L2 Exam

[AfterBurners]

For whatever reason I thought I would try and answer some of the exam questions for the L2 certification. I'm planning on building my L2 rocket, well it may be already built. So I went on NAR's website and down loaded the PDF. So for the last hour I tried my hardest to answer the questions on the 31 pages. I have not done any reading or studying prior to taking the practices test exam questions. I missed about a dozen questions which I think isn't too bad. Most of the ones I missed was calculating distances for launches and those sort of regulations etc. I figure if I review it another 3-5x I'll have it down. Some of the information is common sense. There were a few that just left me scratching my head and if I go back and find them I'll post them in this thread. One question had me really confused?? It was something to the effect of "Which isn't considered a HPR motor?" I need to find it. Anyways I feel pretty good considering I haven't read any related material in over 3 years.

 

[Fattbank64]

Take the practice exams. Review the material from incorrect answers. Repeat.

I recommend having your cert motor in hand to launch ASAP after passing the test.

 

[o1d_dude]

You may well already know most of the stuff already.

My strategy was to write the question down followed by the correct answer. That reduces the 31 pages down to about 10.

Once a day, go through the list. That’s all. Just once a day.

You will soon begin to notice that you’ve actually memorized / learned the answers.

Go through the list one final time before the exam.

Should be a piece of cake.

I missed one question. Flew my cert flight which was actually a bit less impressive than some of my practice flights on big “I” motors.

 

[AfterBurners]

This is the one I was scratching my head on?

Question A21
Which of the following (hypothetical) rocket motors is NOT a High Power Rocket Motor?

A. An F90 with 40 grams of propellant
B. An H60 with 62 grams of propellant
C. A G35 with 66 grams of propellant
D. All of the above are High Power Rocket Motors

 

[ChicagoDave]

This is the one I was scratching my head on?

Question A21
Which of the following (hypothetical) rocket motors is NOT a High Power Rocket Motor?

A. An F90 with 40 grams of propellant
B. An H60 with 62 grams of propellant
C. A G35 with 66 grams of propellant
D. All of the above are High Power Rocket Motors

"C."
A: F90 is a High Power because average n-s > 80.
B: H60 is also because the letter is >G .
C: G35 with 66 grams isn't High Power so that means C is the answer. (66g < 125g so it's not high power by weigh, letter or average newton-seconds)
D: Since C is not High Power then D isn't the right answer.

https://www.nar.org/high-power-rocketry-info/

 

[o1d_dude]

This is the one I was scratching my head on?

Question A21
Which of the following (hypothetical) rocket motors is NOT a High Power Rocket Motor?

A. An F90 with 40 grams of propellant
B. An H60 with 62 grams of propellant
C. A G35 with 66 grams of propellant
D. All of the above are High Power Rocket Motors

Ha ha ha !

That was the one I missed!!

 

[Nytrunner]

I read the answer key a couple times, but after that I tried to take the test based on concept alone. First time i did the test I missed a few of the trickier ones where you need to read and remember the answer key's explanation.
Definitely study the concepts for your own understanding, but when it comes to the test, the best preparation is unfortunately just remembering the answers.

 

[Steve Shannon]

This is the one I was scratching my head on?

Question A21
Which of the following (hypothetical) rocket motors is NOT a High Power Rocket Motor?

A. An F90 with 40 grams of propellant
B. An H60 with 62 grams of propellant
C. A G35 with 66 grams of propellant
D. All of the above are High Power Rocket Motors

Do you understand the reason for the correct answer? I can help.

 

[UhClem]

Rather than study the test, study the information it is based on. Things like Part 101 of the FAR, NFPA 1122 and 1127 and such. (Neither of those have a complete definition of the requirements for what is deemed a model rocket motor. For that you need to go to NFPA 1125.) Then maybe take a practice test.

 

[AfterBurners]

Do you understand the reason for the correct answer? I can help.

Is it because a G motor is a mid power motor?

 

[Steve Shannon]

Is it because a G motor is a mid power motor?

Sort of, although there’s legally no such thing. That G is a model rocket motor. More accurately it’s because of the definitions of High Power Rocket Motors and Model Rocket Motors in NFPA 1122, 1125, and 1127. This is copied from 1125:

3.3.24.2 High-Power Rocket Motor. A rocket motor that has no more than 40,960 N-sec (9209 lb-sec) of total impulse, and that does not otherwise meet all the requirements for a model rocket motor set forth in this code.

3.3.24.4 Model Rocket Motor. A solid-propellant rocket motor that has a total impulse of no greater than 160 N-sec (36 lb-sec), an average thrust of no greater than 80 N (18 lbf), and that otherwise meets the other requirements set forth in this code.

Answer A: The F90 exceeds the average thrust limit, so it’s considered high power.
Answer B: The H60 exceeds the 160 N-sec total impulse limit (anything that is an H does).
Answer C: The G35 has an average thrust of 35 Newtons, which is less than 80 N. It also is a G, so it has a total impulse that is no more than 160.0 N-sec, so it fits the definition of a Model Rocket Motor.
Answer D cannot possibly be correct because C is not a high power motor.

 

[AfterBurners]

Sort of, although there’s legally no such thing. That G is a model rocket motor. More accurately it’s because of the definitions of High Power Rocket Motors and Model Rocket Motors in NFPA 1122, 1125, and 1127. This is copied from 1125:

3.3.24.2 High-Power Rocket Motor. A rocket motor that has no more than 40,960 N-sec (9209 lb-sec) of total impulse, and that does not otherwise meet all the requirements for a model rocket motor set forth in this code.

3.3.24.4 Model Rocket Motor. A solid-propellant rocket motor that has a total impulse of no greater than 160 N-sec (36 lb-sec), an average thrust of no greater than 80 N (18 lbf), and that otherwise meets the other requirements set forth in this code.

Answer A: The F90 exceeds the average thrust limit, so it’s considered high power.
Answer B: The H60 exceeds the 160 N-sec total impulse limit (anything that is an H does).
Answer C: The G35 has an average thrust of 35 Newtons, which is less than 80 N. It also is a G, so it has a total impulse that is no more than 160.0 N-sec, so it fits the definition of a Model Rocket Motor.
Answer D cannot possibly be correct because C is not a high power motor.

Thanks Steve that clears it up. I was thinking of completely something different. I need to pay closer attention

 

[John Cummings]

UhClem has the right advise. 1127 and the NAR study guides are your friends. While it was the Tripoli test, I took mine Saturday. Been studying off and on for the last two months in preparation. Was more worried about the test than the flight.
Good luck to you.

 

[AfterBurners]

I wont be flying anytime soon with this COVID-19. I think I will use my PML Spitfire for the flight. It's already built and I'll get a JL chute release to see how works out. I was considering DD setup, but with my limited time to build I don't want to start another project. Took me over year just to get to where I'm at right now with my PML build and I'm wet sanding the primer and prepping it for paint. I seriously have very limited time. Too many other obligations. When I as unemployed I had nothing but time. I'll throw some paint on this kit and call it done. As time progresses wen I get L2 I'll experiment with some DD kits and enjoy all the cool processes. Of course I may change my mind later and go DD??

 

[ChicagoDave]

I wont be flying anytime soon with this COVID-19. I think I will use my PML Spitfire for the flight. It's already built and I'll get a JL chute release to see how works out. I was considering DD setup, but with my limited time to build I don't ant to start the project. Took me over year just to get to where I'm at right now with my PML build and I'm wet sanding the primer and prepping it for paint. I seriously have very limited time. Too many other obligations. I'll throw some paint on this kit and call it done. As time progresses wen I get L2 I'll experiment with some DD kits and enjoy all the cool processes. Of course I may change my mind later and go DD??

I used a JLCR on my L2. I went with the motor ejection + JLCR because I flew that a bunch of times already. If that's what you're comfortable with then go with it!

 

[AfterBurners]

I used a JLCR on my L2. I went with the motor ejection + JLCR because I flew that a bunch of times already. If that's what you're comfortable with then go with it!

Did you attach a drogue or a streamer to the harness to control the fall? Not even sure if anyone does this?

 

[ChicagoDave]

Did you attach a drogue or a streamer to the harness to control the fall? Not even sure if anyone does this?

So far I've flown relatively light rockets (<2Kg) so the issue I have is controlling drift before the main opens. I've tried it every which way. In theory the streamer *should* keep the rocket falling nosecone up, booster down. But in practice I've just had a tangled mess with the streamers. In my case at least the streamer or drogue is mostly just to help see the rocket up there before the main opens.

 

[dhbarr]

Did you attach a drogue or a streamer to the harness to control the fall? Not even sure if anyone does this?

Same setup for me, no drogue or streamer. Everything fell at roughly the same speed, tail down, chute bundle dragging up.

 

[UhClem]

This is copied from 1125:

The definitions section isn't the best. Section 7.6 contains the complete and controlling list of requirements for model rocket motors.

 

[AfterBurners]

Same setup for me, no drogue or streamer. Everything fell at roughly the same speed, tail down, chute bundle dragging up.

ok perfect!

 

[o1d_dude]

Did you attach a drogue or a streamer to the harness to control the fall? Not even sure if anyone does this?

Drogue chute as my big Polecat Goblin‘s fin can started to “fly” and accelerate groundwards. Adding a drogue chute tamed that behavior.

In the attached picture you can see the drogue, the main, and if you look very carefully you can see the Jolly Logic Chute Release attached ned the bottom of the main. The fin can is already on the ground. I use a Fruity Chutes parachute slipper which is connected to the top of the FC chute canopy because there’s not a lot of room to stuff everything into place. The main chute is 48” and I pop it low (400-500)’.

 

[AfterBurners]

Drogue chute as my big Polecat Goblin‘s fin can started to “fly” and accelerate groundwards. Adding a drogue chute tamed that behavior.

In the attached picture you can see the drogue, the main, and if you look very carefully you can see the Jolly Logic Chute Release attached ned the bottom of the main. The fin can is already on the ground. I use a Fruity Chutes parachute slipper which is connected to the top of the FC chute canopy because there’s not a lot of room to stuff everything into place. The main chute is 48” and I pop it low (400-500)’.

View attachment 418274

It looks like the drogue is attached directly to the nose cone attachment point with a leader line? If so how long was the leader line? Also how do you determine the correct size drogue? Would be the same as determining the descent rate when the rocket is under the main, but if course at a higher rate. I was just guessing that if I did use a drogue on the PML Spitfire I was thinking maybe an 18" chute? Possibly smaller?

 

[downhill_D]

Did you attach a drogue or a streamer to the harness to control the fall? Not even sure if anyone does this?

I do. I use an oversized Nomex blanket (parachute protector) in one of my rockets to slow the fall while the JLCR holds the parachute. It is a 14" blanket holding a 48" chute. It works similar to a streamer, protects the chute until ejection and slows the fall on mine to open safely at 500ft from 4900ft, I forget the actual speed but this was a 3lb, 3" rocket. I think the key is to find your fall rate. Using open rocket (free) or rocksim 10 (free for 30 days I think) makes this very easy.

 

[AfterBurners]

I do. I use an oversized Nomex blanket (parachute protector) in one of my rockets to slow the fall while the JLCR holds the parachute. It is a 14" blanket holding a 48" chute. It works similar to a streamer, protects the chute until ejection and slows the fall on mine to open safely at 500ft from 4900ft, I forget the actual speed but this was a 3lb, 3" rocket. I think the key is to find your fall rate. Using open rocket (free) or rocksim 10 (free for 30 days I think) makes this very easy.

Good info. Thank you

 

[OverTheTop]

I use an oversized Nomex blanket (parachute protector) in one of my rockets to slow the fall while the JLCR holds the parachute.

That is how I normally fly also. Just a nomex blanket before the main comes out.