Have any of you used a centrifuge for propellant settling? If you are
working in pairs of grains or motors it wouldn't have to be very
elaborate, a piece of channel with end stops attached to a motor, like
a scary rocket ceiling fan. 10G would be relatively easy. The spin
cycle on washing machines can be 400G. Tapping it on the ground is the
same idea but much briefer and higher-G.
For larger motors a single motor could be spun like on a lathe.
Supposedly in APCP rockets that will result in the propellant
stratifying as the heavier components move toward the casing. The
density of sorbitol and potassium nitrate are much closer to each
other than that of HTPB and aluminum so it might not be an issue.
On Tue, Nov 24, 2020 at 4:35 PM Richard Nakka
<richard.rocketry@xxxxxxxxx> wrote:
I forgot to mention one important thing regarding obtaining good grain
density. After loading the casting tube with propellant, I immediately tap it
down against a hard surface (such as floor) repeatedly, perhaps a dozen
times. If there is any trapped air, it will be seen to rise to the surface in
the form of bubbles. Only then would I insert the coring rod and cap (if
using compression). Doing this is important whether or not compression is
used.
Richard
On Mon, Nov 23, 2020 at 10:22 PM Bdale Garbee <bdale@xxxxxxx> wrote:
"" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "tadserralt" for
DMARC) writes:
Richard just mentioned the possibility of increase burn rate due to
the modified formula.
Changing the oxidizer grain size definitely changes the burn rate.
I still think a void or crack or disbonding did it because the K-class
24 inch static test went very well
I agree that your most likely cause of CATO was a void. However, don't
ignore the fact that a faster burn rate means a higher operating
pressure for a given KN. Students I mentor seem to forget this
sometimes!
Until/unless you actually characterize the burn rate over pressure of a
"new" propellant after making changes in either the chemical composition
or processing steps (like grinding the oxidizer), assumptions tend to
lead to CATOs...
Bdale
