6 Real-time monitoring of wing position and torsion Theoretical basis A high degree of aerodynamic efficiency can theoretically only be achieved by active torsion, with a small quantity of power required to be supplied by an actuator. With active torsion, the power of the flapping wings is converted very efficiently into thrust. The aerodynamic efficiency factor is the ratio of thrust attained to the flapping and rotary power expended. Scientific investigation of circular flight Investigations and measurements of SmartBird were carried out over the course of its development on the basis of the work of French physiologist Etienne-Jules Marey (1830 – 1904), who analysed the flight of birds that were made to fly in a circular path. To determine the electro-mechanical efficiency, a new apparatus was developed which acts as a dynamometrical brake. SmartBird’s efficiency factors SmartBird and its predecessors have an electromechanical efficiency factor of around 45%. Measurements of circular flight have demonstrated an aerodynamic efficiency factor as high as 80%. The overall efficiency factor is the product of the two partial efficiency factors. Since the aerodynamic efficiency factor can be calculated but not directly measured, it is determined from measurements of overall and electromechanical efficiency. To determine the electromechanical efficiency factor, the absorption dynamometer continuously measures torque and angular velocity to calculate the available power expended during flight. For this purpose, the wing stroke movement is transferred to a shaft that is impeded by a brake shoe; the lever arm of the brake is held by a force sensor. An angle sensor measures the rotation of the shaft. The torque and angular velocity together yield the mechanical power. The electromechanical efficiency factor is calculated as the ratio of this quantity to the electrical power supplied. Optimal use of airflow Propulsion and lift are achieved solely by the flapping of the wings and have a power requirement of only 25 watts. SmartBird has a total weight of around 400 grams and a wingspan of 2 metres. It is thus an excellent example of functional integration and resourceefficient extreme lightweight design, and demonstrates the optimal use of airflow phenomena. The control of the time behaviour of wing bending and wing torsion takes place within the tact of a few milliseconds and results in optimum airflow around the wings. The SmartBird flight model has no rotating parts on its exterior and therefore cannot cause injury.
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