NAR Code E Motor Field Size

[Chris in Idaho]

I've seen discussion that launch site minimum dimensions should be based on apogee altitude and not total impulse, and I have to agree. However for this thread let's assume it makes sense the way it is.

Why, then, is there such a huge jump in field requirement going from D to E, but then no change from E to F to G?

B requires 100% increase from A (100->200).
C requires 100% increase from B (200->400).
D requires 25% increase from C (400->500).
E requires 100% increase from D (500->1000).
F requires no increase from E.
G requires no increase from F.

I would like to fly a rocket that requires at least an E and would likely not break 400 feet altitude. E is 25% the impulse of G, but to comply with NAR I need a field large enough for G impulse. Why?

 

[lakeroadster]

Basing the field size should be based on apogee. But then you would need a simulation, an accurate simulation, to determine field size.

That's why it's based on motor size, not apogee.

 

[Chris in Idaho]

...That's why it's based on motor size, not apapogee.

Fair enough, but that's not my question. Why the huge jump between the D and E requirements? D only needs 25% more field length than C, but E needs 100% more than D. Also E has the same requirement as G which is four times more powerful.

With A B and C it seems to double just like the impulse is doubling, but then D is only 125% the requirement of C, then double again for E, then no increase for F and no increase for G.

It would make more sense if it continued the pattern of doubling along with impulse. Then it would be:
A=100
B=200
C=400
D=800
E=1600
And so on. This would be more restrictive but would at least make sense.

The current requirement is:
A=100
B=200
C=400
D=500
E=1000
F=1000
G=1000

It's not a direct function of impulse. Small increase from C to D, big increase from D to E, no increase all the way to G.

If a 1000 foot field can handle a G, why do I still need 1000 feet for 1/4 of G impulse (E)?

 

[smstachwick]

I have no confirmation on this, but I suspect that the minimum field size may have been crafted with ease of remembering at least partially in mind, but also without being unrealistically restrictive.

I do know that the NFPA 1122 codes on which the Code is based permit a field with a minimum dimension at least half the expected altitude for a given flight, granting more options for heavy-draggy rockets with big motors on small fields. Think pyramids, saucers, spools, and the like.

While this is legal in places that codify NFPA 1122, NAR insurance coverage for such a flight would be a little more iffy or simply unavailable since the Safety Code does not make this provision.

 

[Tractionengines]

If your table was used. How many clubs would loose access to the larger motors "by force"? You would require 6400' for a 'G'... we can't find access to launch sites now, how many clubs can find over a square mile just to fly MODEL rockets. (Remember officially its only 2 classes Model Rockets, and High Power Rockets. Splitting "model" into LPR and MPR is something we as hobbyist do, it's not a real split.)

______________________________

As to the table....This is a chicken-n-egg thing. In the 50s/60s there was no code, then a code was created, then the code was codified in haphazard fashion....That table was created when anything bigger than a 'C' was "BIG" and there was very limited access to them. It didn't even list 'G'.... it said 2xF and 4xF for the last lines. (Or something like that).

At this point NAR/ Tripoli can easily adjust/rewrite their safety codes, BUT are forced to work within the limits of NFPA. (They can be "more restrictive" but not "LESS".) The ONLY way to be less restricted is change that table in a revision to NFPA.

Submitting a request to change NFPA, would likely result in a LOT of scrutiny by people who don't have any exposure or knowledge of this hobby, and could backfire. Any NFPA change needs to be submitted and put out for a "public comment" period. We all know the "general public" can be an unpredictable group.

 

[waltr]

Yea, it is the way NFPA wrote to codes that NAR and Tripoli follows.
The low power stuff is under NFPA1122 whereas the high power is under NFPA1127.
For HPR minimum field size is 1500 feet from smallest motors (H or under HP motor) to M motors. However, this limits flight to 3000 ft apogee.
The other code specifies min distance to pads. These also are the same for a wide range of motor impulse then jump distance for another range of impulses.

No way to make any 'sense' out of why.

 

[smstachwick]

Yea, it is the way NFPA wrote to codes that NAR and Tripoli follows.
The low power stuff is under NFPA1122 whereas the high power is under NFPA1127.
For HPR minimum field size is 1500 feet from smallest motors (H or under HP motor) to M motors. However, this limits flight to 3000 ft apogee.
The other code specifies min distance to pads. These also are the same for a wide range of motor impulse then jump distance for another range of impulses.

No way to make any 'sense' out of why.

I can only assume that these numbers were generated from field testing of model/high-power rockets and motors, as well as full-scale sounding rockets and missiles. Since there are significant changes in design and construction as rockets increase in scale, I doubt these were determined purely mathematically.

 

[Tractionengines]

I can only assume that these numbers were generated from field testing of model/high-power rockets and motors, as well as full-scale sounding rockets and missiles. Since there are significant changes in design and construction as rockets increase in scale, I doubt these were determined purely mathematically.

I doubt originally they were "tested" or "determined mathematically"... I think it was early rocketeers and community officials..... going "that sounds about right", then "it's easier to remember (# '), then "hobbyist will NEVER use motors bigger than (...).

If it was calculated or based on any parameter (total impulse, thrust, altitude, etc.) There would be a hint of consistency to it, somehow. Which there isn't.

 

[86mustang408w]

They give these so you stay away from buildings and have a wide recovery area. Wind no wind a rocket will go far during apogee. And it my case a failed ejection it went about 300 feet straight out on a E motor, not the direction aimed it either. But It doesn't makes why it jumps that far from D to E like that. There are certain rules and distances you have to follow for LOW power. But I really think those field sizes are suggestions for many "successful recoveries" too. With that E motor and a failed ejection my rocket was 300 feet away stuck in a cord field. Weeks later with an F motor, it landed about 100 feet from the pad in soft grass.

But the bad thing about discussing apogee altitude over motor thrust for minimum launch site areas for low power, is not all rockets go straight up. Someone probably thought along the way we nee to think about that too. One spot I launch in a C6-3 in one rocket landed about 600 feet away. Not much later a very similar rocket in shape and weight landed 100 feet away, on a E12-4. So I guess they have to account for it all?

 

[waltr]

If it was calculated or based on any parameter (total impulse, thrust, altitude, etc.) There would be a hint of consistency to it, somehow. Which there isn't.

Exactly. This is what makes the HPR L2 cert written test hard. One must simply Memorize the NFPA Regs to pass the test.

 

[bad_idea]

Exactly. This is what makes the HPR L2 cert written test hard. One must simply Memorize the NFPA Regs to pass the test.

I don't know about the NAR test, but the Tripoli test has only three or four safety-related questions in the test pool that aren't either things you really do need to know or else intuitive without paying attention to specific distances in the safety code. Memorizing the NFPA codes isn't a bad thing of course, but hardly necessary. If you understand how rockets fly and how to fly rockets safely, you can probably take your chances on that handful of questions and still pass handily, but the question pool and its answers are published, and there is a practice test you can take online as often as you like.

 

[samb]

....
Memorizing the NFPA codes isn't a bad thing of course, but hardly necessary. ...

Maybe not a bad thing but... wait for it... a bad_idea IMHO!

Study the question pool, take a practice test or two... ace the exam!

 

[bad_idea]

May not a bad thing but... wait for it... a bad_idea IMHO!

Actually I think it's a good idea for those who have the patience, but I do keep plenty of bad ideas in my quiver.

 

[smstachwick]

Maybe not a bad thing but... wait for it... a bad_idea IMHO!

Study the question pool, take a practice test or two... ace the exam!

I’ve found myself studying it just so I have a better handle on safe practices. I’m currently throwing a L1 project together and not even close to L2.

 

[bad_idea]

I’ve found myself studying it just so I have a better handle on safe practices. I’m currently throwing a L1 project together and not even close to L2.

That's a good idea. There's no downside that I can see.

 

[waltr]

Yep, been going through the NAR L2 practice tests. Got 100% on last try.
Will be taking the test this Sunday so will go through it once more before that.

A buddy took this last year who flies 747 aircraft for a living, missed two questions and both were on NFPA regs.

 

[lakeroadster]

A buddy took this last year who flies 747 aircraft for a living, missed two questions and both were on NPFA regs.

NFPA... Don't miss that one on the test...