On October 4, 2007 Cessna announced its plan to build a diesel-powered Cessna
172 model starting in mid-2008. The planned engine was to be a Thielert
Centurion 2.0, liquid-cooled, two-litre displacement, dual overhead cam,
four-cylinder, in-line, turbo-diesel with full authority digital engine
control.[12] The engine produced 155 hp (116 kW) and burns Jet-A fuel. The
engines were to be installed at the Cessna Skyhawk factory in Independence,
Kansas under an STC. The new model was designated the 172 Skyhawk TD, indicating
"Turbo Diesel".[1]

Cessna had taken special measures to ensure that the Skyhawk TD would be only
fueled with Jet-A and not misfueled with avgas. These included placards,
key-shaped tank fillers that only accept jet fuel nozzles and a spring-loaded
door activated with a jet-fuel nozzle. The aircraft was planned to be certified
for Jet-A only and not automotive diesel.[13]

The TD was to be equipped with only one engine control, referred to as a "power
control", although it resembled the push-pull style throttle used in previous
172 models. The prototype has no carburetor heat or mixture control. The
prototype is equipped with a constant speed MT propeller, but this is controlled
automatically and there is no propeller rpm control.[13]

The TD was designed to have the same gross weight as the "S" Skyhawk, 2,552 lb
(1,158 kg), but at 155 hp (116 kW) was intended to have 25 hp (19 kW) less than
the "S" model. Because it is turbonormalized the prototype's engine produces
full power at all altitudes and actually puts out more power than the "R" and
"S" models above 8,500 feet (2,600 m), where the normally aspirated powerplant's
output drops off.[13]

To account for the fact that Jet-A has a higher density than avgas Cessna
planned to reduce the tank capacity on the TD to 44.6 US gallons, giving the
aircraft a similar range to other models, due to the better efficiency of the
diesel engine. The Thielert 2.0 is reported to burn 5.8 gal/hr at 5,000 feet
(1,500 m) and 75% power. This compares to 8 gal/hr at the same power setting and
altitude for the "R" model and 10 gal/hr for the "S" model Skyhawks.[13]

Even with the reduced fuel tank capacity the full fuel payload of the TD will be
445 lb (202 kg)[13] compared to 519 lb (235 kg) for the Cessna 172S[14] and 440
lb (200 kg) for the 172R.[15]

Direct operating costs for the TD were forecast to be USD$96.39 per hour versus
USD$101.81 for the higher powered "S" model. While the TD would burn less fuel
per hour its engine replacement costs at 2400 hours, instead of overhaul, would
almost make up for the difference, although these numbers will change as the
price of fuel changes in future years.[13]

In early 2008 certification had been planned for the summer of 2008 and Cessna
had forecast delivering about 125 TDs before the end of 2008.[13]

The TD was intended to sell for about USD$15,000 more than the top of the line
"SP" Skyhawk and $35,000 more than the "R".[13] Base price was initially
advertised as USD$269,500 versus USD$254,500 for the "SP" or $234,500 for the
"R".[16]

Early orders for the TD were strong with most of the demand from flight schools
and non-US operators.[13]

In April 2008 the 172TD's engine manufacturer, Thielert filed for insolvency
under German law, throwing the future of the aircraft into doubt.[17][18][19][20]

On May 1, 2008 Cessna announced that they have cancelled all 2008 deliveries of
the 172TD due to the insolvency of Thielert. The company stated: "At this point
we have decided that we will not deliver 172TD aircraft during 2008, and we have
informed our customers accordingly."[21] Cessna has indicated, however, that
they will proceed with the certification of the 172TD.[22]

Cessna has indicated that they still wish to produce a diesel 172 as market
demand is strong for this aircraft with over 100 orders.[21]
--------------------------------------------------------------

Appears to me Chris Dries is going down the same Mercedes A class engine
dead end road.


Twin Star Claims
50% power 7.2 gallons per hour 135 KTS 155 MPH
60% power 8.8 gallons per hour 138 KTS  159 MPH
90% power 14.4 gallons per hour 163 KTS  187 MPH

135 HP each or 270 HP total
90% 243 HP

14.4 gallons is 99 pounds of diesel fuel per hour. BSFC = .4 pounds per HP hour.
A regular leaned Continental is close to that BSFC and a non-leaned Lycoming is
.45 with out the extra weight of the diesels. The rotary is lower weight and
.47 BSFC.

50% power is 135 HP
7.2 GPH or  50 pounds of diesel fuel per hour or BSFC .37 pounds per HP hour.

Nobody is going to buy a $750,000 twin airplane and cruise it at 163 KTS let
alone 135Kts except perhaps flight schools that need twins. People are looking
for something that flies well over 200 Kts for that amount of money.

The hot tip is an engine that runs on car gas like the Mistral Wankel rotary.
Car gas is over $1.50 cheaper per gallon right now than 100LL and about 50 cents
cheaper than Jet A. This is due to the fact there is only 15% diesel fuel in a
barrel of crude while there is 30% gasoline.


Paul Lamar


Paul,

in early 2005 Christian Dries had successfully head-hunted Thomas Müller,
ex-chief development engineer with Thielert Engines. He was made new chief
engineer of Diamond Engines, hence my new boss. After just about half a year he
had acquired all skills (with respect to the EASA responsibilities) necessary to
replace myself - and so he did. He then was asked to develop their own Diesel
engine to replace the existing Thielert 1.7l Centurion engines which proved to
be not quite as reliable as they were supposed to be. This new engine seems to
be the future of Austro Engine, their new company. It is based on the 2.0l
Mercedes Benz engine, data can be found on their homepage.

Apparently they are quite desperate for that replacement as there appear to be
well in excess of 100 Thielert powered Diamond Star and Twin Star aircraft
grounded worldwide due to lack of spares and service!

I still wish I had been given the chance to help developing the then R5, R6, and
R7 called family of all new 400cc Rotary Singles (see attachment), Twins and
Double Twins as they had been on display at the MWE Open Day in Staverton, UK in
back 1999!

Regards

Martin


Thanks Martin for the great insight.

That is going to take years in the mean time there will be a lot of
pissed off Diamond Star and Twin Star owners :) Too bad that money
is not going into the one (75 HP) and two rotor (150 HP) rotary development
and certification.

I think Chris Dries had no choice as he had to do something?
This will keep the owners hopes up until they bail or forget :)
Diesel engines are dumb ideas for aircraft anyway. That was all figured
out back in the 1930's with Packard, Jumo and others. 20:1 compression ratio
is 20:1 compression ratio. There is no getting around the extra weight that
implies unless they can figure out how to make the engine out of carbon
fiber. If you can make a diesel engine out of carbon fiber you can also
make a piston engine out of carbon fiber and you are right back where
you started.

The demands on European engines are no longer as severe as they once where.
There are now more speed limits on the autobahn and the traffic is such you can
no longer drive flat out for more than a few minutes at a time. 140 Km/hour is
about it. 90 or 100 MPH. As I recall the NA Mercedes A class top speed
is about 140 KM/Hour  I rented one in Frankfurt and drove all over Italy
and back with one. It was not the turbo diesel version.

Paul Lamar

Paul,
I use a rule of thumb of about 8/5ths approx. 140 = 87.5 mph; 160 = 100 mph.
You can use 5/8ths to convert the other way.
George ( down under)

1 kilometer/hour = 0.621 371 192 24 mile/hour (mph)
http://www.onlineconversion.com/speed_common.htm

Paul Lamar