Single deployment with a K and L engine

[Walter Longburn]

Every L1000 I've got has had an 18 second delay and black powder included. But like has already been said it is still a requirement to use electronic deployment for either primary or backup.

 

[cerving]

Just to be clear, you DO NOT have to use dual-deployment, you just need to use electronic deployment (and NOT the motor's ejection) to get the parachute out. Single-deploy is fine if you have something electronic to get the chute out. You can ADD a Chute Release to mimic dual-deployment, but something else needs to get the nose cone off.

 

[Walter Longburn]

And once you use electronics for deployment you'll probably never want to turn back.

 

[Steve Shannon]

Is it possible or worth asking for the NFPA to allow direct links to the most up-to-date NFPA codes on the Tripoli/NAR websites. I find it weird that those codes are hard to access.

It’s NFPA 1127 paragraph 4.10.2. It’s free (but painful) to read at NFPA.org, requiring a free login.

We could put a link to the 1127 page, but the process to access the document wouldn’t be easily linked. I wouldn’t worry about it too much though. Just follow the documents in the safety information area of the Tripoli page and you’ll be covered.

 

[jimzcatz]

Members:

I want to fly my newly build fiberglass rocket with DMS engines with time delays. I know that double deployment is recommended for L and above, but I rather use single deployment, along with a Chute release.

Comments?

Right now I don’t intend to get Level 3 certified, so I want to fly the highest engine within my certification ( Level 2).

It's not Duel deploy that's necessarily recommended, its using electronics that is. Just like L3 Certs. DD is not required but using redundant electronic deployment is. . Good luck and have fun.

 

[jimzcatz]

And once you use electronics for deployment you'll probably never want to turn back.

Boy is that a mis-statement as far as I'm concerned. I hate the prep time for electronics and only use them when absolutely required. And when I do, its not 2 altimeters but just one. I'm not advocating this practice, just sharing what works for me.

 

[OverTheTop]

Boy is that a mis-statement as far as I'm concerned. I hate the prep time for electronics and only use them when absolutely required. And when I do, its not 2 altimeters but just one. I'm not advocating this practice, just sharing what works for me.

Once most people use electronic deployment they decide it is a good idea, in my observations anyway. YMMV.

 

[Buckeye]

Even if it does it's not permitted by NAR or Tripoli Safety Codes.

No mention of this in the NAR Safety Code that I can see.

 

[tsmith1315]

No mention of this in the NAR Safety Code that I can see.

NAR recognizes NFPA as the code that regulates HPR:

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

 

[wsume99]

12. Rockets with more than 2560 N-s of total impulse must use electronically actuated recovery mechanisms.

Is "recovery mechanism" defined somewhere? If this is the actual wording from NFPA I can easily see how someone might conclude a chute release satisfies this requirement.

 

[Antares JS]

Is "recovery mechanism" defined somewhere? If this is the actual wording from NFPA I can easily see how someone might conclude a chute release satisfies this requirement.

It takes some ignorance/inexperience to come to that conclusion, since an L or greater motor without motor ejection and nothing but a chute release obviously leads to a lawn dart as there is no mechanism to get the parachute out of the rocket.

 

[wsume99]

It takes some ignorance/inexperience to come to that conclusion, since an L or greater motor without motor ejection and nothing but a chute release obviously leads to a lawn dart as there is no mechanism to get the parachute out of the rocket.

Except there are L motors with delay grains and ejection charges included as was pointed out earlier in this thread

If the requirement is to have an electronically initiated separation event at apogee (which seems to be the case and I'm not arguing it shouldn't be) then why not just explicitly state that?

 

[cerving]

It doesn't necessarily have to be a separation, you could have a trapdoor that releases a parachute. I've seen college teams do that. The point is that the deployment event must not rely on the motor. We've all seen motors that have a short burn then cato, and the electronics brings the remains down on chute. That is a Good Thing.

 

[user 30299]

Except there are L motors with delay grains and ejection charges included as was pointed out earlier in this thread

If the requirement is to have an electronically initiated separation event at apogee (which seems to be the case and I'm not arguing it shouldn't be) then why not just explicitly state that?

AeroTech only makes one L motor with a delay - and that's the L1000 DMS motor. All other L motors are plugged.

I don't know about CTI motors. I don't use them.

So the L1000 is an exception, and it would be interesting to know if that's an accidental exception. As has been pointed out, NFPA requires electronic deployment on motors L and up.

 

[Steve Shannon]

Is "recovery mechanism" defined somewhere? If this is the actual wording from NFPA I can easily see how someone might conclude a chute release satisfies this requirement.

This was not the wording from NFPA 1127. That was the wording from the Tripoli Safe Launch Practices. Unfortunately we cannot define every single word. Fortunately we don’t try . We expect flyers to interpret things from a safety perspective. How safe is it when a chute release releases a chute even though it’s still inside the rocket?

 

[GalantVR41062]

https://wildmanrocketry.com/products/mach-2-rocket
I found this and interpreted the Aerotech L1000w-18 motor was made for a military project, that trickled down to high power rockets.

I flew a L1000w-18 in my 1/4 scale Viking 7 rocket project last year. I had dual altimeters for redundant dual deploy. I used my delay adjustment tool and trimmed the motor delay to 10sec as another backup. I had to be creative in the ejection charge size, 8 grams did not fit in the standard motor eject charge well.

 

[user 30299]

Is "recovery mechanism" defined somewhere? If this is the actual wording from NFPA I can easily see how someone might conclude a chute release satisfies this requirement.

Here is the NFPA section in question:



"Deployment" is used, not "release" which is what a JLCR does.

 

[cerving]

According to NFPA 4.10.2, you could use the motor eject as the primary, as long as you have an electronic backup. That's not a bad idea, except that motor eject is highly variable and not terribly accurate in the long delays.

 

[user 30299]

According to NFPA 4.10.2, you could use the motor eject as the primary, as long as you have an electronic backup. That's not a bad idea, except that motor eject is highly variable and not terribly accurate in the long delays.

Something that we all learn through experience - and asking for advice from experienced people . . .

 

[ThirstyBarbarian]

We need a good Rocket Lawyer.

 

[cerving]

We need a good Rocket Lawyer.

That's the LAST thing we need... for the lawyers to get involved in our hobby. Ask the R/C guys what's happened since drone "incidents" made the lawyers jump on them. They make no distinction between some yahoo creating a You Tube moment with his drone and the guys that have been AMA members for 40 years and fly at established fields.

 

[3stoogesrocketry]

Yes according to NFPA 4.10.2 you can still fly a M1939 on motor ejection and a single radio shack pager built 20 years ago .

TRA however has guidlines they want you to follow.

 

[cerving]

Yes according to NFPA 4.10.2 you can still fly a M1939 on motor ejection and a single radio shack pager built 20 years ago ...

Only if your pager somehow deploys the recovery system... that would be fun!

 

[ThirstyBarbarian]

A rocket buddy and I flew our ginormous second-hand Thumper on a CTI K635 about a month ago. The motor has a delay grain, which we drilled to the ideal length based on our sims. And it sounds like technically we could have just flown it motor eject. But it’s a 35-pound rocket, and it seems like a rocket that big should have a backup. So we used one of the tiny Eggtimer Apogee altimeters. It seemed to us like the deployment was a bit late, and I wondered if the altimeter had actually fired. He was going to take a closer look when he got home and circle back, but I haven’t talked to him since then. The motor eject definitely fired at some point, even if a bit late, and it could be that’s what saved the rocket. It’s a good idea to have redundant deployment systems on big rockets.

 

[Steve Shannon]

Only if your pager somehow deploys the recovery system... that would be fun!

I still have the High Power Rocketry magazine article that shows just that AND when the local Radio Shack was having a clearance sale I bought one of those pagers! It’s never been out of the box. Archeologists are going to love going through my basement someday but my kids might hate me.

 

[ThirstyBarbarian]

We need a good Rocket Lawyer.

I’m making a joke about how these conversations always end up by quoting paragraphs and subsections of regulations and still end up going in circles.

 

[heada]

I just don't get it. There is 1 L motor that has a delay and that appears to have some history outside of hobby rocketry that might justify it. The manufacturer of that motor has said recently that any full K or bigger motor shouldn't rely on the delay grain since burn rate and thus the delay time is impacted by ambient pressure. Most flights that would use such a motor go to altitudes were the pressure change would impact the delay burn rate thus giving an inaccurate delay.

When the motor maker says basically "you really shouldn't do that" why would you then continue to try to do that? It costs a whopping $20 for an electronic deployment option. You're paying more than 10 times that cost on the motor alone. Just add an electronic deployment option already. Why fight something as clear cut as this?

(end of rant)

 

[boatgeek]

I don't know about CTI motors. I don't use them.

All CTI 54mm 6XL loads are plugged, whether they're full K's or baby L's. 75mm and above are all plugged, even the 75mm baby K's.

 

[mikec]

When the motor maker says basically "you really shouldn't do that" why would you then continue to try to do that?

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.

 

[Steve Shannon]

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.

We did. It’s explicitly stated in the Safe Launch Practices document. If people have chosen not to read that, then they’re responsible for their own ignorance.