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Copyright Dr. Eng. Jan PajÄ…k

B2. The basics of propulsion

In this monograph the term "propulsion" is used to describe a device which is able to produce a controllable motion. In turn the controllable motion is the motion whose parameters, form, and timing have been previously defined or can be maintained at a desired level. Therefore the characteristic attribute of all propulsion systems is that every aspect of the motion produced by them allows for their use as the source of motion. Examples of propulsion are: the electric motor, the wheel of a car, or helicopter blades.
There are two main types of propulsion that are currently in use. The first of these is called here a "motor", whereas the second is called a "propulsor". The "motor" is a type of propulsion which produces relative movement of one of its parts in relation to another of its parts. An example of a motor is an internal combustion engine in which the movement of a piston occurs in relation to its cylinder, or an electric motor which causes the turning of its rotor relative to its housing.
When a motor is joined with elements from another machine, it causes a movement of the combined parts, but it is still a relative movement. For example, a motor in a car forces rotation of the wheels relative to the body, a motor in a ventilator causes rotation of the airscrew relative to the base, and a motor in a washing machine causes rotation of the drum relative to the housing. Motors by themselves never create motion of objects relative to their surroundings, although they can supply the mechanical energy necessary for this movement. For example, the movement of a car relative to the ground is caused by the wheels, not by a motor, and we still could make a car to move if the motor is replaced with pedals.
The "propulsor" is the second main type of propelling device, which produces motion of whole objects in their surrounding. Propulsors are completely different from motors because they produce an absolute movement, such as the floating of a boat, the flying of an aeroplane, or the thrust of a rocket. Examples of propulsors are the wheels of a car, treads of a tank, a boat propeller, a hovercraft's outlet, helicopter blades, etc.
It should be noted here that propulsors are always able to operate in the natural environment for which they are created. If, for the operation of a particular propelling device, any man-made rail, bar, duct, channel or transmission pipe is necessary, this device represents the linear motor only (not a propulsor) in which one stationary part is lengthened to the required distance. For example railways represent linear motors, not propulsors. This can be better realized when we look at Blenkinsop's engine (see Img.007 (E1)) which for the purpose of propulsion utilized a cog wheel that slotted into teeth on a track.
In every propulsion system three different components must be present. These are:
(1) a working medium,
(2) an energy transferor and
(3) a working space. The working medium is an agent applied in a particular propulsion, whose function is to absorb one kind of energy and then to return this energy in the form of a force interaction creating the motion. Examples of working medium are: the force of mechanical elasticity (in a bow), running water (in a water wheel), steam (in a steam engine), combustion gases (in a space rocket) or a magnetic field (in an electric motor). The energy transferor is a space or a device within the propulsion system, where the working medium is produced and where this medium absorbs the energy that is later released for the creation of a type of motion. Examples of energy transferors are: the boiler in a steam engine, or coils of electromagnets within an electric motor. The working space is a space or a device in a propulsion system, where the actual creation of motion occurs. In this space the energy contained within the working medium is transformed into the work of providing the motion for a propelled object. Examples of working spaces are: the space between the cylinder and the piston in a steam engine, the outlet in a space rocket, or a gap between the rotor and the stator in an electric motor.

B2.1. The working medium

From the analysis of the propulsion systems completed so far, it becomes evident that only three types of circulating agents can provide usable working mediums. These are: (1) a circulation of forces, (2) a circulation of matter (masses), and (3) a circulation of magnetic field force lines. Thus, all the known working mediums can be classified into one of three general types (see the first column in Table B1), depending on which of the above agents the particular medium represents. Because during the development of our civilization these three consecutive types of working medium were discovered and utilized in sequence, we may talk about three eras in our history when a particular general type of medium was dominant. And so in ancient and medieval times the era of media based on the circulation of forces prevailed (e.g. wheel and axle, flywheel, spring). Since the invention of the steam engine (1769) until now, the era of media based on the circulation of matter has been prevalent (e.g. those used in a windmill, watermill, airscrew, boat propeller, jet propulsion). At present we are approaching the third era, where the circulation of magnetic field force lines will be employed. Up to now we have completed only the first and the most primitive device, the electric motor, which utilizes the circulation of magnetic field force lines. But soon a number of more advanced propulsion systems of this kind will become operational.
For every type of working medium three different generations of propulsion systems are completed (see Table B1). In each subsequent generation further attributes of the working medium are utilized as energy carriers.
The first generation always uses force interactions only (e.g. pushing, pulling, pressure, suction, repulsion, attraction) created by the working medium. The second generation, in addition to these force interactions, also employs inertia-related actions. The third generation of propulsion systems utilizing a particular general type of working medium makes use of force interactions, inertia-related actions, and in addition the impact of internal energy (e.g. elasticity, heat).

B2.2. The primary requirement for building a controllable propulsion system
One of the primary principles of physics, called the "Conservation of Momentum Principle", states that when a system of masses is subjected only to internal forces which the masses of the system exert on one another, the total vector momentum of the system is constant. The consequence of applying this Principle to propulsion systems is that the working medium must always be forced to circulate along closed circuits which also pass through the environment (in propulsors) or through the part (in motors) in relation to which the motion should be created. The above condition represents the primary "requirement to circulate a working medium through the environment to achieve the controllability of a propulsion system". This requirement is met in all commercially useful propulsion systems completed by man to-date, even if sometimes it takes an indirect form (e.g. in space rockets, where the propellant is taken first from the environment and placed in the rockets' tanks, and then during flight it is burned and rejected {circulated} back into the environment). Sometimes the designer of a propelling device ignores the requirement to circulate a working medium through the environment. In effect the motion produced is uncontrollable and therefore can not be utilized to provide useful work. The device producing such uncontrolled motion will be called here a semi-propulsion system (i.e. semi-motor or semi-propulsor). Semi-propulsion can easily be transformed into propulsion, if the appropriate circulation of a working medium is organized. An example of the semi-propulsor so modified is a parachute which, after circulating its working medium (air), takes the form of a hang-glider. The other semi-propulsor still waiting modification is a balloon. If a controllable jet outlet is placed on a side surface of a balloon propelled by hot air, then this very old flying device can also move horizontally in the desired direction and with the speed required. Such a minor modification may transform hot-air balloons into the most simple, inexpensive, pleasant, and at the same time effective means of transportation. The transformation of semi-propulsion into propulsion does not usually require any major change in construction, principles, and the working medium used. Therefore in the light of the Periodic Principle, we will assume that a particular propulsion is completed, independently of whether its final or semi-final form has been obtained.

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