engines when setting them up, from .10 engines running 7" props to DA100s with 28" carbon props. I use a cheapo Tower tach. Having compared many different tachs, accuracy is not a problem; you rarely see as much as 100 rpm difference between tachs.

The el cheapos like mine require you to be a little careful, in low light situations, with the selection of the background scene in front of which the prop is "viewed" by the tach. Also, you sometimes need to hold the tach at an angle relative to the pitch of the prop to get an accurate reading. I use my lawn tractor's headlights as a light source in the shed when the light disappears.

Also, when you leave it out in the sun, LCD screen up, it will black out until it cools down a bit (note to self: don't leave it in the sun).

With those limitations in mind, I am still happy with my nickel and dime tach after all these years.

The black out thing with the sun has gotten me more than once. Grrrr...

I use to just drop the tach by my starter and glow an go fly. I've started getting in the habit of putting my tach and and glow in my pockets.

Next flight I look like I'm trying to find my keys...