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
--
ROC-Chat mailing list
roc-chat@xxxxxxxxxxxxx
//www.freelists.org/list/roc-chat
--
ROC-Chat mailing list
roc-chat@xxxxxxxxxxxxx
//www.freelists.org/list/roc-chat
