Ben,
I'll paraphrase the same response I did last time David made the same
statement here and again the same thing the previous time he made the 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 people
involved 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 Oxide
hybrids. 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 time
and 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.
With regards to TU guys, yes, Andreas sent me some photos and details of their
device. Very nice. I like how he simplified various parts like the 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.
Sounds like you get over there (Europe) a fair bit. I think you've caught up
with just about all the groups doing serious work?
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 of the crop of new launch companies are using hybrids.
Sierra Nevada, which owns SpaceDev and a lot of hybrid building experience,
abandoned the idea of using hybrids on DreamChaser in favor of liquids.
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 should send you pictures if they hadn't.
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
