Good quality tachometer

[Matt Curtis]

Where can I buy a good tachometer these days? The one I have now does not work .

[944_Jim]

May I suggest using an auditory tach app on an obsolete cell phone or tablet?

I checked my optical el-cheepo against the Android App (Android Play store Francesco CarTach by CircleGames) and both displayed about the same engine rpm. They were consistently within 50 rpm of each other.

I strongly recommend NOT using your main/current cellphone unless you want to smell castor/nitro  during each phone call.

[Colin McRae]

Where can I buy a good tachometer these days? The one I have now does not work .

Good quality?  Good luck!

I would not recommend the Hangar 9 mini tach. I have gone thru 3 of them and all prematurely failed.

I recently obtained a GT Power RC mini tach (on Ebay). It is similar in design to the Hanger 9 mini. Hopefully it will be of higher quality and last longer than 3 months. But I'm not holding my breath!

[Brett Buck]

Au I suggest using an auditory tach app on an obsolete cell phone or tablet?

I checked my optical el-cheepo against the Android App (Android Play store Francesco CarTach by CircleGames) and both displayed about the same engine rpm. They were consistently with 50 rpm of each other.

I strongly recommend NOT using your main/current cellphone unless you want to smell castor/nitro  during each phone call.

  Unfortunately I think this is the right answer. Unfortunately because having a dedicated tach is very convenient, not because there anything wrong with the audio tach. the nice thing about the audio tach is you can get the inflight RPM, which I have found highly illuminating*.

     Brett

*mostly to confirm my expectations, with a few surprises. The observation most people won't expect (and probably not believe) is that when your engine goes from a 4 to a 2, it has already slowed down a large amount, and it is much slower after it breaks lean  than it was in level flight.

[Motorman]

My Hobbico tach is still working if you can find one of those.

[Dave Harmon]

  Unfortunately I think this is the right answer. Unfortunately because having a dedicated tach is very convenient, not because there anything wrong with the audio tach. the nice thing about the audio tach is you can get the inflight RPM, which I have found highly illuminating*.

     Brett

*mostly to confirm my expectations, with a few surprises. The observation most people won't expect (and probably not believe) is that when your engine goes from a 4 to a 2, it has already slowed down a large amount, and it is much slower after it breaks lean  than it was in level flight.

Interesting you should mention this as I have never seen anyone else mention this RPM change.
Last year I made some experiments and discovered that some glow plugs promote this problem.
I first noticed it on a club members engine and when I got home I made some test stand experiments on one of my engines and discovered that I can cause it....or fix it....by selecting different plug mfgrs.

These tests were all within 15 minutes of each other using the same engine, prop and fuel.
Carefully adjusting the N/V for fast as possible 4 stroke with a tach, then carefully adj the N/V for just 2 stroking with a tach...the engine lost several hundred RPM.

ALL PLUGS WERE NEW/UNUSED.

Don't anyone ask me what engine or plugs I used....each engine mfgr and the condition of the engine will dictate what plug is best.
I only mention that this condition can/will affect flight performance and that there IS a fix for it.
These tests explain why for years I thought that I noticed a drop in flight performance when the engine went into a 2 stroke....
But you need a tach and some plugs and is best done on a test stand.
It's worth the effort!

[Brett Buck]

Interesting you should mention this as I have never seen anyone else mention this RPM change.
Last year I made some experiments and discovered that some glow plugs promote this problem.
I first noticed it on a club members engine and when I got home I made some test stand experiments on one of my engines and discovered that I can cause it....or fix it....by selecting different plug mfgrs.

These tests were all within 15 minutes of each other using the same engine, prop and fuel.
Carefully adjusting the N/V for fast as possible 4 stroke with a tach, then carefully adj the N/V for just 2 stroking with a tach...the engine lost several hundred RPM.

ALL PLUGS WERE NEW/UNUSED.

Don't anyone ask me what engine or plugs I used....each engine mfgr and the condition of the engine will dictate what plug is best.
I only mention that this condition can/will affect flight performance and that there IS a fix for it.
These tests explain why for years I thought that I noticed a drop in flight performance when the engine went into a 2 stroke....
But you need a tach and some plugs and is best done on a test stand.
It's worth the effort!

   Absolutely, this is absoltuely classic 4-2 break tuning techniques. One thing to note, however is that while you are getting data that is similar to an inflight condition, it is not the same in detail. In particular, instead of varying the needle valve, you would want to vary the prop load while leaving the needle valve alone. Load is the factor causing the break, not the mixture. So, you might set ut up with the flying prop and the appropriate ground setting, them without changing anything, stop the engine and start putting smaller and smaller props until you get the inflight RPM, noting when it moves through from misfiring to 2-stroking.

     Different plugs can make the load at which it stops mifiring/starts 2-stroking. Makes sense - more heat would make it less prone to misfiring, for example.

    And a lot of other factors, too - particularly the compression. This is why it is so difficult to tune and maintain a 4-2 break system operating ideally, there are about 20 adjustments you can make, knowing which ones based on observed performance is a lifetime sort of thing.

     Brett

[Mark wood]

In the last week, I have seen two Heath kit tachs. One was in a flight box and still in use. I put one together when I was a teen.

[Brett Buck]

In the last week, I have seen two Heath kit tachs. One was in a flight box and still in use. I put one together when I was a teen.

    Those worked pretty well, not everything requires a digital readout. Problem is that most of them are pretty trashed, and would need to be refurbed to be stable and reliable enough. Plus, they aren't cheap! 

    Rebuilding them isn't that hard and could be accomplished by anyone who can successfully put together a stunt plane as long as the meter and photocell is intact.

   The phone apps are pretty cheap.

     Brett

[Dave Harmon]

    Those worked pretty well, not everything requires a digital readout.
Plus, they aren't cheap! 
Rebuilding them isn't that hard as long as the meter and photocell is intact.

     Brett

I have one somewhere around here but IMO....the meter scale needs to be expanded for a closer reading.
They do work well though and there is nothing complicated about the electronics.
Personally...I prefer these analogue tachs.
There is a bunch of them on EBay right now...$17 BIN.

[Dave Harmon]

   Absolutely, this is absoltuely classic 4-2 break tuning techniques. One thing to note, however is that while you are getting data that is similar to an inflight condition, it is not the same in detail. In particular, instead of varying the needle valve, you would want to vary the prop load while leaving the needle valve alone. Load is the factor causing the break, not the mixture. So, you might set ut up with the flying prop and the appropriate ground setting, them without changing anything, stop the engine and start putting smaller and smaller props until you get the inflight RPM, noting when it moves through from misfiring to 2-stroking.

     Different plugs can make the load at which it stops mifiring/starts 2-stroking. Makes sense - more heat would make it less prone to misfiring, for example.

    And a lot of other factors, too - particularly the compression. This is why it is so difficult to tune and maintain a 4-2 break system operating ideally, there are about 20 adjustments you can make, knowing which ones based on observed performance is a lifetime sort of thing.

     Brett

Interesting!
I never thought about it before but IYO...does the mixture change when the prop is unloaded as in 4-2-4?
In my bench tests...I would think the RPM loss could be attributed to torque loss....hmmm

[Brett Buck]

Interesting!
I never thought about it before but IYO...does the mixture change when the prop is unloaded as in 4-2-4?
In my bench tests...I would think the RPM loss could be attributed to torque loss....hmmm

    The mixture changes, too, but in complicated ways that don't actually at all correspond to going from 4-2. For instance, when you first start a corner, the airplane abruptly slows down and increases the pressure at the spraybar - but the engine breaks into a 2-stroke. Even takeoff - for a conventional arrangement, the airplane might be 2-stroking before release, you release it, and it abruptly drops, then recover a bit, but still to a lower feed pressure than it was stationary. The engine initially leans out from the forward acceleration, and goes further into a 2, but as the speed builds up the engine goes into a 4-stroke. So, even in that simple situation, the degree of misfiring or not changes all over the place.

    If nothing else, sitting on the ground, it might be going 8500 RPM in a 2-stroke, and in level flight, maybe 95-10000 in the air in a deep 4.

      Brett

[John Rist]

I have a Glow Bee tack and it seems to work.

https://www.ebay.com/itm/276495165332?_trkparms=amclksrc%3DITM%26aid%3D1110025%26algo%3DHOMESPLICE.COMPOSITELISTINGS%26ao%3D1%26asc%3D20220405142716%26meid%3Dc0fe740231a844809474f44350374762%26pid%3D101506%26rk%3D25%26rkt%3D25%26sd%3D165917118410%26itm%3D276495165332%26pmt%3D1%26noa%3D0%26pg%3D4481478%26algv%3DAlgoIndex5SimRanker&_trksid=p4481478.c101506.m1851&itmprp=cksum%3A276495165332c0fe740231a844809474f44350374762%7Cenc%3AAQAJAAABAPUN0fWkGeKRy%252FfsmLQSJIROmfr38Zuk9XBp%252Bc9FyaKTQEr80eotsCVRiNZqZBT0xxB6TRbDBwXlhAye2gSQr4jP2TSF9wFWiAmXsHW75BbFMhn4iT91z04H0MQ5rcnFvH8fP7KQlMAhvuCtsV1CX33KYCFKyzjL5%252B%252B93sBlZnjN2NWZ8l5fVwEYVIV8l35Sjo0XoGTZHuAjv3KS4FJU37HiZbX%252F4PqLmjv%252FQjNoV5AvVdbEi1UMg3a%252FFYcxKsq7EpftBLidh9hg7NfryeQIZpBpfbcr6u34X1EzjTXQiF1irG7aS%252Fk1zkqNFTAFfEoZtjnIhISME%252BKJLeuT1d78U9U%253D%7Campid%3APL_CLK%7Cclp%3A4481478&itmmeta=01HZXPCZGN6KDM7W20WNGRT45X

[Dave Hull]

I just picked up an old Futaba FP-DT1 tach by accident today. Haven't seen one of these in use before, so I'm curious how sensitive it is. It takes two AA(?) batteries.

[Jeremy Chinn]

I still use my old Globee like the one at John’s link above. Works well.

[Dan McEntee]

   For the purist and traditionalists in the crowd, I have a couple Vibra-Tachs, with the original leather pocket holder !! I've never tried one of these yet. I do also have my late younger brother's vibra-tach intended for use on small engines on lawn mowers. It actually seems to work pretty good but I have no way of comparing it to anything else, just go by what see on the internet for a typical idle rpm for whatever engine i was testing it on.
   Type at you later,
    Dan McEntee

[Lauri Malila]

..

[Colin McRae]

Good quality?  Good luck!

I would not recommend the Hangar 9 mini tach. I have gone thru 3 of them and all prematurely failed.

I recently obtained a GT Power RC mini tach (on Ebay). It is similar in design to the Hanger 9 mini. Hopefully it will be of higher quality and last longer than 3 months. But I'm not holding my breath!

I've about 3 months now on my GT Power mini tach. So far so good. Has worked well with good accuracy. The issue, if there is one, will be longevity.

[redout]

Here is something a bit different that was developed for radio control models but may have some possibility for control line if a receiver was able to be carried on-board, as well as having as a transmitter to see the rpm. I think if you set your radio up correctly, you can also log the rpm measurements throughout the flight.

I believe this part mounts closely to the backplate of a glow engine and senses the periodic movement of the steel crankpin.

https://www.horizonhobby.com/product/aircraft-rpm-sensor-and-bracket/SPMA9569.html

[Paul Taylor]

May I suggest using an auditory tach app on an obsolete cell phone or tablet?

I checked my optical el-cheepo against the Android App (Android Play store Francesco CarTach by CircleGames) and both displayed about the same engine rpm. They were consistently within 50 rpm of each other.

I strongly recommend NOT using your main/current cellphone unless you want to smell castor/nitro  during each phone call.

Wonder if it would work for electric? Just to see if it matches the program.

[944_Jim]

Mr. Paul,
I think it hears the exhaust note...and I suspect based on tone qualities. I seem to remember it picked up my Triumph TR6 exhaust note...sadly, my oldest son damaged the car so it isn't on the road right now. I can borrow my FILs TR to confirm that last part. I guess I could check against my lawn mower. I never thought to try that one!


The one I use is free, but the ads pop up at "close app" time. It is only a minor inconvenience. I may set up my old Android so I don't have to care about getting my "day phone" sloppy.
Try it and report back, please. I'm thinking of trying electric some day. This information could be useful.

[Brett Buck]

Wonder if it would work for electric? Just to see if it matches the program.

  Try it and see, it seems to work fairly well. The prop makes all the noise, so the beating will get picked up and analyzed. This is a case where the aliasing helps you, it will fold the frequency up and down and as long as the guess range is correct, you will pick up the right one.

    Brett

[Reptoid]

There are both audio and light strobe apps available for the iPhone. light strobe is likely more accurate on electric. Audio is nice for inflight monitoring (from center of circle to avoid doppler shift)

[Istvan Travnik]

In the good ancient times,
I would like to measure the RPM inflight. There was no flatphone, or any cellphones in the mid seventies.
So I took a scout's pipe from my childhood, connected to a 18 mm dia, 10" long model rocket tube, and fit a piston into the tube. The piston got a long tongue of plywood, and scaled with the help of my electric organ. (numbers of scaling naturally were not in Hertz, but RPM).
It worked surprisingly accurate: the measuring needed to tune the pitch of this "Galton pipe" up to the engine's note.
My friends suffered of innovationphobia laughed, I used and ejoyed the result... 

[Steve Helmick]

   Absolutely, this is absoltuely classic 4-2 break tuning techniques. One thing to note, however is that while you are getting data that is similar to an inflight condition, it is not the same in detail. In particular, instead of varying the needle valve, you would want to vary the prop load while leaving the needle valve alone. Load is the factor causing the break, not the mixture. So, you might set ut up with the flying prop and the appropriate ground setting, them without changing anything, stop the engine and start putting smaller and smaller props until you get the inflight RPM, noting when it moves through from misfiring to 2-stroking.

     Different plugs can make the load at which it stops mifiring/starts 2-stroking. Makes sense - more heat would make it less prone to misfiring, for example.

    And a lot of other factors, too - particularly the compression. This is why it is so difficult to tune and maintain a 4-2 break system operating ideally, there are about 20 adjustments you can make, knowing which ones based on observed performance is a lifetime sort of thing.

     Brett

My recollection is that if you put a larger prop on, the increased load will cause the engine to go leaner at the same NV setting. I never thought about putting a smaller prop on, but because of the above, I'd think it would go richer with the smaller propeller. No?    Steve