1. What's the Radial Engine?

The radial engine is a reciprocating internal combustion engine confirguration in which the cyslinders "radiate" outward from a central  crankcase like the spokes of a wheel.It's also called "star engine"  because it looks like a stylized star when viewed from the front. (see the photo below)  It was commonly used for aircraft engines before gas turbine engines became predominant. It's not in common usage anymore nowadays. 

 2.How Does A Radial Engine Work?

Radial Engine have the similar working principle like a four-stroke engine. The piston completes the separate strokes while turning the crankshaft. The piston compresses the air-fuel mixture in preparation for ignition during the power stroke . The engine has 5 cylinders in most cases, and they fire strokes in an alternating order. 

 （photo from wiki）

3. What are radial engines used for in practise?

Radial engines were generally used marines and ships where no vibration is required.These are also used in aircrafts for its advantage themselves, like easier maintenance, tougher, smoother operation, reliability, versatility and low Overall cost. In  WWII, they are also used on the tank. They were more reliable than conventional inline engine s at that time for its greater power to weights ratios.

4. What's the Benefits of Using Radial Engines?

a.Almost no vibration.

b.High power to weight ratio.

c.More fuel efficient.

d.Flexibility of using any type of fuel.

5. Why are radial engines not used anymore?

It's hard for an air cooled inline engine to make an some huge air cooled radials nowadays. In need of a military application that prefers air cooling, people don't adbandon the radial engine because of the large aerodynamic drag it produces. Now they are rarely used anywhere. You can find them in aviation musiums however some aircrafts with these engines are still operational. Only companies like Vendeneyev and Verner Motor still manufacture these engines.

Today I will recommend two new 3D printed radial engine toy for you. It has 2 versions: assembly version and fisnihed type.Here i'm going to talk about how to assembly this engine. 

a. Teching Radial Engine DM105

2. this assembly engine only has 102pcs accessories for you to rebuild it. The see-through interior design enables you to observe the structure of the radial engine and understand its principle, so that you can have a deeper understanding of the engine. It  doesn't only serve as a collection, as a decoration on the desktop, but can also serve as a toy for children. it's quite easy for the age 6+ kids, not to say of an adult.  The model has a built-in 5V motor, which can be connected by USB cable to make it run. I'm pleased when i see the propellers rotatting, and observe the piston movement in the cylinder.