[AR] Re: Qualification testing and acceptable performance criteria
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Sat, 30 Jan 2021 19:40:58 -0500 (EST)
On Sat, 30 Jan 2021, roxanna Mason wrote:
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.
Which is fine, if all you want to do is admire the pretty Mach diamonds.
If, on the other hand, the engine is part of a larger system -- like, say,
a rocket :-) -- then even if that larger system is still an amateur build,
a bit more attention to specs is in order. That's what the original query
was about: what sort of numerical specs *should* you set for things like
pressure fluctuations, if you want an engine that will behave itself when
it's asked to propel a rocket that considerable time and effort has been
invested in? Even for an amateur project, this isn't at all a ridiculous
question. It may not have a simple *answer* at an amateur level, but the
question is legitimate.
And while an amateur probably wouldn't want to adopt a pro-level spec like
SMC-S-025 in its entirety, it might have useful information to offer.
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...
Even a paying customer will often ask you what the specs should be --
sometimes because they genuinely don't know, but sometimes because they
want to see if *you* do! If you don't know what you're doing, maybe
they'd prefer to pay somebody else who does.
Moreover, if it looks like you do know what you're doing, maybe they'll
take your word for it that those are the specs that should be in the
contract... meaning that you don't get paid unless you can meet them.
And also, that there'll be trouble if you meet them but the engine still
doesn't do the customer's job! Even if you get to make them up, it can
matter whether they're right. If you want repeat business, you can't say
"well, we thought this was going to be good enough, but..." very often.
(Been there, done that.)
And all these things have analogs at the amateur level, too. Even if it's
only your own rocket you're blowing up, it's still lots better if six
months of effort *don't* go up in smoke. :-) So asking "what should I do
to make sure that doesn't happen?" is perfectly on-topic.
Henry
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