Safety at Sea: Morphing Plane to Rescue

Wednesday, September 8, 2010 @ 06:09 PM gHale


A small and cheap-to-build unmanned aerial vehicle (UAV) intended to cut the cost of maritime search-and-rescue missions and reduce risks to material and human lives is now under development.
The seaplane uses shape-changing technology to improve flight stability, enabling it to fly in severe weather conditions. The resulting craft has an endurance of 4.5 hours with a payload of up to 40 kg. It comes with state-of-the-art avionics and onboard cameras. And it links wirelessly to the command center from where the pilot can control the UAV. A prototype is currently undergoing final trials in Cyprus and the design is already attracting interest from governmental and civil rescue and surveillance organizations.
When it really comes down to it, maritime search and rescue often suffers from severe weather, posing a major risk to helicopters or fixed-wing aircraft and their crews. The cost in material and human life can prove high. ASARP set out to design a UAV to undertake such rescue missions more effectively.
“The main problem is that UAVs are small, light and affected by extreme weather,” said project coordinator Dr. Michael Amprikidis of engineering consultancy GGD. ASARP tackled this by using reactive shape-changing control surfaces. The shape-changing elements of the plane: Aeroservoelastic trim tabs, can vibrate in counterphase to wind gusts to reduce loads by as much 25%, allowing the UAV to fly in severe weather. On-board sensors monitor stability and provide constant feedback to the ailerons.
“Aeroservoelastic technology makes it possible to use wind speed and the structural mechanics of the system to our advantage,” Amprikidis said. The technology was the subject of a previous project in which he evaluated design concepts involving aeroelastic deformation of the airframe enabling aircraft to withstand heavy winds. Optimum efficiency occurred through continual adjustment of the aircraft shape.
“Several technologies were used, including aeroservoelastic trim tabs,” he said. This involves three deformable surfaces used in conjunction with the flight controls and able to move at high frequencies. “A tab can have very high oscillation frequency; traditional flight surfaces cannot match these frequencies, leading to up-and-down movement of aircraft during turbulence.”
These trim tabs counteract the effect of a gust by moving in the opposite phase to keep the aircraft steady. This was the key to making ASARP UAVs stable in extreme weather conditions.
As the aircraft in its early testing stage got bigger and heavier, the force needed to deflect the control surfaces kept growing as well.
“We concluded electromagnetic actuators would work the best and found there was sufficient deflection at satisfactory frequencies,” Amprikidis said.
“We developed a prototype, designed the wings, fuselage and control system. The UAV was finished in June 2009 and the first flight was on a salt lake near Akrotiri, selected for its very windy conditions. The aircraft flew first without the tabs and appeared very steady in crosswinds of up to 60 knots – very severe conditions.”
They wanted to make sure they had maximum stability even without the tabs – for example using a special aerofoil profile optimized for high lift at low speeds. The whole configuration contributes to stability in severe weather. The ground-based pilot, who was an experienced head of training for an airline, reported the flight as very smooth.
The trial aircraft weighed 50 kg with no fuel and 270 to 275 kg mission ready, fully fuelled and equipped. Initially it flew with a conventional remote control operating joystick and throttle. The UAV base station now has two screens to exploit the plane’s avionics. One screen shows the instruments and the other the image from the on-board camera. The control base unit is self supporting with an electric generator to provide power and dual-computer system communicating with the on-board computer.
The ASARP UAV can take off from and land on the sea as well as land. Aircraft operating in these conditions needs to be very light and strong.
GGD is now in the final stages of testing. It has established the flight envelope in terms of take-off speeds, weight, stall angle and endurance range but is still improving the avionics – including autopilot and global positioning system (GPS) and inertial navigation. “Each test flight adds to our knowledge but is time consuming and needs the right weather,” Amprikidis said.



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