NAR Level 2 Certification test question that seems to have a wrong answer.

Where am I going wrong here?

C39) What is the distance around a launcher for a rocket using a 3-motor cluster of J motors that must be cleared of easy to burn material, assuming the motors aren’t "sparky?"

The answer provided is "75 feet."

Now, using this NFPA chart...


The question doesn't give you the total impulse of the J motors being used, so you have to assume the maximum. If there are three motors, and each has an impulse of 1280 Ns, then the total impulse of the rocket is 3840 Ns. That makes it equivalent to an L, and thus the amount clearance required is 100 feet, not 75 feet as the answer guide indicates.

Or it automatically assumes the minimum impulse which would be 1920 Ns, which is in the K range, thus 75 ft. Don't remember which is the right answer now. I'll be watching to see what develops.

Adrian

C39) What is the distance around a launcher for a rocket using a 3-motor cluster of J motors that
must be cleared of easy to burn material, assuming the motors aren’t “sparky?“

A) 10 feet
B) 30 feet
C) 50 feet
D) 75 feet

-----------------

The answer is “D“. Refer to paragraph 4.15.1 of NFPA 1127, and Section 7 and the minimum distance
table in the NAR High Power Rocket Safety Code.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- Multiple choice question.
- Three J's will have at least 1920ns - could be more perhaps as much as 3840ns.
The question doesn't specify exactly how many Ns total. (hint - don't assume anything)
The answers do have A)10ft and B)30ft - which are not even an option per 1127 4.15.1.

The correct answer must be either C)50ft or D)75ft.
Per 1127 4.15.1 50ft is good for up to 1280ns (a single J)
The only answer left is D - 75 ft good for up to 2560ns per 1127 4.15.1.

I guess those are 3x Cesaroni J330's

There ya go. :handshake:
Lesson here is to not overthink the answers. Given the other options, this makes sense.

Adrian

Makes sense, although it's not like the exams I took in school.

As I recall, the answer was 75'. It is best not to overthink. Look at it this way. It generally takes 2 K's to make an L. It generally 2 J's to make a K. 3 J's therefore do not generally make an L. Stop thinking at that point.

1 J is 50. So 3 would have to be more. Of the answers provided, the only one more than 50 is....?


Later!

--Coop

Thanks, all. My concern isn't that I can't get the right answer. Obviously it has to be 75 by process of elimination.

My concern is that perhaps the very organization that is providing the safety code has chosen an ambiguous, possibly unsafe answer for their exam. I think it is a poorly designed question. They didn't give us the total impulse of the three motors. It comes down to "choose the best answer of the ones provided," as opposed to "choose the right answer."

That's all I'm getting at.

qquake2k said:

The question states three J motors. It doesn't state impulse. Therefore you assume the minimum impulse for three J motors. Easy peasy.

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Why would you assume the minimum? It seems safer to assume the maximum. This is about safety, right?

True. Assuming the maximum would be safer, as would be clearing 100 feet. However, with multiple-choice exams, it's often choosing the best answer listed.


Later!

--Coop

Bat-mite said:

Why would you assume the minimum? It seems safer to assume the maximum. This is about safety, right?

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In this case, it's about the test. Since it's not real life, you have to go with the information provided.

Or a J cluster is a complex rocket so the impulse is bumped up a class to K?

"Complex" is only used to determine personnel distances, not cleared area around the pad.

Total Impulse is used to determine the cleared area around the pad.

Only one answer fit within the possible total impulse range for 3 J motors.

falingtrea said:

Or a J cluster is a complex rocket so the impulse is bumped up a class to K?

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I agree that this is a poorly designed test question.

You can get at the "right" answer for the test through process of elimination, but it would make a lot more sense to list the total impulse for each of the motors in the cluster so that a person could calculate the answer using the correct methodology. The correct methodology is to add up the total impulse and find the safe distance, not to assume the smallest impulse for each motor based on its class and add that up, compounding the error of your assumptions.

EeebeeE said:

As I recall, the answer was 75'. It is best not to overthink. Look at it this way. It generally takes 2 K's to make an L. It generally 2 J's to make a K. 3 J's therefore do not generally make an L. Stop thinking at that point.

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My thought on this is that if your J cluster adds up to 3840 Ns, you launch it with 75' clearance when you should have 100', there is a fire and an insurance claim --- you don't want to tell them, "Three J's do not generally make an L, so I stopped thinking at that point."

The system is mathematical, not alphabetical. They should have put the question in terms that required a person to calculate the right answer, not surmise it from the choices available, unless they want people to just add up the letters in practice.

How about a question like this? --- A rocket is designed to be flown on a 3-motor cluster. The launch area has been cleared of flammable material to a distance of 75'. There are two types of J-class motors available: one with total impulse of 800Ns per motor, and one with a total impulse of 900Ns per motor. Neither motor type is "sparky." Which motors can be used in the 3-motor cluster under these conditions:

A) Both types of motors are allowable.

B) Neither type of motor is allowable.

C) Only the 800Ns motors are allowable.

D) Only the 900Ns motors are allowable.

ThirstyBarbarian, you and I think alike. Which should scare both of us.

Have a grog on me.

Bat-mite said:

ThirstyBarbarian, you and I think alike. Which should scare both of us.

Have a grog on me.

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You may want to get Art Upton's thoughts on this. He's the NAR committee chairman for HPR services. I don't know if he's seen this thread but he is on TRF and I believe his handle is his name ! :surprised:

The question asked is:

C39) What is the distance around a launcher for a rocket using a 3-motor cluster of J motors that
must be cleared of easy to burn material, assuming the motors aren’t “sparky?“

A) 10 feet
B) 30 feet
C) 50 feet
D) 75 feet

The correct answer is 75', which is the minimum distance listed in the safety codes for a K range total impulse which is the minimum total impulse and thus is the minimum distance you have to clear for a cluster of 3 J motors, as none of the other answers satisfy the minimum distance requirement.

While you might have to clear 100' from the pad if the motors are > 67% J motors, the question does not ask for the maximum distance you might have to clear, nor is 100' an option for the answer so there is only one correct answer listed for the problem.

Bob

ThirstyBarbarian said:

My thought on this is that if your J cluster adds up to 3840 Ns, you launch it with 75' clearance when you should have 100', there is a fire and an insurance claim --- you don't want to tell them, "Three J's do not generally make an L, so I stopped thinking at that point."

Click to expand...

By no means do I advocate skirting safety regulations because I believe there was implied permission to do so based on a poorly written test question. The flier needs to know the total impulse of his rocket and make sure the correct distance is cleared. Test or no test. It is incumbent upon everyone who sends a rocket up and bring it back down safely to understand all the guidelines, rules, and regulations set forth by NAR.


The root of this discussion is about taking and passing a test. That's all. Nothing else. In this case we have an ambiguously and poorly written question, as are some others in the test. Your task in this case is not to come up with the "right answer." It is to come up with the "most right answer." And in this case, the "most right answer" is 75'. In many cases, 75' is right. It could be 100', but that is not one of the choices given to you. So check 'D' and move on. All I was implying was that you should not overthink the question.

All this being said, I really think we need to rewrite the test so that any ambiguity like this is removed and we can talk about flying rockets instead of passing bad tests.

bobkrech said:

The question asked is:

C39) What is the distance around a launcher for a rocket using a 3-motor cluster of J motors that
must be cleared of easy to burn material, assuming the motors aren’t “sparky?“

A) 10 feet
B) 30 feet
C) 50 feet
D) 75 feet

The correct answer is 75', which is the minimum distance listed in the safety codes for a K range total impulse which is the minimum total impulse and thus is the minimum distance you have to clear for a cluster of 3 J motors, as none of the other answers satisfy the minimum distance requirement.

While you might have to clear 100' from the pad if the motors are > 67% J motors, the question does not ask for the maximum distance you might have to clear, nor is 100' an option for the answer so there is only one correct answer listed for the problem.

Bob

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All of the answers to Bat-Mite's question seem to about test-taking strategy --- how to pick the right answer from the choices given. I think his point is that the question is poorly designed, not that he can't pick the right choice. Obviously the only possible choice is 75', but Bat-Mite's question shows a deeper understanding of the issue.

I also think he is right that it is more appropriate to assume a big motor not a small one if the impulse is not given. If you were an RSO, and I called you up to ask if I could fly my 3-J cluster on your field that had only 75' feet of clearance, would you ask for the impulse of the motors? And if I said, "I dunno. All I know is they are J's," would you then assume a baby J and just say "Good to go"? Or would you say, "Without knowing the exact impulse, I'm going to have to assume you need 100' of clearance, and I can't approve your launch until we know the total impulse"?

Bat-mite said:

ThirstyBarbarian, you and I think alike. Which should scare both of us.

Have a grog on me.

Click to expand...

This does scare me, but now that I've had my grog, I feel better. Thanks!

EeebeeE said:

By no means do I advocate skirting safety regulations because I believe there was implied permission to do so based on a poorly written test question. The flier needs to know the total impulse of his rocket and make sure the correct distance is cleared. Test or no test. It is incumbent upon everyone who sends a rocket up and bring it back down safely to understand all the guidelines, rules, and regulations set forth by NAR.


The root of this discussion is about taking and passing a test. That's all. Nothing else. In this case we have an ambiguously and poorly written question, as are some others in the test. Your task in this case is not to come up with the "right answer." It is to come up with the "most right answer." And in this case, the "most right answer" is 75'. In many cases, 75' is right. It could be 100', but that is not one of the choices given to you. So check 'D' and move on. All I was implying was that you should not overthink the question.

All this being said, I really think we need to rewrite the test so that any ambiguity like this is removed and we can talk about flying rockets instead of passing bad tests.

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I totally agree. I think everyone understands how to pass this question by picking the most-right answer, but this is a poorly designed question.

In response to people suggesting to "assume the lowest end of J impulse", I disagree. The question is a question about safety. In any question of safety, that requires you to assume something, common sense says you assume the worst case.

Now I also understand the "don't over think it", or what we said in the Navy "don't nuke it out". But the question is poorly written in my opinion (and his).

ThirstyBarbarian said:

All of the answers to Bat-Mite's question seem to about test-taking strategy --- how to pick the right answer from the choices given. I think his point is that the question is poorly designed, not that he can't pick the right choice. Obviously the only possible choice is 75', but Bat-Mite's question shows a deeper understanding of the issue.

I also think he is right that it is more appropriate to assume a big motor not a small one if the impulse is not given. If you were an RSO, and I called you up to ask if I could fly my 3-J cluster on your field that had only 75' feet of clearance, would you ask for the impulse of the motors? And if I said, "I dunno. All I know is they are J's," would you then assume a baby J and just say "Good to go"? Or would you say, "Without knowing the exact impulse, I'm going to have to assume you need 100' of clearance, and I can't approve your launch until we know the total impulse"?

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Yes, you would be asked that question, not only because of the clearance issue, but more importantly because of the separation issue.

A single J motor require a 100' separation distance, K motors require a 200' separations distance but a complex K rocket requires a 300' separation distance which is the same as a single L. A complex L requires a 500' separation distance which is the same as a simple M.

In the first case, the rocket is classified as a complex K rocket which requires a 300' separation distance versus a complex L which requires a 500' separation distance. If you can't tell me otherwise, on my range you're going to a 500' M pad which has a 125' clearance requirement so my butt is covered! If you can tell me you qualify as a complex K, you're going to a 300' L pad which is required to have a 100' clearance anyway because I'm not going to have 300' pad that I can't launch a simple L from. But then again, that's how I set up ranges and assign pads at big launches.

BTW: These rules apply to both NAR and TRA launches.

https://www.nar.org/NARhpsc.html

https://www.tripoli.org/LinkClick.aspx?fileticket=RhLaGq2C+HY=&tabid=326

Bob

I didn't design the question, its from the change that occurred with the allowing of sparkin' motors more than a decade ago. I think it would be best on the next test revision [which happens when rules change] to change it to 2 motor cluster of Js. BUT the test is not what you refer to when looking for safe distances. This is what you refer to listed in the TEST STUDY GUIDE which is what you should use for safety questions: Refer to paragraph 4.15.1 of NFPA 1127, and Section 7 and the minimum distance
table in the NAR High Power Rocket Safety Code. Lets not have HPR pink book lawyin'... been thru all that.

Edit: Old Time memory....Back in the day that was written, most "entry level" level J motors were just larger I motors crossing over the line to be a small J. Marketing, folks see J motor and low price, bit really just a big I. You Know the most common 29mmm H motor folks certified on back then was just a Big G a few newtons over the limit.

qquake2k said:

In this case, it's about the test. Since it's not real life, you have to go with the information provided.

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After all, who launches in a field 2 mi by 2 mi with the farmer's house in the dead center? (C9)

Art Upton said:

I didn't design the question, its from the change that occurred with the allowing of sparkin' motors more than a decade ago. I think it would be best on the next test revision [which happens when rules change] to change it to 2 motor cluster of Js. BUT the test is not what you refer to when looking for safe distances. This is what you refer to listed in the TEST STUDY GUIDE which is what you should use for safety questions: Refer to paragraph 4.15.1 of NFPA 1127, and Section 7 and the minimum distance
table in the NAR High Power Rocket Safety Code. Lets not have HPR pink book lawyin'... been thru all that.

Edit: Old Time memory....Back in the day that was written, most "entry level" level J motors were just larger I motors crossing over the line to be a small J. Marketing, folks see J motor and low price, bit really just a big I. You Know the most common 29mmm H motor folks certified on back then was just a Big G a few newtons over the limit.

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Whatever you decide, I'm glad it has been brought to your attention. Mission accomplished.

jmattingly13 said:

After all, who launches in a field 2 mi by 2 mi with the farmer's house in the dead center? (C9)

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Right.

When I took the L2 exam, I found these “what is the required distance for…” questions to be excessive and tedious. How many newbie L2 fliers are actually responsible for setting up new range operations, anyway? For the few that are, these numbers are easily looked up in a book – no need for rote memorization. Likewise with the “How many N-s in such and such motor." Any good teacher will tell you that questions easily answered in the first hit of a simple Google search are not a good indicator of comprehension.

Buckeye said:

Right.

When I took the L2 exam, I found these “what is the required distance for…” questions to be excessive and tedious. How many newbie L2 fliers are actually responsible for setting up new range operations, anyway? For the few that are, these numbers are easily looked up in a book – no need for rote memorization. Likewise with the “How many N-s in such and such motor." Any good teacher will tell you that questions easily answered in the first hit of a simple Google search are not a good indicator of comprehension.

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Excessive and tedious indeed. As a professor teaching graduate and medical students I have to come up with exam questions that test the student's knowledge and comprehension of the subject. I do not think that a number of the L2 questions test the examinee's practical knowledge of what being a L2 flyer requires.