JET PROPULSION

[Music] [Applause] [Music] Aviation today with its huge machines of riveted metal has advanced far beyond the first simple structure which the Wright brothers flew at Kitty Hawk now a major form of transportation modern airplanes which carry more than half a hundred passengers have been standard on commercial airports they're powered by giant air-cooled engines designed to generate thousands of horsepower each the propellers which these super engines turn a fashion of metal with variable pitch controlled by the pilot and yet despite such advances the basic principles by which these aircraft operate are still the same as those first used by the Wright brothers a propeller driven by a piston engine this power unit has been developed and refined until today's aircraft with gross weights of more than 50 tons can fly through the air as fast as the fastest bird as high as any bird has ever flown never satisfied man has designed special-purpose aircraft to fly an extremely fast speeds and high altitudes but in spite of constant improvement engineers found what seemed to be inherent limitations in the efficiency of the piston engine propeller power system up to 400 miles per hour the efficiency of the propeller driven power units been current increased as the speed of the airplane increased above 400 miles per hour the efficiency began to decrease slightly above 500 miles per hour a limit seemed to be reached beyond which at that time conventional aircraft were unable to go the break through this apparent limitation seemed to require an entirely new form of aircraft propulsion the answer developed in England before World War 2 was jet propulsion [Applause] the basic principle of Jet Propulsion is known to every child who is blown up a toy balloon what will happen when the balloon is let go that makes the balloon move this way Sir Isaac Newton formulated what happens in his third law of motion for every action there is always an equal and opposite reaction let's go back to the balloon as long as the neck remains closed the air pressures inside the balloon are distributed equally throughout the balloon thus all the pressures are counterbalanced when the neck is opened however the air rushes out releasing the pressure on that side of the balloon the pressure is on the opposite side are now no longer counterbalanced and they propel the balloon in the direction away from the net the action referred to in Newton's law is the release of pressure through the neck reaction is the movement of the balloon in the opposite direction we see action and reaction demonstrated many times each day and we know what'll happen when this boy jumps off his wagon the action of his jump is accompanied by a reaction of the wagon being pushed in the opposite direction the lawn sprinkler is a common application of this principle water is under pressure in each arm of the sprinkler except at the opening the action of the escaping water is accompanied by an opposite reaction caused by the unbalanced internal pressure thus turning the sprinkler the capsule of compressed gas used power toy models is another example its action is similar to that of the balloon [Applause] the pressure of gas inside the capsule is equally balanced when the end of the capsule is pierced the pressure at that end is released the pressure on the opposite side propels the capsule in that direction action reaction it is the unbalanced internal pressure which propels the capsule not the action of the escaping gas striking against the outside air even if a solid wall is placed behind the capsule for the escaping gas to strike the amount of movement of the capsule remains the same because the internal pressures have not been changed the principle by which this capsule operates is essentially like that of an airplane jet engine except that the jet engine contains a built-in gas turbine for continuously creating internal gas pressure this engine has basically only three moving parts an air compressor a turbine and a shaft which connects them the front end of the engine is open for air intake inside a compressor compresses the incoming air the compressed air is carried to a ring of burners where it is sprayed with fuel once started by means of a spark plug this mixture of fuel and air burns constantly so no continuous ignition system is necessary a high temperature gas is produced by the burning mixture tremendously increase the volume of the gases inside the engine before they can escape however they must pass through the turbine they caused the turbine to spin in much the same way that wind spins a pinwheel the spinning turbine is connected by means of a shaft to the compressor unit in the forward part of the engine bus it provides the power which turns the compressor but the escaping gases have lost only part of their pressure in spinning the turbine the remaining pressure pushes the gasses out through the jet nozzle leaving the pressure inside the engine unbalanced this unbalanced pressure causes the engine to move in the opposite direction from the jet nozzle action is the release of pressure through the jet nozzle reaction is the movement of the airplane the airplane moves because of internal pressures in the engine and not because of the escaping gases striking against the outside air in actual use the turbojet engine has many parts in addition to those already mentioned at the forward end of the engine geared to the shaft a number of accessory units such as a fuel pump and an oil pump the shaft of course must be supported by bearings as it turns yet even with all these items the jet engine contains only a small percentage of the number of moving parts found in a conventional piston engine this comparative simplicity permits easier control of the engines and the cockpit of a jet airplane contains pure instruments and simpler controls and the cockpit of propeller driven aircraft there are many other advantages to the rotary motion of a jet engine produces very little vibration compared with the reciprocating action that is the back-and-forth action of the many Pistons in a conventional engine the jet engine is much lighter for horsepower delivered an extremely important factor in airplane engines its streamlined shape permits great flexibility in the design of the airframe which the engine powers since there are no propellers the airframe can be much closer to the ground permitting a shorter landing gear and safer ground handling characteristics there are some disadvantages to jet aircraft are not able to climb as steeply as propeller-driven airplanes they are not as efficient that speeds up to about 400 miles per hour fuel consumption is high in comparison with that of piston engines the jet airplane is easier to handle aloft since there are no propellers to disturb the flow of air over the wing surfaces in addition there is no propeller torque to contract propeller torque is the tendency of propeller driven airplanes to turn in the opposite direction from that of the propeller jet aircraft have no such tendency but by far the greatest advantage of jet propulsion is at extremely high speeds required of many present-day aircraft unlike propeller driven aircraft whose propulsive efficiency depreciates at high speeds the efficiency of a jet aircraft increases proportionately as the speed of the airplane increases so that theoretically as the speed of the airplane approaches the speed of the gases escaping from the jet nozzle the propulsive efficiency approaches 100% there are many different ways to use jet propulsion one of these is the turboprop engine this engine is essentially like that of a standard turbojet engine already described except that a propeller is attached to the forward end of the rotating shaft the power of the engine is used to turn the propeller rather than to create a jet there are two other types of jet engines simpler than the turbojet one is a pulse jet whose only moving part is a hinged shudder in front of the engine it operates through intermittent firing of the fuel mixture the ramjet is even simpler it is merely a tube in which the fuel mixture is burnt both of these engines depend on high forward speeds for efficiency speed must first be obtained by other means before the engines can take over still another type of jet propulsion is rocket propulsion rockets differ from other forms of debt propulsion in the fey contain their own oxygen and fuel and hence are not dependent on the Earth's atmosphere however rocket engines require great amounts of oxygen and fuel for comparatively short flights the greatest development so far has been with the turbojet engine and many high-speed aircraft are being flown today with these engines jet aircraft are in everyday use throughout the world today speeds in excess of 600 miles per hour are no longer unusual altitudes over 40,000 feet are common this new type of power has broken down many of the previous barriers to aviation progress so far we have only begun to explore its vast potentialities for as jet propulsion is further developed its uses will be carried far beyond the special requirements of high-speed flight to serve as a basic power unit for all types of aircraft [Music]