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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.