GaryDean L3 Build Thread - Prometheus 6

[GaryDean]

Hmmm, so where did that 43.75 inch location for the Forward Rail Button come from? It started with my consideration of the longest motor which I will be installing in the rocket. I will NOT be installing a CTI 98mm 6XL Grain motor or an AT 98mm 18000 / 20480 motor. They could fit, but it's my perception, using the "bang for the buck" theory, specific to this rocket, that a CTI 98mm 6-Grain or AT 98/15360 will make me happy. I already have a CTI 75mm 6XL Grain Motor Case, which is 42.25" in length. A CTI 98mm 6-Grain Motor case is 42.21" in length, and an AT 98/15360 case (and hardware) is 41.711" in length. Also, the Motor Retainer positions the thrust face of the motor exactly 0.75" back from the Thrust Plate. So, I am prepared to assemble the Drogue Shock-Cord Tether Platform exactly 41.75" from the backface of the Thrust Plate. That dimension will apply specifically to the bottom of the plywood centering ring, part of the platform. The total components to consider in this assembly, which make up the complete Tether Platform are;
1. Stop Ring (coupler diameter x 1/2" width), which will sit below (aft end direction) the plywood centering ring.
2. Plywood Centering Ring (6" OD x 75mm ID x 1/4" thickness).
2. FG Bulkplate (6" OD x 1/8" thick), which sits directly above (forward end direction) the plywood centering ring, which it is J-B Weld adhered against..
3. Stop Ring (coupler diameter x 1 1/8" width, which will sit directly above the FG Bulkplate. The design intent of this ring is to help absorb the forces applied by the Drogue Shock-Cord during apogee ejection.

I usually place the forward Rail Button exactly 1/3 of the length of the total rocket, from the base. In this case that would be 43.31". Hmm, interesting, that just happens to be exactly where components for the Tether Platform will be mounted. I thought about placing it below (aft direction) the Tether Platform. What if it requires some type of service / repair on the inside. NO ACCESS! Ok, it will be placed above (forward end) the Tether Platform, after those components are assembled. Specifically at 2.00" above the bottom of the plywood centering ring. Sure, it's a little further up the rocket than I would normally choose, but it's the best compromise in this situation.
Even though I know, and have marked the location, it is too early to drill the hole for the forward rail button.

 

[tim cubbedge]

Its pretty common to put the forward rail button at the CG with no motors installed but there are really no set rules.

 

[GaryDean]

Its pretty common to put the forward rail button at the CG with no motors installed but there are really no set rules.

Hello Tim,
Thanks for reminding me! I kind of avoided that choice because RocSim is currently showing the CG at the upper end of the E-Bay (64 inches from base of Thrust Plate), on a 130 inch rocket. Of course, with all the weight from epoxy added to the aft-end, the CG will move downward. That's another reason why I did not drill the forward rail button hole, it gives me options when I have more information available on which to make the decision.

 

[GaryDean]

Now is a good time to finish up the Aft End of the Airframe. Filed the ID and OD of a plywood centering ring, along with a notch for the rail button flange nut until it could slide easily into its' proper position. Refer to picture 60. Then cut some short strips of blue tape and put them around the MMT and the Airframe ID to help identify the specific location at which I wanted the J-B Weld to be positioned. Mixed a batch of J-B Weld and used a popsicle stick to apply the epoxy fully around the MMT and Airframe ID. Refer to picture 61. Then assembled the centering ring in place, but did not quite push it the full distance into the aft end. Refer to picture 62. Assembled the Thrust Plate into its' axial position, which did the same for the centering ring. Refer to picture 63. Waited 30 minutes and removed the Thrust Plate. With the centering ring exposed, I removed any epoxy residue on the MMT, Airframe, centering ring, and backside of the Thrust Plate, because I did not want the Thrust Plate to be epoxied in place, nor epoxied to the centering ring. Waited 2 hours to allow the epoxy to cure and assembled the Thrust Plate back into place to confirm it assembled correctly. It did. Then drilled 3 holes for the wood screws, and screwed those wood screws into place. Refer to picture 64. The Aft End is complete, except for the flanged motor retainer, which I am not assembling at this time to avoid the chance of damage as I continue work on the Aft Airframe.

 

[GaryDean]

Moving forward on the Aft Airframe, its' a good time to install the Aft Stop Ring for the Tether Platform. This Stop Ring, made from a 1/2" width of nosecone coupler, will provide support below the Tether Platform, specifically providing axial resistance when the drogue ejection charges are ignited. The Stop Ring was cut previously. My initial effort here was to consider the best process to ensure the Stop Ring can be pushed to its' correct final location. First tried to slide it down the airframe by hand. It could be done, but it did not slide smoothly and I was not so confident it would not end up cocked in the airframe. My second trial used the E-Bay Coupler to push the stop ring into position. Ah, that was perfect! It slid nicely, and was clearly positioned correctly. So, how did I know it was positioned correctly, when the Aft Airframe is thick, black fiberglass? I put a shop light inside the airframe, from the aft end. That method provided an easily recognizable picture of what was happening inside the airframe! Then, questioned how I was going to apply the J-B Weld in the correct position, without making a huge mess. Took a wooden dowel and laid it on top of the airframe so I could identify how far the should be inserted to exactly place the epoxy, when the last 1/2" of the dowel has the epoxy on it. Then, took a short section of PVC tubing,and taped it to the wooden dowel, as a positive stop for the wooden dowel. Seems like it could work.
Pulled out the Stop Ring, carefully sanded the OD, and then sanded the ID of the airframe by reaching in with sandpaper. Cleaned the sanded areas with Acetone, then mixed a batch of J-B Weld. Refer to picture 65, which shows the Stop Ring, one end of my application tool, and the J-B Weld to be mixed. When I was confident I had a workable process, mixed the J-B Weld, and applied it to the ID of the airframe, using my special tool. It actually worked quite well. No time to take a picture as the heat from the shop light was expected to shorten the epoxy curing time!!!
With J-B Weld applied, I inserted the Stop Ring in the forward end of the airframe, then used the E-bay Coupler to push it into position, which was really very easy due to the clarity generated by the shop light. Picture 66 shows the scribed line identifying the intended final location. Picture 67 shows the actual final location versus the intended. It's perfect! Turned the light off and pulled it out, leaving everything to cure in place.

 

[TheTank]

Lookin good!

 

[GaryDean]

Last projects for the day will include cutting the Payload Airframe down to size, along with the E-Bay Coupler. I had substituted a 48" Payload Airframe with my purchase, in lieu of the standard 34", thinking I might want to increase the overall height of the rocket. After considering the weight increase, along with the change in CG, I have decided to stick to the original design intent. That means the 48" Payload Airframe has to be cut to the correct length. Wrapped paper around the airframe to provide a straight-edge and positioned it to the cutting location. My standard cutting method with FOREDOM rotary tool will not work with this large diameter tube. So, taped the tool down to a 2x4, with the cutting blade just exposed enough to achieve the necessary depth of cut. Positioned the airframe tube against a straight-edge such that the airframe could be rotated by hand, and the cutting line would not waver with rotation. Turned on the FOREDOM (with diamond blade), allowed the airframe to roll into the blade to start the cut, then slowly rotated the airframe for the 360 degrees necessary for the full cut. Refer to picture 67.
Picture 68 shows the cut edge of the payload airframe sitting on sandpaper taped to a flat surface. I rotate the airframe back and forth, by hand, around its center axis, such that material is removed evenly on the face. I continue until all imperfections are eliminated from the cut face. Picture 69 shows better detail of this set-up, and picture number 70 indicates the amount of material removed to achieve a flat face. I also face sanded the uncut end of the payload airframe.
Then turned my attention to the E-Bay Coupler. The supplied coupler is 15" long. My design intent is to have the E-Bay inserted into the Aft Airframe for 6", as this provides a full caliper of length for this separating interface. For the non-separating interface between the E-Bay and Payload Airframe, I have designed for the E-Bay to be inserted 4" into the Payload Airframe, as metal bolts will be used to prevent separation at this interface. So, I need a coupler length of 10", and I will not be using the Switch Band.
Cut the E-Bay Coupler just like the Payload Airframe described above, and sanded both ends of the coupler in the same manner as the payload. Refer to picture number 71 to see the cut and finished to its final length.

 

[GaryDean]

Made yesterday a relatively low effort day on the rocket, due to other appointments. What I could accomplish included;
a. Picture 71 - Sanded the interface between the nosecone and payload sections to get a smooth transition, after shimming (masking tape and cellophane tape) the nosecone for a consistent, smooth fit with the payload tube.
b. Fitted my Featherweight Tracker Mount to the nosecone faceplate, along with a screw-switch. Still need to do the wiring with the tracker. Now I will not have to remove the faceplate to turn the tracker ON / OFF. Reduces complexity and save time / battery life.
c. Added a thin layer of epoxy to the OD of the Tether Platform identified in an earlier post, and after curing sanded the OD to achieve a tighter slip-fit into the forward end of the Aft Airframe. Goal is to help ensure this part is perfectly square with the airframe, when it is epoxied into place against the Tether Platform Stop Ring. Probably an unnecessary effort, but gives me added confidence in the build.

 

[GaryDean]

While waiting for the drogue shock-cord material to arrive, it is a opportune time to proceed on the E-Bay. Started with a piece of cardboard to represent the fiberglass platform, cut to a width of 5 7/8" wide and 9 inches long. I know it won't be the final size, but easier to start big, and trim it down. Laid out all the components (altimeters, batteries, and terminal blocks) on top of the proposed platform. When trying to visualize the wiring and spacing necessary, it seemed that the platform would end to overly large, and reduced airflow within the e-bay. When I realized that there was just as much potential space on the backside, I made the decision to place the batteries on the back, allowing a considerable reduction in the required space. Constructed a platform for the batteries, shown in picture 75. One of my primary considerations in this layout was to position the altimeters along the plane with the 3 vent holes, to provide better real-time atmospheric pressure. Not shown in this picture are 2 terminal blocks which will be position on the left and right side of the altimeters. My original design was to use Schurter switches. But, after a Schurter switch failure at Airfest (no problem, it was on the secondary altimeter) I am not so confident with them. Going to go with the tried-and-true method of twisted wires. The terminal blocks will run the wire for the twisted wire "switchs" to 2 of the vent holes.
The platform in this picture has been cut down to 5 7/8" wide and 5 3/4" long. The length is final. After the aluminum tubes are epoxied to the main platform, and cured, I will trim away most of the fiberglass platform which overhangs the threaded rod on the left and right side. That will reduce some weight, while improving airflow within the E-bay.
Next step is to run some wire........

 

[GaryDean]

Got started on wiring the E-bay platform and realized that there was still some fiberglass cutting to do, and I do not want to leave fiberglass residue / dust on the platform, with a chance to damage the altimeters. So, stopped the wiring and focused on trimming the fiberglass platform to the final dimensions, cutting the aluminum tubes to their final size, and then epoxying the platform to the aluminum tubes. The aluminum tubes allow excellent adjustment of the platform location along with convenient access for inspection and repair.
Picture 76 shows the final result for the fiberglass platform. The "wings" are where 2 additional terminal blocks will be installed for the twisted wire "switches". The location of the platform has been adjusted such that the centers of the "wings", along with the working parts of the altimeters are exactly on the plane for the intended vent holes.
Picture 77 shows a side view of the platform epoxied onto the aluminum tubes. Will now focus on those additional terminal blocks, the twisted wire "switches", finish the wiring, mount the battery platform, with batteries, and then check the function of the altimeters.

 

[GaryDean]

Because my needed drogue shock-cord material arrived yesterday, decided that today would be a day for;
a. The Tether Platform, which is the connection point on the rocket for the drogue shock-cord.
b. Sewing the Kevlar lines between the Tether Platform and the drogue shock-cord attachment swivel.
c. Sewing the drogue shock-cord (final length will be 40 feet).
d. Sewing the main parachute shock-cord (final length will be 30 feet).

The Tether Platform consists of a plywood centering ring (6" OD x 98mm ID) and a G10 fiberglass bulkplate, with 2 welded eye-nuts. The centering ring and blukplate are epoxied together with J-B Weld, while clamped tightly together. Drilled the 2 holes for the 5/16" eye-bolts, installed the bolts, with washers on both sides, and used Permatex Red Threadlocker on the bolts. Pictures 78 and 79 show both sides of the completed platform.
Pulled out my Speedy Stitcher, LOTS of 100 lb. Kevlar thread, and my Fruity Chutes Tubular Kevlar. Proceeded to sew the Kevlar to the first Tether Eye-Bolt. Refer to picture 80, showing the backside of the stitching. Yes, the backside is the "messy" side. Should have shown the front! Then, using the swivel onto which the drogue shock-cord will be attached, along with the tether platform, very carefully determined where the swivel should be positioned on the Kevlar coming off the Eye-Bolt. My design intent is that the swivel will extend about 3 inches beyond the forward end of the Aft Airframe. Heavy duty shrink-wrap, along with a foam collar will help protect the airframe from zippering. After double checking the swivel position I finished the first Kevlar strap, and then constructed the 2nd Kevlar strap, connecting to the 2nd tether platform eye-bolt. Made a serious effort to ensure these 2 kevlar straps are the same length! Picture 81 shows the completed Tether Platform, with heat-shrink tubing over the stitching.
Next is the drogue shock-cord. Picture 82 shows the front side of the first end I stitched, along with one of the 5,000 lb. Kevlar soft-links I use to connect the shock-cords to the rocket, parachutes, etc. Picture 83 shows that same end, with heat-shrink tubing. Picture 84 shows the completed drogue shock-cord, along with the attachment point for the drogue parachute. This Fruity Chutes Tubular Kevlar has a rated breaking strength greater than 6,000 lbs. Fruity Chutes even provided a Certification Document showing 10 samples tests, ranging from 6,681 - 7,318 lbs., with an average of 7,121 lbs.
And to finish up my sewing for the day, Picture 85 shows the completed main parachute shock-cord, using 1/4" tubular Kevlar, rated at 2,000 lbs. breaking strength.

 

[GaryDean]

Plan for today is to focus on the forward end of the Aft Airframe, with the goal to;
a. Epoxy the completed Tether Platform into position.
b. Epoxy the Retention Ring (immediately forward of the Tether Platform), which provide additional retention during drogue deployment.
c. Epoxy the E-Bay Stop Ring into position. This ring will position the E-Bay during rocket assembly, because I am not planning to use a switch band.

The Tether Platform is easy to epoxy in position, as it is pushed directly against the Stop Ring which was installed in an earlier posting.
First action was to sand the Tether Platform OD, along with the ID of the Airframe at the correct location, and clean with Acetone. Then assembled my special tool for applying epoxy to specific depths / locations, mixed a batch of J-B Weld, and used my tool to apply a ring of epoxy just in front of the Stop Ring. Inserted the Tether Platform and pushed by hand to within 1 inch of the final location. Then, slide a 4 inch section of coupler into the airframe, up against the Tether Platform, and then the final distance (approx. 1 inch) to position the Tether Platform straight against the Stop Ring. Pulled out the section of coupler, cleaned up areas of excess epoxy, and allowed to cure, as shown in picture 86.
Spent qualify time on the E-Bay while the epoxy cured.......
Next step is the Retention Ring, which will be positioned directly against the Tether Platform. This is a 1" wide section of coupler. Sanded and cleaned it (picture 87), along with the airframe OD, adjusted my special tool for applying epoxy, mixed a batch of epoxy, applied the epoxy, and inserted the Retention Ring by hand a short distance into the airframe. Then used that 4 inch section of coupler to push the Retention Ring into position. Pulled out the section of coupler, cleaned up areas of excess epoxy, and set aside to cure.
The next objective is the E-Bay Stop Ring, which to me is a very important component of the design. It's important because without a switch band, I need some method to position the e-bay during the rocket assembly process. It's especially important that it is installed perfectly square with the airframe to ensure any loads are equally distributed. This Stop Ring is a 1/2" long section of coupler tube. It is the original end from the nosecone coupler, so it is an excellent surface for the e-bay bulkplate to sit against. Again, sand the ring OD, airframe ID and clean with Acetone. Adjusted my special tool for applying epoxy (picture 88), and applied blue masking tape onto the E-Bay (picture 89) to act as a stop when the Stop Ring is in position. Mixed and applied the epoxy (picture 90), and then inserted the Stop Ring, followed by the E-Bay. Inserted the E-Bay to the blue tape stops (picture 91). I let it sit for 2 minutes and removed the E-Bay. Visually, it looked good! Cleaned up excess epoxy from the airframe and E-Bay and reinserted the E-Bay. Removed the E-Bay, did additional clean-up, and reinserted the E-Bay. After removal, used a metal scale to determine whether the Stop Ring was located in the correct position. Hmmm, it was not, being out of position by almost 1/8", into the airframe. Why? Cleaned the E-bay, along with more cleaning of the airframe. Pulled the ring about 1/4" forward by hand, and reinserted the E-Bay, hoping this time to achieve the anticipated result. Close, but no cigar, by 1/16". I am not satisfied, but not confident that using the E-Bay will position it perfectly. So, positioned it by hand and measured in 4 locations with my scale to confirm it was finally in its intended position. Refer to picture 92. When I checked it again after 1 hour of cure, it was still in the correct position.
Picture 92a shows the view into the Aft Airframe along with the location of the drogue shock-cord swivel attachment.

 

[GaryDean]

Might be a smart idea to install the forward 1515 Rail Button now, before I forget about it and discover my mistake at the launch pad. I had previously marked the intended location and will first confirm that location. Slide my shop light into the airframe and confirmed that all the previously installed parts were in the correct location(s) and that there was clearance for the rail button flange-nut backing. Drilled a very small pilot hole to minimize fiberglass splintering. Then put heavy tape over the inside of the hole, and jammed a wooden stick (rounded end) against the tape to minimize fiberglass splintering when drilling the final (1/4" diameter) hole. Drilled that hole and used a needle file to clean the edges. Put a slight bend in the flange-nut backing so that it would conform better to the airframe ID. Then sanded the airframe ID along with the flange-nut surfaces and cleaned with Acetone. Mixed a small batch of J-B Weld and applied it to the face of the flange-nut that will contact the airframe. Turned on the shop light (inside the airframe), placed the flange-nut on the tip of a left-hand finger and positioned the flange-nut below the drilled hole, using the the light from the shop light to follow my hands position. When directly below the hole, brought it up into the hole, placed the button onto the threaded post, and then installed the screw. After curing for 1 hour I removed the screw and button and cleaned up the threaded post, on the chance that some epoxy reached that surface. Reinstalled the button and screw and I am finished, with the result show in picture 96.

 

[GaryDean]

My plan is to complete the E-Bay today. Ran all the wiring for the altimeters and batteries, but none of the ejection charge wiring to the bulkplates at this time. Then installed the twisted wire "switches", running them between terminal blocks mounted on the backside of the main platform, and holes drilled into the "wings" on the main fiberglass platform. Refer to picture 94.
Although my Bill of Materials indicates Lithium Polymer batteries, The specific batteries I have experience with when using these altimeters are no longer available. So, going with 9 volt batteries. Installed the batteries, and unhappy with their retention in the battery mounts, added 2 loops of Tie-Wraps to each battery, and installed the battery platform onto the main fiberglass board. Refer to picture 95.
Now to adjust the position E-Bay Sled so that the twisted wire "switches" line up exactly with the end of the Aft Airframe, where the vent holes will be located, with half holes in both the Aft Airframe and Payload Airframe. Refer to picture 96. It is a bit difficult to see in the picture, but one of the holes in the fiberglass "wing" lines up perfectly when the drogue-end of the E-Bay is inserted into the Aft Airframe. The hole on the other side is about 1/16" off. My mistake by drilling these holes without making specific measurements, only visuals. No worry. Just fill the bad hole with epoxy and drill a new hole. With that effort, both holes are now perfect!
With the sled positioned correctly, then ran all the ejection charge wires from the terminal blocks on the sled, through the bulkplate(s), to the terminal blocks on the face of the drogue and main bulkplates. On the main parachute side I have used solid wire from FireWire igniters. On the drogue parachute side I have used locking disconnects because this is the bulkplate which is removable to provide access to the E-Bay Sled. The orange wire is the Primary (Raven 4 altimeter) and the red wire (red for emergency) is the secondary wire connected to the MissileWorks RRC2L altimeter. Applied a clear adhesive / sealer to the holes where the wires come through the bulkplates to prevent gunpowder residue from entering.
And with that, the E-Bay is complete. Refer to pictures 97 (front of main platform), 98 (backside), 99 (drogue bulkplate), and 100 (main parachute bulkplate).

 

[GaryDean]

That E-Bay Stop Ring leaves a sharp / square edge on the aft side, which might become a problem during drogue deployment, with the shock-cord and drogue chute possibly passing quickly against that edge. So, applied a layer of epoxy (J-B Weld) around that aft face, and after curing will sand to achieve a gradual, smooth transition from the airframe ID over the stop ring. Refer to picture 101.

 

[GaryDean]

Will start the day with some sanding. First, I forgot to sand the forward end of the Aft Airframe before all of the aft airframe work of the last week. It is not as smooth as I would prefer, so back to my sanding set-up for airframes and couplers. Picture 102 shows the aft airframe sitting on the sandpaper, where I rotate very slowly / carefully around the center axis until I have achieved a smooth consistent surface.
Then, back to sanding the epoxy applied at the backface of the Stop Ring. Picture 103 shows the sanded results. Sure, it's not perfect,with some small voids, but it is smooth and leaves absolutely no edge at the stop ring.
While waiting for epoxy to cure I took the opportunity to update RocSim weights for the specific items which were modified by cutting, trimming, sanding, and/or the addition of epoxy. These included;
- Nosecone Assembly (with tracker, battery and tracker bulkplate) = 1,567.01 grams
- E-Bay Assembly = 1,480.80 grams
- Payload Airframe = 1,556.20
- Aft Airframe Assembly (everything epoxied to the airframe!) = 8,073.90 grams, with CG @ 39.0 inches
With these updates, the final ready to launch weight (with AT M2050X, CTI 75mm 4G case, and motor adaptor = 20,451 grams (45.1 lbs.)
This is 33 grams greater than my projected weight when creating the RocSim file before the build had begun.

 

[GaryDean]

Moving on, I will mark an alignment line on the forward section of the E-Bay, to ensure correct alignment during rocket assembly, and then locate and drill the Static Port Holes (3), and 2 holes for the twisted wire "switches". Prepared a sketch of my plan (picture 104), in relation to the "C" Fins and the Forward Rail Button. I also measured the thickness of the altimeter platform (7/16"), which was used to determine the height above the centerline through the altimeter platform to drill the 2 holes for the twisted wire "switches", so they would be slightly above the "wings" of the altimeter platform. Then, scribed an alignment line into the e-bay coupler and top end of the aft airframe. Refer to picture 105, showing the alignment line, along with the mark (very small half circle) for one of the static port holes. Checked and rechecked my numbers before proceeding with drilling holes.
Offwegorocketry (Resources section) indicates that I should make the 3 Static Port Holes 13/64" in diameter. I will use a 1/8" drill for the twisted wire "switch" holes, which will allow the FireWire Igniter wire I plan to use to just fit through the holes, with very little clearance for movement.
Drilled those 5 holes, and then spend considerable time using a needle file to create a chamfer on the ID (e-bay coupler) so there would be a smoother movement of air both in and out of these holes.
Picture 106 is a view from the drogue-end of the inside of the coupler, showing the location of 2 of the Static Port Holes above the altimeters, along with the twisted-wires "switch" wires going through their respective holes. Very pleased with the results!
Next effort will be the three (3) 2-56 shear pins holes in the aft airframe.

 

[GaryDean]

Goal for today is to assemble this rocket by the end of the day. First step will be to scribe locations for the three (3) 2-56 shear pins, where the Aft Airframe and E-Bay separate. Refer to picture 107. I am placing these shear pins in alignment (aft) with the Static Port Holes, but 3.5" below them. Drilled the holes, then disassembled the E-Bay to place small mounds of J-B Weld epoxy around the holes inside the e-bay coupler, to provide support. After curing, filed a flat surface on these mounds, then reassembled the aft airframe and e-bay and redrilled the holes and tapped them as shown in picture 108. After tapping each individual hole, I inserted the respective 2-56 shear pin, to help prevent any movement of components during this process. Oh my, in my haste this morning to make serious progress, forgot to take picture of most the process for the aft airframe shear pins and the payload section retention bolts / flange nuts.

With the aft airframe shear pins installed, moved to the payload section retention bolts / flange-nuts. Used the same alignment guide shown in picture 107, and located these bolts offset 60 degrees with the Static Port Holes, in alignment with the fins. My reason for this is to keep the turbulent airflow caused by these bolts from interfering with the Static Port Holes. Similar process to the shear pins. But, with the e-bay installed in position in the payload airframe, and drogue-end removed, after filing a "flat" onto the epoxy mound, I placed a 8-32 flange-nut (sanded and cleaned with acetone) on the epoxy "flat", inserted a 8-32 stainless steel bolt, and tightened it lightly. Then, added fresh epoxy onto the flange section. With all 3 internal locations completed, I assembled the drogue-end bulkplate and wing-nuts onto the threaded rods. Inserted the bottom end of the e-bay into the aft airframe, installed the shear pins, and when satisfied that all components were in alignment, tightened the three (3)8-32 stainless steel retaining bolts. Left it to cure. Picture 109 shows an epoxy mount, filed flat, with flange-nut, and the additional epoxy placed on the flat of the flange-nut to bond it to the payload airframe.

 

[GaryDean]

Now to work on the Payload Airframe / Nosecone shear pins (3 4-40 pins). Remembered to take more pictures for this process! Started with that alignment guide from picture 107 to determine the shear pins locations. These will be straight up from the payload retaining bolts, again to minimize turbulent airflow over the static port holes. Drilled the three holes with the appropriate size drill for 4-40 thread, and removed the nosecone from the payload section. Prepared the ID of the nosecone by using a marker to show the position of holes, so that when epoxy is applied, I will still know where the hole is located. Refer to picture 110. Then, added a mound of J-B Weld epoxy (picture 111) at all 3 locations. After curing (accelerated with a heat lamp), I filed a "flat" on each mound and reassembled the nosecone to the payload airframe and redrilled one hole. Tapped that hole (picture 112), and inserted the shear pin (picture 114), before proceeding to the next location. When these three (3) locations were completed, I disassembled all of the shear pins and retention bolts. After a bit of detail work I will reassemble everything to confirm all components fit together correctly.

Noting that the altimeter platform had been removed from the e-bay for all of the shear pins / retention bolt work noted above, that detail work I mentioned above consists of;
a. Replacing all the standard nuts retaining the altimeters with plastic insert Lock-Nuts.
b. Added double nuts to the Battery Platform retaining bolts.
c. Hooked up the main parachute ejection charge wires to the forward bulkhead.
d. Shortened the twisted wire "switches" wire to make them more convenient to maneuver.
e. Added blue threadlocker to the 4 stainless steel 5/16" x 18 nuts on the threaded rods, holding the altimeter platform in place.

Then, reassembled the rocket. Picture 115 shows the positioning of 2 Static Port Holes, 1 payload retention bolt, 2 aft airframe 2-56 shear pins, and one of the twisted wire "switches". Viewing the assembly make me question my thinking on location of the aft airframe shear pins!!!!! I may just have to relocate them to be in alignment with the payload airframe retaining bolts, for better esthetics.

And, to end the day, picture 116 of the assembled (almost) rocket. Seems the nosecone needs an aluminum tip, and what about the missing motor retainer / cap? OK, almost have an assembled rocket.

 

[GaryDean]

Started yesterday will drilling vent holes in the aft airframe (just above the tether platform), payload airframe (just below the nosecone), and nosecone (just above the bulkplate mount).
Recalculated the ejection charges using the Off We Go Rocketry (resources section) calculator. The calculation for the Main Parachute charge was unchanged from my theoretical (pre-build) calculation, at 3.0 grams.
The calculation for the Drogue deployment was substantially lower due to my design change to the Tether Platform to retain the shock-cord. The pre-build number was 1.35 grams, and now with the shorter area (length) requiring pressurization, the new number is 0.75 grams. Both of these numbers are based off my use of a 50% safety factor, increasing the gunpowder recommendation by 50%. This method has been working for me to-date.
So, initialized the primary (Raven 4) altimeter to be sure it was operating correctly, and had to download the latest software. Then measured out the ejection charges for drogue and main and put that gunpowder in plastic vials, labeled. Installed igniters and confirmed the altimeters recognized the valid circuits.
Headed out to a very remote location for these tests, as I am sure our HOA would not welcome the idea of gunpowder charges being ignited in areas where residents, children, and wildlife roam around.
Upon arrival I transferred the gunpowder to the charge containers, sealed them, and assembled the rocket, with all recovery equipment included, along with all shear pins and retaining bolts. The Raven 4 has a very convenient software feature that allows you to perform "Ground Tests" from your phone, via Bluetooth with the altimeter. At this point the iPhone software is showing both the Drogue and Main circuits as "armed". I do not want to fire both charges at this moment, so I "disarmed" the Main. Proceed through the 5 second countdown, and the drogue charge fired. The result surprised me, as it was so ........... dismal. Sure, the upper section (e-bay, payload airframe, and nosecone) separated from the aft airframe, but only went forward approximately 1 foot. Not posting the video as it's pointless. Gonna need some more gunpowder!
Unable to do the Main Parachute test as I got called back home on an issue. Tomorrow!

 

[GaryDean]

With a new day I'm back to evaluating ejection charges. I am revising my Drogue ejection charge from 0.75 grams to 1.3 grams. Because it was not yet tested, the Main ejection charge stays at 3.0 grams. Results are shown in the attached short videos. This is a nice feature of the Raven 4 iPhone interface, to make Ground Tests possible, and then to generate videos. Unfortunately, the timing between the sound and actual deployment seem to be substantially out-of-sync. The results were;
- Drogue: 1.3 grams fired the upper section 11 feet and the drogue chute was fully exposed. But, not fully convinced this would have been acceptable if deployment occurred with air resistance. Will increase to 1.5 grams for added security.
- Main: 3.0 grams fired the nosecone 8 feet and the main parachute package was fully exposed. Again, not fully convinced of the "authority" of this deployment, and will increase the charge to 3.5 grams for added security. I will pay close attention to this main deployment in the first flight, hopefully with video, to determine whether any further changes might be necessary.

 

[GaryDean]

With the ejection charges settled, I'm getting down to the final details. After all the hassle of installing, removing, installing, removing, etc. the e-bay in the Ground Testing, have decided to eliminate the twisted wire "switches", in favor of FingerTech 40A Mini Power Switch. A friend of mine from Titusville who is heavily involved in fighting robots (250 lb. class) gave me some of the FingerTechs, saying they are small, reliable, shock-proof, vibration-proof, and indestructible. Well then, OK, I will try them. They are turned ON / OFF with a hex wrench. Currently have one installed (primary circuit), and while the epoxy cures on that, will move on ......

Wired the screw switch into the Featherweight Tracker which is mounted in the removable faceplate of the nosecone. Refer to picture 117.

 

[GaryDean]

Finished installing (epoxy) the secondary FingerTech 40A screw switch and then cut and soldered the wire for both altimeters. Refer to picture 118. Tested the switches and both altimeters initialized correctly. Double-checked the solder joints to ensure good adhesion. They seem good. Assembled the e-bay and checked the access holes to confirm the switches were aligned correctly. Refer to picture 119. Perfectly centered! The E-Bay Assembly is 100% completed.

 

[GaryDean]

Literally at the end of the build. Been spending considerable time sanding and trying 3 different white sandable primers on the fins. Will not be officially painting this rocket until after the Certification Flight, if successful.
Minor items I recently resolved include;
- Sewed the chute protectors to the shock cords.
- Programmed the altimeters, as;
a. Primary Altimeter (Blue Raven) to deploy drogue at Apogee, and main parachute at 800 feet.
b. Secondary Altimeter (MissileWorks RCC2l) to deploy drogue at Apogee + 1 second, and main parachute at 700 feet.
- Completed some detail work around the Altimeter access holes, for improved access to the switches.
- Checked for updates to the Featherweight software for Raven altimeter and GPS Tracker.
- Sanded separating interfaces on the airframe / nosecone to provide a smooth transition for aerodynamics.
- Attached the aluminum tip to the nosecone, using blue threadlocker to keep it securely in place.
- Installed the flanged motor retainer (12 screws) and cap. Refer to picture 120.
- Updated my RocSim file with the final weights. Ran simulation flights for the intended motor(s).
- Assembled the complete rocket (refer to picture 121) and measured the actual CG, with motor case and motor adaptor installed. In RocSim, I used the mass overide function for the completed rocket to include the final weight, along with the measured CG. Based on this information, with installation of my AT M2050X motor, the Stability Factor should be in the range of 2.61, a reasonable number for my launch.

My TO-DO LIST is getting shorter, with the only items left being;
1. Build the AT M2050X motor (grains bonded to liner), and a Trial Flight motor (CTI L2375WT or AT L2200G, also grain bonded to liner) if I decide in favor of 1 flight prior to Certification Flight.
2. Charge ALL the batteries.
3. Determine the final actual CG, put markers on the rocket, and confirm launch-ready Stability Factor.
4. Create my checklists for;
- Pre-flight preparation @ home
- Pre-launch preparation @ launch site
- Launch Pad preparation @ launch pad

My target is still October 21 / 22 at Tripoli Tampa. If weather is forecasted to be good on both dates, will do a trial launch with a big L motor on Saturday, with the Certification flight planned for Sunday. If good weather is expected for only 1 day, then only the Cert Flight on that day. If the weather is projected to be bad through the weekend, ......... no, not going there......

 

[GaryDean]

Now waiting on Elmer's Glue-All MAX before doing the motor(s) build. Had Gorilla Glue on-hand, but started to panic when I saw a video where the AT representative stated that Gorilla Glue can be used, but do not use too much, because it can crack the phenolic liner. Hmm, they did not quantify "too much". I though the amount of glue used was a direct function of the amount of space between the OD of the grains and Liner ID. Interesting, the label on the Gorilla Glue states "While curing, glue will expand 3 - 4 times. Be careful of squeeze-out". Great, don't know what the expansion is on the Elmers! OK, since I believe I have no actual control over the amount of glue I will set the Gorilla Glue aside and count on Amazon to deliver Elmer's Glue-All MAX by the end of the day Tuesday. Seems that if there are any issues in the motor assembly, my launch plan for Saturday may be in jeopardy. Well, I have about a day to investigate, think, and plan the specific process in detail.

Meanwhile, finished all the Checklists (attached). These certainly cover more details than what I normally do, but for a Certification Launch, it's better to be safer than sorry. Other than the motor(s) build, 100% of the Pre-Flight Preparation @ Home is completed.

 

[GaryDean]

Yay, received the Elmer's Glue-All MAX with enough time today to grain bond my AT L1520T (initial practice) and AT M2050X motors. Picture attached. After viewing a few of the on-line videos I created a simple jig (shown in picture) that mounts in my vise which made the process quicker, smoother, and more organized (less messy) than some of the videos I watched. It was necessary to trim various amounts of the "glassine" outer layer off some of the grains to achieve the right fit before bonding.
I will not be doing a trial launch (AT L2200G motor), now focusing exclusively on the L3 Certification Launch, hoping for this Saturday at Tripoli Tampa in Florida. Although I will be unable to do any video myself, I am cautiously optimistic that someone in attendance will come through for me, with something that can be posted here.

 

[GaryDean]

Yay, success today with the L3 Launch at Tripoli Tampa. Great weather although a bit gusty at times, as you could spot with the immediate weathercocking into the wind off the launch rail! Unfortunately, about the only real cloud we saw all day just happened to be along the flight path at the end of my countdown. 45.1 lbs. on the pad, with an AT M2050X reached 6,686 feet versus the RocSim 7,150 feet. Max velocity @ 828 fps, drogue descent averaged 74 fps, while the very short (deployed at 800 feet) main descent averaged 35 fps. All electronics performed nominal, all ejection charges fired, and rocket was fully functional after recovery in the open field. The best video was my TAP signing the paperwork for the successful L3 Flight / Certification!!!!

 

[loopy]

Congratulations! Great job!

 

[WV8KE]

Congratulations @GaryDean!
Enjoyed this thread.
What’s the next planned flight? The L1520T?

 

[bunkermonkey9]

congrats, it was an awesome flight. hope to see you fly it again at another launch.