Just to show the importance of addressing the variability of each batch of
propellant: Note that the space shuttle required that both solid rocket
boosters be cast from the same propellant batch - they were concerned about
differential thrust if they were cast from different mixes using the same
formula!
https://www.space-shuttle.com/srb.htm
Thanks!
-David Summers
On Mon, Apr 24, 2023 at 5:40 AM John DeMar <jsdemar@xxxxxxxxx> wrote:
Kevin,
You will get up to speed with APCP more quickly if you join the
Tripoli Rocketry Association and find a mentor. https://tripoli.org/
It appears you are in the St. Louis, MO area. Check out:
https://www.stlouisrocketry.com/
Another suggestion is to purchase Terry's book: Terry McCreary's book
"EXPERIMENTAL COMPOSITE PROPELLANTS" : http://rimworld.com/book/
The 'a' and 'n' values in St. Robert's law burn rate equation are
determined empirically through propellant testing. There are too many
real-world variables which make it impractical to model and predict.
However, there are known factors which affect the *trend* in the burn rate
as well as the Isp. Once you have a basic APCP formula characterized, you
can experiment with those factors.
There are also practical limitations when designing a solid motor, such
as the casing material and insulation. Trying to scale from a small motor
to a larger motor has additional challenges.
Burnsim is very useful for grain design and motor simulation. But, you
need to have experimentally determined the burn rate coefficient and
exponent through testing. PropEP will not give you these values, but it
will allow you to see the trends in Isp, combustion temperature, etc, while
varying ingredients.
-John DeMar
Las Cruces, NM
On Mon, Apr 24, 2023 at 8:57 AM Terry McCreary <prfesser@xxxxxxxxxxx>
wrote:
I see...
Guess I'll leave it to the Arocket community...if I were to do a third
edition of ECP (probably won't), does Kevin's comment mean that I need to
make a correction? Do I need to delete much of the material in Chapter 4 on
specific impulse? Whaddaya say, folks?
Maybe my thought processes are going downhill faster than I
thought.....sigh.....
TWM
------------------------------
*From:* arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> on
behalf of kevin ward <kevinward46@xxxxxxxxx>
*Sent:* Monday, April 24, 2023 1:37 AM
*To:* arocket@xxxxxxxxxxxxx <arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Re: APCP properties, was Re: Re: starship abort?
Btw... Specific impulse does not change due to psi, though the produced
thrust, will
On Sat, Apr 22, 2023, 1:57 PM Terry McCreary <prfesser@xxxxxxxxxxx>
wrote:
Kevin,
You will likely get more replies if you start a new thread with a new
subject line, rather than tacking a question onto an unrelated existing
thread.
The properties of APCP vary hugely with the composition. Burn rate can be
anywhere from 0.1"/s to 1"/s or even somewhat higher. Exponent anywhere
from zero to 0.6 or higher; additives can have an enormous effect. Specific
impulse from roughly 140 to 260 s. And all those figures are usually quoted
for 1000 psi; ballistic properties can be greatly---even
dangerously---different at higher pressures.
To find burn rate, a, and n.....make and burn the propellant.
Thermodynamic properties can be predicted/calculated fairly accurately from
composition. But kinetic properties generally require actual testing.
Changing to a different source for some of the ingredients? Re-testing is
almost a given. Many of those who do a lot of work with APCP often buy
ingredients in bulk to avoid concerns about different properties. (Despite
the fact that AP is a compound, 200 micron AP from Gary Rosenfield is
likely to be at least somewhat different in its behavior from 200 micron AP
purchased from, say, Skylighter or another pyrotechnics source. Morphology,
proportion of fines, etc.)
TM
------------------------------
*From:* arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> on
behalf of kevin ward <kevinward46@xxxxxxxxx>
*Sent:* Saturday, April 22, 2023 9:30 AM
*To:* arocket@xxxxxxxxxxxxx <arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Re: starship abort?
Hi everyone...
Can anyone give all propellant characteristics of Ap\Htpb+Al (BurnSim) ?
We've found all but the burn rate a, n.
Unsure if best recipe, as well. (Shuttle SRB's ?)