End-burning grains

The mechanical and physical properties of the inhibiting material must be fairly similar to those of the propellant in order to minimize the differential expansion. In this respect the use of several layers with possibly different compositions is favorable. With long burning timers (more than 20 sec) the development of a reliable inhibitor poses a fairly difficult problem, especially with end-burning grains. 

The use of solid, end-burning grains containing axially oriented wires is a particularly attractive way of utilizing the technology of fine metal wires to increase burning rate. 

For the actual compositions tested, the theoretical values were somewhat lower than optimum. In all, 18 acetylenic polyurethane propellant grains were test fired in small motors. These ranged in weight from 0.40 to 6 lb. and included both 3-inch and 6-inch diameter end-burning grains. Motor firings are reported in Table III for a 77.8% oxidizer-loaded composition having a theoretical hp of 249 seconds. These can be compared... 

Fig. 14.19 shows a typical set of pressure versus time curves obtained from tests on a rocket motor. When the I/D ratio defined in Fig. 14.19 is increased, the head-end chamber pressure is increased drastically immediately after the ignition stage. These grains are seven-pointed-star-shaped neutral-burning grains (diameter D = 114 mm), and are made of an AP-Al-CMDB propellant with the composition nc(0-25), ng(0-31), Ita(0-08), ap(0-27), and ai(0 09). The ratio of the initial burning surface area (Ayg) to the nozzle throat area (Aj), = AygjAp and the ratio of the... 

When the propellant grain burns in an end-burning type of rocket motor in which L changes from 4 m to 20 m during burning, typical pressure-time records are as shown in Fig. 9-18. In zone I, pressures above 3.7 MPa, the burning is very stable as expected. In zone II, where the pressure exponent is approximately unity, a... 

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