I'll throw in my 2 cents regarding oxidizer choice. Definitely nitrous
for hybrids, and either nitrous or LOX for liquids, depending on the
requirements of the project. I have experience with all 3
(nitrous-HTPB, nitrous-ethanol, and LOX-kero).
The reasons for nitrous hybrids: good performance at a wider range of
AF ratios (great for hybrids), no cryo headaches (frozen valves,
seals, tanks, fingers, etc.), easily storable and transportable, and
the massive amount of information and experience already out there
that makes it easy for beginners.
Nitrous for liquids can be a good choice when LOX makes things
difficult. The performance will be lower, but no cryo issues.
Pressures might run a little high during hot weather. Chilling the
nitrous and adding inert gas pressurization helps.
But, if you are after performance and are prepared to take on the cryo
challenges (they aren't that bad really, just depends on preference
and requirements), then LOX is the go-to for liquids. Long history and
lots of information out there.
-Daryle
On Sun, Mar 14, 2021 at 4:38 PM Troy Prideaux
<troy@xxxxxxxxxxxxxxxxxxxxx> wrote:
Ken,
I genuinely believe that LOX is the preferable oxidizer of choice for
*liquids*. Even maybe smaller ones. I just don’t believe that’s the case for
hybrids. Maybe with today’s additive technology my understandings might be
dated – regarding larger ones.
I bow to your experience with liquids.
Cheers,
TP
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of roxanna Mason
Sent: Monday, 15 March 2021 10:29 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Hybrid High Powered Rocket
It's what you're used to, how you were taught and who did the teaching. I was
blessed to have met and worked with Bob Truax for 35 years, couldn't have had
a better teacher/mentor.
He helped me learn how to handle and design LOx systems. All I want to do
now, now that I'm retired is to pass on what he taught me and so be it..
I'm currently in the finishing phases of designing a flight LOx/Kerosene
rocket for a small group of high school students in Texas. They learn fast,
35 years of knowledge assemulated in under 6 months, impressive. They'll be
future engineers.for SpaceX and who knows what other companies to be.
Bless their little souls,
Ken
On Sun, Mar 14, 2021 at 4:10 PM Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx>
wrote:
Yes okay, they can be self-pressurized but at modest pressures (200-300
psi(ish) without significant drops over the depletion but then you have to
also allow for pressure drops over the injectors and again, we are talking
hybrids here not bi-props or liquids where the O:F ratio will vary with grain
regression. LOX hybrids sound easy in theory.
Troy
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of roxanna Mason
Sent: Monday, 15 March 2021 9:47 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Hybrid High Powered Rocket
Troy, have you designed built and hot tested LOx systems yourself?
Just curious because all the minor negatives are easily dealt with. BTW, LOx
can be self pressurizing,
The first liquid rocket flight by Goddard in 1926 was done this way, he used
it to pressurize the fuel tank as well.
I wouldn't recommend it but it worked.
Being an engineer I don't believe in fixing something that works and if
someone is already using Nitrous safely then great. But if a newcomer to
liquid rockets asks what oxidizer to try out, I'd recommend LOx. It will
help him/her in their future career in aerospace more than nitrous experience
too.
Ken
On Sun, Mar 14, 2021 at 3:12 PM Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx>
wrote:
How to make hard-line clerics look like consummate pragmatists…
Now there’s a Best Seller just waiting for pen to paper…
Ken,
There’s a reason (no, multiple reasons) why N2O has been the only liquid
oxidizer approved for use with Tripoli and that’s not through the
hand-waving-chest-beating-table-thumping preaching of biased dogma. It’s by
pure *practicalities* and even the extra fuss needed for N2O proved over time
to rendered them unpopular against the vastly more practical solids.
HPR hybrid flyers could go out and fly their birds without the need for a
dewar or the need to have it filled just prior to the launch or to deal with
cryo sealing or potential embrittlement of a neighbouring parts or needing a
separate pressurant and accompanying plumbing with that or the requirement
for more specialised injectors. The hardware was cheap and simple. The
assembly could be fairly simple.
Again, it’s horses for courses. Yes, beyond a certain size system, LOX
becomes more practical, but the intended audience was quite clearly spelled
out as HPR.
Troy
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On ;
Behalf Of roxanna Mason
Sent: Monday, 15 March 2021 8:06 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Hybrid High Powered Rocket
I wish certain folks would lose their cryo phobia, LOx is such a superior
oxidizer and the self pressurizing 'advantage' of nitrous is all but lost
with the very few cons.
If you have a misfire in a LOx system just let it evaporate away. Of course
all pressurized systems will have relief valves or burst discs or both, which
is my favorite passive doubly redundant design philosophy. A 40-50 gallon
dewar of LOx can run anywhere between $75 and $300 depending on many factors.
A well maintained dewar will have only 1-2% loss per day so if you have a
week or two delay no problem.
My mom used to take me down to the welding supply store when I was in my
single digits age and get a liter of LOx or LN2 to 'play' with, price was
always $2. Get used to its properties and work your way up to closed systems.
When I was about 15 I asked an Aerojet engineer that was visiting our group,
"what is LOx like?" He said to me: "It's like water" He meant a Newtonian
fluid, the cold is largely inconsequential once understood. Some
seals/o-rings need changing and all non ferrous metals are com[patabler with
LOx. Insulation is usually non necessary with test stand components only
extended storage is insulation necessary nother like LH2 which requires
insulation under all circumstances.
My friend Glenn May died in a nitrous explosion along with two of his
co-workers. I guess you could argue I have nitrous phobia, maybe so but it's
based on fact not a misperceived fear of an industrial gas that is produced,
transported.and used by the thousands of tons per day world wide w/o mishap.
Read and learn as much as it takes to understand the nature of any beast.
LOx Rocks,
Ken
On Sun, Mar 14, 2021 at 12:39 PM Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:
On Sun, 14 Mar 2021, Troy Prideaux wrote:
The one glaring point to laser focus on with a Chill-and-Fill hybrid
is to ensure your tank is *rated* to hold the required pressure. If
you’re making it yourself, allow at least a x3 safety factor with a
pressure relief device.
For reference, normal non-aerospace pressure vessels are required to have
a safety factor of 5x. That can be relaxed to 4x with some precautions
like X-ray inspection of welds, and sometimes to 3x in certain cases with
elaborate precautions. Safety factors are calculated on fairly-worst-case
low strength against fairly-worst-case high loads, *not* on nominal
strength against nominal loads, and all known issues are figured into the
strength or the load (that is, you shouldn't use safety factor as margin
against issues you know about -- it is solely a hedge against surprises).
Now mind you, that's for pressure vessels that are meant to have the
uninvolved public literally standing beside them. You can be a bit less
generous for things that will always be filled remotely... but only if you
make provisions to *empty* them remotely when (not "if") something goes
wrong. And properly speaking, "I'll just wait for the safety valve to
pop" is not a valid answer -- such valves are meant to be emergency
backups only, so you shouldn't be relying on them for reasonably
foreseeable situations.
Particularly if you're developing your own gear rather than flying
something off-the-shelf, situations like valve trouble or computer crashes
or long launch delays are most definitely "reasonably foreseeable".
Never mind the uninvolved public -- it's *your* head and hands that might
have to get "up close and personal" with the hardware when things go
wrong, as they will. Thinking about this beforehand is a lot better than
having to improvise ways to defuse the bomb.
Henry