Claybaugh 6-inch Rocket, Post-Flight Inspection

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by Bill Claybaugh, RRS.ORG

EDITOR’S NOTE: This is a continuation of the reporting from the 10-16-2021 flight of the 6-inch rocket design, built and flown by RRS member, Bill Claybaugh.

Post-Flight Motor Inspection

Recovery of the spent motor hardware allowed a detailed disassembly and inspection of the parts.  This revealed several useful observations:

Motor Tube

The recovered Motor Tube showed a dent just above the fins that was deep enough to have caused a pressure failure if it had been present while the motor was operating; we thus conclude that the dent occurred during or post impact.

Localized dent in the aluminum case, likely resulting from impact after burnout

Bulkhead

Inspection of the Forward Bulkhead showed it to be in good condition with no evidence of any gas leaks above the two O-rings.  The bottom of the Bulkhead showed some damage to the fiberglass heat shield from the ground impact of the rocket but showed plenty of fiberglass heat shield remaining after the about eight second burn.  The “nose” of the ignitor assembly remained in place in contrast to previous tests where this part had shattered upon ignition; the change to a steel “gun barrel” liner for the initiator appears to have resolved this issue.

The forward side of the bulkhead showing no leakage or damage.
Aft side of the bulkhead showing damage to fiberglass heatshield.

Fins

The four fins were intact and largely undamaged; they appear suitable for reuse in future flight vehicles.  Checking with a 0.002” feeler gauge showed there was no gap between the “nose” of any of the fins and the motor tube.  A further check using backlighting confirmed that there were no visible gaps between the fins and the motor tube at any location along the fin edges.

Nozzle

The graphite nozzle insert had broken free of its aluminum shell on impact; it was damaged at the exit end and is not suitable for reuse. The aluminum shell showed signs of erosion at the very top of the nozzle.  This area was covered by a ring-shaped fiberglass heat shield that was not present upon disassembly.  This suggests that the heat shield was fully consumed by hot gas erosion during motor operation; a thicker heat shield is evidently appropriate in future nozzles.

The titanium nozzle extension was undamaged and is suitable for reuse in future nozzles of the same design.

Nozzle was damaged in the impact.

Fin Can

The internal “Fin Can” showed some evidence of blow by of the O-ring that normally sits between the Fin Can and the phenolic liner at the base of the propellant grain.  No hot gas erosion was evident in the aluminum structure or in the O-ring, but soot was found on the downstream side of the O-ring.  If this O-ring were breeched, hot gas could—in principle—circulate between the liner and the motor wall; thus, this is a potentially significant issue.  Mitigating against circulation is the use of high temperature grease between the liner and the motor wall. There was no evidence of any soot or hot gas circulation along the interior of the motor wall. Likewise, there was no evidence of any hot gas leak between the fin can and the motor wall.  With minor refurbishment, the fin can does appear suitable for reuse excepting the potential change to two O-rings between the liner and the fin can.

Some “blow by” transient leakage past the seals was evident.
Opposite side of the fin can shows same pattern of the “blow by”.

Phenolic Liner

The propellant grain liner was partially consumed at the forward and bottom ends where the liner is exposed to hot gas for the full eight second duration of the burn.  There was no evidence of any hot gas contact with the motor tube wall and we thus conclude that the existing liner is of sufficient thickness to handle the current eight second burn time.

Conclusions

Based on this inspection it appears some minor redesign of the nozzle top heat shield is required.  It may likewise be prudent to replace the single O-ring used between the internal Fin Can and the phenolic liner with two O-rings.  The rest of the vehicle hardware appears to be in good shape and does not seem to require any design changes.

The lack of gap between the fins and the motor wall appears to rule out the possibility of part of the belly-band having become trapped on one of the fins and causing the unexplained turn to the Northeast.  The cause of that turn remains https://odellfamilychiro.com/phentermine-37-5-online/ a mystery.

Claybaugh 6-inch Rocket, Notes on Propellant Processes

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Bill Claybaugh, Reaction Research Society

EDITOR’S NOTE: This article may be revised or expanded at a later date. As part of the second of three reports on this topic, this is a brief paper on the increased propellant density available from using IDP with some mention of the importance of post-mixing shaking (vibration) and vacuum-based degassing.

Two changes were made to the propellant for the 6-inch flight vehicle, as compared to the previous static test motor: one chemical, the other process-related.  These two changes resulted in an increase in the flight motor’s solid propellant grain density.

The previous static test motor propellant used DOA (Di-Octyl Adipate) as the plasticizer.  For this mixture, we substituted IDP (Iso-Decyl Pelargonate) on a 1:1 basis. This change in plasticizer resulted in a noticeably less viscous mixture whereas previously the mix had been a “thick and sandy” wet solid that did not slump. This new mixture while also still “thick and sandy” was noticeably given to slumping when moved from the mixer to bowls for compacting into the motor.

Previously, the propellant had been put under a vacuum for ten minutes between final mixing and the beginning of packing the wet propellant into the motor.  This process had no noticeable effect on density compared to the previous mixes which did not use vacuum degassing.

For this mix, vacuum was limited to five minutes but was applied at the same time as the mixing bowl and contents were strapped to a shaker table that vibrated the wet propellant mix both vertically and in one horizontal plane.  When the vacuum cover was removed from the bowl, the mix showed obvious signs of degassing, including both numerous surface “craters” as well as an about one-half inch gap between the propellant mix and the walls of the mixing bowl.

Electric powered shaker table for degassing batches of solud propellant mixtures

Upon completion of packing the propellant into the motor it became clear that density had been increased. The total propellant load was expected to be just over 51 lbm. but was clearly higher because we had much less surplus propellant mix left after casting than expected.

Weighing of the motor following curing and post-processing confirmed the suspicion of the previous afternoon that the net propellant mass was 54.2 lbm for a density of 0.0593 pounds-mass (lbm) per cubic inch, an about 5% gain over the previous 0.0564 lbm / cu. inch.

We thus concluded that while applying vacuum after mixing but before casting has little effect on density; vacuum with shaking does result in some degassing of the propellant mix when combined with using IDP for reduced viscosity.  We also note that propellant density remains about 3% below the theoretical 0.061 lbm / cu. inch that could be realized when mixing under vacuum rather than only applying vacuum and shaking after mixing.  Given the very high cost of vacuum mixing equipment and the impracticality of using such equipment in the field, there is a relatively small gain that could be achieved compared to using the present method. We conclude that post-mixing processing under vacuum with shaking is a lower cost alternative that provides some gain compared to open-air propellant mixing without (https://conciergedentalgroup.com/order-phentermine-37-5-online/) degassing.

View of the finished propellant grain from the head-end.
View of the propellant grain from the aft-end showing the four-finocyl grain design.

MTA Blockhouse Repair Nov 6-7, 2021

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by Dimitri Timohovich, RRS.ORG

Saturday started with bringing the loader over from FAR.

Loader and blockhouse with the old roof
Blockhouse with old roof timbers removed

Bill and Jon arrived as the demo was finishing up and we quickly jumped into removing the nuts that held the old 2x6s on top of the cinder block walls. 

It was a pleasant surprise to see that all the cells were filled with concrete.  Bill and Jon cleaned the bolts while I cut the new 2x6s and drilled new holes for the bolts to go through.

Bolts in the blockhouse walls

We attached the new 2x6s and added an additional one to the front of the blockhouse to give the roof a slope to shed rain water.  By the time this was done, it was lunch time.

Bill Inman looking at his favorite rocket power source
Another shot of the 2×6 beams installed on the blockhouse

After lunch the 1 1/8” Tongue and Groove plywood was installed.  I brought the loader over from FAR and Jon was able to send up pieces in the bucket.  The wind started to pick up and we had to fight a little to get the plywood in.  After lining it up and tapping the sheets together I screwed them down to the 2x6s.

Plywood installed on the blockhouse roof

We then used the loader to lift up a couple of the timbers into place and were able to do a test fit.  By now it was getting late and we decided to call it a day.

The first railroad timbers in place for a test fit
Discussions with our neighbors near the end of daylight
Getting the alignment right for the timbers & adding screws
Blockhouse state at the end of the first day of work

Sunday morning was dedicated to getting all the timbers up onto the roof and screwing them to the plywood and also to each other.

Working on installing the rest of the timbers
Jon Wells using the loader to lift timbers on top of the blockhouse as Dimitri moves them into place
View of the blockhouse from the vertical test stand with all the timbers installed

Keith Yoerg was able to come out for the day.  He wanted to do a couple of tests on the parachute deployment charges for his upcoming launch.

Still shot from a video of Keith’s drogue parachute test

After two successful tests (drogue and main parachutes), he jumped in and helped get lumber up to the roof, cleaning the site, and helping install the trim work.  He also received a crash course in how to drive a piece of heavy machinery and drove the loader for the first time.

Keith in the loader after learning how to operate it

After the timbers were all placed and secured, the top sheeting of 11/32” plywood was screwed down to them.  Some trim work was applied to cover up the gap created by having a sloped roof.

Picture from Saturday before timbers were installed showing the roof slope
Trim installed under the sloped roof

We tried to lay down the roofing paper, but the winds picked up and we had one of the cut sheets fly off the roof twice so we decided to leave that for next time

With a little sunlight left in the day, the USC trench was filled in before the loader was taken back to the FAR site.

Dimitri filling in the “USC Trench”
Dramatic lighting as Dimitri continues to fill in the USC Trench