US3115004A - Catapult launcher - Google Patents

Description

Dec. 24, 1963 A, c .uscURLocK 3,115,004

CATAPULT LAUNCHER Filed June 30, 1952 4 Sheets-Sheet 1 IN VENTOR ra/ l. Jalal/w15' AGENT Dec. 24, 1963 Filed June 30, 1952 PRESSURE A. C. SCURLOACK CATAPULT LAUNCHER 4 Sheets-Sheet 2 PBWn-s'z gunna:

ra/v Jams/704% Assur Dec. 24, 1963/ A. c.- scuRLocK 3,115,004*

vCA'IAPULT LAUNCHER l Filed June 30, 1952 4 Sheets-Sheet 3 AVERAGE ACCELERATION n: [2g 50o lbs DEAD LOAD IOO ,INVENTOR l'e Javi/M1 AGENT United States Patent O "ice 3,115,004 CATPULT LAUNCHER Arch C. Scurlock, Fairfax, Va., assigner to Atlantic Research Corporation, Alexandria, Va., a corporation ori Virginia Filed lune 30, 1952, Ser. No. 296,331 2 Claims. (Cl. oli-26.1)

This invention relates to an improved catapult device for launching planes or missiles.

The conventional catapult, in which the pressure in the combustion chamber is substantially the same as that in the catapult tube, possesses a number of disadvantages. Powder charges for such catapults can be designed so that the same charge can automatically launch varying dead weights to substantially the same acceleration. Ir" a change in the acceleration is desired, however, a different charge must be employed.

Another dificulty stems from the fact that it is sometimes desirable to maintain catapult tube pressures at levels below those at which many propellants will burn reliably. Although certain double-base propellants can be produced which will burn successfully at pressures down to about 3G() p.s.i., the range of propellant choice is greatly limited and, in some cases, it may be desirable to operate at even lower pressures in the catapult or piston tube.

The object of this invention is to provide catapult launchers which are designed in such a manner that they permit the launching of different dead loads at any desired acceleration within a range with the same propellant charge.

Still another object is to provide catapult launchers which can operate successfully with substantially any type of propellant powder charge, including those which require high pressures for reliable combustion.

Other objects and advantages will become obvious from the drawings and the following detailed description.

FIGURE l is a diagrammatic view of a longitudinal section through the catapult showing the essential features of the invention.

FIGURE 2 is a cross section taken along line 2-2 of FIGURE 1.

FIGURE 3 is a graph illustrating the relationship between combustion chamber pressure and orifice cross sectional area for a given propellant charge.

FIGURE 4 is a graph illustrating the relationship between orice cross sectional area and dead load for a given acceleration.

FIGURE 5 gives catapult performance curves for a given dea-d load and shows variation in acceleration and piston chamber pressure at different oriiice cross sectional areas.

The catapult of my invention comprises a combustion chamber which communicates with the catapult or piston chamber through a small oriiice, the throat area of which may be varied in any desired manner. As shown in the drawings, the combustion chamber is large enough to contain the solid propellant charge and, while providing some free volume, the free volume is substantially small relative to the size of the propellant charge. By reducing communication between the chambers to a small oriice for passage of the combustion gases, high pressures 3,ll5,@04 Patented Dec. 24, 1963 are maintained in the combustion chamber and relatively low pressures in the piston chamber.

In the drawings, 1 is the combustion chamber and 2 the propellant charge. The piston 4 is located in the catapult chamber 3. The walls 5 of the combustion chamber should be heavy enough to withstand the high pressures. Because of the lower pressures maintained in it, the walls 6 of the catapult chamber need not be as thick as those of the combustion chamber. The combustion gases pass from the combustion chamber into the piston chamber by way of a small oriiice 7. The cross sectional area of the orice may be varied as desired by any suitable means, as for example, by gate valve 8, which may be inserted into the orice or withdrawn by screw 9. The screw may be calibrated so that the Valve may be set for the desired orifice area. The valve may be recessed into slot itl until end Il is ush with the orifice wall. It will be understood that any suitable means for varying the cross sectional area of the oriiice may be employed.

By providing an orifice of sutliciently small maximum throat area, substantially any pressure within the relatively low range desirable for catapult propulsion may.

be maintained in the piston chamber while high pressures which ensure the rapid and reliable combustion of the propellant grain are maintained in the combustion chamber. A maximum oritice area from about 1 ten thousandth to 1 hundredth of the cross sectional area of the catapult tube is generally satisfactory for most purposes. However, the orifice may be proportionally larger or smaller depending on such factors as the desired differential in pressure between the two chambers and the like.

By varying the throat area of the oriiice, the pressure in the combustion chamber and the corresponding pressure in the piston chamber can be controlled and varied in such a manner that different dead loads can be moved at any desired acceleration with the same propellant charge. In other words, the same dead load may be launched at different accelerations; different loads may be launched at the same acceleration; and both the load and the acceleration may be varied. The orice cross sectional area is set at the predetermined size prior to combustion of the charge and remains in this position until launching of the particular load is completed.

Decreasing the throat area of the orice causes an increase in pressure in the combustion chamber which, in turn, causes a marked increase in burning rate of the propellant charge. The resulting increase in combustion chamber pressure is considerably larger proportionately than the decrease in orilice throat area. Neglecting such minor factors as the density of the propellant gas and the free volume in the combustion chamber, the relationship between the pressure in the combustion chamber and the oriiice throat area may be expressed as follows:

1 P 1 ati-.i

where Pc is the pressure in the combustion chamber, A, is the orifice throat area and n is the burning law pressure exponent for the particular propellant composition used. In the case of the usual propellant having a burning law pressure exponent of about 0.5, the relationship is ap- In other words, reducing the throat orifice area by half produces approximately a four fold increase in combustion chamber pressure. Doubling the throat orifice area decreases the chamber pressure to approximately one fourth of its original value.

In the case of a propellant charge having a burning law pressure exponent which is less than 0.5, the Value of the exponent will be greater than 2. Where the burning law pressure exponent is higher than 0.5, the value of will be correspondingly lower. Since the value of lz for any practical propellant charge is always less than 1, the value of is always higher than l.

It would appear that the decrease or increase in orifice throat area causes a corresponding and directly proportional decrease or increase, respectively, in the mass flow rate of the powder gases from the combustion chamber into the piston chamber. The relationship between the mass flow rate of the powder gases m, the pressure in the combustion chamber Pc, and the orifice throat area At is as follows:

m=CDPcAt where the constant of proportionality CD is known as the nozzle coeticient.

However, since the combustion chamber pressure increases or decreases at a considerably greater rate than the corresponding decrease or increase in orice throat area, substituting the values of Pc for dilferent values of At results in a net overall increase or decrease in the mass flow rate of the powder gases for decreased or increased values of At, respectively. Increasing the mass flow rate of gases increases the effective pressure in the piston chamber and, conversely, decreasing the mass flow rate of the gases through the orice decreases the effective pressure in the piston chamber.

For the case of constant acceleration, the equation of motion is as follows:

where P is the pressure in the piston tube, W is the effective gross weight of load in motion, a is piston acceleration, A is the cross sectional area of the catapult tube and g is the conversion factor from pounds of force to poundals (32.2 poundals/1b.). Thus an increase in the pressure in the piston chamber may be utilized to increase the acceleration for a given load, to move a larger load at the same acceleration or to vary both the load and the acceleration. Conversely, a decrease in piston chamber pressure may be utilized to decrease the acceleration for a given load, to move a lighter load at the same acceleration or to vary both factors.

The equation which relates conditions in the combustion chamber with those in the piston chamber is as follows:

PAat NRTCDAL gas per unit mass, R is the gas constant and T is the gas temperature in the piston chamber. Substituting will Ag for P,

z lVa'lt NRTCD/ltg The latter equation shows that the pressure in the combustion chamber is proportional to the weight of the load times the square of the acceleration and that these two factors may be varied as desired by changing the combustion chamber pressure. Since the combustion chamber pressure may be controlled in a predetermined manner by varying the orifice cross sectional area, it will be seen that, by changing the latter, different dead loads may be launched at any desired acceleration with the same propellant charge.

Practical limitations are imposed by the sufficiency of the charge or its economical utilization. The weight of the load and acceleration may be increased to the point where the given propellant charge may be consumed bcfore the piston has travelled the full length of the tube. Under these conditions a larger charge with an increased available burning distance would be desirable. On the other hand, the load and acceleration may be reduced to the point of such incomplete utilization of the charge as to cause an undue amount of waste of propellant material. In such a case, a smaller charge with a decreased available burning distance would be more economical.

FIGURE 3 shows the relationship between orifice cross sectional area and combustion chamber pressure for a given propellant charge. The propellant employed in this case has a burning law pressure exponent of about 0.5. The considerably greater rate of change in combustion chamber pressure as compared with the rate of change of orifice cross sectional area is clearly illustrated. The powder grains used were designed for ideal operation with a dead load of lbs., an orifice cross sectional area of 0.019710 in?, an initial gas pressure in the combustion chamber of 0 p.s.i. and a nal gas pressure of 20,000 p.s.i.

FIGURE 4 illustrates the changes in orifice throat area required to give the same average acceleration to different loads while using the same powder charge.

FIGURE 5 gives the performance curves for a catapult operating with a given weight load of 150 lbs. at different orifice throat areas and the same powder charge. It shows the increase both in piston chamber pressure and in load acceleration obtained by decreasing the size of the orifice and vice versa. The powder grains employed here are the same as those used in FIGURE 3.

A comparison of the combustion chamber pressures as shown in FIGURE 3 and the piston chamber pressures as shown in FIGURE 5 clearly illustrates the relatively low pressures which may be maintained in the piston chamber while high pressures, which ensure reliable burning of the propellant at a high combustion rate, are maintained in the combustion chamber by means of the reduced orifice. Thus substantially any type of propellant charge, regardless of the pressures required for reliable combustion, may be employed in the highlow pressure catapult.

An important advantage of the high-low pressure catapult stems from the fact that it does not require propellant grains designed to give such high progressivity as those required by the conventional catapult so that standard perforated grains may be adequate for ecient operation of the former.

Although this invention has been described with reference to illustrative embodiments thereof, it will be apparent to those skilled in the art that the principles of this invention may be embodied in other forms, but Within the scope of the appended claims.

Iclaim:

1. In a catapult launcher, means forming a combustion chamber for a solid propellant charge, the combustion chamber being characterized by a substantially small free volume relative to the propellant charge, and means forming a piston chamber, said combustion chamber opening directly into said piston chamber through a restricted orice having a maximum cross sectional area which is substantially smaller than that of said combustion chamber, and a valve which is operable to adjust said orifice to a predetermined cross-sectional area prior to combustion and which remains fixed throughout the launching cycle.

2. The catapult launcher of claim 1 in which the orifice has a maximum cross-sectional area which is about one hundredth of the cross-sectional area of the combustion chamber.

References Cited in the lle of this patent UNITED STATES PATENTS 1,161,744 Sparre Nov. 23, 1915 1,535,475 Jeansen et al Apr. 28, 1925 1,935,123 Lansing Nov. 14, 1933 2,289,318 Pratt July 7, 1942 2,289,766 Fieux July 14, 1942 2,555,333 Grand et al June 5, 1951 2,670,596 Whitworth Mar. 2, 19,54 2,723,528 Stark Nov. 15, 1955 FOREIGN PATENTS 441,053 Great Britain Jan. 6, 1936

Claims (1)

1. IN A CATAPULT LAUNCHER, MEANS FORMING A COMBUSTION CHAMBER FOR A SOLID PROPELLANT CHARGE, THE COMBUSTION CHAMBER BEING CHARACTERIZED BY A SUBSTANTIALLY SMALL FREE VOLUME RELATIVE TO THE PROPELLANT CHARGE, AND MEANS FORMING A PISTON CHAMBER, SAID COMBUSTION CHAMBER OPENING DIRECTLY INTO SAID PISTON CHAMBER THROUGH A RESTRICTED ORIFICE HAVING A MAXIMUM CROSS SECTIONAL AREA WHICH IS SUBSTANTIALLY SMALLER THAN THAT OF SAID COMBUSTION CHAMBER, AND A VALVE WHICH IS OPERABLE TO ADJUST SAID ORIFICE TO A PREDETERMINED CROSS-SECTIONAL AREA PRIOR TO COMBUSTION AND WHICH REMAINS FIXED THROUGHOUT THE LAUNCHING CYCLE.

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