AOPA Pilot Magazine - February 2015 - 70

THE 135-HORSEPOWER diesel engine

THIELERT'S STORY

CD-135's identical twin, the 155-horsepower Continental CD-155, in Piper
Archers, including the new DX; Warriors;
and the Cessna 172 (see "Going Global,"
December 2014 AOPA Pilot). The CD-135
gained 20 more horsepower primarily
by tweaking the software of the CD-155's
FADEC computers.
The biggest advantage comes from fuel
savings. At the engine manufacturer's recommended cruise setting of 75-percent
"load," as it is referred to in the pilot operating handbook, the CD-135 is producing
about 95 horsepower. During climb the
engine generates 132 horsepower, and I saw
a climb rate of 700 feet per minute with two
people aboard and a reduced fuel load.
WHAT YOU'LL NEED

To retrofit the engine to an existing 172
you'll need a $65,000 kit that includes
the MT propeller, digital panel displays,
FADEC computers, and the engine itself.
(The CD-155 engine costs an additional
$5,000 to $8,000 depending on the value of
the euro.) That number can vary depending
on the value of the euro on the day you purchase, but it does include shipping. Labor is
extra. After 1,500 hours TBR (time between
replacement) you'll need to replace, not
overhaul, the engine. There are efforts to
increase that time, and a flight school in
New Zealand has run the same engine to
3,000 hours with oversight from local airworthiness authorities. Once 1,500 hours is
reached, the replacement engine will cost
$40,789. By comparison, a new Lycoming
180-horsepower gasoline engine commonly used in the Skyhawk is listed on the
Lycoming website at $46,000, with a cost of
$29,000 for a rebuilt engine and $26,000 for
an engine overhaul. You can find a Cessna
172 F through N model yourself and provide it to Premier and Premier will install it
for $85,000 (that includes $20,000 labor), a
price that depends on the value of the euro
on the day of your transaction. You can ask
Premier to find an airplane and do the conversion for a total 0f $179,000, but that price
can increase depending on avionics and
70 | AOPA PILOT February 2015

The engine has had a somewhat tortured
history. The Thielert 1.7, offered in 2002, had
only 1,000 hours' time between replacement
and lost the confidence of customers like
Diamond Aircraft, resulting in today's
redesign.
Today's two-liter engine was designed in
2005, but the cost of development and production sent the company into bankruptcy.
Centurion was created as an agent between
the bankrupt Thielert and the customer, and
later was bought by the same Chinese government entity that also owns Continental
Motors-China's AVIC International Holding
Company.
All assets of the Thielert company,
a.k.a. Centurion (the CD-135 engine was
the Centurion 2.0 back then), were placed
under Technify Motors as part of the Chinese
acquisition. The pilot operating handbook's
engine supplement that is used by Premiere
still uses the name Thielert on its pages.
Before Continental Motors took over the
diesel engine line in 2013, there had been 44
engine failures in Europe involving Thielert
engines between 2003 and 2011-27 of them
were the first-generation Thielert 1.7 engine,
and seven of those were related to the clutch
design.
Other engine problems were found to
be caused by operator or repair error. Causes
ranged from electrical issues to fuel pumps.
All were investigated by BEA, the French
civil aviation safety investigation authority.
The problem engines had been installed
on Diamond DA40 and DA42 aircraft, the
Cessna 172, the Piper PA-28, and the Robin
DR400; most were based at three French
flight schools that aided in the study. "The
statistics...indicate that the rate of in-flight
shutdowns for Thielert engines is no greater
than that of other engines in general aviation," the report stated.
In fairness it should be noted that more
than 4,000 Thielert Centurion engines have
been produced. A company spokesman said
the engines have a total of more than four
million operating hours.
-AKM

other choices. The process takes up to eight
weeks, including three weeks for actual
installation at Premier and the rest for manufacture of a custome engine kit (including
propeller and FADEC) and shipping.
Four inspections of the CD-135 are
required during its 1,500-hour lifetime,
including removal of the gearbox after
600 hours for inspection at the factory in
Germany. Most operators opt instead to
replace the gearbox, getting credit for the
old one and paying $3,500 to $4,500 for the

makes the Cessna 172 a little
slower than a gasoline-powered
172, but speed will return when
the FAA approves the 155-horsepower diesel. The 155-horsepower
diesel engine 172 at 8,000 feet
using 80-percent power will cruise
at 120 knots true airspeed burning
6.8 gallons per hour.

replacement, rather than grounding their
aircraft for a month. A gearbox is necessary to reduce the speed of an automotive
engine to propeller speed. A decade ago the
engine was produced by Mercedes-Benz for
small cars and a light truck, and shipped
to Thielert, the company that developed
today's Continental diesel engine. Parts
today include a few from Mercedes suppliers, but engines are no longer shipped from
Mercedes for conversion.
Diesel engines create a mechanical
jolt, one that would cause cracks in metal
propellers. The solution is to use composite props, such as the MT propeller
with a wooden core reinforced by layers
of epoxy Fiberglas, Kevlar, or carbon fiber,
and sealed by several coatings of acrylicpolyurethane paint. Inside the gearbox is a
torsional damper that further reduces the
pulsing of the diesel engine. A flywheel was
a welcome replacement for a troublesome
clutch-which must be replaced during
the lifetime of the engine-found in an earlier iteration of this engine, the Thielert
Centurion 1.7 (see "Thielert's Story," at left).
My in-flight impression is of an engine
that inspires confidence. I conducted two
flights, one for the usual student pilot
maneuvers (stalls, steep turns, slow flight)
and another in formation for photos with
a Piper Cherokee Six carrying photographer Chris Rose. The formation flight
involved frequent excursions of the power
lever (especially in outside turns as I tried
to keep up with the Cherokee Six), and the
engine handled power changes smoothly.
I had been warned ahead of time to make
smooth throttle adjustments. While broad
throttle excursions would cause dramatic
surging of a turbocharger in a gasoline
engine, it was barely noticeable with the
turbocharged CD-135.
The most serious problem Hallaran has
seen occurs when the aircraft is refueled.
"Be there when the fuel truck shows up,"
he advises. "You don't want them putting
avgas in there."
AOPA
EMAIL alton.marsh@aopa.org
AOPA Pilot Magazine - February 2015

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