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,
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
