Wilhelm, J., Close, J., Huebsch, W., and Gautam, M., "A De-Spin and Wings-Leveling Controller for a 40 mm Hybrid Projectile," SAE Int. J. Aerosp. 6(2):683-692, 2013, doi:10.4271/2013-01-2262.
A Hybrid Projectile (HP) is a round that transforms into a UAV after being launched. Some HP's are fired from a rifled barrel and must be de-spun and wings-level for lifting surfaces to be deployed. Control surfaces and controllers for de-spinning and wings-leveling were required for initial design of an HP 40 mm. Wings, used as lifting surfaces after transformation, need to be very close to level with the ground when deployed. First, the tail surface area needed to de-spin a 40 mm HP was examined analytically and simulated. Next, a controller was developed to maintain a steady de-spin rate and to roll-level the projectile in preparation of wing deployment. The controller was split into two pieces, one to control de-spin, and the other for roll-leveling the projectile. An adaptable transition point for switching controllers was identified analytically and then adjusted by using simulations. The initial roll position may never be the same due to the round being inserted into its launch tube at any roll angle, therefore an adaptable method was used to shorten the time required to become wings-level. An aerodynamic model was constructed, in house, in Simulink using a 6 DoF simulator. Aerodynamic data from literature sources was collected and tail forces and moments were estimated. Each tail was assumed to have an adjustable local angle of attack for increased moment generation during de-spin and fine control during roll-leveling. Results show that the round can be expected to de-spin in 4%, wings-level in 5%, and be ready for wing deployment in a maximum 10% of flight time.