Coolant is an essential automotive fluid, but you won’t find it in most airplanes. Whether it’s a small Cessna 172 or a jumbo-sized Airbus A380, most airplanes don’t use it. Airplanes use other types of fluid, such as oil and hydraulic fluid, but they typically don’t use coolant. So, why don’t airplanes use coolant?
What Is Coolant?
To better understand why airplanes don’t use coolant, you must familiarize yourself with this otherwise common automotive fluid. Coolant is a fluid that, as the name suggests, is used for “cooling.” In automobiles, it’s used to lower engine temperatures through a heat exchange process. Coolant will absorb heat as it travels through an engine. It will then travel to the radiator — typically at the front of the automobile — where it will release the heat.
High Altitudes
One of the reasons why airplanes don’t use coolant is because they fly at high altitudes where the air is particularly cold. Most coolant formulas consist of a 50-50 mixture of antifreeze and distilled water. While is can handle mild-to-moderate subfreezing temperatures, though, coolant can still freeze at about minus 35 degrees Fahrenheit. Commercial airliners fly at roughly 30,000 to 40,000 feet where temperatures can reach minus 60 degrees Fahrenheit.
Weight
Another reason airplanes don’t use coolant is to save weight. Airplanes are meticulously designed to minimize their weight. The more an airplane weighs, the more thrust it will need to take off and maintain lift. This is why most airplanes feature fuselages made primarily of aluminum and carbon fiber rather than heavier materials like steel.
Air-Cooled Engines
Rather than using coolant, most airplanes use air to cool their engines and protect against overheating. They don’t rely on coolant to remove heat generated during the combustion process. Instead, most airplanes use the surrounding air.
Airplane engines are equipped with fins known as cooling fins. These fins function as heat exchangers. They will absorb heat from the engine. As the cool air blows over the fins, they will release the heat. Cooling fins eliminate the need for coolant, which in turn allows airplanes to fly at high altitudes and maintain a low weight.
When compared to using coolant, air-cooling is also more reliable. Coolant involves the use of many components, such as a radiator, hoses and thermometers. These components can fail, and failure midflight can force airplanes to make an emergency landing. Air-cooling offers a more reliable means of cooling an airplane’s engine or engines. As long as the cooling fins are intact, they will remove heat.
