Fair point (the range) I was thinking of APCP when I came up with that lower
end. Yes, a G candy motor would generally be easier to construct, but around
here these days, it's not so easy finding suitable KNO3. The stuff that tends
to be available is now full of anti-caking agents that tend to puff the casting
up to nuisance levels for reliability in particular. Finding good suitable
grade KNO3 seems next to impossible. Candy enthusiasts have resorted to
purifying the KNO3 prior to processing to avoid these issues which is a serious
PITA.
Troy
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On
Behalf Of Ben Brockert
Sent: Monday, 20 March 2017 12:24 PM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: List of universities with liquid rocket engine development
programs
I agree that there's a sweet spot for nitrous hybrids, same as there is for
NTO/MMH or jet vanes or rockoons or any other niche of rocketry technology.
But that doesn't run contrary to what David said.
I'm surprised by the impulse range you suggest, though; that's basically
perfectly covering all of level 1 and 2 of high power rocketry and I can't
see how
a G hybrid could possibly be easier to build than a KNSB G. I saw Rick
Mascheck
had high school students making KNSB grains on Saturday at FAR. A skilled high
school student could certainly build a hybrid, but anyone who can follow a
recipe for macaroni and cheese could make a sugar rocket. (Regarding FAR,
SDSU fired a solid and a liquid there on Saturday. Hopefully Carl will post
their
drone video, but here's my videos of the firings:
https://www.youtube.com/watch?v=s-Em5uUMn2I and
https://www.youtube.com/watch?v=6fplIw3_-6Q ;)
Regarding European groups, it was nice to visit a few of them. Swiss
Propulsion
Labs and DARE of TU Delft are still on my list to visit, and I'm sure there
are
others. Talking with space people is a memorable part of any of my trips; I
had
beers with some space interested guys in Zagreb a couple years ago who knew
of me somehow from the internet, and after a tour of the Cu Chi Tunnels in
Vietnam I ended up having a conversation about SpaceX with a Sri Lankan guy.
On Sun, Mar 19, 2017 at 5:20 PM, Troy Prideaux
<troy@xxxxxxxxxxxxxxxxxxxxx> wrote:
Ben,statement here and again the same thing the previous time he made the
I'll paraphrase the same response I did last time David made the same
statement here. The previous 2 times before that I didn’t bother responding.
Remember this is an amateur rocketry list and there are still some peopleinvolved in the list who are doing amateur rocketry - not developing orbital
launch systems or commercial suborbital ventures.
Around the 100Ns - 5000Ns range is a very sweet spot for Nitrous Oxidehybrids. Over the years I've constructed over 1000 solids and over 100 hybrids
within this range and I can comfortably state that it takes me considerably
less
time and effort to construct a working and reliable N2O hybrid within this
range than a solid and yes that does include very basic candy motors. Yes,
there's a hit with density performance, but the added Isp does make up for
that in relation to candy. As I've stated previously, mixture ratio isn't an
issue
for N2O hybrids within this range - anything between 5:1 to 10:1 O:F worked
fine from my experience. Instability isn’t an issue if you follow the
guidelines as
is 2 phase flow. If you follow the rules (don't try and push Pc too high,
injector
pressure drop too low, thrust too low for cold days etc) it's amazingly easy
to
make a N2O hybrid within this range.
As for liquids, it would comfortably take well more than 10 times the timeand effort and expense to construct something with comparable performance
and reliability within this range of impulse and these are the metrics are the
ultimate comparison.
As I've said previously (again in response to the same statement here)hybrids have much to prove for larger multi hundred thousand Ns upwards
propulsion systems - so far the runs are not on the board and the issues you
raise are amongst the many challenges they provide in offering a viable
alternative.
their device. Very nice. I like how he simplified various parts like the
With regards to TU guys, yes, Andreas sent me some photos and details of
latching
system. That's what it should be all about (within the amateur/educational
sphere), someone comes up with a concept and someone else takes it and
improves it.
with just about all the groups doing serious work?
Sounds like you get over there (Europe) a fair bit. I think you've caught
up
of the crop of new launch companies are using hybrids.
Troy
-----Original Message-----
From: arocket-bounce@xxxxxxxxxxxxx
[mailto:arocket-bounce@xxxxxxxxxxxxx] On Behalf Of Ben Brockert
Sent: Monday, 20 March 2017 10:27 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: List of universities with liquid rocket engine
development programs
Seems accurate to me. Hybrids manage to have most of the downsides of
both solids and liquids, while adding new ones like complexity in
mixture ratio control and propellant depletion, unusual instability
modes, unfavorable CG and/or diameter mismatch, and--while not
required to be a hybrid, still quite common in hybrids--the
complexity of two phase flow. It's not a coincidence that none or near none
liquids.Sierra Nevada, which owns SpaceDev and a lot of hybrid building
experience, abandoned the idea of using hybrids on DreamChaser in favor of
should send you pictures if they hadn't.
Unrelated to hybrids, but related to you, Troy, I visited TU Wien in
Austria over the summer and they showed me their hardware. They have
a lot of very pretty stuff, like 3d printed metal fin cans for
minimum diameter rockets, but also built one or more of your balanced
piston pyroless deployment devices. It was neat to see the hardware
"in the wild" after seeing you post it here; I mentioned to them that they
On Sun, Mar 19, 2017 at 2:15 PM, Troy Prideaux
<troy@xxxxxxxxxxxxxxxxxxxxx> wrote:
As a generic blanket statement - that's absolute bullshit.
Troy
Hybrids combine the complication of solids with most of the
complication of
liquids: you have to rebuild the "hot section" of the motor to put
in more fuel for each firing, even though you have a feed system
with tanks and valves to deal with etc.
-dave w
