## Richard Nakka's *Experimental Rocketry* Web Site

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### Example of Chamber Pressure Calculation due to Igniter Charge Combustion

Consider the rocket motor and igniter shown in the figure above (dimensions are inches).

The motor chamber volume is Vc = p/4 (3) ^{2} (12) = 85 in^{3}

And the grain volume is Vg = p/4 (2.75 ^{2} - 1 ^{2} ) 11 = 57 in^{3}

Therefore the free volume is V = 85 - 57 = 28 in^{3}

The igniter volume is Vi = p/4 (0.5) ^{2} (2) = 0.39 in^{3}

The charge material is Black Powder (non-commercial grade) with an impetus of 75000 ft-lb_{f} / lb_{m}

and has a mass density of 0.057 lb_{m} / in^{3}

Charge mass is C = 0.057 (0.39) = 0.022 lb_{m}

Loading density is D = 0.022 / 28 = 1 / 1273 lb_{m} / in^{3}

Let G = 1 since we are interested only in the maximum pressure that results from the charge combustion

The ambient pressure is Pa = 14.7 psia

The effective force is l = 75000 (12) = 900 000 in-lb_{f} / lb_{m}

This gives the resulting chamber pressure of

#### Last updated July 1, 1999

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