Very interesting read Aidan! Please keep us up to date with your progress!
Gary W
----- Original Message -----
From: "Aidan Sojourner" <aidan@xxxxxxxxxxxx>
To: tccrockets@xxxxxxxxxxxxx
Sent: Sunday, July 19, 2015 9:27:17 PM
Subject: [tccrockets] Re: July Launch
Ok, here are some details about the static test that.
The formula itself is not very interesting, pretty typical low solids pourable
stuff. The interesting part is the grain design. As you guys know, most motors
have a small number of grains which usually have the same diameter core.
This motor is based on a design by Geoff Huber, in turn based on the Super Loki
motor. The design was one giant (25.375") grain that continuously tapered from
the top to a small diameter about 40% of the length of the motor and then out
again to larger diameter for the remaining length (see attached drawings). This
is extremely advantageous because the propellant essentially serves as a
thermal insulator for itself - burning only from the inside out, and not at the
faces of the grains like in typical BATES motors. This makes the design useful
for odd case sizes where liners might not be easily acquired.
In addition to slowing down the gas flow as it exits the motor- resulting in
less erosion and less pressure, the tapered core also raises the port/throat
ratio to a comfortable level. The port/throat ratio is proportional to gas flow
velocities out of the core and throat; If the port/throat ratio is too low, the
motor can experience severe erosive burning and potentially spike the pressure
to unsafe (CATO) levels.
This motor simulated out to a 20% L710. I do not have any data acquisition
equipment as of now, this static test was a "proof of concept" scaled down
version of a 3.5" N motor I am designing for next year. It burned a bit faster
than was expecting, and I think it had a lot less total impulse than the
simulation says. The simulation thinks that the propellant mass is 1450 grams
when in reality it was around 1320. I am not really sure where I lost 100 grams
of propellant but I think it has to do with simulating the motor in 0.25"
chunks rather than the reality, a smooth taper. I was originally going to fly
this motor in a 54mm minimum diameter at Aeronaut in two weeks but I think I'm
gonna stick to a typical BATES motor for that flight.
Aidan
On 19/7/15 18:26, James Dougherty wrote:
Awesome! What was the formulation Aidan?
On Sun, Jul 19, 2015 at 5:50 PM, Cliff Sojourner < cls@xxxxxxxxxxxxx > wrote:
<blockquote>
On 2015-07-19 10:01, Eric Melville wrote:
<blockquote>
I am editing now and will post shortly. Of course, I am totally self centered
when
it comes to flights and I do not have a single rocket shot other than my own. I
did
get one of the Aiden L static test, though!
OK, finally got to a place with wifi to upload. here's the 210 frames per
second slow-motion of the L static test
https://www.youtube.com/watch?v=q_hFb65pObI
enjoy! maybe Aidan will fill in details of the motor, it's an interesting
design.
sorry didn't trim the first realtime second of nothing which means 7 seconds on
the video. the focus isn't perfect, the video looks fine in 640x480. there is
a way to get the camera to precision focus but it is too hard in the heat and
sun.
</blockquote>
</blockquote>
