The International Cessna^® 170 Association

Digital tachs don't twitch, ever.

No firewall penetrations or cables to wear out either.

You're absolutely right! Digital tachometers don't twitch. But the sunnuvabitch will drive you nuts with a resolution of one and the fourth digit in the instrument will never settle down even for a moment.
I asked Horizon Instruments if they could change their instrument to having a resolution of ten and they said it couldn't be done.
I just never liked having that fourth digit constantly changing.
Unfortunately, the IO-360D engine that I installed in my airplane did not have a standard tach drive, nor were the internal gears to the tach drive installed, accoring to the Continental people in Mobile. As a result, a tach driving off of the magneto "P" leads was the only option. Horizon Instruments was the only one I could find, and I never did like it. Another manufacturer made an analog type tach to drive off of the "P" leads, but they wouldn't guarantee that it would work with Bendix Magnetos.

Do you find a "twitchy" tach to be a distraction?

You ain't seen nothin' ..until you get a digital!

It's my experience that digital tachs are more "twitchy" than analogs.
When digital "twitches" ....like bluEldr points out...the digits flicker ALL the time, expecially distracting at night, IMO.
In fact...an analog will appear steady....compared to the constant changing of the digits in a digital.

Regarding their digital tach, the E-I web site makes the claim "proprietary algorithms ensure that the RPM reading is rock solid when the engine settings are stable...." (http://www.buy-ei.com/Pages/R-1/R-1_Overview.html)

I thought my original comment might gin up some discussion on the subject.........again.

I have used cable-drive tachs and both the Horizon and EI electronic digital tachs. The digital are both are accurate, easy to read and work all the time without any problems. It does take some getting used to looking at the digital display after being used to the analog tachs. But once you use one of the digital tachs long enough to get used to it (more than an hour or two), either one is preferrable to the cable drive's, twitching, and questionable accuracy. Getting used to the single digit rpm flickering is a small price to pay for the added safety and other features of the digitals.

If all you want is some sort of idea what rpm is, then the original tach does that. The digitals indicate exact rpm plus have additional features not on the original.

The Horizon has some diagnostic tools that will indicate if a mag or mag switch fails, it will record max rpm and actual mag drop, and will warn of overspeed or caution range rpm (info from the Airplane Flight manual).

The EI will display all of the same items as the Horizon plus elapsed flight time.

The EI is a 2-1/4" instrument and the Horizon is a 3-1/8" so you have an option if you need it. Whether you like the original tach or newer technology digital tachs with additional features that improves the safety of the flight, it's usually personal preference in the end kinda like ice cream, some like chocolate, some like vanilla.

hilltop170 wrote:I thought my original comment might gin up some discussion on the subject.........again.

I have used cable-drive tachs and both the Horizon and EI electronic digital tachs. The digital are both are accurate, easy to read and work all the time without any problems. It does take some getting used to looking at the digital display after being used to the analog tachs. But once you use one of the digital tachs long enough to get used to it (more than an hour or two), either one is preferrable to the cable drive's, twitching, and questionable accuracy. Getting used to the single digit rpm flickering is a small price to pay for the added safety and other features of the digitals.

If all you want is some sort of idea what rpm is, then the original tach does that. The digitals indicate exact rpm plus have additional features not on the original.

The Horizon has some diagnostic tools that will indicate if a mag or mag switch fails, it will record max rpm and actual mag drop, and will warn of overspeed or caution range rpm (info from the Airplane Flight manual).

The EI will display all of the same items as the Horizon plus elapsed flight time.

The EI is a 2-1/4" instrument and the Horizon is a 3-1/8" so you have an option if you need it. Whether you like the original tach or newer technology digital tachs with additional features that improves the safety of the flight, it's usually personal preference in the end kinda like ice cream, some like chocolate, some like vanilla.

Richard, ...for those of us too lazy to study the advertisements for the various tachs, and as someone who obviously is already familiar ... can you give some fast/simple answers to the following questions?

1- How is a digital tach that diagnoses bad magneto/switches better than an ordinary/regular run-up where the pilot checks his magnetos and switches?
2- How would a digital tach be better in-flight for such diagnosis, when the pilot makes an in-flight check of both mags (perhaps due to noticing an increased EGT, RPM loss, or rough engine?)
3- How is a digital tach better at recording the time or the elapsed time than an ordinary recording tach and clock (which most aircraft already have?)
4- How is a digital tach (relative to an analog tach) better at depicting trend ...or relative change at a glance?

I got tired of having mechanical tachs going bad on me or having tach cables crapping out and especially having oil leak problems with the tach drive adapter. I may be the only one who had the latter problem, but it nearly drove me nuts---not that it had to drive very far I also didn't care for the oil wicking up into my tach & ruining it. Fortuately I didn't have the bad experience with that that George did. I resisted the digital tack because I had heard others talk about tachs as well as other digital instruments flickering all the time. Also the cost. I finally got one of the Horizon units & installed it. At first I thought it was defective due to the wild rpm fluctuations until an engineer friend confirmed that the engine rpm was indeed fluctuating that much. Like Richard said, after a bit of experience you get used to the rpm changes and pretty much ignore them. The other data the tack provides is useful also. In smooth air at cruise there is little fluctuation. I would imagine the digital tack would be really nice on a constant speed set up. That tach and my gps's are about all the "glass cockpit" I think I want or can afford

OK, Guys...this is tongue-in-cheek....but...

Why would you buy a micrometer and go to all that trouble to measure your backyard ....and then ignore any results smaller than one-foot?

Soo..... I'll buy a DIGITAL tach to obtain accuracy to the single-revolution... then ignore the ten/twenty revolution indications as errors... and accept the tach mfr's explanation as to why their unit is less-than-useful for single-digit indications. Have I got that right?

If one prefers an electrically-driven tach (to get rid of a mechanical drive-cable) one can look at the UMA tachometer:

The 3 1/8” indicator utilizes a high torque pivot and jewel movement. The hour meter can be factory set to start at any desired RPM point. This unit gives the pilot the analog display that is easiest to scan and provides electronic accuracy and ease of installation. Custom dial markings in color and internal Electro-Luminescent lighting are available at extra cost

http://www.aircraftspruce.com/catalog/i ... ometer.php




Here's a link to ALL the available tachs from Spruce:
http://www.aircraftspruce.com/menus/in/tachometers.html

gahorn wrote:

hilltop170 wrote:I thought my original comment might gin up some discussion on the subject.........again.

I have used cable-drive tachs and both the Horizon and EI electronic digital tachs. The digital are both are accurate, easy to read and work all the time without any problems. It does take some getting used to looking at the digital display after being used to the analog tachs. But once you use one of the digital tachs long enough to get used to it (more than an hour or two), either one is preferrable to the cable drive's, twitching, and questionable accuracy. Getting used to the single digit rpm flickering is a small price to pay for the added safety and other features of the digitals.

If all you want is some sort of idea what rpm is, then the original tach does that. The digitals indicate exact rpm plus have additional features not on the original.

The Horizon has some diagnostic tools that will indicate if a mag or mag switch fails, it will record max rpm and actual mag drop, and will warn of overspeed or caution range rpm (info from the Airplane Flight manual).

The EI will display all of the same items as the Horizon plus elapsed flight time.

The EI is a 2-1/4" instrument and the Horizon is a 3-1/8" so you have an option if you need it. Whether you like the original tach or newer technology digital tachs with additional features that improves the safety of the flight, it's usually personal preference in the end kinda like ice cream, some like chocolate, some like vanilla.

Richard, ...for those of us too lazy to study the advertisements for the various tachs, and as someone who obviously is already familiar ... can you give some fast/simple answers to the following questions?

1- How is a digital tach that diagnoses bad magneto/switches better than an ordinary/regular run-up where the pilot checks his magnetos and switches?
2- How would a digital tach be better in-flight for such diagnosis, when the pilot makes an in-flight check of both mags (perhaps due to noticing an increased EGT, RPM loss, or rough engine?)
3- How is a digital tach better at recording the time or the elapsed time than an ordinary recording tach and clock (which most aircraft already have?)
4- How is a digital tach (relative to an analog tach) better at depicting trend ...or relative change at a glance?

The fast/simple answer is I never said digital tachs are better.

It's Monday morning so, I thought I'd stick my neck out there.

IMO, it's all in what you're used to or what you like looking at.
Some people prefer digital watches; they feel they have a better sense of the exact time.
For me? The difference in being 15 minutes late or 17 minutes late doesn't matter. They are both about 1/4 of an hour past when I was supposed to be there. Outside of a computer, life is plus or minus five minutes anyway.

Some people like technology. Maybe it makes them feel closer to the machine.
Others don't care for too much technology. Maybe they feel it removes them from the machine.

I do notice people getting more wrapped around the axle to more they are able to accurately measure the diameter, length, temperature or RPM of said axle.

It's a recurring theme on this (and other) forums.

If I was to replace my bouncy tack at all and if I was to spend money the level a new one might take, I'd like to buy an electronic version that has both an analog and digital display.

Analog displays have proven to be the best at a quick glance to determine and process needed information and that is what I'd reference the most.

I'd like to have a small digital readout for when I'm tediously adjusting for max rpm during my leaning procedure in order to get the last few minutes out of every gallon of gas to arrive at my destination and spill 2 tenths of a gallon of 100LL over the wing when it's full.

As it is use my superior helicopter pilot skill to gauge the bounce and figure the center and swag the RPM. I pull my stock smooth mixture cable out the distance of my first knuckle on my index finger which is much like George's 5 clicks from another thread. I leave it like that and am satisfied. When I'm really trying to save fuel I try to only dump a tenth of gas rather than the usual 2 over the wing at full.

Bruce:
If you're only spilling .2 of a gallon over the wing, I can see I've got a lot to learn from you!
Bruce R.

bagarre wrote: I do notice people getting more wrapped around the axle to more they are able to accurately measure the diameter, length, temperature or RPM of said axle.

The only person getting wrapped around the axle is the one who doesn't like digital tachs.

The rest of us are only pointing out available options and features, not trying to talk someone out of it.

If you're looking for a nice steady, exact RPM reading, I have a "Proptach Digital Optical Aircraft Tachometer" for sale in the "Trademart" forum.

BL-
If you had offered the prop tach before I got used to the flickering last digit I would have bought it! Now it doesn't bother me at all.