L2 Written Exam Study Guide

Overview

Getting an L2 certification consists of two parts: successfully launching and recovering your L2 rocket, and passing a written exam.

The NAR website has a pool of all possible exam questions. Because a fair number of these questions rely on only a few concepts, this article serves as a summary of the information needed to pass the written exam. The notes below are abbreviated because reading lots of words is gross. If something doesn't make sense, this is the original NAR question pool. 

Sections of the Written Exam: (linked are the practice exams for each section. The fractions refer to the number of questions there will be out of the total number of questions in that section.)

• Section A: Applicable Regulations (10/22)
• Section B: Storage Requirements (1/3)
• Section C: Range and Safety Practices (20/55)
• Section D: Rocket Stability (3/8)
• Section E: Rocket Motor Designations (2/9)

Summary of Concepts in the NAR Question Pool

Random things u should know (you don't have to know it to pass the exam but ya should know it)

• HPR = high-powered rocketry
• FAR = Federal Aviation Regulations
• NFPA = National Fire Protection Association
• CATO = catastrophe (catastrophic failure of a launch - for example, the motor explodes)
• LCO = launch control officer
• RSO = range safety officer
• CP = center of pressure
• CG = center of gravity

Answers are in blue. Particularly important things to know (not just for the exam, but in general) are in orange.

Section A: Applicable Regulations (*N-s = Newton-seconds)

Rules, rules and more rules

• Govt. code for HPR: NFPA 1127
• Part of FAR governing rocket activity: Part 101
• A person shall fly HPR only in compliance with: NFPA 1127, FAR Pt. 101, federal, state and local laws
• FAR 101 requires ___ for an FAA waiver: "All of the above" (there are a lot of options so check out the question pool cause I'm too lazy to type them all out)
  

Explosives are fun but dangerous

• Per AFT Explosives Law + Regulations, black powder is considered: low explosive 
• Purchasing an "L" motor: does NOT require an Explosive User's permit
  

Being old enough to do things

• To launch HPRs: must be minimum 18 years of age
• Min age for explosive permit application: 21 years

I can't "weight" to get my L2 Cert!

• Max launch weight allowable for rocket (no FAA waiver): 3.3 pounds (1500 grams)
• Max propellant weight allowable for rocket (no FAA waiver): 4.4 ounces (125 grams)
• Max launch weight when complying w/ FAR 101 (no waiver): 3.3 pounds (1500 grams)
• Max allowable weight permitted in HPR per NFPA 1127: There is no limit, provided the rocket weighs less than 1/3 of the average certified thrust of the motors intended to be ignited at launch

It's ok to be "impulsive" 

• Max total impulse allowable for rocket (no FAA waiver): There is no impulse limit (the limit does not exist! lol)
• Max total impulse permitted in HPR per NFPA 1127: 40,960 N-s*
• Definition of HPR motor: total impulse more than 160 N-s

Definitions and other things

• Which characteristic does NOT meet definition of HPR: The motor uses a "composite" propellant (i.e. your rocket doesn't need to use a composite propellant to be considered a high-powered rocket)
• Which is true for complex HPR per NFPA 1127: The rocket is multi-staged or propelled by a cluster of rocket motors
• Launch site contains: launching, recovery and parking areas (so "All of the above" on the exam)
• Which is true concerning the definition of hybrid rocket motors? fuel is in a different physical state than the oxidizer
• Which (hypothetical) rocket motor is NOT an HPR: G35 with 66 grams of propellant

Section B: Storage Requirements

• Max net weight of regulated materials that may be stored in an Indoor Type 4 magazine: 50 pounds
• NOT a requirement for an indoor magazine: writing "50 POUND MAXIMUM" on it
• According to NFPA, where may an Indoor Type 4 magazine be permitted. assuming the authority having jurisdiction and the BATF approve? In the attached garage of a single-family residence

Section C: Range and Safety Practices (the long section)

General launch day know-how

• Max launch angle (from vertical) for HPR: 20 degrees
• Max wind velocity allowable for launch ops: 20 miles per hour
• When higher winds cause the rocket to drift into the neighboring fields: limit flights to lower altitudes AND move launchpad closer to the wind source AND don't fly on days w/ problematic winds
• If you're on a 1500 x 1500 ft field with an FAA waiver up to 3000 ft AGL, and parachutes that slow the rocket to 20 ft/s: max wind speed should be 6 mph if the pads are upwind and the rocket vertical

Being safe on launch day

• When may onboard energetics and/or electronic controls be activated and when shall they be inhibited? Inhibited until in launching position and prior to removing from launch position. May be activated when non-essential personnel leave the pad area
• What equipment is required at launch sites? Fire suppression devices, first aid kits and a method of communicating with everyone on the launch site
• When flying an unproven design, it is not acceptable to: fly it as a "head-up" flight on the first flight
• Your HPR lands in a power line: you must leave it alone and call the power company
• Prohibited activity on launch day: consumption of alcohol, use of medication that could affect judgement, movement or stability
• Store HPR, motor reloading kits and pyrotechnics: at lease 25 feet from smoking, open flame, etc.

Going the distance

• For a launch site with min. dimensions = 1500 ft, the minimum distance between launch site boundary and the launcher (for a 320 N-s motor) is: 100 ft. AKA the "minimum personnel distance"
• Minimum personnel distance for O-impulse cluster: 2000 ft
• Min launch site dimensions: >/= 1/2 max expected altitude OR 1500 ft, whichever is larger
• Min distance allowable between HPR launch pad and freeway: 1500 ft
• Min safe distance from HPR with "I" motor: 1500 ft
• Min safe distance from HPR with 3 x "H" motors: 200 ft
• Min safe distance from HPR with 2 x "K" motors: 500 ft
• Distance around launcher for "J" powered model that must be cleared of easy-to-burn material, assuming the motor isn't "sparky": 50 feet
• (see above) for a 3-motor cluster of "J" motors, this must be: 75 feet
• (see above) for a single "J" motor that burns Ti (titanium) sponge to emit sparks: 75 feet

Ignite your passion for rocketry! (are you cringing at these puns yet??)

• Which of these igniters may be ignited by continuity test of some launch controllers? Flashbulbs, very low current electric matches
• Unless manufacturer instructs otherwise, igniters for clustered rocket motors should be wired together in: parallel
• When should igniters be checked for continuity? Only on the launch pad, while installed in a rocket motor
• When clustering combos of black powder and composite motors: composite motors ignited first (slower to ignite)
• If individual igniters are used for igniting clustered model's motors: launch control must provide additional current to ignite the additional igniters
• Advantages of using a "relay" type launch control: can deliver more power to motor igniters (shorter wires = higher power)
• Titanium sponge: ingredient used in some rocket motors that causes them to eject sparks in exhaust
• Not required feature of rocket motor ignition system: audible or visual indicator showing continuity through the rocket motor igniter

Under pressure

• Small hole is recommended near the top, below the nosecone/payload section in order to: vent internal pressure
• Parachute ejection system needs to vent to the outside for barometric readings in order to: give outside air pressure readings
• Parachute ejection systems that sense barometric pressure can malfunction during supersonic flight because: the outside pressure distribution is not continuous around the model

Things fall apart

• Most likely to cause CATO of black powder rocket motor: temperature cycling
• Petroleum-based lubricants should not be used with oxygen or nitrous-oxide systems used in hybrids. Why? Risk of spontaneous ignition or explosion
• Safety hazards associated with hybrid rocket motors: high pressure gas, low temperatures (frostbite)
• A rocket returned from flight with "zipper" damage (shock cord tears through the model) is caused by: parachute ejection occuring too soo, after motor burnout AND occuring too late after apogee
• A payload section (with a heavy payload) separates immediately after motor burnout. The cause: payload shoulder too loose AND rocket motor had failure of its delay system
• Consequences of inadequate motor retention: motor being ejected at apogee instead of the parachute AND motor being ejected from the cluster and flying on its own AND motor flying through the rocket, destroying it
• According to NAR, the vast majority of unsuccessful flights are because of: recovery system failures
  

Being responsible and all that

• If the range safety officer (RSO) says that your model is unsafe to fly: back to square one! The RSO's decision can't overturned by anyone.
• The final authority in permitting an HPR to fly is the: range safety officer (RSO)
• The ultimate responsibility to ensure that the rocket was built in a safe manner falls with the: rocket owner/builder (that's you!)
• When can launch organisers violate NAR safety code? When local laws are followed, and 2/3 NAR Board of Trustees give written permiss
•   
  

Glue and attaching things

• Preferred method of attaching fins: "through the wall" mounting
• Which adhesive should not be used on rubber (or elastic) shock cord? Superglue (CA) (CA = cyanoacrylate)
• Which adhesive is most likely to be weakened under humid/wet conditions? White "Elmer's" glue
• Best adhesive for motor mount construction w/ phenolic motor tubes? Slow-curing epoxy adhesives
• Best adhesive for strong joint (centering ring): Slow-curing epoxy adhesives

Section D: Rocket Stability

• For a rocket to be stable: the center of pressure must be behind the center of gravity (CP behind CG)
• An unstable rocket can be made stable by: adding sufficient weight to the nose cone
• Rocket stability can be measured by: determining the relative positions of the CP and CG
• A rocket's CP can be estimated by: the "Barrowman" method AND the "cardboard cutout" method
• An unstable rocket can be made stable by: increasing the size of the aft fins
• During boost, a rocket powered by solid rocket motors tends to become: more stable in flight
• Which can cause unstable flight? Weak tubes/couplers AND misaligned motor mount AND inadequate speed
• How far should the CP be from the CG? CP should be at least 1.0 body tube diameters behind the CG

Section E: Rocket Motor Designations

• General naming system for a motor:        H-5
  • Letter (H) = total power range or impulse range of the rocket motor
  • Number before the hyphen (100) = average thrust (Newtons) of the rocket motor. Divide by 4.45 to get the average thrust in pounds
  • Number after the hyphen (5) = ejection charge delay time (seconds)
• Total impulse = average thrust x burn time
• Assuming that each motor has the full allowable impulse, how many "H" motors have the same total impulse as a single "J" motor? 4
• H64-8 rocket motor with an impulse of 320.00 N-s has an approximate burn time of: 5 seconds (burn time = total impulse / average thrust.   Using this formula,  320.00N-s / 64N = 5 seconds)
• What impulse class is a 690 N-s motor? J class motor (see table below)
• Test data for a motor shows an average thrust of 100N for 6 seconds. What impulse class is this motor? Total impulse = average thrust x burn time, so 100N x 6s = 600 N-s (I-class motor)

This table shows the impulse corresponding to different class motors. Every letter signifies a doubling of impulse. The ones highlighted in blue are the ones that the written exam references, so you should know these (or you could always just memorize the answers to the questions but it helps to know the table)

That's the end of my notes! Now that you've reviewed these notes, scroll up and click on the links to take the practice exams!