sugarfoot

I once saw a club member use a techometer while the engine was running. I know nothing about this instrument. But I get the idea that it has everything to do with the amount of RPM's turning. Now if that is correct, then there must be an acceptable/unacceptable amount in which you should have before actually launching your plane.
My question is: How do you know for which engines what is the amount of RPMs that is within the acceptable range? So many different engines and sizes. I read the info on three of them that Tower Hobbies has on the internet, but I saw nothing that told the amount of RPM's required for each size engine.
Anyone out there in RC land that can clear this up for me?
Thank you

Newc

As you surmised, a tachometer measures the roational speed of the something in Revolutions Per Minute (RPM). In this case it's the speed of the propeller (and the engine since the prop is spinning at the same speed as the cranksaft of the engine. This isn't always the case, as some props - such as with a gear driven prop on an electric motor - spin at speeds different from the engine/motor).

First of all, look at a plane's recommendation for an engine, then look at the specs for the engine that you have decided to use.

If you look at the specs for an engine - not the specs of the plane - you will find what the manufacturer suggests as the proper engine speed for best operation. Choose a prop that allows the engine to run within the recommended engine speed. A tach is very helpful to ensure that you don't run the engine too lean, as you can easily see what the peak RPM is and then richen the mixture to reduce the RPM by 200 - 300 RPM.

Good luck!

da Rock

The one thing a tach will do that's never mentioned, is that you can learn to set a needle by sound with it and not need it later. It will tell you what that sound MEANS. The sound alone won't tell you squat if you're a newbie.

It's a good learning tool.

Use it awhile and you'll learn ACCURATELY what pitch to listen for when setting your favorite engine. Make sure to use it on one engine almost every time and it won't take long until you can hear the right rpm.

It's also a good tool to use to find out just how much more rpm you're getting from changes in fuel or prop. It's worthwhile to know exactly what the difference is in the change in rpm. Anyone can hear faster or slower, but nobody can hear "how much". With a tach, you ain't guessing.

sugarfoot

Newc and darock...thank you both so much for your replies. The information that you supplied to me has helped me understand a whole lot more. Now I will purchase a tachometer and start using it. It is members like you who help people like me want to keep learning more from these forums. Thank you once again.

Gringo Flyer

My Feedback: (18)

Tachs are great but I was flying for a couple of years before buying one. I generally use it if I am changing props, etc to see what kind of difference I am getting, like what darock. But most of the time I tune an engine by ear. Theres no doubt when an engine is running like it should. It takes some time to get a feel for it and is more obvious on 2 stroke than 4 stroke engines.

Do I like my tach? You bet. Do you have to have one? No, if I was a newb there is probably a lot of other stuff I would try to spend my money on first (starter, power panel, building tools, voltmeter, etc) But thats up to you. When your starting in the hobby it takes a little while to get all the bells and whistles.