Are we on the brink of new era of flying machines able to stay airborne for weeks, months or even years at a time? RICHARD GARDNER looks at ultra long endurance UAVs.This is an excerpt from an article published in Aerospace International: November 2010 [caption id="attachment_3322" align="alignnone" width="198" caption="QinetiQ's Zephyr UAV - aloft for a fortnight (QinetiQ)"][/caption] The intensity of operations in Afghanistan has placed enormous reliance on space-based military assets to enable air and ground forces to maintain a technological edge. Satellites have provided secure, reliable, surveillance and communications capabilities that have transformed the way the war is being waged, even though they remain unseen and attract little media attention. GPS is now an essential tool for both navigation and precision attack. Without these capabilities it would be difficult for local commanders to maintain a dominant position on the ground without needing many more troops than are in theatre at present. Regardless of the end result of this particular conflict, the pattern of operating, with reliance on space assets and air power domination, is likely to remain a key feature of warfighting for the rest of the century. But it is becoming colossally expensive, even for the US, and the availability to NATO of global positioning and space surveillance space assets, largely provided by the US taxpayer, is now very much taken for granted. The UK has its own highly successful Skynet military communications network, but it is completely dependent on the US for GPS and space surveillance. Unless it starts to invest in its own ‘Son of Topsat’ small surveillance satellites, this dependency will remain. Closer to earth, the RAF’s current armed UAV capability provided by General Atomics Reaper drones, is equally dependent on US-supplied infrastructure, with No 39 Squadron based at Creech AFB, Nevada. If military space assets and UAVs are growing in importance to the UK, and the RAF in particular, as frequently espoused by the Chief of the Air Staff, ACM Sir Stephen Dalton, then how is the future requirement for persistent surveillance to be met — and kept affordable? Ultra high altitude long endurance (HALE) unmanned air vehicles (or remotely piloted vehicles) could be a part of the answer.
UK World record beater[caption id="attachment_3323" align="alignnone" width="300" caption="QinetiQ's Zephr 7 UAV taking off (QinetiQ)"][/caption] The UK defence technology company QinetiQ has developed an ultra-lightweight solar-powered UAV, the Zephyr which, last July broke the world endurance record for an unmanned air vehicle, remaining airborne for 336 hours and 22 minutes (over two weeks). It also broke the absolute altitude record for a UAV at 70,740ft. This flight, conducted over Arizona, USA, beat the previous UAV endurance record by more than a factor of five, and was only terminated by ground control after it had proven all the test parameters that had been set for it. The Zephyr programme was aimed at designing a HALE UAV that could fly for months at a time, with a year round performance in mid-latitudes. The concept centred on an ultra-light and cheap solar electric aircraft with solar charged batteries providing power during the night and with an operating ceiling of between 50,000-70,000ft. The work on Zephyr dates back to an earlier QinetiQ project for a high altitude manned balloon attempt on the world altitude record in 2003. A 12m span proof-of-concept prototype tethered UAV was built, and was intended to be launched from the balloon at above 140,000ft. Although the balloon record attempt failed, the Zephyr UAV concept showed considerable promise and two years later Zephyr 4 was launched from a balloon over the Woomera test range in Australia. This led to further ground-launched test flights of Zephyr 5, this time conducted at the White Sands Missile Range in New Mexico. Two variants were flown — one powered by primary battery power only, and the other by both primary battery and solar power. Between 2005-2006, Zephyr 5 flew with the first solar powered propulsion system for a maximum of 18hours, with a 1kg payload and at an altitude of 36,000ft. From 2007-2009, Zephyr 6 acted as a technology proving test platform for the concept of multi-day missions at an altitude of 62,000ft. The Zephyr 5’s wingspan of 15m was extended to 18m for the Zephyr 6, which achieved an endurance of 82 hours, 37 minutes. In 2010, the latest Zephyr 7, with a 23m wingspan, a 2.5kg payload and a 70,000ft altitude capability, proved that multi-weeks, or months could be flown non-stop, paving the way for the development of a vehicle with an operational capability. The Zephyr 7 proved its improved reliability over Zephyr 6, with increased performance in flight duration and overnight altitude capability. The in-flight performance data will be used for future system improvement.
Aerospace International Contents - November 2010 News Roundup - p4 News Focus - p13 Five priorities for the post-SDSR environment Sizing up the flyweights - p14 Phenom 100 and Mustang battle it out Making security work - p21 New trends in airport passenger screening The shape of aerospace to come - p 24 Report on ICAS 2010 conference Patent predictions can open doors - p28 Monitoring aerospace technology trends Deal or no deal - p30 Focus on EU merger and alliances rules The Last Word- p34 Keith Hayward on airport competitionZephyr has become a remarkable low-profile breakthrough air vehicle. By no means the first solar-powered aircraft, it has nevertheless taken a very simple, but desirable, aim and turned this into a viable vehicle with real potential for growing into a transformational technology. The key to success to date has been the achievement of low cruise power at high altitude. The design required low mass, low wing loading and low drag, with high propulsion system efficiency. The onboard avionics package required minimum power requirements with high energy density power storage, with a good cycle life and efficient power generation. Although at first sight the Zephyr air vehicle resembles a giant model aircraft, its design has involved extremely sophisticated computational analysis and development of every aspect of the structure, propulsion and avionics systems, the batteries and solar array. The carbon composite airframe features a very low-drag wing section with efficient propellers. The brushless direct drive electric motors have high efficiency speed controllers and the avionics systems are light weight and low power. SION Power has developed the secondary batteries with lightweight insulation and low power heating system used to maintain battery temperature. United Solar Ovonic thin film silicon array covers most of the wing area and forms the flying surface. Zephyr is intended to be capable of carrying a useful 2.5kg payload and this can be carried either in a nose pod or within the wing. There is rich potential for developing the platform for communications relay use as from an altitude of around 65,000ft the line of sight diameter is 1,000km. Payloads can include cross band VHF-UHF repeaters and dual channel SINCGARS VHF relay. An ISTAR payload can include visible real-time video pan and tilt camera and far IR real-time video. Demonstrated ISTAR performance has shown large field of regard for pan and tilt visible payload and a zoom capability for wide field of view for detection, and narrow for identification. QinetiQ has also built low level test aircraft (LLTA) based on scaled versions of Zephyr to be used for aero-proving and avionics/ground control station integration. Each is a test bed for systems demonstrations, payload investigations and crew training. The current Z7 ground station is a container-based transportable unit with all the air-ground data links. The July flight trials of Zephyr 7 which set the recognised absolute world records for UAV endurance and altitude (beating the Global Hawk’s altitude record by 5,000ft and flying ten times longer non-stop) proved that the concept works and that it can be developed into a reliable air platform.