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300 400 600 1000 2000 3000 Chamber pressure, psi

FIGURE 11-6. Plot of the burning rate versus chamber pressure for several typical solid rocket propellants, some at three different temperatures. A particular double base plateau propellant shows a constant burning rate over a fairly wide pressure range.

Example 11-1. Tabulate the variation of burning rate with pressure for two propellants with a\ = 0.00137, = 0.9, a2 = 0.060, and n2 = 0.4, with p expressed in pounds per square inch and r in inches per second.

SOLUTION. Use Eq. 11-3 and solve for several conditions, as shown below.

500 0.367 0.720

1000 0.685 0.95

1500 0.994 1.11

2000 1.28 1.26

2500 1.56 1.33

From inspection of these results and also from Eq. 11-3, it can be seen that the burning rate is very sensitive to the exponent n. For stable operation, n has values greater than 0 and less than 1.0. High values of n give a rapid change of burning rate with pressure. This implies that even a small change in chamber pressure produces substantial changes in the amount of hot gas produced. Most production propellants have a pressure exponent n ranging between 0.2 and 0.6. In practice, as n approaches 1, burning rate and chamber pressure

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