After hearing/seeing all this discussion it seems a bit out of place in an
amatuer,i.e. aR site. Before I got into 'professional rocketerty, that's
making money at your hobby, the only requirement(s) was that the engine
didn't burn out or explode. Shock diamond with no sparks meant a successful
test.
So what are you doing what you're doing or is it for someone else like a
paying customer? They make the requirements, if they don't have any then
you make them up which gives you as much wiggle room as you want/need.My
first customer screamed YEAH, ALRIGHT! Before even reviewing the data which
was only a video camera. Steady state combustion to tank depletion was the
only requirement which was about 10 seconds LOx/Kero @ 3KLbF.
K
On Sat, Jan 30, 2021 at 2:27 PM John Schilling <
john.schilling@xxxxxxxxxxxxxx> wrote:
For liquid rocket engine qualification testing, SMC-S-025 is the place to
start. But note that, however frightening that document may look, it's
more like guidelines anyway. As Henry Vanderbilt notes, the requirements
that matter are the requirements for your mission. S-025 is *always*
tailored to the mission; nobody ever meets every word of the spec. But it
compiles a great deal of hard-earned experience about what sort of things
you need to look for (not all of which are obvious) and what is usually a
good level of testing.
W/re steady-state operation, it is what it is and even the letter of S-025
doesn't specify a particular value. You determine by test how long it
takes your engine to settle down to steady state, then A: verify that your
mission can tolerate unsteady operation for that long and B: make sure the
*rest* of your testing is done long enough to reach steady state. Because,
yes, there are people who have "qualified" their engines by testing at the
corners of the mixture ratio box for less than the steady-state timescale,
said "didn't blow up, so we're good", then found that the steady-state
condition at one of those corners was too hot for the chamber material to
handle.
There's a recent version of S-025 at
http://54.237.174.144/USAF/USAF-SMC/SMC-S-025_26JUL2017_55747/
And a paper describing the history and rationale at
https://arc.aiaa.org/doi/abs/10.2514/6.2019-4025
John Schilling
On 1/27/2021 11:20 PM, Nathaniel Van Rumpt wrote:
My student team (12kN, LOX/Kero) is trying to determine what flight engine
qualification criteria should look like. Most old literature merely contain
phases such as "the engine shall be tested to confirm acceptable
operation," yet they often don't define what "acceptable operation" looks
like.
We had a few questions in particular about:
- What would be an acceptable level of chamber pressure fluctuations?
- How would one measure and determine an acceptable vibration level?
- How quickly should steady state operation of the engine be
achievable?
- How long should one test the actual flight engine before assembling
into the rest of the rocket?
Furthermore, what other engine acceptance criteria should we be
considering?
Cheers,
Nathan