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Unmanned
Air
Vehicles
By Bob Young
Unmanned air vehicles have
come a long way since the Gulf
War in 1991. Some time this month,
Global Hawk, one of the largest UAVs
ever produced, will make an historic
crossing of the Pacific, from the USA to an
air base near Adelaide in South Australia.
– a force to be
reckoned with
Y
ou can forget any idea that
UAVs are just tiny radio-controlled model aircraft with
perhaps a video link for remote monitoring.
Global Hawk (pictured above) is big,
a full-sized aircraft; it weighs more
than 11 tonnes and has a payload of
over 900kg. And it has a wing-span of
35.42 metres and is 13.53 metres long.
Not only that, Global Hawk has a
range of more than 25,000km, an en8 Silicon Chip
durance of 36 hours and a maximum
altitude of more than 65,000 feet.
By comparison, a Cessna Citation
business jet weighs about 16 tonnes,
has a payload of about 620kg, a wingspan of 19.4 metres and is 22 metres
long. Its range is about 5,500km and
ceiling (maximum altitude) is 50,000
feet.
Yes, Big Brother in the form of a
UAV could be watching you right now!
Global Hawk is one of many in a
long line of UAVs which really came
into their own during the Gulf War in
1991. SILICON CHIP had a series of four
articles on UAVs during 1993 and a
review of the models described then
shows just how far we have come in
the intervening eight years. UAVs are
now very complex devices.
Here is a machine that requires the
most advanced computer technology,
electronic control and surveillance
equipment, aeronautical engineer-
ing, and finally a unique approach to
mission planning by the UAV control
team. They might be unmanned but
they require a skilled team to control
them.
And the Holy Grail of UAV dreamers?
Nothing less than the UCAV, the
Unmanned Combat Air Vehicle, the
pilotless air superiority and/or ground
attack fighter. To date it remains a fabulous dream and it will be for some
time to come. Or at least it will until
the arrival of artificial intelligence (AI)
and control links free of jamming or
interference.
The simple fact is that a human
pilot is an extremely difficult item to
replace. But that does not mean that
the UAV has no place in military and
civilian endeavours. Far from it! The
proliferation of UAVs has reached
staggering proportions, ranging in size
from micro vehicles, with a wingspan
of just 150mm, to the huge Global
Hawk mentioned above. Without
doubt, UAV technology will progress
very quickly from here on.
Australia, after showing the world
how it should be done with the Jindivik, one of the most successful UAV
programs the world has yet seen, has
let matters slide and is now almost
totally reliant on imported UAVs to
fill the needs of the Australian Defence
Forces.
Australian UAVs
However, in the commercial field
there is quite a deal Australian activi-
The original Aerosonde, an Australian-made UAV which undertook the first
successful crossing of the Atlantic, covering some 3270km in 27 hours on just
six litres of fuel!
ty. Probably one of the best known and
most successful is the Aerosonde, a
robotic aircraft capable of fully autonomous operation over vast distances.
SILICON CHIP featured an article on the
first successful crossing of the Atlantic
by the Aerosonde in the May 1999
issue. That flight took approximately
27 hours and covered some 3270km.
During the flight the engine consumed
just six litres of fuel for an average
fuel consumption of 1600 miles to
the gallon!
A deceptively simple-looking UAV, the Avatar electric powered glider is
manufactured in Canberra by Codarra Advanced Systems. It is designed as a
man-portable tactical system, with an “over the hill or look around the corner”
capability within a localised area of interest (up to 5km).
It was a stunning achievement and
proved beyond a shadow of a doubt
that the small UAV was now capable
of major undertakings.
Designed and built in Melbourne,
initially as a meteorological research
aircraft, the Aerosonde is now being
used in an ever widening range of
tasks. Subject to a constant program
of upgrading, the Mark 3 Aerosonde
is a much improved machine, featuring a new airframe, a more powerful
fuel-injected engine and Low Earth
Orbit satellite communications.
The author was fortunate enough
to attend a UAV conference held
in Melbourne in February, during
which Dr. Greg Holland, the CEO
of Aerosonde Ltd, stunned those in
attendance with a presentation of the
operational capabilities of the Mark
3. The simplicity of operation and
the capability of this little aircraft
left the audience “gobsmacked” (to
use a phrase often overheard after the
presentation). Coming straight after
several presentations of extremely
complex military UAVs, Dr Holland
provided us with a refreshing view
of a system that was ideally suited to
small commercial operations.
The Aerosonde has a wingspan of
2.9m and weighs in at 13-14kg. Fitted
with a 24cc fuel-injected engine running on unleaded petrol, it has a speed
range of 18-32 metres per second and
April 2001 9
The Prowler II
from Aeronautical Systems,
claimed to be the
next generation in
tactical UAVs. It
can operate over
a 200km range
from its base and
is designed to
give the latest
information
to front line
elements without
risk to aircrew.
a climb rate of 2.5 metres per second.
Range is 3000km and endurance 30
hours. Operational altitude range is
100-6000 metres. Payload is 2kg with
a full fuel load.
Standard instrumentation on all
Aerosondes consists of a set of Vaisala
RSS901 meteorological instruments
for pressure, temperature and humidity, and a proprietary system for determining winds. These instruments
provide information that is critical to
the aircraft operation and valuable observations that are fed into the global
meteorological observation system.
Additional instrumentation packages in use or in development include
still and video cameras, atmospheric
chemistry and air pollution monitors,
range finders, altimeters and remote
sensing instruments for monitoring
conditions on the Earth’s surface.
As an example, the camera system
is being used to monitor and survey
items as diverse as crops to Arctic
ice formations. All in all, it is a very
simple and useful UAV.
Codarra’s Avatar
Another deceptively simple looking
UAV, manufactured in Canberra, Australia, by Codarra Advanced Systems,
is the Avatar CX-1 electric powered
glider. Designed as a man-portable
tactical system, the Avatar is intended
to provide the commander of a small
ground force (a platoon or company)
with an “over the hill or look around
corners” capability within a localised
area of interest (up to 5km).
This type of UAV is particularly
useful for scouting ahead of convoys.
The ship is full size,
the aircraft is not: it’s
the Fire Scout “Vertical
Takeoff and Landing
Tactical Unmanned
Aerial Vehicle” (why
don’t they say helicopter?) made by
Northrop Grumman.
It’s designed to supply
navies with intelligence
and targeting capability
“in littoral battle
space” (ie, close up and
personal without the
person!).
There is no “area of interest” more demanding of prior knowledge than that
bit of road up ahead and just around
the corner. Controlled from the lead
vehicle, it can look at the road ahead,
providing up-to-the minute tactical
information. In this regard, it is vitally
important that the camera system can
discern objects as small as a single
Aeronautical
Systems’ “Altair”,
an unmanned
aircraft developed
in partnership with
NASA for scientific
and commercial
users. It features
large payload
capacity, 52,000ft
ceiling and can stay
airborne for up to
32 hours.
10 Silicon Chip
man in the open or the number of
people in a group.
Avatar is fitted with two video cameras, one under each wing and these
are switchable in flight to provide
look-ahead or lateral views. They
are daylight CCD cameras of varying
focal lengths to provide switchable
wide angle and zoom capability. The
use of a thermal imager has also been
investigated.
If you think the Avatar looks just
like an ordinary electric-powered
model glider then consider the following illustration, involving a small
group of personnel. They could be
military but could just as easily be
emergency services, law enforcement
etc).
The AVATAR UAV is first removed
from its carrying container and put together. This is a simple exercise which
basically requires that the wings and
fuselage are clipped together and the
batteries inserted. The flight path for
reconnaissance is programmed into
the on-board autopilot via a notebook computer, merely by selecting
way-points on a digital map using a
pointer. Altitude is also controlled
by a barometric altimeter through the
autopilot.
Separate search patterns at each
way-point can also be programmed.
The selection of the operator’s position as the final way-point will ensure
that the AVATAR returns on completion of the flight. It is also possible to
program events to occur at each waypoint, such as camera on, camera off,
etc. This assembly and programming
procedure is expected to take no more
than 10 minutes.
Once programming is complete,
the AVATAR is hand-launched. The
flight program then takes over and
Look! Up in the sky: is it a bird? Is it
a plane? Is it a washing machine? No,
it’s a tiny Micro Craft duct-fan micro
UAV which, unlike fixed wing craft,
has the ability to “perch and stare”
with little chance of being seen or
heard, even when directly overhead a
target.
automatically moves the UAV onto
the flight path at the set altitude. Further investigation of objects observed
during flight can be achieved by taking
manual control of the UAV and flying
it via a set of virtual reality goggles.
On completion of any such manual
over-ride, AVATAR can be returned
to autopilot and it will resume the
programmed flight path. Way-points
may also be changed during flight.
Images from AVATAR are currently received on the same notebook
computer while the UAV is within
line of sight. (Codarra are also investigating methods of storing imagery
onboard when beyond line of sight,
and then down-loading later). Images
captured on the notebook computer
are transferred to other command
systems or headquarters via a mobile
telephone or other communications
link, including being published on
the Internet. The actual track flown by
the aircraft is painted onto the moving
map display.
AVATAR is a reusable platform. The
UAV is recovered at the end of the
sortie with a parachute and prepared
for flight with additional batteries and
new flight programming.
The all-up weight of the aircraft is
approximately 3.5kg and wing span
is 2.5 metres. Endurance is approxi-
mately 20 minutes on a standard set
of NiCd batteries and cruise speed is
40 knots.
Flight trials have indicated that the
AVATAR is a very stealthy vehicle,
almost impossible to hear when operating at about 100 metres. The use of
electric propulsion reduces the infrared signature to undetectable levels.
Even when the earlier CX-1 vehicle
was painted in bright colours, visual
detection was very difficult when only
a few hundred metres away.
Launch, recovery and control are
very important considerations for
tactical UAVs which more often than
not operate out of rugged, uncleared
terrain. The Avatar is hand-launched
and the onboard autopilot reduces
flight training to minimum levels.
Landing is usually by parachute while
conventional landings require only
a small clearing for an experienced
operator.
Keep in mind here that the CX-1 is
a very small aeroplane with a small
dia-meter fuselage. One wonders how
the designers have managed to fit this
level of sophistication into such a
small airframe.
Do-it-yourself UAVs
Technology is moving fast and has
now made the small commercial UAV
a definite proposition.
In fact, relatively ordinary model aircraft can now be effectively
converted to UAV operation with a
variety of autonomous flight control
modules, some of which are pictured
in this article.
All of these modules are designed
to interface into a standard model aircraft radio control system: the PDC10
GPS steering unit, the PDC20 altitude
hold and the PDC25 auto-throttle (airspeed) control. Each modular control
unit is designed to plug into a standard
R/C airborne system between the receiver and the servos. A GPS receiver
or GPS module is also required.
PDC10 GPS steering module
The microprocessor-based PDC10
receives data from a handheld GPS receiver and converts it to an R/C servo
position command. Your GPS receiver
performs the navigation calculations
and manages way-points and routes.
Simply connect the handheld’s PC
data cable to the PDC10 and it will
translate the track/bearing error into a
servo position command. The PDC10
also corrects for cross-track error so it
will stay on course for long distance
navigation. It has an enable input for
transparent pass-through control, a
Gain adjustment and an exclusive
PDC TRIM-MATCH feature which
eliminates the need for a servo centre
pot.
So the PDC10 and a handheld
GPS receiver are all that are needed
to steer a boat, ground vehicle or
stable aircraft to a way-point. Add a
wing-leveller and a PDC20 altitude
hold and you have a complete aircraft
control system at a fraction of the
cost of a traditional autopilot. The
PDC10 is designed to be a functional
component of an unmanned guidance
system and its low cost makes it ideal
for expendable UAVs.
To get the modules to automatically
take control when the R/C radio loses
command signal, you need to use an
R/C system such as PCM that comes
with a built-in fail-safe (preset) feature. The PDC modules can also be
used with standard AM or FM (PPM)
R/C radios but to get the units to
enable automatically, you will need
to add a “missing pulse detector”
(P.O.D.) fail-safe accessory. The type
Just some idea of the
information available
back on the ground can
be gleaned from this
screen grab of one of the
UAV control programs
from CDL Systems.
A high-res location
map (linked to GPS),
video image from the
plane with the target
highlighted and complete
flight/status information
about the aircraft itself is
displayed on screen in
real time.
April 2001 11
of encoding (PCM, PPM) is not relevant, only the fact that the
radio has a built-in fail-safe feature.
Altitude & Air speed hold
The PDC20 (Altitude hold) and PDC25 (Airspeed hold) operate
as set and hold units. To
program these units, the
model is flown manually
at the speed and altitude
required and then each
unit is enabled. The current speed and altitude
are then stored in memory
and remain as the default
(fail-safe) settings. To
re-program either speed
or altitude, the appropriate unit is disabled and
the aircraft is flown at the new speed and/or altitude and the
module enabled again. Upon loss of signal, either accidental or
deliberate, the modules will default to the last setting.
These two units can be a boon to pupils and instructors during initial flight training. Pupils have a great deal of difficulty
holding the throttle lever in the mid-range setting and there is
a tendency for the throttle to gradually be pushed to the full
open setting, thus increasing the speed of the model to an uncomfortable level. The PDC25 takes care of this automatically.
Likewise, when teaching the pupil to steer the aircraft, elevator
control can be handed over to the PDC20 which will then hold
the aircraft at a safe altitude. This takes considerable strain off
both the student and the instructor.
Using the PDC10 in conjunction with a GPS receiver, a wing
levelling unit (optical
or gyroscopic), a PDC20
and a PDC25 (optional),
an aircraft can be sent
off on a fully automatically controlled
mission to any point
within range of the
aircraft. Manual control
via the transmitter is only required for take-off and landing. The
transmitter may be switched off for the rest of the flight. Such
a system costs in the order of $1500 - $2000.
The PDC3200 is the command module for a more elaborate
(and expensive, about $10,000) full autopilot system. Inputs
are provided for two rate-based gyros, altimeter and airspeed
sensors, fuel, RPM, battery voltage. Aircraft attitude and all
data inputs are relayed to a computer ground station which
displays the information on a cockpit like screen. GPS waypoints and airdata (speed, altitude) settings may be updated in
flight if required.
This type of system is ideal for extended range missions,
such as aerial photography, fire detection, traffic surveillance
etc. If a video link is mounted in the aircraft, the PDC1200 (or
PDC1200PAL for Australia) is a most effective method of transmitting data back to the ground station.
The PDC1200 is a video overlay unit. In other words it can
overlay text onto the video display as shown in one of the
photos in this article. Here we see Compass Bearing, Airspeed,
Altitude, Time, Date and Position overlaid.
As you can see, automatic flight systems make possible projects that were only dreamed about several years ago.
SC
12 Silicon Chip
All the information a pilot
would normally read from his
instruments can be read from
the ground. The inset at right
shows the same information
overlaid onto a pilots-eye
view via an on-board camera.
Entering “waypoints” or locations over which the
aircraft must travel is as simple as entering their
latitude, longitude, altitude and time. These are then
referenced against an on-board GPS receiver.
Likewise, the information required by the aircraft in
“autopilot” mode is simply entered – the plane will
then obey these commands until instructed otherwise.
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