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GLOBAL HAWK UAV STARTS FLIGHT TESTS
by Karl SchwarzThe maiden flight of a new aircraft is always thrilling. This is especially true to an UAV (Unmanned Air Vehicle). In order to exclude all possible risks, Teledyne Ryan Aeronautical had therefore gone through all the tests very thoroughly on the ground. If the software was changed, the complete program was checked again. This is why it took 14 months longer than anticipated before Global Hawk was ready for take off.
At dawn on 28 February the largest current US drone finally started moving on the apron of Edwards AFB. It did a sharp turn onto runway 08, accelerated and then took to the skies at a flat angle and at a speed of 200 km/h. At around 280 km/h Global Hawk climbed to an altitude of 9750 metres.
Because the landing gear did not lock up properly and the sensors showed temperatures that were too low in the front avionics room, the test crew decided to descend to an altitude of 6100 meters and finally decided to cut the flight short. A command was sent up to enable the drone to touch down on runway 22 after almost one hour. It landed with a sink rate of 70 cm/sec., and came to a standstill with the help of spoilers and brakes after 1,200 meters. Thanks to the differential GPS, the deviation from the middle line was less than 50 cm.
A start has thus been made. Until the end of phase II, 15 further flights of 250 hours total duration are planned. For this purpose the second Global Hawk is being assembled in San Diego right now. It will be fitted with the complete sensor system and is going to carry out flight no. 7. The first plane will also be equipped with radar at some stage in the future. At 40 hours the 14th flight will be the longest. Teldyne Ryan wants to have both drones airborne at the same time with flights 15 and 16.
The next phase of the program is envisaged for 1999. The US Atlantic Command is planning to carry out extensive unit trials. For this purpose the DARPA (Defense Advanced Research Projects Agency), which is managing the program for the DARO (Defense Airborne Reconnaissance Office), has ordered three further Global Hawks. Eight had originally been planned, but since the cost of Phase II rose from 164 million US dollars to over 220 million US dollars, money had to be saved.
If the high expectations for Global Hawk are fulfilled during these trials, 50 of the unmanned planes could be acquired. On average they are said to cost 10 million US dollars, i.e. without spares, logistic etc., at 1994 prices. The price, which will not be kept this low because of some changes in the program, was the only fixed "item" in the order catalogue. All performance data had to fit this target.
Despite the strict limit with regard to cost, Global Hawk will, according to the manufacturer, fulfil or come close to all guidelines. And that was no easy task. One requirement was a maximum distance of 25,900 km, which means that the UAV can fly half way around the world non-stop. The altitude for deployment is supposed to be 65,000 ft (19,800 meters), and the maximum flight duration is almost two days.
Teledyne Ryan is no stranger to extremes, because this company had, as early as the 60's and 70's, developed "high altitude drones", capable of covering great distances. It was able to build on previous experience, even if today's technologies are much more advanced.
The wing, built by Boeing, (which used to be Rockwell), consists entirely of carbon fibre. Although it has an aspect ratio of 25, it is extremely stiff and dips by only 60cm under strain.
The V-tail unit, which is manufactured by Aurora Flight Sciences, is made from composites as well. It has two steering surfaces. Two spoilers and two ailerons have been added. Redundancy in the flight control system is carried through to the computers in order to limit the risk of failure.
Teledyne Ryan is fashioning the fuselage very conventionally from aluminium. There is room for the sensors in the front, a big tank is fitted in the middle and the Allison AE 3007H-engine is installed in the tail section. The turbofan is taken, almost without any changes, from the Citation-X-business jet and the EMB-145. A few adjustments to the controls allow it to operate at altitudes of up to 21,300 meters.
For self-defence Global Hawk has been fitted with radar warning receivers and jammers. On top of this, the ALE-50 towed decoy can be dragged behind if necessary. It is claimed that even without Stealth characteristics the UAV is very survivable. Simulation exercises have allegedly shown that Global Hawk can survive more than 200 missions without sustaining any damage if its flight path is planned carefully (i.e. around high treat areas).
The plane itself is only a platform for reconnaissance sensors, of which there are three aboard Global Hawk. They work on different wavelengths and complement each other as follows:
* The synthetic aperture radar manufactured by Raytheon (formerly Hughes) is suitable for all weathers. It offers a resolution of one meter in normal search mode. 138,000 sq km can be covered per day at a distance of 200 km. Alternatively it can use "spotlight" mode, which surveys 2x2 km sized areas in 24 hours with up to 1,900 photos at a resolution of 30 cm. Finally the radar, which works in X-Band, can be used to follow moving targets, as long as their speed is higher than seven km/h.
The two antennas, (which are fitted to the sides of the lower fuselage and are 1,21 m long), and the necessary electronics have a weight of 290 kg and need 6,000 watts electricity. First flight tests were carried out last October using the HISAR-derived radar on board an A-3 Skywarrior.
At daylight the CCD camera also built by Hughes supplies pictures with high resolution. The 1,024 x 1,024 pixel detector is linked to a telephoto lens with a focal length of 1,750 mm. Depending on the program, a 10 km wide stretch is being scanned, or detailed pictures are taken of a 2 x 2 km sized area.
For night pictures a heat-seeking sensor (640 x 480 pixel), which operates within 3-5 microns can be used. It uses the same telephoto lens, which can be turned through 80 degrees sideways.
Radar and electric-optical infrared sensors can be used at the same time, which obviously generates a vast amount of data. The EO/IR camera on its own supplies 40 million pixels per second, which corresponds, depending on the depth of colour to 400 million bits. At least the raw information is being stored onboard and saved. The digital pictures can be compressed, as is commonly done on home PCs.
Despite all this the demands made on the transfer of data are enormous. Up to 50 million bits per second (Mbps) are being transmitted via satellite. For this purpose there is a swivelling Ku-Band antenna, 1.22 meters in diameter. The data transmission is up to 137 Mbps if there is a direct link to a ground station via UHF.
The information either goes directly to the mission control station, or to the Global Hawk control station, which is housed in a container. This is mobile, just like the separate start and landing control stations. Two C-17 Globemaster III suffice to transport these containers and other accessories anywhere in the world.
Global Hawk would be able to fly itself towards its distant deployment bases. The scenarios of the US military assume that these will be up to 3,100km away from the crisis areas under surveillance. In more favourable cases, for instance the surveillance of Bosnia from Italy, patrol times above the target area would be increased to over 35 hours.
Possibilities like these are not only interesting for the US military. Australia, Great Britain, Israel and Saudi Arabia have expressed an interest in the Global Hawk. This means great prospects for Teledyne Ryan which also has many other ideas for the deployment of the "King of the Drones": For example, it could also be used as a relay station, a research platform high in the skies or a carrier for guided missiles to destroy ballistic rockets.
From page 44 of FLUG REVUE 5/98
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Last updated April 7, 1998
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