Why are most APCP rocket motors central burning?

The correct answer highlights that the burn rates of Ammonium Perchlorate Composite Propellant (APCP) rocket motors are typically too low for the efficient operation of useful end-burning configurations. Central burning designs allow the propellant to be ignited from a central core that burns outward, leading to a more effective combustion process.

In contrast, end-burners rely on the propellant being consumed from one end only; if the burn rate is inadequate, the thrust generated by such a configuration would be insufficient for achieving efficient performance. Therefore, choosing a central burning design ensures that the propellant can burn more uniformly and maintain a more consistent thrust profile throughout the flight.

This design approach also helps maintain the structural integrity of the motor under operational conditions, which can be beneficial for performance and reliability. The characteristics of central burning motors harness the advantages of the materials used while aligning with the desired thrust profiles necessary for successful rocket operations.