How Does Radial Engine Work?

Radial engines:-

Radial engines are Internal Combustion Engines same alike the piston-cylinder arrangement except for one change – the piston in the cylinders radiate(oscillate/reciprocate) outward from the central crankcase(like the rims of a tire). Radial engines are also called “Star engines” as they resemble the shape of a star when viewed from the front side. The radial configuration was very commonly used for aircraft engines before the gas turbine engines came into existence.

C. M. Manly constructed a water-cooled 5 cylinder radial engine in 1901 – conversion of rotary engine for an Aerodrome aircraft. The machine was unsuccessful, but the Manly-Balzer engine(later in 1903) pointed the way to high power, low weight aircraft engines.

Piston – The piston is used to transfer the expanding force of gases to mechanical rotation of crankshaft via a connecting rod. The piston is able to do this because it is secured tightly within the cylinder using piston rings to minimize the clearance between cylinder and piston!
Crankshaft – A crankshaft is a part which is able to convert the reciprocating motion to rotational motion.
Connecting rod – A connecting rod transfers motion from a piston to crankshaft which acts as a lever arm.
Inlet & Outlet valves – It allows us to enter fresh air with fuel & to exit the spent air-fuel mixture from the cylinder.
Articulating rod assembly – The assembly joins all the connecting rods of pistons with a single part as the cylinders are coplanar (discussed later).
Spark Plug – A spark plug delivers electric current to the combustion chamber which ignites the air-fuel mixture leading to the abrupt expansion of gas.


Radial engines work like any other 4 stroke engines. They both have similar parts but their construction & design are different. Each cylinder has an intake, compression, power & exhaust stroke.
If you consider the above engine consisting of 5 cylinders, numbering the top as 1 & going clockwise, then the firing order is 1-3-5-2-4 & again 1!
Nothing complicated to understand, the firing order & opening/closing of valves are such adjusted that the ongoing power stroke directly helps compress the next cylinder to fire, making the motion more uniform.

Why an odd number of cylinders?
For the smoother operation of the engine, consistent power should be produced. For producing consistent power, an odd number of cylinders are used so that every other piston firing order can be achieved.

  1. Smoother operations:- Radial engines are great at producing consistent power(contribution of each piston) as discussed earlier. This consistency helps the engine to run smoother.
  2. Tougher & easier maintenance:- All thanks to a simple design which makes it less vulnerable to damage as well as it makes much easier for maintenance workers during a routine check-up.
  3. Cost:- Radial engines’ parts, repair costs, & maintenance costs are inexpensive. A cheaper option is welcomed blindfolded in an expensive field of work.
    1. Drag:- As the cylinders are clearly exposed to the airflow during flight, drag increases considerably.
    2. Visibility :- The pilot may experience visibility problems, due to huge single engines located near the nose of aircraft.
    3. Installation:- It is more difficult to ensure adequate cooling air in buried engine installation.

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