Dextrose Testing

So the TR-1 didn't go the way that I had hoped but it wasn't all bad.  It reinforced the idea that making even a small change to your plan should be very carefully considered.  A lesson worth reinforcement.  The damage was not nearly as bad as it could have been and was, for the most part,  limited to the casing, pressure gauge , and the bulkhead.  The bulkhead will need to be re-drilled and tapped but there is enough space left to do that.  The Casing is relatively easy to fabricate and I have already procured new stock.  The nozzle surprisingly was relatively unscathed and after removing a few bolts that had been sheared off in it, it's good to go.   I have continued going through all of my boxes of rocket and rocket related stuff in an effort to organize my workspace and found that I actually have enough sorbitol on hand to cast this motor.  I will take a more stepped approach geared towards a full scale test before proceeding with another full on motor test.  Hopefully this winter around December or January.  The first step is a smaller single grain test motor sized for the 4" diameter grain segment.

In addition to prepping the TR-1 motor for another test I will be doing some smaller scale testing utilizing Dextrose.   I plan to use the 2.375" motor that designed, tested, and flew back in 2009/10.

 

Originally this motor was designed for sorbitol based propellant.  Ultimately it was fired with KNSB based propellant and a 50/50 sorbitol/Erythitol mix based propellant.   I have constructed a four segment casing for this motor which would produce a low MEOP of 600psi with KNSB and 950psi with KNDX.

SRM screen grab

 

 



TR-1 Cato

Theo and I tested the TR-1 motor on Saturday and unfortunately suffered a cato.  It was an impressive sounding motor for that first few milliseconds though.  Apparently I should have rethought my decision to use Dextrose in place of Sorbitol.  On paper the change seemed fine but I had limited experience with Dextrose and never in something of this size.  The actual casting of the grain segments went fine but I experienced some slumping in two of segments that I cast.  At the time I decided that the slumping was due to having removed the segments in question too soon from the mould.  I believe that segment slump either contributed to or was the direct cause of the cato.  Fortunately I had cast an extra segment and at the end of the day, long after the firing, that segment which had been stored in the same conditions as some similarly sized Sorbitol segments that Rick had cast had slumped.  The sorbitol segments remained fine.  The dextrose segment had slumped so severely that the core was essentially gone.  I know of many folks that have use dextrose based propellants with no reports of slumping so I’m unclear of the reason, maybe the size of the segments?  For now I will switch back to Sorbitol in the TR-1 motor and save the dextrose for some much smaller scale motor testing.  We had a good time regardless.  The guys at FAR were very helpful, and the site had grown quite a bit since our last visit there some three years or so ago.  Rick Maschek also provided lots of assitance and camera work.  Rick also had a nice firing of a KNSB motor with a Double-D grain configuration.  The third photo is of Rick's firing.  The last photo is af an  AP motor firing that anomther FAR member (Erik, I think) conducted.

 

 

SUGAR SHOT TO SPACE SUCCESSFUL FIRING

The Sugar shot to Space project had a much needed successful firing this past weekend.  After the spectacular CATO of the impressive DoubleSShot motor nearly one year ago there was a lot of discussion and investigation into what exactly happened and why.  This test represents the first in a series that will lead SStS to the successful firing of one of the largest amateur motors of all time.  Certainly the largest "Sugar" motor of all time.
Congratulations to Rick Maschek, Paul Avery, and Richard Nakka for their dedication and perseverance, as well as the many other numerous volunteers that have contributed to the project.

Static Test Results

I finally got around to looking at the data from the static test from back in April. The motor was mostly comprised of hardware from a previous motor that I lengthened to make room for another propellant segment. That results in the initial Kn rising from 340 to 425. The other big difference was that I added 1% RIO to the propellant. I also changed the closure method from snap-rings to a bolt-ring closure designed for the increased chamber pressure. The propellant grain consisted of 5 segments in a bates grain configuration weighing 9.247 lbs with a port/throat ratio of 1.5625. The propellant was mixed in a ratio of 65/35/01 (KNO3/Sorbitol/RIO) and cast into 3" mailing tubes that have an ID of 3" and an OD of 3.125". The casing insulation consisted of four layers of rosin paper. The casing and bulkhead are fabricated of 6061-t6 aluminum. The nozzle is fabricated from 12L14 "leaded steel" and had a throat diameter of 0.64" and an expansion ratio of 12.

The total impulse was 1213 LB-Sec (5395 N-Sec.) making it a small M-class motor. I was also pleased to find that the calculated ISP was 131. Slightly higher than I expected given the fact that I didn't spend a lot of time premixing the propellant ingredients and used the KNO3 as received.

There was no measurable throat erosion post firing and the nozzle appears to ready for another firing. When I took the motor apart post test I found that the insulation was severely breached at the bulkhead end. I think that the higher chamber pressure created a much harsher environment for the insulation than I was expecting. The insulation breach resulted in a small blister in the casing about .125" in diameter and about .005" high. I'm happy to replace the casing since it was one of the most out of round 6061 tubes that I have ever purchased. The casing thickness provided for a fairly significant safety margin, so I'm considering pushing the design a bit by using a .065" walled casing which will allow the insulation to be more than doubled and should make for a very lightweight and powerful motor. Overall, I'm pretty pleased with the results.

Photos from November

Last November my friend James and I participated in a propellant class at the FAR site. James took some great pictures of the days events. The pictures above are of my KNO3/sugar motor and of my AP/AL/HTPB motor. The photo of the composite test was taken during the day but was "stopped down" in an effort to reveal the shock diamonds. Video of both of these firings can be seen here. More of James' photos of the days events are online here.

Static Test

This past Saturday I participated in a sugar propellant class at the Friends of Amateur Rocketry (FAR) facility. Brent Dougherty did a nice job presenting a general overview of how to safely work with and cast sugar based propellants. Thanks to the FAR guys Kevin, Mark, Ted and the others for letting us use the site. They have done an amazing amount of work on the site, including a massive vertical test stand (I don't remember what it's rated for).



As part of the class I fired an L-class KNO3/Sorbitol demonstration motor. The firing went well and good data was collected. This is a simplified set-up from what I've used in the past and it worked well. I'm planning on making some adjustable steel brackets that mount with bolts rather than the cargo straps. Here is the set-up:




In the picture taken just after the firing you can see the nozzle glowing red hot, once I got the motor torn apart and cleaned, everything appeared to have survived the firing just fine. The gauge measuring thrust began to register data about a tenth of a second or so before chamber pressure began to be recorded. I suspect that the pressure port was briefly clogged by the igniter initially. After tearing the motor apart I found a glob of melted plastic that used to be the soda straw that held the BP.

Early Dual Burn Motor Test

This is a video of a static test that I conducted back in 2005 when I first got involved with the Sugar Shot project. The dual burn concept is not new, but I haven't heard of any amateurs pursuing it. At this size, I don't think you'd realize much benefit. However, in a slightly larger motor, such as the one that we are currently constructing, you begin to see some real benefits. The concept is similar to staging, but in some ways simpler to execute. One of the major difficulties is that the first half of the casing and the nozzle are subjected to twice the heating that they would have to endure in a two stage design. The motor that we are currently working on has the potential to reach nearly 50,000 feet, which is considerably higher than you would expect to go with a "standard" motor that expends all of it propellant close to the ground in denser air. Despite some minor problems, I considered this early test to be successful. The o-ring on the upper bulkhead was damaged, and I didn't have a replacement. That resulted in a small leak during the 2nd burn. However, there were several key things that did seem to work. Most notably:
The first propellant grain burned properly and ignited the epoxy plug .

The epoxy plug burned through without igniting the second propellant grain.
The burnt remains of the epoxy plug did not obstruct the nozzle.
The mid-bulkhead did not seem to have a significant effect on the 2nd phase thrust.