1
NOORDZEE VLIEGCLUB OOSTENDE
DIESEL POWERED ROBIN
DR400/140B
Supplementary information
Remark:
This text is for info only, not to be known by heart, but it helps to
understand the Diesel engine. May help you to fall asleep as well.
INFORMATIONS BASED ON SUPPLEMENT PILOT’S OPERATING HANDBOOK
AND SUPPLEMENT AIRPLANE MAINTENANCE MANUAL PUBLISHED BY
THIELERT AIRCRAFT ENGINES GmbH
Met bijzondere dank aan de collega’s van de RAAC voor het ter beschikking stellen van de
informatie ( F. Gardin –voorzitter NZVC)
Revision History:
V0.1 Initial text - Luc Sobry
V0.2 Initial editing - Danny Cabooter
V1 Some items in description set in bold to draw attention - Marc Teugels
Various layout changes - Marc Teugels
V2 Syntax and grammar review – Paul Hopff
System descriptions corrected – Paul Hopff
Aanpassingen voor NZVC OO-NZV – Gardin Franky
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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
1 Supplemental Type Certificate
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instrument panel. This knob, labelled “ALTERNATE AIR”, should be pulled out if significant
airframe icing happens to be encountered during flight.
No fuel priming is required for engine start and furthermore, as we will see, there is no mixture
control to be taken into consideration.
Perhaps the most interesting part is the fact that the required fuel is diesel (DIN2 EN590), which may
be obtained at any car station-service and which is considerably cheaper than the usual aviation
gasoline. It is unfortunate that, at least presently, few airports (if any) are equipped to provide diesel
fuel. However, as said previously, the TAE 125-01 operates equally well on Jet A1 fuel (ASTM
3 1655),
which is normally available at any major or regional airport. On the other hand, assuming that
diesel fuel would ever be used, one must remember that the fuel temperature in the tank
must be closely monitored, before takeoff as well as during flight to avoid formation of
paraffin (see below).
At any rate, keep in mind that whenever a refuelling stop is required elsewhere than at the
home base, make sure that you don’t plan a stop at an airfield where these fuel types are
not available!
THE TAE 125-01 ENGINE AND ITS PROPELLER
Although most light aircraft engines feature four or six horizontally opposed cylinders, the TAE 125-
01, also referred to as the CENTURION 1.7, has four cylinders in line with double overhead camshaft
(DOHC). In fact, the engine is based on the Mercedes Series A automotive design.
Another major difference is that, unlike most light aircraft engines which are air-cooled, the TAE 125-
01 is liquid-cooled. This, in turn, results in a significant change, not only in the engine’s cooling
system, but in the cabin heating system as well (see below). The power plant also includes a
turbocharger.
Let us first clarify the term “double overhead camshaft”, and have a few words about the
turbocharger:
Double overhead camshaft
Without digging in the constructional details of engines, recall that each cylinder is fitted with (at
least) two valves: the inlet valve and the exhaust valve. Incidentally, the
TAE 125-01 features four valves
per cylinder: two for the inlet, two for the exhaust. The four valve
configuration contributes amongst other things to a lesser fuel consumption and to an improved
quality of the exhaust gases. All these valves are driven by cams (NL: nokken) located on a shaft, the
so-called camshaft (NL: nokkenas) which is itself driven by the crankshaft (NL: krukas).
The camshaft can be located either in the lower part of the engine, close to the crankshaft (NL:
onderliggende nokkenas), or higher up, close to the cylinder head, in which case one talks about an
overhead camshaft (NL: bovenliggende nokkenas), or OHC, operating all inlet and exhaust valves in
the required sequence. Double overhead camshaft, or DOHC, means that two overhead camshafts are
used: one which operates all inlet valves and one which operates all exhaust valves.
Turbocharger
A turbocharger is in fact a form of supercharger and has the very same purpose, namely to increase
the amount of air flowing in the induction system, thus increasing the manifold air pressure (MAP),
and consequently the total power output of the engine. Note that with the TAE 125-01 installed, the
2
: Deutsche Industrie Norm
3 : American Society for Testing and Materials
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induction air inlet and filter is not longer located on the lower part of the front engine cowling (this is
now for cabin heating purposes), but on the rear upper right hand side of it, as seen from the cabin.
The main difference between a turbocharger and a supercharger is that the latter is mechanically
driven by the engine crankshaft, whereas the former is driven by the exhaust gases acting on a
turbine which, in turn, drives a compressor through which the induction air passes on its way to the
cylinder inlet valves. As this compressed air reaches considerable temperatures, an additional
intercooler is often located downstream of the compressor. The TAE 125-1 features such an
intercooler, the cooling outside air originating from the right upper inlet in the front of the engine nose
cowl, as seen from the cabin.
Turbochargers are fitted with a so-called waste-gate which can either be fixed or of the variable type,
either manually, or automatically by hydraulic or, as is the case for the TAE 125-01, mechanical
means. The waste-gate is a valve which offers free passage to a part of the exhaust gases on their
way to the exhaust, while another part of the gases is deviated towards the turbine driving the
compressor. In the variable type, the wastegate is modulated (usually automatically) in order to admit
more or less gases to the turbine, depending on the density altitude and the power setting.
Turbochargers are compact pieces of equipment. However, as they can reach rotation speeds in
excess of 100000 RPM, they are liable to become extremely hot. This is the reason why, whenever a
turbocharger is installed, the temperature of the exhaust gases must be kept in check and may not
exceed a maximum value, which is 900°C for the TAE 125-01. Nonetheless, as the temperature
regulation of the exhaust gases is automatically taken care of, you will not find an EGT (exhaust gas
temperature) indicator on the instrument panel.
One might rightly believe that the basic purpose of the addition of a turbocharger is to allow higher
cruising altitudes. With the TAE 121-1 engine, it is only 16500 ft for the Robin 135CDI. So, why a
turbocharger? Fact is that many diesel engines perform well without it, but lack somewhat “spirit”.
The main reason for the turbocharger is to increase the volumetric efficiency of the cylinders. In other
words, the more air can be crammed into the cylinders during the induction stroke, the greater will be
the power output. In addition, the presence of an intercooler, located downstream of the compressor,
contributes even more to improve efficiency. Indeed, compressed air heats up and tends to expand
when leaving the turbocharger, but the cooling effect of the intercooler significantly reduces its
volume, thereby increasing its specific mass which leads to a greater weight of air entering the
cylinders at each induction stroke. Both the turbocharger and intercooler, in association with the
constant speed propeller system (see below), contribute to the fact that the performances of the
diesel equipped Robin are fairly close to the original aircraft, despite the considerable lower HP rating.
The engine develops 132.8 HP at 2300 RPM (propeller RPM). However, the propeller is not driven
directly by the crankshaft but through a gearbox whose purpose it is to reduce the
propeller RPM by 1.69. This means that if the propeller RPM is 2300, the crankshaft
rotates in fact at 3887 RPM. In other words, if the TAE 125-01’s propeller would rotate at the
same speed as the crankshaft, i.e. nearly 4000 RPM, the noise would probably exceed tolerable values
and the propeller efficiency would suffer severe losses at the tips.
Besides being driven by the gearbox, and despite the fact that only one single thrust lever is available
on the control pedestal, the propeller is referred to as a constant speed type. Perhaps this calls for
some explanations:
1°) The usual constant speed system implies a variable pitch propeller, i.e. a propeller whose blade
angle can be changed (see PILOT NOTES). A propeller lever allows the pilot to select a chosen RPM
for a selected manifold air pressure, or MAP, which is set by means of the throttle. Variable pitch
propellers are mostly fitted with a so-called constant speed unit, or CSU. The CSU is controlled by
normal engine oil. It includes a flyweight and valve system which ensures that, once a certain RPM
value has been selected for cruise, this value remains unchanged even when the aerodynamic forces
on the propeller vary, hence the term “constant speed propeller”. Remember that on a fixed pitch
propeller, i.e. a propeller whose blade angle cannot be changed, if you increase speed by diving the
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RPM increases, if you decrease the speed by pitching up, the RPM decreases whereas, with a constant
speed propeller, the RPM remains unchanged because the CSU automatically varies the propeller
blade angle so as to maintain the RPM unchanged.
2°) As said, with the TAE 125-01 there is no propeller lever available to the pilot. Here, the CSU is a
system which has been developed by Thielert Aircraft Engines. A pump delivers oil from the gearbox
to the CSU. Incidentally, gearbox oil is NOT the same as the engine oil (see below). Within the CSU,
the oil passes first through a micro-filter, then a pressure relief valve which regulates the oil pressure
to 20 bar prior to reach the propeller control valve (more or less similar to the valve system
mentioned previously) which varies the blade angle. The propeller control valve is electronically
(FADEC) controlled. In other words, the pilot has no propeller lever and consequently, has no control
over the propeller RPM, at least no direct control, as is the case with usual constant speed systems.
3°) If you have a look at the “CRUISE PERFORMANCE, RANGE AND ENDURANCE” chart (page 5-9 of
the “Supplement”), you will notice that the propeller RPM value is not mentioned. Only the percent of
load, in fact the percent of power which is selected by means of the thrust lever, is indicated for
various pressure altitudes, together with the resulting KTAS, the fuel flow in litres per hour, and the
nautical air miles (NAM), i.e. the range under no wind conditions. At any rate, assuming that you
cruise at 2000 ft pressure altitude and at 50% load, you will obtain about 1840 RPM, at 60% about
1960 RPM, at 80% about 2140 RPM, etc… and at 100% 2300 RPM. This implies that, although the
pilot cannot change the propeller RPM at all, the FADEC produces the most efficient blade setting for
the selected load.
Two final remarks:
1°) During the external inspection, you will probably notice that the engine exhaust pipe shows
some play whereas, on gasoline engines, it is supposed to be absolutely fit in a rigid way. On
the TAE 125-1, this somewhat flexible mounting is intentional to the purpose of dampening all
sorts of mechanical vibrations, which are usually much stronger in diesel power plants than on
their gasoline counterparts, and which you will probably notice during engine start, and even
more during engine shutdown.
2°) As the propeller is three-bladed and made of composite material, when manoeuvring the aircraft
on ground with the towbar, great care must be taken not to damage the blades.
THE FUEL SYSTEM
Refuelling procedure
At EBOS airport, Jet A1 is available via Jet A1 refuellers.
When closing the filler cap, a locking device ensures that the cap is secured.
Following each refuelling, the amount of loaded fuel MUST be written in the aircraft’s log-book (as per
checklist). As said before, the most usual fuel is Jet A1 but, assuming that common diesel fuel should
ever be tanked, it is IMPERATIVE that this fact is CLEARLY indicated in the aircraft’s log-book together
with the fuel loaded. Indeed, the limiting temperatures of diesel are much more acute than for Jet A1
(see below) because diesel fuel tends to form paraffin which is likely to block filters at lower
temperatures.
Fuel tank
Except for additional sensors providing fuel temperature readings on the instrument panel, the fuel
tank provides a total capacity of 110 l including 1 l of unusable fuel.
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Fuel temperature limitations
According to the “Supplement”, assuming Jet A1 fuel, the minimum permissible fuel
temperature in the fuel tank before takeoff is -30°. For diesel, this minimum must be
above 0°C. On the other hand, minimum permissible fuel temperature in the tank during
flight is -35° for Jet A1, against -5°C for diesel. It is thus obvious that using diesel might
lead to problems if temperatures are not carefully monitored, particularly during
wintertime.
Diesel and Jet A1 may be mixed. However, as soon as the proportion of diesel in the tank
is more than 10%, or if there is uncertainty about which type of fuel is in the tank, the
fuel temperature limits for diesel operation must be observed.
Fuel circuit, common rail, direct injection
With the advent of electronic control, and provided that direct diesel injection is used, as is the case
for the TAE 125-01, the common rail technology can be applied to further improve the quality of the
exhaust gases, to reduce noise and to further reduce fuel consumption, as compared to conventional
diesel engines.
1°) The electric pump, originally installed for priming purposes only, must be “ON” for
takeoff and landing. According to Thielert, the electrical pump “supports the fuel flow to the fuel
filter module, if required”; according to Maintenance a possible reason is that the high pressure pump
(see below) is located on the far front of the engine, which is why the electrical pump acts as an
additional safety in case of failure of the engine driven fuel pump feeding the high pressure pump. At
any rate, no fuel pressure indicator is located on the instrument panel.
2°) From the fuel tank, the fuel goes through the fuel selector to a small reservoir (probably a
remainder from the original gasoline system), then through the shutoff valve via the electric pump.
Thus far, the system is similar to the original one, except for the fact that, for takeoff and
landing, the electrical pump must be “ON”.
3°) Beyond the shutoff valve, the fuel is ducted towards a so-called filter module which includes a
fuel pre-heater system. This pre-heater, typical for diesel engines, is thermostatically controlled to the
effect that the fuel is heated until the operating temperature of 60°C is reached. The heating is
obtained by exchange between excess fuel returning to the tank (see below) and the cold
supply fuel.
4°) Downstream of the filter module, a camshaft driven pump, i.e. the engine driven pump, increases
the fuel pressure to 5 bar (72 lbs/sq.in.), after which a high pressure pump, also camshaft driven,
further increases the pressure up to 1500 bar (21700 lbs/sq.in.), and delivers the fuel to a duct known
as the common rail.
5°) The common rail acts as a sort of high pressure accumulator which supplies all cylinders (hence its
name) through an equal number of injector duct connections, and contains highly pressurized fuel
ready for injection at any required moment. However, an electronically (FADEC) actuated pressure
control valve in the common rail, lowers its internal pressure to a maximum of 1350 bar (19500
lbs/sq.in.). This gives way to an excess of fuel which is returned to the tank.
6°) The fuel injectors, whose operation is also electronically (FADEC) controlled, deliver highly
pressurized fuel into the combustion chamber of each cylinder. This is known as direct diesel injection,
or DI, as opposed to the indirect diesel injection, or IDI.
In the IDI system, the fuel is initially injected either into a swirl chamber or into a so-called
prechamber, located in the cylinder head, prior to enter the usual combustion chamber in the cylinder.
In a way, in both these “sub-systems”, the combustion chamber is divided in two parts. Both swirl- or
pre-chamber have their own specific advantages and disadvantages which will not be discussed here.
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As for the difference between the DI and IDI, here again, both have their own advantages and
disadvantages. For instance, amongst other things, the DI tends to produce more noise, more
vibrations and more harshness than the IDI. On the other hand, the DI gives way to a lesser fuel
consumption than IDI. However, the use of the common rail technology, which seems to be only
applicable for DI, tends to combine the advantages of both DI and IDI.
FUEL SYSTEM
With the TAE 125-1 installed, only two draining points are to be found, a main tank drain valve and a
fuel drain valve.
OIL SYSTEMS
The TAE 125-1 includes two separate oil systems, one for the engine, and one for the gearbox, each
system requiring its own very specific type of oil. Be aware that these oils are not available at the BP
refuelling services at Antwerp/Deurne airport, and must be obtained through Maintenance.
The engine oil system
Let us first emphasize that, according to the “Supplement”, the only approved oils are Shell EP
75W90 API GL-4 and Shell Spirax GSX 75W-80
The engine oil system is a wet oil sump system containing up to 6 litres. A wet sump system means
that the oil is stored in the engine’s casing rather than in a tank (in which latter case one talks about a
dry sump system). The oil level can be checked by means of a dipstick located on the upper center
nose cowling. It should not be less than 4.5 litres, as indicated by the level being between two red
markers at the extremity of the dipstick . The maximum engine oil consumption should not exceed 0.1
litres/hour.
The system is rather straightforward: its main line supplies the various engine parts with the
necessary engine driven supply pump, oil pressure sensor, oil filter and oil temperature sensor, the
used oil being then returned partly by gravity, partly via a so-called catch-tank and associated gear
pump, back into the sump. An additional oil line supplies the turbocharger, and also drains into the
catch-tank.
Downstream of the oil filter, a thermostat ensures that whenever the oil temperature is lower than
78°C, the oil streams directly to the engine and the turbocharger. If the temperature is between 78°C
and 94°C, the oil is partly directed to an oil cooler adjacent to the cooling fluid’s heat exchanger (see
below), then further through the normal path. Above 94°C, all of the oil goes through the oil cooler,
thus ensuring a maximum oil temperature of 140°C.
Note that, although the maximum oil pressure is normally 6 bar, when starting in cold weather
conditions, it is allowed to build up to 6.5 bar for up to 20 seconds. Assuming a low oil pressure
condition, this will activate the “OIL” warning on the original annunciator panel.
The gearbox oil system
This is also a wet sump system, the oil being used for lubrication and cooling of the gearbox, as well
as for the propeller’s constant speed unit. The gearbox oil is not the same as the engine oil: according
to the “Supplement”, the Shell EP 75W90 API GL-4 type is solely to be used.
The system contains only 1 litre. The oil level can be checked by means of a viewer located behind a
small panel at the left lower front side of the engine cowling.
Note:
Although the engine and gearbox oil pumps are said to be engine driven, in fact
they are one single unit, known as a combined system, driven by the gearbox.
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THE ELECTRICAL SYSTEM, THE FADEC & RELATED INSTRUMENTS, ENGINE MASTER
SWITCH
General
The operation of the electrical system is very much the same as prior to the engine retrofit, the most
important difference being the addition of the FADEC system. As the operation of the engine depends
largely on the proper operation of the FADEC, the important thing to be aware of is that the TAE 125-
1 engine, besides fuel, also needs electrical power to keep it running.
According to the “Supplement”, the alternator field is supplied by a 12V excitation battery, whose
secondary purpose it is to supply the FADEC (at least for some time) in case of failure of the main
battery. The complete battery arrangement, main battery and excitation battery, is located in the
fuselage, behind the baggage compartment.
Note that, unlike the main battery, the excitation battery is not recharged by the alternator.
Consequently, besides regular inspections by Maintenance, the excitation battery must be replaced
once every 12 months.
The master switch is a single battery switch controlling the main battery only, the alternator being
controlled by an adjacent circuit-breaker supposed to remain pushed in all the time. Selecting the
battery switch “ON” supplies all busses and their associated users, except the navigation aids which
require the selection of the avionics power switch. Neither does it power ALL of the FADEC
components, some of these being activated by the engine master switch (see below).
The FADEC
FADEC stands for Full Authority Digital Engine Control, i.e. the heart for the functioning of the TAE
125-01 engine. Just as is the case on gasoline power plants where the magneto system is dual, the
FADEC consists of two identical redundant halves labelled A and B or, to put it simply, two computers
operating independently, one being the “active” system the other being the “standby” system, ready
to take over automatically should the “active” fail. FADEC A is normally the active one. Both these
computers are located behind the right hand part of the instrument panel. As said earlier, the FADEC
system is designed to operate on a tension of 14V.
Each FADEC registers a total of 16 signals from sensors in the various parts of the engine. The
sensors are in communication with a total of 9 so-called actuators, i.e. the users of the various
signals, through 5 main control loops. These loops are activated partly by the main battery switch,
partly by the engine master switch.
As an example, let us consider the sensors related to the barometric pressure, the manifold air
pressure, the outside air temperature and the thrust lever’s potentiometer. All these signals allow the
FADEC to calculate the exact amount of fuel to be injected in the cylinders in order to obtain the
required power. Similarly, a propeller signal (sensor) allows the FADEC to select the most suitable
propeller blade angle (actuator). In other words, as the pilot must not be worried by fuel/air mixture
problems, there is no mixture control lever, and, as said before, there is no propeller lever either. In
fact, the pilot has no direct control on the engine: he orders a certain power setting through the
thrust lever and its associated potentiometer, the FADEC performs the required calculations and
executes.
Controller Area Network, CED, AED
The FADEC is fitted with a so-called Controller Area Network system, abbreviated “CAN”. The purpose
of the CAN system is to ensure fast and efficient communication between the various FADEC sensors
and actuators, thus improving the global efficiency of the electronic system. The CAN also allows a
laptop computer with suitable program to be connected to the FADEC. This feature is for maintenance
only, and allows the rapid detection and location of possible FADEC malfunctions. Incidentally, the
laptop computer also shows the total engine running time.
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It is also through the CAN system that the FADEC transmits information to two related instruments,
the CED 125 and the AED 125. The indications on these instruments occur through light emitting
diodes whose intensity may be adjusted by an adjacent additional rheostat.
a) CED stands for Compact Engine Display. It integrates all engine data which are to be
monitored during flight, namely the RPM, both in digits and range, the oil pressure(OP), the
oil temperature (OT), the coolant temperature (CT) and the gearbox temperature (GT), all in
range only, and finally the % of load both in digits and in range.
Range indication are colour coded green, amber and red. Any time a reading is in the amber
or red range, the “Engine Caution” warning light illuminates on the FADEC’s central warning
system and extinguishes only when the adjacent “CED Test/Ack” pushbutton is depressed
(see below).
b) AED stands for Auxiliary Engine Display. It displays the fuel temperature, the fuel tanks
contents and voltage.
FADEC’s central warning system
[HOP2]
The FADEC’s central warning system comprises a red “Engine Caution” annunciator and a common
“test/ack” pushbutton which can be used either for testing both instruments or to extinguish the light
if it is caused by a yellow or red warning showing on the CED.
A separate “GLOW” annunciator is located close to the Starter Key.
In addition, the central warning system includes two red warning lights, one for FADEC A and one for
FADEC B. Assuming that FADEC A, the active one, fails, its associated red warning light will flash, and
the system will normally switch over automatically to FADEC B. Should this not be the case, as made
evident by the engine’s abnormal behaviour, the switching from FADEC A to FADEC B can be done
manually by pulling the “Auto FADEC – Pull to Force B” breaker, adjacent to engine master switch.
Assuming that both these lights should flash simultaneously, this may be indicative that a fuel tank is
running dry (see fuel system above).
Assuming however that, although the fuel level status is satisfactory, both FADEC red warning lights
are flashing, according to the “Supplement”, this situation does not necessarily lead to an engine
failure but, even if the engine continues to run, the load display may not correspond to the current
value, and a total engine failure might be expected at any moment anyway.
The engine master switch, engine starting system
As mentioned earlier, because of its basic operating principle, no ignition system is required for diesel
engines. However, some engines are difficult to start when they are cold because the temperature of
the induction air at the end of the compression stroke is still too low to produce spontaneous ignition
and combustion. It is only once the engine is running that sufficient heat is produced to sustain
combustion.
This is particularly the case with IDI which requires induction air preheat assistance. This is achieved
by electrically heated glow plugs, one located in the combustion chamber of each cylinder, and which
momentarily produce a temperature close to 1000°C.
Although DI engines are less prone to starting problems, the TAE 125-1 is fitted with a similar glow
plug system to improve the starting behaviour when the engine is cold, particularly in combination
with low outside air temperatures. On the TAE 125-1, the glow plugs are FADEC-controlled, as are the
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fuel injectors in each cylinder, both systems being electrically supplied when the engine master switch
is “ON”.
The engine starting procedure is extremely simple. With the main battery switched on, the selection of
the engine master switch to “ON” causes the glow plugs to heat up, which is indicated by the “GLOW”
warning light momentarily illuminating. It also causes the fuel injectors to open and allow fuel under
pressure stored in the common rail to be injected in the cylinders, the whole operation being FADEC
controlled. As soon as the “GLOW” warning light extinguishes, and with the thrust lever in full idle
position, engine starting may be initiated by turning the starter key.
Small detail: the engine’s hobbsmeter (hourmeter) starts “counting” as soon as the engine master
switch is selected to “ON”, whether the engine is running or not. Switching the engine master switch
to “OFF” causes the engine to shut down.
[HOP3]
CAUTION: Selecting either the battery switch or pulling the alternator circuit-breaker to
“OFF” will not cause the running engine to stop, at least not immediately (see below).
However, if both battery and alternator are switched off, as the FADEC is no
longer electrically supplied, the engine will stop at once. If the alternator fails,
electrical power will be provided by the battery only. The time the engine can run on
battery alone will depend on total electrical consumption supported by the battery.
ENGINE COOLING AND CABIN HEATING SYSTEMS
Both these systems are closely related. As was mentioned earlier, the engine uses liquid coolant
instead of being air-cooled. One advantage of the liquid cooling system is that shock cooling during
descent is eliminated. The coolant is stored in a tank within the engine compartment, and is a fiftyfifty
mixture of water and BASF Glysantin Protect Plus/G48, again a product which is only available
through Maintenance.
Prior to start engine, the pilot must check the coolant’s level. This is done by means of a yellow
“COOLANT LEVEL” warning light. When the battery switch is selected to “ON”, it is imperative to verify
that the warning light initially illuminates (mostly very shortly) then extinguishes. Assuming that the
light remains illuminated, the coolant level is too low and engine starting is prohibited. Note also that
engine starting is not allowed if the coolant temperature happens to be lower than -30°C. Incidentally,
the same limit is also applicable to the engine oil and gearbox temperatures.
Engine cooling circuit
The coolant leaves the tank and is pumped into the engine where it evidently picks up heat. Upon
exiting the engine, the coolant is directed to a three-way thermostat of which one exit is unregulated
and relates to the cabin heating system (see below). The two other exits regulate the coolant flow
between a so-called short circuit and/or a large circuit (also referred to as “external circuit”),
depending on the coolant’s temperature:
a) Assuming that the coolant’s temperature is less than 84°C, the coolant circulates through the short
circuit which directs it immediately back to the engine via the pump.
b) Assuming that the coolant’s temperature is between 84°C and 94°C, the coolant is caused to flow
partly through the small circuit, partly through the large circuit. This latter circuit includes a heat
exchanger (radiator) located on the left side of the engine, where the fluid is cooled by outside air
coming from the left upper air intake on the front part of the cowling. This heat exchanger is divided
in two parts, one serving the coolant’s fluid cooling, the other serving the engine oil cooling (see
engine oil system). Upon exiting the heat exchanger, the coolant fluid is directed partly back to the
tank, partly back to the engine.
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c) Assuming that the coolant’s temperature is more than 94°C, the short circuit is completely
bypassed and all of the fluid is directed through the large circuit, thus ensuring a maximum coolant
temperature of 105°C.
Cabin heating and defrosting system
Except for the fact that when the cabin heating is operative, windshield defrosting operates as well.
Outside air is still used, but it is now heated by contact with the hot coolant fluid exiting the engine
through the third non-regulated thermostat’s outlet in a second heat exchanger. The air inlet for this
heat exchanger is located in the lower part of the front engine cowling.
This heat exchanger is fitted with a valve which is controlled by a knob on the instrument panel: the
so-called cabin heat shutoff (unfortunately simply labelled “CABIN HEAT”) which can be selected in
open or closed position:
a) In the open position (knob pulled out), the valve in the heat exchanger directs the heated outside
air to a second valve located in the engine firewall. This latter valve is controlled by a second knob on
the instrument panel (also labelled “CABIN HEAT”!!! find it on the right hand side of the first one,
immediately above the “CABIN AIR” control) and admits or prevents the heated outside air to enter in
the cabin (exactly as was the case in the original system). When this second knob is pushed in, the
outside heated air is dispersed in the engine compartment.
b) In the closed position (knob pushed in), the valve in the heat exchanger pre- vents the outside air
to flow to the firewall, also dispersing it in the engine compartment. In other words, when the cabin
heat shutoff knob is closed, the usual cabin heat knob has no effect. The open position (knob pulled
out) is the normal position during flight.
VACUUM SYSTEM
Only one vacuum pump remains available since the installation of the TAE 125-1 engine.
EMERGENCIES
Section 3 of the “Supplement” covers the TAE 125-1 related emergencies.
In addition to Section 3 please find below some helpful hints:
01.- Assuming an engine failure in flight, selecting the thrust lever in middle position and cycling the
engine master switch “OFF” then “ON” may help to restart the engine. In addition, no restart should
be attempted above 13000 ft.
02.- Considering the propeller stopped case, the best is to consider that, if the propeller stops at more
than 70 KIAS, the engine or propeller is blocked and refrain from using the starter.
03.- Considering the FADEC malfunctions in flight (pages 3-6 and 3-7 of the “Supplement”) three
cases are considered: (a) one FADEC light is flashing, (b) both FADEC lights are flashing and (c)
abnormal engine behaviour. Regarding this latter item, the text says (page 3-5): “If the engine acts
abnormally during flight and the system does not automatically switch to the B-FADEC, it is possible to
switch the B-FADEC manually”. The question is: how can the pilot know that B FADEC has not
automatically replaced A FADEC? Probably by the fact that, following the illumination of A FADEC
warning light, the engine shows “abnormal behaviour”.
If we consider the “BOTH FADEC WARNING LIGHTS ARE FLASHING” case, if this happens with
satisfactory fuel contents, one may believe that it may be due to the fact that B FADEC has not
automatically taken over, and that switching manually to B FADEC might restore normal engine
operation.
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AIRCRAFT PERFORMANCES & LIMITATIONS
The “Supplement” contains charts for takeoff distance, time fuel and distance to climb, cruise
performance including range and endurance… but for some reason, no short field landing distance.
Regarding the takeoff distance charts (page 5-2 of the “Supplement”), two conditions are considered:
takeoff at maximum allowable weight 980 kg, and at 880 kg. Note that TAE considers 1 litre of fuel for
engine start, taxi and take-off.
With regard to range and endurance, the values are based on 109 litres on departure.
The aircraft is certified for both Normal and Utility categories.
Maximum allowable altitude is 16500 ft.
WEIGHT & BALANCE
Remember that diesel and JET FUEL are heavier than AVGAS and they carry more energy
per volume. Because the fuel in the Robin series is in an aft location, fuel consumption shifts the CG
forward. The DR400/135CDI delivers greater range and, at altitude, greater speed, than
AVGASpowered Robin of equivalent sea-level power ratings, for a given volume of fuel.
Normal category
Maximum ramp weight: 980 kg
Maximum takeoff weight: 980 kg
Maximum landing weight: 980 kg
Utility category:
Maximum ramp weight: 910 kg
Maximum takeoff weight: 910 kg
Maximum landing weight: 910 kg
Consequently, assuming two occupants of 80 kg each + 10 kg of baggage (flight cases, etc…) + fuel
up to 110 litres, we have:
600 + 160 + 10 + 89 = 859 kg ramp weight, 858 kg takeoff weight
Needless to say that a third person on board would significantly reduce the allowable fuel load. As for
operations in utility category, it seems that only two persons can be on board.
Note also that the “Supplement” includes only a “LOAD MOMENT” graph. This document is to be used
together with a copy issued from the original POH for the “LOADED AIRPLANE MOMENT/1000” and
“AIRPLANE C.G. LOCATION” graphs. These documents are those which must be used for load &
balance calculations
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