Hello! And welcome back for part 2 of our series on “A Brief History of the Turbocharger”. To read part 1, which compares superchargers and turbochargers, and explains the early history of turbochargers and forced induction from the turn of the century through to World War 1, click here. Having covered all of that, let’s pick up from where we left off!
Following World War 1, and the work of Dr. Sanford Alexander Moss, Alfred Büchi, who had created the first true turbocharger, had continued innovating following the failure of his first design. By 1925, he had a working turbocharger design that consistently and reliably worked (1).
Following this breakthrough, the turbocharger saw its first commercial application on ten-cylinder diesel engines. Since diesel engines are typically built to withstand the high-pressures required by their operating conditions, the pressures generated by using forced induction are easily accommodated. As a result of adding the turbochargers, the engines upped their horsepower ratings from 1750HP, all the way to a whopping 2,500HP. (1)
For Büchi, this was a great achievement, as it marked the first commercial application of a machine that he had first begun working with more than 20 years prior. For the turbocharger, however, this was just the beginning.
Büchi went on to license out his design to multiple companies across the globe, and soon these magical machines were being put to use in rail, stationary, and in other marine applications.
Interestingly, however, turbochargers were not initially popular in the automotive world. You may ask, “why?” While this question has no clear cut answer, it’s important to keep in mind the first turbocharger applications were in large-displacement engines, such as those found in ships like the above-pictured, as well as locomotives and stationary engines. These applications are a far cry from the parameters and operating conditions of an automotive engine, which is much smaller, and almost never runs at “steady” state conditions the way that a large ship’s engine does. For example, a large-displacement ship’s engine may spend hours or days on-end rotating at the same speed, but an automotive engine will almost never be operating at the same speed unless it is on a flat road with the vehicle’s speed remaining steady, or at idle. In short, the technology wasn’t there yet for turbochargers to be used in everyday cars.
As the world entered the 1930’s however, turbochargers were being found more on large diesel truck engines, which operate at a variety of conditions similar to a car, but are also built for durability and reliability similar to locomotive and ship engines.(1) Alongside trucks, the turbocharger also found a home in race cars. It was a while however, before they reached the automotive world, and before they became ubiquitous in diesel engines and industrial machinery. The turbocharger as we know it, would first find use in vehicles used by militaries around the world, in the Second World War.
By the time 1939 rolled around, a lot had changed in vehicle and vessel design. The biplanes that were flown in the first World War were considered obsolete for the most part. Most new warships were being designed with an emphasis on maneuverability and speed, not just artillery and armor. New kinds of engines were being used in warplanes. Whereas in the Great War planes would use inline 6 and 8 piston driven engines, V12 engines like the famed Rolls-Royce Merlin were starting to be used in iconic warbirds including the Supermarine Spitfire.
The need for airplanes to fly faster at higher altitudes for longer periods of time, meant that forced induction was going to become a requirement for aircraft engines. Horsepower ratings in the neighborhood of 2,000 HP were becoming standard procurement requirements by the time the Second World War began.(2) As a result, emphasis was placed on smaller engine design details that would allow the piston engines to crank out as much horsepower as possible. Early on, the easy answer was to supercharge the engines. Interestingly, some of these engines would use two-stage superchargers, which enabled the pilot two switch between 2 different impeller speeds/pressures depending on altitude and performance needs; this was, however, extremely hard on the engines and significant shortened engine lifespans.(2)
While some aircraft like the famous Boeing B17 utilized a Curtiss-Wright radial engine with a supercharger provided by General Electric, smaller fighter-bombers like the Republic P47 Thunderbolt would make use of the extremely popular Pratt and Whitney Double Wasp engine. There were numerous variants bored out to different displacements, and these engines were used on everything from large heavy bombers like the Consolidated B24 Liberator to the PBY Catalina to the Grumman F4F Wildcat.
The P47 had an extra ace in the hole for power, however, and it came in the form of what Pratt and Whitney called, the turbosupercharger. The Thunderbolt was one of the few single-engine aircraft that made used of an intercooled turbocharger as seen below.
Unlike present day turbocharged engines where the turbo is mounted to the engine or is very close by, the turbo in the P47 was in the tail of the plane, with the ductwork going past the cockpit and pilot. Despite the added complexity and material cost presented by a turbocharger, the upsides were astounding.
The P47 had a rated horsepower of more than 2400 horsepower(!), and could fly at a maximum speed of 433 miles per hour, with a ceiling of 42,000 feet. To put that in perspective, most commercial airliners fly at 35,000 feet, and the fighters of the First World War, could only fly at about 20,000 feet. The Thunderbolt enjoyed a reputation by ground soldiers and airmen alike of being extremely tough, being able to absorb heavy groundfire and remain in the air, as well as escort bombers on long missions, and deal out punishment to enemy aircraft and ground forces alike. Its famed speed, reliability, and durability, can all be traced back to that turbocharged Pratt and Whitney Twin Wasp.
Now obviously he P47 is just one example of the turbocharger coming into use during the Second World War; another great example of a turbocharged warplane that saw heavy use was the Lockheed P38 Lightning. The P38 made use of two turbocharged Allison V-1710 V-12 engines. This made the P38 excel in high altitude combat where the air density is very low, and forced induction gives an engine a serious advantage of naturally aspirated engines. General Electric again provided the turbocharger for these engines.
Like the P47, the P38 saw extensive use by the United States and its allies throughout the Second World War, and enjoyed a popular reputation among pilots, due in no small part to the General Electric turbochargers supplying air to the beating heart of the Lightning.
While this series is devoted to covering the history of the turbocharger in different vehicles we would be remiss not to cover the turbochargers uses in these and other airplanes of World War II. They can be seen as one of the last steps where piston engines were being heavily used in military aircraft, before the inventions of Frank Whittle and Hans von Ohain took the skies later in the war. Following the inception of the gas turbine jet engine, turbochargers would retain popularity in piston-driven aircraft engines, and their popularity in the skies would soon transition to more R&D ventures in the automotive, marine, and rail industries as we shall see in the next entry.
Keep an eye out for our next and last entry on the history of the turbocharger, where we’ll be looking at the postwar to modern day timeline of turbos, and how they came from being military grade technology, to near-ubiquity in modern cars and trucks.
Do you currently design turbocharger components and systems? Or perhaps you’re an OEM buying turbochargers “off the shelf”? Whichever the case may be, you don’t want to miss our upcoming webinar on utilizing AxSTREAM and GT-POWER to design and simulate entire turbocharger systems, both on the component and cycle level. This free to attend event is happening on September 2nd at 10AM EDT. Learn more and register here!
- Culy, Doug. (2016, September 28). The Aircraft Engines of World War II. Retrieved from Defense Media Network: https://www.defensemedianetwork.com/stories/aircraft-engines-world-war-ii/
- Scoltock, J. (2010, July 15). Alfred Büchi the inventor of the turbocharger. Retrieved from Automotive Engineer : https://web.archive.org/web/20150405003800/http://ae-plus.com/milestones/alfred-bchi-the-inventor-of-the-turbocharger/page:1