1. TASK OF THIS MANUAL
This manual gives all information
required by the owner or user to understand all functions of the instrument, to
install it, if necessary to program it, to maintain it, and finally, to use it
in flight.
It is not necessary to study this
manual in an intensive way in order to be able to use the instrument. Rather
superficial reading will enable the user to find a particular subject, later,
with the help of the list of contents, in case there is a question. For the
rest, the manual is written in a way to inform the interested user very
thoroughly on the instrument, for him to draw a maximum of benefit from it
Because the manufacturers are convinced
that a good manual contributes substantially to the benefit a user will draw
from an instrument, they have invested much effort and experience in this
manual.
The right place for this manual is the
main file of the aircraft into which the instrument is installed. Ideally it
should be made available to every pilot who uses the SB-8.
Before installing the instrument, and
under all circumstances before making any electrical connection, the chapter on
installation must be read. Before any opening of the instrument the chapter on
adjustments and programming must be read.
Chapter 7 (The SB-8 variometer in
flight) is thought as an annex for the more advanced and/or interested pilot.
It has been written in such a thorough way because this matter is not being
treated in the general literature on soaring.
WARNING: This instrument is to help the
pilot to plan his flight on the basis of data he has. It does not relieve him
from his responsibility to control his aircraft in a safe way. Under no
circumstances can the SB-8 replace an airspeed indicator or any other element
of safe piloting.
This manual is continuously being
updated, and therefore up to our latest knowledge, as well as adapted to the
latest technical state of the instrument. Accordingly it applies only to
instruments with the serial numbers below, and at any rate to the instrument it
has been delivered with.
This
manual applies to all standard instruments of the SB-8 type from serial number
6900 onwards.
State:
March 1990
LIST OF CONTENTS
2.3.
Variometer audio generator
2.5.
Audio generator of speed command
2.8.
Distance- and Final glide computer
5.
ADJUSTMENTS AND PROGRAMMING
5.2.
Zeroing of the Transducers
5.6.
Indicator Options (Configurations)
7.
THE VARIOMETER SB-8 IN FLIGHT
7.1.
The 1-second and the 3-second responses
7.4.
Flying with the Speed Command
7.6.
Looking for thermals with the speed command
7.7.
Influence of normal Acceleration on the Indication of a TE-vario
2. Description of the System
2.1. Principle of measurement
The transducers for vertical- and
airspeed are thermal flow measurement devices using thermistors at constant
temperature (which makes the difference). They excel by a very good stability
of zero output, by a very short response time of 5 milliseconds, and strong
independence of their calibration, of changes in the instrument's temperature.
They ensure the instrument's high precision, amongst other things.
2.2. Variometer
The raw variometer signal coming from
the transducer is fed to 3 different electronic filters to shape it into 3
different response types, this in parallel in order not to have to wait for
them to settle down. The variometer indicator (visual as well as acoustic) can
be switched alternatively to the 1-second- or the 3-second-response by means of the filter
selection switch on the front of the instrument.
1s-filter:
Second order active filter, with fast, however strongly damped response.
3s-filter:
First order active filter, response nearly equal to moving vane vario.
Averager: Similar to 1s-filter, however, sporting much
larger time of averaging.
(For
a more comprehensive treatment of the filters see appendix)
2.3. Variometer audio generator
The full-scale range of the generator
is +/- 15 m/s (30 kts). In this way vertical speeds far outside the range of
the visual indicator will still be perceived.
The method of modulating the frequency
of the base tone, as developed by ILEC, offers an advantage over the simply
interrupted tone. Even after an infinite time, one will perceive the absolute
value of the climb rate, 0,5 m/s (1 kts) e.g. or 3 m/s (6 kts), without the
need to go back to the visual indication to find out whereabouts one really is.
With the only interrupted tone, after a few seconds, one will merely perceive
the tendency of the signal (faster up = slower down, or faster down = slower
up?), however one will no more hear where on the vertical scale one actually
is. In other words: with the modulated tone, one will have to look less
frequently to the visual indicator than with the well known interrupted tone.
There are pilots who do not want this
larger information, or who have become accustomed to the old, well-known sound
and want to stay with it. For these pilots the tone can be changed to the
interrupted one by internal programming.
The base tone itself consists of 3
single tones, it is more agreeable to hear than the single base tone known so
far, meaning, that it is much more bearable after some hour's flight. He, who
prefers less, can program a double, or the well-known single tone.
On top of that one can adjust frequency
of the base tone as well as frequency of the modulation to one's own
preference.
The volume of the sound is servoed to
airspeed such that it is always found equally loud, whether at 70 or at 220
km/h (40 to 120 kts) (noise of the aircraft changes drastically in this speed
range). The volume button needs to be adjusted only once, and at high speed one
still hears the audio. (Upwards the volume is limited by maximum power of the
built in speaker, in case of need, an external speaker can be used.)
2.4. Speed command
The polar to be used by the computer is
being selected (Pn = normal polar, Px = bug polar e.g.), wing loading and
McCready-value are set at the front panel.
Wing loading is quite simply the
aircraft's all up weight, divided by the known wing area (22 to 50 kg/sqm, or
4.5 to 10 lb/sqft).
The speed command system computes the
optimal cruise speed on the basis of the polar chosen, the wing loading and the
McCready-value set, plus the actual meteorological vertical air speed being
continuously measured.
What is being indicated is the
difference between the - actual - optimum speed (the McCready-speed) as
computed, and the airspeed as - actually - flown. Indication is direct in km/h
(kts) in the range +/-100 km/h (+/-50 kts), this being the ideal scale, taking
into account ease of control. With the help of this clear information the pilot
is in a state to steer the optimal speed easily and fast. (The contrary: the
usual speed command systems. They give a sink command, no speed command. As the
optimum sink depends strongly on the flight speed flown, the pilot normally
controls poorly).
Signal conditioning in the time domain
in the SB-8 is done in a way to make the control loop - consisting of pilot and
aircraft - as stable as possible. (In the case of poor systems, the speed
command's indicator can even diverge, despite the stick being moved correctly:
The optimal speed will never be reached here, only the pilot will do much work,
and this for nothing).
2.5. Audio generator of speed command
When one flies too fast, one will hear
about the same sound as with a climb of 5 m/s (10 kts), when flying too slow,
the one of a 5 m/s (10 knots) descend. This system enables one to thermal with
the speed command as well (in the speed command mode = SF) if one does not want
to switch mode.
As long as air speed is within a
tolerance band around the optimal speed (the limits of which can be adjusted
from 0 to 30 km/h (0 to 17 kts)), the signal is muted. Upon approaching the
limits of the dead band, the signal appears gradually, the pilot not being
induced to overreact.
2.6. Mode switching
In most cases one has to tell the
vario, what it is to indicate, visually as well as acoustically; vario or speed
command e.g. In order for that to happen, one has to switch mode (what - then -
will indeed change on the various remote indicators, depends on the indicator
option selected, see next chapter)
In the middle position of the mode
switch ("A") mode is automatically determined by the Remote Control.
The 2 other switch positions override the remote control signal (for electrical
connection see circuit diagram 1 in the annex).
In this way one can determine mode by
oneself, and ignore the command of the remote control system. To do that, one
only has to set the mode switch to the appropriate position.
In practice, it turned out that for
remote control the simplest, best method is by the flap switch (Any manufacturer
of gliders will know the best positions to use and the way to fix the
switches!)
In case one has no flaps, one best
mounts a switch near the position of rest of the pilot's left hand or on the
stick: The pilot himself does the mode switching better than any automatic
device. He himself only has eyes, and only he himself knows what he intends to
do next; the automatic device does not have eyes, nor can it know.
In case no remote control has been
connected, the instrument will be in speed command ("SF") already in
its middle position ("A").
2.7. Indicators
Depending on the configuration of
remote indicators used, the built in indicator will automatically be switched
to a different signal, this as a function of mode. To take care of the
configuration of remote indicators, the instrument can be programmed
internally. A maximum of 2 out of the 3 signals "Vario",
"Integrator" = averager, or "speed command", can be
indicated on the built in indicator (No sweat, ILEC will already have executed
the programming for the configuration ordered).
By principle, the 3 signals mentioned
above are fed to the connector at the rear of the instrument, this without them
being influenced by the mode in which the instrument actually is. If one
connects remote indicators to the rear connector, the corresponding signals
will be indicated p e r m a n e n t l y. This feature is particularly
interesting for two-seaters!
There are 4 options for the basic instrument, which determine the configurations possible, they are assembled in the table below. (Instructions for connecting the remote indicators are to be found in chapter 3.4., for programming in chapter 5.6.
|
OPTION |
MODE |
AUDIO |
MAIN
INSTRUMENT |
REMOTE INDICATORS |
|
M = mono-bloc |
Vario Speed
Command |
Vario Speed
Command |
Vario Speed
Command |
|
|
B
= Two-bloc |
Vario Speed
Command |
Vario Speed
Command |
Averager Speed
Command |
RAZ
always Vario |
|
V
= always Vario |
Vario Speed
Command |
Vario Speed
Command |
Vario Vario |
DAZ Averager and
SC |
|
I
= always Averager |
Vario Speed
Command |
Vario Speed
Command |
Averager Averager |
RAZ
Vario and RAZ100
SC |
The
Monobloc system is ideal for small instrument panels.
The 2-block system delivers all
important information, without the need to push a button (in case of the
Monobloc system one has to call off the "Averager" by pushing a
button). Advantage: the very short remote indicator for the "Vario"
can be mounted right on the top of the panel, the generally strongly reclining
cover will not disturb here. On top of that the vario indicator is on the top
rim of the panel where it should be.
The 2 other options offer the most
complete systems, with all 3 important indicators in parallel and permanent.
Nothing is being commutated, except the audio. Additional advantage: one can
mount the instruments where one wants them.
For two-seaters the aft configuration
is completely independent of the front one: the signals are always there.
One word should be said on the choice
of optical indicators: Round meters are - by principle - faster to be read than
flat meters. They also do have a much smaller parallax error. On top of that
their scale length is much larger: their range can be larger. One should
therefore use round meters, whenever possible.
Additional
functions
Upon
pushing a button, the following information will be displayed on the built in
meter:
State
of the battery:
On the inner rim of the scale disc
there is a separate battery scale consisting of a pattern of points and a „0“. As long as the pointer is to the
right of the 4 points, the battery is still 4/4 full, in case the pointer
stands on the 3 points, it is still 3/4 full, and so on. When the pointer has
arrived at the 0 of that scale, then the battery is practically empty (the 0
corresponds to about 11 volts of battery voltage). However, the SB-8 can still
be run from this "empty" battery for a long time - if all other loads
are switched off! It consumes very little current and it will still work at 9
Volts of battery voltage.
Outboard
temperature:
Is
being indicated in the range +/- 50 degree C on the normal scale: one big
division corresponds to 10 degrees C.
2.8. Distance- and Final glide computer
Nearly all signals which the Distance-
and Final-glide-computer (ASR) needs, are drawn from the SB-8. This means, that
one will set the necessary parameters (wing loading, McCready-value, polar,
mode) on the SB-8, to forget them then. In particular the mode does not have to
be switched separately. Exceptions to the rule: Wind and distance, they are set
on the ASR itself.
For this to be possible, the ASR has to
be connected to the SB-8 via the cable provided by ILEC.
2.9. Precision
For
general specifications see the prospectus.
Altitude
error:
The Calibration factor (not the zero!)
of the variometer depends on air density and therefore on altitude. (Other systems are also dependant on
altitude, only in a different way, as long as they are not actively corrected
for the effect, correction, which is generally only done on expensive
instruments). When measuring vertical speed with the SB8 (vario), the
indication decreases at a rate of 5 % per 1000 meters increase in altitude (= 5
% per 3 000 ft), measured against the value, which relates to IAS. This value,
the only correct one, takes into account the increase in TAS at constant IAS
with increasing altitude, it is the only correct one to be used for computing
speed command.
A moving vane variometer, by principle
indicating t r u e v e r t i c a l speed - as one would measure it with stop
watch and altimeter -, will indicate 5 % too much, measured against the correct
scale!)
As the transducer for total pressure
also shows a decrease in magnitude of output with increasing altitude, both
errors cancel one another partially for computing optimum speed. The residual
error depends on the aircraft’s polar, the McCready-value entered, and actual
air speed. It is approximately - 5%
per 1000 m altitude difference (-5 % per 3 000 ft), where the averager output of
the SB-8 is taken as the basis for the McCready input.
The amount of error in the speed
command finally remains within +/- 4 % in the altitude band of 400
to 2 000 m (1 200 to 6000 ft)
and with this smaller than the calibration error of most other instruments.
On
top of that it acts such that one will fly a bit slower than theoretically
optimal if at an altitude of less than 1 200 m (3 600 ft), and a bit faster if
above (maximum error: 4 % in the normal altitude band).
Despite that, calibration altitude can
be changed to 3 000 m (9 000 ft) by internal programming, for people who
permanently fly at high altitudes. One can also set the McCready-value a bit
lower, by about 0.1 m/s for every 1 000 m altitude (3 000 ft). One will fly
pretty much correct then.
Precision of
the speed command computer
The computer itself works at high
precision (much more precisely than one can possibly fly) in the speed range
from 70 to 220 km/h (39 to 122 kts): better than 2 %. It functions, however, up
to 270 km/h (150 kts) to avoid
large errors at extremely fast flight.
The approximation of the plane's polar
- on which computation at the end is based - by the parabola programmed, is
better than +/- 5 cm/s (0.1 kts) in the most important range of 70 to 150 km/h
(39 to 83 kts). It is better than +/- 10 cm/s (0.2 kts) beyond that up to 180
km/h (100 kts). On the other side there can easily be uncertainties of up to 50
cm/s (1 kts) in the polar due to bugs!
3. INSTALLATION
3.1. Unpacking, packaging
Unpack instrument carefully and inspect
it for possible external damage by transport. In case of damage keep packaging
material to substantiate claim against the carrier and to return the
instrument.
When packaging the instrument, for any
reason whatsoever, take care to close the rear pneumatic nipples to prevent contamination
of the measuring system!
Use large case and fill void with soft
material (Styrofoam chips e.g.) for shock absorption.
3.2. Warranty
Warranty of the manufacturer covers
failures in material and manufacturing of the product for a period of 2 years
after delivery. ILEC will replace or repair parts of the instrument that have
failed in the warranty period, provided the instrument has been returned free
of charge, and provided, it had been operated within the limits specified in
this manual and in the prospectus. ILEC cannot be held responsible for consequential
damages caused by a failure of the instrument, or any other cause, which might
be connected with the instrument.
In particular, no warranty can be
claimed, where any liquid (water e.g.) or foreign particles have been allowed
to penetrate into the pneumatic ports.
In case of trouble, describe the
problem as exactly as possible, to avoid unnecessary enquiries (statements such
as "vario out of order", or similar, will not always do the job). Please
give a telephone number, under which a person competent technically can be
reached.
3.3. Mechanical Installation
When
choosing the place where the instrument is to be installed, the following
points should be considered:
As the vario is read rather frequently,
the vario INDICATOR should be placed at the upper rim of the instrument panel
(main instrument or remote indicator, depending on configuration of
instrument).