Performance Analysis and Redesign of Tow Target SM10

Abstract: In this master thesis a performance analysis and redesign of the tow target SM10 was carried out on behalf of the Swedish Defence Materiel Administration's (FMV) branch in Vidsel. At Vidsel Test Range various types of tests and training campaigns involving air space sanctioned by the Swedish government are carried out for both national and international clients. The tow target itself is used as a target in missile target testing and is towed by unmanned aerial vehicle (UAV) where velocity and other parameters such as altitude are given by the client.

The initial objective of this thesis was decreasing the force of drag in-flight but it was expanded to also increase the stability of the tow target through design changes. Since there was no performance data of the current design these were obtained in order to make a comparison between the designs. The lack of data also led to the creation of a theoretical model for validation of the simulated values and it was created using both pure theory and values based on experimental data.
Another objective was to investigate how changes in some of the design parameters affected the drag and stability. This was done in order to choose the final design and ensure improvement in the performance parameters of interest. Some secondary objectives were to see how factors like winching speed as one scenario and the presence of the wing and winch-house on the UAV as a second scenario would affect the performance. Due to the time factor these objectives were of lower priority since the in-flight case takes up a higher percentage of the flight time.

The results of the validation of the simulated values proved that the simulated values can be considered valid within an acceptable margin of error. The results of the simulations of the current design formed a baseline for the following design tests and the vortex created behind the tow target was the main issue of the current design causing great instabilities. The design tests were made for three parameters separately the nose- and endcones and the angle of sweep. These designs showed a decrease in the coefficient of drag in all but one of the designs tested but the forces along the y- and z-axis were dangerously high in some for some of the designs. The drag and stability forces as well as the manufacturing viability of the cones were taken into account when choosing the new design. The new design was tested in the same fashion as the current design with both series of steady state simulations and one transient simulation to validate the results from the steady state simulations. The simulations showed a mean decrease in coefficient of drag by 27 %, a mean decrease in force along the y-axis by 26 % and a mean decrease in force along z-axis by 47 %.

Additional testing looking at the scenario of winching speed and the scenario of a wing and winch-house present in order to see how these factors affect the forces acting on the tow target. In all cases the new design showed an improvement in stability and little or no difference in the coefficient of drag when compared to the results of its steady state simulation. This stands to prove that with the testing made within this thesis the new design is clear improvement in performance as compared with the current design.