Single deployment with a K and L engine

[jmasterj]

Agreed, now that we know. Of course AT could add in the instructions that you shouldn't use the ejection charge, and TRA could explicitly put this weird NFPA factoid on their website instead of burying it by reference in a document that few will read and which is non-trivial to access. That would keep people from not following this obscure rule out of ignorance.

It's one of the questions on the L2 test you have to take before using those L motors, too.

 

[MClark]

We have a local member who before the electronic deployment rules were in place did his L3 with a motor deployment M, simple timer for backup. Big low and slow.
Original AT 98mm motors came with a delay forward bulkhead.

 

[boatgeek]

We have a local member who before the electronic deployment rules were in place did his L3 with a motor deployment M, simple timer for backup. Big low and slow.
Original AT 98mm motors came with a delay forward bulkhead.

If I understand the rules right, that would be acceptable now (well, if M's came with ejection, and not for a cert flight) since there's electronic deployment (timer) in the system. I would expect an RSO to give it the hairy eyeball though.

 

[mikec]

It's one of the questions on the L2 test you have to take before using those L motors, too.

Was it there in 2009 when I took that test?

 

[mikec]

We did. It’s explicitly stated in the Safe Launch Practices document.

Fair enough. Maybe if that document was mentioned in the High Power Safety Code people would be more likely to read it. As it is, it's under a heading of "guidelines" on the TRA website, which might lead someone to think it doesn't have hard-and-fast rules like this one.

 

[mtnmanak]

Agreed, now that we know. Of course AT could add in the instructions that you shouldn't use the ejection charge, and TRA could explicitly put this weird NFPA factoid on their website instead of burying it by reference in a document that few will read and which is non-trivial to access. That would keep people from not following this obscure rule out of ignorance.

This is an odd statement, for sure. Steve said it well - this is explicitly stated in the Safe Launch procedures, which is a very short document designed to be used at the field. It is attached below. In my opinion, this document should be in every range box (or the NAR equivalent. Preferably, both.)

jmasterj is also correct. This information appears on both NAR and Tripoli Level 2 exams. The NAR exam actually makes reference to it several times. Those guides are also attached below.

Moreover, any RSO should be using the SLP and asking the question "what is your recovery method?". I realize this is sometimes overlooked, especially with flyers they know well and in a rocket they have seen before, but I know I at least ask the question when I RSO.

 

[Steve Shannon]

Fair enough. Maybe if that document was mentioned in the High Power Safety Code people would be more likely to read it. As it is, it's under a heading of "guidelines" on the TRA website, which might lead someone to think it doesn't have hard-and-fast rules like this one.

We’ll include it when we update our safety code.

 

[jmasterj]

Was it there in 2009 when I took that test?

I couldn't tell you that for sure, but it was in NFPA 1127 in the 2008 edition.

 

[wsume99]

This is an odd statement, for sure. Steve said it well - this is explicitly stated in the Safe Launch procedures, which is a very short document designed to be used at the field. It is attached below. In my opinion, this document should be in every range box (or the NAR equivalent. Preferably, both.)

jmasterj is also correct. This information appears on both NAR and Tripoli Level 2 exams. The NAR exam actually makes reference to it several times. Those guides are also attached below.

Moreover, any RSO should be using the SLP and asking the question "what is your recovery method?". I realize this is sometimes overlooked, especially with flyers they know well and in a rocket they have seen before, but I know I at least ask the question when I RSO.

It seems to me that someone could genuinely misinterpret the Tripoli safety guidelines which is why I asked what the definition of "electronically actuated recovery mechanism" was earlier in this thread. I expressed a concern that someone could interpret a chute release as meeting that criteria. I have no doubt that the RSO would inform any person wanting to use a chute release with an L1000 and motor ejection of their incorrect interpretation. However, why not simply revise the safe launch guideline to avoid anyone making that mistake? If you don't want people using motor ejection for L impulse or larger then why not say that explicitly?

Rockets with more than 2560 N-s of total impulse are not permitted to use motor deployment of the recovery system.

 

[AlexBruccoleri]

Okay this thread is really weird. It is common sense in rocketry that motor ejection systems are fairly dubious. When I got back into hobby rocketry I was kinda disappointed larger motors did not have ejection charges as a backup, but given the responses in this thread, it seems removing them is wise.....

 

[Buckeye]

NAR recognizes NFPA as the code that regulates HPR:

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

It is not written here, which most people will read:

High Power Rocket Safety Code | National Association of Rocketry (nar.org)

Agreed, now that we know. Of course AT could add in the instructions that you shouldn't use the ejection charge, and TRA could explicitly put this weird NFPA factoid on their website instead of burying it by reference in a document that few will read and which is non-trivial to access. That would keep people from not following this obscure rule out of ignorance.

Exactly. NAR can do the same and put this weird factoid on their website as well. If this NFPA code is so critical to the hobby, then why do they make it so hard to to find?

 

[mikec]

I couldn't tell you that for sure, but it was in NFPA 1127 in the 2008 edition.

Interesting. I'm virtually certain there was nothing about it in the NAR question pool in 2009. The L1000 wasn't certified until May 2014, and I can't find the TMT cert documents online to see if TMT tested the delay times or not. Certainly Aerotech said at the time and AFAIK continues to advertise the motor as having an adjustable delay.

Look, I'm not trying to be a jerk here, and the rule is a reasonable one (though I don't know how NFPA came up with the L threshold for it.) But imagining that everyone reads NFPA 1127 with a fine tooth comb, or studies revised L2 questions years after they get their cert, or reads all the well-intended safety guideline documents, doesn't fit with my experience at a typical launch.

Used to be, or so I remember, that the Safety Code was pretty self-contained. The more we add elsewhere and incorporate by reference, the more likely something will slip through the cracks. FWIW, I can't find this anywhere in the NAR HPR Safety Code, which only mentions 1127 in the context of mass launches, but it is in the NAR question pool.

 

[ThirstyBarbarian]

It probably would be best if the rule were prominently displayed. But in practice, it sounds like the only motor where this would be an issue would be with an L1000. Realistically, how often are you going to have someone try to fly an L1000 with motor eject only, and no electronic backup? I guess the reason we are talking about it is that someone mentioned that’s the kind of flight they want to do. But I think the OP now knows they can’t do that, and other than this thread, how often does it come up?

 

[AlexBruccoleri]

Interesting. I'm virtually certain there was nothing about it in the NAR question pool in 2009. The L1000 wasn't certified until May 2014, and I can't find the TMT cert documents online to see if TMT tested the delay times or not. Certainly Aerotech said at the time and AFAIK continues to advertise the motor as having an adjustable delay.

Look, I'm not trying to be a jerk here, and the rule is a reasonable one (though I don't know how NFPA came up with the L threshold for it.) But imagining that everyone reads NFPA 1127 with a fine tooth comb, or studies revised L2 questions years after they get their cert, or reads all the well-intended safety guideline documents, doesn't fit with my experience at a typical launch.

Used to be, or so I remember, that the Safety Code was pretty self-contained. The more we add elsewhere and incorporate by reference, the more likely something will slip through the cracks. FWIW, I can't find this anywhere in the NAR HPR Safety Code, which only mentions 1127 in the context of mass launches, but it is in the NAR question pool.

Again, common sense. I can think of safe examples of motor ejection, such as odd-rockets with lots of drag, launched far away, etc, but for the most part it is a bad idea. A lot of clubs have altitude rules where if you go above a certain limit, you need redundant deployment. Frankly that makes more sense than impulse, but it really is common rocket sense.

 

[mikec]

I can think of safe examples of motor ejection, such as odd-rockets with lots of drag, launched far away, etc, but for the most part it is a bad idea.

I can't speak for your club, but I'd say at least 75% of the flights we see are motor ejection. We see an increasing number of Chute Release flights but those of course use motor ejection for apogee deploy.

 

[BBrown]

Again, common sense. I can think of safe examples of motor ejection, such as odd-rockets with lots of drag, launched far away, etc, but for the most part it is a bad idea. A lot of clubs have altitude rules where if you go above a certain limit, you need redundant deployment. Frankly that makes more sense than impulse, but it really is common rocket sense.

Interesting. I'm virtually certain there was nothing about it in the NAR question pool in 2009. The L1000 wasn't certified until May 2014, and I can't find the TMT cert documents online to see if TMT tested the delay times or not. Certainly Aerotech said at the time and AFAIK continues to advertise the motor as having an adjustable delay.

Look, I'm not trying to be a jerk here, and the rule is a reasonable one (though I don't know how NFPA came up with the L threshold for it.) But imagining that everyone reads NFPA 1127 with a fine tooth comb, or studies revised L2 questions years after they get their cert, or reads all the well-intended safety guideline documents, doesn't fit with my experience at a typical launch.

Used to be, or so I remember, that the Safety Code was pretty self-contained. The more we add elsewhere and incorporate by reference, the more likely something will slip through the cracks. FWIW, I can't find this anywhere in the NAR HPR Safety Code, which only mentions 1127 in the context of mass launches, but it is in the NAR question pool.

Mikec,
Perhaps in the near future, TRA will be able to provide a single, self contained safety code. It would be a massive undertaking and would take months to produce, review and approve.
Bob Brown
President, Tripoli Rocketry Association

 

[AlexBruccoleri]

I can't speak for your club, but I'd say at least 75% of the flights we see are motor ejection. We see an increasing number of Chute Release flights but those of course use motor ejection for apogee deploy.

I fly motor ejection on smaller HPR birds too. And I got into the chute release as well. It can be done safely, but on larger rockets that gets less and less sensible, and more so when rockets go high enough to be hard to see.

 

[UhClem]

They have to be accurate wouldn't they have been certified that way?

They are accurate when tested at sea level. When flown to high altitudes, not so much. Remember that the burn rate of APCP is pressure dependent.

Once upon a time the Aerotech 98mm forward closure had a charge well.

The electronic deployment requirement for larger motors appeared in the 2002 edition of NFPA 1127.

 

[mikec]

Perhaps in the near future, TRA will be able to provide a single, self contained safety code. It would be a massive undertaking and would take months to produce, review and approve.

I find use of the word "massive" to be a little chilling, to be honest. I've always appreciated the brevity of the current HPR codes from both NAR and TRA, and it makes me wonder what you think needs to to added, or what's been lurking in NFPA1127 that we've not been aware of somehow.

 

[AlexBruccoleri]

I find use of the word "massive" to be a little chilling, to be honest. I've always appreciated the brevity of the current HPR codes from both NAR and TRA, and it makes me wonder what you think needs to to added, or what's been lurking in NFPA1127 that we've not been aware of somehow.

I do not think the codes need to be changed. The RSOs should be able to have discretion, and I think most will not allow large or high performance rockets to fly without a back-up ejection system.

 

[Troy3003]

In basic terms a chute release does not satisfy any electronic requirements whatsoever, including redundant DD requirements. It can be added into the mix of electronics if so desired, but is not a susbstitute to "ejection inducing" devices.

 

[FredA]

They are accurate when tested at sea level. When flown to high altitudes, not so much. Remember that the burn rate of APCP is pressure dependent.

Really doubt this: AP basically self-extinguishes/chuffs unless the pressure is over 300PSI - a 14.7PSI change is not a factor.

 

[PSLimo]

I fly electronics in all my conventional rockets.

However, where do large saucers fit in?

 

[AlexBruccoleri]

Really doubt this: AP basically self-extinguishes/chuffs unless the pressure is over 300PSI - a 14.7PSI change is not a factor.

The burn rate under pressure is 1/8" a second under pressure and 1/32" a second at ambient, so yes ambient pressure changes could have a meaningful impact. I do not know the chamber pressure under the delay phase though.

 

[FredA]

The burn rate under pressure is 1/8" a second under pressure and 1/32" a second at ambient, so yes ambient pressure changes could have a meaningful impact. I do not know the chamber pressure under the delay phase though.

Yea -- thought about it a bit more after I posted - but really counts is the burn rate difference between 14.7 PSI and something like 10PSI which is probably noise.

 

[AlexBruccoleri]

Yea -- thought about it a bit more after I posted - but really counts is the burn rate difference between 14.7 PSI and something like 10PSI which is probably noise.

I do not know and Aerotech or the other manufacturers do.

 

[BBrown]

I find use of the word "massive" to be a little chilling, to be honest. I've always appreciated the brevity of the current HPR codes from both NAR and TRA, and it makes me wonder what you think needs to to added, or what's been lurking in NFPA1127 that we've not been aware of somehow.

The impetus to undertake a project like this wouldn’t be to add regulations but to take the requirements from four existing documents (Tripoli High Power Safety Code, Research Safety Code, Best Launch Practices and NFPA 1127) and combine them into one, easy to access and read document. This whole discussion of an existing NFPA regulation that both national organizations adhere to but some folks seem to not know about (or has forgotten) is a very compelling reason to undertake this endeavor.

 

[rocket_troy]

Yea -- thought about it a bit more after I posted - but really counts is the burn rate difference between 14.7 PSI and something like 10PSI which is probably noise.

I know exactly where you're coming from Fred and as of a couple of days ago, I would've thought along similar lines - until Steve's post in another thread from the results of testing delays at different altitudes.
I guess the thing to be mindful of with typical APCP and pressure is the typical exponents associated with APCPs are less than 1, typically less than 0.5 even. So, anything with a pressure exponent less than 1 will have a upwardly curved plot on a linear scale. Meaning that the effect of pressure at the lower ranges will have a far greater influence than influence at the top end in *linear* scaling. Edit: The lower the exponent, the more pronounced that curve will be and ideally, you'd want to design a delay composition to have the lowest exponent as possible so there's less difference in burn rate between motor operation and coast mode. Especially helpful for retro work on the delay slug by the user, such as drilling out for timing reduction.
Normally you would plot this on a log scale, but I've just chosen a linear scale to highlight the effect.

edit2: this explanation might sound a bit contradictory to itself, but it's actually not. Point is, the lower the pressure exponent is, the less effect pressure changes will have on burn rates over a broad range, but the more effect small changes will have in a narrow range at the lower end.

TP

 

[jmasterj]

I fly electronics in all my conventional rockets.

However, where do large saucers fit in?

View attachment 516055

IIIC. Rockets that employ passive recovery (e.g. tumble recovery, aero-braking) need not employ an electronically actuated recovery system

 

[joe7]

"old white men that like to say no" ..

It seems like the "rules" are from the days before we figured out how to pack more than 2560ns into a 54mm liner.

Sure electronic deploy is better. But is there something about an L1090 that somehow makes it less safe with motor deploy than a K1050? Probably not.