Elbit Systems Inc. is developing an autonomous drone for long range missions. In order to save time and to use electrical batteries having short time power supply, this drone is designed to be launched to its remote operation zone inside a 120 mm mortar shell. During the launch the pressure in the mortar barrel creates on the shell an acceleration pulse with a peak of about 10,000 g within about 3 milliseconds. This work examines the durability of the designed drone having the extreme launch acceleration.
This work includes three steps. First, the original design of Elbit was analyzed and approved to meet the geometrical and functional conditions while keeping its rigidity. Then, based on this updated design and its CAD model, a FEA model was built, using the ANSYS Workbench software package with the Explicit Dynamics (Autodyn) solver. In the second step the FEA model was calibrated and verified using drop tests results. The drop tests were performed with a dummy mortar shell having an equivalent FEA model and equipped with two accelerometers. A fast video camera was also used for redundancy and for measuring the impact velocities in the drop tests. Those velocities were used as inputs for the ANSYS simulations, and their acceleration results were compared to the accelerometers readings for the calibration of the numerical FEA model. Finally, the calibrated FEA ANSYS model was used to simulate the drone structure response to the forces acting on the mortar shell during its launch. The launch simulation results showed that most of the drone structure withstand the extreme acceleration conditions during its launch inside the mortar shell. However, the magnets of the selected COTS (Commercial Off-The-Shelf) propeller motors, do not withstand these conditions and therefore these motors must be chanced or redesigned. In addition, based on the FEA results, it is recommended to strengthen some parts in the current design.
