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.
February 21, 2001
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
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.
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
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
...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.
by the Numbers
Fuel Burn Before And After Installation
180-HP Lycoming O-360
Best Economy, Leaned To
+20 F Rich Of Peak
Power, Leaned To +100 F Rich Of Peak
Figures are averages
of three or more flights at each power setting.
Altitudes flown ranged from 6,000 msl to 9,000
Consumption was derived via timed runs on one tank and refilling that
tank to a marked level.
Power settings obtained from POH and adjusted for temperature and
Your results may vary depending on the engine, the installation and
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
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
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
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.