FAA Powerplant Written Practice Test

Cam-ground pistons are utilized in some aircraft engines to achieve what?

1. Higher compression ratios

2. A better fit at operating temperatures

3. Reduce engine weight

4. Increase piston speed

The correct answer is: A better fit at operating temperatures

Cam-ground pistons are designed with a shape that is slightly elliptical rather than perfectly circular. This unique design allows the piston to achieve a better fit within the cylinder at operating temperatures. When the engine operates and heats up, the piston expands, and the cam-ground shape accommodates this thermal expansion more effectively than a standard circular piston. When the piston is cold, it is narrower in the direction of travel, allowing for easier movement within the cylinder. As it heats up, the expansion occurs in a controlled manner, helping to maintain a consistent and tight fit against the cylinder wall. This is crucial for reducing oil consumption, minimizing wear, and ensuring optimal performance of the engine. The other options involve concepts like compression ratios, engine weight, and piston speed; however, they don’t accurately reflect the primary advantage offered by cam-ground pistons. The main focus is really on improving the fit and reducing friction under varying temperature conditions, which directly relates to the operational efficiency of the engine components.