For the BionicFlyingFox, our developers from the Bionic Learning Network took a close look at the flying fox and incorporated its special flying characteristics into the technology. The combination of the integrated on-board electronics with an external motion capture system enables the ultralight flying object to move semi-autonomously in a defined airspace.
The flying fox belongs to the order Chiroptera – the only mammals that can actively fly. A particular characteristic is their fine elastic flying membrane that stretches from the extended metacarpal and finger bones down to the foot joints. In flight, the animals control the curvature of the flying membrane with their fingers, allowing them to move aerodynamically and agilely through the air. They thereby achieve maximum uplift, even when performing slow flying manoeuvres.
With a wingspan of 228 centimetres and a body length of 87 centimetres, the artificial flying fox weighs only 580 grams. Like the natural flying fox, its wing kinematics are also divided into arm and hand sections and covered with an elastic membrane that extends from the wings to the feet. As a result, its wing area is relatively large and allows for low wing loading. As with the biological role model, all the articulation points are on one plane, meaning that the BionicFlyingFox can control and fold up its wings individually.
The model’s flying membrane is wafer-thin, ultralight and also robust. It consists of two airtight films and a knitted elastane fabric, which are welded together at approximately 45,000 points. Due to its elasticity, it stays virtually wrinkle-free, even when the wings are retracted. The fabric’s honeycomb structure prevents small cracks in the flying membrane from getting bigger. This means that the BionicFlyingFox can continue flying even if the fabric sustains minor damage.
Sophisticated design: the on-board electronics built into the body combined with the mechanical system in the wings
So that the BionicFlyingFox is able to move semi-autonomously in a defined space, it communicates with a motion capture system. The installation detects its position continuously. At the same time, the system plans the flight paths and delivers the necessary control commands for this. The human operator performs the launch and landing manually. An autopilot takes over during the flight.
One important part of the motion capture system is two infrared cameras which rest on a pan-tilt unit. This allows them to be rotated and tilted in such a way that they can track the entire flight of the BionicFlyingFox from the ground. The cameras detect the flying fox by means of four active infrared markers on the legs and wing tips.
The images from the cameras go to a central master computer. It evaluates the data and coordinates the flight from outside like an air traffic controller. Also stored on the computer are preprogrammed paths which specify the flight path for the BionicFlyingFox when performing its manoeuvres. The wing movements required for optimum implementation of the intended paths are calculated by the artificial flying fox itself with the help of its on-board electronics and complex behaviour patterns.
The flying fox receives the control algorithms necessary for this from the master computer, where they are automatically learned and constantly improved. The BionicFlyingFox is thus able to optimise its behaviour during flights and thereby follow the specified courses more precisely with each circuit flown. This is controlled by the movement of the legs and the adjustable wing area.