"Several technologies were used, including aeroservoelastic trim tabs," he says. 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.
Electromagnetic actuators developed
As the aircraft in its early testing stage got bigger and heavier, the force needed to deflect the control surfaces was growing as well and innovative solutions had to be found. "We concluded electromagnetic actuators would work the best and found there was sufficient deflection at satisfactory frequencies," says Dr Amprikidis.
"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."
Efforts had been made to ensure maximum stability even without the tabs for example using a special aerofoil profile optimised for high lift at low speeds. The whole configuration contributes to stability in severe weather. The ground-based pilot 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, when fully fuelled and equipped. It was flown initially with a conventional remote control operating joystick and throttle. The UAV base station has now been modified with two screens to exploit the plane's avionics one screen
|Contact: Piotr Pogorzelski|