NAR HPR Propulsion Systems & Motor Handling 2 — Questions and Answers
Question 1: What does the letter 'I' in a motor designation like 'I211W' indicate?
- Total impulse between 320.01 and 640 N·s (Correct answer)
- The motor igniter type
- The propellant weight in grams
- The burn time in seconds
Correct answer: Total impulse between 320.01 and 640 N·s
The letter in NFPA 1125 motor designation indicates the total impulse range, with each letter doubling the previous; 'I' represents 320.01–640 N·s.
Question 2: When storing high-power rocket motors, what is the maximum quantity of propellant that may be stored in a Type 4 magazine under NFPA 1124?
- 50 lbs (22.7 kg) net explosive weight (Correct answer)
- 25 lbs (11.3 kg) net explosive weight
- 100 lbs (45.4 kg) net explosive weight
- 10 lbs (4.5 kg) net explosive weight
Correct answer: 50 lbs (22.7 kg) net explosive weight
NFPA 1124 allows up to 50 lbs net explosive weight (NEW) in a Type 4 storage magazine for consumer and high-power rocket motors.
Question 3: What is the primary function of the forward closure (nozzle end cap) in a reloadable motor casing?
- To seal the combustion chamber and retain forward thrust pressure (Correct answer)
- To hold the propellant grain in place during shipping
- To mount the motor in the rocket motor mount tube
- To provide a surface for attaching the ejection charge
Correct answer: To seal the combustion chamber and retain forward thrust pressure
The forward closure seals the aft end of the casing opposite the nozzle, containing combustion pressure and directing thrust through the nozzle.
Question 4: A motor with designation '29/180-360' on its casing refers to which specification?
- 29mm diameter casing rated for 180 to 360 N·s total impulse (Correct answer)
- 29-grain motor with a 180-second minimum and 360-second maximum burn
- A reloadable motor requiring 29mm nozzle throat and 360-grain propellant
- Certification number 29, version 180-360 from the NAR motor list
Correct answer: 29mm diameter casing rated for 180 to 360 N·s total impulse
This designation describes the casing diameter (29mm) and the range of reload total impulses (180–360 N·s) it is rated to accommodate.
Question 5: Which propellant type used in many high-power motors produces a characteristic white smoke and is known for high specific impulse?
- Ammonium perchlorate composite propellant (APCP) (Correct answer)
- Black powder
- Nitrocellulose single-base propellant
- Potassium nitrate / sugar (KNSB)
Correct answer: Ammonium perchlorate composite propellant (APCP)
APCP is the standard propellant for certified high-power motors, producing white exhaust and offering higher specific impulse than black powder.
Question 6: What safety practice must be followed when installing an electric igniter into a loaded motor before launch?
- Keep the igniter leads shunted until the moment before arming the launch controller (Correct answer)
- Connect the igniter leads to the launch controller as soon as installed
- Apply electrical tape over the igniter leads immediately after insertion
- Insert the igniter only after the rocket is on the launch rod
Correct answer: Keep the igniter leads shunted until the moment before arming the launch controller
Shunting the igniter leads prevents accidental ignition from stray electrical currents until the rocket is ready for controlled ignition.
Question 7: Under NAR safety codes, what minimum distance must spectators remain from a high-power rocket launch pad for an 'L' class motor?
- 1500 feet (457 m) (Correct answer)
- 500 feet (152 m)
- 1000 feet (305 m)
- 2000 feet (610 m)
Correct answer: 1500 feet (457 m)
NAR High Power Rocket Safety Code specifies a 1500-foot minimum spectator distance for L-class motors.
NAR HPR Propulsion Systems & Motor Handling 2
What does the letter 'I' in a motor designation like 'I211W' indicate?