Engine RPM

Any of the cheap battery powered tachometers with a one-wire inductive pickup will give you an accurate RPM.  They're available from Amazon, eBay, etc.  You shouldn't have to pay more than $20.  Basically the same thing as a Tiny-Tach for 1/6 the price.

Have a dynamic prop balance done, it’s good for your aircraft and will provide an accurate prop rpm for comparison.

Hi Sean,

A 2% to 4% error in the Dynon EMS's RPM measurement seems unlikely to me. I'd presume that Dynon uses a quartz oscillator (which should have less than 0.01% error) as a timebase to measure the signal frequency.

Just to be certain, are you using the built-in Rotax RPM pickup wired to pin 32 and ground on the SV-EMS-220 as per page 7-48 of the SkyView installation manual (rev. AR)? The calibration value in that case should be exactly 1 pulse per revolution. (which would make sense because the signal comes straight off the flywheel)

If you're using the Airmaster prop's RPM sensor for the Dynon's RPM, the appropriate calibration value should be 0.4118 (assuming you want to show crankshaft RPM on a 912 S/ULS)

That being said, I have no direct experience of configuring the Dynon EMS for a Rotax engine because when I applied to RA-Aus for a MARAP to install a SkyView system in my Gazelle, they gave me a MARAP for a pair of G5's instead. At that point I decided to stop struggling against the bureaucracy and just install the G5's.

I suppose to check/validate the Dynon's reading you could try using a multimeter with a frequency range to read either the prop RPM signal from the Airmaster slipring or the alternator AC output. To obtain the RPM, multiply the multimeter reading in Hertz by 145.7143 (for the slipring sensor) or by 6 (for the alternator AC leads - I'm assuming here that there are 20 magnets of alternating polarity in the alternator's rotor)

In case I made a mistake in my maths, here's how I calculated the conversions:

Slipring sensor: 1 pulse per prop rotation, multiply by 51:21 (2.4286) to obtain crankshaft rotations, multiply by 60 to convert from cycles per second to cycles per minute.

Alternator: 10 pole stator (8 poles for alternator plus 2 ignition charging coils) gives 10 cycles per revolution, divide by 10 to get crankshaft rotations, multiply by 60 to convert from cycles per second to cycles per minute.

Hi Eric

"Any of the cheap battery powered tachometers with a one-wire inductive pickup will give you an accurate RPM.  They're available from Amazon, eBay, etc.  You shouldn't have to pay more than $20.  Basically the same thing as a Tiny-Tach for 1/6 the price."

I have one of these, for tuning my chainsaws & other small motors - cant see how the pilot can check the reading - cable a tad short. I suppose it could be done with the help of a second person willing to stand in the prop blast at 5200 rpm😈