A key element of understanding planes and aviation involves having a good basic understanding of types of engines – and this includes radial engines.
In this article, we will take a closer look at radial engines, including how they work, where they are used, and what they can do.
What Is A Radial Engine?
Radial engines are the most common type of engine used on aircraft and spacecraft. They are also the most common type of engine in use on cars.
A radial engine is an internal combustion engine with pistons arranged around the circumference of the cylinder block.
This arrangement allows for more cylinders to be fitted into a given space than other types of engines, and this means that radial engines are often smaller and lighter than comparable inline or V-engine designs.
The main advantage of using a radial design is that it makes possible the installation of many cylinders within a small volume. The disadvantages of radial engines include their inherent complexity, which leads to higher costs and maintenance requirements.
Also, because of the layout of the cylinders, there is no direct drive from the crankshaft to the propeller shaft. Instead, the power must first be transferred through the gearbox before reaching the propeller.
Radial Engines: How Do They Work?
Radial engines operate by forcing air inwards through a series of ducts, called vanes, which are located inside the engine’s cylinder heads. These vanes act as guides for the incoming fuel/air mixture.
When the piston reaches top dead center (TDC), the intake valve opens allowing fresh air to enter the cylinder. At the same time, the exhaust valve closes, preventing any burnt gasses from escaping back out of the cylinder.
As the piston moves down towards bottom dead center (BDC), the intake valve remains open while the exhaust valve closes. This causes pressure to build up inside the cylinder, pushing the piston downwards.
As the piston approaches TDC again, the intake valve opens once more, sucking in additional air. This process repeats itself until the piston has reached BDC.
At this point, the exhaust valve reopens, releasing the spent gas from the cylinder. Once the cycle has finished, the intake valve closes and the next cycle begins.
In some cases, the intake and exhaust valves may remain open throughout the entire cycle.
In other cases, the intake valve may close when the piston is near TDC, but reopen when the piston is approaching BDC.
Examples Of Radial Engined Planes
Radial engines have been used in aircraft since the early days of flight.
Early examples included the Wright Brothers’ 1903 Flyer, the Curtiss JN4 “Jenny” biplane, and the de Havilland DH.60 Moth – although these aircraft were not powered directly by radial engines, they did demonstrate the advantages of the design.
Early radial engines were very heavy and required complex systems to control them. However, advances in technology allowed engineers to make improvements to the design.
By the 1930s, radial engines had become much lighter and simpler to maintain. In addition, they could be made to run at high RPM, making them ideal for powering aircraft.
The Me 163 And Me 262
The first successful application of a radial engine was in the German Messerschmitt Me 163 rocket plane. It was designed to fly at supersonic speeds and carry its own weapons. It was also one of the first planes to use jet propulsion.
The Me 163 was built during World War II and proved to be an effective weapon against Allied bombers. Its success led to further development of the design, culminating with the production of The Me 262 fighter.
The Me 262 became the most advanced fighter ever produced. It was capable of flying faster than sound and carried multiple machine guns that fired rockets (see also “Do Pilots Carry Guns?“).
Despite their impressive performance, however, the Me 262 never saw combat. The Allies developed radar-guided missiles that could destroy them easily.
Aircraft designers continued to improve on the basic radial engine design, creating engines that ran even faster and were easier to maintain.
One such example was the Rolls-Royce Merlin engine. Developed during the Second World War, the Merlin was the world’s fastest piston engine, with a maximum speed of over 2,000 miles per hour.
The Merlin remained in service after the war ended. It powered many military and commercial aircraft through the 1950s and 1960s.
As the years passed, however, the Merlin began to show signs of wear. Engineers eventually came up with a new version called the Rolls-Royce Turbomeca Adour.
The Rolls-Royce Turbomeca Adour
The engine of this radial design was much smaller and lighter than the Merlin, allowing it to operate at higher altitudes.
The Turbomeca Adour was widely used in helicopters and other small aircraft and, as time went on, more powerful versions of the Turbomeca Adore were introduced.
These engines were known as the Turbomeca Arrielle and Turbomeca Marboré.
The Arrielle was a large turboprop engine that was used in many types of aircraft. It was especially popular in military transport aircraft.
The Marboré was a similar engine that was used in light business jets. Like the Turbomeca Marble, it was also a turboprop.
The Wankel Rotary Engine
In the 1980s, another type of radial engine was developed. This engine is called the Wankel rotary engine.
Wankel rotary engines are particularly well suited to aircraft because they can be operated at extremely high RPM without overheating, and also have fewer moving parts than conventional engines – this helps to make maintenance easier and smoother.
Wankel engines have been around since the 1920s, but only recently have they gained widespread acceptance. Today, they power everything from cars to boats to motorcycles. They are also being considered for use in automobiles.
There are two main types of Wankel engines: the single rotor and the twin-rotor.
The single rotor engine has just one rotor attached to the crankcase. The rotor spins inside the cylinder, which causes the pistons to rotate.
The twin-rotor engine has two rotors mounted side by side. Each rotor turns independently of the other, so each piston moves twice as fast as in a normal engine.
Though the Wankel engine is not very efficient when compared with traditional designs, its compact size makes it an attractive option for aircraft.
Today, the most common type of radial engine found in aviation is the Pratt & Whitney R-2800.
This engine is made up of three cylinders arranged radially around the crankshaft and it is used primarily in jet aircraft, including passenger planes and cargo carriers, as well as some military aircraft.
Another popular type of radial engine is the Allison 250 series.
These engines are also made up of three cylinders, but the arrangement is different. Instead of having them all around the same axis, they are grouped together in pairs.
One pair of cylinders is located above the others, while the third pair is below. This allows the engine to produce more thrust per unit of weight. This type of engine is often used in business jets.
A final type of radial engine is commonly found in older airplanes, such as the Cessna 172. This engine is known as the Lycoming IO-360. It is a four-cylinder horizontally opposed engine.
The Horizontal Oscillation System (HOS)
Radial engines are usually connected to the propeller shaft through some sort of transmission system. In order to do this, the propeller shaft must turn at a certain speed. This speed is determined by the engine’s RPM.
If you look closely, you will see there are two gears on the propeller shaft. These gears allow the propeller shaft to move smoothly. However, if the engine is too slow, these gears won’t mesh properly.
As a result, the propeller shaft will begin to vibrate or “oscillate” and, if the oscillations become severe enough, the gear teeth may even break off.
To prevent this from happening, engineers developed a new kind of transmission system called the HOS. The HOS was invented by Dr. Rudolph E. Wankel, who later went on to develop his own version of a Wankel engine.
In addition to preventing the propeller shaft from breaking, the HOS can also help improve efficiency. When the HOS is engaged, the propeller shaft is able to spin much faster than it would otherwise be capable of doing.
As a result, less energy is lost during the conversion process.
The HOS is actually composed of two separate systems. The first is the primary drive mechanism. This is where the HOS engages and disengages. The second is the secondary drive mechanism. This is what actually drives the engine.
When the HOS is engaged and the primary drive mechanism is activated, the engine begins to rotate.
Once the engine starts turning, the secondary drive mechanism takes over.
This means that the engine’s pistons continue to move back and forth, causing the engine to generate power.
However, when the HOS is disengaged, the primary drive mechanism comes into play again. This time, however, the engine stops rotating.
At this point, the secondary drive mechanism turns the propeller shaft.
The radial engine is a major boost to the world of jet engines, and the overall aviation industry. It has allowed amazing advances to be made in the development of some of the most popular engines and aircraft.