The Development of Jet Engines

Overview

Jet engines, invented in 1930 by Frank Whittle (1907-1996), have become the dominant form of propulsion for the multimillion-dollar commercial air transportation industry. Jet aircraft's ability to deliver products and services at fast speeds has changed the way business is conducted, and its affordability has enabled more people to travel by air.

Background

Before the development of jet engines, the aviation industry had an absolute limit on how fast, how far, and how high their planes could fly, and how much they could carry. Frank Whittle had a dream to eliminate these boundaries.

In 1923, at the age of 16, Whittle entered RAF College at Cranwell. When he was selected for officer and pilot training in 1926, he wrote his thesis on Future Developments in Aircraft Design. Whittle explored new possibilities for propulsion, which, in 1929, led to his idea of using a gas turbine for jet propulsion. Whittle applied for a patent in 1930, but interest (and funding) from the government was meager. The only report on file regarding the idea of jet propulsion was discouraging, and, even though the analysis was based on outdated materials, the Air Ministry developed an attitude of skepticism toward Whittle's research, which lasted for years.

In fact, the British government thought so little of Whittle's patent on the jet engine that they allowed its publication when it was approved in 1932. Within a year, Germany had its own jet research program under way. Whittle continued to work on his project with little official encouragement. In fact, when his patent ran out in 1935, Whittle did not have the five pounds to renew it, so he never received royalties for his invention.

To properly fund experiments, Whittle brought investors and colleagues together to form Power Jets Ltd. in 1936. Ironically (and too late), by then the government had decided to classify his research, putting Whittle in a position where he could not tell investors what they were investing in. At the same time, the government was not willing to provide sufficient funding for Whittle to continue his research.

Whittle faced daunting technical challenges as well. The three basic elements of a jet engine are the compressor, the combustion chamber, and the turbine. A jet engine sucks in air, compresses it by three- to 12-fold, mixes it with fuel (burned to superheat the air, with a small amount used to turn the turbine for more air compression), and forces air and combustion products out the end to create thrust. Though gas turbines existed, Whittle had to rethink them entirely. The goal of contemporary turbines was to harness as much of the energy of combustion as possible to drive machinery. Whittle's jet engine took most of the combustion products and used them for thrust, using only a small portion to drive the turbine. In addition, Whittle needed to develop materials that could stand the enormous forces the engine generated, and he needed to find the optimum way to mix fuel and air in his system.

Despite many obstacles, Whittle was able to test the first jet engine, the WU (Whittle Unit) turbojet, in 1937. (By that time, Whittle had also patented his idea for the turbofan engine, but the conditions of his funding did not allow a test of this new idea.) That same year, aircraft designer Hans Pabst von Ohain (1911- ) secretly tested a jet engine at Germany's Heinkel Aircraft Works.

With a working prototype, Whittle continued to develop his engine, working to make it more durable, more powerful, and more efficient. The work often involved physical courage, as the test engines roared, fan blades broke, and machinery seized at thousands of rpm. On some occasions, everyone fled from the machinery but Whittle. He not only had to solve technical problems, but he also had to continue his fight against official resistance. Even as work had shifted to a jet aircraft, the National Academy of Sciences Committee on Gas Turbines said the goal "seems beyond the realm of possibility."

By August of 1939, however, there was little room for disagreement. The Germans tested the first operational jet aircraft, the Heinkel He 178. By 1941, the Germans had a production model aircraft that could go at 100 mph (161 kph) faster than the fastest Allied fighter.

Impact

The first British jet aircraft did not fly until 1941, weeks after the German production model had had its maiden flight. The Gloster E.28/39 (Pioneer) was piloted by Gerry Sayer. It was powered by Whittle's W1A engine and had a top speed for level flight of 370 mph (595 kph) at 25,000 ft (7,620 m). Plans for the next generation W2 engine and the Meteor aircraft were taken out of the hands of Power Jets Ltd. and given to competitors—first to Rover, then Rolls-Royce—and the British jet did not see action until 1944, when it shot down a V-1 rocket. (With Whittle's plans, the Americans built their own version of the Meteor, the P-59, which was secretly tested as early as 1942, but never used in combat.)

Luckily for the Allies, the Germans did not exploit their lead in jet aviation. The Germans concentrated on rocketry, and the Messerschmitt Me-262, first used in combat in 1942, was used as a ground attack aircraft rather than a fighter. There were no dogfights between the Meteor and the Me-262.

While the impact of jet aviation during World War II was minimal, it has been crucial in most major conflicts since. The 1950s, with its test pilot heroes, has been called the Golden Age of Aviation. Jet engines allowed aircraft to fly higher and faster than was possible for propeller-driven craft. Though the sound barrier was broken with a rocket-powered vehicle, all production models of supersonic aircraft were powered by jet engines. Jet fighters, capable of traveling at Mach speeds, are components of the arsenals of most industrialized nations today. The manufacture of military jets has had an economic impact as well. As an example, a single order of 50 F-16s by Greece in the year 2000 was valued at $2.1 billion.

Jet engines themselves continued to develop. The first major commercial application was the turboprop. These engines used most of their power to turn the turbine rather than to create thrust. The turbine was used to drive propellers, and took advantage of the high power to weight ratio of jet engines. The turboprop could be used with traditional airframes and became popular in Europe. It did not compete well in the U.S., where longer flights and greater fuel economy were demanded. The first pure jet was the Boeing 707, which began operations in 1958.

Whittle's turbofan, which forces more air through the jet, increasing thrust without increasing fuel consumption, has assumed a prominent place in aviation and is the engine for the popular Boeing 757. There are also several versions of the jet engine, including the ramjet and the scramjet, designed to push performance for aircraft beyond the limits of Whittle's turbojet.

The effect of the jet engine on commercial aviation is incalculable and came as a surprise. Introduced at first to shorten travel time for passengers, jet engines soon became a means of opening up a much wider market for commercial flight. The carrying capacity of a jet engine far exceeds that of a propeller plane, meaning that more passengers and freight can be carried with each trip. Jets require less maintenance than propeller planes, and they last longer. Economies of scale came into effect and, over time, drove consumer costs for air transportation down to less than half (in constant dollars). As a result air travel is competitive with alternatives such as driving or taking a train. U.S. airlines carried over 600 million passengers in 1998, 10 times as many as they did in 1960. Airfreight also has become popular, with a five-fold increase in tonnage carried from 1970 to 1998. In 1998, profits for all U.S. airlines were $9 billion. In 1955, the peak year for non-jet aircraft, the profits were $140 million. The commercial aerospace manufacturing industry has had important economic impacts as well. As an example, in the year 2000 Kenya Airways ordered five jets from Boeing at a cost of half a billion dollars.

The broad availability of economical air transportation has made long distance travel common. It has facilitated the development of international businesses and global trade. The speed of jet aircraft has made overnight delivery of mail and packages commonplace. Economical air transportation has also increased the speed at which ideas are shared across borders, but it also has accelerated the spread of diseases, as passengers unwittingly carry bacteria across borders.

Whittle saw his dream come true, often in the face of almost unexplainable resistance, but, personally, he only benefited modestly from his contribution to aviation. When the British government nationalized Power Jets Ltd., Whittle resigned. His genius was more appreciated in America, and he became a research professor at the U.S. Naval Academy in 1953.

PETER J. ANDREWS