GaryDean L3 Build Thread - Prometheus 6

GaryDean

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Submitted my L3 Documentation and now have approval to begin the build of my Composite Warehouse Prometheus 6. Important consideration for me is the TAP request for LOTS of pictures! The components for this build are shown in the pictures below, while the Bill of Material consists of;

Prometheus 6 – Bill of Materials
Nosecone Assembly

Nose Cone: 6.00” dia. x 34.125” length 6:1 VK FG w/ aluminum tip
Nose Cone Coupler: Coupler 6.00” long G12 FG

Internal Bulkplate Mounting
1. Plywood: CR 6” x 75mm” x 0.250” thick – plywood
2. Fiberglass CR: 6” dia. x 75mm x 0.125” thick
3. Bolts / Nuts: 3 pcs. 1/4" X 20 X 1.00" length (1,750 lb. proof load)
4. Locking Nuts: 3 pcs. – ¼” x 20 Locking nuts

Removable Bulkplate + Switch: 6” dia. x 1/8” thick – black FG (trim OD for fit)
1. ON / OFF Switch: Schurter 110-220 + Binder Design Quick Disconnect

Eye-Bolt for Bulkhead: 1/4” x 20 x 2” length eye-bolt (1,750 lb. proof load)
Tracker + Battery + Mount: Featherweight GPS Tracker with battery + mount


Payload Airframe Assembly
Airframe Tube: 6.17 / 6.00” dia. X 34.3125” long G12 FG
Shear Pins: 4-40 plastic shear pins (3) @ nose cone end
T-Nuts + Screws: (3) 8-32 x ¼” Brad Hole T-Nuts + 3 ½” screws

E-Bay Assembly
Coupler: 5.998 / 5.800” dia. x 10.00” length G12 FG
End Covers: aft & forward 1 pc. coupler bulkheads G10 FG
FG Altimeter Sled: 5.5” x 8.0” x 1/16” thickness G10 FG
Primary Altimeter: Featherweight Blue Raven 4
Secondary Altimeter: MissileWorks RRC2L
Batteries + Wiring: 2 x Venom 2S 800mAh 7.4V LiPo
Switches + Wiring: 2 x Schurter 110-220 switches
Threaded Steel Rod: 2 pcs. – 5/16” x 18 x 12” (2,900 lb. proof load)
Aluminum Angle: 1” x 1” x 1/16” thick aluminum angle
Nuts & Lock-nuts: 5/16” x 18 nuts, wing nuts, washers & lock nuts
Eye-bolts: 2 5/16” eye-bolts (2,400 lb. tensile strength)
Washers, nuts, Loctite: 5/16” washers, nuts, red Loctite
Bulkhead Terminals: 4 pcs. – Utilitech Barrier Strip + screws / nuts
Charge Cannisters: 4 pcs. – 3 gram cannisters w/ screw
Igniters: Firewire Electric Matches (4)
Locking Disconnects: Binder Design Locking Disconnects (2)
Stand-offs & Screws: plastic 4-40 stand-offs and screws
Battery Holders: (2) LiPo battery holders (2)

Aft Airframe Assembly

Airframe Tube: 6.17 / 6.00” dia. x 60.00” length G12 FG
Shear Pins: 2-56 plastic shear pins (3) retaining e-bay
E-Bay Stop Ring: FG coupler x 1.00” length
Forward Rail Button: 1515 rail button (0.625 dia. X 7/16" high)
98mm Motor Mount: 98 mm x 33.00” long
Forward Fins Front CR: 6" x 98mm x 1/8" thick - black G10 FG
Forward Fins Rear CR: 6” x 98mm x 1/8” thick - black G10 FG
Aft Fins Front CR: 6” x 98mm x 1/8” thick - black G10 FG
Aft Fins Rear CR: 6” x 98mm x 1/8” thick - natural G10 FG
Aft Rail Button: 1515 rail button (0.625 dia. x 7/16” high)
Aft Thrust Plate CR: 6” x 98mm x 0.250” thick - plywood
SC Precision Thrust Plate: 6” dia. x 0.250” thick – 6071 aluminum
98mm Motor Retainer: AeroTech motor retainer + cap & screws
Kevlar Tether: 92” x ½” Kevlar tether
Tether Swivel: 5/16" steel swivel (5,280 lb. breaking load)
Forward Fin Set: 3 fins – 3/16” thick G10 FG

Aft Fin Set: 3 fins – 3/16” thick G10 FG

Drogue Recovery System
Drogue Chute: Rocketman 36” or 24" pro-X drogue
Chute Protector: 18” x 18” kevlar chute protector
Shock Cord (40 feet): 1/2” (3,500 lb.) kevlar + 3 soft links (5,000 lb.)
Kevlar Thread: 10’ of 100 lb. kevlar thread
Heat Shrink Tube: 1 foot of ¾” heat shrink tube to protect loops

Main Parachute Recovery System
Main Parachute: Rocketman 12’ standard parachute
Chute Protector: 24” x 24” kevlar chute protector
Shock Cord (30 feet): 1/4” (2,000 lb.) kevlar + 3 soft links (5,000 lb.)
Kevlar Thread: 10’ of 100 lb. kevlar thread
Heat Shrink Tube: 1 foot of ¾” heat shrink tube to protect loops
 

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  • E-Bay and Tracker Parts.jpg
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GaryDean

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First step in this process, after the package arrives, is to wash and sand the parts to remove mold release, etc., and to prepare all surfaces for bonding. Used warm soapy water and cleaned all internal and external surfaces carefully, with plastic gloves to avoid possible splinters. After drying in the sun, sanded all surfaces which I expect to be bonded with epoxy. Used 100 grit sandpaper, and wiped everything down with Acetone. For me, sanding at this point is something of a back-up, because just prior to the process of applying epoxy, etc., I always sand again, and clean-up with Acetone.
 

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  • 1 - Wash in Warm Soapy Water.jpg
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  • 3 - All Fiberglass After Sanding.jpg
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  • 4 - Close-Up of Sanded Parts.jpg
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  • 5 - Aft Airframe Internal Sanding.jpg
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GaryDean

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Well, let's do a dry fit with the Aft Airframe parts (fins), Centering Rings, and MMT. A bit disheartening when NOTHING fits. Not a single fin can be inserted and the issue is a bit more pronounced for the 3 Forward fins, probably because those fin slots are longer. None of the Centering Rings will slide onto the MMT. And, without the MMT in place, there is severe restriction when inserting the Centering Rings, especially near the center (lengthwise) of the fin slots!
Regarding the fin fit, the issue is due to the fin slots being narrow, but unable to quantify the amount of interference.
Had to open up the Centering Rings ID to get them over the MMT. No big deal. Then fitting them into the Airframe tube is a different matter. The issue appears to be a result of deformation of the tube exactly in the areas of the fin slots. The center (lengthwise) of the fin slots has the greatest deformation, inwards.
Got out my FOREDOM tool (like Dremel) with Tungsten Carbide carving tool, and ran that tool back and forth across both side of the fin slots until the fins could be inserted. This was a relatively quick process.
Got out my Craftsman drill and 4" abrasive Paint Removal Disc and ran that tool up and down the fin slots, internally. This WAS NOT a quick process, but achieved a condition where the Centering Rings could be inserted straight into the airframe tube.
Then, I was surprised to find that the fins no longer could be inserted! Seems that the material removal on the internal diameter of the fin slots allowed them to deform a bit more. Ran the Tungsten Carbide tool back and forth a few times and the fins again fit.
Pictures below show my tools used in this process, and the final results with a successful dry fit of the Aft Airframe Assembly.

Last picture shows the 3 screws I mounted to the Rear Fins Rear CR to allow east removal during the assembly process, which allows access to the Rear Fin internals, depending on how I decide to apply epoxy to those internal interfaces.
 

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  • 6 - Set-Up to Widen Fin Slots and Internal Sanding.jpg
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  • 8 - Rear Centering Ring Removal Screws.jpg
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rfjustin

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First step in this process, after the package arrives, is to wash and sand the parts to remove mold release, etc., and to prepare all surfaces for bonding. Used warm soapy water and cleaned all internal and external surfaces carefully, with plastic gloves to avoid possible splinters. After drying in the sun, sanded all surfaces which I expect to be bonded with epoxy. Used 100 grit sandpaper, and wiped everything down with Acetone. For me, sanding at this point is something of a back-up, because just prior to the process of applying epoxy, etc., I always sand again, and clean-up with Acetone.
I love seeing properly scuffed pieces parts... :)
 

GaryDean

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Next step in my process is to get the Front Fins Forward Centering Ring in place. Fortunately for me, that CR provided a slight press fit condition during the dry fit in the last step. Did a complete disassembly of the Aft Airframe components, sanded all surfaces of that CR, along with the internal diameter of the Aft Airframe and cleaned everything with Acetone. Then, reassembled everything to get that CR into the correct position, and removed all components except that CR. Mixed up a batch of J-B Weld, and used a shop light and wooden dowel to apply J-B Weld to the interface of the CR OD with the Aft Airframe ID, trying carefully to avoid the surface of the CR at the fin slots. Refer to attached pictures.
 

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  • 9a - Forward Centering Ring Position.jpg
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  • 9b - Forward CR After Tacking and J-B Weld.jpg
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GaryDean

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After the ease of assembly of the very front CR from the last step, I was a bit optimistic for the next step of tacking the Front Fins Rear CR and the Rear Fins Front CR in place onto the MMT. Well, both these centering rings chose not to cooperate. From the previous step I identified the area on the MMT where these centering rings will be placed (see picture below). I sanded this area and cleaned with Acetone. Also sanded and cleaned the ID and both faces of these centering rings.
Assembled the Aft Airframe, and discovered that both these centering rings were not a firm press-fit in their locations. Fortunately, J-B Weld is both thickish and gummy. I carved a wider slot in the Rear Fins fin slots for better access. Then, used a small diameter wooden dowel to apply J-B Weld onto the interface between the Front Fins Rear CR and the MMT, using the rear fins slot for access. See pictures below. After applying the J-B Weld through all 3 fin locations, I then pushed the centering ring into its intended position against the back of the Front Fin, and taped short sections of the wooden dowel to maintain this position.
Did something very similiar for the Rear Fins Front CR. Because I could not push this CR against anything, I pulled that CR back a bit, and applied J-B Weld to the backside of the interface for the 3 fin slots. Then, pushed the CR to its intended location, using that J-B Weld as something of a "buffer" to maintain position. Then, applied J-B Weld to the backface interface in the 3 locations. Finally, used those small diameter wood dowels, taped into position to keep the CR secure as the epoxy cures. Will know the results in a few hours.
 

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  • 12a - Rear Fins Forward CR Tacking.jpg
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  • 12a - Rear Fins Forward CR Tacking Detail.jpg
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  • 11b - Front Fins Rear CR Tacking Detail.jpg
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  • 11a - Front Fins Rear CR Tacking.jpg
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  • 10 - Area to Sand on MMT for Tacking CRs.jpg
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GaryDean

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Got some free time so sanded, cleaned (Acetone), and epoxied (J-B Weld) the fiberglass and wooden centering rings that will become the internal bulkhead mount for the nosecone.
Then did the same for Shock Cord Tether Platform (minus bolts, kevlar, etc.) that will go into the Aft Airframe to hold the shock cord.
 

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  • 13 - Internal Nose Cone Mount.jpg
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  • 13a - Shock Cord Tether Platform.jpg
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GaryDean

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Disassembled the Aft Airframe and pulled out the MMT with the two (2) centering rings tacked in place. It resisted my removal, but came out perfect, even after all the effort with the narrow wooden dowels. Now have to create a secure bond at these interfaces, but at the same time recognizing that I must protect the area in which the fin tabs will eventually fit. So, wrapped a piece of paper around the MMT to determine the circumference = 12.75 inches. Easy to divide by 3 to yield 4.25 inches from fin centerline to fin centerline. Marked off the paper accordingly, and used those markings to ensure the eventual fin locations are protected from my J-B Weld application. Refer to attached pictures!
This application of J-B Weld is the initial effort at these interfaces. One of the final stages of the fin can build is to "flood" these areas with epoxy to ensure that ALL internal interfaces are bonded securely.
 

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  • 14 - Middle Centering Rings in Place.jpg
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  • 15 - Epoxy at Complete Interface except Fin Location.jpg
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GaryDean

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Time to assemble some fins onto the Aft Airframe. Will start with the more forward set of fins. First, sand the Motor Mount Tube in the areas where the fins contact, along with the Centering Rings on all faces, then clean up with Acetone. Second, although hard to see in picture 17 below, put black markings on the OD of the centering rings at the location of the fins. Third, sand the Aft airframe's internal surfaces where the fins contact the fin slots, and the centering ring OD will contact, along with most forward centering ring on both faces and ID, and clean these areas with Acetone. Refer to first 2 attached pictures.
Now, cut shallow grooves into the fin tab (see attached picture), and then sand and clean (Acetone) all contact surfaces.
Mix up a good sized batch of J-B Weld and apply;
A. A good-sized ring around the MMT approximately 1/4" forward of where the Forward Fins Centering Ring will rest, when assembled.
B. On the fin tab to cover the cut grooves, trying to leave some hanging down below the fin tab, to be forced into the groove upon assembly.
C. Using a popsicle stick, apply epoxy into the fin slot, onto the MMT for its full length.
With J-B Weld seemingly hanging off of everything;
1. Assemble the MMT into the Aft Airframe, pushing it forward to the correct final location, based on the view of the centering rings.
2. Rotate as necessary such that the black markings on the centering ring OD lines up with the fin slots.
3. Assemble the Rear Fins Rear Centering Ring into position, to ensure the MMT is correctly aligned.
4. Assemble the fin into the appropriate fin slot, applying downward pressure to seat it firmly against the MMT.
5. Clean-up excess epoxy along the OD of the airframe tube, using it, where possible, to fill any gaps between the airframe slot and the fin.
6. Assemble the fin alignment guide onto the fin, and then assemble the other two (2) fins into the guide, to help ensure the correct relative location for all fins.
Finally, give it a few hours to cure, then proceed with steps B, C, 4, 5, and 6 for the other two (2) Forward Fins.
 

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  • 16 - Sanded MMT and CRs.jpg
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  • 17 - Sanded CRs including Fin Location.jpg
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  • 18 - Grooved and Sanded Fin (typical).jpg
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  • 19 - Fin with  J-B Weld.jpg
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GaryDean

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With the Front Fins assembled, the next action will be the Rear Fins.
The areas to be bonded in this step were sanded and cleaned in when prepping for the Front Fins.
Like the Front Fins, I am cutting shallow grooves into the fin tabs (see attached picture) to provide greater area for contact with the J-B Weld. After grooving, sand and clean (Acetone) all contact surfaces.
A. Mix up a good sized batch of J-B Weld and apply;
B. On the fin tab to cover the cut grooves, trying to leave some hanging down below the fin tab, to be forced into the groove upon assembly.
C. Using a popsicle stick, apply epoxy into the fin slot, onto the MMT for its full length.
D. Assemble the fin into the appropriate fin slot, applying downward strong pressure to seat it firmly against the MMT.
E. Clean-up excess epoxy along the OD of the airframe tube, using it, where possible, to fill any gaps between the airframe slot and the fin.
F. Rather than using another fin alignment guide, I am clamping a straight-edge between the Front Fin and the just assembled Rear Fin. See attached picture. Using this procedure will ensure the fins are in perfect alignment with each other from front to back.
Finally, give it a few hours to cure, then proceed with steps A thru F for the other two (2) Rear Fins.
Gave the final assembly a good heat soak in the Florida sun for good measure.
 

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  • 20 - Rear Fins Grooved and Sanded.jpg
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  • 21 - Mix Up a Batch of J-B Weld.jpg
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  • 22 - First Rear Fin Held in Place.jpg
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  • 22a - Final Cure Process in Sunlight.jpg
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GaryDean

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Used the free time while waiting for the epoxy to cure on the rear fins to complete the Internal Mount for the Nosecone, which will hold the Featherweight Tracker on flights. Took the bonded (plywood CR and fiberglass CR) part from earlier post, drilled holes for the retaining bolts, inserted washers (backside only) and bolts, using J-B Weld (not shown) on the bolts for additional retention. Then shaved the washer overhang on the ID and OD with a hand grinder (see attached picture). Finally, applied additional J-B Weld on the backside of the mount to help ensure the bolts do not loosen during the process of installing the lock nuts. The backside assembly will be mounted in the nosecone, against the coupler.
 

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  • 27 - Finished Internal Nosecone Mount.jpg
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  • 26 - Backsides of Finished Cover Plate and Mount.jpg
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  • 25 - Finished Cover Plate and Mount for Nosecone.jpg
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  • 23 - Backside of Internal Nosecone Bulkplate Assembly.jpg
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  • 24 - Holes Drilled and Bolts Inserted for Nosecone Bulkplate Assembly.jpg
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GaryDean

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With completion of the internal mount, can now finish the nosecone assembly. The Nosecone Shoulder (Coupler) has a non-load bearing interface with the Nosecone. So, have decided to only insert the coupler into the nosecone for a length of 2 inches, bonded with J-B Weld. An important consideration for me is the alignment of the coupler with both the payload tube and the nosecone itself during the bonding, because I hope to achieve a clean split-line where the Payload Tube and the Nosecone touch in the completed assembly. Best way to achieve that goal is to use all the involved parts in the bonding process. I start by inserting the coupler into the Payload Tube, laying horizontally (see picture 28), with 2 inches of the coupler exposed. Then, use gaffers tape to tape the end of the Coupler inside the Payload Tube. You can barely see the large clamp in picture 28 that I use to apply a very slight "squeeze" on the payload tube, to help keep the coupler in the correct position when the nosecone in assembled. This is a good time to roughen up both bonded surfaces with sandpaper, and clean-up with Acetone. Then, cut small pieces of wax paper, fold them in half with a sharp crease, and insert them around the full circumference between the Coupler and Payload Tube (see picture 28), with a slight edge to edge overlap. This helps prevent excess epoxy from bonding the Coupler to the Payload Tube. Picture 29 shows the Tracker Mount Assembly inserted into the Nosecone. Next step is to mix up the batch of J-B Weld and use a popsicle stick to apply a thin layer of epoxy to both the Coupler and internal Nosecone surfaces. I had previously determined the optimal orientation between these parts and used masking tape to mark this desired alignment. Now, the REALLY busy part! Assemble the Nosecone onto the coupler, twisting slowly to help spread the epoxy. With the Nosecone in place;
1. Reach through the back end of the Payload Tube and remove the gaffers tape.
2. Remove the large clamp so the coupler is no longer restrained in the Payload tube.
3. Push (from inside the payload tube) the Nosecone / Coupler slightly out of the Payload Tube.
4. Remove all the pieces of wax paper.
5. Use alcohol to clean-up any excess epoxy at the interface between the Nosecone and Payload Tube. Look carefully and do this correctly!
6. With the Nosecone held horizontal, reach into the Nosecone and pull the Tracker Mount Assembly up against the internal end of the Coupler. There will be excess epoxy at this interface which was pushed out, which will hold the Tracker Mount in position.
7. Stand the assembly up vertically, to keep the Tracker Mount in the proper position.
8. Wait about 30 - 40 minutes and use a razor blade and alcohol to clean-up any excess epoxy at the internal interface between the coupler and Tracker Mount.
9. Used this opportunity to assemble the nosecone back into the Payload Tube to determine whether any adjustments were necessary.
Everything seems to be OK, so set it in a vertical position to finish curing.

When fully cured I wrapped paper around the coupler end to leave 4 inches for insertion into the Payload Tube, and used my diamond rotary blade to cut the excess coupler length off. Cleaned up the cut edge, assembled the aluminum tip onto the Nosecone, and assembled the black bulkplate which will hold the Tracker into place on the internal mount. The Nosecone is completed. Pictures 30 and 31 show the external and internal views.
 

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  • 29 - Tracker Mount Inside Nosecone.jpg
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  • 30 - Completed Nosecone - External View.jpg
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  • 31 - Completed Nosecone - internal View.jpg
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GaryDean

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With all the Fins in place, have to consider how to apply epoxy to all of the internal interfaces that have not yet been bonded. I will be using West Systems 105 / 205 epoxy at all interfaces, except as noted below, in which I will use J-B Weld. My application plan, in the exact order it will be accomplished, is;
a. Forward face of Front Fins Front Centering Ring: Use wooden dowel, plastic tubing, and syringe to get into this narrow, but visible area (1 place.
b. Aft face OD of Rear Fins Forward Centering Ring: Use wooden dowel to apply J-B Weld into these narrow, but visible areas (3 places).
c. Aft face of Front Fins Front Centering Ring: Injected by syringe into holes drilled near fins (3 places).
d. Forward face OD of Front Fins Rear Centering Ring: Injected by syringe into holes drilled near the fins (3 places).
e. Forward face ID and OD of Rear Fins Rear Centering Ring: Manual application of J-B Weld through open Aft end of airframe, before pressing the CR into place.
f. Rear face ID and OD of Rear Fins Rear Centering Ring: Manual application of J-B Weld through open Aft end of Airframe.
g. MMT / Fin and Fin / Airframe interfaces for the Front Fins: Injected by syringe into holes drilled near the fins (6 places).
h. MMT / Fin and Fin / Airframe interfaces for the Rear Fins: Injected by syringe into holes drilled near the fins (6 places).
i. Aft face OD of Front Fins Rear Centering Ring: Injected by syringe into 1 hole drilled in the airframe tube between the middle centering rings, with airframe in vertical position, fins up (1 place).
j. Forward face OD of Rear Fins Forward Centering Ring: Injected by syringe into 1 hole drilled in the airframe tube between the middle centering rings, with airframe in vertical position, fins down (1 place).

Then, install the rear 1515 Rail Button before proceeding with the plywood centering ring for the Thrust Plate.
 
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GaryDean

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Now begins the process of applying the epoxy to the necessary fin-can interfaces.
For "a." identified in the previous post, I stood the Airframe upright, assembled the wooden dowel, plastic tubing, and syringe to the necessary length, and mixed up an approximate 25ml batch of West Systems epoxy, using the correct proportions of Resin and Hardener, by weight. Used the syringe to suck up about 10ml at a time and applied the epoxy to the full forward face of the front CR, ensuring it was well distributed to the ID and OD. Refer to picture 33.
After a full cure, turned my attention to "b.", identified in the previous post. Orientated in a upright position again, but this time with the fins up. This application was easier due to the shorter depth. Mixed up a batch of J-B Weld and used a wooden dowel to apply the epoxy to the OD interface, in the 3 areas between the fins. Refer to picture 34.
Waited for a full cure, laid the airframe horizontal, and then drilled a series of holes along every fin, and 1 hole between the fins. The hole size works with the nozzle of my syringe. Picture 35 shows the typical holes.
Now to work on item "c." from the previous post. This requires the airframe to be vertical again, with the fins up so that the epoxy will move downward to the intended location. Mixed up 30ml of West Systems, and injected approximately 10ml into each of 3 drilled holes near the front of the Front Fins. After injecting all the epoxy I rotated the airframe around at an angle to try to achieve a distribution that favored the OD, because the ID here was bonded with J-B Weld when the MMT was assembled. Then, returned the airframe to vertical for full curing.
 

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  • 34 - Aft Face of the Rear Fins Front Centering Ring.jpg
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  • 35 - Drilled Holes for Epoxy Application by Syringe (typical).jpg
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  • 36 - Hole Near Front of Fins to Inject Epoxy (typical).jpg
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GaryDean

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Now, to work on area "d." identified in my 8:05 pm post, flip the aft airframe over so that the fins are down, allowing the epoxy injected into the aft holes near the Front Fins to go downward to the appropriate interface. The ID on this Front Fins Rear CR was previously done with J-B Weld, so the focus here is to try to get the epoxy to the OD. Mixed up a 30ml batch of West Systems and injected equal amounts into holes for each of the 3 chambers. After all epoxy is injected, rotated the airframe around in a manner which is intended to position the epoxy towards the OD of the centering ring. No relevant pictures are possible here.
 

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Because I intend to do epoxy applications for areas "g." and "i." mentioned in my 8:05pm post, at the same time, I need to complete the work on the centering rings on both ends of the fins first. This means that areas "e." and "f." for the Rear Fins Rear CR will be next on the agenda.
First step here is to sand the MMT OD, Airframe ID, back edge of Rear Fins, and the Centering Ring itself, all in areas that will be bonded. Then, clean-up with Acetone. Completed that step and snapped picture 37 for the rear of airframe. Mixed up a batch of J-B Weld and carefully applied this onto all the contact surfaces. On the MMT and Airframe I tried to place the epoxy a bit rearward of it's final resting place, so that during installation of the centering ring there would be certain contact with the epoxy, and it would be pushed by the CR, to help ensure contact between the bonded surfaces and the epoxy. Refer to picture 38.
Gave the assembly a short break and then removed the three (3) screws, mixed up some J-B Weld, and applied a small bead to the contact surfaces between the MMT OD, Airframe ID, and the Centering Ring. Ran a popsicle stick at these interfaces to achieve a smoother, more consistent bead. Finally, filled the holes with epoxy, and did some clean-up on the messy surfaces. Picture 39 shows the completed centering ring.
 

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  • 39 - Completion of Rear CR Installation.jpg
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GaryDean

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Now to work on the interfaces between the fins, MMT, and ID of the Airframe. For each of the Front and Rear Fins there are six of these interfaces. I will be doing 2 interfaces in each epoxy application, for both the Front and Rear Fins. Will start with what I refer to as the A-B interfaces, as noted in my sketch in picture 41. This sketch helps me keep track of what's been finished. The MMT applications are easy to remember, but the Airframe IDs not so much, because they are done in different pairs, and the assembly is turned after injection to ensure the epoxy flows to the correct location. Details later! Mixed up 2 separate batches, each of 25ml of West Systems 105 / 205 epoxy, and after stirring for 1 minute minimum, used my syringe to inject the epoxy as follows;
- 15ml between the 2 holes (approx. 7 1/2 ml into each) for the "A" Front Fin
- 15ml between the 2 holes (approx. 7 1/2 ml into each) for the "B" Front Fin
- 5ml into each of the 2 holes in the "A" Rear Fin
- 5ml into each of the 2 holes in the "B" Rear Fin

The Rear Fins are getting a bit more epoxy with this distribution. My thinking is that the Rear Fins will certainly contact the earth first, taking most of the force of impact. More impact = More epoxy!

Picture 40 shows the layout, and use of a level gauge to ensure the epoxy is distributed evenly, I hope. A bit difficult to recognize in the picture, but the airframe is turned 60 degrees, with the level gauge at the top ("UP"), and the A and B Fins 60 degrees from "UP".
Cleaned up the tools and excess epoxy around the holes, and now waiting for a full cure.
 

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  • 40 - Layout for Syringing Epoxy for MMT - Fin Interface.jpg
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  • 41 - Treasure Map for Planning the Fin to MMT Interfaces.jpg
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GaryDean

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You gonna be ready to fly it at the Buc Blast?
That's the plan! Have an AT L2200G ready for a trial flight on Saturday (October 21st), and if all goes well, my AT M2050X goes into the rocket for a Sunday Level 3 Certification flight. Tripoli Tampa has a capable launch pad, and they've promised outstanding weather for the weekend.
Had bit of a scare yesterday when I checked my supply of RocketPoxy for the fin fillets. Hmmm, probably not enough, and no supply available right now due to shortage of a needed chemical. Identified a reasonable alternative (Loctite EA 9462) and ordered a serious supply, with quick delivery. Fruity Chutes will soon ship material for an upgraded (5/8" tubular Kevlar) Drogue Shock-Cord, and then I will have all the necessary materials on-hand.
 

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The application of epoxy for the A - B Fins seems satisfactory. So, rotate the airframe 120 degrees and do the B - C Fins in the same manner as outlined in my post 4:26 PM from earlier today. Will do the C - A Fins in the morning, and when those have cured will proceed to the application of epoxy at the Fin / Airframe intersections.
 

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All the Fin / MMT interfaces are complete. Time to move to the Fin / Airframe ID interfaces. I am going to do these 6 interfaces separately, because the application process is;
1. Orientate the rocket so that the previously drilled holes are perfectly horizontal.
2. Inject the appropriate amount of epoxy.
3. Block (tape) the hole.
4. Proceed through steps 2 and 3 for the other 3 holes along that fin.
5. Immediately rotate the airframe so that the interface of interest is placed at approximately a 60 degree angle (downward) from horizontal, so that the injected epoxy will flow to the interface, which is now very much like a "V".

With 3 fins it is impossible to obtain the optimal V angle at 2 locations at the same time. So, will do them individually, Starting with the A Fin side towards C.

Before starting the process outlined above, sand the surface of the 4 holes through which epoxy will be injected, to help create a hole that will be successfully sealed with tape, after injecting the epoxy. I also tore off pieces of tape and put them close to the holes, so I could quickly block the holes after injecting epoxy.

So, proceeded through this process for the 1st Fin / Airframe ID interface, and the attached pictures show the blocked holes, along with how the rocket is orientated while the epoxy cures. After approximately 3 hours will continue on..............
 

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  • 43 - View from Aft End to Show Orientation.jpg
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GaryDean

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The next day ....... Just applied the epoxy to the final Fin / Airframe ID interface. After that cures it will be on to the last 2 interfaces, the ODs of the middle centering rings.
During my spare time while waiting for the previous 5 applications of epoxy to cure, I accomplished some work on the E-Bay. This includes;
- Inspecting the parts.
- Laying out the hole locations and drill sizes. Refer to picture 44. Note: Drogue canisters are 3-gram and Main canisters are 6-gram, with different diameter screws being used.
- Clamped the 2 bulkplates back-to-back to save time in drilling the necessary holes.
- Drilled all holes, dry fit screws, and chamfered holes. Refer to picture 45.
- Assembled all components to the bulkplates, being careful to ensure the lock-nuts for the 5/16" threaded rod are on the same bulkplate as the 6-gram charge canisters. This is the non-accessible end. The Wing Nuts are on the Drogue side to allow internal access. The terminal blocks are installed with 1/8" stainless steel bolts / Lock-Nuts. I feel this is more secure and reliable than using epoxy to hold them in place. Used stainless steel washers. Refer to picture 47 for the Drogue side of the assembly.
- Picture 48 shows the backside of a bulkplate. During assembly I used silicone in every hole (except the center eye-bolt which will connect to the shock cord) to help seal these holes against the entrance of burnt gunpowder. I used Blue Threadlocker on the 5/16" Eye-Bolts. And I will be using Blue Threadlocker on all of the 5/16" stainless steel nuts on the threaded rod.
- Picture 49 shows the complete assembly at this stage. Please note that the final length of the E-bay, and thus the threaded rod length, has not yet been decided. My design intent is to use a coupler length of 10". But, cannot commit to that length until I have done a component layout on the fiberglass sheet to be sure that a 10" length will be sufficient.
 

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  • 45 - All Holes Drilled.jpg
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  • 46 - Unclamped, Chamfered, and Inspect.jpg
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  • 47 - Drogue End Assembled (typical).jpg
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  • 48 - Backside of Bulkplate (typical).jpg
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  • 49 - Assembly - Not Finshed Length.jpg
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GaryDean

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Completed the final Fin / Airframe ID interface, and ready to move forward with the OD interfaces between the middle 2 centering rings. Proceeded to do the further aft interface first, by standing the Airframe vertical, with the fins downward. Mixed and injected the epoxy through the one (1) hole drilled previously between these centering rings. After injection, I proceeded to slowly rotate the airframe around its' axis, tilted about 45 degrees. The intent with this rotation is to distribute the epoxy more towards the OD of the centering rings. Did the rotation for about 20 minutes, which was the point in which a small sample left in my mixing container had become quite stiff. Waited 3 hours, reversed the position of the airframe (fins UP), mixed 25 grams of epoxy, and continued the previous process with this batch.

Next step will be the fin fillets, using RocketPoxy. That work will begin after removal of all the tape, filling holes as necessary, sanding all the fin fillet areas, and finishing with an Acetone clean-up. Tomorrow morning (NOT midnight tonight) seems like a good time to begin that work.
 

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  • 50 - Completion of Internal Epoxy Injection.jpg
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GaryDean

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I feel really good about the efforts on applying epoxy to the Fin / Airframe ID interfaces. When I removed the tape from the holes, essentially every hole was filled with epoxy, which tells me that my process worked well.
So, with only the drilled hole between the middle 2 centering rings to fill, I can move quickly to sanding all the fin fillet area. Refer to picture 51. Then, clean-up with Acetone.
I will be using a 1 1/8" diameter PVC tube to pull the fillets, and need to determine the location of the masking tape used to create nice edges. So, used a magic marker to spread ink on the OD of the PVC tube, and ran that down a short section between a fin and the airframe. The lines were 7/16" from the intersection of the fin and airframe. I then proceeded to create small markers (masking tape) for this 7/16" dimension, and then ran a long pieces of masking tape onto the fins and airframe, along those markers. Refer to picture 52.
Then created masking tape "dams" at both ends of both fins to keep the epoxy in place as much as possible. Refer to picture 53.
Made use of my level gauge to ensure that the airframe was level from Aft End to Forward End.
As shown in picture 53, I plan to apply epoxy along 2 sets of fins in each go-around, mixing separate batches for each set of fins.
I was a bit unsure how much epoxy would be required for each set of fins, so started with 9 grams each of the RocketPoxy Resin and Hardener. Add 1 drop of black dye. I proceeded VERY QUICKLY through this process because my RocketPoxy is a bit more than 2 years old, and seems to be curing faster now, compared to my previous uses! Mixed the epoxy for 1 minute then used a popsicle stick to transfer from mixing cup to the fillets. Oops, made too much and then compounded the problem by putting too much into the grooves. Well, the excess certainly came out when I started the process of pulling the fillets with the PVC tube! To create a better epoxy surface, I apply Denatured Alcohol onto the PVC tube before each pull. Usually leaves the epoxy with a smooth, glassy appearance. When I was satisfied that this first set of fillets had set enough that no major shifting of the epoxy would occur, I mixed the next batch of epoxy, this time with 7 grams of each component, and proceed though the process of pulling the fillets.
Allowed these to cure for 3 hours, rotated the airframe 120 degrees and proceeded through the same process for these sets of fins, finally settling on 6 grams of each epoxy component as the correct amount for these fins.
And finally, after another 3 hour cure, finished the last sets of fins. When that wait was over, removed all the tape to reveal the results shown in picture 53. There's lots of finish sanding which must be done, and I am sure some body filler will be needed to achieve the desired finish and taper.
 

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  • 52 - Taped Off Ready for Epoxy.jpg
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GaryDean

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I had written a general comment about "my RocketPoxy is a bit more than 2 years old". I should have clarified that .... Not only is my RocketPoxy more than 2 years old, but there is very little left in the containers, and what's in there is so dry that it was necessary to scrape it out. The resin was in the worst condition, and because the hardener had some appearance of moisture, I thought it would work OK. I knew my RocketPoxy was "iffy" and Tim Cubbedge was kind enough to do me a solid and loan me his supply. I used my RocketPoxy on the first 2 fins, to my regret. It was impossible to mix correctly, as I found out when the epoxy has cured with small clumps / bumps in the fillets, rather than nice smooth surfaces.
The end result was 6 hours of sanding, filling (Bondo Glazing & Spot Putty), and more sanding. Lesson learned: Always use RocketPoxy that still has its creamy texture!!!
ln the end they are not the best fillets I've done, but considering the hassle I created by using old RocketPoxy, they will do. Refer to picture 55. The reddish Bondo Spot Putty is an indication of how much of the area could not be sanded smooth with a reasonable effort.
 

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  • 55 - Finished Sanding - Filling - and Sanding.jpg
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Now is a good time to identify the locations for the 1515 Rail Buttons and mark a line the full length of the Aft Airframe as part of the assembly process for the rail guides, along with the Tether Platform, Vent hole, and E-bay. Started by finding a centerline between the A and B fins by cutting a piece of paper to the exact distance between the centerline of these fins. Folded the paper in half and used it to mark centerline points at the Aft End of the airframe, along with the front of the Forward Fins. Then took my 5 foot aluminum angle and drew a line along those centerline marks and extended it to the forward end of the airframe.
Now to identify the location for the Aft Rail Button. At the Aft End of the airframe I measured the distance (1 1/16") from the backface of the Aft Centering Ring to the bottom of the airframe, along with the distance (7/64" that the Thrust Plate will entend into the Aft Airframe. Pulled a flange nut from the 1515 Rail Button bag and laid it in a position in which it would not contact either the rear centering ring or installed Thrust Plate. Marked that location and drilled a guide hole. Pressed a PVC tube between the MMT and the Airframe, to help minimize the chance of splintering the fiberglass in drilling the hole(s). Refer to picture 56.
When satisfied with the location of the guide hole, used the correct sized drill (1/4") for the final hole, again with the PVC piece in place. Sanded the ID side and used a small diameter round file to clean up the hole edges. Used my vise and vise-graps to create a small angle on the flange of the flange nut, trying to mirror the form of the airframe ID. Tried the flange nut in the hole and it was a perfect fit. Refer to picture 57.
Sanded both sides of the flange nut hole, sanded both sides and stem of the flange nut, then mixed up some J-B Weld. Rotated the airframe 180 degrees so that gravity would be my friend in this assembly. Put the screw in backwards, giving me something to grip while applying the epoxy. Applied a small amount to the face of the flange nut which goes against the airframe and installed the flange nut. Made sure it was orientated correctly with the airframe. Refer to picture 58.
Finally, installed the button and screw and tightened the screw down to ensure a tight interface between the flange nut and airframe. Added more J-B Weld to the backface of the flange nut and left it to cure. After curing I disassembled, put a drop of Permatex Blue Threadlocker on the threads, and reinstalled, adjusting the screw so that the button can just spin freely.
I cannot install the Forward Rail Button at this time due to other items (Tether Stop, Shock-Cord Tether, and Tether Retaining Ring) which must be installed first. But, I did identify the intended location for the Forward Rail Button, 43.75 inches from the bottom of the installed Thrust Washer.
 

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  • 57 - Final Sizes Flange Nut Hole.jpg
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  • 58 - Flange Nut in Place with Epoxy.jpg
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  • 59 - Tightend Down Screw with Final Epoxy.jpg
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