Hot Stuff: Unison's LASAR Ignition System (Part Two)

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Unison's LASAR is the first microprocessor-based, FAA-certified engine control system available for widespread application in general aviation aircraft. But how does it work? How involved is the installation? Does it require changing the way you fly your Lycoming engine? AVweb's Dave Higdon just installed a LASAR in his Piper Comanche and answers those questions and more in this long-awaited final installment of a two-part series.

In the aftermath of Part One of this two-part series on installing and flying with Unison Industries' Limited Authority Spark Advance Regulator ignition system, or LASAR, for short, many readers wrote me, complimentary and kind, inquisitive about various points and, ultimately, impatient for the appearance of this Part Two. Patience may not be its own reward, but patience has finally paid off, as it ultimately had to. Office demands and inhospitable weather finally gave way enough for my bride and me to venture east from Wichita for a Christmas visit to family and friends in southern Indiana and the Washington, D.C. area.

It's our version of over the river, through the woods to the grandmothers' houses. We fly this round-trip route several times a year; more than a dozen times in the past five years. Our final flying trip of the old millennium finally gave me a lengthy trip over a known, well-traveled route, my first since installing the LASAR hardware in late September. It was this final flying of Y2K that allowed me to check the performance of our LASAR-equipped Piper Comanche 180, 1961 vintage, against fuel burn numbers from prior trips flown over the identical route in the pre-LASAR Comanche.

Despite several other long trips and some plain-old, hole-boring flights around southeast Kansas, I still didn't hit the 50-hour mark I had set for delivering this wrap-up of my LASAR system story. But 42 hours of flying time with legs ranging from an hour to nearly five still provided me with a clear view of the system's benefits, certainly enough to offer a few conclusions.

The Executive Summary

My impressions became apparent very quickly, developing with more data into my baseline conclusion you can read right now: LASAR is a move into modern technology that improved our airplane's fuel efficiency and available power. As you'll see below, converting to the LASAR ignition system provided an easy, direct method to improve the performance and efficiency of our aircraft's engine. The benefits include easier starting, smoother running, reduced fuel consumption and improved performance. For you instant-gratification types, a table, below, summarizes the fuel consumption numbers.

Of course, there is no free lunch. The downsides include (with yeah-buts):

  • Cost, since the LASAR hardware is relatively expensive, compared to brand-new conventional mags and harnesses, but pays for itself in long-term fuel savings;
  • A bit of added weight, but not even two whole pounds; and,
  • An increased load on the electrical system, but it's hardly noticeable on alternator-equipped airplanes.

Installing LASAR is something I'd do again to any other airplane of mine used as heavily as our current bird. In fact, my only serious regret is not making the change sooner, say immediately after we bought the Comanche in mid-1997. Had we opted for an ignition upgrade instead of a one-piece windshield at our first annual, the fuel savings alone would have us within a couple hundred hours of recovering our costs.

The Benefits

Easier Starting Is Only The Beginning

The object of our discussion, the author's 1961 PA24-180 Comanche, tied down at Oshkosh. Image by Joseph E. (Jeb) Burnside.

You might recall from Part One that installing the LASAR hardware in our Comanche involved overcoming a number of generally minor problems unrelated to the equipment itself; Murphy prevailed over a process in which the ignition switch broke and in rewiring the new switch we literally got some of our wires crossed. But once the wiring was right, the little O-360 Lycoming came to life with an energy and enthusiasm unseen with the old Slick magnetos we replaced.

After more than 20 cold starts since, only once did the engine not light off on the fourth pass of a propeller blade. That happened one cold November morning after the Comanche hadn't been started in more than two weeks. Two shots of primer did the trick, though, a practice I use anytime the plane has sat longer than four or five days. Any other time, one cycle of the throttle to actuate the accelerator pump is all it takes to prime the engine. Either way, the engine seems anxious to start turning. Hot engine, cold engine, flooded engine; the LASAR system overcomes all of them much more easily and quickly than with the conventional magneto-based ignition system.

The reason? Simple: LASAR engages both magnetos for starting, so the engine gets fire from all eight plugs in our Lycoming. And with LASAR providing four times the spark voltage at start, compared to the conventional system, even engines with old, slow-turning starters like ours should fire up faster with less wear and tear on the starter and battery. Less work by the battery and starter should improve their lives, an intangible source of some savings.

The week before I put the finishing touches on this Part Two, the Comanche went in to "Dead Cow International" (Westport, Kan., 71K) for its annual inspection and the condition of the Autolite plugs we installed during the LASAR conversion was hard to believe. More than 42 hours of flight time and they look like they just came out of their plastic shipping sleeves. No trace of lead contamination, not even a little residue. Remember this point the next time the shop tells you that one or more plugs suffered terminating damage while a mechanic tried to clean lead-fouled plugs and salvage them for one more year of service. Less need to clean translates to less physical abuse and reduced exposure to the potential for cracking an insulator or damaging the conductive surfaces.

How LASAR reduces your potential to lead-foul plugs goes to the heart of the value of variable timing.

Speed Vs. Economy 101

You Still Make The Choice And You Still Win...

The complete Unison LASAR system components for a Lycoming O-180, sans sparkplugs.

Basically, as we explained in Part One, the LASAR system reads engine speed, crankshaft position, manifold pressure and cylinder head temperature to calculate the best point in the combustion cycle to send a spark through the plugs. The result is a combustion event perfectly timed for the engine power you set. In contrast, conventional mechanical magnetos fire plugs at a fixed point in the engine's rotation, a compromise that delivers peak performance at one and only one setting. Run the engine at any other load or speed and the timing is no longer optimum, resulting in some wasted fuel and reduced efficiency.

But that isn't the case when the spark plugs fire at the perfect time. For example, say your engine is set to fire the plugs at 26 degrees before top dead center (BTDC). With the conventional ignition system, you can lean the mixture beyond the point where it would run smoothly at the fixed 26 degrees BTDC. Instead, the LASAR system uses its electronic "brain" to adjust the spark timing for optimal ignition timing, based on a "map" of various RPM and manifold pressure combinations it stores on some silicon. It's this ability to adjust the ignition timing to suit the operation that produces reduced fuel consumption and improved power at all power settings. In turn, the reduced fuel consumption, cleaner spark plugs and easier starting all combine to pay off the investment in a LASAR system.

...But, How Much Do You Win...?

My experience has varied, of course, just as Unison gives a range for fuel savings from 8 percent to 12 percent. At altitudes above 6,000 msl, with the engine leaned to peak EGT, our Comanche's fuel consumption has varied from as little as three quarts per hour lower than before, to as much as five quarts per hour. In no case, significantly, has fuel consumption increased.

The best numbers first showed up flying home non-stop from New Orleans after the NBAA's Annual Meeting and Convention in mid-October 2000. Flying at 8,000 feet, with the engine set for 75-percent power, the Comanche consumed 42 gallons of 100LL during a 4.3-hour flight, compared to the 47 gallons typical for similar legs before. That works out to 1.25 gallons an hour less gas. The week before, on an IFR flight southbound to NEW, pulling 75-percent power at 7,000 msl, the Comanche consumed 41 gallons during a four-hour leg. On previous flights at the same altitude, power and duration, the Lycoming consumed 44 gallons. The savings worked out to not quite one gallon per hour.

At a fuel price of $2.50 a gallon, to use an easy example, saving five quarts an hour translates to an operating-cost reduction of $3.13 an hour. Saving .9 gph cuts the hourly fuel costs by $2.25.

Like to fly for best power instead of best economy? The same savings curve applies here as well, compared to the best-power consumption levels of past trips.

...Another Real-life Example...

For another example, on December 23 we flew nonstop to Leesburg, Va. (JYO), from Clark County Regional Airport (JVY) in Jeffersonville, Ind., my hometown on the Ohio River. Level at 7,000 msl with the engine set for 75 percent and 100 degrees rich of peak (ROP), the Comanche consumed fuel at a rate of 10.2 gallons an hour in cruise, compared to 11.3 GPH before. The entire 2.6-hour leg required 29.2 gallons when we topped off at Leesburg, versus 32 and change before. The return flight at 6,500 msl and 75 percent took 2.9 hours and the fuel tab came to 33 gallons. On that leg, the in-cruise fuel consumption was 10.3 gallons an hour.

Interestingly, these best-power legs gave me true airspeeds of about 146, between three and five knots faster than before, while the best-economy legs came in at about the same true airspeeds of 137, about the same as before.

For those of you trying to make the math work, a note: After nearly 600 hours in the Comanche, it's consistently shown to burn about three gallons an hour more during the first hour than it does in cruise, where climbs didn't go above 9,000 feet. But to eliminate any fudge factor, all four examples used here were confirmed by flying cruise legs precisely timed on one fuel tank, using the other tank for the takeoff and landing legs. Of course, overseeing the refueling process was necessary to assure myself that the lineman brought the fuel back to a starting point marked before the prior departure. And the lower hourly fuel-consumption numbers applied almost exactly to both tanks.

...Putting Them All Together

While not as precise as using a fuel totalizer, this method is close enough for me to be comfortable with my numbers. The before-and-after data presented in the table below sums up the results I've obtained so far.

LASAR, by the Numbers

Fuel Burn Before And After Installation
180-HP Lycoming O-360

Best Economy, Leaned To +20 F Rich Of Peak

% Power GPH Before LASAR After LASAR Average GPH Savings Average % Savings Best/Worst %
75 10.2 9.0 1.2 11.7 12.1/10.5
65 9.0 8.0 1.0 11.1 11.5/9.9
55 7.6 6.8 .8 10.5 10.8/9.0
Best Power, Leaned To +100 F Rich Of Peak
% Power GPH Before LASAR After LASAR Average GPH Savings Average % Savings Best/Worst %
75 11.3 10.3 1.0 8.8 9.6/8.3
65 9.9 9.0 0.9 9.1 9.3/8.6
55 8.4 7.6 0.8 9.5 10.0/8.2


  1. Figures are averages of three or more flights at each power setting.

  2. Altitudes flown ranged from 6,000 msl to 9,000 msl.

  3. Consumption was derived via timed runs on one tank and refilling that tank to a marked level.

  4. Power settings obtained from POH and adjusted for temperature and pressure.

  5. Your results may vary depending on the engine, the installation and operating techniques.

Cautionary Points

EGT Changes And CHT Limits...

The old Slick magneto removed from Dave Higdon's Comanche is on the right. The new Slick mag, with the LASAR pigtail, is on the left.

All this technology comes with a cost, of course, in dollars and cents and in operating considerations unnoticed by me at first. First off, whatever numbers you see at peak EGT will change, as will whatever values you typically see for CHT. My EGT readings dropped largely because of the smaller amount of fuel needed at any given engine setting while my CHTs increased because of the more-complete combustion of fuel in the cylinder. At least, that's how the Unison guys explained it to me. Of course, peak EGT is just that: peak EGT. No one should worry about obtaining or not obtaining a specific EGT value because this value will change from day to day and flight to flight.

As for the higher CHTs, that should only be an issue if your engine already develops temperatures closer to your aircraft's limit than you would like. The CHTs on our Lycoming increased about 30 degrees with the LASAR system installed, and the change surprised me. But they haven't been a problem, remaining stable and reliable at their new, higher levels. One of these days, I'll get out to the hangar and see about tightening up the cooling baffles to get those CHTs back down. Unison's technicians have a much better handle on the changes to expect, so you or your mechanic should pose the question to them to get the straight scoop for your engine/airframe combination.

...And Electric System Load

Another consideration I discovered involves an increased load on our old girl's electrical system, one which still used the original-style 35-amp generator. With humid, frigid atmospheric conditions along the route during our holiday travels, the 4 amps or so that the LASAR draws brought my electrical system close to its limit when asked to handle all the other equipment installed: two nav/coms, a Loran, a portable color GPS, navigation lights, beacons, strobes, landing lights and, the worst of them all, pitot heat.

Since pitot heat gets rarely used and since the old beacons are still installed solely for redundance, the excess electrical demand is short-term. But you should consider the additional electrical demand of the LASAR system and the existing capacity of your plane's electrical system. If your electrical source is already running at close to capacity, you should add that fact to consultations with your A&P prior to installing the LASAR system. (We fixed that electrical-load problem at annual with some equipment upgrades I'll write about later this year.)

Finally, a note on LASAR's inherent limitation. Timing advances for most engines are at their lowest at altitudes below 6,000 msl, the Unison reps told me, so the lower fuel-consumption rates don't kick in unless you reduce manifold pressures and, hence, power. The plugs still burn cleaner and the engine still runs more efficiently because of LASAR's ability to reduce spark advance below the fixed setting, but you won't see dramatic fuel savings until you get to 6,000 msl and higher. Conversely, the higher you go, the closer you get to the optimum savings available from the system, or the optimum power, if you choose.

The Bottom Line?

Regardless Of Your Flying, LASAR Pays

The LASAR system's electronic "brain" was mounted to a plate bolted to the engine mounting tubes just forward of the firewall in Dave Higdon's Piper Comanche.

It's hard to quantify the benefits like easier starting, longer spark plug life and reduced maintenance demands that Unison promises from its LASAR ignition system, but not impossible. Unfortunately, AVweb's editors and readers were as impatient as me to see tangible results. But think about those intangibles for a moment: Easier starting means less wear and tear on the starter and battery; less wear and tear should allow them to last longer with less maintenance. Hotter spark can deliver cleaner-burning plugs, which in turn require less maintenance at annual and longer potential life. Together, these ultimately should save any owner a few bucks here and there a lot more than a few where starters are concerned.

Conversely, quantifying the benefits of lower fuel consumption is comparatively easy. It's the main benefit we've examined and the one where we can comfortably calculate a cost/benefit connection.

Taking into account the 42 or so hours flown with the LASAR system installed, lower fuel consumption has already saved us more than $120 in direct operating costs. If our usual annual use rate continues, we've got less than three years to go before fuel savings alone recoup our investment. The typical pilot should expect a payoff period of between 650 and 700 hours on an engine using fuel in the 10-to-12-gallon-an-hour range. That's not that long for the heavy business or personal pilot, but a long time for the average 50-hour-per-year flyer.

Pilots flying hardware that burns 14, 16, 18 or more gallons each hour will see fuel flow reductions of a much higher level, accelerating the payback period proportionally. For example, someone flying a 16-gallon-an-hour single can expect to save up to 1.9 gallons an hour, enough to pay off the $2,700 retail price in a bit more than 500 hours, based on $2.50 per gallon fuel costs. Of course, the higher the fuel costs at any given FBO, the greater the impact on your savings.

And In Conclusion...

Guess this pretty much wraps up what needs to be said about Unison's LASAR system. You need learn no new procedures to use it; you also won't see much of it. Except for those happy little reminders every time you visit the fuel pump. And even if it won't pay off for you for years and years, isn't the added safety of a dual-redundancy ignition system and instantly lower fuel bills worth thinking about?

We thought so before, we know so now, and we'd do it all over again.

Happy flying.

Editor's Note:

Be sure to check out the first part of this two-part series, covering installation of the Unison LASAR ignition system in Dave's Comanche.

To learn more about Unison's LASAR ignition system, be sure to check the Unison web site.