Australia backs study to explore airborne payload delivery
Australia's RMIT University plans to demonstrate the use of a tether cable deployed from a fixed-wing aircraft as an airborne precision point delivery and recovery system later this year using a small-scale remotely operated aircraft as the tow platform.
The research project, which is being funded by the Australian Research Council and supported by the Australian Defence Science and Technology Organisation, is exploring the potential use of tethers for airborne payload delivery roles. The technology may also have potential application as an insertion and recovery system for Special Forces personnel, or in search and rescue missions.
The concept is based on the progressive letting out of a multi-kilometre length cable from a fixed- wing aircraft that is flying a constant speed orbit above a ground target. As the tether descends, its tail is able to be steered in space by variations to the aircraft flightpath and speed.
RMIT researchers believe sufficient control can be exercised over the position of the tether end such that it can be brought into a stable hovering position less than 1.5ft (0.5m) above the ground while the launch aircraft is orbiting several thousand feet overhead.
Related orbiting and tether control techniques are already used by US Navy Northrop Grumman E-6A TACAMO aircraft to deploy 8,000m-long airborne communications antennas into a near vertical profile.
RMIT has developed an automatic tether controller as part of its research programme. That system uses fuzzy logic processing algorithms to translate movements in the cable end position in space into corresponding changes in the carriage aircraft flightpath.
Computer simulations carried out by RMIT indicate a 3,000m tether, carrying a 25kg (55lb) payload, would take about 600s to reach the ground after deployment.
However, the simulations also indicate that the deployed tether effectively acts as a spring, and once the payload is released, the cable snaps back into the air. There is also a potential for the tether control system to respond to the spring action by unwinding additional cable, causing the end of the tether to then strike the ground, delaying the start of recovery by around 150s.
RMIT researchers say they are exploring options for a more-efficient response by their prototype tether-control system to overcome this issue, with this to be investigated further in the subscale flight demonstration. The option of temporarily fixing the end of the tether to the ground during the unload-load phase of a mission is also being considered.
PETER LA FRANCHI / MELBOURNE
Source: Flight International
