Airframe

Roll Control: A Preventative and Corrective Tool

Roll control aims to control the rotational motion about the longitudinal axis of a vehicle. At LRI, we apply roll control to our flight vehicle to prevent and correct unchecked rotational motion. This ensures that our vehicles fly straight up and do not spin about the longitudinal (roll) axis of the rocket.

Roll control is particularly important in our efforts to construct a pump-fed liquid rocket as excess rocket rotation can induce pump cavitation, a phenomenon where vapor bubbles form in low pressure regions and violently collapse, causing rotor damage.

Our team has chosen to perform aerodynamic control due to the constraints of other techniques such as thrust vectoring if they were to be implemented into our project charter. Aerodynamic control works by transferring the momentum of the working fluid - in this case, the air moving relative to the rocket - to exert a force on the control surface. Our rocket ailerons do just this, applying a force at a lever arm from the rocket's center of mass to create a torque about the rocket's roll axis.

Control Design and Computational Fluid Dynamics

Making in-flight corrections is difficult for two reasons.

Firstly, knowing where a rocket is located during flight, and in particular accounting for its dynamics, is not trivial. We solve this problem by implementing the optimal linear estimation algorithm, a Kalman Filter, and using the state estimate to implement a linear feedback controller that determines aileron deflection.

Secondly, calculating how much of a force each of our ailerons exerts on our rocket is key to implementing an accurate control scheme. To do this, we use ANSYS Fluent, a powerful computational fluid dynamics (CFD) software.

Using these tools, our team is advancing our vehicle design by sizing ailerons, making vehicle aerodynamic optimizations, and retrieving control surface induced moments.