Re: Clustering/Staging for Certification?

Not only is the impulse over the limit of 320ns (for at least 120 NS motors), but the propellant limit is over 125g. Either one makes the rocket HPR, and requires L1 certification to fly.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

A cluster isn't necessarilly unbalanced.

As to discouraged: I recommend to any one who will listen that their L1 flight be a single motor. In fact I go as far as recommending either the H128-SW for 29mm MMT birds (preferred), or the H123-SW for 38mm MMT birds. IMHO if that isn't the right motor for your rocket, you've got the wrong rocket for your L1 attempt. A 4" diameter rocket at least 40" long is ideal. My first choice is still the LOC-IV, but anything about that size is fine.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

" Level 1 high power certification (160.01 to 640.00 Newton-seconds impulse)

1. The modeler must demonstrate his ability to build and fly a rocket containing at least one H or I impulse class motor. Cluster or staged models used for certification may not contain over 640.00 Newton seconds total impulse. Single use, reloadable, or hybrid technology motors are permitted. The modeler must assemble the reloadable motor, if used, in the presence of a certification team member."

"Level 2 high power certification (640.01 to 5120.00 Newton-seconds impulse)

1. The modeler must demonstrate his ability to build and fly a rocket containing at least one J, K, or L impulse class motor. Cluster or staged models used for certification may not contain over 5120.00 Newton seconds total impulse. Single use, reloadable, and hybrid technology motors are permitted. The modeler must assemble the reloadable or hybrid motor, if used, in the presence of a certification team member."

Seems pretty clear to me.

Phil Ste> You made me do it - I looked it up. NAR didn't seem to be have much

Exactly... I'm not sure what others just don't get about this! Seems quite clear to me!

Before you get enough D motors to exceed the NS limit you exceed the propellant limit. It would take just over 19 D12s to exceed the 320NS limit, but only 6 D12s put your rocket over the 125g propellant limit, thus requiring L1 certification, a 200' safe distance, and an FAA waiver.

BTW, for the E9 its 11.5 and 4 respectively.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

Safety code rule 7:

7.Size. My model rocket will not weigh more than 1,500 grams (53 ounces) at liftoff and will not contain more than 125 grams (4.4 ounces) of propellant or 320 N-sec (71.9 pound-seconds) of total impulse. If my model rocket weighs more than one pound (453 grams) at liftoff or has more than four ounces (113 grams) of propellant, I will check and comply with Federal Aviation Administration regulations before flying.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

} > " Level 1 high power certification } > (160.01 to 640.00 Newton-seconds impulse) } >

} > 1. The modeler must demonstrate his ability to build and fly a rocket } > containing at least one H or I impulse class motor.

This is, in itself, clear enough.

That, however, does nothing to resolve the illogic of being required to certify using a motor classed according to its total impulse, in order to be allowed to fly a clustered bird with relatively that same total impulse, yet comprised entirely of engines two levels less than that class. You have to fly an H (

} >

} > On Thu, 15 Apr 2004 16:59:52 -0400, Doktor DynaSoar } > wrote: } >

} > >

} > >Unbalanced thrust seems dangerous to me. } > >Surely this WOULD be discouraged, no? } >

}

I'm talking about a triangular 3-cluster.

I think that it's not so much a question of "logical reasons" as "historical reasons": the interaction between the ancestral "who's afraid of the big bad H motor?" paradigm of the original TRA "consumer confirmation" process and the NAR attitude that if they were going to accept "high power" rocketry at all, it had to be strictly distinguished from "Model Rocketry". This creates anomalies at the boundary, such as the present instance, where one has to fly a "high power motor" to become certified to fly a "high power rocket" even if it does not use any "high power motors" (but qualifies as a "high power rocket" by aggregating the impulse of multiple "model rocket" motors).

I'm not defending the present weirdness, I'm just giving my best guess as to how it came to be that way.

-dave w

Though not called out in the requirements (as it is "possible" to do it otherwise), I've yet to see a L1 cert where the flier did not have to "construct" the motor (RMS or Hybrid). There just that many SU H+ motors (I don't think I've ever even seen one!)

If you cluster f/g SU motors, one thing that will be in the back of the Cert team's mind is "I wonder if he can assemble a motor?". The truth of the matter is that 99.999% of L1 or above flights do require this, along with figuring out how much BP to use, etc.

I've seen people who could do a Hobby RMS, but really struggled with a HP RMS (the case/procedures are different).

IMHO, doing ANY cluster for a cert is a bad idea - the KISS principle. Plus, you got to consider that if you attempt to cert with a "complex" rocket, it will take you more time to prep, meaning it will take more time for the Cert team to watch you prep. It's also a greater chance of failure - i.e. one motor fails to light. Which means the cert team will have to watch you reprep everything! (two motors did burn...).

If the cert team is also trying to fly their own stuff at the launch, they might start getting a little uptight if the time is becoming to great!

Bad example. You CAN fly a cluster of three F20's without a high power certification.

NAR HPR certification limits are based on total installed impulse.

Level 1: "Certification at this level permits single or multiple motor rocket flights with motors having a maximum total impulse of 640.00 Newton seconds."

Level 2: "Certification at this level permits single or multiple motor rocket flights with motors having a maximum total impulse of 5120.00 Newton seconds."

I think that Tripoli allows you to cluster/stage motors up to a maximum of

1280NS for a level 1 certified flyer and 10,240NS for a level 2 flyer. My ancient TRA certification documents state this but I can't locate anything on the TRA web site to confirm that this is the current policy. My ancient TRA certification documents also state that an uncertified member is allowed to fly A through G motors. No mention of impulse limits or clustering.

There is a gray area between model and high power due to the definition of a model rocket contained in NFPA 1122 which allows up to 320NS of model rocket motors in a model rocket. Stay within the limits and you are flying a model rocket requiring no user certification. Exceed them and you are flying a high power rocket and must be certified.

The requirement that a high power motor be used for the certification flight is unlikely to be changed. Certification requires that the user demonstrate "knowledge and competence in handling, storage, and using a high power solid propellant rocket motor and high power rockets". (NFPA 1127) This cannot be done if the user is using a cluster of model rocket motors for the certification flight.

Except that this is an "appeal to authority" that you have expressly declared to be irrelevant. Too bad.

If you want to change this, the obvious way is to get the definition of a model rocket changed so that only up to 160NS of impulse can be installed. NFPA 1122 is coming around for another revision cycle soon. Check the NFPA site to see how to submit a proprosal.

Don't expect to get a lot of support for that change.

Or you could try and change the certification language in NFPA 1127 so that it drops the requirement for demonstrating competence with high power rocket motors and just leaves the high power rocket requirement. This might have a better chance of passing than changing the definition of a model rocket.

It's because certification relates to two different things, in two different ways. The first is that you have to be certified in order to legally purchase a high power MOTOR. The second is that you have to be certified in order to legally fly a high power ROCKET. Since certification allows you to buy and fly high power motors, you have to show proficiency with a high power motor.

Certification was primarily intended to allow people to buy and fly high power motors. The only reason it also is required to fly large clusters of smaller motors is because the authorities (Fire marshals, FAA, ATF, etc) don't want to leave a loophole for getting around the cert requirements. They want certs for all flights containing total thrust in the high power range.

Of course, the "large cluster/small motor" issue has very little teeth. The only enforcement mechanism is the RSO at a club launch. If you're not at a club launch, there's no one to stop you from flying rockets loaded with dozens of G motors without a cert. High power motors, on the other hand, do have an enforcement mechanism -- the vendors who don't want to put their butts on the line by selling to uncertified individuals.

I suspect that's not because the procedure is more difficult, but because the user wasn't expecting it to be different.

I disagree. I see no reason for a cert flight to be any different from any other flight I'd make. Yes, if it's more complex there's more risk of failure, but that's true whether it's a cert flight or not.

Like I said, it's not a requirement - but I think that NOT using a SU is a good idea. Gives the cert team a bit more understanding of what the flier knows. It's an "image" thing

Ray, you must consider not only the fliers' time, but that of the cert team.

More complex means more prep time More complex means more chance of failures More chance of failures, means more time for the cert team doing the above, at the next launch, when another attempt is made...

Case in point.. Chris Taylor's Grrrrrrrr.. Not a cluster, but a non-KISS bird.. He's been trying this for how long? There were others on the cert team that lost hours observing him...

Case in point #2. Chris Taylor's saucer. I forget if this was a cluster or not, as when ever I think of it, I laugh thinking about how he strapped it to his jeep and drove "real fast" to see if it would hold up! Another non-KISS bird.

"Fly a simple bird in the power level to prove that you understand that power level" "Get your cert" "Do complex birds in that power range, where you don't impose on others to observe, and you can waste your own time"

Where in the cert process is "hand-holding" required? The closest thing is on Level 3 certs, where the design and construction of the rocket must be approved by the TAPs. For Level 1 and 2 flights, the person signing off on it, merely has to observe the flight. Good flight, pass. Bad flight, no pass.

How much time does it take to observe a flight? There's no requirement that the pre-flight prep must be observed.

Since they aren't required to hold his hand through the prep, it was their choice to "waste" that time.

Was a cluster. Or at least an attempted cluster of 2 different H motors on each flight.

Haven't seen this. What's he up to now...

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!