When the nozzle departs the motor you get a "signifiant" impulse, the
nozzle gains a signifiant velocity in the other direction.
High speed shrapnel has a habit of not behaving as you would expect it to.
Be safe.
On 19/04/2023 12:17 pm, kevin ward wrote:
Just thinking... If this motor, encased in Kevlar, we're 2 fail, it would be a seam leak, maybe popping the nozzle... I don't c all of it going, evenly throughout, and impossible to shatter ???
I test burned some 1% rich aluminum candy, without insulation, one wrap over phenolic, maybe 100psi nozzle... The stainless steel "fender washer" nozzle leaked. Fibers intact, minus epoxy, possibly reusable, though no more pretty yellow
Not saying I'm not gonna prepare 4 explosion
On Mon, Apr 17, 2023, 6:37 PM Henry Spencer <hspencer@xxxxxxxxxxxxx> wrote:
On Mon, 17 Apr 2023, kevin ward wrote:
> Can anyone help with this equation...
> More psi in combustion chamber, no matter what, results in more
thrust ?
> BurnSim says so...
>
> But dad insists NASA knows best and may 1 at the throat is
penultimate.
Both are right. :-)
Yes, under anything resembling normal rocket conditions, gas
velocity at
the throat is Mach 1 (note that this is relative to the speed of
sound in
the exhaust gas there, which is a function of its composition and its
temperature -- often faster than the normal sea-level speed of sound).
However, higher pressure makes the gas *denser*. It's still
coming out at
the same velocity, but there's more mass per cubic centimeter and
hence
more mass per second. And so more thrust, at the cost of more fuel
consumption.
Higher pressure also has some secondary effects, like encouraging
more
complete combustion, but those are smaller.
Beware of analogies to liquids -- the gas is compressible, and
that makes
a BIG difference in flow behavior.
> I could see a different analogy that proves me wrong as in with
a boat
> and it's propeller. There is a point before velocity increases,
that if
> you apply too much torque, you're going to cavitate. Does that
apply in
> rockets ?
Not in the chamber. (In pumps and in the feed system in general,
yes.)
Again, gases and liquids are quite different.
> I insist that NASA is limited in acceleration due to what they're
> sending up; people, equipment, O-rings that go bang, etc. And
the whole
> point is to "attain escape velocity as quickly as possible".
"Other things being equal." But other things aren't equal. Notably,
higher thrust generally requires heavier engines, which reduces the
payload, the amount of fuel that can be carried, or both.
Optimizing for maximum payload, or for maximum final velocity with
a given
payload, usually pushes upper stages toward small, light engines
with long
burns and big tanks.
First stages are a bit different, because they've got to haul the
upper
stages up off the ground and clear of the atmosphere for long
enough to do
those long burns (I oversimplify slightly). But even they often
optimize
to thrust less than twice takeoff weight, depending somewhat on
details.
That's the general picture for sizable rockets. For small ones,
air drag
during ascent is more of an issue, and that can push toward lower
thrust,
to keep velocity down until the rocket has cleared most of the
atmosphere.
There are a bunch of other issues that can also affect the numbers.
Henry