NAR HPR Propulsion Systems & Motor Classification 3

Question 1

What is 'specific impulse' (Isp) as it applies to rocket motors?

Accepted Answer

A measure of propellant efficiency expressed in seconds

Answer

Specific impulse (Isp) measures propellant efficiency as thrust produced per unit weight flow of propellant per second, expressed in seconds.

Question 2

Which motor thrust curve type delivers the majority of its thrust near the beginning of the burn?

Accepted Answer

Regressive

Answer

A regressive thrust curve delivers peak thrust early in the burn, which then decreases as the propellant grain burns away.

Question 3

For NAR Level 2 certification, what is the maximum motor class a certified rocketeer may purchase and fly?

Accepted Answer

L

Answer

NAR Level 2 certification authorizes the purchase and use of motors up through and including L-class (total impulse up to 10,240 N-s).

Question 4

What is the function of the forward closure in a reloadable motor casing?

Accepted Answer

It seals the nozzle end of the motor and retains the propellant grain

Answer

The forward closure seals the forward (top) end of the motor casing, retaining chamber pressure and the propellant assembly.

Question 5

Which of the following best describes a 'progressive' thrust curve?

Accepted Answer

Thrust increases throughout the burn as the grain surface area grows

Answer

A progressive thrust curve shows increasing thrust over the burn duration due to a grain geometry that exposes more burning surface area as it burns.

(NAR HPR) NAR High-Power Rocketry Certification Practice Test