Powerplant Chapter 10 Flashcards
Cooling Systems
What is the purpose of cooling fins?
They provide a larger cooling surface area for removing heat from cylinder heads of air-cooled reciprocating engines. Airflow around the cooling fins transfers the heat from the cylinder heads to the air.
What effect does excessive heat have on reciprocating engines?
It shortens the life of the engine parts, changes the behavior of combustion, and impairs lubrication.
What are the reasons for using engine cowlings, baffles and cowl air seals?
The cowling performs two main functions: it streamlines the engine area to reduce drag, and is used together with the baffles and cowl air seals to direct airflow over the cylinders for cooling.
What is the purpose of cowl flaps and how are they operated?
They are used to control the amount of airflow through the cowling. They are either mechanically, electrically or hydraulically operated.
How does an augmenter cooling system work?
An outer tube placed over the exiting exhaust gas creates a venturi effect that draws more airflow over the engine, thus providing additional cooling.
Where should cowl flaps be positioned for ground operations?
Fully open.
What type of power is used to operate cowl flaps?
Manual, hydraulic, or electrical.
What should be done when cooling fin damage is discovered?
Depending on the scope of damage, some cooling fins may be repaired subject to the manufacturer’s overhaul and repair limitations. If an excessive amount of the cooling fin is broken off, the cylinder should be replaced.
Why is cowl flap adjustment important?
The movement must be within tolerances to keep cylinder head temperatures within allowable limits.
How are turbine engines cooled?
They are cooled by air passing through the engine. About 75% of the air passing through the engine is used for cooling which leaves only about 25% for combustion. This air is used to cool the combustion chamber and turbine.
In a turbine engine, where does bleed air come from that is used to cool bearings and other parts?
The engine compressor.
What is the relationship between turbine engine upper temperature limits and power produced?
The higher combustion temperatures that an engine can withstand without damage, the more power it is capable of producing.
What is the approximate percentage of air passing through a turbine engine that is used for cooling rather than combustion?
Approximately 75%.
What can be done to effectively allow higher gas temperatures in the turbine section of some engines?
Compressor bleed air ducted through hollow sections in the turbine inlet guide vanes and first stage rotor blades can lower temperatures enough to prevent heat damage.
