my question is which is more accurate, a hand held tach that reads air or a tach that you plug into a motor? are all of the onboard tachs universal for any gas motor?

most modern ignition systems come with a spare lead just for that, RCXCEL IGNITIONS http://www.petenplanes.com.au/engine.../prod_811.html

3W ENGINES http://www.aircraftinternational.com...4/Default.aspx

the best tachs are http://www.fromeco.org/products/05frctnc/ they work in any light basically

i use this one and its not quite as accurate on cloudy days or when the sun is going down
http://www.hobbico.com/fieldequip/hcap0401.html

I have the TNC but the tach that is connected to the engines are great. Until you want a tach for another plane that doesn't have the on board unit. I was fooling with a DLE last week with the ignition tach, I really liked it!! If I was getting a new engine with the ignition plug for one I would order the tach at the same time. Joe and I were talking aBOUT THEM AND HE BROUGHT UP THE USE OF THE ON BOARD FOR TWINS, great idea, would make life easier. It never even crossed my mind.

Gray beard, so part of my question was are the onboard tachs universal? I have a jba,zenoah and a dle 20 and wondering if i can buy just one tach?

The tach is but you need an ignition with the extra wire for the tach. My gas engines are older and don't have the added lead. I need a new ignition for my RCS and plan on buying the ignition used for the DLE 30 so I will order a tach when I order the ignition. Hobby King has some good prices on both. The tach is very small too and the one I was fooling with was hard mounted in the planes fuse.

The handhelds don't read air. They read the flashes caused by the prop going by. They work just like the chronographs used for measuring bullet speed. A big factor in their accuracy is the background in front of the plane. A plain white board or building gives lots of contrast for the little electric eye to read the prop's movement against.

And they go nuts under house lighting. Point one at a light bulb or a florescent light and you have 3600RPM on the screen. They just count the light/dark transitions and divide by two for a two blade prop or by three for a three blade prop. It's one way to verify your tach is counting OK.

Don

Not quite Don, I have three other tachs you can point at the light and get a perfect reading, point them at a prop with any background and they can't read it. I gave up on the cheap tachs and bought the TNC, it works under any light conditions you would fly in. These new little tachs wired into the ignition are slick. Like all tachs, not often really needed but I have a couple of engines that are way easier to tune with a tach.

Hmmm - my handhold tach don,t make no never mind bout light or background

For one thing, aircraft radio systems for aircraft even look different than the 75 MHz car radios. They have a pair of sticks, one on the right and one on the left. Depending on what "mode" you are on, the right stick has aileron and elevator, the left stick has throttle and rudder.

Most car radios have two channels.. steering and throttle. The steering is on the rotating knob and the throttle and braking are on the trigger.

It is obvious, just by looking at them, that the radios are different. Many flying clubs have very strict frequency control for operating 72 MHz radio systems. One pin for each frequency. So, if someone wants to fly on, say channel 42, he/she would grab that pin, put their AMA card or club card, in the slot where the pin came from, and then go fly. If someone else has channel 42 and wants to fly, they need to first obtain the pin BEFORE turning on their transmitter. If it's being used, it shows that person that channel 42 is in use.

They, clubs, check to make sure that the members are aware of what frequencies are in use and that they are using aircraft authorized frequencies only. It's in their best interest to do so. The FCC does check from time to time.

Other than that, it is on the honor of the operator that he/she is using the right frequency for the operation in progress, ie. aircraft = 72 MHz, or cars = 75 MHz, and so on.

CGr.

That's a sweet piece of high tech machinery you've got there, John Buckner. I'll bet it's good on battery life too, isn't it?

I have been flying R/C for about 39 years. Never used or had a tach till I built a twin engine plane about 7 years ago. It seemed reasonable that a tach was needed for a twin. I bought the type that is light sensitive and could read the prop coming by. I never was happy with it because it was a bit of a struggle to get a reading with it. As I learned more about special features of R/C twins I used the tach less and less, and then just stopped using it. I tuned each engine individually, to run the best it could. I never tried to match the RPM. The engines were identical and the same age (purchased for the twin). I still have the tach but it is stored, with the battery removed. I just tune the engine by ear and sight and performance. I always tune for maximum reliability rather than maximum RPM.

I like using the tach. I learned to tune by ear and then when I bought a tach I found that I had been running more rich than I really needed to. I can put the nose up with low fuel and find my worst case scenario peak for any plane, then check it again full and level to see how rich I need to be. It also tells me how well my low end is tuned and how steady the engine is running in general. It takes lots of the guesswork out of setting the needles and makes turning the low end quick and easy. I can and have done without it, but anything that makes the task easier or faster I'm all for it.

John, that engine didn't come from the LHSlast week either. Lets see, I'm guessing that engine is about 1965 vintage. How close am I

By the way, your tach would get some interference from my shaky hands

Don

Gene, I've had a couple of those tachs also. The one I have had the best service out of is a Magnum tach. I've had two, the first met it's end when one of the Helicopter guys borrowed it and got to close to the main rotor. I found a replacement when the LHSwent under. The others wouldn't give you a good reading at all.

Who handles the ones that tie into the ignition? I would like to get a look at them.

Don

The one I have seen was bought at Hobby King for the DLE 30. The 30s ignition has the wire to plug it into. It's just a small LED screen you can mount in a plane. Very cool.
I need a new ignition for my 1.40 22cc RCS engine so I plan on buying one from HK and just get the tach at the same time. I have a friend that buys all his engines from Hobby King so I will ask him to just tack my stuff onto his next order.He uses the express shipping and gets it here in just a couple days.

Ya Don you are pretty darn close I bought that little OS Pet .099 with a two position throttle (one big hole and one small one in the barrel) in 1964 at Ed's Covina Hobby east of Los Angeles. Hmm still flying it.

Sorry guys just could not resist throwing that old harmonic tack into the fry. Ok there is one more type that has not been mentioned yet probably because it not used to often.

So far we have the old harmonic vibrating pin, The optical sensor which senses rapid changes in light density, The electronic type that counts firing pulses from an electronic spark ignition and one more thats avalible for glow engines and that is the the magnetic hall sensor. This last one is rare but is electronic but counts a rotating magnet attached to the prop driver bushing.

I know this one is out there because it is included with complete telemetry accssory package for the Aurora 9 radio system. Amazingly that system include your choice of two types both a sensor for an optical tack with a little bulb pointed at the prop and if you choose a magnetic hall sensor type these are for inflight real time readings.

Now I think the original question was which of these types is more accurate and I think the only realistic answer is it does not matter not one wit. Think about it what we use tacks for is referance only and as long as the repeatability is good then so what if it a little off we are only using it to referance changes we may have made.

The vast majority of my engines are two stroke glow and for those I choose to tune high speed to a pinch and I find this is actually better for me and my ear rather than using a tach. What I do use a tack for is for comparisons between props, fuels, plugs and so on and on. This is why for two stroke glows I always have the carb line accessable for a pinch cowling or not.

John

I have seen your harmonic tach once before in a post. Never seen one in use though . Seeing one is a good thing. Next time someone is at an auction and going through one of those great boxes of stuff will know they just didn't stumble on an old Afro Pick. One tach I saw demonstrated, scared the peewaddle out of me, was one that looked like a starter and you held it onto the spinner and read the rpms. I put that right up there with the old clear plastic props.
As John mentioned, tachs have there place but most the time they just sit in the flight box. I tune a lot of different engines and some of them require a tach for one reason or another. The needles on one of my Brison engines face the prop and have about a half inch of room before you loose fingers. I tach the engine then shut it off, make an adjustment then fire it up again and take a reading. I do this when I change props. I have a couple of YS engines you adjust with the regulator, you can't hear an engine change but you can see it on the tach. They do have there place but don't get used all that often.