Final answer:
A multiple-point priming system with a central spider is designed to prime all cylinders of a nine-cylinder radial engine by providing an even distribution of primer fuel to facilitate starting.
Step-by-step explanation:
The student's question pertains to the functioning of a multiple-point priming system in a nine-cylinder radial engine. A multiple-point priming system is used to deliver fuel directly to the cylinders of an engine to facilitate starting. The central spider in this system is a hub-like distribution component that allows for an even distribution of primer fuel to each of the engine's cylinders. When activating the priming system, the pilot has the option usually to prime all cylinders equally or may have the option to selectively prime individual cylinders depending on the design of the system.
In the case of a nine-cylinder radial engine, the priming system will typically be set up to administer primer fuel to all cylinders to ensure an even start. The distribution through the central spider ensures that each cylinder receives an appropriate amount of fuel. The goal is to provide just enough fuel for initial combustion when the engine is cold, as a radial engine's cylinders require the fuel-air mixture to be evenly distributed to start efficiently. The success of the priming process is crucial for reliable starting and performance of the radial engine, particularly in aviation applications where these engines see common use.