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
1.
TASK OF THIS MANUAL.. 3
LIST
OF CONTENTS. 4
2.
Description of the System... 5
2.1.
Principle of measurement 5
2.2.
Variometer 5
2.3.
Variometer audio generator 5
2.4.
Speed command. 5
2.5.
Audio generator of speed command. 6
2.6.
Mode switching. 6
2.7.
Indicators. 6
2.8.
Distance- and Final glide computer 8
2.9.
Precision. 8
3.
INSTALLATION.. 9
3.1.
Unpacking, packaging. 9
3.2.
Warranty. 9
3.3.
Mechanical Installation. 9
Figure1:
Panel cut out 10
3.4.
Electrical Installation. 10
3.5.
Pneumatic connections. 12
4.
MAINTENANCE.. 13
4.1.
General indications. 13
4.2.
Verifications. 13
4.3.
Cleaning the Instrument 14
5.
ADJUSTMENTS AND PROGRAMMING.. 14
5.1.
General 14
5.2.
Zeroing of the Transducers. 15
5.3.
Calibration Altitude. 15
5.4.
Audio Generator 15
5.5.
Programming the Polar 15
5.6.
Indicator Options (Configurations) 15
6.
REPAIR.. 16
7.
THE VARIOMETER SB-8 IN FLIGHT.. 17
7.1.
The 1-second and the 3-second responses. 17
7.2.
Turbulence and gusts. 18
7.3.
The Averager 20
Figure
4: Averager 20
7.4.
Flying with the Speed Command. 21
7.6.
Looking for thermals with the speed command. 22
7.7.
Influence of normal Acceleration on the Indication of a TE-vario. 22
8.
APPENDIX Circuit Diagrams. 23
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.
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)
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.)
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).
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.
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").
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.
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.
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!
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.
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.
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).
If a compass is being installed in the
instrument panel, all other nonmagnetic instruments should be grouped around it
(altimeter, air speed indicator, moving vane variometer); all electrical
instruments at a distance of some 10 to 15 cm. The analog applies to compasses
mounted on the cover of the panel: the loudspeaker at the rear end of the
instrument may disturb this compass. Remedy: mount SB-8 further down, or have
loudspeaker taken out by the manufacturer and use remote speaker.
When respecting these hints, the
compass will not be disturbed by more than +/- 15 degrees and can be compensated
to good precision, say to +/- 5 degrees easily.
Instruments
that are read infrequently, radio sets e.g. should be placed low on the panel
(see also chapter 2.7.).
During transport, take off, and
landing, the glider will be submitted to rather severe shocks. These should be
kept away from ALL instruments. Contrary to a widespread opinion, the best
suspension is none at all: Best is the one that will link all instruments to
the primary structure of the fuselage in the MOST RIGID way (the fuselage itself
is very stiff, and has a large mass). For this reason panels should be designed
for maximum rigidity and fixed to the fuselage rigidly. Nothing is more
damaging than the shocks handed out as a too softly suspended panel hits the
structure limiting its free travel.
Temperature
transducer
The most favorable place for the
temperature transducer is the ventilation duct near the air inlet, as there it
is well stirred by the air, protected from the sunrays, and, on top of that
protected against accidental damage. For mounting, drill a hole 5,5 mm
diameter, push the transducer head through it, and fix it with some adhesive
tape.
General
remarks
Main, or master switches in the
electrical system can be a source of serious trouble, in particular, where
there are radio sets connected to them. When turning on the main switch with
the radio on, heavy negative going pulses may be generated on the - positive -
bus line during the typical 1 ms bouncing periods of the main switch. These
Pulses can destroy instruments, if not at once, then they will do it in the
long run, also yours!...We have measured pulses of more than 10 Amps!
If master switches are not avoided
altogether, individual instruments MUST be switched ON AFTER the main switch,
and OFF BEFORE it.
The smallest possible number of
switches, cable connectors, sockets, fuses, etc. in the wiring: contact
problems! Instruments will no longer work!
All current carrying parts must be
insulated: Short circuits and fuses blown: no current on the radio e.g. This is the rule the most violated. It
applies to battery connectors also!
All connectors must have a solid
mechanical lock: danger of opening! No current!
Exclude all possibilities of false
polarity connections by at least using color codes, much better: keyed
connectors.
Use only professional components, no
cheap automotive or do-it-yourself components. They are unreliable! (Your
glider is worth too much for this type of botching!)
Cables must be fixed at critical
points; no pull may be transmitted to them, unless they may break when
stressed!
When crimping or screwing wire, never
tin: tin flows under stress and releases tension: open circuits or intermittent
contacts!
Every conductor going to the battery
MUST have a fuse NEAR the battery: Burning wires are a danger to your life!
Use only cable with fire retardant
insulation material: development of smoke can be mortal! Use Mil-spec or
aircraft type cable: this is worth the investment.
Use one fuse per one instrument,
wherever possible: In case of a short circuit somewhere: Only one instrument
will be dead, instead of all of them, including the radio.
Use only female connectors on the
battery side: protruding pins are a - real - short circuit hazard! Also to you!
(See also rule on insulation!)
Insulate connector solder lugs with the
help of rubber sleeves or heat shrinkable tube after soldering: avoid short
circuits!
Use a soldering pin compatible with the
size of contacts to be made; a 1 Kg/100 Watt iron is definitely not the right
equipment here. Better still: look for an electronic technician to do the job
for you! He is there everywhere!
To reduce electromagnetic interference
to ALL instruments, in particular the one caused by a VHF transmitter: (this is
a general nuisance)
All
wires must be as short as possible, also those not carrying RF.
Use only good antennas, poor or poorly
adapted antennas return a large fraction of the RF energy being sent to them on
the exterior of the antenna cable: The whole aircraft will be polluted by this
stray RF radiation!
Keep
the antenna cable away from any other wire (a foot is not too large!)
ALL grounds must be returned to one single
point (every equipment has a supply and a return, even if the latter is by its
case). Cases of all electrically operated instruments also are to be connected
to this central "GROUND". This central ground point itself must be
bonded - via a very short wire - to the structural metallic ground of the
aircraft, (the steering system e.g.) this is not just for the above reasons,
but also to protect the pilot in case of a lightning strike.
A very good central grounding point is
a metallic instrument panel. This is the reason why they are to be preferred
over the more modern plastic insulating ones.
The negative terminal of the battery
must be linked to the central ground point by a very short heavy wire.
Cable harness
The SB-8 is being delivered with a
standard cable harness comprising: connector, battery wires, temperature
transducer, remote control cable, cable 60 cm long for vario separate
indicator.
In case an ASR is ordered at the same
time with the SB-8, or in case this is desired, this harness is being
complemented by a cable and its connector for the ASR. In case an ASR is being
attached to the SB-8 without the harness having been prepared in advance, a new
cabling set will be delivered with the ASR. The old temperature transducer must
be connected to this new harness, as the instrument has been calibrated with
this transducer (cut through flat double cable white/blue of the old harness,
solder transducer to the corresponding end of the new harness, insulate).
Schematic 1 shows the wiring of the
main instrument. Remote Speaker and Remote Control according to need. For
Monobloc configuration no other wiring is necessary. Insulate all wire ends not
used.
Schematics 2 to 6 show other
configurations of indicators and corresponding wirings for single- and two-seaters.
For two-seaters the instruments for the
aft panel are being connected completely independent of the ones of the front.
NOTE: electronic technicians must do
the cabling: it determines to a large part reliability of the complete system.
Special
Remarks:
Wires
for the separate (remote) indicators are color coded as are the connectors.
As far as possible, all inputs and
outputs are protected against false connections. However, it is not possible to
foresee all false connections one can possibly make. Therefore total protection
is not feasible. The nearly only dangerous connections are those where the
negative terminal of the battery is linked to a signal out-, or input, and the
battery's positive terminal to the Minus input of the instrument. (This happened!).
Inversion of the battery's polarity on the two input cables of the instrument,
otherwise, is without consequences. Therefore:
Never
hook up the battery to anything else than its proper cable and input terminals.
ILEC
will give no warranty in case of false electrical connections.
Remote Control
There is not yet a truly satisfactory
solution for automatic control of the mode (thermal/cruise) of a vario/speed
command system. Not to talk of a distance counter. No automatic system
whatsoever will have eyes, or intentions, as has the pilot.
In the case of gliders with flaps one
can control the instrument via the position of the flap lever. The manufacturer
of the plane must install the controlling switch, mostly a magnetically
operated reed switch. He has the necessary material, and more important: the
specific expertise. For gliders with fixed airfoils the best solution (the best
solution for all planes indeed) is, to mount a small switch near the usual rest
position of the left hand, or on the stick. In this way it is very easy - and
carried out more or less automatic by the pilot - to switch to the right mode,
and on top of that, it is done at the right moment, just as the pilot knows and
wants it. The automatic device will do the job also, however poorly usually.
Very quickly the correct switching becomes a routine, not demanding any
attention.
Input
pressures
The instrument must be connected to
Total Pressure (measurement pressure of
the airspeed indicator) and to a Te-probe via the 2 nipples on the rear. As the
quality of the variometer's response depends entirely on the quality of the
TE-pressure, a good TE-probe should be used. It should be sufficiently insensitive
to slip and changes in angle of attack.
The best tube is worth nothing, if
mounted in the wrong position. The best position is still the one high up on
the tail fin. For details see brochure "Total energy compensation in
practice" which ILEC will send you against a protective fee. It contains,
in short form, the results of several years of research into the subject.
Protection
against water and dust
ANY pneumatic instrument can be damaged
by dust or water ingested. Therefore a water separator must be inserted into
any line leading outboard. As, on top of that, most tubing on gliders is being,
or has been, heavily contaminated by dust from sanding, small gasoline filters,
available in car shops, must be inserted into each tube next to the instrument.
They should remain there forever, also when returning an instrument. Certainly
they should never be reversed: This would be the best way to drive the dust
collected so far right into the instrument.
These
filters are excellent water separators at the same time!
It must be repeated here, that ILEC
will refuse any warranty where instruments have suffered from water or dirt
ingestion.
Connecting tubing
Nipples are for flexible tubes with
inner diameter of 4 to 5 mm. In case a tube sits too tight: do not pull with
brute force, cut it open carefully - without damaging the nipple! Use an
adaptor where tubing is too wide or too narrow, collets are normally
unreliable. Best tubing is rubber tubing with textile shroud (= gasoline tube): it remains elastic
at low temperatures, never becomes soft, maintains its seal even after years,
is easily pulled off, does not shut off in tight bends, and holds water
ingested in a film without forming drops that clog the line. Have tube end run
straight into the nipple, without bend. Transparent PVC tubes 5 x 1.5 mm are
acceptable. However, they become hard when cold, and over the years. They must
be replaced every 2 years to avoid potential leaks. Leaks are usually fatal for
a variometer indication.
Leak tightness
The line from the measuring head of the
TE-tube up to the variometer must be tight. The following is a rapid test; it
should be carried out at least at the start of the season.
1. Seal the total pressure port on the
variometer (piece of tubing closed off at one end with a piece of
6mm round brass bar, no screw! Or melted
tight by soldering iron).
2. Press flexible tube next to vario.
3. Seal off TE-probe (finger or
adhesive tape).
4. Release tube: vario produces a pulse
in positive direction.
5. Wait 10 seconds.
6. Open TE-probe: vario produces a
pulse in negative direction of about the same magnitude as above.
If not, the system is not tight.
Mutual
interference between Variometers
Where an SB-8 is run alone at a
TE-tube, there is normally no problem, be it, and the line is clogged. Where a
variometer with a big flask (big means here some liter, to be found with
certain moving vane Varios or gust filters), is hooked up to the same tube:
caution! The response of the SB-8 may be distorted by the large airflow in the
system in case of sink or climb. Here, a test flight with all other instruments
disconnected should be done for comparison, under all circumstances. (Although
we have not seen many problems there!)
Never should there be any capillaries
or so called gust filters in the conduit between TE-tube and the SB-8, although
this may be required on some Variometers, to make them more readable (by making
them slower). At best they would only cause a delay in the response of the
SB-8. Contrary to the widely distributed opinion, errors of a poor TE-compensation
cannot be cured this way. (In doubt consult "TE -compensation in
practice")
The SB-8 normally does not need any
maintenance, nevertheless some hints to ensure reliable operation and long
life:
Most cases of malfunctioning (including
those where we repair perfectly working SB-8s) are due to leaks! Next in the
row of causes are problems with electrical contacts (see also under
"Electrical Installation").
Too much heat is of no good to ANY
instrument. The glider should not be abandoned carelessly in the naked sun
without the cockpit being covered somehow. Temperatures in an uncovered cockpit
can easily reach 70 degrees C. There are at least some momentary measurement
errors to be expected, if not worse. (We have seen SB-8s with holes burnt into
them!) If no cover is available, then at least open the canopy for air to
circulate rather than stagnate.
All tubing must be checked from time to
time - and at any rate at the start of the flying season - for leak tightness,
good tension around connecting elements, sharp bends and squeezes. Tubes gone
hard must be replaced! (This is particularly necessary in the case of soft PVC
tubing!)
Protect
your instruments, and their tubing, against dust and dirt!
Before doing any repair on your glider,
disconnect all tubes and shut off their ends. Take all instruments away.
Must be checked from time to time:
Connectors, switches, fuse holders, for good contact, insulation; and all
cables for chafing, kinks, jamming, in order to spot intermittent contacts
before they arise.
Use only new, flawless fuses. Never try
to repair them! You may destroy an instrument right on the spot, or loose it
later.
An old, feeble battery, or a doubtful
one must be replaced immediately, not later.... The battery test function of
your SB-8 will help you there.
Recharge the battery systematically
after every flight. You will not do it otherwise, on an occasion!
The instrument panel hitting some
structure of your fuselage upon bouncing around during take off and landing
because of too sloppy a suspension, must be put right immediately.
Mechanical
Zero:
There should be no problem with
mechanical zero of the indicator. However it should be checked, because this is
so simple. (Just look at the pointer, when the instrument is off!)
As a consequence of an extremely hard
shock, during transport e.g. one of the 2 spiral springs of the meter movement
may become trapped in its support; the needle then will be wrong by half a
division of the scale typically, and will show much friction. Here the
instrument must be returned to the manufacturer. A watchmaker can usually cure
the problem.
Electrical Zero:
Shut off both of the pneumatic
connections of the instrument, or leave the glider in a constant temperature
environment for at least an hour (in the hangar e.g.). The instrument must be
on for at least some 15 minutes.
Vario:
Switch to Vario mode. The needle of the
vario indicator (built in or separate, does not matter) should now be within
+/- 0.1 m/s of the mechanical zero. In case the offset is larger, adjust the
vario zero (see chapter 5 for details). (After a very long rest period, several
weeks or months e.g., larger errors may show up after switching on, they should
disappear, however, gradually within a quarter of an hour or so.
Speed
Command:
To check zero of the transducer for the
dynamic pressure, PUSH the POLAR SELECTION SWITCH to the extreme right. In case
the built in meter indicates more than, say the width of the needle, electrical
zero must be readjusted (see 5.2.)
Verification
of measurement of speed:
To be taken care of when testing for
speed measurement: the pressure actually taken as a measure for speed is TWICE
the dynamic pressure. This is so for very valid reasons. (Total pressure, or
Pitot pressure - TE-pressure = 2 x dynamic pressure). On the ground, when the
TE-tube does not produce its suction, the IAS used as a pressure gauge must
indicate root 2 times the corresponding speed!
For cleaning the exterior, the meter
screen e.g., one must never use a strong solvent like tetra, or nitrocellulose,
because they will damage or even destroy the plastic parts. Well suited are:
lighter gasoline, turpentine (often used as thinner), or watered alcohol with a
maximum concentration of 40 %.
The screen of the indicator is of
polycarbonate and sensitive to static electricity. It should not be rubbed with
a dry cloth. In case static charges trap the needle, humidify the screen and
cleanse it with an antistatic product. This will last for a season!
Normally there is no need for any
adjustment or programming, as the manufacturer does this, normally knowing the
glider type for which the instrument is intended and the configuration of
indicators desired.
We intend this chapter for the case
where the customer wants to change something.
For all adjustments one of the 2 half
shells of the case must be removed. To do this, first remove the 6
corresponding self-tapping countersunk screws and pull off the half shell up-,
or downwards. Never take away both half shells at the same time, as the
instrument's parts will no longer be held together. After finishing the job,
mount the half shell in the reverse order again.
ATTENTION!
When remounting a half shell, first
turn the self tapping screws backwards until they fall back into their old
track, then turn forward. The threads in the plastic parts might get fouled
otherwise!
When
mounting the lower shell, take care not to squeeze the silicon tube!
Observe the most stringent measures of
cleanliness. Even the smallest magnetic particles can disturb seriously the
meter movement!
Always
pull off the battery connector before working on the instrument.
Do
not touch sealed trim pots because calibration would be lost!
Proceed as described under 4.2. Take
away the upper half shell after having pulled the battery connector. Reconnect
battery. For adjustment turn trim pots identified on the last page of this
manual using a small screwdriver (max 3 mm wide) until zero is correct. (Switch
to the 3-s response for the variosignal). Pull battery connector, close
instrument again.
Normally the instrument is set to a
calibration altitude of 1 200 m NN, which is correct for 99 instruments out of
100 (see chapter 2.8.). To change to 3 000 m hook the 2 wire springs of the
programming switches on the rear circuit board (see photo on last page) into
the corresponding small hook.
If not specified otherwise by the
customer, the ILEC tone will be programmed. To change to the interrupted tone:
(see photo on last page) change the right one of the 3 wire springs from the
second small hook from the right to the most right one.
If a double tone is wanted, unhook one
of the 2 left springs; for a single tone, unhook both of them.
For adjustment of the pitch (the
frequency) of the base tone, or for adjustment of the frequency of modulation
of this base tone, turn the corresponding trim pots.
The dead band of the speed command tone
is factory set to +/- 15 km/h, it becomes narrower by turning the trim pot to
the right.
Remark:
One should test the effect of an adjustment on the audio
generator. For this, open the upper half shell, then insert the rear connector
(cable loom in the glider), and switch on. Make the vario play with the help of
a piece of flexible tubing connected to the TE-nipple, shut off at the end, and
listen to the sound. Switch to the other mode for speed command audio.
If the polar programmed by the factory
is to be changed, the lower half shell must be taken off. Set the 4 programming
switches to the new values using a small screwdriver (see last page).
The parameters for the usual types of
gliders are available from the manufacturer or his representative and will be
communicated on request. For non-standard cases there is a written procedure
for computation of the parameters.
The configurations described in chapter
2.7. , are taken care of with the help of the programming switches on the 2nd
printed circuit board. The table below shows how to do it:
|
Option
|
Upper spring
|
Lower spring
|
|
M
= Monobloc
|
Open
|
Hooked
upwards
|
|
B
= Two bloc (Vario at RAZ)
|
Open
|
Hooked
downwards
|
|
V
= SB-8 indicates Vario
|
Hooked
|
Hooked
upwards
|
|
I
= SB-8 indicates Averager
|
Hooked
|
Hooked
downwards
|
The instrument has been produced very
carefully. To eliminate initial failures that arrive with all components, it
has been burnt in for a long time before its delivery. Nevertheless there are
failures, arriving statistically at a later date, failures which we cannot
eliminate. In case you should have a problem, please check that everything has
been done as specified in this manual. (In particular in the case of a new
instrument! Should the instrument already have worked correctly for some time,
then most probably a component failure is the culprit! At the beginning of the
flying season, very often the batteries are at their end of life! Often leaks
have developed over the cold season!)
In the regrettable case of a necessary
repair, please call us or our representative, or return the instrument
immediately, not only when you just want to fly: As everybody wants the same,
we will be overloaded with work. We try to fix a repair within one week. In
case there is no trouble with transport, you will have the vario back for the
following weekend, if you send us the instrument on Monday. Sometimes we prefer
to run the instrument for some time to make sure everything is all right, but
then we will tell you.
In case you send the package from
abroad, please make sure you declare a low enough value for the merchandise to
pass through customs without any trouble (this will save work to us, and time
to you!). You will get the corresponding green sticker to glue on the package
and the advice from the local mail office.
Please
describe the malfunction, the instrument produces, as exactly as possible on a
piece of paper and also state a telephone number for queries. You make it
easier for us to find the cause, this way you speed up treatment of this
regrettable matter. (For the rest proceed as said at the beginning of the
chapter on Installation)
The following chapter has been written
in order to help the user to draw a maximum of benefit from the information
delivered by the instrument. It is always worth while to read it, as the matter
treated here is rarely or not at all covered in the general literature on
soaring.
Figure 2 shows what happens upon flying
through an idealized thermal, and the corresponding responses of the 2
different filter outputs, or otherwise, the indication of the vario needle when
one or the other response has been selected. For the example a standard class
glider with normal wing loading has been assumed. Airspeed is 90 km/h (50 kts),
and constant.
The thick square trace 1 shows the
updraft as a function of time: in front of the jump, there is calm air, within
it, the air rises at 2 m/s (4 knots) diameter be 100 m (100 yards).
Before entering, the plane sinks
steadily at 0.7 m/s (1.4 kts). Upon entering, it is accelerated upwards, (and
very slightly forwards, but this assumes no reaction from the pilot) the pilot
will feel this clearly on the seat of his pants. The transition to the new
vertical speed is fast, the time constant being only 0.4 seconds. (Gust-?)
Acceleration at the beginning is 0,5 g, the g-meter will jump from its steady
state indication of 1 g to 1.5 g. (Upon leaving the same sequence will happen,
however this time downwards.) Curve 3 describes the indication by the 1-second
filter: after a short hesitation of about .2 s the needle swiftly swings
upwards, after 2 seconds already 90 % of the change are reached, after 2.5 s
100 % of the real climb rate of the glider, now being 1.3 m/s (2.6 kts)
upwards, are attained. The indicator needle remains there to the very end of
the updraft, and returns to its original sink of .7 m/s (1.4 kts) as fast as it
mounted upon leaving the thermal (gust?).
Figure 2:
Passing through an updraft
REMARK:
For a first order filter to be as fast,
its time constant would have to be 1 second. Such a filter would be useless in
normal thermal conditions as one would not be able to read it because of its
permanent random jitter induced by turbulence.
Curve 4 shows the behavior of the slow
3-s filter. This one corresponds to the response of a good moving vane
variometer: The output creeps up slowly. For it to reach 90 % of the change in
input, one would have to wait 7 seconds. At the end of our thermal it just
arrived at 0.8 m/s (instead of 1.3!).
Which response to use to search for
thermals?? As the main problem here consists of discriminating between
"gusts" and useful lift, a short consideration: diameter of the
general useful thermal is about 150 m.
This distance at a speed of 90 km/h (50 kts) will be covered in about 6 s, at
180 km/h (100 kts) in 3 seconds. With this in mind, one can say that it is
worthwhile to take on a "thermal" when the climb lasts at least 3 to
5 seconds, (and when on top of that it has the strength looked for. Be it, one
is convinced to have cut the lift just on its border.
If now we look at figure 2, we can set
up a simple rule for day to day use very quickly (it has proven its validity in
practice): When the FAST vario climbs to the lift waited for, then COUNT TO
3. If the needle is still there, then
take it on: this thermal is large enough to be centered in 9 out of 10 cases;
if not, continue straight on!!
In case the slow filter has been
selected, one will have to not only observe the position of the pointer, but
also its tendency: Does it STILL CLIMB
(after 3 seconds), and does it at least indicate HALF of what is waited
for, then take it!! In case it STANDS STILL or even FALLS, continue on your
way.
(One thing needs to be said: No vario
of this world can predict, what the climb rate will be in the thermal just
taken on. The good pilot will be able to do that, because he sees infinitely
more than the vario. A vario will be able to tell only AFTER the circle has
been flown, NOT BEFORE!!).
Everything that is shorter than a
useful lift is only a disturbance. This is particularly so for horizontal
gusts, which are so widely distributed, but rarely recognized as such.
Therefore it would be nice, if a vario would simply suppress those short
"gusts".
(Suppression of horizontal gusts by
TE-vario is - by principle - impossible. At the end: because it is its
measurement principle to eliminate "stick thermals". As a way out,
one can look at flight speed as well as vertical speed individually, and then
draw one's conclusions: one has to - at least for short time intervals -
disregard compensation of the stick thermals. This means taking into account a
simple altitude variometer (non compensated vario), look at the TE-vario later
only, and draw one's conclusions from a comparison of the 2 signals. The good
pilot does something similar all the time, and even more. The whole procedure
happens in his brain. He uses all his senses. Therefore his high concentration)
For the time being, we have to be happy
with filtering out "gusts" as efficiently as possible, without
loosing too much in speed of reaction. This is already difficult enough.
To show the influence of a gust on the indication of a
TE-vario, let us assume the following case: A standard class glider flies at
150 km/H (83 kts). On the one hand it enters a thermal with a vertical air
speed of 2 m/s (4 knots), on the other hand a zone with wind shear or - what is
the same - a whirl with horizontal axis such that the plane's airspeed
increases suddenly by 2 m/s (4 kts). What happens in those two cases?
Well, figure 2 shows it for the case of
the thermal. There is some difference to fig.2, though: the initial sink rate
is 1.8 m/s (3.6 kts) rather than .7 m/s (1.4 kts). The initial thrust of
vertical acceleration is stronger, due to the higher airspeed. The plane is
accelerated upwards from -1.8 m/s to +
0.2 m/s, 150/90 times as strong as in fig.2. The g-meter would bounce from 1.0
g, its steady state value to 1.8 g and back again to 1 g with a time constant
of only 0.25 s. The response of the variometer is exactly as in Fig.2, the
curves only a bit lower.
Figure 3: Entry into a horizontal Gust
Fig.3 shows the case of the horizontal
gust: The airspeed indicator jumps from 150 to 157 km/h (from 83 to 87 kts),
damped by its inertia (this makes the bounce practically invisible). Contrary
to what we have seen in the case of the thermal, the plane is being accelerated
upwards only a little bit, just 0.1g. The trajectory of the glider that follows
depends mainly on the pilot's reaction: He can continue at the increased
airspeed, or swap the kinetic energy he has gained for a bit more altitude. In
the example this would be 8.7 m !! and then continue at his original airspeed.
His maneuver however has little influence on the TE-vario: at entry into the
whirl, the TE-vario "sees" a jump in dynamic pressure corresponding
to the altitude jump of 8.7 m. It will interpret this pressure jump correctly
as a gain in energy and produce a positive pulse. This pulse will be
proportional to the potential gain in altitude. Thereafter it is irrelevant to
the TE-vario whether the potential gain in altitude is realized or not, as
there would be no change in total energy involved in the maneuver, only an
exchange between kinetic and potential energy.
The
needle's excursion is larger here than in the case of the thermal.
The
needle’s movement will die out again, how fast; this depends on the kind of
filter used (in the case of some Varios one does not need any filters, because
the transducer itself is slow and therefore imposes its - usually very slow -
response on the whole system).
The slow 3-s response can make the
pilot think there is some lift, which is no longer there, really.
It must not be forgotten, that in
practice, turbulences, as well as thermals, are rarely as sharp edged as drawn
here, for clarity reasons. The leading edge of the indication will therefore
mostly be "rounder" than shown in figures 2 and 3.
1. When the vario climbs fast, without
being accompanied by a strong acceleration upwards, then most frequently we
have to deal with a horizontal gust. One can "pull out" the excess
speed, however one has to reckon with being forced to "push over" a
rather short time afterwards again, because a negative jump follows.
2. When the vario departs upwards after
an upward thrust of vertical acceleration, mostly there will be lift.
3. In weak thermal conditions the vario
will usually climb slowly. In principle now a large field of lift can announce
itself, however, it does not have to be so. Mostly one will not feel single
acceleration signals, and one will have to entirely rely on indication of the
vario and one's "feeling".
Newer measurements indicate that the
leading edges of thermals are mostly very poorly defined, reason why there are
no clear accelerations.
In case 3 it is advisable to reduce
speed and follow the vario very carefully.
The average vertical speed whilst
spiraling in lift, is by far the most important value to know, for distance
flying. It decides whether the thermal, one is exploiting at the moment, is
good enough to reach the goal. It plays a decisive role when setting the McCready
value. Thus it helps to determine the right speed for cruise. As one will
overestimate the average climb rate by 50 to 100 % when relying on the vario
signal and one's power of estimation alone, the SB-8 is fitted out with an
averaging filter (often called an Integrator). It is in fact an analog to the
fast 1-s filter, however with a much longer time constant, and damping
optimized for that purpose.
Figure 4 shows the response of the
averager to a glider entering and circling in a thermal of some constant 2 m/s
(4 knots). The plane, curve 2, accelerates very fast to its new climb rate of
1.3 m/s (the slight increase in the sink rate of the glider has been
neglected). After one full circle, exactly 25 seconds, the so- called 30-s-Filter,
as it is called on the faceplate for convenience, indicates the new vertical
speed (see curve 3).
One should realize, that after the time
span one needs to finish a circle, no matter when, or where one has started,
the average is available. (With integrators of lower standard this takes
considerably more time, with the most frequently used filter of the 1st order
e.g. twice as long. This means that not the average of the last circle is
indicated, but that of the last but one circle. The indication of the SB-8
averager is still correct, even where the lift is very irregular, e.g. if it
varies between 0 and 4 m/s. Here a poor averager does no longer give true
indications).
In
case the lift vanes, this can immediately be seen on the scale of the averager.
We
retain: The averager gives CONTINUOUSLY the average vertical speed of the last
25 seconds. Said differently, the running average of the last circle, or the
so-called integrated climb rate.
We will not treat general tactics in
transition or dolphin flying here, one will find this in the special
literature, see "Reichmann" e.g. We only give some hints to pilot the
glider and to interpret the speed command signal.
One will set wing loading according to
the overall mass of the glider (empty weight of the glider + weight of the
pilot + parachute + water ballast) divided by wing area. (Computed in kg/sqm or
lb/sqft, depending on the scale of the SB-8). Accuracy here is of no concern.
(Most 15 m gliders have about 10 sqm of wing area, in this case take 1/10th of
the all up weight, when using the metric McCready scale).
Depending on the number of bugs on the
wing l e a d i n g e d g e one chooses
either the N-, or the X-polar, the
latter at about 1 bug every 5 to 10 cm (2 to 4 inches), or worse.
The by far most important parameter is
the McCready-value that has to be set according to the tactical situation.
Basis for this setting is always the average of the e x p e c t e d climb (it
is to be estimated on the basis of the value one has had earlier during the
flight, and the weather conditions ahead, conditions which really only the
pilot can know). Particular tactical situations require particular values:
flying over an obstacle at a distance e.g.
Even large deviations from the optimal
value lead to relatively minor losses in average cross-country speed.
Therefore, it appears wise to use reduced settings, and to avoid too great a
risk.
It is not even unnecessary, but harms
the physical condition of any pilot, if one blindly follows the needle, and
practices violent dolphin flying. Adjust speed only, therefore, if a speed
error stays there for some time, or if it menaces to do so!
Follow the signal attentively, and
react only, if it is worthwhile! (in case one begins to fly through an area of
heavy sink e.g.)
NOTA BENE: Any correction of speed to
be carried out, must remain a tactical decision by the pilot, adapted to a
particular situation. There can be no automatic reaction!
How
to change Airspeed following the speed command?
There are 2 different methods, to
adjust speed - in a controlled fashion - unfortunately they are not known. (As
it does not work otherwise, as proven a thousand times by o l d speed command
systems, the SB-8 has a computer which calculates the difference between the
speed actually held, and the optimal speed of the moment. (Indication is
calibrated in km/h or kts).
Adjustment
is done in the following way:
1. As a habit, the nose of the glider
is pushed down or pulled up by the same angle, say 15 degrees e.g. with
reference to the normal attitude, each time, speed is to be changed. One
maintains this new attitude just so long as for the speed to change by the
amount wanted. After a short while, this will become automatic, meaning, the
time span will be chosen such as to be the correct one by the pilot, right from
the start of the maneuver. He does not have to look to the IAS any more to see
whether he has reached the new speed or not.
The whole thing works so well, because
with this method, the time span during which the nose of the aircraft remains
inclined, is proportional to the speed change made: one doses the time span and
by doing this, the change in airspeed intended.
2. Pilots who already master the above
method can now hold constant the time span, during which there is to be
acceleration or deceleration. Now, they must dose the inclination change. This
method adapts itself to the meteorological conditions: One flies softer in weak
conditions, tougher in strong conditions. In most cases one arrives, after some
experience with the SB-8, automatically at combining the 2 methods.
What counts: To change attitude by a
certain angle for a certain time span, and this knowingly in advance. It is
wrong to wait for the IAS to show the wanted speed, or even worse, for the
speed command to show zero. This way, one will mostly dolphin about the correct
value.
Here
2 cases are to be distinguished:
1. Upon a sudden change in the
indication of the speed command, one best proceeds according to what has been
said in 7.1. by using the speed command as a vario. However be careful, zero
position is set off, one should not change speed too much, as speed has a
strong influence on the zero reading of the speed command. The time response of
the speed command is the 3s one. (In the case treated here, a permanent vario
indicator is very useful). In case of a justified suspicion, switch to vario
and continue your search with that.
2. Upon a slow increase of the speed
command indication, one will automatically be guided towards a slower speed. In
case the speed command indication has arrived at the speed of minimum sink and
the indicator needle still is on zero or higher, one has arrived in lift, being
m o m e n t a r i l y at least as strong as the McCready value set. Here, at
the latest one's attention should be aroused. (The experienced pilot will
already have noticed at the seat of his pants that something has happened, and
he will have reacted accordingly).
When pulling up, in particular at low
speeds, drastic increases in the proper sink rate of a glider may arrive, as a
result of its increased load factor. These additional energy losses naturally
are indicated by a good TE-vario. They are not to be taken as errors of
compensation.
Whilst pushing over at low speed,
on the other hand, the proper sink rate will be diminished; it can go nearly up
to zero. (Influence of the air column in the longitudinal direction can
reinforce this effect, and drive the vario needle even to above zero (in still
air!) (The effect of the air column is a real measurement error; influence of
the normal acceleration, however, is not an error, the losses indicated are real!!).
