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Checking tachometer accuracy

I’ve never flown a plane with an engine analyzer.

I could without the slightest trouble fly my A-65 powered plane without a tachometer, or any other engine instrumentation. It would have no measurable effect on fuel consumption, which I can regardless afford quite easily at $20/hr of 100LL… Unless I were to fly 200 hrs a month

As described in my post above, I could fly my O-320 powered CS prop plane with no tachometer, because the engine speed control is digital and accurate. This makes the tach mostly redundant except that its the only way I know airframe hours from one year to the next.

Last Edited by Silvaire at 13 Mar 19:32

O200 owners.

Maoraigh
EGPE, United Kingdom

Yes, of course.

Do Rotax have mechanical tachs, or are all displayed engine data derived from the ECU lke my Inntec 800? Although that also has a battery-powered TinyTach, in case of total electrical failure.

Glenswinton, SW Scotland, United Kingdom

Jacko wrote:

but is there really anyone who is rich enough to operate an aircraft piston engine without an engine analyser?
P.S. …or without a Dynavibe gizmo to balance the prop?
Most Rotax pilots
Last Edited by a_kraut at 13 Mar 13:58
Bremen (EDWQ), Germany

Half joking, but is there really anyone who is rich enough to operate an aircraft piston engine without an engine analyser?

P.S. …or without a Dynavibe gizmo to balance the prop?

Last Edited by Jacko at 13 Mar 13:51
Glenswinton, SW Scotland, United Kingdom

I would not recommend the cheap handhelds. They are unreliable and inconvenient to use.
Either a Proptach or a Truetach II placed on top of your panel in plain sight will give you the comfort, accuracy and constant readouts you need.
https://www.aircraftspruce.com/catalog/topages/trutach.php

Last Edited by cessnatraveller at 13 Mar 08:42

Following from A-Kraut’s post:

There are some mobile phone apps for model helicopter fliers to check their rotor RPMs based on sound. They may work for aircraft. My guess is that they may either be very precise, or wildly inaccurate – i.e. if they are picking up on a harmonic you may get a multiple of the RPM multiplied by the number of blades, or perhaps they will only hear the engine noise (which if you don’t have a gearbox will still give you a multiple of the RPM).

Google also shows some apps like this:

https://play.google.com/store/apps/details?id=com.javiery.rpmgauge&hl=en

Last Edited by kwlf at 12 Mar 23:02

At Inverness EGPE the maintenance firm lent their device to allow an O200 tach to be checked. I saw the small box, but not the device. I believe it was placed on the dash and the engine run.
Your maintenance organisation might lend it to you, as they’ll get trade if it’s inaccurate.

Maoraigh
EGPE, United Kingdom

Will those hobby ones work on an aircraft? It says the distance in the one in Post 05 is:

Distance: 50 to 500mm/ 2 to 20 inch

Buying, Selling, Flying
EISG, Ireland

I have for perhaps 15 years used the “Proptach” from Cardinal Electronics, Lansing, Michigan. It run on a standard 9V battery and is as simple to use as can be. Switch it on, check the 2 or 3 blades switch, put it on the glareshield and let it look at the prop. Unless it is dark or the sun it right it its “eye”, it will provide a RPM readout with a 1 RPM solution and a 1 RPM accuracy (quartz). Whether it is still on the market, I have no idea. Back then it cost around $ 300, AFAIR.

In my experience, standard mechanical tachometers read between 0 RPM and 250 RPM low, with an estimated average error of around 40 RPM low. Reading high is very rare, I recall only one, and that was only at specific RPMs.

Having a tach read 200 RPM low has a number of implications, one of which was demonstrated many years ago when it was deemed partly responsible for a pilot running out of fuel. Leaning at a power setting too high to allow leaning (setting 85% thinking the engine is doing 75% pwr), and thus risking too high CHTs, is another problem.

An overreading tach is a very common cause of planes apparently overperforming, when compared to indicated RPM. Many owner pilots do not react appropriately to this. Beating POH speeds is something that makes some aircraft owners very, very proud, and so any suggestion – or worse, any proof – that a miscalibration could be involved, should be presented carefully, especially if the owner is a valued friend, in which case it could be considered to let someone else break the sad news.

Edit: no need to look for the “Proptach”, if the unit Silvaire mentions above does the job, it is very much cheaper. Same working principle, I think.

Last Edited by huv at 12 Mar 19:16
huv
EKRK, Denmark
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