Always consider the effect of high
heat or fire on engine cooling system
components and use materials
approved for aircraft use.
Aircraft Engine Cooling
A baffling situation
BY MIKE BERRY
AN INTERNAL COMBUSTION ENGINE is a heat machine, converting
chemical energy into mechanical energy at the crankshaft. Since air
is used as the cooling medium for 99 percent of reciprocating aircraft engines, this transfer of heat must be carefully controlled to
permit reliable, long-term engine operation. Air cooling (as opposed
to liquid cooling in automotive applications) is the preferred heat
transfer method in aircraft because it saves weight. It is important to
ensure that your cooling system is up to the task to ensure reliability
and efficiency of your powerplant.
Aircraft engine cooling systems consist of the propeller, spinner,
engine cowling, engine baffles, cylinders and engine case, exhaust
systems, oil coolers, and possibly augmenter tubes and cowl flaps.
All of these components are designed as a complete system to
remove excessive heat from the engine. Excessive heat is
undesirable for three principal reasons: it affects the behavior of the
combustion of the fuel/air charge; it weakens and shortens the life of
the engine, components, and accessories; and it impairs lubrication.
If the temperature inside the engine cylinder is too great, the fuel/air
mixture will be preheated and combustion can occur before the
desired time. Since premature combustion causes detonation,
knocking, and other undesirable conditions, there must be a way to
eliminate heat before it causes damage. In a typical aircraft
powerplant installation more than half of the heat goes out the
exhaust while the remainder is absorbed by the engine. The engine
oil picks up part of the heat absorbed by the engine and transfers it
through the oil cooler to the outside air, with the engine cooling
system taking care of the rest, dissipating heat through the cylinder
fins and engine case. An important
component of the cooling of an aircraft
engine is that of airflow. If the aircraft is
stationary or taxiing, there is little or no
airflow to carry away the heat so the cooling
system will be ineffective.
SYSTEM COMPONENTS
A thorough understanding of the system
components and the relationships that each
share is necessary to properly construct,
inspect, and maintain the proper cooling and
performance of your engine. As a builder,
consider the design of your aircraft and the
relationship among cooling system components before making changes or
modifications. When maintaining a certified
aircraft, it must be maintained in the original
and unmodified condition according to
acceptable and approved aviation practices
or in accordance with a supplemental type
certificate or field approval. Any modifications or deficiencies in the system most
likely will impact the operation and performance of your aircraft, and errors or
oversights can significantly impact your
bank account.
