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UAVs: an Australian perspective By BOB YOUNG Most readers would be aware that UAVs (unmanned aerial vehicles) are used extensively for surveillance and for bombing missions in Afghanistan and Pakistan. But did you know that UAVs are being made in Australia? Not only that but they are being sold around the world for a range of applications. The manufacturer is Silvertone, a company with decades of experience and run by Bob Young. S ilvertone’s latest UAV is the 4-metre wingspan Flamingo, shown above in a hangar at Bankstown airport with a slightly larger cousin. The Flamingo is a lightweight, modular unit designed to operate in the under-20kg class of UAVs, thereby avoiding the complications and costs of larger UAVs which are subject to more stringent Civil Aviation regulations. The modular construction makes the Flamingo extremely versatile, allowing a variety of mission configurations as well as making it easy to transport. Broken down into its separate components, the Flamingo will easily fit into a family sedan. While it is a relatively small UAV, it can carry payloads double the weight of its air-frame. It uses a small motor, 14  Silicon Chip rated up to 3.5HP driving a 16-inch (diam) x 8-inch (pitch) wooden propeller, giving it a maximum speed of 78 knots (144km/h) and maximum ceiling of 15000 feet (4500m). The Flamingo is a pusher prop aircraft, as are many larger UAVs. Pusher aircraft have several advantages over tractor aircraft, particularly when used in surveillance aircraft. They give an unrestricted view forward for the camera as well as being more aerodynamically efficient. The efficient aerodynamic design gives vice-free flight characteristics combined with an excellent speed envelope, making the Flamingo an ideal UAV trainer. The aircraft’s endurance is rated up to seven hours, depending on payload, throttle settings and altitude. And while 15000 feet is the ceiling, in practice this is set by the siliconchip.com.au Silvertone Flamingo F-08 UAV kitted out for real work. Note the antenna arrays quality and range of the optics used in any surveillance video cameras. The most efficient altitude for flight is around 11000 feet which gives 25% of the fuel consumption achievable at sea level. As well as its modular design, the Flamingo has a large payload area (in front of the propeller) which has a bolt-on pannier which may be replaced to allow the aircraft to be re-configured quickly for different missions. The pannier can be constructed to suit the customers’ requirements, with the payload mounted above, below or with the Pannier plate mounted vertically, on each side. Overall, the pannier has been optimised for surveillance equipment. Maximum payload is 10kg while the all-up weight (AUW), which includes airframe, fuel and payload is 20kg. Undercarriage Because the Flamingo will be employed in a variety of situations, its undercarriage may be configured in three ways: (1) Fixed undercarriage. This is ideal for local missions, pilot training and other tasks where landing and take off requires a fixed undercarriage. (2) Drop off dolly. This configuration is mandatory for long range, long endurance missions. It gives maximum aerodynamic efficiency and the fuselage is tough enough to permit belly landings on return. This configuration is also ideal for catapult launching. (3) A small single wheel fitted to the fuselage as in full size gliders. (4) The single boom configuration allows the safe use of the more efficient wooden propellers even with the dropoff undercarriage. Endurance & speed The 5.6 litre fibreglass fuselage fuel tank gives an endur- Broken down into its separate components, the Flamingo will easily fit into a family sedan. siliconchip.com.au ance of up to seven hours depending upon factors such as the aircraft all up weight (AUW), motor type and size, throttle setting etc. As noted above, top speed is around 78 knots (144km/h) while cruising speed is around 52 knots (96km/h) and stall speed is about 24knots (44km/h), so the speed range is of the order of 3:1. These figures are dependent on the motor fitted and the payload. The Flamingo is designed to handle winds up to about 17 knots (32km/h) with safety. The Flamingo is designed for local and export markets, including the following applications: • Pastoral live stock inventory & mustering. • Agriculture – farm management; crop growth; crop damage; water storage. • Environmental monitoring; fence damage. • Security/Military – surveillance; intelligence; target drones. • Real Estate/Mining – property images/mine layout/ environmental monitoring Practical aspects The Flamingo has been used in a variety of applications. It was entered in the 2007 Outback Challenge and was fitted with an Ezi-Nav autopilot manufactured by Dave Jones of AUAV, Florida USA (www.auav.net). Flamingos have been sold to various Universities, private individuals, the Royal Thai Air Force and the USAF and are all out there doing useful and very interesting work. For example, a Flamingo F-08 belonging to the Queensland University of Technology is fitted with a Micropilot autopilot and has at various times been controlled via the 3G telephone network. It has also clocked up a lot of hours doing collision avoidance under the Smart Skies Project (www.smartskies.com.au). The twin boom Flamingo F-15. Note the canopy style access hatch on the nose-cone and the three blade prop fitted to the larger Saito FG-36 four stroke engine. June 2010  15 1 BATTERY THROTTLE SERVO THROTTLE FAIL-SAFE ENABLE LINES RADIO CONTROL RECEIVER 2 DATA LINES CONTROL LINES 3 AILERON SERVO IMU ATTITUDE CONTROL MODULE ALTITUDE HOLD ELEVATOR SERVO 4 5 6 RUDDER SERVO GPS STEERING MODULE GPS RECEIVER BATTERY Block diagram of the Flamingo Autopilot showing the essential control elements. FLAP SERVO TO CHANNEL 5 THREE POSITION FLAP SWITCH Ezi-Nav modified by Silvertone to include IMU and 2.4GHz receiver. This is part of an ongoing worldwide project aimed at integrating UAVs into shared air space, ie, occupied by both UAVs and manned aircraft. The successful integration of UAVs into shared air space is currently a major concern of aviation authorities all over the world. Small UAVs are being touted as economical solutions for such tasks as border surveillance, crop health analysis, livestock and wild animal survey, traffic monitoring and even as a monitoring system for game poaching in Zambia. The concerns of aviation authorities in regard to small UAVs are easily understood. Capable of ranges in excess of 500km and able to operate at altitudes of up to 5,000 metres under full autonomous control these are no longer model aeroplanes. A 20kg UAV colliding with an airliner does not bear thinking about! If UAVs reach the levels of acceptance that proponents have in mind for them, then air traffic control will take on a whole new meaning. Add to this the concerns of authorities in regard to misuse by terrorists and it becomes perfectly obvious that UAVs must be handled with great care. The Ezi-Nav fitted to Flamingo F-05 comprises a series of software modules, which together with solid-state sensors combine to make up the autonomous flight control system. The autopilot software features a GPS steering module, the altitude hold module, a solid-state attitude hold module plus various navigation and housekeeping modules. There is also provision for a data modem uplink/downlink. In the Flamingo, a real-time video downlink system with a video overlay can be fitted. The overlay displays groundspeed, altitude, compass-heading, GMT time and GPS location in real time on the ground control station monitor. There is more on the video installation to follow. The Ezi-Nav can also provide a complete and more traditional data downlink giving the Ground Control Station with such data as speed, altitude, battery voltage, engine RPM and a host of other data as well as mapping information. The data link, when combined with the autopilot log file, can provide some very interesting information. For example the photo below is a track-plot overlaid on Google Earth but rotated to show the UAV flight path from a horizontal viewpoint. Now the interesting thing about the photo below is that the white path shows the flight-path under manual control and the purple path shows the flight-path under autonomous control. Looking closely, you will notice that the white path leaves the airfield after take-off and during climb to altitude and then switches to purple when auto Ezi-Nav Ground Control Station showing instrument displays and mapping data. Horizontal view of a track-plot overlaid on Google Earth. This UAV came down rather more quickly than it went up! Guidance 16  Silicon Chip siliconchip.com.au Finished Ezi-Nav. Note the tiny receiver antenna (left side) and neat wiring installation. mode is switch in. But where is the white track tracing the flight-path back down to the landing? Uh-oh! There isn’t one, because the autopilot (no, not an EziNav) failed in flight and the UAV dived vertically into the ground from 600m, destroying it and all of the components on-board, including the autopilot. So we have no way of knowing what failed except for the log file transmitted back to the ground prior to the crash that clearly recorded the fact that the autopilot stopped generating the log file probably at the same time as it stopped flying the UAV. It was a shattering experience in more ways than one and drives home once again the fact that choice of reliable components is a vital element in the success of any project. So back once more to the Ezi-Nav. The microprocessorbased GPS steering module receives output data from a dedicated GPS receiver and converts it to an R/C servo position command. The GPS receiver provides the raw GPS data to the autopilot and the autopilot performs the navigation calculations and manages waypoints and routes. Simply connect the dedicated GPS to the autopilot and it will translate the track/bearing error into a servo position command. This module also corrects for cross-track error so it will stay on course for long distance navigation in heavy crosswinds. The Altitude hold module is pre-set in the flight planning stage. The waypoint data contains an altitude parameter that will instruct the aircraft to climb or descend while on route to the next waypoint. In order to achieve this it may be necessary to insert a loiter command to allow the aircraft time to arrive at the defined altitude. The Ezi-Nav is also fitted with a waypoint management system that allows waypoints and altitude data to be uploaded in flight via the data modem if required. When uploading waypoints, most small commercial Autopilots are restricted to 300km radius of operation due to Government regulations and will automatically return home if this distance from home is exceeded. Using the GPS-enabled system with an attitude control unit (optical or IMU) and an altitude hold makes it possible for an aircraft to be sent off on a fully automatically siliconchip.com.au Dave Jones (AUAV) working on the Flamingo F-05 prior to the Outback Challenge 2007. Note the ease of access to the avionics using the pannier style nose configuration and a sensible stand. 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. Autonomous landing and take-offs are very difficult to achieve reliably and it is best to stay with manual control for these functions in low-cost UAVs. To get the modules to automatically take control when the R/C radio loses command signal or is switched off deliberately, you need to use an R/C system that comes with a built-in fail-safe and servo hold (preset) feature. The autopilot-enable channel is programmed so that the fail-safe will activate Autopilot Enable once the transmitter is switched off or fails. From this point the UAV is in full autonomous mode. Video downlink One of the big problems facing civilian UAV operators is that of restrictions on RF power and frequency allocations suitable for use in UAVs. The most serious of these is the video transmitter output power legally allowed on the commonly used 2.4GHz ISM band. While the UAV is free to roam across vast tracts of terrain, getting back real time video images using transmitters abiding by the Australian A circular tracking plot painted over a Google Earth display. The Aircraft used was the Silvertone Aerocommander, a very fast (120kph) small UAV. An excellent plot recorded on quite a windy day. The red track is part of a proposed flight plan to be flown at a later date. June 2010  17 legal limit for analog FM video transmissions of 10mw effectively clamps the operational range to only hundreds of metres – that is, if you want to see what is happening in real time on the ground. If the application can tolerate stored video to be reviewed at a later date then that really is a very nice way to do it, as the video images are of a much higher quality and well worth waiting for. Another avenue is stored still images spliced together in a photo mosaic such as shown below. The mosaic below is made up of a series of near infrared stills used in agricultural survey to determine crop health. The type of system outlined above is ideal for special projects where real time images are not required. The more typical UAV missions such as fire detection, traffic management or surveillance do require real time images. In keeping with the requirements for these missions, the Flamingo is fitted with a real time video downlink. The block diagram opposite shows the basic layout of the various components. There is one further aspect to video and that is First Person View (FPV) wherein the pilot flies the aircraft out of sight using an attitude control combined with a video downlink. There need be no autopilot used in this system, therefore it falls more correctly into the RPV (Remotely Piloted Vehicle) category. The IMU or optical sensor keeps the aircraft level and the flying is done via virtual reality goggles or just simply a good video monitor. There is an enormous amount of interest in this aspect of R/C flying as it removes the “fly-around-incircles” element from the typical old-style flying session. Once again, however, governing bodies become hypersensitive when confronted with this sort of thing and exert their muscle via the insurance policy. It is however very exciting once you are involved. This system combined with an autopilot is a potent combination as each system provides back-up for the other. In the event of an autopilot Antenna array used in the Outback Challenge 2007. This array included antennas for the video, radio control and duplex data transmitters. failure the aircraft can be flown home visually provided the control receiver is still in range of the transmitter. The video system The heart of any video system is the video camera and we recommend the best that can be justified under the project budget. One of the frame grabs shown below was taken with a 625-line camera and even that is of quite poor quality compared to the stored video. Vegetation suffers Photo mosaic taken during early morning in Near Infra-Red. A series of stills spliced together using a suitable software program. Used to determine crop health. Photo courtesy of IDETEC Chile. 18  Silicon Chip siliconchip.com.au RCVR BATTERY PAN SERVO FAILSAFE 1 RECEIVER DUAL SERVO SLOW FAILSAFE 2 VIDEO LINES TILT SERVO POWER LINES TV CAMERA OVERLAY SWITCH CONTROL LINES VIDEO OVERLAY TV TX BATTERY Xtend Modem used in the Flamingo for the 900MHz data link very badly with low-resolution cameras. By far the best quality video is obtained with an on-board digital video camera and using a low-resolution real-time mini camera as an aiming guide. There is always the risk of the loss of a very expensive camera but that has to be balanced out by the results obtained. There is another method for real-time video coverage using the mobile phone system but for this to work the UAV must obviously be operating inside the area covered by the phone network. Interestingly enough, Digital Spread Spectrum (DSS) video transmitters are legally allowed up to 4W – the problem is finding a good commercial unit at a reasonable price. There is an excellent dual diversity, digital unit available but the price is around US$25,000 and this is only for the video transmitter and receiver. A good gyro-stabilised, GPS targetable optical and infrared camera which is integrated into the autopilot, can cost as much again. The DSS video TX/RX unit above will Frame grab showing the definition possible with a good video system Silvertone recommend the best possible camera, despite the risk of total loss in a crash. siliconchip.com.au TV TRANSMITTER Block diagram of the real-time video downlink installed in the Flamingo. work over ranges in excess of 50km. Even that range is still short of the range of the UAV so unless UAV operators can get access to real time satellite image transmission the effective operational range of the small UAV is governed by the range of the real time video link. As shown in the above block diagram, the system begins with the TV camera (with a cameraman seated at a ground video monitor). The video output is fed into a relay-switching module, which either routes the video directly to the TV transmitter or through a video overlay unit. This relay is controlled from a separate video control transmitter, along with the signals to control the pan and tilt servos for the camera. Alternatively the camera may be integrated into the autopilot for GPS targeting or even a combination of both. The camera is able to pan through 170° in the horizontal and 100° in the vertical. To hold panning speeds to an acceptable level (fast panning speeds give a very jerky look to the finished video), a dual servo slow unit is fitted between the fail-safes and the pan and tilt servos. The fail-safes are fitted to serve as set-locks. If the transmitter is switched off in flight the camera will move to the pre-set position and sit absolutely still in order to further enhance the quality of the finished video. All of these refinements are fitted to give maximum flexibility combined with a rock-solid finished video. Finally, the video receiver antenna; here only the best will do. As the airborne video transmitter is a low power unit, a very good antenna is required on the video receiver. We are currently using a 17dB hand-held Yagi, pointed at the aircraft by an assistant. At the 2007 Challenge we used a dish and this gave much better range. As both the Yagi and dish antennas are very directional, aim is a tedious and somewhat boring task for any assistant and their minds often tend to wander! As a result there are occasionally blocks of scrambled video in the middle of the clip where the antenna drifts off target. A better arrangement would be an auto tracking antenna or possibly an omnidirectional antenna such as a high gain collinear antenna. SC June 2010  19