When can steel nozzles be utilized in research motors?

Steel nozzles can be utilized in research motors when the nozzle throat is recessed within the case of a sugar motor. This configuration minimizes the thermal and mechanical stresses exerted on the nozzle, as it is shielded from direct exposure to the combustion gases. The design helps to protect the steel from overheating and potential failure, as the recessed position allows for better control over the thermal profile and reduces the likelihood of hot gas erosion that can otherwise compromise the nozzle's integrity.

Using a recessed throat also takes advantage of the inherent structural strength of steel, permitting it to maintain performance under the specific conditions of a sugar motor, which operates differently than other types of solid propellants. This design consideration assures that the nozzle can effectively handle the unique combustion environment presented by sugar motors.

In contrast, other scenarios, such as the use of steel nozzles at high altitudes or based solely on user discretion, do not provide the same guarantees of safety and performance without thorough testing and analysis of the motor's specific operation context.