Which Tach?

[N6893U]

Hey All,

I'm buying a new Mitchell tach to replace my TU one.  The application chart says to use one with a normal cruise RPM of 2300.  I normally run closer to 2400. So the question is, would it be acceptable to use one designed for a normal cruise of 2400?  Seems obvious to me, but...

Thanks,

Jerry

 

[jetdriven]

[carusoam]

For your consideration...

I would think the replacement should match what the aircraft has in it already.

The tach time should add consistently as the OEM gauge.  (as wacky as that sounds).

Yellow markings and redline in the proper places.

When TBO is stated as 2,000 hrs, that is based on tach time being counted the OEM way.

Since TBO is a guidance, exact engine hours are not that meaningful.  

The most important thing is accuracy of the gauge in RPM reading.

Go digital, get away from rotating tach cables.

If you don't have a Hobbs meter, airframe hours are determined by tach. By changing this factor you will be changing the way these hours are reported by a few percent.  My 65C was tach based.  My m20r is missing the tach hours and only has a hobbs meter.  In JetD's case, he has both tach and Hobbs.

My opinion, shared.  Sorry JohnG, it is not the facts today, just opinion...

Best regards,

-a-

[danb35]

I would (and did) look at the EI digital to replace my mechanical tach.  Works great, and tach time runs at 1:1 when the engine's over 1300 RPM, and not at all when under 1300.

[Seth]

I went digital when my Tach stopped working in my F Model.  Ended up deciding between the EI and Horizon units.  Originally chose the EI, then changed my mind and went wih the Horizon unit.  I was very pleased with it.  After a few flighs, the digital vs radial readout became second nature.  I also noticed slight changes in the RPM when climbing/decending, which meant I may have had a prop governor problem for a while and didn't know it. 

That being said, the Missile I now fly has an anaolg tach.  However, I also have an JPI 830 that shows the manifold pressure and Tach in a digital and arch readout.

Whenever something breaks, I try to take that change to make an improvement to the aircraft.  I could just overhual or replace with older less expensive techonolgy, and sometimes I do, but depending on the situation, if the price delta is not huge (or significant depending on the item), I try to update with newer technolgoy.

The 800 RPM start clock time on the Horizon did bug me a bit, but I deided that small percentage would not be a huge factor as long as I remembered it and factored it in for oil changes and resale value.

Take care,

-Seth

[xftrplt]

When my analog tach failed, I opted for the EI.  I like the 1300 RPM clock and the monitoring of the mags.

[jetdriven]

I've flown those EI tachs and I cannot get used to the display when moving the throttle or prop. All 1888's.  And the last digit must have a 1/10th second response time.  Its almost unusable. I had to set the RPM, wait, then tweak, and tweak again.  A pointer shows instant relative position. Digits require processing. 

I stand corrected.   I was thinking of the Horizon.  The EI is a much better solution.

[xftrplt]

JD,

Are you sure you don't have EI and Horizon mixed up?

The EI has an analog display (albeit LED's), while the Horizon is digital only.  

I haven't encountered the readability problem you mention with the EI.  In fact, the last digit is always zero, as the the device reads in 10 RPM increments.  (And I'm rarely concerned with setting RPM to that precision.)

[jetdriven]

Yeah, good catch. It was the Horizon tach.  Drives me crazy.  I have never flown with an EI.

 

[Piloto]

I noticed that in the automotive sector most of the new car still have analog displays for all the parameters. Anyone knows why?

 

José

[xftrplt]

Quote: Piloto

I noticed that in the automotive sector most of the new car still have analog displays for all the parameters. Anyone knows why?

 

José

[carusoam]

José,

Chevy corvette tried introducing digital guages in the early 80s.  It was a flop, mostly because people resist change.  The resistance increases with the value of the object they are buying.  Fortunately, through the magic of GM, exact pressure and temperatures are available on an LCD screen with a few button pushes.

My 92 vette and my 94 M20r share the same guage style.  They are digital with a fake analog looking needle.  It is exact information, dumbed down with an approximate read out.  This is probably the result of product testing with focus groups.  The result "feels" like high quality.

My MP guage changes in distinct steps like a Seiko watch.

Two failed introductions in my lifetime.  The metric system and digital guages.

Even glass panels were not well received for quite some time.  Now we have knobless touch screens.

Cars marketed towards young people are full up with digital stuff.  Cars marketed to the retired crowd, not so much.

Digital presentation is slowly making its way in.  Do you think the metric system will make it back?

Best regards,

-a-

[jetdriven]

I think studies have shown that raw numbers on a screen are not totally useful as an instant data readout, they require processing. Newer aircraft have speed and altitude tapes and it takes a couple seconds to interpret that. A needle pointing at 9 o'clock will always be 310 KIAS in a 747, however.  In the 1900D we had EFIS screens. There was a test mode you could put it in that had a black screen with raw numbers for pitch and bank. Trying to fly the aircraft with a black screen that showed bank as L19.4 degrees and pitch as +1.4 was almost impossible.   NASCAR cars have the guages twisted in the mount where they always point  straight up when normal. I wish for that in our 201. 

[carusoam]

I only fly one plane.  I have many hours of experience.  Memorized each switch. I know exactly what numbers I am expecting.  I don't have any competitors inches away from my cockpit.  I prefer the digital data.  With today's technology, we can have both.

Do NASCAR drivers still look at the instrument panel?  They have an engineering team and millions of fans on FOX that will watch the telemetry for them.  At one time, all there needles green zones were pointed straight up.  Then somebody calculated side loads on analog needles and decided pointing in the green should have a particular angle.

Recently, mooney tried to serve both clients with a needle and an accompanying digital readout.  Moritz guages.

I don't use the graphic part of the JPI as much as the raw data it provides.  If a cylinder fails, I will probably see it on the JPI graph first.

The future seems to be electronic monitoring with alarms for hard data information and pictures for nav type flight status monitoring. Because we can.  Technology allows for this, at a price we can nearly afford, in a package that fits in our instrument panel.

Best regards,

-a-

[DaV8or]

Quote: Piloto

I noticed that in the automotive sector most of the new car still have analog displays for all the parameters. Anyone knows why?

 

José

[Piloto]

I also noticed that all aviation new watches have analog readout like the old ones. Is this for looks, fashion or what? I personally have the Citizen Skyhawk and love the analog looks, but that may be because I grew up in analog era.

 

José

[carusoam]

José,

Just got a new Seiko.  It is digital at heart.  The hands adjust themselves to whatever the digital clock is set to.  It is a breeze to change time zones or day light savings.

Dav8,

What we need is a place to enter the rpm desired, and the digitally controlled governor makes it happen.  You want 2501 rpm?  Bzzz....there it is.  I work with machinery that has this type of reality.   

Incredibly low head down time.

I Would be really happy to have an altitude set point.

Best regards,

-a-

[Hank]

I prefer analog gages, like analog clocks. I can tell at a glance if the MP/RPM is set correctly, if the temps are OK, and if it's time to head to a meeting or not. Often when glancing at the clock, I dont' even realize the time, but can tell by hand position in a fraction of a second if I'm good or need to get moving. With digital, that won't happen--I have to look long enough to recognize the number and get it into short-term memory to compare to what I am looking for and decide if it's good or not.

And lord help me if the digital number is changing. There seem to be two popular ways of displaying those:  88888, or put up a number once or twice a second. Try making sense of that on your altimeter! [There are tall, pointy, tree-covered rocks where I live. No thank you!] And the glass-panel, fighter-style tapes where you always look in the same spot and have to read the number are not a lot better, it's like looking at a digital clock with the last number only half shown or blurred out.

glance at a hand, I know what it's pointing at and if it's right. Glance at a number, wonder what it was, look again longer, read "21.9" and then decide if that's close enough to my desired "22" setpoint or not. Nope, not for me.

[jwilkins]

Tachs are set up so that one hour use at some specific RPM will yield one hour of tach time. Hobbs are set up to show how many clock hours the oil pressure was up (most Hobbs meters are set up with an oil pressure switch so they don't start counting until the oil pressure is up).

I think what Mitchell is referring to is not what RPM you normally cruise at, but what RPM will yield one hour of tach time for one hour of clock time. If Mooney originally designed the tachs so that one hour of cruise at 2300 RPM would indicate one hour of tach time, then you probably should use that 2300 tach.

If you ever ran a plane with both a tach and a Hobbs you probably noticed that high RPM cruising in a long XC made the Tach time higher than the Hobbs time. Normal training T&G and low RPM cruising made the Hobbs read higher. Most rental planes for training charge by Hobbs.

The tach on my K doesn't even have a tach hour counter. All I have is the Hobbs. If the tach dies I'll change it out for one with a tach hour counter. I miss having one.

Jim

 

 

 

 

 

 

 

[carusoam]

Jim,

Where is your Hobbs meter?

Mine is in the baggage compartment back wall.  (m20R)

I guess MAC did not want me to be constantly reminded of my next Mx expense.

Best regards,

-a-

[Vref]

Best of both worlds an analog display format with in the middle a digital readout. The analog readout gives additional information e.g a rate-change, tendencies that you will have difficult to see on a pure digital readout....

For instance my EDM800 has both..what I hate is pushing the step button quickly scan through all info, it's distracting and time consuming.....One has to make a ditinction between situational awareness, flight and engine data to be interpreted each one needs a different format of representation......

[Seth]

Quote: carusoam

  Do you think the metric system will make it back?

 

 

 

Yes - though I do not think in Metric, I think it will make it back in another 10 to 50 years.

 

-Seth

[jwilkins]

On my 80 K the Hobbs meter is in the co-pilot foot well on the nose wheel housing. I've got rooom in the panel and will probably move it sometime. I like to record flight hours and tach (Now Hobbs) for my trips but with the location it's really hard to read. It's not a normal shuitdown procedure; I need to read it with a flashlight getting in the plane.  I really don't understand why they eliminated the tach hours. It always made more sense to me than Hobbs for an indication of engine use.

 

 

[scottfromiowa]

O.K. so some are so anal that they would rather have a more inaccurate analog instrument because it "bugs them" that the RPM is 2501.  O.K. Whatever.  The EI tach has analog lights that are just as easy in a quick view to identify once you are used to the gauge...which took me NO time.  Yes it is tougher to get an exact number, but when you do it is exact...not just a warm fuzzy saying it is when it is really not.  I like the hours on the tach too.  For those that prefer analog knock yourself out.

[N6893U]

Thanks to all of you for your insights.

Jerry