Before we can go into the development of blades, we first need to look at where and how it all started.
THE HISTORY OF JET ENGINES
Before we can go into the development of jet engine blades, we first need to look at where and how it all started.
For 2021, 22.2 million global airline flights were projected. This is a sharp decline from the 40.3 million projected for 2020, due to the COVID-19 pandemic. These flights carried an estimated 2.8 billion passengers. How many of these passengers ever think about the innovation and technology of a jet turbine blade and how a jet engine works?
The jet engine is the powerplant of today's jet aircraft. It generates not only the thrust that powers the aircraft, but also the energy that powers many of the aircraft's other systems. Jet engines operate according to Newton's third law of motion, which states that any force acting on a body produces an equal and opposite force. The jet engine draws in some of the air through which the aircraft is moving, compresses it, combines it with fuel, heats it, and finally expels the resulting gas with such force that the aircraft is propelled forward and takes you to your favorite vacation destination or planned business trip.
LET'S GO BACK TO THE HISTORY OF JET ENGINES, WHERE IT ALL BEGAN, AND LOOK AT HOW TURBINE BLADES EVOLVED.
You can go all the way back to the Egyptian aeolipiles developed by Hero of Alexander in 150 BC. Chinese rocket technology of the 1230s, Leonardo Da Vinci's "chimney sweep" roasting spit, Italian engineer Giovanni Branca's impulse turbine for a stamp mill. Not to mention Bernoulli's principle, which can also be directly derived from Newton's second law of motion, and while all of this had an impact, it wasn't until World War I that it was taken to the next level, and amidst all the devastation and disruption, it accelerated the rise of aviation and the development of jet turbines, which is directly related to the development of turbine blades.
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Swiss engineer Alfred Buchi patented the turbocharger in 1910, but the device failed in flight tests in France. General Electric (GE) at the time focused mainly on building turbines and other equipment for power plants, but in November 1917 the U.S. government wanted to develop its own version of a turbocharger and asked the company to help develop the device for the American military.
The task of managing the secret project fell to a GE gas turbine engineer named Sanford Moss.
Moss built a turbocharger that used the hot exhaust gases from the aircraft engine to spin a radial turbine he designed and compress the air entering the engine.
The breakthrough came in 1930, when Royal Air Force Lt. Sir. Frank Whittle filed a patent for a jet-driven gas turbine. His engine, with a single-stage centrifugal compressor coupled to a single-stage turbine, was successfully tested on the test stand in April 1937 and formed the basis for the modern jet engine.
Meanwhile, in Germany, Hans von Ohain, while pursuing his doctorate at the University of Göttingen, formulated his theory of jet propulsion in 1933. Von Ohain and Dr. Max Hahn patented a jet engine in 1936, and on August 27, 1939, history was made in Rostock with the first pure jet flight
In 1939, the Air Ministry awarded Power Jets Ltd (a company in which Whittle had an interest) a contract to develop an aircraft engine. On May 15, 1941, Whittle's W1 engine made its maiden flight in the Gloster Model E28/39, an aircraft that reached 370 mph (595 km/h) in level flight with 1,000 pounds of thrust. Following the success of the Whittle engine, the British immediately sent a prototype to their allies in the United States, where General Electric immediately began producing copies. During this time, a group of GE engineers called the Hush-Hush Boys developed new parts for the engine, reworked it, tested it, and delivered a top-secret working prototype called the I-A with a thrust of 1,300 pounds!
Like many technological innovations, the jet engine took time to develop from concept to design to execution, but two world wars eclipsed aeronautical engineering. Toward the end of World War II, modern turbine engines were introduced, including blade cooling, ice prevention and the variable section exhaust nozzle.
In 1930, Sir Frank Whittle's prototypes were made entirely of steel. Steel is excellent for strength and surface hardness, but if you need high-temperature performance, you should look elsewhere, because the maximum temperature of steel is 450-500 °C.
A major limiting factor in early jet engines was the performance of the materials available for the hot part (combustor and turbine) of the engine. The need for better materials spurred extensive research into alloys and manufacturing techniques, and this research led to a long list of new materials and processes that make modern gas turbines possible.
In addition to improving materials and alloys, one breakthrough has been the development of directional solidification (DS) and single crystal (SC) processes and the development of thermal barrier coatings. The pursuit of high performance materials, innovative design and improved production methods in blade development will be discussed in depth in next week's Jet Turbine Blades Part 2 blog. The development over the years and the continuous improvement is not possible without measurements.
It takes about two years to build and assemble the components of a jet engine, following a development and testing phase that can last up to five years for each model. Throughout the construction process of an engine, the components and assemblies are inspected for dimensional accuracy, responsible workmanship and material integrity.
Since 1968, WENZEL has strived to provide better measurement solutions for the manufacturing industry with its innovations in metrology . State-of-the-art measurement systems are offered for turbine blades of various sizes. The complex curves of turbine blades have critical dimensions that must be measured at numerous locations of the limited by the reach of conventional tactile systems. Typical measurements include blade cross sections at multiple locations, and this too is a very special challenge. This primarily involves measuring radii at the leading edge, trailing edge, root shape, and the position and size of cooling holes. (Learn more about turbine and blade functionalities in next week's blog post).
Limited by the diameter of the stylus, shape deviations and defects on small features cannot be detected. A tactile probe has the effect of a mechanical filter on the measurement and can make the results appear better or worse than they actually are.
Optical measuring systems can be used as an alternative. Reflective surfaces must in many cases be prepared and coated with a special powder. This process adds additional material to the part and leads to incorrect results when evaluating small features. In addition, not every method is able to detect small radii or even measure features that are difficult to access.
WENZEL has developed the CORE , an optical measuring system that meets all these requirements. The innovative sensor means that no preparation of reflective and polished surfaces is necessary. The measuring points are detected with a small light spot with a diameter of 35 μm. With this measuring system, even small radii can be measured in detail with a high number of points and shape deviations and defects can be analyzed.
The journey of jet turbine blades began with a determination to go faster, and over the next two weeks we will look at the technical aspects and design of jet turbine blades. Just look how far we have come in the last six decades. From the first jet aircraft in 1939 with a thrust of 1100 pounds, to a typical jetliner engine's thrust of 5,000 lbf (22,000 N) (de Havilland Ghost turbojet) in the 1950s, to 115,000 lbf (510,000 N) (General Electric GE90 turbofan) in the 1990s, not to mention much higher reliability in terms of shutdowns per 100,000 engine flight hours.
Combined with the sharp drop in fuel consumption, this made routine transatlantic flights with twin-engine commercial aircraft (ETOPS) possible at the turn of the century, which previously would have required multiple refueling stops.
Today, the development of gas turbine technology continues with new engines offering even greater fuel efficiency and significantly lower noise levels. Two of the largest gas turbine engines ever built entered service on the Airbus A380 - the Rolls-Royce Trent 900 and the GP 7200 from Engine Alliance (a partnership of GE and Pratt & Whitney). These massive engines generate 70,000 pounds of thrust each.
Follow us on our platform and join our series All About Blades, a journey you won't want to miss! Our team and external experts will share more about jet turbine blades, the geometries and challenges in production as well as quality assurance. We look forward to sharing #allaboutblades with you!
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