Understanding Aircraft Air Bleed Systems

The many systems within aircraft can be confusing; however, it is important to understand the function and significance of each system. This blog will delve specifically into the purpose of aircraft bleed systems, or engine cooling systems that release hot air from aircraft. Excessive heat poses many threats to engines, fuel systems, and flight in general, so cooling systems serve the purpose of significantly reducing temperatures within aircraft. Air bleed systems are alternative solutions to liquid coolants used in turbine engines to reduce temperatures. Unlike liquid cooling systems, reciprocating engines rely on air bleed cooling systems to transfer heat from the engine’s cylinders into the surrounding air. Without a cooling system in place, cylinders can overheat, causing combustion to occur too early.

Aviation gasoline produces a significant amount of heat when burned, and it burns very quickly while the engine is running, leading to high temperatures and the need for air bleed systems. The process of internal-combustion engines converting chemical energy to mechanical energy by burning this gasoline is very high in heat waste. The process uses fuel in the engine to move a crankshaft, but even in the most efficient engines, 60-70% of this energy is wasted in the form of unnecessary heat. Aside from leading to premature combustion, excess heat can also damage engine parts and impair lubrication, so it must be removed as efficiently as possible. Typically, half of this heat is expelled with the exhaust and the other half is absorbed by the engine. Circulating oil removes some of the heat from the engine and the air bleed system does the rest of the work of removing heat trapped in the engine’s cylinders.

In systems that rely on reciprocating engines, the cylinders are placed in the path of the airstream and employ cooling fins on the surface to increase cooling by radiation. Additionally, cylinders rely on cowlings and baffles as part of their exterior design to direct airflow in a way that prevents hot pools of air from forming. Blast tubes in the baffles direct jets of cooling air onto the rear spark plug elbows of each cylinder to prevent overheating of ignition leads. On the other hand, cowl flaps function by opening like doors. They can be opened and closed by electric motor-driven jackscrews, by hydraulic actuators, or manually to allow cool air in and release hot air out.

Another common type of air bleed system uses an augmentor, which pressure-cools the engine through two openings in the nose cowling. In this system, exhaust ejectors expel exhaust gas from the back of the nacelle. The exhaust gas mixes with air that has passed over the engine and draws cool air over the engine. Air that enters the outer shells of the augmenter absorbs heat and then goes to the cabin heating, defrosting, and anti-icing system. More than this, augmentors also use exhaust gas velocity to direct air over the engine to create cooling that is not entirely dependent on prop wash. Vanes control the volume and temperature of air from inside an augmentor and nacelle flaps that lead to outside the aircraft are used for additional cooling, similar to cowl flaps.

Overheating is a danger to any aircraft or engine, so being familiar with your cooling system is important for safety. At ASAP Supply Chain, we offer access to reliable parts you need for your aircraft’s air bleed system as well as over 2 billion other new, used, obsolete, and hard-to-find parts. Owned and operated by ASAP Semiconductor, quality is the cornerstone of our business and we guarantee premium parts by operating with AS9120B, ISO 9001:2015, and FAA AC 00-56B accreditation and a strict NO CHINA sourcing policy. Additionally, countless parts are subject to quality assurance testing and inspection, so leave the sourcing, logistics, shipments, and quality control to us so that you can focus on what you do best!