JET PROPULSION - ELEMENTARY PRINCIPLES [Main Title]
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- Title: JET PROPULSION - ELEMENTARY PRINCIPLES [Main Title]
- Film Number: AMY 355
- Other titles:
- Summary: A technical film illustrating the elementary principals of jet propulsion, featuring the first flight of the jet engine developed by Frank Whittle. The advantages of jet propulsion, and the huge potential for development of the gas turbine for shaft power rather than emitting a jet of hot air are noted.
- Description: The film opens with prototype Meteor F.9/40 DG202/G taxying. The commentary notes that faster speeds than is possible with propeller can be achieved with jet propulsion, as piston engine combinations and efficiency maintained at very high altitudes can be obtained with engines lighter and more compact than the internal combustion engine of equivalent power, capable of running on almost any type of fuel, and requiring practically no lubricating oil. “Hero’s Aeolipile”: The dependence of jet propulsion upon the unbalanced pressure set up at the outlet nozzle was first illustrated 2000 years ago by Hero of Alexandria. This reaction effect of the jet was later demonstrated by Sir Isaac Newton when he propelled his carriage without any reciprocating parts. The commentary notes over views of radial (Hercules) and in-line (Merlin) piston engines that propellers have to be designed to absorb the power of these new engines and the stage has been reached where four or five bladed and contra-rotating propellers have been developed. When the resultant speed of the blade (vector sum of blade rotation and aircraft forward speed) exceeds the speed of sound shock waves are produced causing a rapid decrease in efficiency. A limit is thus set for the speed attainable by a propeller driven aircraft. Above this speed increasing the number of engines only increases the load capacity of the aircraft as illustrated by the Lancaster bomber. “Air Propulsion”: In a cold jet system heat energy is converted to mechanical energy which is transmitted to a propeller thus causing the rearwards flow of air in the form of a fluid jet. In thermal jet systems the heat energy directly controls the fluid to the fluid jet. Thermal jet systems include rockets and the engine jet propulsion, illustrated by footage of rockets being fired during a rescue at sea, and of the German Nebelwerfer multi barrel projector, known as the “Moaning Minnie” by Allied troops. The theory and development of these systems is addressed with the use of a series of animated diagrams. Air entering an intake duct is compressed internally and pressure energy is converted into pressure velocity at the exit nozzle. Without any heat, the input and output velocities are equal, assuming a frictionless duct. Heating the air in a convergent duct will increase it’s volume so output velocity is faster than the input velocity. The greater the air pressure in a duct the more heat can be added to it in a given space, and the greater its efficiency to convert air to kinetic energy. The simplest device making use of the thermal jet principal is the air inducted radiator, illustrated by footage of the large air duct on a Hawker Typhoon. The injection exhaust principle, another example of the propulsive force of air is illustrated by footage of the twelve exhaust stubs of a Merlin engine. Since a simple duct cannot produce a means of compressing the air, some form of engine is required to produce the fluid jet. The first stage of any such engine is the compressor stage. The simplest form of air compression is the piston or reciprocating type but even several of these compressors would not supply enough air for a jet engine. Film cuts to the turbine blades of a jet engine with the top cover removed, each stage comprising a row of fixed blades and a row of moving blades. Large quantities of air can be handled by this rotary axial flow compressor. Nine stages are required for a compression ratio of four to one. Rotary compression is familiar in the aero engine supercharger, illustrated by footage of the superchargers of the Merlin engine and the Pratt and Witney engine of the Boeing B17, the latter driven by the exhaust gases. A series of animated diagrams of the Whittle engine is used to illustrate how a gas turbine engine operates. As propeller propulsion is likely to remain more efficient than a jet engine at low speeds, the gas turbine can provide a superior engine than a petrol engined aircraft at low speeds. Gas turbines for aircraft require energy to remain in the hot gases after passing through the turbine, only sufficient energy is supplied from the turbine to drive the compressor. In practice the turbine absorbs about two-thirds the energy of the gases. Work on superchargers has aided engine design as have the development of heat resisting steels for turbine blades and combustion chambers. Frank Whittle is seen taxying in one of his prototype Meteors. Whittle began work on designing a jet engine in 1928 and in 1930 made a patent application on his work. The first engine was manufactured in 1936 and the first ground runs took place in April 1937. In May 1941 test pilot Gerry Sayer successfully made the first flight of a British jet propelled aircraft in the Gloster E.28/39 fitted with a Whittle W.1 engine, and footage is seen of the flight. In October 1941 plans of the complete Whittle engine were flown to America and the first American built jet propulsion aircraft flew twelve months later, built by the Bell Corporation and called the XP59A, seen here taking off. Meteor prototype DG202/G is manoeuvred outside its hangar, demonstrating how the absence of propellers enables the fuselage to be quite low, a great advantage in towing and taxying as the whole undercarriage can be of much simpler design. The film ends with footage of DG202/G in flight and landing.
- Alternative Title:
- Colour: B&W
- Digitised:
- Object_Number: AMY 355
- Sound: Sound
- Access Conditions:
- Featured Period: 1939-1945
- Production Date: 1945
- Production Country: GB
- Production Details: Ministry of Aviation (Production sponsor) Science Films (Production company)
- Personalities, Units and Organisations:
- Keywords:
- Physical Characteristics: Colour format: B&W Sound format: Sound
- Technical Details: Format: 35mm Number of items/reels/tapes: 3 Footage: 2559ft; Running time: 28 mins
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