US3267721A - Apparatus for determining the burning rates of solid rocket propellants - Google Patents

Description

3,267,721 BURNING LANTS Aug. 23, 1966 K. H. JACOBS ETAL APPARATUS FOR DETERMINING THE RATES OF SOLID ROCKET PROPEL 2 Sheets-Sheet 1 Filed Nov. 15. 1963 5 1 W 5 1D mmkm N a s 5 R m rmm mHPE Jr whi e m w m s h Q P K 0 United States Patent "ice APPARATUS FUR DETERMINING THE BURNING RATES 9F SQLID ROCKET PROPELLANTS Kenneth H. Jacobs, Redlands, Calif., and Joseph Pinsky, Skokie, and Philip Rosenberg, Highland Park, Ill., assignors to the United States of America as represented by the Secretary of the Army Filed Nov. 15, 1963, Ser. No. 324,142 1 Claim. (Cl. 7335) This invention relates to the design of an apparatus for determining the burning rates of solid rocket propellants or similar materials at various pressures.

The use of solid propellants in the rocket and missile field is widespread and particularly in the field of rocket assisted projectiles and boosters. In order to be able to accurately predict the performance of such devices it is necessary to know the burning rates of the solid propellants at various pressures. The pressures at which the propellant burns in use depends upon the design of the particular rocket in which it is used.

Previous research has been conducted in which the burning rates of solid propellants at relatively low pressures were determined using different gaseous atmospheres to develop the pressures. These tests established that the burning rates were substantially diiferent for different gaseous atmospheres. In view of this it is apparent that it is necessary to establish burning rates by burning the propellants in an atmosphere of their own gases as would occur in operation.

The apparatus of this invention is comprised essentially of an expansion chamber, a smaller elongated test chamber adjoining the expansion chamber, a number of timing devices fastened at intervals along the length of the test chamber, a pressure gauge and means for igniting the propellant to be tested.

An object of the invention is to provide a testing device for determining the burning rate of solid propellants.

Another object of the invention is to provide a testing device for determining solid propellant burning rates at different pressures.

Another object of the invention is to provide a testing apparatus for solid propellants having a pressure measuring means and spaced timing means to measure the rate of burning of the propellants.

Yet another object is to provide a testing device for determining the rate of burning of solid propellants in an atmosphere of their own gases.

These and other objects of the invention will be more apparent when reference is had to the following detailed description and drawing in which:

FIGURE 1 is an axial sectional view of the test apparatus,

FIGURE 2 is a schematic diagram of the apparatus for recording the pressure and rate of travel of the flametront, and

FIGURE 3 is a schematic showing of one part of the thyratron bridge of FIGURE 2.

The test apparatus or burning rate bomb of the present invention comprises in general two sections, an expansion chamber section and a propellant and test chamber section.

The expansion chamber section is indicated in general in FIGURE 1 by reference character 1 and has a generally cu-p shaped body 2. The body 2 is externally threaded at 3 and is counterbored at 4 and further counterbored at 5. Extending through the body at spaced points are the apertures 6 and 7. Threaded into the aperture 6 is the pressure gauge 8 which may be of any known type, such as for example, an electrical resistance ferrule type. The aperture 7 threadedly receives the ignition 3,267,721 Patented August 23, 1966 member which has the body portion 9 and the sealing washer 10 is clamped between the ignition member and expansion chamber body 2. Ignition current is carried through conducting rod 11 which is insulated from the body portion 9 by Micarta 12. The ground connection for the igniter is indicated at 13 and is connected to the stud 14 which is carried by the body 2 of the expansion chamber.

The propellant and test chamber section is indicated in its entirety at 15 and is generally bottle shaped. The larger end of this chamber carries the flange 17 which is received in the bore 4 of the expansion chamber. The sealing ring 18 is mounted between the flange 17 and expansion chamber body 2 in the counterbore 5 and the chambers are clamped together by means of the threaded member 19.

The body portion of the propellant and test chamber is enlarged at 20 to form the large diameter chamber 16 which forms a part of the expansion chamber and has the reduced elongated neck section 21 which forms the small diameter test chamber 22. The end of the test chamber is sealed off by threaded cap 23 and sealing washer 24. Threaded into the neck portion 21 at axially spaced points are the three timing terminals 25 which communicate with the test chamber by means of apertures 26. Each timing terminal includes a central conductor rod 27 having a head portion 28 which is insulated from the body portion by Micarta 29.

Operation In operation a quantity of solid propellant P is placed in test and propellant chamber 15 so as to fill the test chamber 22 and at least partially fill the enlarged chamber 16. The quantity is varied and it has been found that by varying the distance S different pressures can be obtained within the bomb. The bomb is then closed and sealed and the ignition member 9 fired. By use of a small quantity of black powder or the like this ignites the solid propellant P. It has been found that due to the large size of chamber 16 and the relatively small size of chamber 22 that the propellant in expansion section 16 burns and produces a certain pressure in the two sections and after the flame front has entered the relatively small volume of test chamber 22 the subsequent pressure rise is small and the test portion of the propellant burns at an essentially constant pressure. The pressure attained is measured by pressure gauge 8.

As the propellant burns ionic gases are formed and these gases are effective to close the circuit between the timer conductor heads 28 and the bomb case 21 which is grounded. Thus, as the flame front travels along the test section chamber 22 the circuits including the timing terminals are successively closed and by accurately measur ing the time interval between closing of these circuits and knowing the distance between the terminals the rate of burning can be accurately determined.

FIGURE 2 illustrates a circuit for recording the pressure and time of closing of the timing terminals. There is provided a two channel oscilloscope recorder 30 and the oscilloscope screens are photographed by a high speed camera. The pressure gauge 8 is of the electrical resistance ferrule type and is one leg of a Wheatstone bridge. The signal from this bridge is applied to one channel of the oscilloscope recorder through line 31. The burning rate bomb body is grounded as indicated at 32. At 33 there is schematically shown the oscilloscope control and power supply. A thyratron bridge is shown at 34 and leads 35 connect the timing elements 25 to the bridge. Batteries 36 are included in the lines 35. Successive signals from the thyratron bridge are conducted through line 37 to the second channel of the oscilloscope recorder.

FIGURE 3 shows the timing circuit which forms a part of the circut shown in FIGURE 2. The potential at point A is held at minus 9 volts by the battery 40. The thyratron tube is set to fire at minus /2 volt. When the circuit is closed by the presence of ionized gases at timing terminal 25 the thyratron will fire since the potential at A will be about plus 67 /2 volts as applied by the battery 39. The firing of the thyratron tube is then recorded on the oscilloscope as a break in the line. The thyratron bridge 34 as shown in FIGURE 2 will contain three of the circuits as shown in FIGURE 3 for the three timing terminals, each providing its signal to line 37.

An alternative method for measuring the timing is to connect each timing terminal by way of a resistance to a balanced Wheatstone bridge. When the timing terminals are closed by the ionized gases the bridges are unbalanced and provide signals. In this arrangement separate oscilloscope channels are required for each timing terminal.

It will be apparent that the embodiment shown is only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claim.

We claim:

An apparatus for determining the burning rate of a propellant comprising in combination, a cup shaped body forming a first part of an expansion chamber and having external threads and a counterbore at its open end, a tubular body having open ends and adapted to receive a solid propellant for testing therein, said tubular body defining an enlarged portion adapted to fit snugly within said first part of said expansion chamber and forming the second part thereof, said tubular body diverging towards one end to form an elongated test chamber of uniform dimension throughout and of smaller diameter than said second expansion chamber part, there being an external, annular flange on said tubular body and being disposed adjacent said divergence, said flange adapted to fit snugly within said counterbore in said cup shaped body, sealing means between said flange and said cup shaped body, a threaded collar adapted to tightly secure said tubular body in said cup shaped body, a closure cap for threadalble engagement with said elongated test chamber, pressure sensing and igniting means in said expansion chamber, a series of longitudinally spaced, timing terminals in communication with said elongated test chamber, each terminal including a member threadably secured therein and a conductor carried by and insulated from said member whereby ionic gases caused by combustion of said propellant is effected to form a closed electric circuit between said conductor and said test chamber, and electric circuitry in connection with said pressure sensing means, said igniting means and said terminals, said circuitry including a power supply for energizing said igniting means and indicating pressure from said pressure sensing means, and means in said circuitry for recording the time of said closing of an electric circuit by said ionic gases including a thyratron tube connected to each said conductor in each said terminal and fired by said circuit closing and an oscilloscope connected to said thyratron tubes.

References Cited by the Examiner UNITED STATES PATENTS 2,395,902 3/1946 Nisewanger et al. 7335 X 2,925,729 2/1960 OBrien 73-35 3,191,426 6/1965 Wilhite et al. 7335 RICHARD C. QUEISSER, Primary Examiner. JAMES J. GILL, Examiner.

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