Radial engine was commonly used for airplanes before the gas turbine engines became predominant. Radial engine have mechanism similar to an internal combustion engine but its unique arrangement of pistons make it more effective for airplanes. Internal combustion process is also explained in this video.
Radial engines have applications in various components.
INTERNAL COMBUSTION PROCESS
AIRPLANE ENGINES
RADIAL ENGINE
ROTARY ENGINE
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Please watch: "Airplane Hydraulic system | Cockpit ECAM
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