F Shahmiri - Malek Ashtar University of Technology- Aerospace Research Institute- Tehran- Iran.

Hover performance of a twin-rotor test model in terms of rotor overlap sweep, blade collective pitch angle, and rotor rotational speed was examined experimentaly. The test model consisted two three-bladed rotors with a diameter of 1220 mm and constant chord of 38 mm, giving a blade aspect ratio of 16.05. The blades were rectangular planform with NACA 0012 cross sections made of composite carbon fiber and had no twist or taper. In this model, the rear rotor was fixed on the fuselage and the front rotor could move longitudinally for tests up to 40% rotor overlap sweep. The test plan was prepared based on Central Composite Design (CCD) that was found as a low cost experimental design method. The mathematical expressions of thrust and power required showed that optimal performance at hover (i.e., minimum power required at maximum thrust) can be obtained for non-overlapped rotors at 11.5o collective pitch and 1600 RPM.

The optimal performance (i.e., minimum power required at maximum thrust) was obtained for non-overlapped rotors at 11.5o collective pitch and 1600 rpm