Growth of Jet Propulsion Systems

1. Growth of Jet Propulsion Systems P M V Subbarao Professor Mechanical Engineering Department Great Success due to Combination of Wright Brothers Airfoil & Newton's Jet !!!

2. Innovation with Right Boundary Conditions and Right Need Sky is the Limit

3. The Limitless Propulsion Method • Dr. Hans von Ohain and Sir Frank Whittle are both recognized as being the co-inventors of the jet engine. • Each worked separately and knew nothing of the other's work. • Hans von Ohain is considered as the designer of the first operational turbojet engine. • Frank Whittle was the first to register a patent for the turbojet engine in 1930. • Hans von Ohain was granted a patent for his turbojet engine in 1936. • However, Hans von Ohain's jet was the first to fly in 1939. • Frank Whittle's jet first flew in in 1941.

4. The Flight He178 by Dr. Hans Von Ohain A successful bench test of one of his engines was accomplished in September 1937. A small aircraft was designed and constructed by Ernst Heinkel to serve as a test bed for the new type of propulsion system - the Heinkel He178. The Heinkel He178 flew for the first time on August 27, 1939. The pilot on this historic first flight of a jet-powered airplane was Flight Captain Erich Warsitz.

5. Whittles Jet Engine • In 1935, Whittle secured financial backing and, with Royal Air Force approval, Power Jets Ltd was formed. • They began constructing a test engine in July 1936, but it proved inconclusive. • Whittle concluded that a complete rebuild was required, but lacked the necessary finances. • Protracted negotiations with the Air Ministry followed and the project was secured in 1940. • By April 1941, the engine was ready for tests. • The first flight was made on 15 May 1941. • By October the United States had heard of the project and asked for the details and an engine. • A Power Jets team and the engine were flown to Washington to enable General Electric to examine it and begin construction.

6. XP-59A The Americans worked quickly and their XP-59A Aircomet was airborne in October 1942, some time before the British Meteor, which became operational in 1944. The jet engine proved to be a winner, particularly in America where the technology was enthusiastically embraced.

7. The Jet Plane Vampire • The first to exceed a speed of 500 miles per hour. • A total of 3,268 Vampires were built in 15 versions, including a twin-seat night fighter, trainer and a carrier-based aircraft designated Sea Vampire. • DH108 was a newer version was built and released for test. • Initially DH 108 behaved very nicely. • As the speed was stepped up in was unsuspectingly drawn closer to an invisible wall in the sky. • It was unknown to anyone. • One evening the pilot hit this wall and the plane was disappered.

8. 1940-50’s Flying StoryCruising at High Altitudes ?!?!?! • Aircrafts were trying to approach high altitudes for a better fuel economy. • This led to numerous crashes for unknown reasons. • These included: • The Mitsubishi Zero was infamous for a peculiar unknown problem, and several attempts to fix it only made the problem worse. • The rapidly increasing forces on the various surfaces, which led to the aircraft becoming difficult to control to the point where many suffered from powered flight into terrain when the pilot was unable to overcome the force on the control stick. • In the case of the Super-marine Spitfire, the wings suffered from low torsional stiffness.

9. More Stories • The P-38 Lightning suffered from a particularly dangerous interaction of the airflow between the wings and tail surfaces in the dive that made it difficult to "pull out“. • Flutter due to the formation of thin high pressure line on curved surfaces was another major problem, which led most famously to the breakup of de Havilland Swallow and death of its pilot, Geoffrey de Havilland, Jr.

10. Philosophy of Science • The goal which physical science has set itself is the simplest and most economical abstract expression of facts. • The human mind, with its limited powers, attempts to mirror in itself the rich life of the world, of which it itself is only a small part……. • In reality, the law always contains less than the fact itself. • A Law does not reproduce the fact as a whole but only in that aspect of it which is important for us, the rest being intentionally or from necessity omitted.

11. Thus spake : Ernst Mach • In mentally separating a body from the changeable environment in which it moves, what we really do is to extricate a group of sensations on which our thoughts are fastened and which is of relatively greater stability than the others, from the stream of all our sensations. • It is highly an economical reason to think that the fastness of a flying machine is described in terms of velocity (km/hr) !!!! Need for A Strong Thought Experiment !!!

12. Effect of Disturbance in A Fluid • As an object moves through a fluid medium it creates pressure waves. • Pressure waves travel out at the speed of sound which in term depends on fluid properties and temperature. • If the object is traveling significantly slower than sonic velocity, then pressure waves travel out uniformly similar to waves on the surface of a pond.

13. Moving Disturbance In A Fluid • As the object approaches the speed of sound, it begins to catch up with the pressure waves and creates an infinitesimally weak flow discontinuity just ahead of the aircraft

14. Moving Disturbance In A Fluid • As the vehicle breaks the speed of sound, the infinitesimally weak Shock waves begin to add up along a “Mach Line” and form a strong pressure wave with highly compressed air, called a shockwave.

15. Mach’s Cone • As Mach number increases, the strength of the Cone increases and the Angle of the shockwave becomes increasingly severe • Mach Angle

16. Moving Disturbance of Finite Size In A Fluid • • Mach’s thought experiments are limited to infinitesimally small object. • What is minimum size of the object, which will follow Mach’s cone? • Later experience proved following: • As mach number becomes very large for a given size of the object, the Mach wave becomes a shock wave and gets bent so severely that it lies right against the vehicle; • resulting flow field referred to as a shock layer.

17. Mach’s experiments Ernst Mach's photo of a bullet in supersonic flight Mach was actually the first person in history to develop a method for visualizing the flow passing over an object at very high speeds. He was also the first to understand the fundamental principles that govern high speed flow and their impact on aerodynamics. "Photographische Fixierung der durch Projektile in der Luft eingeleiten Vorgange" that he presented to the Academy of Sciences in Vienna in 1887.

18. Mach Number : A True Measure of High Speed Systems For an ideal and calorically perfect gas: Mach number of a flight

19. Speed of Sound in Solids • The situation with solids is considerably more complicated, with different speeds in different directions, in different kinds of geometries, and differences between transverse and longitudinal waves. • Nevertheless, the speed of sound in solids is larger than in liquids and definitely larger than in gases. • Sound speed for solid is: