For a student liquid-rocket propulsion project with a chance of
successful completion in four years of your no-doubt plentiful undergrad
spare time :-D
I'd suggest starting with a fairly basic known-workable engine
configuration, then aim not to perfect it, but to build then thoroughly
test and characterize it. Maybe, if things go amazingly well, to
iterate a second-gen version with lessons-learned then thoroughly test
and characterize that.
I'd go with LOX-alcohol as propellants. Learn cryo handling with
something cheap where the proper safe handling procedures and gear are
also relatively cheap and accessible (and where you can do initial
hardware safety & function testing with also-cheap and much-lower-hazard
LN2). Alcohol - isopropyl is cheap and relatively low-toxicity -
meanwhile is less tricky than kero to get to burn and shut down
reliably, and it also allows you to sneak up on full performance and
full thermal stresses by diluting with water.
Thoroughly test and characterize... Run the engine across a range of
mix-ratios, propellant temperatures, ambient temperatures, and other
operating conditions (humidity!) roughly representative of some
interesting real-world operating scenario. Collect good data - then
organize it into usable form! And, by the way, pick an engine design
where you can fab a new copy fast & cheap so when you (inevitably if
you're exploring the envelope) send metal vapor out the exhaust you can
get back to testing quickly. (Ideally, have a spare or two in stock, so
you can run again as soon as you're reasonably sure you know what
happened and have a useful adjustment to test.)
You're almost certainly not going to advance the liquid biprop SOTA in
this. What you will do is learn a huge number of useful lessons in the
real-world care and feeding of liquid biprops, plus develop and
demonstrate some highly useful leadership and organizational skills.
And maybe, if you do a good enough job of documenting things, you can
build a higher base for future students to start from.
And for a graduation exercise, early in your senior year pick out a few
of the most promising younger types, and by the end of the year have at
least one of them ready to step into your shoes, take over, maybe carry
on with putting the by-then thoroughly understood engine into some sort
of flying testbed and thoroughly characterizing /that/.
good luck!
Henry
On 5/25/2019 2:41 PM, Shepherd Kruse wrote:
I’m a student headed to the Air Force academy this Fall. I like the thought process of going directly to liquids and spending all the time and resources perfecting an engine. I’m hoping to get backed by the Astro department and getting the rocketry program up and running again. I’ve done a lot of work on my own, but as far as success goes, what would you advise for me to focus on potentially leading a USAFA rocketry team?
Regards,
Shepherd Kruse
On May 25, 2019, 1:04 PM -0600, D K <dougchar001@xxxxxxxxx>, wrote:
Having done student projects involving rocketry for the last 15 years or so, while none this big, this is a major accomplishment. Students come and go administrations come and go, risk tolerance of management varies, and interest at the institution can vary as well. To work this long this hard and build upon the knowledge to make it work is a major accomplishment in my opinion.
The caveat on student rocketry programs is one bad mistake, test, flight can often ruin the whole program. Forgiveness for my perspective is rare. Ending a multi-year program that affects multiple students is not worth certain risks, IMO. Why liquids are a completely different ballgame at University settings.
And the reality is in a university setting we're training students to go out and work in different industries, oftentimes not involving rocketry, especially in small programs such as mine. Ultimately the student is more important than the rocket not the other way around. The student is our real deliverable. Why I'm only now starting to consider hybrids but at a very small scale initially. And like the previous poster said you can do a whole lot involving rocketry systems with solids as the propellant.
Doug Knight
On Sat, May 25, 2019, 1:58 PM Henry Spencer <hspencer@xxxxxxxxxxxxx <mailto:hspencer@xxxxxxxxxxxxx>> wrote:
On Sat, 25 May 2019, Bruno Berger SPL wrote:
> Starting with a solid motor (eg a commercial one) is IMHO not
wrong. So
> you get your experience with the airframe, avionics, telemetry,
recovery
> etc before you maybe switch to liquids. The chance is great
that you
> will never fly something if you start with the development of a
liquid
> engine first...
The flip side of this, though, is projects that decide to fly
first with
solids and then switch to liquids, but die when they try to make that
transition.
Whether starting with solids makes sense depends on your goals.
For sure,
getting something liquid working is a big hurdle. But if you
*must* jump
that hurdle to achieve your goals, flying with solids first might
not be
the best use of effort. For example, if your goal is a system
that does
DC-X-style powered landings, then learning how to do reliable
parachute
recovery (which is harder than it looks, especially given that almost
every failure means building a new rocket) might be a costly
distraction.
Part of the problem is that there's a hidden mistake here, lurking in
Bruno's own wording. Quite likely it *is* a mistake to start with
development of a liquid *engine*, if your goal requires
development of a
liquid *propulsion system*. With solids, the engine pretty much
is the
whole propulsion system. With liquids, not so -- not even
close. People
seldom do post-mortems on failed projects, but I think a lot of
them would
show that the project died between "engine drawings complete" and
"first
successful firing", because getting the *rest* of the propulsion
system
working was planned to take a weekend, and after two 14-hour days
they
realized they were only getting started.
People who want a liquid propulsion system should not start, as
so many of
them do, by trying to design their ideal liquid engine. Better to
start
with the simplest and crudest engine possible, with no intention
that it
will ever fly, to get experience with plumbing, fluid handling,
controls,
ignition, plumbing, data acquisition, test operations, plumbing,
etc. :-),
before you maybe switch to a more sophisticated engine design.
Not least,
because that experience is going to change your ideas about what
the more
sophisticated engine should look like.
> for student projects it's important that you see results soon
to keep
> them motivated.
Agreed, and in fact I would omit "for student projects" -- seeing
results
soon is important for any volunteer effort, and it sure doesn't
hurt for
investor relations either.
For low-budget projects with an inexperienced team and nervous
sponsors,
the dinospace dogma of all-up testing -- build and fly the
complete final
system the first time, and of course it will work -- is a snare and a
delusion(*). Think incremental development and testing instead.
(* In fact, if you look at how the all-up concept developed -- most
notably, its use for Project Apollo -- the people involved didn't
believe
for an instant that the first test was certain to succeed. They
tried for
it, they hoped for it, and they were prepared to exploit it if it
happened, but they were far from sure of it. The "and of course
it will
work" part got added later, by the ignorant and overconfident. )
Henry
