BE481852A - - Google Patents

Description

       

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  Rocket, in particular for assisted take-off, and its method of loading.



     The present invention relates to jet propulsion, and more particularly to methods and devices for increasing the operating safety of rockets using solid propellant fuels.



   In general, a rocket comprises a combustion chamber provided in its wall with a nozzle, a fuel charge placed in this chamber, and a device ensuring the ignition of the charge. Rockets of the type under consideration use solid propellant mixtures. During the combustion of the charge, gas is generated at high temperature and high pressure inside the combustion chamber, and this gas escapes through the nozzle, producing a thrust which can

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 be used for propelling or controlling a vehicle, for example an airplane, on which the rocket is mounted.



   In an important application of jet propulsion, rockets mounted on an airplane are used to generate auxiliary thrust during take-off; thus making it possible to reduce the distance necessary for this take-off. However, the reduction in the take-off distance is extremely important, for example when it is desired to take off heavily loaded airplanes from the flight deck of an aircraft carrier or on short runways.



   For assisted take-off of an airplane, it is desirable to cause the rocket to operate while the airplane is still stationary, or while it is still moving at a reduced speed, so that the pilot is sure that the rocket works and can consequently control the control surfaces of the plane. In this case, the effectiveness of the rocket for the. The reduction in take-off distance depends not only on the total momentum generated by a rocket, but also on the time interval during which this thrust is available. This particularity is due to the fact that this efficiency does not depend only on the impulse generated, but on the average speed of the vehicle in the time interval during which this impulse is applied.

   So, generally speaking, if rocket operation begins at the start of the take-off period, such rocket producing a thrust of 450 kg for 10 seconds will be. more effective for the reduction of.



  take-off distance that a rocket producing a thrust of
2250 kg. for 2 seconds, although the pulse is within

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 two cases of 4500 kg.



   For assisted take-off, it therefore appears desirable to provide rockets capable of operating for long intervals of time. Even in other applications / rockets, a longer run time than heretofore available (one or two seconds) is desirable, because of the resulting reduction in strain or fatigue to which the rockets are subjected. elements of the frame supporting the rocket, and also because of the resulting reduction in the weight of the rocket necessary to obtain with certainty a given impulse.



   Rocket operation for long intervals of time can be achieved by limiting the combustion of a slow-burning propellant mixture to a limited (or exposed) part of its surface, so that combustion progresses slowly from that limited area. towards the neighboring part of the charge to form a new limited combustion surface, and so on from one end of the charge to the other, gradually. When the combustion of the charge is determined in this way, this phenomenon is referred to as "limited combustion".



  Otherwise, we will say "unlimited combustion".



   Previous attempts to adapt rockets to vehicle propulsion have proved impractical because of the excessive thrust which occurs for short periods of time. This characteristic was mainly due to the absence of "limited combustion".



   Consequently, the main object of the invention is to provide a limited combustion rocket which is of greater operating safety than those known hitherto.

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     Other objects of the invention are in particular: to produce a rocket exhibiting a better ratio between propulsion and weight; to produce a rocket specially designed for the assisted take-off of an airplane; to produce a rocket on which one can rest in order to obtain a substantially constant thrust during a prolonged operating time; to provide a combustible mixture for rockets of this type, and particularly a combustible mixture which will operate safely over a wide range of temperatures;, and to provide a charged rocket capable of being returned to working condition if it has been subjected to extreme temperatures or other conditions such as to render its operation unsafe.



   Other objects are also to provide a process for the preparation of these rockets and a suitable process for the production of these propellant fuel mixtures.



   In one of its general forms, the invention relates to the charging of a rocket with the aid of a thermoplastic propellant mixture having a limited exposed surface on which combustion is generated, the latter then being propagated len - gradually and gradually to the rest of the charge, and the adhesion to the wall of the combustion chamber of those parts of the surface of the charge in which combustion is prevented. The combustion of this charge is limited at an exposed end.



  In a preferred embodiment of the invention, a thermoplastic propellant mixture of two constituents is poured into a cylindrical container provided with a thermoplastic coating designed to adhere both to the wall of the container and to the propellant charge.

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   Although a wide variety of propellant mixtures can be used to achieve the desired "limited combustion", in a preferred embodiment a propellant mixture formed by fine particles of a solid oxidant uniformly dispersed in a plastic fuel is used. in an amount at least sufficient to fill the interstices between the particles of the atomized oxidant.



   As an oxidizer, potassium perchlorate (K Cl 04) is preferably used because it contains a large amount of oxygen available for combustion due to its stability, both alone and in combination with plastic fuels, because of its ease of obtaining in commerce and comparatively low price, and also because of its non-hygroscopic character.



   As the fuel, a semi-solid organic fuel is preferably used, and particularly a fuel having a predominantly hydrogen and carbon content. Hydrocarbons are preferred over other organized solids because of their high heat of combustion. For this reason, it was thought that bitumens, and particularly asphalts, were particularly suitable,
Asphalts will be given preference over other hydrocarbons because of the wide range of atmospheric temperatures in which they remain plastic.

   Among the asphalts themselves, it has been determined that asphalts oxidized by air blowing, based on naphthenic alone or naphthenic mixed with paraffin, were the most satisfactory, especially when they were mixed with a small proportion of 'a high viscosity index oil, with which they are compatible.

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   By incorporating about 3 parts of (K Cl 04) to one part of asphalt, a sufficiently plastic, substantially impermeable propellant mixture can be produced which at the same time contains excess fuel.



   Although a propellant of this type can be used on its own when cast in a rocket to provide a limited combustion fuel assembly that operates with greater certainty, tests have determined that its safety can be significantly increased. operation using an asphalt-based coating as a binder between the filler and the wall of the combustion chamber.



   According to a preferred method of manufacturing a rocket in accordance with the invention, the container studied to constitute part of a combustion chamber is first of all covered with a thermoplastic coating designed to adhere to both to the wall of the chamber and to the propellant mixture which it is desired to use, then this propellant mixture is poured into the container provided with its coating, by pouring said mixture into this container at a high temperature such as propellant mixture flows easily without causing the coating to melt.



   If rockets loaded with thermoplastic propellant mixtures operating at too low or too high a temperature failures (extinctions) can easily occur.



   Although the exact cause of these low temperature failures is not known with certainty, it is believed that they occur as a result of the propellant charge's tendency to fracture as a consequence of excessive brittleness or failure. tendency to separate from the wall of the combustion chamber as a result of contraction and lack of plastic

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 Sufficient at low temperatures. Regardless of the explanation for these failures, experimental research has determined that they occur frequently if the penetration of the propellant charge is less than about 6.

   determined by the tests described below,
The upper limit of the temperature above which explosions can occur is not so well determined. At elevated temperatures, failures occur when the propellant charge is excessively fluid. Thus, if (the viscosity of) the propellant is too fluid, it can flow easily and separate as a result of the chamber wall when left to stand in an inclined position for more than a few hours, thus exposing a larger surface.

   Although the exact limit of the upper safe value for penetration will depend on the time elapsed between the change in the rocket position and the firing of the rocket and other similar factors, it has been possible to determine that A satisfactory "limited burn" can usually be obtained if the penetration is less than about 100.
Thus, the preferred plastic propellant has a penetration of between about 6 and 100 at the operating temperature of this rocket, and preferably a penetration of about 25 at mid temperature, of the temperature range to 1. Inside which it is desired to cause the operation of a rocket loaded with this propellant mixture.



   Although the invention is described herein as relating to propellant charges of specific composition and to

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 particular methods of preparing and casting these propellants, technicians will understand that the principles of the invention can be applied to other propellant mixtures and to other preparation and casting processes without departing from the within the scope of this invention.



  It will also be understood that the invention is not limited to the theoretical explanations given herein, as they are provided primarily to aid in the understanding of the invention.



   Other objects and advantages of the invention, as well as embodiments and characteristics, will be better understood from the description which follows, made with reference to the appended drawings in which
Fig. 1 is a graph showing the relationship between the flow velocity and the applied force for a plastic material.



   Figure 2 is a sectional view of a rocket constructed according to the invention and using a bond coating. between the propellant charge and the. chamber of this rocket.,
Fig. 3 is a partial profile view, in elevation and in partial section, of the nozzle and of the cover. the rocket, this cut being made by line 3-3 of fig 2.



   Fig. 4 is a similar view of another embodiment using a cartridge to which the propellant is bound.



   Fig. 5 represents curves showing how the pressure prevailing inside the chamber of a rocket varies as a function of the time that its operation lasts, with application of the invention and without this application.

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   Fig. 6 is a diagram showing the main operations of a process for preparing a rocket according to the invention.



   Fig. 7 is a graph showing the curves representing the penetration as a function of temperature for some of the explosive mixtures of the invention.



   DEFINITIONS
Some definitions have been given below to aid in the explanation of the invention.



   Propellant mixture: a distinction is made in the present description between propellant mixtures and explosives.



   As used herein, the expression "propellant mixture" denotes a substance which, upon ignition at any point on its surface, can burn progressively from that point to others at a rate of propagation. perceptible to the eye. Propellant mixtures enclosed for example in a perforated chamber can burn at a rate of the order of about 7 mm to 75 cm per second when the pressure of the combustion gases in contact with the combustion surface is respectively. around 14 kilos to about 4,200 kilos per cm2.



   On the other hand, the term "explosive" is used to denote a substance in which combustion propagates almost instantaneously. Thus, combustion, for example in the case of most explosives, can propagate at speeds comparable to the speed of sound and even greater than it.

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   Plasticity: A material is said to be "plastic" if it is capable of being continuously and permanently deformed in any direction and without rupture under a tension exceeding the deformation index. In other words, a substance is plastic if it does not return to its original form when the force applied to it is removed. The plasticity of a substance is a measure of its aptitude for such deformation.



   There is shown in FIG. 1 a graph showing the properties of a typical plastic substance, In this graph, the abscissas represent the shear stress (or force).



  The ordinates represent the resulting rates of permanent deformation. It will be noted that, below a certain value of tension (known under the denomination index of deformation), no permanent deformation occurs, while, for higher shear stresses, the rate of deformation increases as a function of voltage. For tensions below the deformation index, the material has elastic properties. Above this value, it exhibits some of the properties of a viscous fluid. I, the deflection index depends on the tensile stress and partly determines ductility or cohesion.

   The deformation index of asphalts and propellant mixtures considered is very low, but the deformation index of asphalt oxidized by air blowing is higher than that of asphalt refined by steam having the same origin.



   Ductility: As used herein, the term "ductility" is a measure in cms of the cohesion of a plastic material, determined by the well-known Dow method (see for example the work entitled "Asphalte and Allied Substances "by H. Abraham,

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 page 848, 4th edition, published by Van Nostrand in 1938).



   Penetration: As used herein, the term "penetration" is the degree of plasticity measured at any temperature by distance in hundredths of cms. of which a specific needle can be introduced by pressure into a plastic material under the action of a force of 100 grams acting for 5 seconds.



   The process applied for these tests is described under the title "Test N D5-25" from the Society called: American Society for Testing Materials (A.S.T.M.). A substance whose penetration varies with temperature is called "thermoplastic".



   Penetration Sensitivity: As used herein the expression "Penetration Sensitivity" should be considered as the variation of the ordinary logarithm of the penetration for a temperature variation of 1 (d log 10 p) / dT .



  The penetration sensitivity of the fuels and propellants described here is virtually independent of temperature over a wide range, and is thus represented approximately by a straight line when plotting the curve representing the logarithm of penetration as a function of temperature. .



   GENERAL STUDY
There is shown in FIG. 2 a rocket containing a plastic propellant charge cast in a plastic-lined combustion chamber. For simplicity, the rocket will be described in its vertical position (its axis being vertical) which is the normal position of this rocket during its storage.



   This rocket has an elongated cylindrical container

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17 whose sectiari is uniformly circular over a significant part of its length, and whose axis of thrust X-X is vertical. The bottom (closed) of the container is rounded. The upper end is threaded to allow its closure by a threaded cap 19. The cap carries an ignition device 21 and a converging-diverging nozzle 23 of the type of lavai shown. Subject to the opening of the nozzle 25 of the nozzle, the vessel and the cap form a closed combustion chamber.



   The ignition device and the nozzle are not shown to scale. In practice, this device and the nozzle have such proportions and an arrangement on the cap that the gases escaping through the nozzle do not run the risk of burning the ignition device.



   The nozzle may be fixed to the end plate by any suitable device, for example by means of a collar 31 projecting from the outer periphery of this nozzle and fitting with some clearance in a larger bore. diameter provided on the inside of the cap 19.



  The nozzle can be held in place by means of a stop ring 33 held against its underside inside the combustion chamber by means of screws 35 implanted in the wall of the cap, as shown in more detail. in fig. 3.



  The minimum section of the nozzle nozzle is significantly smaller than the cross section of the combustion chamber, so as to allow the gases generated at high pressure and at elevated temperature within the combustion chamber. combustion chamber to escape at high speed through the nozzle.

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   The ignition device comprises an elongated hollow body 36 having a smaller open end. 37 fixed by screwing on the cap, in a thread 38 passing through the wall thereof. This ignition device contains a firing charge 39 comprising a nickel-chromium alloy filament 40 housed in this charge towards its upper end. A second firing charge 43 has a channel aligned with the axis of the body of the device and enclosed in the wide portion of this body, between the firing charge 31 and the open end 37. Insulated electrical conductors 41 connected to the filament pass through insulated channels in the wall of a cap 42, which sealingly closes the upper end of the body 36 of the igniter.



   An explosive charge 27, composed of a thermoplastic material, fills this container to a predetermined level and has a substantially planar horizontal (free) exposed surface 28 towards its upper end. A coating 29 connects the propellant charge to the wall of the container at least towards the upper part of the side surface of the charge, but preferably over this entire side surface. For ease of manufacture, the coating is poured into the vessel and covers the entire surface of the portion of the vessel which contains the propellant charge.



   This coating is of a material which can readily adhere to the wall of the chamber and to the propellant charge, and is preferably thermoplastic in nature. This plastic coating increases the operational safety of the rocket, particularly if the propellant charge contains a finely granulated substance; it is preferably in a more plastic

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 tick than the propellant itself, so as to reduce any tendency for the propellant charge to fracture when subjected to shock or thermal stresses.



   This rocket can be fixed to the lower part of an airplane in any suitable manner, for example by legs (not shown) fixed to the airplane and made integral with a certain clearance of the wall of the combustion chamber. - tion. The operation of this rocket can be determined by passing an electric current through the filament 40, by connecting the conductors, using a switch placed in the cockpit, with a battery or other source of electrical energy. . When the combustion temperature of this firing charge 39 is reached, said charge explodes and ignites the secondary charge 43, which again projects hot gases against the exposed surface 28 of the propellant charge, thereby generating the secondary charge. combustion of it.



   On burning, the propellant charge turns into gas at high temperature and high pressure. As the pressure in the open portion 43 of the combustion chamber increases, this combustion propagates throughout the section of the rocket, and the charge burns more quickly. If the charge is operating satisfactorily, that is to say when the combustion is suitably limited, it progresses through the charge in a direction parallel to the X-X axis of the rocket. always leaving a substantially planar exposed surface normal to the axis of the rocket, until all the charge is consumed. The propagation of combustion to the remaining external surface of the propellant charge is prevented as a result of the fact that a gas-tight connection is made between this surface and the wall of the container.

   In this case, the suitable binding

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 is provided by the plastic coating.



   When the rocket is operating, the gases escape at high speed through the nozzle of the nozzle 23. During the early stage of operation, the pressure of the gases inside the combustion chamber increases rapidly, reaching soon a maximum value indicated by part a of the curve R shown in fig. 5, in a short time of the order of 1 sec. about. As combustion continues, the volume of the unloaded portion 43 of the combustion chamber increases, and the pressure usually decreases gradually to a lower rate, as indicated by the slightly sloping portion b of this curve. Finally, at the end of the period of operation of the rocket, the pressure decreases rapidly as indicated by the steep part c of this curve.

   The temperature of the gases varies in the same way. Thus, during the period of time corresponding to the progressive decrease in pressure, the thrust produced by the rocket when the gases escape through the nozzle is substantially constant. This constant is obtained by limiting the combustion of the charge at any time to the flat surface, of uniform cross section across the vessel, and by continuing this combustion for a long period of time. Even if the free end of the charge is not originally flat, it soon takes this shape, and combustion continues progressively in the direction of the axis of the rocket.



   If, for some reason, the propellant charge is pushed away from the chamber wall towards the exposed end, this propellant charge may burn on the separated part and consequently give rise to the interior of the chamber.

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 combustion, at a pressure with an unexpectedly excessive rate. This combustion laterally to the charge can spread very rapidly over a larger area and therefore produce unlimited combustion of that charge. In this case, the combustion of the propellant charge is accelerated, thus generating gases at a higher average pressure and for a shorter period of time, and it can burn itself rapidly as indicated by the peak curve. pointed u 'of FIG. 5.



   Similar failures can occur as a result of deep cracks that may exist on the exposed end of the propellant charge. These cracks can occur, for example, by a fracture produced by thermal stresses generated within the load during rapid temperature changes prior to operation. In this case, combustion occurs which is not limited enough thereby giving rise to pressure rising at an excessive rate and consuming the propellant charge in a short period of time.



   However, if the charge separates from the chamber wall at a point remote from its exposed end, or if 'cracks' occur in the mass of the' charge, 'the danger' of unrestricted combustion is less. . This is probably due to the fact that when building up the pressure of the gases inside the. combustion chamber, the plastic load is applied towards the closed end of the chamber, consequently applying with certainty the load on the wall at this point of separation, and closing these cracks.



   A second embodiment is shown in FIG. 4. Here the combustion chamber is flat at the far end of the

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 nozzle and is designed to contain a cartridge containing a plastic propellant charge.



   Thus, as shown, a soft paper cartridge
50, of cylindrical section, is filled with a plastic propellant charge connected to the wall of the cartridge. The latter fits freely in the container 17 forming the combustion chamber, the open end of this cartridge being towards the nozzle of the rocket.



   In this case, the combustion of the propellant charge is limited to the exposed end of this charge due to the fact that said charge is strongly connected to the wall of the cartridge, and that the material which constitutes this wall burns more slowly than the cartridge. . propellant charge itself. In these also, it is advisable to store the loaded cartridges or rockets in a vertical position to avoid separation of the propellant charge and the wall of the cartridge and to ensure the automatic sealing of any cracks which may occur. could occur in the propellant charge or towards its open end.



   The propellant mixtures which have been found to be particularly suitable for this purpose contain fine particles of solid oxidizing agents dispersed substantially uniformly in a matrix formed by a plastic fuel. These matrices serve as binders for the oxidants and, used in sufficient quantity, make the resulting propellant mixtures substantially impermeable, if they are slightly porous due to incomplete compactness. A matrix of this type gives the resulting propellant charge both its consistency and its plasticity.

   Besides her

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 acts as an agent and filler, this matrix acts as a shock absorber between the particles of oxidant, thereby reducing the transmission of shocks from one part of the oxidant to another. Without this damping effect, the shocks could be propagated quickly, and a detonation would ensue.



   For all the plastic propellant mixtures for which penetration measurements have been made, it has been found that these propellant mixtures become too brittle to act with certainty if the penetration is less than about 6, and that these propellant mixtures become too fluid for work satisfactorily if the penetration exceeds about 100. Depending on the individual peculiarities of the propellant mixtures, satisfactory operation can be achieved over a wider or narrower range. The exact penetration limit that can be relied on for a particular propellant mixture can be determined empirically.



  At the average temperature of the range within which the rocket is desired to operate, the penetration should be about 25. Representative examples of some of these specific propellant mixtures and their method of manufacture which have been found to be satisfactory will be given below.



   In all these examples of propellant mixtures considered, the composition is 75% K Cl O4 and 25% fuel by weight, although the amount of oxidant can be varied between about 50 and 90% while producing still a satisfactory propellant mixture. All of these propellants are slightly porous, although impermeable, and have specific densities ranging from about 1.5 to 1.8.

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   The main operations carried out for loading a rocket are shown in the diagram and the work table in fig. 6. We will refer to this diagram in the study which follows.



   The penetration measurements of the different propellant mixtures are shown on the graph in fig, 7. The indices attached to the letters? on the given curves indicate the row of the example below, in which the corresponding propellant mixture is studied. In this figure, the ordinates represent the ordinary logarithms of the penetration, and the abscissas the temperatures in C.



   On the penetration curves, the points marked with a small cross (+) indicate the limits of the temperature range outside which tests have revealed that extinctions tend to occur.



   The potassium perchlorate commonly used is 99% pure and contains less than 0.2% moisture at 1%, less than 0.15 1% potassium chlorate (K Cl O3), and less 0.15 of 1% potassium chloride (K Cl).



   The potassium perchlorate is ground and filtered so as to obtain one of the following states:
State N 1:
Through the 100 mesh 100% sieve
Through the 200 mesh 15% sieve
State? 2:
Through the 125 mesh 100% sieve
Through the 150 mesh screen 97 to 99.75%
Through the 200 mesh screen 90 to 96%
Through the 325 mesh screen 70 to 80%

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In Examples 1 and 2, potassium perchlorate in the state? 1, 'and in the other examples of potassium perchlorate of, state? 2.



   Example 1: A container is provided with an asphalt coating called "Floatine S", this coating having a thickness of approximately between 1.75 and 2.5 mm. If the coating is much thinner, a bare part may form between the propellant charge and the wall of the vessel during the casting of this charge. If the thickness significantly exceeds 2.5 mm, there will be an unnecessary reduction in the thrust obtainable from the rocket.



   The process used to obtain the coating consists of pouring into the container a sufficient quantity of asphalt at a temperature of about 175 ° C., with the open end pointing downwards, at a reduced angle. with the horizontal, and rapidly rotating the container as the asphalt moves by gravity downward along the side faces of the container. The thickness of the coating obtained depends partially on the angle of inclination, on the speed of rotation, on the temperature of the. coating substance at the time of pouring and its viscosity.



   A propellant mixture is then prepared by gradually adding finely pulverized potassium perchlorate to a mass of "Floatine S" asphalt maintained at a temperature of 175 ° C. in an oil bath. When adding the potassium perchlorate, the mixture is stirred to fully incorporate this potassium perchlorate, to obtain a uniform dispersion of the oxidant in the resulting mixture. The resulting propellant mixture exhibits a penetration of approximately 18-21 C

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 and a sensitivity of about 0.016. The variations of the penetration with the temperature of the resulting propellant mixture are indicated by the curve P1 of FIG. 7.



   After cooling and hardening of the coating on the inner wall of the vessel, the propellant mixture at a temperature of 175 ° C. is poured into the vessel provided with this coating, and allowed to cool there to atmospheric temperature while the vessel is standing. in its normal storage position, that is to say with its vertical axis XX.



   Rockets of the type shown in FIG. 2 charged following this process work satisfactorily under a variety of conditions. This propellant mixture acts satisfactorily between 7 C and 55 C approximately. The temperature limits between which satisfactory operation can be obtained are indicated by xs on the P1 curve.

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  TABLE I
 EMI22.1
 . # - ## - # ------ # --- # --- #### '- ## ---- # --- # - # "" "-" "" '"*" "" ""' "" "" "*
 EMI22.2
 
<tb>
<tb>
<tb> Floatine <SEP> S <SEP> Floatine <SEP> S
<tb>
 
 EMI22.3
 ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯ ¯. [¯¯, ¯¯¯¯; + 15% â \ dAristo
 EMI22.4
 
<tb> ignition point <SEP> <SEP> (determined <SEP> at <SEP> the
<tb>
<tb>
<tb>
<tb>
<tb> cup <SEP> open <SEP> of <SEP> Cleveland) <SEP>:

   <SEP> 240 <SEP> C <SEP> 207 <SEP> C
<tb>
<tb>
<tb>
<tb>
<tb> <SEP> point of <SEP> softening <SEP> (determined <SEP> by
<tb>
<tb>
<tb>
<tb>
<tb> ring <SEP> and <SEP> ball) <SEP> 72 <SEP> C <SEP> 58 <SEP> C
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> -Penetration <SEP> (0.01 <SEP> cm / 100 <SEP> g / 5 <SEP> sec.)
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 0 <SEP> C <SEP> ll
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 7 C <SEP> ------ <SEP> 23
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 25 <SEP> C <SEP> 26 <SEP> 71
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 38 <SEP> C <SEP> 59 <SEP> 166
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Ductility <SEP> (5cm / min)
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 0 <SEP> C <SEP> 1, <SEP> 0 <SEP> cm <SEP> 4,

  5 <SEP> cm
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 7 <SEP> C <SEP> ------- <SEP> 5.7 <SEP> cm
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 13 <SEP> C <SEP> ------- <SEP> 7.2 <SEP> cm
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 25 <SEP> C <SEP> 5.8 <SEP> cm <SEP> 53 <SEP> cm
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> 38 <SEP> C <SEP> 24.7 <SEP> cm <SEP> plus <SEP> of <SEP> 100 <SEP> cm
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Solubility <SEP> in <SEP> CS2 <SEP> 99.98 <SEP>% <SEP> 99.90 <SEP>%
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Solubility <SEP> in <SEP> CCl4 <SEP> 99.85 <SEP>% <SEP> 99.80
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Specific <SEP> density <SEP> (25 C / 25 C) <SEP> 1.0375 <SEP> 1.0229
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Calorific <SEP> value <SEP> (large <SEP> calories)

   <SEP> 4673.5
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Sulfur <SEP> 3.3% <SEP> to <SEP> 4.2%
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Hydrogen <SEP> 7.8% <SEP> to <SEP> 10.0%
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb>
<tb> Carbon <SEP> 81.8% <SEP> to <SEP> 84.60%
<tb>
 

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 "Floatine S" is the trade mark designating an asphalt oxidized by air blowing produced by the Company known as: Paraffin, Companies Inc., headquartered in E meryville (California) United States. This asphalt is derived from crude oil obtained in an oil field located in Orcutt (California) United States.



   Example 2: A fuel designed for satisfactory operation over a wide range of temperatures is obtained by adding 15% "Aristo" oil having an SAE viscosity level of 10, to 85% "Floatine S" asphalt. to form a combustible mixture. The two components of the fuel are thoroughly mixed by heating and stirring at a temperature of 175 C.



     The "Aristo" oil is produced by the Company called: Union Oil Company of Wilmington (California) USA by a process applicable to solvents. The characteristics of this oil are shown in Table II. The characteristics of the resulting fuel mixture are given in column 2 of Table I.



   A coating having a thickness between 1.6 and 2.4 mm is formed in the container by pouring therein a sufficient quantity of combustible mixture at a temperature of 1750 ° C., and by tilting and rotating the container as described above in. example 1.



   Potassium perchlorate is incorporated into the oil and asphalt mixture by gradually adding it, and stirring the mixture thoroughly, while maintaining the temperature of the resulting mixture between about 105 and 175 C.



  If, inadvertently, the temperature of the propellant mixture is

 <Desc / Clms Page number 24>

 too high (above approximately 205 C), potassium perchlorate may decompose. Below a temperature of about 105 C, the mixture becomes difficult to process.



   The propellant mixture is then poured into the coated vessel while the mixture is at a casting temperature of between 115 and 127 ° C., and is distributed regularly while stirring with a bar to reduce build-up. bubbles and air pockets in the load.



   It has appeared desirable to determine the casting temperature exactly. At the temperature indicated, the propellant has a consistency which is comparable to that of the DU mastic of bread dough, and can be poured easily. Below this temperature, the propellant mixture becomes more difficult to process. If this propellant mixture is poured at a higher temperature, the coating may melt at certain points.



   TABLE II properties of "Aristo" SAE 10 oil
 EMI24.1
 
<tb> Flow <SEP> temperature <SEP> - <SEP> 1 <SEP> C
<tb>
<tb> Density <SEP> 20, <SEP> 5 <SEP> A.1.1
<tb>
<tb> Viscosity <SEP> (Universal <SEP> Index <SEP> of <SEP> Saybolt)
<tb>
<tb> to <SEP> 33 <SEP> C <SEP> 210.5 <SEP> sec. <SEP>
<tb>
<tb> to <SEP> 100 <SEP> C <SEP> '<SEP> 44 <SEP> sec.
<tb>
<tb>



  Sulfur <SEP> 0.75 <SEP>%
<tb>
<tb> Carbon <SEP> 87.11 <SEP>%
<tb>
<tb> Hydrogen <SEP> 12.14 <SEP>%
<tb>
<tb> Thermal <SEP> coefficient <SEP> (kilos / calories) <SEP> 4834.
<tb>
 

 <Desc / Clms Page number 25>

 



   The penetration as a function of temperature for the propellant mixture of Example 2 is indicated by curve P2 of FIG. 7. The propellant has a penetration of about 20 to 21 ° C and a penetration sensitivity of about 0.016.



   Rockets constructed by application of this process operate satisfactorily between −1 and 50 C. The limits being indicated by x's on the curve of penetration as a function of temperature.



     . Example,. 3: Another composition fuel containing 70% "Floatine S" and 30% "Aristo" oil is prepared, and a propellant charge is prepared by charging a rocket by applying substantially the same process as in the rocket. example 2.



   Rockets coated with this fuel and loaded with a propellant mixture containing a fuel of this type have been found to operate satisfactorily over a temperature range from -22 to 32 C. The limits of the safety operating range are also indicated by xs on the curve. The penetration as a function of the temperature data for this propellant charge is represented by the curve P3 in fig. 7. The propellant charge has a penetration of about 80 to 21 ° C, and a penetration sensitivity of about 0.016.



   It will be appreciated that the propellant charges of Examples 1 and 2 exhibit approximately the same penetration sensitivity although the penetrations of the compositions differ markedly at any given temperature. The addition of light oil thus makes the propellant softer and allows operation at lower temperatures.

 <Desc / Clms Page number 26>

 



   Example 4: A propellant charge is prepared using a fuel containing 85% "Floatin S" and 15% Pennsylvania oil sold under the trademark "pure Penn Oil" by the so-called Union Oil Company. Except as regards the oil and the grinding of the perchlorate, this propellant charge has the same composition as that of the example.
2. The resulting curve representing the penetration as a function of temperature for the propellant charge is shown at P4 in fig. 7. This propellant charge exhibits a penetration of approximately 22 at 21 C and a pene sensitivity. tration of about 0.0137.



   This propellant charge is plastic over a wide range of temperatures, wider than that described in Examples 1 to 3 inclusive. The improvement in the penetration sensitivity is due to the fact that the oil in the mixture has a paraffinic nature and exhibits a relatively high viscosity index (100).



   Rockets fitted with this charge and constructed substantially in the same way as -described in FIG. 3 have been shown to function satisfactorily over a temperature range of -11 to 50 C. Temperature limits are indicated by x's on the penetration versus temperature curve.



   Example 5: A propellant of the same composition as in Example 3 below is prepared, except that "Pure Penn Oil" is used instead of "Aristo" oil. This propellant charge has a penetration of 45 to 21 C and a penetration sensitivity of 0.0116. This propellant charge operates safely between -20 and 40 C.

 <Desc / Clms Page number 27>

 



   Example 6 A propellant charge is prepared from a fuel composed of 85% asphalt called “Economy” and 15% pure Penn Oil. ”The penetration curve as a function of temperature is shown for this. propellant charge through line P6 in Fig. 7. This propellant charge has a penetration of about 20 to 21 ° C and a penetration sensitivity of about 0.0065.



   The rockets are coated and loaded according to the methods described above, and these rockets are found to operate safely above -7 C. However, the upper safe temperature limit has not been exceeded. could be determined, although it is well above 50 C.



   The asphalt called "Economy" is manufactured by the Company known as: Whishire Oil Company (Los Angeles, California) from crude oil extracted at Ojai California.



     RANGE OF OPERATION
It will be noted from the preceding examples that, when the penetration of a propellant charge falls below approximately 6, that is to say below a value between 4 and 8, the propellant charge becomes so brittle that failures can easily occur. Likewise, if the penetration becomes significantly greater than about 100, the propellant becomes too liquid to operate safely. When using these propellants in their service condition, the penetration should be between about 8 and 80, or even between 10 and 75.



   The penetration at the average temperature of the safe operating range for each of the propellant charges studied in Examples 1 to 6 is designated by small

 <Desc / Clms Page number 28>

 circumferences on curves indicating penetration as a function of temperature. From these data it becomes evident that, if rockets loaded with a given propellant charge are to be used over a given temperature range which depends on atmospheric conditions or similar conditions influencing the ambient operating temperature. , this load must have a penetration of approximately
25 (that is to say between approximately 20 and 30) towards the middle of its operating range.

   The propellant charge should preferably have a reduced penetration sensitivity. This low penetration sensitivity can be achieved, for example, by using as fuel a mixture of high viscosity paraffin oil and mixed asphalt, such as those obtained from crude oils of
Mexico or central,. RECONDITIONING OF LOADED TRACKS
Rockets loaded with a thermoplastic mixture can be safely used if they have been stored without impact at temperatures within the operating range of each individual propellant charge.



   If, for some reason, the rockets have been subjected to temperatures outside this range for a significant period of time, or have been roughly handled during transport, they can be repackaged by subsequent storage at a suitable temperature within. this garnished.



   As another aid for the reconditioning of the rocket, it can be packed down by dropping it on its bottom. The length of the reconditioning period required will depend on the conditions to which the rocket was previously subjected.

 <Desc / Clms Page number 29>

 and the temperature at which this reconditioning is carried out.



   Satisfactory regeneration of this type by heat treatment of the propellant charge is made possible by the thermoplastic nature thereof. The loads easily remain in a safe operating condition partly because of ductility, which allows the load to maintain its mass, and partly because of these plastic flow characteristics.

   When storing a rocket of the type described with the axis of this rocket in the normal storage position, that is to say vertical, the plastic propellant charge tends to flow slowly under the 'influence of its own weight and at a speed which depends on its temperature, both by plugging, thus all the cracks which could exist on the surface of this load or in its mass, and by making it also adhere to the bedroom wall.

** ATTENTION ** end of DESC field can contain start of CLMS **.


    

Claims (1)

CONCLUSIONS In general, the range of temperatures in which a propellant can be used with a high degree of safety can be varied by including a suitable emollient or plasticizer in the thermoplastic component. In the case of Floatine S asphalt, Examples 1, 2 and 3 show how the average temperature of the safe operating range can be shifted by the incorporation of a naphthenic base oil. Examples 4, 5 and G show how propellant charges exhibiting lower sensitivity, and hence operating ranges <Desc / Clms Page number 30> larger, 'can be obtained by adding paraffin-based oil. of high viscosity index to an asphalt with which it is compatible. In general, asphalts oxidized by air blowing are more satisfactory, than asphalts refined by air, for the applications envisaged, because they have lower penetrating capacities or higher flow temperatures. All these fuels derive their satisfactory property from the fact that a large proportion of bituminous or asphaltic hydrocarbons are suspended in the oil and give it a plasticizing effect. Although the invention has been embodied by referring specifically to fuels formed by mixtures of asphalt and asphalt-based oil, it will be understood that thermoplastic propellants can be prepared. satisfactory from other fuels with suitable combustion characteristics and comparable plasticity. Materials which can be used as fuel. These include cup lubricating grease, gummy-type vegetable oils, mixtures of coal tar and ethyl cellulose, mixtures of various asphalts and other combustible thermoplastics. Other oxidants can also be used. By charging a container (or cartridge) designed to form part of the combustion chamber of a rocket with a suitable penetrating thermoplastic propellant charge within the operating range, one can obtain certain limited combustion. This loading is preferably carried out by casting the propellant charge in the <Desc / Clms Page number 31> high temperature rocket. In the preferred embodiment of the invention, the container is provided with a thermoplastic coating which does not contain an oxidant less harsh than the propellant charge itself, and which is designed to adhere to both this charge and to the wall of this container. These coatings increase the operational safety of the rocket at extreme operating temperatures and particularly at low temperatures, owing to their limited combustion characteristics, which is certain to be achieved for long periods after firing. loading, rockets loaded with these propellants have an extremely safe operation, and at the same time provide a high efficiency of use of the thermal energy of these loads, particularly for the sit-down take-off. - summer. It will be noted diaprés the above that is obtained, better propellant charges and rockets designed to obtain limited combustion, as well as a simple process for preparing these charges and loading these rockets. CLAIMS 1. - Rocket equipped with a combustion chamber, characterized in that the combustion chamber contains a thermoplastic propellant whose main ingredients are asphalt and a solid oxidant finely divided and intimately distributed in this asphalt, the The propellant charge being thermoplastic and exhibiting a penetration varying between about 6 and 100. ' 2. - Rocket according to claim 1, in which the proportion of solid oxidant varies from approximately 50 to 90% by weight. <Desc / Clms Page number 32> mixture of asphalt and oxidizer. 3. Rocket according to claims 1 and 2, characterized in that the finely divided solid oxidant is sodium perchlorate. 4. - Rocket provided with a combustion chamber according to claim 1, characterized in that it comprises a thermoplastic coating on the. internal wall of the chamber and a thermoplastic propellant charge filling the part of the chamber provided with this coating, 5, - Rocket according to claim 4, characterized in that the combustion chamber has' a closed end which is also provided on its internal face of a thermoplastic coating coming into engagement with the thermoplastic propellant charge filling the part of the chamber provided with this coating. 6. - Rocket according to claim 4, characterized in that the thermoplastic coating is designed to adhere to the propellant charge as well as to the wall of the combustion chamber, de.manière to connect this charge and this chamber. 7. - Rocket according to claims 1 and 4, characterized in that the propellant charge contains an asphalt-based fuel and an oxidant, while the coating connecting the propellant charge to the wall of the chamber contains an adhesive asphalt substantially cleared. oxidant and designed to prevent combustion of the side walls of the load. 8. - Rocket according to claim 1, characterized in that the thermoplastic propellant charge has a ductile consistency. 9. - Rocket according to claims 1 and 4, characterized 'in that the propellant charge contains a fine solid oxidant. <Desc / Clms Page number 33> sprayed,, suspended in a combustible mixture of asphalt and oil ,. while the coating consists of a mixture of asphalt and oil. 10. A rocket according to claims 1 and 8, characterized in that the oxidant, which is finely pulverized potassium chlorate, represents about 50 to 90% by weight of the. propellant charge, while the remainder of this charge is a combustible mixture of asphalt and oil. 11. - Rocket according to claims 1 and 4, characterized in that a portion of the surface of the propellant charge is arranged to be exposed in the open gap of the combustion chamber, while the coating material assembles the remaining surface of this load and the wall of the chamber, 12. - Rocket according to claim 4, characterized in that the coating forming a binder between the wall of the combustion chamber and the thermoplastic propellant charge is formed by a layer of thermoplastic material with relatively slow combustion. 13. - Rocket propellant charge according to claim 1, characterized in that it consists of a thermoplastic mixture of fuel and oxidant, the fuel being formed of two petroleum-based constituents having different viscosity characteristics. 14. A propellant charge according to claim 13, wherein the petroleum-based constituents of the fuel mixture are formed by an asphalt mixed with a low viscosity oil. 15. - Propellant charge according to claims 13 and 14, wherein the fuel mixture contains, to form one <Desc / Clms Page number 34> constituents, asphalt.oxidized by air blowing. 16. - Propellant charge. according to claims 13 and 14, characterized in that the oxidant combined with the fuel mixture contains at least about 50% by weight of fine particles of a solid material dispersed in the thermoplastic fuel. 17. - A propellant charge according to claim 13, characterized in that the thermoplastic fuel contains a normally solid oxidant and a solid organic material plasticized with a small amount of liquid solvent. 18. - Propellant charge according to claims 13 to 17, characterized in that it contains a mixture of which the major part consists of a material containing a large proportion of oxygen, the remainder, which is the smallest part, containing a material substantially free of oxygen, and these two materials being mutually combustible. 19. -Process for loading a rocket comprising a combustion chamber formed partially by a container, characterized in that it consists in providing: the wall of the container with a coating of thermoplastic material designed to adhere to this wall and to the load propellant, in pouring part of the propellant charge into a part of the container provided with this coating, and in allowing the poured part to cool to atmospheric temperature to form a charge bound to the container except in its upper part. 20. -Process for loading a rocket according to claim 19, characterized in that it consists in incorporating fine particles of a solid oxidant into a thermoplastic fuel. <Desc / Clms Page number 35> tick at high temperature, and pouring the resulting mixture into the container at high temperature, allowing it to cool there. 21. - Rocket, substantially as described and shown, and for the stated purpose. 22. - Rocket propellant charge substantially as described and for the stated purpose. 23. - Method of loading a rocket, substantially as described and for the established purpose. Brussels, April 14, 1948 P.Pon .. Company known as: A E R O J E T E N G I N E E R I N G .CORPORATION A. & P. HANSSENS Minister, We have the honor to let you know that on April 14, 1948 we applied for a patent in the name of the Company called: AEROJET ENGINEERING CORPORATION, for "Rocket, in particular for assisted take-off, and its charging process" and issued under the number 481.852. In this patent, FIG. 6 of the drawings schematically shows a plan of distribution of the main operations of a method for preparing a rocket according to the invention. The purpose of the present invention is to facilitate the reading of this diagram and there is appended the same figure comprising a brief summary of the main operations of the method of loading a rocket according to the description given to the specification of the aforementioned patent. The Administration is requested to attach a copy of this letter and of the drawing annexed thereto to the copy of the corresponding patent. For the good rule, it would be nice if you would acknowledge us receipt of this, stipulating that the rectification is admitted to be valid as of right and to return to us, at the same time, duly initialed by your department, the duplicate of the present and of said appended drawing, the original of which is intended to be attached to the patent file. We enclose herewith, in fiscal stamps, the regularization tax provided for by article 1 of the royal decree of August 29, 1926 amended by article 6 of the royal decree of June 30, 1933 as well as of article 1 of the decree of November 25, 1939. ± read you, please accept, Mr. Minister, the assurance of our highest consideration.