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INTRODUCTION
The Robin DR400 is originally fitted with a gasoline Textron Lycoming power plant developing 160
BHP at 2700 RPM. It features four horizontally opposed cylinders and is of the normally aspirated,
direct drive, air cooled type. The engine, the O-320-D2A, is coupled to a Sensenich two-bladed metal
propeller.
Because of the soaring prices of aviation gasoline, the NZVCgot interested in the recent
developments of the diesel technology for light aircraft. Thielert Aircraft Engines GmbH
[HOP1]
obtained
a STC
1
to install their TAE 125-01, a diesel engine, but which also operates on Jet A1 fuel (kerosine),
along with a new, three-bladed propeller in composite material manufactured by MT Propeller
Entwicklung GmbH. Both diesel fuel and Jet A1 are considerably cheaper than the usual 100LL
gasoline. In addition, both turn out to be less inflammable, thus reducing the fire risk in case of
mishap. This retrofit entails in turn a few changes in other aircraft systems, as well as in the basic
weights and performance.
Assuming that you read the “Aircraft Flight Manual Supplement” further simply referred to as the
“Supplement”, you have probably noticed that this text is rather superficial, sometimes a bit obscure,
and it even contains some errors once in a while. Although this compilation attempts to explain or
clarify a few things, the “Supplement” mentioned above remains the only official document. In
addition, you will find a questionnaire which may help you in testing your knowledge on the subject.
DIESEL ENGINE GENERALITIES
Present day diesel and gasoline engines are usually operated according to the four stroke cycle:
induction, compression, expansion and exhaust. The major difference in a diesel engine, is that the
cylinder(s) do not compress a fuel/air mixture as is the case in the gasoline version, but solely air.
Typical for diesel engines is that there is no throttle valve. During the induction stroke, the air can
freely enter the cylinder. Unlike in gasoline engines where the fuel/air mixture must be very carefully
metered, diesel engines operate with an excess of air which, amongst other things, significantly
contributes in reducing smoke emissions. Furthermore, as solely air is compressed, no detonation and
engine knocking can occur.
Incidentally, due to the absence of a throttle valve, the lever often referred to as the throttle lever is
no throttle lever at all:
it is a thrust lever through which only the fuel injection at the end of
the compression stroke may be caused to vary, thus regulating the load and RPM
conditions.
Compared to the gasoline engine, the compression ratio in a diesel is much higher. For the TAE 125-1
it is 19/1 or 18/1 (depending on the serial number), i.e. more than twice the value of the original
power plant, thus raising the temperature of the induction air to such a high value that, once fuel is
injected under very high pressure in the cylinder, it ignites spontaneously. This means that a diesel
engine does not require an ignition system, i.e. neither spark-plugs nor magnetos and the associated
intricate wiring system. Consequently,
there is no need to be afraid of spark-plug fouling
during taxi, which may be carried out at idle power without any problem.
Note that in a diesel engine, as the fuel is always injected in the cylinders, there is no such a thing as
a carburettor,
and thus no risk of carburettor icing either
. Nonetheless, if carburettor icing is
non-existent, airframe icing is still likely to occur. Unlike the original Textron Lycoming which features
an automatic spring-loaded door against this condition,
the TAE 125-1 is fitted with an alternate
air door, located at the induction air inlet filter and controlled by a knob on the
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Supplemental Type Certificate
Versie oktober 07
