Final answer:
The primary shortcoming of the ramjet engine is the absence of thrust at rest, making it dependent on high-speed airflow. The main disadvantage of a ramjet engine is the lack of thrust when the engine is at rest, making it inefficient for initial take-off.
Step-by-step explanation:
A major shortcoming of the ramjet engine is the lack of thrust at rest. Ramjets require a high initial speed to operate because they don't have onboard compressors; instead, they use the engine's forward motion to compress incoming air, which only becomes effective at high speeds. They cannot produce thrust when stationary, making them inefficient for take-off or at low speeds. Therefore, they are typically used in conjunction with other propulsion types or launched at high speeds. The performance limits of a ramjet reflect the principles that dictate rocket acceleration and thrust. The greater the exhaust velocity (Ve), the higher the acceleration, but the practical limit for Ve of hot-gas propulsion systems is about 2.5×10³ m/s. Variables such as the rate at which mass is ejected from the propulsion system (represented as Am/At) and the mass (m) of the rocket also play crucial roles. As the rocket burns its fuel, the mass decreases, continually increasing acceleration until the fuel is exhausted.