Electronic tachs: UMA is a top value: with electronic guts and an analog display, it combines the best of both worlds. Second choice is Horizon's P-1000, which has diagnostics, but needs a facelift.
If you're like us, you're flying around in something built during the last century but lusting after some of the panel-mounted goodies available in newer aircraft. While it's easy enough to shoehorn in a color moving map and some digital radios, modernizing other areas of your panel isn't. And that's a shame, since much of the engine and systems instrumentation in older aircraft appears borrowed from a 1947 Buick.
But, as usual, the aftermarket has provided in the form of engine monitors, fuel flow instruments and a smattering of tachometers. The tach market is not widely populated, so if you want one, the choices are somewhat limited. Here's a run-down on the pros and cons of this technology, plus a look at the major players in the field.
Of course, the microprocessor in digital instruments does little more than count. Conveniently, a mechanical tachometer does the same thing. The big difference between the two involves how they receive a signal: The microprocessor counts electrical impulses sent to it via wiring, while the mechanical tachometer's many moving parts count the number of times a cable attached to the engine revolves. The former is lighter, more accurate and less likely to fail, at least as long as the aircraft's electrical system powers the microprocessor. The latter is none of those things.
Electronic tachs also have something else going for them: They can do more than just count. Since they generally tap into the magnetos' electrical impulses--although some models can be configured to use a gear-driven tach generator--they also compare the received signals, alerting the pilot to a magneto failure. Further, they can display the mag drop during runup and even advise of a loose p-lead, resulting in a hot magneto. Using LEDs, they also can alert to overspeed situations or when operating in a restricted RPM range. And, of course, they count up the hours the engine is running, although each does it differently, something we'll get to in a moment. The current market for electronic tachometers suitable for certified aircraft includes three products: the Electronics International R-l, Horizon Instruments' P-1000 and an analog but still electronic offering from UMA Instruments, the T19-801 series. As a rule, these tachometers are designed for piston singles, though we are aware of dual installations in twins. Each is approved under TSO C49a and both the EI and Horizon products come with a supplemental type certificate including a broad approved model list allowing use as a primary instrument. Since it's TSO'd, the UMA electronic tach can be installed either as a minor alteration and a logbook entry, or with a Form 337 as a major one.
Other electronic tachs are available but lack a TSO or an STC/AML, making problematic their installation in a certified piston aircraft. These are mainly marketed to the experimental or ultralight/LSA crowd. If you're flying a turbine, you have other choices. Through our online sister publication www.avweb.com, we surveyed pilots and aircraft owners flying an electronic tach. With only one or two exceptions, respondents were uniformly happy with their decision to install an electronic tach and frequently reported that they identified unknown magneto issues and helped isolate other known problems with e-tachs. The table above summarizes these three products' main features.
Electronics International's R-1 ($529 list, before options) offering is the smallest of the electronic tachometers, sized to fit into a 2 1/4-inch panel opening (an adapter plate is available for 3-inch openings). Its size and design complements EI's other instruments, so if you're re-doing your entire panel now or later with EI stuff, everything will look and function pretty much the same. In its center is a four-digit LCD, directly presenting the engine's speed to the nearest 10 RPM. This resolution eliminates one of the complaints about the R-I's chief competitor, Horizon Instruments' P-1000, which resolves down to one RPM: Even the smoothest engine/ prop combination fluctuates some, and the constantly dithering display can be a distraction.
Around the top of the instrument's face is a semi-circular array of 17 color-coded LEDs, representing increments of 100 RPM, an arrangement EI believes provides the best compromise between an analog instrument's ability to display trends at a glance and the electronic version's accuracy. The LEDs are matched at the factory to the specific aircraft type and color-coded green, yellow or red, to denote normal, caution and minimum/maximum RPM ranges.
Two push buttons are mounted below the LCD panel, allowing access to the device's hour and flight-time counters. The R-1 counts real-time engine hours at 1300 RPM and above, while the flight timer starts counting after 10 seconds at or above 2000 RPM, then stops when it drops below 1200. Finally, a circuit is built into the R-1 allowing an external annunciator--a buzzer, for example, or an idiot light--to be energized along with any warning on the instrument itself. The R-1 is TSO'd and comes with STC paperwork, including an AML covering a wide range of makes and models. Installation can require connecting up to eight wires.
The P-1000 electronic tachometer from Horizon Instruments ($609 list) is a larger instrument, sized to fit 3-inch panel openings without an adapter. Horizon uses all that extra real estate to install more and larger buttons, plus an area for mounting a placard advising of any RPM limitations. Backing up that text are six LEDs indicating restricted (red), warning (yellow) and normal operating RPM ranges. Like the R-l, the P-1000 doesn't directly read engine hours. Instead, that information is retrieved using the push buttons.
Also like the R-l, the P-1000 traps and stores that flight's peak RPM, and includes a dimmable back-lighting feature designed for connecting to the aircraft's panel lighting circuit. It also computes the mag drop and any difference during runup. During flight, the P-1000 will immediately alert if a magneto fails and advises of a possible grounded magneto situation.
The R-1 will do this also, but only when RPM is reduced toward the end of a flight. Like the R-l, the P-1000 also comes with STC paperwork and an approved model list. Installed, the P-1000 requires connecting only four wires. One additional feature: The P-1000's mounting bezel allows up to a seven-degree tilt, making it easier to read when mounted across the panel.
If there are any user gripes with the P-1000, they focus on its starting to count engine hours at a miserly 800 RPM and the aforementioned one RPM resolution, which dithers constantly. "The constant hunting of the display is a little distracting until you get used to it. If there was a selectable damping mode, maybe allowing the display to show the nearest 10 or 25 RPM, then the display would not be quite so active," Ric Travis of Germantown, Tennessee, wrote us, summarizing similar comments from users.
UMA Instruments, which supplies a wide variety of gauges to OEMs and others, also offers an electronic tachometer, the TSO'd T19-801 series. Essentially, the UMA tach (about $415 list, before options) has electronic "innards" driving a conventional analog pointer in front of a dial. As with a mechanical tach, arcs and lines applied at the factory for the customer's specific airplane denote normal, cautionary and prohibited operating ranges. Internal lighting is optional, as is an hour meter.
But that's pretty much it; there are no "whiz-bang" features offered by the UMA tach such as magneto monitoring, unless you consider electronic smoothness and reliability, along with a traditional look and feel close to the mechanical tach you removed. That said, one interesting feature of the UMA tach is the RPM at which it starts recording engine and airframe hours. Unlike the offerings from EI and Horizon (see the sidebar), UMA'S tach starts counting hours either at 1800 RPM, the factory default, or some other customer-specified value.
If our mechanical tach failed and we had to replace it tomorrow, we'd be tempted to go with the UMA electronic tachometer after marking it for our application. The result would be a fairly seamless exchange, but we wouldn't get much more out of the deal than a new, more-reliable instrument along with maybe a pound or two increase in useful load. It's the least expensive of the electronic tachs available for a certified aircraft we've found, at least before adding on various options like internal lighting, and when the hourmeter is built in, it eliminates any button-pushing to read engine hours.
Our next choice is the Horizon P-1000. It's a drop-in replacement for most 3-inch panel openings, requires connecting only four wires and offers some much-needed magneto diagnostics sorely missing from most aircraft in the fleet today. Downside: the one RPM distraction and it starts counting hours at too low an engine speed for our taste, needlessly inflating airframe/engine total times. Finally, its look and feel doesn't appeal: The relatively large buttons at the bottom and unused space on each side scream 1985 to us. It could use a face lift.
For around $80 less than the P-1000 (MSRP), we could replace our mechanical tach with an R-1 from EI and get the magneto-related bells and whistles switching to all-electronic offers. If we did it right, we could even save some panel space by mounting the R-1 in a smaller instrument opening. Plus, the R-1 can be connected to a remote annunciator and even an optional data recorder. It's a simpler, cleaner design--at least when compared to the P-1000--and offers what we feel is the best of both worlds: a digital readout accurate to 10 RPM, plus colored LEDs simulating a traditional tachometer needle's trends and arcs. So, even though it's a close call--and the P-1000's tilting bezel may change an individual's calculus-adding the R-1 is what we'd do.
Until, that is, someone comes up with an electronic tach that catapults us squarely into the 21st century. It should be TSO'd/STC'd/AML'd, use a 3-inch form factor, be built around a full-color, touch-screen plasma display, have no moving parts, depict a conventional tach needle and a digital readout along with engine hours, include the magneto diagnostics of the P-1000 and R-l, record RPM, magneto health and flight time and come with some other bells and whistles we haven't even thought of. And retail for $500, installed. While we're waiting and dreaming, we'll be happy with the R-1.
(+) E-tachs are more accurate and more durable than mechanical tachs.
(+) Installation is relatively easy thanks to STCs and AMLs. Small sizes accommodate most panels.
(-) Aesthetics are a toss-up. Horizon looks dated to us. El is hard to read.
(-) Digital only displays aren't a human factors home run, in our view.
The Zen of the Count
For some, the way an electronic tach counts hours is a real issue, leading to racking up engine and airframe hours faster than with a mechanical tach. In extreme cases, life-limited components can be consumed faster than normal.
In contrast, a mechanical tach will tick over a real-time hour at some specific RPM, usually around 2500. At any power setting below that, it will lag behind real time. The exact lag is determined by the instrument's design and the measured RPM. By starting to count hours at 800 RPM, Horizon Instrument's P-1000 counts faster than a mechanical tach and earlier than the competition.
In contrast with the P-1000, El's R-1 starts counting hours at 1300 RPM. That means most taxi operations aren't counted, nor is idling in the penalty box awaiting clearance. Meanwhile, the UMA electronic tach can be custom-configured to start counting hours at any RPM, according to the company. Without a customer specifying otherwise, the factory default is 1800 RPM.
"The electronic tach will show more hours on the airframe and engine than the mechanical tach," Tony Parziale of West Palm Beach, Florida, wrote, adding that his Piper Arrow "is already old with a lot of hours and there is no need to have the tach make it older." Parziale's solution?
"I decided to replace the tach with a new Mitchell mechanical tach and use a JPI EDM-800 to see the RPM and manifold pressure digitally. The JPI digital readout is excellent and I cross-check it to the mechanical tach to make sure they are both in sync."
But are these alternate versions of time really significant? On any given flight, we probably spend 10 minutes taxiing and warming up before takeoff. We perform a runup at 1700 RPM--higher than either the Horizon or El threshold, but lower than UMA's factory default--for a minute or so. At the end of the flight, we'll spend another five minutes taxiing at relatively low RPM before shutting down. So, for a flight time of, say, two hours, we nominally spend 15 minutes running at low engine speed, but usually at or above 800 RPM.
All of our taxiing and idling for that hypothetical two-hour flight--12.5 percent, by our math--will be added to the aircraft's total time with the Horizon. A much smaller amount would be added by the El (or a mechanical tach) and none of it with the UMA.
For us, aircraft ownership is expensive enough--we don't need to make it more expensive. Of course, if you're running a flight school, the considerations are entirely different.
HOW DID WE GET HERE?
ANALOG PREFERENCE AND THE RISE OF THE MACHINE
Pilots may like electronic displays, but they love steam gauges. How do we know? When we were researching this article, UMA's Sefik Mujakic told us that the company has offered digital-only displays in lieu of its electronic analog tachometers. UMA finds few buyers for the digital version--analog rules.
Then we noticed something curious. On its cutting edge EFIS systems, where digits, tapes or dancing bears could show RPM and MAP, both Garmin and Avidyne use--you guessed it--graphically derived analog steam gauges. If that's true, then why do we have tape displays for altimeters and airspeed indicators on the PFD?
Good question, says Steve Jacobson at Avidyne, which did the first mass rollout of glass systems. As Jacobson recalls it, Avidyne and all of the manufacturers did extensive human factors reviews of the display options before committing to certification. He says at review meetings, the FAA reps would frequently question whether the proposed displays would reduce pilot performance.
But Avidyne was forearmed with enough actual pilot flight test data to show that this wasn't the case at all. Tape displays along with electronic renditions of AIs and HSIs seemed to have no measureable effect on pilot performance. But he concedes that little testing was done comparing pilot performance using electronic round gauges against tapes. It's anybody's guess which way that would have gone, but Jacobson thinks it's a wash.
So why do we have tapes for altitude airspeed, but round gauges for RPM and MAP? Did we decide to ape airline or military displays which before 2000 were using tapes and digitally-derived round power gauges? Maybe, says Jacobson, but more likely, we wound up with tapes because they fit into the PFD display better than round gauges would. Besides, Jacobson argues that once you've gotten used to tapes, you never want to go back to dials.
"Getting used to" is the operative phrase here, because anyone who transitions to glass always says the tapes are hard to use, but you can adjust. If there's any human factors benefit to the tapes, the data hasn't been developed for the civil world. Nor were customers polled to ask if they preferred tapes or dials.
"There was no market pull one way or another," he says. In the end, PFD tapes are probably just another example of man adapting to his machines rather than the other way around. And the fact that round gauges endure and are preferred for tachometers proves the point.
MANUFACTURER/ BASE DISPLAY DISPLAY WEIGHT MODEL MSRP TYPE SIZE ELECTRONICS $529 DIGITAL 2.25 7.0 OZ. INTERNATION- LCD/ INCHES AL/R-1 LED HORIZON $609 DIGITAL 3.125 12.0 OZ. INSTRUMENTS/ LCD/ INCHES P-1000 LED UMA $415 ANALOG 3.125 9.0 OZ. INSTRUMENTS/ INCHES T19-801 MANUFACTURER/ RECORDING RESOLUTION LIGHTING MAG DROP/ MODEL RPM MONITOR? ELECTRONICS > 1299 10 RPM INTERNAL YES/YES INTERNATION- AL/R-1 HORIZON > 799 1 RPM INTERNAL YES/YES INSTRUMENTS/ P-1000 UMA > 1799/ 100 RPM OPTIONAL NO/NO INSTRUMENTS/ CUSTOM T19-801 MANUFACTURER/ STC/AML? TSO? MODEL ELECTRONICS YES/YES YES INTERNATION- AL/R-1 HORIZON YES/YES YES INSTRUMENTS/ P-1000 UMA NO/NO YES INSTRUMENTS/ T19-801
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|Title Annotation:||AIRCRAFT UPGRADES|
|Author:||Burnside, Joseph "Jeb"|
|Publication:||The Aviation Consumer|
|Article Type:||Product/service evaluation|
|Date:||Jul 1, 2009|
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