Hi TerryTerry,
Please do not think for a moment that you're being a pain or asking too
many questions. That's exactly what this forum is for. The responses you
are receiving are from seasoned and very experienced rocketeers who have
seen first hand the evolution of model and high power rocketry. You have
the right frame of mind knowing that safety is our biggest concern. A lot
goes into a successful 2-stage flight. There are so many variables to
contend with while staying within the Tripoli and NAR guidelines. These are
the organizations that insure us. Stability, ignition of the sustainer,
recovery of both pieces and on and on. The beauty of ROC is that we all
have a common hobby. We all gained knowledge through experience and by
asking our fellow rocketeers for advice and help. And most of us are
willing to share what we know.
I realize I'm not of any help with your 2-stage questions as I myself am
learning too. My first high power 2-stage project is taking longer than I
expected to complete because I want and need to be sure it's done right.
Mike Ostby
ROC President
On Sat, May 12, 2018, 10:52 PM Terry McKiernan <terry@xxxxxxxxxxxxx> wrote:
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
On May 12, 2018, at 8:52 PM, Eric Melville <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> 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 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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