[SS2S-Main] Re: Sugar Shot Weekly Activity Report -Dec.16-20, 2013

  • From: Rick Maschek <rickmaschek@xxxxxxxxxxxxxx>
  • To: "sugarshot@xxxxxxxxxxxxx" <sugarshot@xxxxxxxxxxxxx>
  • Date: Thu, 2 Jan 2014 12:23:51 -0800 (PST)

I included the picture of the nozzle and exhaust deflector post firing to show 
what happens to the nozzle bell and in this case, the deflector, with low 
pressure sugar motors (at 5:15 in video). That has also been common with this 
two grain motor in the past when using BATES grains. The throat of this nozzle 
is sized for a full 6-grain motor that when fired, shows little slag build up. 
This same nozzle is used with the short 2-grain motor when we've tested new 
things, ie. casting tubes, grain geometry, propellant changes, igniters, etc. 
to reduce the cost of doing these tests (and risk of CATO) on the first test of 
such changes. 
 
Also of note was the slag buildup on the side of the nozzle closest to the 
exhaust deflector. There could be a connection with the hole pattern in the 
sliver catcher plate but I have a feeling the asymmetric build up had something 
to do with the proximity of the deflector but only a test without the deflector 
would determine this. Next time I will lower the test stand deflector plate to 
see if it was the cause of that buildup pattern. Ben's suggestion of silicone 
oil could be tried in another test to determine if it works with sugar 
propellant...maybe even make the grains less brittle?

The propellant sliver catcher and forward bulkhead were both coated with Hi 
Temp RTV before the test. Post test, the coating on the sliver catcher was 
completely burned/eroded away with no slag deposits present, only a light 
coating of carbon that was easily cleaned off revealing the pristine unaffected 
steel plate. The coating on the bulkhead was still intact after cleaning the 
carbon off and the aluminum underneath completely protected (at 5:30 in the 
video). During ProtoSShot motor development, I experimented with different 
materials (cork, phenolic, etc) as insulation/protection for the bulkhead 
surface and attached them using RTV and found most were burned away or damaged 
but the underlying RTV was still intact. A subsequent test showed RTV was all 
that was needed for bulkhead protection.
 
The teacher in me likes to show everything and be open to outside comments; 
that is something that I've really appreciated about the Sugar Shot project.
 
Rick
 
ps Mark said "I did see, at 3:56-57, a gum-wrapper size piece of thin 
metal/thick foil fly through the frame. Any idea what that was?" 
     I believe it was a piece of electrical tape that was on the deflector.

From: Richard Nakka <richard.rocketry@xxxxxxxxx>
To: sugarshot@xxxxxxxxxxxxx 
Sent: Thursday, January 2, 2014 10:35 AM
Subject: [SS2S-Main] Re: Sugar Shot Weekly Activity Report -Dec.16-20, 2013


On Wed, Dec 25, 2013 at 5:36 PM, Cliff Bates <cliff@xxxxxxxxxxxxxx> wrote:
>    I kind of wonder about the terrific amount of build up of slag in the
> diversion part of the exhaust nozzle however.  It would appear that in
> flight if this happened it could cause a considerable yawing in the
> trajectory.

I wouldn't be too worried the slag buildup on the nozzle. This buildup
occurs only during the tail-off, when the pressure in the motor is
decaying down to zero. For this motor, the max chamber pressure was
low, and tail-off duration was particularly long,  which explain the
excessive buildup.


>    Also it appeared to me that the exhaust velocity was noticeably lower
> than normal.  But I'm kind of negatively bias on this diffusion plate idea
> anyway.


On Rick's urging, we decided to be particularly conservative with this
2-grain motor test, keeping the Kn low and therefore maximum chamber
pressure was particularly low (max 265 psi). The next two test
firings, 4 and 6 grain respectively, will see proportionally higher
chamber pressures.

Richard 


>
>> Date: Mon, 23 Dec 2013 22:25:28 -0600
>> Subject: [SS2S-Main] Sugar Shot Weekly Activity Report - Dec.16-20, 2013
>> From: richard.rocketry@xxxxxxxxx
>> To: sugarshot@xxxxxxxxxxxxx
>>
>> Highlights of recent developments on the DoubleSShot project
>>
>> ---------------------------------------------------------------------------------------
>> -As planned, Rick Maschek test fired the 89mm (3.5”) 2-grain rocket
>> motor with DD-slot grains on Saturday Dec.21st. The test firing was
>> conducted at the FAR site, with the motor mounted nozzle down on one
>> of the vertical test stands. The base of the stand was fitted with a
>> blast deflector to help prevent smoke from obscuring the pressure
>> gauge used to record chamber pressure. This worked well, and good
>> pressure readings were recorded over the full duration of the burn,
>> which was nominal. Maximum chamber pressure was about 260 psi
>> (1.9Mpa), which compares well with the predicted pressure of 248 psi.
>> Due to problems with the igniter, the planned firings of the 4-grain
>> and 6-grain motor had to be postponed. Rick will be modifying the
>> forward bulkhead with an igniter fitting to prevent a similar igniter
>> issue from re-occurring.
>> Rick and Richard Dierking setting up the motor:
>> http://sugarshot.org/downloads/setup.jpg
>> Richard Dierking connecting the pressure gauge:
>> http://sugarshot.org/downloads/setup1.jpg
>> Motor at full thrust:
>> http://sugarshot.org/downloads/thrusting.jpg
>> Gauge reading at full thrust:
>> http://sugarshot.org/downloads/gaugereading.jpg
>> DD-slot grain details:
>> http://sugarshot.org/downloads/dd_grain.pdf
>> Video:
>> http://www.youtube.com/watch?v=h1mYHtsD7a8&feature=youtu.be
>> (video courtesy Rick Maschek)
>>
>> -Richard has made further progress on fabricating the carbon composite
>> nozzle exhaust cone for the VIC-2 motor. All 10 plies of carbon
>> prepreg were wrapped around the mandrel. After each ply was laid,
>> heat-shrink tape was wrapped around the prepreg, then shrunk using a
>> heat gun to consolidate the layers. The product was then vacuum bagged
>> in preparation for curing. Curing will be done in an autoclave at
>> elevated temperature (300F/150C) and pressure (4 bar).
>> --------------------------
>> -Sugar Shot to Space is on facebook. Check us out.
>> http://tinyurl.com/2exr92k
>>
>
>

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