level 2 renewal test question

[Lt72884]

I find one of the safety questions a little confusing. Maybe im not understanding their context.

The answer is indeed "A" but i always think its "B" because i am constantly looking at the stability of the rocket in OR and during the design process. So i am not sure i understand the context of this question (obviously haha)

any insight would be great.

thanks

 

[tsmith1315]

Because “A” is when it matters.

This is the safety perspective, the situation at “go time” is everything.

 

[Worsaer]

When you load the motor, recovery system, all the stuff for flight, it is then ‘real’, no longer a simulation.

I agree, getting the simulation right will help avoid surprises when it gets real.

 

[Rob Campbell]

I find one of the safety questions a little confusing. Maybe im not understanding their context.
View attachment 574910
The answer is indeed "A" but i always think its "B" because i am constantly looking at the stability of the rocket in OR and during the design process. So i am not sure i understand the context of this question (obviously haha)

any insight would be great.

thanks

Different motors have different masses, which will give different centers of gravity. I rocket may be stable with a 2 grain motor like an H-123, but unstable with a 6 grain motor like a J-350.

 

[Lt72884]

Because “A” is when it matters.

This is the safety perspective, the situation at “go time” is everything.

ok, i think i see what you mean. the RSO cant just trust that i have done the sims and design correctly. Since the RSO's decision can not be overridden for safety, they are the one that will check for stability during prep.

thanks

 

[Lt72884]

Different motors have different masses, which will give different centers of gravity. I rocket may be stable with a 2 grain motor like an H-123, but unstable with a 6 grain motor like a J-350.

but OR would show this would it not?

thanks. still wrapping my head around everything the last couple of weeks haha

 

[Lt72884]

When you load the motor, recovery system, all the stuff for flight, it is then ‘real’, no longer a simulation.

I agree, getting the simulation right will help avoid surprises when it gets real.

true, and the RSO should never trust anyone saying "trust me, the sims are correct" haha

 

[Blast it Tom!]

I must admit that "A" is of course correct, but I find it somewhat confusing, as it could be taken as, "when you are out on the flight line prepared for flight". I can imagine a bunch of folks out there swing testing their rockets...
Maybe "A" should read something like, "In full flight configuration" or some such...

 

[Lt72884]

I must admit that "A" is of course correct, but I find it somewhat confusing, as it could be taken as, "when you are out on the flight line prepared for flight". I can imagine a bunch of folks out there swing testing their rockets...
Maybe "A" should read something like, "In full flight configuration" or some such...

thats a simular image i had, hence why i went with B. The way i am trying to look at it is related to the RSO. If the RSO checks the stability and finds my rocket safe during flight prep, then im good and happy.

 

[tsmith1315]

RSO cant just trust that i have done the sims and design correctly

The RSO will depend on the sim for CP prediction. And probably for rail exit speed, if you’re asked.

but OR would show this would it not?

Yes, assuming that the .eng in OR is correct. What if the mass is wrong in there? What if you mistakenly simmed an H550 instead of an I550?

Check it with your eyeballs.

 

[Blast it Tom!]

thats a simular image i had, hence why i went with B. The way i am trying to look at it is related to the RSO. If the RSO checks the stability and finds my rocket safe during flight prep, then im good and happy.

Right, but how would he know? Markings on the tube? Swing test? I'm genuinely curious!

 

[tsmith1315]

When you load the motor, recovery system, all the stuff for flight, it is then ‘real’, no longer a simulation.

This is worth repeating.

 

[Lt72884]

Right, but how would he know? Markings on the tube? Swing test? I'm genuinely curious!

i know for the renewal and level 2 exam, you have to show the CP on the tube and demonstrate the CG.

 

[Lt72884]

The RSO will depend on the sim for CP prediction. And probably for rail exit speed, if you’re asked.



Yes, assuming that the .eng in OR is correct. What if the mass is wrong in there? What if you mistakenly simmed an H550 instead of an I550?

Check it with your eyeballs.

always check your selections and measurements. Its very easy to sim with the wrong motor by accident. or if you have to many motos selected, you could acidnetaly read the wrong values. that happened to me once. i selected all the 38mm motors and then simed them at once. bad idea

 

[tsmith1315]

Right, but how would he know? Markings on the tube?

Yes. If it looks wrong, you may need to show how you determined that point.

I take a print out along just in case.

 

[Ronz Rocketz]

Speaking as a Level 0, A is the more correct answer, but just barely.

 

[NateB]

Speaking as a Level 0, A is the more correct answer, but just barely.

Is it?

A safe stability margin should be determined when designing and building the rocket with the intended motors and recovery.

The safe stability should then be proven to the RSO when the rocket is prepped for flight.

 

[tsmith1315]

Perhaps this is a better way to 'splain it. Look at the wording of the question.
"When must the stability of a rocket be determined?"

It should be determined with every applicable change throughout the design process. It would be wise, but not a must at this point.

It must be determined in flight-ready condition when it's ready for the pad. This is a must, no excuses.

 

[Lt72884]

Is it?

A safe stability margin should be determined when designing and building the rocket with the intended motors and recovery.

The safe stability should then be proven to the RSO when the rocket is prepped for flight.

this is exactly how i read the question and how i decipher it haha.

 

[Lt72884]

Perhaps this is a better way to 'splain it. Look at the wording of the question.
"When must the stability of a rocket be determined?"

It should be determined with every applicable change throughout the design process. It would be wise, but not a must at this point.

It must be determined in flight-ready condition when it's ready for the pad. This is a must, no excuses.

i like this^^^^

 

[Ronz Rocketz]

Logically, if you're rocket is unstable at the design phase, you're rocket is gonna be unstable at the launch pad. I don't think it's possible to accidently make your rocket stable at the launch pad, or at least highly unlikely.

 

[user 30299]

During the design of the rocket, if using simulations, and confirmed
once the rocket is prepared for flight in its as-built configuration.

 

[Steve Shannon]

i know for the renewal and level 2 exam, you have to show the CP on the tube and demonstrate the CG.

The act of showing the Flight Safety Officer the CP on the tube and demonstrating the actual CG when fully prepared is when you truly “determine stability”. Up until that time things can change, such as changing chutes, or choosing a heavier or lighter motor.
If the rocket isn’t stable at that point, it doesn’t fly.

 

[Banzai88]

i know for the renewal and level 2 exam, you have to show the CP on the tube and demonstrate the CG.

Something that should also be happening with every prospective rocket to be launched at the RSO table.