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