NAR HPR Electronics & Avionics 3 — Questions and Answers
Question 1: What is the recommended method for securing an altimeter sled inside an avionics bay to prevent vibration damage?
- Hot glue along all edges
- Foam padding and standoffs with nylon screws (Correct answer)
- Cable ties looped through the tube
- Epoxy bonded directly to the airframe
Correct answer: Foam padding and standoffs with nylon screws
Foam padding absorbs vibration and shock while nylon standoffs and screws secure the sled without creating rigid stress points that could crack the board.
Question 2: Why do some NAR HPR flyers use two independent altimeters with separate battery supplies?
- FAA regulations require dual electronics on all Level 2 flights
- Redundancy ensures recovery deployment if one system fails (Correct answer)
- Two altimeters double the altitude measurement accuracy
- The second altimeter controls the motor ejection charge
Correct answer: Redundancy ensures recovery deployment if one system fails
Redundant independent altimeters with separate power supplies ensure parachute deployment even if one altimeter or battery fails during flight.
Question 3: What parameter do most barometric altimeters use to detect apogee?
- Accelerometer zero-crossing
- Rate of pressure change transitioning from decreasing to increasing (Correct answer)
- GPS altitude reaching maximum value
- Radio signal time-of-flight from the ground
Correct answer: Rate of pressure change transitioning from decreasing to increasing
Barometric altimeters detect apogee when atmospheric pressure stops decreasing and begins increasing, indicating the rocket has stopped climbing.
Question 4: What is the purpose of a 'motor delay' setting available on some avionics systems?
- It delays motor ignition after the launch button is pressed
- It prevents apogee detection for a set time to avoid triggering during fast coast phases (Correct answer)
- It adds time before the altimeter arms
- It pauses data logging during motor burn
Correct answer: It prevents apogee detection for a set time to avoid triggering during fast coast phases
A motor delay (or lockout time) prevents false apogee detection caused by pressure transients during the motor burn coast transition.
Question 5: Which connector type is most commonly used in HPR avionics bays for pyro circuit connections due to its positive locking mechanism?
- RCA phono connectors
- JST or Deans connectors with locking tabs (Correct answer)
- Standard headphone jacks
- Wire nuts
Correct answer: JST or Deans connectors with locking tabs
JST or Deans-style connectors with positive locking tabs resist vibration-induced disconnection and are compact enough for tight avionics bays.
Question 6: After a flight, a flyer notices their altimeter recorded a main deployment at 1,100 ft instead of the programmed 800 ft. What is the most likely cause?
- The altimeter battery was too weak
- The vent hole was partially obstructed, slowing pressure equalization (Correct answer)
- The e-match resistance was too high
- The drogue parachute tangled with the avionics bay
Correct answer: The vent hole was partially obstructed, slowing pressure equalization
A partially blocked vent hole delays pressure equalization inside the airframe, causing the altimeter to read a higher apparent altitude than actual.
Question 7: What is the correct action when an altimeter emits a rapid beeping sequence after powering on during pre-flight?
- Proceed to launch immediately while it self-calibrates
- Consult the altimeter manual — rapid beeping often signals an error condition (Correct answer)
- Remove and reinstall the battery to reset the code
- Cover the vent holes to re-zero the sensor
Correct answer: Consult the altimeter manual — rapid beeping often signals an error condition
Most altimeters use beep codes to communicate status and errors; a rapid or unexpected sequence must be decoded from the manual before flight.
NAR HPR Electronics & Avionics 3
What is the recommended method for securing an altimeter sled inside an avionics bay to prevent vibration damage?