Piston Engines: Cooling

1. Piston Engine Propulsion
Cooling

2. • Almost all modern aircraft engines are air
cooled. However, to be effective, an engine
must have a great deal of surface area that
gives up heat.
• To accomplish this, all air-cooled engines
utilize cooling fins that are either cast or
machined into the exterior surfaces of the
cylinder barrels and heads.
• The fins provide a very large surface area for
transferring heat to the surrounding airflow.

3. There are two types of cooling engines.
• Air cooling, and
• Liquid cooling

4. Air Cooling
• The cylinders on early opposed engines were
also stuck out into the air stream to provide
cooling.
• However since the cylinders were directly
behind each other, a thin sheet metal hood
had to be installed on each side of the engine
to force air down between the cylinder fins.

5. • Now all opposed engines also have cowlings
that surround the entire engine.
• With this type of cowling, cooling air enters
through forward facing openings and exits out
one or more openings in the bottom rear of
the cowling.
• The rest of the cowling is sealed with rubber
strips to prevent excessive air leakage.

6. • Because of the ram effect produced by the
forward motion and prop wash, cooling air
enters a cowling at a pressure above ambient.
• This produces what is known as pressure
cooling.

7. • To facilitate the pressure cooling process, the
outlet on lower cowls is flared so that when
the outside air flows past the opening, an area
of low pressure is created in the bottom of the
cowling.
• This low-pressure area draws air down
through the cylinders and into the lower cowl
where it can exit the cowling.

9. COOLING SYSTEMS – Air Cooling
Cross section of
typical light aircraft
Modern flat-four air cooled engine
Air Cooling Flows
Cylinders
Engine and MountsProp
and
Spinner
Cowl
Outline
Air
Intakes
Air Outlet
Ramaircoolingflow

10. Liquid Cooling
• Liquid cooled aircraft engines are constructed with a
metal water jacket that surrounds the cylinders.
• As coolant circulates in the water jacket, heat passes
from the cylinder walls and heads to the coolant.
• A coolant pump circulates the coolant in a pressurized
loop from the water jacket to the radiator, where heat
is transferred from the coolant to the air.
• To allow for higher engine temperatures and a smaller
radiator, many liquid-cooled systems are pressurized.

11. COOLING SYSTEMS – Liquid Cooling
Water
Passages
Radiator
Engine
Assembly
Thermostatic
Valve
Water
Pump
Top
Hose
Bottom
Hose
Pressure
Relief Cap
Cooling Fan
Over Flow

12. Thermostatic
Valve CLOSED
Coolant circulates around engine block only
Coolant/engine COLD:-
COOLING SYSTEMS – Liquid Cooling

13. Thermostatic
Valve OPEN
Coolant circulates around engine block and radiator
Coolant/engine HOT:-
COOLING SYSTEMS – Liquid Cooling

14. Typical
Radiator
Top Hose
Connection
Bottom Hose
Connection
End
Chamber
COOLING SYSTEMS – Radiator
Cool Air
Flow In
Warm Air
Flow Out
Expansion
Chamber
Connection
Hot Coolant
In
Cooler
Coolant Out
Cooled
Coolant

15. CLOSED
Thermostatic
Valve
OPEN
No Flow Flow
Rubber
Diaphragm
Wax
pellet
‘Jiggle’
pin
Typical
Thermostatic
Valve
COOLING SYSTEMS – Liquid Cooling

16. Feet
Other features:-
Screen
Demist
Facia
Expansion
Tank
Heat control
valve
Fan
Heating
Unit
Control
valves
Heater
matrix
Air
intake
duct
COOLING SYSTEMS – Liquid Cooling