Air Cooled Engines Flashcards
How does air cooling work?
The use of outside air directed around the cylinder fins to obtain heat transfer.
Two ways of heat transfer
Conduction and convection
Conduction
Transfer of heat between substances that are in direct contact with each other.
Convection
The transfer of heat from one place to another by the movement of fluids.
Parts of air cooled engines
Cooling fins, baffles/deflectors, engine cowls, cowl flaps, augmenter tubes.
Cooling fins
Provide a large surface area around the cylinder for heat transfer.
Baffles
Used with deflectors. They direct and force cool air into close contact with the cylinder for effective cooling. Has blast tubes.
Blast tubes
Directs jets of cooling air onto the rear spark plug elbows to prevent overheating of the ignition leads.
Engine cowlings.
Forces air down between the cylinder fins. Reduces drag and controls airflow. There is a rubber strip to prevent excessive air leakage.
Pressure cooling
Due to ram effect, cooling air enters a cowling at a pressure above ambient. The outlet on the lower cowls are flared creating an area of low pressure in the bottom of the cowling. This results in air being drawn out through the cylinders into the lower cowling where it can exit the cowling.
Cowl flaps
Decreases or increases the exit area at the rear of the engine cowling. Controlled electrically, manually, and hydraulically. Opening these makes the exit area larger.
Augmenter tubes
Increases air flow to the cooling fins by a venturi effect made by slightly flared opening of the two exhaust pipes making low pressure. This draws more air to the cooling fins.
Inspection for cooling fins
They are inspected at 100 hr, annual inspections, and during overhaul. They should be examined for cracks and breaks.
Fin profiling
Small cracks or sharp corners can be filed or reshaped. Use engine specifics maintenance manual for limits and procedures for fin profiling. If the total fin area broken off exceeds the maintenance manual specs, the cylinder must be replaced.
Inspection for baffles and cowlings
They are both visually inspected for cracks, dents, tears, and loose or missing hardware. Cowling seals must be inspected for general condition and tears. Seals have the job of sealing the air in the cowling area, forcing it to circulate around the baffle and fins.
