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

A boat tail is a design feature that tapers the rear end of a rocket or projectile. This tapering helps streamline the airflow around the rocket as it moves through the atmosphere, especially in a subsonic regime. By reducing abrupt changes in cross-sectional area at the rear of the rocket, the boat tail minimizes the turbulence generated and the size of the wake left behind the rocket.

This design leads to a decrease in base drag, which is a significant component of the overall drag experienced by the rocket. Base drag results from low-pressure buildup at the rear of a blunt-ended object, and by employing a boat tail design, the rocket can maintain a more streamlined flow, resulting in a lower coefficient of drag (Cd). Consequently, the streamlined shape allows the rocket to move more efficiently through the air, enhancing its overall performance during flight.

In contrast, options that suggest an increase in Cd, no effect on Cd, or a focus on supersonic speeds do not accurately capture the aerodynamic benefits provided by a boat tail in subsonic flight conditions.