Min Diameter Carbon L2 Cert Build

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This is my first forum post and my intent is to gain some wisdom from people who have been doing this way longer than I have and hopefully avoid learning some lessons the hard way. This build is my L2 rocket that I plan to fly on 19 Dec 2020 and is also a test bed for an eventually minimum diameter L3 build that I plan for next year. After losing my first L2 attempt rocket (never deployed and never found it due to not having GPS…) I wanted to build on what I learned and be sure to have GPS capability.



Build

  • 1.6” Carbon Fiber Mongoose from Madcow with modified fins, else stock
  • Nose cone is FW fiberglass
  • Aeropack min diameter retainer (5/16 nut JB welded into top of DMS motor for retention)
  • Acme aluminum conformal rail guides
  • RRC3 Sport altimeter on Missile Works 3D printed sled (9V)
  • Featherweight GPS in a Lab Rat Rocketry nosecone 3D printed mount
  • Fruity Chutes 30” main and simple nylon 10” drogue
  • Using 2x2-56 shear pins to hold the nosecone and aft section together (grounded tested)
  • 3x4-40 steel screws hold payload section to AvBay
  • Both Shear pins and screws are drilled and tapped
  • Aerotech DMS J425R Motor
  • Dry weight 1050g
  • RockSim says 10,400ft with max of Mach 1.2


All BS flags and feedback are greatly appreciated.



-Tony
 

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Look at this post for eyebolt mounting in a dms. https://www.rocketryforum.com/threads/at-l-1000-dms-–-flying-case-with-a-nose-cone-and-4-fins.162266/post-2053896

Although you way would work too I think.

not sure about the featherweight in carbon fiber might want to range check it in deployed form.

anyhoo... looks like fun. Good luck!

Tapping the DMS is a great idea, I will definitely do that next time to give the bond even more strength.

The nose cone is fiberglass so I don’t think the GPS will have an issue but I will be sure to check it.

Thank you
 
Nice rocket.

Is your nose cone CF?
If so, GPS signal may be inhibited or blocked.
 
He did state it is a FW NC. So that will work fine. I myself would not trust JB Weld on a metal part for shock cord attachment point. At the very least I would yank on it with a hammer in a shock cord while it is mounted in a vise. Make sure all ground tests are done as it is flight ready. Love the carbon rocket. And good luck with her.
 
He did state it is a FW NC. So that will work fine. I myself would not trust JB Weld on a metal part for shock cord attachment point. At the very least I would yank on it with a hammer in a shock cord while it is mounted in a vise. Make sure all ground tests are done as it is flight ready. Love the carbon rocket. And good luck with her.

Which attachment points are you referring to? The shock cord chain starts with the eyebolt on the Aeropack min diameter retainer in the booster section (which is JB welded to the airframe) then the eyebolt on the av bay which is connected via 2 #8 all threads and aluminum bulkplates to the eyebolt on the other end of the AvBay. Next the eyebolt on the nosecone is connected to the shoulder with steel set screws which are anchored in the fiberglass coupler (shoulder) and the 3d printed Featherweight mount. I agree that the JB weld on the Aeropack retainer isn't necessarily ideal but my thinking is that any force from chute deployment should be transferred directly through the aluminum only (Acceleration generates a "downward" force on motor which pulls on steel threads which pull on aluminum retainer and then to the eyebolt) Does that check?
 
He did state it is a FW NC. So that will work fine. I myself would not trust JB Weld on a metal part for shock cord attachment point. At the very least I would yank on it with a hammer in a shock cord while it is mounted in a vise. Make sure all ground tests are done as it is flight ready. Love the carbon rocket. And good luck with her.
I saw his post.
In the past they have shipped CF nose cones with the CF Kit.
 
Which attachment points are you referring to? The shock cord chain starts with the eyebolt on the Aeropack min diameter retainer in the booster section (which is JB welded to the airframe) then the eyebolt on the av bay which is connected via 2 #8 all threads and aluminum bulkplates to the eyebolt on the other end of the AvBay. Next the eyebolt on the nosecone is connected to the shoulder with steel set screws which are anchored in the fiberglass coupler (shoulder) and the 3d printed Featherweight mount. I agree that the JB weld on the Aeropack retainer isn't necessarily ideal but my thinking is that any force from chute deployment should be transferred directly through the aluminum only (Acceleration generates a "downward" force on motor which pulls on steel threads which pull on aluminum retainer and then to the eyebolt) Does that check?


I suspect he's talking about the motor retaining nut jb welded to the top of the motor. It should work.. but as Tony has done before tapping threads and then threading it in with JB weld would be even stronger. Another possibility would be is to thread it. Set the fitting in place drill a horizontal hole through the dms and the screwed in place fitting and utilize a pin that pushes and locks in place or even just a set screw that threads into one side of the metal fitting and dms and would keep the fitting from backing out. Plenty of ideas.
 
I'm looking into some nose cone tracking bays for 3 inch minim diameter project im doing and wasn't sure how well these would work. Im curious how strong the set screws would retain the nose cone.
 
I suspect he's talking about the motor retaining nut jb welded to the top of the motor. It should work.. but as Tony has done before tapping threads and then threading it in with JB weld would be even stronger. Another possibility would be is to thread it. Set the fitting in place drill a horizontal hole through the dms and the screwed in place fitting and utilize a pin that pushes and locks in place or even just a set screw that threads into one side of the metal fitting and dms and would keep the fitting from backing out. Plenty of ideas.

That’s valid, I made sure to rough up both the nut and the plastic first but it is a weak point. The nut is a 1 inch long coupling nut though not a standard size nut. This also worked with a 54mm I motor on my L1 flight and took the strain with no issues.
 
I'm looking into some nose cone tracking bays for 3 inch minim diameter project im doing and wasn't sure how well these would work. Im curious how strong the set screws would retain the nose cone.

I’ll let you know how it holds up. You could definitely add more than the two included set screws to make it stronger or use something like a motor retainer to create a screw on joint I suppose.
 
I’ll let you know how it holds up. You could definitely add more than the two included set screws to make it stronger or use something like a motor retainer to create a screw on joint I suppose.


The nose cone has an aluminum tip. Its threaded inside. So I could add something but looking to keep weight down as much as possible. Long burn light weight min diameter looking for big altitude
 
Flight was a success. Rocksim was dead on to within 50’ of max altitude and .03 Mach. 10,400ft and 1.2 Mach. Recovery was clean and the Featherweight GPS more than paid for itself. Landed in a corn field and never would have found it without the tracker.
 

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Flight was a success. Rocksim was dead on to within 50’ of max altitude and .03 Mach. 10,400ft and 1.2 Mach. Recovery was clean and the Featherweight GPS more than paid for itself. Landed in a corn field and never would have found it without the tracker.


Congrats on the great flight. Im currently having to vicariously live through others as we have had fire bans due to high fire danger and covid restrictions that have kept us from launching. But Great job!! what motor did you end up flying with? what did you end up doing on your tracker bay in the nose cone for attachment, threaded rod or other?
 
Thank you! I ended up just using the steel set screws to hold the tracker sled in the nose cone and it help up very well. It flew on the J425R and I think next time I’ll step up to the 435WS and see if the construction methods can handle the extra speed and G. Forgot to seal the avbay lid holes for the igniter completely so I got some residue on the altimeter but it is still fully functional.
 
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