Turbojet

The invention:

 A jet engine with a turbine-driven compressor that
uses its hot-gas exhaust to develop thrust.

 The people behind the invention:

Henry Harley Arnold (1886-1950), a chief of staff of the U.S.
Army Air Corps
Gerry Sayer, a chief test pilot for Gloster Aircraft Limited
Hans Pabst von Ohain (1911- ), a German engineer
Sir Frank Whittle (1907-1996), an English Royal Air Force
officer and engineer




Developments in Aircraft Design


On the morning of May 15, 1941, some eleven months after
France had fallen to Adolf Hitler’s advancing German army, an experimental
jet-propelled aircraft was successfully tested by pilot
Gerry Sayer. The airplane had been developed in a little more than
two years by the English company Gloster Aircraft under the supervision
of Sir Frank Whittle, the inventor of England’s first jet engine.
Like the jet engine that powered it, the plane had a number of
predecessors. In fact, the May, 1941, flight was not the first jetpowered
test flight: That flight occurred on August 27, 1939, when a
Heinkel aircraft powered by a jet engine developed by Hans Pabst
von Ohain completed a successful test flight in Germany. During
this period, Italian airplane builders were also engaged in jet aircraft
testing, with lesser degrees of success.
Without the knowledge that had been gained from Whittle’s experience
in experimental aviation, the test flight at the Royal Air
Force’s Cranwell airfield might never have been possible. Whittle’s
repeated efforts to develop turbojet propulsion engines had begun
in 1928, when, as a twenty-one-year-old Royal Air Force (RAF)
flight cadet at Cranwell Academy, he wrote a thesis entitled “Future
Developments in Aircraft Design.” One of the principles of Whittle’s
earliest research was that if aircraft were eventually to achieve
very high speeds over long distances, they would have to fly at very
high altitudes, benefiting from the reduced wind resistance encountered
at such heights.
Whittle later stated that the speed he had in mind at that time
was about 805 kilometers per hour—close to that of the first jetpowered
aircraft. His earliest idea of the engines that would be necessary
for such planes focused on rocket propulsion (that is, “jets” in
which the fuel and oxygen required to produce the explosion needed
to propel an air vehicle are entirely contained in the engine, or, alternatively,
in gas turbines driving propellers at very high speeds).
Later, it occurred to him that gas turbines could be used to provide
forward thrust by what would become “ordinary” jet propulsion
(that is, “thermal air” engines that take from the surrounding atmosphere
the oxygen they need to ignite their fuel). Eventually, such
ordinary jet engines would function according to one of four possible
systems: the so-called athodyd, or continuous-firing duct; the
pulsejet, or intermittent-firing duct; the turbojet, or gas-turbine jet;
or the propjet, which uses a gas turbine jet to rotate a conventional
propeller at very high speeds.



Passing the Test

The aircraft that was to be used to test the flight performance
was completed by April, 1941. On April 7, tests were conducted
on the ground at Gloster Aircraft’s landing strip at Brockworth
by chief test pilot Sayer. At this point, all parties concerned tried
to determine whether the jet engine’s capacity would be sufficient
to push the aircraft forward with enough speed to make it
airborne. Sayer dared to take the plane off the ground for a limited
distance of between 183 meters and 273 meters, despite the
technical staff’s warnings against trying to fly in the first test
flights.
On May 15, the first real test was conducted at Cranwell. During
that test, Sayer flew the plane, now called the Pioneer, for seventeen
minutes at altitudes exceeding 300 meters and at a conservative test
speed exceeding 595 kilometers per hour, which was equivalent to
the top speed then possible in the RAF’s most versatile fighter
plane, the Spitfire.
Once it was clear that the tests undertaken at Cranwell were not
only successful but also highly promising in terms of even better
performance, a second, more extensive test was set for May 21, 1941.
It was this later demonstration that caused the Ministry of Air Production
(MAP) to initiate the first steps to produce the Meteor jet
fighter aircraft on a full industrial scale barely more than a year after
the Cranwell test flight.


Impact

Since July, 1936, the Junkers engine and aircraft companies in
Hitler’s Germany had been a part of a new secret branch dedicated
to the development of a turbojet-driven aircraft. In the same period,
Junkers’ rival in the German aircraft industry, Heinkel, Inc., approached
von Ohain, who was far enough along in his work on the
turbojet principle to have patented a device very similar to Whittle’s
in 1935.Alater model of this jet engine would power a test aircraft in
August, 1939.
In the meantime, the wider impact of the flight was the result of
decisions made by General Henry Harley Arnold, chief of staff of
the U.S. Army Air Corps. Even before learning of the successful
flight in May, he made arrangements to have one of Whittle’s engines
shipped to the United States to be used by General Electric
Company as a model for U.S. production. The engine arrived in
October, 1941, and within one year, a General Electric-built engine
powered a Bell Aircraft plane, the XP-59 A Airacomet, in its
maiden flight.
The jet airplane was not perfected in time to have any significant
impact on the outcome ofWorldWar II, but all of the wartime experimental
jet aircraft developments that were either sparked by the
flight in 1941 or preceded it prepared the way for the research and
development projects that would leave a permanent revolutionary
mark on aviation history in the early 1950’s.

See also : Airplane; Dirigible; Rocket; Stealth aircraft; Supersonic
passenger plane;