NAR safety code launch site sizes

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SolarYellow

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Another discussion about how best to use field space led me to look at my across-the-street field on Google Earth and then to contemplate the NAR safety code launch site dimensions requirements. It occurs to me that it is yet another example of an error in denominator selection, of which I have encountered several notable ones in this hobby. The basic problem is that the site dimensions are tied to motor size, not apogee height.

Consider, for example, a Citation Patriot and a Wizard. Both are well-liked, popular models with long production history from the industry giant. Both have essentially the same recommended motors. The Citation Patriot is advertised to fly to about 600 ft (presuming the largest motor, a C6-5). The Wizard is advertised to fly to about 1600 ft on a C6-7, the exact same impulse. The NAR safety code requires minimum site dimensions of 400 ft for any rocket flying on a C. Likely reasonable with the CP, obviously a foolish decision with the Wizard.

This set of guidelines, because it's published by the NAR as part of its fundamental safety practices, in various locations and circumstances may actually carry the weight of law. And yet, it's laughable as an actual guide, as is obvious immediately to anyone with a lick of common sense who thinks things through. In reality, every rocketeer is burdened to apply reasonable judgement to the circumstances present at launch and conduct themselves accordingly, and the NAR site size guidelines are frankly of so little help as to be useless. Maybe they're intended for middle of the road rockets like Alpha, Der Red Max, or the range of ARF stuff that's available. Fine, but it doesn't say that, and there's nothing to prevent a kid and her parents who pick up a Hi-Flier, 220 Swift, or similar kit for their first try at model rocketry from following the rules as written, and to their detriment. Essentially, if a rocketeer follows these guidelines without overriding them completely with their own judgement and flies a random selection of commercially available kits built according to the instructions on recommended motors, said rocketeer will inevitably run into trouble.

The most basic question in deciding whether an otherwise reasonable site is appropriately matched to a flight is, "How high will it go?" Wind is a factor, descent rate, etc. But if you were to put together a chart of launch site dimensions vs. one variable, making some assumptions about the other factors all being within typical ranges, that one variable would have to be apogee. Using motor impulse instead of apogee turns the guideline into a clear example of garbage-in-garbage-out.

If a guideline is wildly inadequate and fundamentally misconceived, what's the point of even publishing it, let alone embedding it as part of the most fundamental document directing the overall safety of the hobby?
 
Easy answer: Field size as a function of motor size as defined in the safety code because the "energy/power" in the motor if it cato's, etc. (Edit: Any non-standard dissipation of motor potential energy.)

Altitude that a particular motor takes a rocket too is up to the FLYER being able to "fly the field".

( A rocket coming in ballistic will reach terminal velocity very quickly, so energy dissipated in the "lawndart" is almost equal falling a few hundred feet, or a few thousand feet. )
 
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Your point is well taken.

I tend to be of the "follow the rules or else" camp when it comes to safety. But when safety rules are so...incomplete such that inconsistencies arise, they result in either:

- Frustrated people
- People who ignore the rules

On the other hand, if rules get too complicated, it can produce similar results. For example, say we used apogee as the field determining factor. Well, what about wind and type of recovery system? Those play major roles in how much space a rocket needs. So I also get the pickle companies and organizations can be in when trying to create guidelines.
 
Easy answer: Field size as a function of motor size as defined in the safety code because the "energy/power" in the motor if it cato's, etc.

Altitude that a particular motor takes a rocket too is up to the FLYER being able to "fly the field".

( A rocket coming in ballistic will reach terminal velocity very quickly, so energy dissipated in the "lawndart" is almost equal falling a few hundred feet, or a few thousand feet. )
I doubt that, as safety relating to engine catos is taken care of by making launch controllers (the basic ones for most LPR and MPR flyers) have wires of a minimum length.
 
Common sense needs to compliment the safety codes. If you wish to fly a rocket on a C that goes to 1500 ft. in the minimum field size that is up to you. It is possible to lose it, again up to you. Should it lawn dart, cause damage somehow, you will be covered by insurance. You can if you wish to disregard any of the rules/safety code, that is up to you. You can forget about any insurance coverage though if you decide to go that route.
 
NFPA 1122 (which has been adopted many places and thus actually is enforceable by local AHJs; no, the NAR Model Rocket Safety Code does not carry the weight of law) offers an alternative means of determining minimum field size based on apogee.
 
You were saying (unless I misunderstood you) that the field size rating was decided, at least in part, due to the overall power of the engine in case of a cato. I'm saying I don't think that's correct.

Well.... not just a cato, if your thinking motor blows up as only form. ... But cato as in any "non-correct" dissipation of the energy within the engine.

From the safety perspective as the potential energy in the motors increases the minimum field size increases.

For example, say we used apogee as the field determining factor. Well, what about wind and type of recovery system? Those play major roles in how much space a rocket needs.
This falls into "fly the field" not safety codes. A rocket decending at acceptable speed that drifts out of the field due to wind, is not in itself dangerous...
 
I design mid-power scratch built rockets, and always try to fly under 1,000 feet, typically around 800 feet. So the NAR "launch site size" aren't applicable.
 
NFPA 1122 (which has been adopted many places and thus actually is enforceable by local AHJs; no, the NAR Model Rocket Safety Code does not carry the weight of law) offers an alternative means of determining minimum field size based on apogee.
https://link.nfpa.org/free-access/publications/1122/2018
4.9.3 As an alternative to the minimum launch site dimensions of Table 4.9, the size of the launch site shall be permitted to meet one of the following criteria:
(1) It shall be not less than one-half the maximum altitude as stated by the manufacturer or as calculated by flight simulation for the model rocket and motor(s) combination being flown.
(2) It shall be of a size approved by the AHJ based on flight demonstration of data required to substantiate the anticipated altitude.

Table 4.9 is the same as the NAR safety code.

So if you had a big, low & slow rocket, this allowance (1) might get you onto a smaller field with more impulse than permitted by the table, but there's still nothing to suggest you would be well advised to find a field much larger than 400 ft. when launching your Wizard with a C6-7.
 
https://link.nfpa.org/free-access/publications/1122/2018

Table 4.9 is the same as the NAR safety code.

So if you had a big, low & slow rocket, this allowance (1) might get you onto a smaller field with more impulse than permitted by the table, but there's still nothing to suggest you would be well advised to find a field much larger than 400 ft. when launching your Wizard with a C6-7.
Or if you had a lick of sense you would apply the analysis recommended by the alternative method to determine whether the table dimensions were adequate.
 
Another discussion about how best to use field space led me to look at my across-the-street field on Google Earth and then to contemplate the NAR safety code launch site dimensions requirements. It occurs to me that it is yet another example of an error in denominator selection, of which I have encountered several notable ones in this hobby. The basic problem is that the site dimensions are tied to motor size, not apogee height.

Consider, for example, a Citation Patriot and a Wizard. Both are well-liked, popular models with long production history from the industry giant. Both have essentially the same recommended motors. The Citation Patriot is advertised to fly to about 600 ft (presuming the largest motor, a C6-5). The Wizard is advertised to fly to about 1600 ft on a C6-7, the exact same impulse. The NAR safety code requires minimum site dimensions of 400 ft for any rocket flying on a C. Likely reasonable with the CP, obviously a foolish decision with the Wizard.

This set of guidelines, because it's published by the NAR as part of its fundamental safety practices, in various locations and circumstances may actually carry the weight of law. And yet, it's laughable as an actual guide, as is obvious immediately to anyone with a lick of common sense who thinks things through. In reality, every rocketeer is burdened to apply reasonable judgement to the circumstances present at launch and conduct themselves accordingly, and the NAR site size guidelines are frankly of so little help as to be useless. Maybe they're intended for middle of the road rockets like Alpha, Der Red Max, or the range of ARF stuff that's available. Fine, but it doesn't say that, and there's nothing to prevent a kid and her parents who pick up a Hi-Flier, 220 Swift, or similar kit for their first try at model rocketry from following the rules as written, and to their detriment. Essentially, if a rocketeer follows these guidelines without overriding them completely with their own judgement and flies a random selection of commercially available kits built according to the instructions on recommended motors, said rocketeer will inevitably run into trouble.

The most basic question in deciding whether an otherwise reasonable site is appropriately matched to a flight is, "How high will it go?" Wind is a factor, descent rate, etc. But if you were to put together a chart of launch site dimensions vs. one variable, making some assumptions about the other factors all being within typical ranges, that one variable would have to be apogee. Using motor impulse instead of apogee turns the guideline into a clear example of garbage-in-garbage-out.

If a guideline is wildly inadequate and fundamentally misconceived, what's the point of even publishing it, let alone embedding it as part of the most fundamental document directing the overall safety of the hobby?


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