Over the past few months there have been a lot of developments with this build. I have been fortunate to learn a lot from many people along the way. While it is still my eventual goal for this rocket to fly on the O3400 I now understand that this flight will not be my L3 cert flight, nor with this rocket be allowed to be my L3 cert project. It is not my intent in posting this update to challenge these decisions, it is my goal to share what I have learned and continue to learn from others. I am embarrassed to say that along the way I have allowed my ego and frustration to get the better of me when talking with those who have far more experience from myself. I hope that my apologies to them and my continued work in this hobby will show I am better than that.
I would like to address upfront the rumor that I started this build without TAP approval, that is not correct, there were 4 on board at the start of construction.
As always, BS flags are always welcome.
-Tony
Deployment proof of concept - 17 April 2021
Eagle CO2 System
- 35 gram CO2 cartridge
- Dual firewire igniters
- Test Device
- 4” diameter PVC pipe
- Lower cap interior was leveled with epoxy for ease of mounting and secured with 4x steel screws
- Upper cap is mildly friction fit and held with 3x #6-32 nylon shear pins
- A 1/8” vent hole was drilled in the tube
The Eagle system was ignited using my low power rocket launch box with a 12V battery. The test was conducted twice with a totally empty tube to allow for the largest margin of safety. A video of the test is located here:
Both tests demonstrated the 35 gram cartridge was more than sufficient to shear the pins, launching the cap over 20’ from the tube.
Mako Line Cutter
- Loaded with single firewire igniter and secured to an old DMS motor tube
- Zip tie was 0.05” thick and 0.2” wide and was tightly secured
Mako success severed the zip tie and functioned as advertised. Small amount of exhaust is not a concern as the chute will be wrapped in a Nomex blanket.
Fin Beveling Practice – 24 April 2021
The rocket design calls for a 5 degree fin leading and trailing edge bevel. To accomplish this I will use my router table, a jig, and a 5 degree carbide burr.
Router Table
- Standard router table and a DeWalt ¼” shank router
Carbide Burr
- Foredom fine abrasive 5 degree carbide burr
Jig
- 8” x 24” white shelving board from Lowe’s
- 2x Toggle clamps from harbor freight
Testing with ¼” thick woods and scrap fiberglass showed very good results. There will be plenty of cutoffs from the CF plate used for my fins so that will allow for additional practice when the fins arrive. The biggest advantages of the jig setup I have observed are
- Allows your hands to be further from the burr
- Allows for far better control of the fin as the clamps can hold it very tightly
- The clamps can produce a lot of clamping force so be sure to step up the pressure slowly to avoid cracking the material
- The wider edge at the bottom of the board and the larger contact area on the back with the fence makes it much easier to keep the fin path correct
I would recommend using at least to passes to remove the desired amount of material. This reduces stress on the material (tip can break off) and makes it easier to push the material through the machine. Some light sanding was required to remove the grooves left by the bit.
AvBay Prototyping – 25 April 2021
First step in prototyping the AvBay assembly is to drill out the mounting holes for the 2 Eagle CO2 systems. This was done using a 1” hole saw and then a 9/64’ bit for the mount screw holes. The fit is good but I plan to use some tape on the face of the sled between the sled and the Eagle to create a “gasket” to help seal the NC better.
Next step in the Avbay prototyping was the “machining” of the fixed ring that the sled base will seat against and be screwed to. This started as an SC Precision 98mm-75mm thrust plate and using a Dremel and some files I reduced the diameter until the aft face seated ~4.3” inside the NC. This will allow the coupler to have 4” of purchase in the NC for epoxying and give about 0.1” of extra room for the sled base which is 0.25” thick. Obviously, this will need to be epoxied in before the coupler as it is larger than the coupler inside diameter. The thinking behind this is 4 fold.
- Give the sled base a positive seat closer to the aft end of the nosecone to ensure clearance for all AvBay components. If I did not have this ring the sled base, which must be slightly smaller that the coupler inside diameter to be inserted, would sit much higher in the NC (about 1.5” higher). This increased seating height doesn’t allow sufficient clearance for the Eagle CO2. Additionally, there would be a relatively small contact area between the sled base outside edge and the NC wall.
- I will utilize 2 of the pre-drilled 6-32 holes in the thrust ring to help hold the sled base secure during flight. This will also help to make sure the sled base is properly aligned for switch access during arming.
- By filling the unused screw holes in the ring and adding a layer of tape on the ring I will be better able to seal the Avbay components off from the CO2 systems at Apogee.
- The epoxied thrust ring in addition to being a positive seat for the sled base will help to distribute the large pressure loading at Apogee. ~200 pounds of force are required to shear the 3x #6 shear pins and while they will quickly give way there will be a small period of time where the sled base will have to withstand that pressure, and possibly a lot more if the CO2 systems fire near simultaneously. The surface area available on the FWD side of the thrust ring to apply epoxy will allow for a better distribution of that loading and reduce the chance of a sled base failure.
Following these proof of concepts wooden prototypes were ordered from SendCutSend and used to further refine the design and fit before ordering the final aluminum and titanium versions.
Motor Retainer Skeletonizing – 28 April 2021
I got the Wildman order in the mail today and I am still waiting on the motor hardware and fins so I can’t start major assembly yet, but I was able to do the modifications I planned on the Aeropack retainer. Full disclosure this only reduced the mass by about 10% so take it with a grain of salt. Other than the weight reduction my goal in drilling out the material was to provide more bonding area/access for the epoxy. The fit in the Wildman tube was spot on but I wanted to give the epoxy more ways to get between the tube wall and the retainer. I felt this was more important given the retainer is ~48” from the aft end of the tube and I won’t be able to easily add more epoxy after the fact.