Allen, Eric, David,
Thanks for all your responses. I'm still pretty new to rocketry and so
I have a lot of questions and learn new things each launch.
I do want to stress that I'm in favor of safety and following the
rules! I'm an aerospace engineer by trade and work on government
contracts, and trust me, they have LOTS of rules ... I'm used to it :).
I'm just trying to find out what they are.
As you can imagine, my situation is this: I did some research, selected
what I thought were the right components, assembled the rocket, and now
with only a few weeks remaining before the June launch, noticed
something in a forum that said maybe it would not be allowed. So sure,
I could go buy a Raven or similar altimeter and probably get it before
the June launch but hey, it's another $150 so if I don't have to, I'd
rather not. I just bought & assembled my EggTimer TRS which was quite a
project, plus 2 PET2+ units, and was hoping this combination would give
me the flexibility for lots of different flights.
Allen, the Tripoli document you provided is very helpful. I read
through it and as you said, there are specific guidelines for
multi-staged flights. In particular on page 20:
"The upper stage(s) of HPR rockets must be using electronic recovery,
and not rely on motor ejection."
That's covered; the EggTimer TRS will be in charge of the chute deployment.
And then:
"If required, make sure that the staging electronics have a feature to
inhibit staging events if the rockets flight profile does not follow
expected behavior."
That's where I get stuck -- the "if required" phrase. I can't tell if
it's required or not.
If it matters, this staged rocket is made of 2 L1 rockets that we've
flown with H and I class 38mm motors, and that what I want to use for
the staged flight. I have two I-180W motors on hand so I could use
those, or perhaps get an H class for the sustainer if that would improve
safety.
Once again I appreciate everyone's input, and I'm not trying to be a
pain. I'm trying to avoid 2 things: either buying something (like
another altimeter) that I don't really need, and/or showing up in June
and finding out I can't launch.
Terry
On 5/12/2018 9:43 PM, Allen Farrington wrote:
Tripoli has guidelines for us to follow on multi-staged flights. You can find them at:
http://www.tripoli.org/Portals/1/Documents/Safety%20Code/Range%20Safety%20Guidelines%20v1.3.pdf
on page 20.
A staged rocket is automatically a special flight and it is recommended that it be reviewed using the guidelines above.
They leave the details of timer use up to the RSO/FSO at the event. I know, for example that if you are under the Class 3 review (>40kNs or >50 kFt), you have to use electronics to prevent the ignition of the second stage if the flight is not nominal.
BTW, the guidelines don’t allow motor ejection for the upper stages of a multi-stage rocket. The failure mode that I’ve seen most often is no lighting of the second stage resulting in no motor burn and a ballistic crash. Altimeter-based electronics will still work under that condition.
Personally, I use a Raven as my sustainer electronics. It has four channels and comes out of the box ready for this type of 2-stage flight. It can be set to make sure that your rocket is flying up, above a certain altitude, and at a good speed.
Allen H. Farrington
www.allenfarrington.org <http://www.allenfarrington.org>
On May 12, 2018, at 8:52 PM, Eric Melville <eric@xxxxxxxxxxxxx <mailto:eric@xxxxxxxxxxxxx>> wrote:
I think the reality is that no one truly knows and we are struggling to find a reasonable set of rules.
Personally if I was RSO and you were adhering to minimum distance etc, I would let you fly without giving it a second thought.
- iPhone mail
On May 12, 2018, at 6:31 PM, Terry McKiernan <terry@xxxxxxxxxxxxx <mailto:terry@xxxxxxxxxxxxx>> wrote:
Hello all,
Thanks to everyone who provided suggestions on my 2-stage rocket / coupler problem. Now I have a second question I hope you can help with.
Is a MissileWorks PET2+ an OK device to use for the sustainer airstart? When I come out for ROCstock in June will I be allowed to launch?
The PET2+ is certainly marketed as a way to do airstarts -- both on the MissileWorks site and on retail sites like Apogee. It includes wiring diagrams showing how to do exactly what I have planned for my 2-stage rocket.
However, today I found some postings on www.rocketryforum.com <http://www.rocketryforum.com> where some people were saying that a "simple timer" was no longer allowed for airstarts and no RSO would approve it. This was followed by a long discussion about what a "simpler timer" means, and is this really a rule or just a best practice of some TRA prefectures, and what really are the rules anyway etc. Some people seemed to think it was perfectly OK and had used PET2's even for L3 rockets and some said no, you have to have an advanced altimeter like the Raven or TeleMega 3 that will check the altitude and make sure you rocket is going up and sufficiently vertical before firing the sustainer. But no one seemed to have a hard and fast answer that was documented in a TRA or NAR rulebook.
Note that the PET2+ does use "X gees for Y seconds" to detect main engine ignition (MEIG), main engine cutoff (MECO), and similar sustainer events (SEIG and SECO). It also does some X/Y/Z orientation checks at power on (i.e. on the pad) and won't initialize if the rocket is pointed funny. It's not just a timer that starts counting down when you apply power.
My plan (repeating myself from my previous posting) is to have both the PET2+ and an EggTimer TRS in the payload bay of the upper stage. The PET2+ will be set to ignite the sustainer at either MEIG + booster motor burn time + 0.5 sec (or so) or at MECO + 0.5 sec (or so). I am thinking about actually putting 2 igniters in the sustainer and using both pyro events of the PET2+ maybe 0.5 second apart, so if the first igniter burns the second one still has a chance to get the sustainer going.
The TRS is there to help find the rocket and also as a backup in case the airstart ignition fails and thus there's no sustainer motor charge to release the main chute. Per Andrew's suggestion it will be wired up to a backup ejection charge for the main chute. It's not going to be involved in the airstart at all, and has its own battery, so it's a completely separate system.
So, what do you think? Is this a flyable configuration?
Thanks!
Terry McKiernan
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