I agree with David that this discussion is exactly what this chat is for!
The idea of doing a sim and setting the logic triggers is what most staged
rocket flyers do. It’s what I do as well.
The “if required” clause in the guidelines are there to allow for some
discretion based on the range situation. For example, at a ROC launch,
especially a ROCStock Saturday, we have lots of spectators and new LPR flyers
so I would stray to the more safe configuration. If it were Friday morning when
it’s primarily experienced flyers in a small crowd, I’d let you fly the timers,
put it on the back row, and call it a heads-up flight.
Additionally, while your rockets are previously flown, you are trying a new ISC
and if it fails during boost, you could light a tumbling sustainer. That’s a
bad situation at a ROC launch, but would be OK from the away cell at black rock.
I could come up with more situations, but the guidelines purposely leave it up
to the RSO/FSO at the specific launch. I know that makes it hard to prepare
before hand.
Allen
Terseness and mis-spelling courtesy of my iPhone
On May 13, 2018, at 8:34 AM, Terry McKiernan <terry@xxxxxxxxxxxxx> wrote:
Ah, interesting. I was wondering how this worked. In the rocketryforum.com
post someone said "a PET2+ can't do it, but an RRC3 can". So I read the
manual for the RRC3 and it said nothing about detecting if the rocket is off
vertical when it fires the sustainer. But, it does have the ability to use
up to 3 logic gates to trigger the airstart, including ranges for velocity
and altitude. So I see what you mean -- you sim the flight, figure out how
high you should be if things go well, and set the triggers appropriately.
The Raven has even more features, and 4 pyro channels, but it's similar in
that the logic gating is based on velocity and altitude, and also optionally
barometric pressure, but not tilt. So for both altimeters the "safe to
airstart" is inferred from other data, not directly determined by
pitch/roll/yaw.
So ... suppose I replaced the PET2+ with an RRC3 (yes, I'm being cheap) or a
2nd EggTimer (if I'm being really cheap and I like soldering) and used the
velocity & altitude gating to determine if it's OK to airstart. Would that
satisfy the safety requirements?
Thanks
Terry
On 5/13/2018 7:03 AM, Dave Peterson wrote:
I had the same confusion as well until it was made apparent that the
protections are against a sustainer motor starting in a horizontal or
downward facing orientation. Slightly off vertical or high dispersion
flights are not what the guidelines are concerned about. With a Raven or
RRC3 you can program the sustainer start using simulations to predict how
high the sustainer is at a particular point in time in a "reasonably
vertical" flight. The Eggtimer can sort of do this via the launch detect
altitude (LDA), but then you cannot use it for recovery because LDA may not
be reached. The simulations are better if they can be matched up with some
actual flight data of the sustainer alone or the stack flown without
actually starting the sustainer. The later often happens unintentionally as
the sustainer start criteria are dialed in to match the simulation.
On May 12, 2018, at 11:29 PM, David Erbas-White <derbas@xxxxxxxxxxxxxxxx>You're not remotely being a pain - I think it's a great item to discuss.
wrote:
On 5/12/2018 10:52 PM, Terry McKiernan 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.
I was struck by the "if required" portion of the guidelines as well, and I
don't think it's very far off from what I had stated previously.
If you'd asked me about 3 years ago, I probably would not have personally
'required' it for launches that I would have been associated with (as
either RSO or overseeing CP3). However, with failures that I've witnessed
since that time, along with associated advances in electronics that help
mitigate staging failures, I probably would 'require' it if I were asked to
be associated with a project.
There are areas of the sport where we're not given leeway, and areas where
we DO have some leeway -- this appears to be one of them. I'm just
suggesting how I might lean in this situation.
One other item that would perhaps come into play were I involved in this -
is it a proven two-stage design? In other words, I've you've purchased a
two-stage kit that has been proven to work by others, that would tend to
remove that factor from the equation in terms of it being a safe design.
The fact that you're experimenting with your own new design, with your
associated 3D printed coupler, would tend to make me want to ensure that
other safety factors were followed more cautiously. I would say this of
ANY new, unproven design - not just yours, so don't take it personally.
Thanks again for bringing this up as a topic, it's appreciated!
David Erbas-White
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