National Association of Rocketry (NAR) codes, such as C6-3, appear on hobby rocket motors, as follows:
· The letter, which can be from 1/2A to K, specifies the total impulse, with C indicating 5.01 to 10.00 N s. A letter's range is double that of its predecessor, so that an impulse in the range of 1/2A is the smallest, and that in the range of K is the largest. Thus, the total impulse for rockets with letter B is from 2.51 to 5.00 N s.
· The subsequent number, such as 6, indicates average thrust (in newtons). The average thrust with total impulse indicates the length of time over which the motor releases its total energy.
· The number after the dash, such as 3, gives time delay (in seconds), or the time from motor burnout until activation of a recovery parachute. During that time, the rocket coasts to a higher altitude and slows.
For the following questions involving total impulse, use the higher range value, such as 10.00 N s for type-C motors.
a. Approximate the length of time for which a C6-5 motor delivers its energy.
b. Repeat Part a for a C4-5 motor.
c. Repeat Part a for a C10-5 motor.
d. Repeat Part a for a C5-3 motor.
e. Which of the preceding three engines is most powerful?
f. The C5-3 burns 12.7 g of propellant. Calculate its specific impulse.