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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