SECTION 3. Engine operation overview
3
Engine operation overview
This is summary of how the ECU controls various stages during the engine operation to better understand the
following section about using the GSU (Section 4). The details about how the ECU controls the engine and the
various settings can be found in 5.
3.1
Engine operation modes
The ECU define several modes of engine operation, which can be controlled by the RC (see Section 5.2).
1.
Off:
The engine is off. Settings can be adjusted via GSU (see Section 4). The engine can then be put
into standby mode using the RC. In standby mode, the ECU accepts a starter signal from the RC and
commences the autostart sequence.
2.
Autostart:
The engine goes from standby mode to operation mode and idle RPM by performing several
steps like pre-heating, switching on the burner, fuel ignition and finally increasing the RPM (see Section
5.3).
When using an analogue (brushed) pump, there is also a phase called
auto calibration
(see Section
5.4), which is needed to determine some characteristic voltages for specific fuel flows and RPM. This is
due to brushed pumps slightly differing in their operation characteristic.
A H
ORNET
-III-ClubSport with brushless pump does not need the auto calibration because all brush-
less pumps of the same model have the same operation characteristic (with only negligible differences).
3.
Automatic:
The engine is running. The ECU responds to the RC’s throttle position, which can govern
thrust or RPM or any linear combination between these two characteristic curves (see Section 5.2). It
automatically adapts the fuel flow to match the user’s input, depending on the RPM and temperature
sensors and monitoring both signals to ensure a safe operation of the engine (see Section 5.5). Telemetry
is transmitted (if using a telemetry module). It is possible to turn off the engine and going into
cool-down
mode
.
4.
Fail-safe:
If the ECU recieves errors from the RC during the
Automatic
phase (e.g. no signal or signal
errors), it switches to
fail-safe mode
if it is configured (see Section 5.6). After a user-defined delay,
fail-safe mode is activated for up to 10
s
and the ECU assumes a prescribed throttle position.
5.
Cool-down:
After the ECU shuts down the engine, the starter will hold the start RPM for several seconds
to allow the engine to cool down. The ECU automatically switches to
off
afterwards.
3.2
Differences in operating behaviour between H
ORNET
-III and H
ORNET
-III-ClubSport
As mentioned in the introduction, the ProJET H
ORNET
-III and H
ORNET
-III-BLC use different hardware,
but the same firmware (as of writing, the firmare version is 2.8). Most notably, they use the same code for
controlling the pump’s behaviour and require auto calibration (see Section 5.4).
To better leverage the brushless pump’s quicker response and the fact that different pumps of the same model
have the same operating behaviour (pump voltage and flow at a specific pressure) up to negligible differences,
AeroDesignWorks modified the firmware of the H
ORNET
-III-ClubSport. This new firmware is designated v3.0.
The AeroDesignWorks H
ORNET
-III-ClubSport uses
a priori
knowledge of the pump’s characteristic curves
and also employs a PI controller for controlling the fuel flow to match the user’s throttle input (and thus RPM).
The result is a much more responsive feel of the jet engine. A comparison of measurement data can be
found in Figure 2. This was done with the same engine by only changing the ECU and fuel pump between
measurements.
•
nrpm
: The normalised RPM, where 0 corresponds to idle and 1,000 to full RPM (in the case of the
B140F 130,000).
•
Controller signal
: This corresponds to the normalised throttle position, where 0 corresponds to idle and
1,000 to full throttle.
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