FAA Powerplant Written Practice Test

How are cylinder head temperatures measured?

1. Using a mercury thermometer

2. By an infrared sensor

3. With an indicator and a thermocouple sensing device

4. Using a barometric pressure gauge

The correct answer is: With an indicator and a thermocouple sensing device

Cylinder head temperatures are measured using a thermocouple sensing device, often in conjunction with an indicator. This method is effective because thermocouples can provide accurate temperature readings over a range of operating conditions typical in aircraft engines. The thermocouple consists of two different metal wires joined at one end, which generates a voltage when exposed to temperature differences. This voltage can be correlated to temperature, allowing for precise and reliable readings of the cylinder head temperatures crucial for engine performance and safety. The indicator translates these readings into a format that can be easily monitored by the pilot or maintenance personnel. Other methods, such as a mercury thermometer, are not practical for aircraft applications due to the risk of breakage and the inability to measure high temperatures effectively. Infrared sensors, while useful in some applications for non-contact temperature measurements, are less common in cylinder head temperature monitoring in aviation. Barometric pressure gauges measure pressure, not temperature, and are thus irrelevant to this context. Using thermocouples is a well-established practice in aviation, contributing to the safety and operational efficiency of aircraft engines by providing real-time temperature data and allowing for timely adjustments and maintenance.