jib

I've reached my limit of tuning by ear and I think it's finally time to buy a tachometer. I am looking for some suggestions. While cost is important, getting a dependable (accurate and durable) tool is more important.

If engine/prop size matters, we currently run .42-53 sized engines, but have .75 and .90 sized two stokes in the pipeline, pending and increase in flying skill.

Thanks in advance,

Jack

Gray Beard

My Feedback: (-1)

I don't use mine often for two stroke glow engines but I tune a lot of four strokes and gassers and needed a good one. I went through four of them before I broke down and spent the money for a good TNC tach. I have tested a bunch of different tachs with it and found the tach/volt meter sold through Horizon is a pretty good one. Sometimes it doesn't like some light conditions but for the most part it works very well. The TNC is the best one I have found in a very long time but the Horizon would be my first choice for the cheaper units. The added volt meter is a big plus too.

brett65

My Feedback: (18)

I have used one of these, http://www3.towerhobbies.com/cgi-bin...&I=LXPX81&P=ML but I don't like to tune with them. If you tune the plane while level for max rpm then your gonna end up too lean and it will die when going straight up. It can be a useful tool to compare props, but I wouldn't actually tune with it. That's just how I feel.

Gray Beard

My Feedback: (-1)

You mean you don't bring the engine down a couple of 3 or 4 hundred RPM so it can unload??

w8ye

My Feedback: (16)

I first bought a Glow Bee when they came out but after much frustration I bought a TNC some years ago. It is in a drawer somewhere around here. I don't really need one. I can tell how the engine is running without a tach.

The TNC works great I just don't use a tach anymore.

Before I bought the Glow Bee I used a Vibra Tach and it's on a shelf somewhere around here too.

MinnFlyer

My Feedback: (4)

I agree. A tach is nice if you're really into numbers, but I would never use one to tune an engine

w8ye

My Feedback: (16)

If I am doing a comparison of mufflers, fuel, props, or something, I'll bring out the tach to the bench but I don't take the tach to the flying field.

MikeL

My Feedback: (3)

I can't imagine tuning a four-stroke without a tach. My ears are simply not good enough to do that. I can't hear a 300-400RPM change at between 8,500 and 10,000RPM. I use an inexpensive $20 tach that does what I need it to do. Nothing fancy.

At the same time, I can't imagine tuning a two-stroke with a tach. Totally unnecessary.

w8ye

My Feedback: (16)

I lean'em till it starts to slow and then back out the needle some. Works like a charm. You have to be quick on the too lean part on a four stroke or it will quit on you. The Y-S will even throw the prop.

I might do this a couple times to assure myself that I'm where I want to be. You do it for a few years and you will get into the routine.

It's kinda like pouring molten iron. You do it all day every day and keep checking the temperature, after a few months you can tell the temperature of that iron by eye with as close an accuracy as your I-R gun and you can learn to adjust your judgment for the ambient light and how much air is blowing over the iron and how much carbon is in the mix.

brett65

My Feedback: (18)

BTW: I have never had a 4 stroke, so my experience is limited to the 2 strokes.

w8ye

My Feedback: (16)

It's six of one and a half dozen of the other after you get used to them. They are more alike than different.

MikeL

My Feedback: (3)

Been doing it for a long time, but my ears just don't work that way. $20 and a pair of batteries each year removes all of the guess work for me. Why attempt to dissuade someone from getting the tools they need to "calibrate" their ears? You talk about how a person learns to check temps of molten iron by using a gauge, and can then do it my eye. Well, my experience with estimating cloud heights is the same - - I needed a ceilometer to give myself a reference before I could accurately work without one. Two-stokes provide that reference via their sound, but four-strokes don't (for most people).

Like I said, not necessary for two-stokes, but necessary for four-strokes.

w8ye

My Feedback: (16)

Well I used to do cloud heights too but I'm out of practice now. I have to tell the first deck cloud heights by temperature/dewpoint if I'm interested. I cannot pass a physical anymore so I don't need to know the ceiling height.

Many people say they cannot tell a four stroke rpm delta but for some reason the four strokes are no different than a two stroke to me. Each to his own devices and abilities.

MikeL

My Feedback: (3)

That method only works for estimating convective cloud heights when they first form. I used to be a USAF observer. Best job in the world!

Gray Beard

My Feedback: (-1)

Like 8 said, they really aren't used that much and I tune my engines about the same way as he does. I use mine a lot when I'm testing different props on engines or just making sure I'm not going over the rated RPM range on a new engine. I always use one on a new engine just to be safe. I don't think I have use a tach on one of my own engines in over a year, I just know when they are right. I did use it on a new gasser a few weeks ago and discovered I was getting too close to the top of the RPM range and went to a bigger prop to get it where I wanted. They do come in handy.

w8ye

My Feedback: (16)

I'm right there with ya Gray Beard

MikeL

My Feedback: (3)

I guess my point is this: Without using a tach to develop an experience-based calibration for what is "about right," how is a beginner supposed to know what they're doing? I rather doubt that many of us have an instinctual understanding of it all. For two-strokes, such the OP asked about, a tach isn't needed by most people. That flips when it comes to four-strokes, with most people needing one to safely and accurately tune their engine.

Gray Beard

My Feedback: (-1)

I would get the Horizon Tach/Volt Meter and use it to learn with, they do come in handy and it's good to have one in your box, my TNC is always with me. If I didn't have a Tach when I was doing the tune on my gasser I could have set up up way out of it's best RPM range. That's a torque thing. I wanted to get my engine around 7000 to 7500 RPM. The first prop I had was too small and it was hitting 8700, Zenoah states 9000 max but the best torque between 7 and 75. I changed props and it's right at 7300. I couldn't tell with this engine what it was putting out, I'm not used to hearing it yet. I needed the Tach. I will use it on this engine for quite a while when I change prop size or even prop make. For small two stroke glow engines I have been doing them so many years i just bring them up to full rpm then back off until i hear the drop, I may even do a pinch test if I can get to the main fuel line? Most the time I'm pretty close. When I was a pit man for racing class planes I always used the Tach. Racing is different, too lean and the engine craps out, too fat and the engine isn't running at peak. Buy a Tach!! You will use it and learn a lot.

w8ye

My Feedback: (16)

I apologize Mike, I had originally assumed your were an old timer like me that had built models ever since they made glow engines and your dad and uncle before that.

I've got to tell a tale about now

It was like 1950 and my dad was showing me how to set the needle valves on the lawn mower. Me being a kid and full of questions I inquired about why the throttle seemed to move on its own and not necessarily with the throttle lever. He went on to explain that there was a governor inside the cover of the engine that limited the speed but when you got into heavy grass how it would open the throttle to give more power and to try to maintain the engine speed. He removed the cover from the engine to show me how it worked.

All the while he was explaining, I was trying to see the "little Governor of the State" in the engine and all I could see was a spring loaded paddle that the cooling fins of the flywheel blew air against to limit the speed of the engine. Then latter that night I was wondering why the government would require some dumb thing like that in an engine. The government sure was being pushy. Eventually I figured it out that B&S had put the governor in the engine to keep it from blowing up yet have extra power when it was needed.

Along about then I also asked him why the bottom blade on the three bladed props on the planes when he was in the Air Force was longer than the other two? He went on to explain that the props were made that way to "drain the pitch" out of them. So I went back to my plastic model - turning the three bladed prop - trying the figure out how the bottom blade always got longer? I didn't expect any pitch to drain out of the prop for after all, it was just a plastic model. . . . .

Charlie P.

I have a "cheapie" from Tower that I found for $12 on one of their bargan sales. I use it quite a bit.

http://www3.towerhobbies.com/cgi-bin...&I=LXPT31&P=ML

One of those things I never thought I needed until I tried one. Hasn't changed much in my flying, but it sure simplifies finding a good top-end starting point. I wind up the engine and set the high end to maximum rpm and then back down 400 rpm. Also a help when choosing the right prop for a given engine & plane. It still depends on flight testing but it is never bad to have additional useful information.

bigtim

My Feedback: (13)

I use that one as well, it works great for my needs, since I run primarally 4strokes its a handy tool for the first tune of the day, I always start up on the rich side lean to max rpm and back it off 4-500 RPM the tone difference is imperceptable at full throttle the tach takes the guess work out of the loop,for me at least when I notice a tone difference and check with the tach its at least a 1,000 RPM change from peak for a 4 stroke that a big drop in power.

when tuning the few 2strokes I have the pinch test is all you need for a smooth running tune.

Campgems

I first started out with a Magnum tach. Never had any problems with it until I loaned it to one of the guys to "get a reading" on his helicoptor rotor. He got it a but close and the rotor took it out of his hand sort of crunched it. He bought me a Globee as a replacement. Lots more features, but the one thing it won't do is give me a good measurement on RPM. Every now and then, it will show my 52 OS four stroke cranking 23000 at half throttle. When one of the LHS went under, I picked up another Magnum and have been a happy camper since. It has the option of 2 or 3 blade props and that's all, and it works. Lilttle cheap 9V batteries that last forever if you remember to turn it off when you are done.

Don

Sandmann_AU

I use a glo-bee and haven't had any problems with it as long as I'm outside - inside they pick up the florescent lights flickering and give false readings (then again, you shouldn't run a glow engine inside anyway).

Having said that I'd never use it for tuning a single engine since the temptation is too great to tune for max rpm and have the engine run lean in flight. What I do use it for is synchronising twin engined planes (though the ear's probably more accurate than the tach for this), and comparing performance with different props and fuel mixes.

Campgems

Matt, my problem is outside with bright sun. It looks as if it needs more of a light/dark transistion than the Magnum does. Oh well, I have two now

Don

LuftwaffeOberst

I use mine... it's Magnum Mini Tach designed for 2 or 3 blade props. I bought mine for $24.99 and I use it all the time do to I always experiment with different prop sizes and pitch. It's also good to have if you down the road want to fly twins, you can sync the engines better. Also with a tach, you can keep tabs on how hard your engine is working. I also have a Radio Shack IR Thermometer to know how hot my engine is in those " In Cowel " setups. But that's a different topic. [X(]