[SS2S-Main] Re: Sugar Shot Weekly Activity Report -- Mar.10-24, 2014

  • From: monsieurboo@xxxxxxx
  • To: sugarshot@xxxxxxxxxxxxx
  • Date: Fri, 28 Mar 2014 10:36:29 -0400 (EDT)

Rick, as always, thanks for the wealth of first-hand details.  I test my 
paraffin-blend hybrid grains nozzle-downward too, for the same reason -- 
inverted or even horizontal testing doesn't let the considerable paraffin 
"slag" escape from the engine, so it's not an ideal simulation of flight 

So it seems the pressure drop may not be an artifact?  It'll be interesting to 
see the next set of results with engine orientation flipped 180 degrees.  

Mark L.




-----Original Message-----
From: Rick Maschek <rickmaschek@xxxxxxxxxxxxxx>
To: sugarshot <sugarshot@xxxxxxxxxxxxx>
Sent: Thu, Mar 27, 2014 6:22 pm
Subject: [SS2S-Main] Re: Sugar Shot Weekly Activity Report -- Mar.10-24, 2014

Hi Mark, 

I don't think the pressure began decreasing because the pressure port was 
becoming blocked by slag. I've done many static tests with the nozzle up and 
instead of most of the solids (slag) being blown out the nozzle, some will 
collect at the bottom bulkhead end. Add to this the nozzle throat on this motor 
is sized for a 6-grain burn and you end up with lower pressure for the motor. 
If you look at the video, the motor exhaust is clearly decreasing after the 
high until it starts 'coughing' up black smoke and flame and post burn there 
was a great deal of slag on the nozzle because of the low pressure.

Here is an example of a previous static test with the motor with nozzle up. You 
can see as the gauge bounces around the 300-350 psi level it stays at that 
place as the motor burns down because the port became blocked, trapping that 
pressure in the line to the gauge. 

https://www.youtube.com/watch?v=_xk4dMEUS8I ;

There was no change in formulas or suppliers, both KNO3 and Sorbitol came out 
of the same bags. I will be doing another test of the exact same motor at the 
next FAR date except it will be mounted in a vertical nozzle down orientation. 
Since that is how the motor will be positioned for flight it makes sense to do 
the motor testing that way and this will be the orientation I will use for 
future static tests unless there is a compelling reason to do it nozzle up or 
mounted horizontally. 

I think our first 4-grain January 4th motor may have burned through the motor 
case because of an inadequate liner and because of the horizontal mounting...it 
burned through just above the nozzle on the bottom side where one might expect 
slag to build up. The pressure readings of these two 'identical' motors were 
completely different probably due to the type of inhibitor used on the grain 
surfaces and possible orientation (see video starting at 2:00)

https://www.youtube.com/watch?v=oF04Uyz_cxA ;

In the Jan 4th motor, the inhibitor consisted of a 'thick mixture' made of 
polyester resin with quartz micro-balloons mixed in and then painted on the 
propellant surfaces in two coats. This probably burned away quickly causing the 
entire surface of the grains to ignite leading to a high Kn and pressure. On 
the second 4-grain March 7th motor, this same 'thick paint' mixture was applied 
to the propellant surface with 3.8 ounce fiberglass and the burn pressure 
profile for it does not ramp up to a high pressure like the Jan 4th motor did 
and did its job of inhibiting the surfaces applied to.

And we have been using a slag catcher in front of and in the pressure port (  :
I've been using steel wool over the port and in the first 1/2"


  On Thursday, March 27, 2014 11:27 AM, "monsieurboo@xxxxxxx" 
<monsieurboo@xxxxxxx> wrote:

"The pressure decay ishypothesized to be a result of the unusually large 
build-up of slagthat had pooled on the forward bulkhead, which likely blocked 
thepressure port leading to the gauge."

So the takeaway is that the pressure decay is purely artifactual due to the 
slag buildup and doesn't reflect an actual grain performance issue?  Makes 
sense, considering the history of pretty close matchups between our previous 
designs and their real world performance.

Any hypotheses about the cause of the increased slag?  Change in formula or 
suppliers?  I just don't wanna hear that now we have to add a slag catcher in 
front of the pressure port...!  ;-)

Mark L.



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