What effect does a boat tail have on a subsonic rocket's coefficient of drag (Cd)?

The presence of a boat tail on a subsonic rocket is designed to improve aerodynamic efficiency. Specifically, it helps to streamline the shape of the rocket, which reduces the turbulence and pressure drag associated with the base of the rocket. By tapering off the rear end of the rocket, the boat tail reduces the base area where flow separation typically occurs.

This modification leads to a decrease in the coefficient of drag (Cd) because a well-designed boat tail minimizes the wake created behind the rocket. As a result, the flow remains attached to the body of the rocket for a longer distance, which lowers the overall drag force experienced during flight. This makes the rocket more efficient in its performance, leading to better fuel economy and increased range. Overall, the addition of a boat tail actively works to optimize the rocket's aerodynamics by targeting and reducing specific sources of drag.