Analog Display
The display screen is arranged into three sections. The top
left is the RPM and MAP section. The bottom left is the Scanner® section. And
the right side is the Bar Graphs section.
RPM and MAP Section Display
The upper semicircular bar graph shows the RPM (Revolutions
per Minute) and the lower semicircular bar graph shows the MAP (Manifold
Pressure). These are shown both graphically and digitally. Power settings
entering red line are displayed by flashing the ALERT icon and flashing message
on the bottom left scanner section of the screen. Percent horsepower is
displayed digitally underneath the MAP arc
Bar Graphs Section Display
The Bar Graphs section contains nine dedicated 12 segment
bar graphs with digital display. The default displays are (left to right, top
to bottom):
- Oil temperature
- Oil pressure
- Fuel pressure
- Bus voltage
- Amps load or charge/discharge
- Outside air temperature (or owner select able )
- Fuel flow, units per hour
- Left fuel quantity (or owner select able)
- Right fuel quantity (or owner select able)
The top of the bar is red line and the bottom of the bar is
zero for O-T, OP, F-P, amps load. For amps charge/discharge the center of the
bar is zero and the top and bottom is red line charge and discharge,
respectively. For volts the top of the bar is high red line and the bottom of
the bar is low red line.
The top of the bar for Fuel Flow is set by the MAX FF
parameter. The white horizontal line indicates freezing for OAT. The ranges and
alarm values are user settable and are described later in section Section 10 -
First Time Setup and Customization on page 36.
Basic Scanner Operations
Let’s examine the scanner section analog display. Central to
the display is the exhaust gas temperature— or EGT— bar graph presentation. The
height of each column represents the EGT. The last column shows turbine inlet
temperature. The range of the EGT columns is red line at the top down to one
half of red line at the bottom. This is called the percentage view because you
are looking at a percentage of red line. The Normalize view allows you to see
small, subtle changes in temperature. When you change to the Normalize
view—hold the Lean Find button for three seconds all column heights are set to
the identical half-height. Any changes are shown as an increase or decrease in
column height. A one-bar change in column height represents a 10 degrees
change.
The Normalize view permits rapid visualization of EGT
trends, rather than a percentage of red line. The missing segment in the column
represents the cylinder head temperature. Above each column is a number
corresponding to the engine cylinder number. The rightmost column displays
turbine inlet temperature. Beneath the bar graph is the alphanumeric display. A
single index dot above one column indicates which cylinder is being displayed
on this numerical display. When the index dot is beneath a cylinder number, 1
through 6, the digital display shows the EGT on the left four digits and the
CHT on the right three digits. Two other derived measurements are shown in this
display:
The rate of shock cooling of the most rapidly cooling
cylinder, in degrees per minute. Lycoming recommends that you keep this value
below 50 degrees per minute. The difference between the hottest and coolest exhaust gas
temperatures.
EGT
EGT is shown on the first four or six Scanner bar graph
columns. These are labeled 1 through 4 or 1 through 6 above the columns. The
lower limit of the graph range represents half of the TIT alarm red line
(default is 825°F) and the top of the range represents alarm red line (default
1650°F). The numerical value of the EGT is shown on the left side of the
digital display for each cylinder when there is a dot under one of the cylinder
numbers above the column—cylinder 2 in this example. There are two views:
Normalize view levels the EGT columns and increases the sensitivity of the
Scanner bar graph columns to 10° per segment. To enter the Normalize view, hold
the LeanFind button for three seconds. The NRM icon will be displayed above the
Scanner section. Hold the LeanFind button for three seconds to return to the
Percentage view.
CHT
The Cylinder Head Temperature—CHT—is represented by a
missing segment in the Scanner bar graph column. If the EGT is too low for
there to be a missing segment, the CHT is represented by a lone segment in that
column. The scale is shown to the left side of the columns. The numerical value
of the CHT is shown on the right side of the digital display for each cylinder
when there is a dot under one of the cylinder numbers above the column.
TIT
If you have TIT, it will be shown on the right-most Scanner
bar graph column and will be labeled with a T above it.
Normalize View Indicator Percentage view (when the NRM icon
is not lighted): the columns indicate percent of EGT red line. Each column is
composed of a stack of segments. A maximum height column depicts 100 % of red
line and a one segment-high column depicts 50 % of red line. For example, if
the red line is 1650°F, a maximum height column represents 1650°F and a one
segment high column represents half that value, or 825°F. The Percentage view
permits comparison of EGTs across all cylinders. Hotter cylinders display
higher columns than cooler cylinders.Normalize view (when the NRM icon is
lighted): the EGT columns are displayed normalized. When you change to the
Normalize view, all columns are initially set to the same half height level for
trend analysis. Any changes are shown as an increase or decrease in column
height. A one-segment change in column height represents a 10°F change. The
Normalize view permits rapid visualization of EGT trends, rather than a
percentage of red line. You can use normalize in level cruise and run-up. The
Normalize view allows you to see small, subtle changes in temperature. When you
change to the Normalize view — hold the right button for three seconds — all
column heights are set to the identical half-height. Any changes are shown as
an increase or decrease in column height. A one-bar change in column height
represents a 10 degrees change. The Normalize view permits rapid visualization
of EGT trends, rather than a percentage of red line. Above each column is a
number corresponding to the engine cylinder number. The rightmost column, if
present, displays oil temperature. If turbine inlet temperature is installed,
then the rightmost column will indicate this with a T above that column.
Beneath the bar graph is the alphanumeric display. A single index dot above one
column indicates which cylinder is being displayed on this numerical display.
When the index dot is beneath a cylinder number, 1 through 6, the digital
display shows the EGT on the left four digits and the CHT on the right three
digits.
To toggle between Percentage and the Normalize views, hold
the LF button for three seconds until the NRM icon toggles. The analog display
becomes half height and the display changes to the Normalize view. Selecting
the Normalize view does not affect the digital display nor alter the measurement
sequence. The scale of the CHT display—described later—is not affected by the
Normalize or Percentage view. You may select the Normalize view in either the
Manual or Automatic mode. Normalize view is most helpful for engine trend
monitoring of each cylinder’s operation during cruise. When using the Normalize
view during engine run-up, a fouled spark plug will appear as a higher column.
A common misapplication is to be in the Normalize view and then change your
power setting, causing all columns to go off scale, high or low. Select the
Percentage view before adding or reducing power. Always select Percentage View
when beginning your descent.
Buttons?
There are four buttons on the front panel. From left to
right they are the STEP button, the Lean Find button, the GMT button, and the
EGT fuel flow button. Ten minutes after the EDM-900 is turned on, it will
automatically index through all measurements.
Tapping the STEP button will always take you into the manual
indexing mode. Here you can observe each measurement value for as long as you
want. To the resume the automatic indexing, tap Lean Find and then tap STEP. To
switch between the percentage view and the Normalize view, hold the Lean Find
button down for five seconds. The GMT button displays the time in the lower
left scanner section. It also shows to which measurement each of the nine bar
graphs is configured. You have a choice of three display indexing options as
selected by the EGT-FF button. · The EGT position will display only
temperature-related measurements· The FF position will display only the fuel
flow-related measurements, and· The ALL position will display all measurements.
The display indexing option does not affect the bar graph
display, nor does it effect the alarms. Any alarm, such as an over temperature
alarm will immediately display the alarm message regardless of which display
indexing option is selected.
What about Lean Find Mode ?
In a piston engine only a small portion of the energy from
combustion produces movement of the piston during the power stroke. The
majority of energy passes into the exhaust pipe as hot gasses. By monitoring
the temperature of these exhaust gasses you will have an indication of the
quality of the combustion process. Low compression, non-uniform fuel distribution,
faulty ignition, and clogged injectors diminish the efficiency of the
combustion process that generates power. From the cockpit you can adjust the
fuel/air ratio by a process called leaning. Retarding the mixture control
changes the fuel/air ratio and hence the resulting Exhaust Gas Temperature
(EGT).
The following figure depicts the mixture and temperature
relationship.
As the mixture is leaned, EGT rises to a peak temperature,
and then drops as the mixture is further leaned. Peak power occurs at a mixture
using more fuel than at peak EGT. Best economy occurs at peak EGT. Accurate
leaning yields optimal engine temperatures. By being able to precisely adjust
the mixture, your engine can produce either the best fuel economy or maximum
power, whichever you choose.
As the mixture is leaned, EGT rises to a peak temperature,
and then drops as the mixture is further leaned. Peak power occurs at a mixture
using more fuel than at peak EGT. Best economy occurs at peak EGT. Accurate
leaning yields optimal engine temperatures. By being able to precisely adjust
the mixture, your engine can produce either the best fuel economy or maximum
power, whichever you choose.
So how do I use the Lean Find Mode?
Upon reaching cruise configuration, you can use the LeanFind
mode to identify the first cylinder to reach peak EGT. Note that this is the
leanest cylinder, not necessarily the hottest cylinder.
You begin the leaning process by pre-leaning the mixture to
about 50 degrees below the estimated peak on any one of the cylinders. For example,
let’s say that you have determined that 1350 is the pre-lean value for your
aircraft. Now wait about 30 seconds for temperatures to stabilize.
You can enter the LeanFind mode by simply tapping the
LeanFind button. You will then see the exhaust gas temperature of the hottest
cylinder on the left display. Now you slowly lean the mixture at a rate of
about 5 degrees per second. When there is a 15° rise in EGT, the Lean Find will
become active, indicated by the flashing cylinder number of the hottest cylinder.
If you have the fuel flow option, the fuel flow rate will be shown on the right
display. Stop leaning when the column begins flashing. You will see PEAK EGT on
the display, followed by the value of the exhaust gas temperature of the first
cylinder to peak.. In most cases you will now be on the lean side of peak by
about 10 degrees. While the column is flashing, slowly enrich the mixture. The
temperature will increase, returning to peak. Stop enriching at the desired
exhaust gas temperature, usually peak to 20 degrees rich of peak for best
economy.
