RW 6-inch Stinger build

[Tobor]

I just drill a hole through the bottom of the copper cap and bolt the charge wells to the bulkhead.

That is what I did on my MC Pike, but on this build there is not enough clearance between the top of the charge wells and the piston assembly I am using to protect the recovery gear in the nosecone. Using the holders assures me there is adequate clearance.

 

[Tobor]

Some progress today.



Mounts for EggFinder and Proton w/Mini WiFi switch.

 

[Tobor]

More progress and a confession....

Two new "Features" were actually mistakes I have corrected.



The pic above show both of them.

1st Mistake: When I began assembling the AV Bay (#27), what I did not realize was that the fwd CR (RH Side) had been rotated to the wrong position, placing the allthread passthrough holes in the wrong spots. This mistake placed one of the 1/4-20 allthreads directly inline with the plywood platform for the EggFinder.

My fix is the "tube" next to the EggFinder. It was originally a (Madcow or LOC) 1/4 inch launch lug I had in my spare parts pile. Using it allowed me to anchor that side of the platform to the vertical support.

2nd Mistake: The 3D printed grommet for the EggFinder's antenna was not originally part of the design. It came into existence because I was not paying attention when I drilled the hole with the wrong size Forstner bit, 3/4" instead of 1/2". You think the size difference would be readily apparent....

So why do I call these mistakes features? It's is because of a comment by Youtuber Steve Ramsey - Woodworking for Mere Mortals. In one of his videos, he gives advice to beginners, (to paraphrase) "If you make a mistake on a project, turn it into a feature!" I like that concept.

 

[Tobor]

Update:
Shortly after my last post, I broke my 3D printed "Badass Rocketry" styled fin guide while test fitting (Fitment was a tad too snug). So I designed and printed a pair of old school fin guides with corrected IDs.

And last night I had time to use them for the dry fit.






Edit: Forgot to mention that this morning I tacked the fwd CR in place using thin superglue and then mixed up some Aeropoxy + colloidal silica to complete the bond.

 

[Tobor]

This evening I installed the rail button anchors (2nd pic in post #15), MMT and fins. But, before I describe that process, a pic...

An ugly but functional fillet of Fwd CR.



Dry fitting the aft end yesterday helped me plan the "Order of assembly".

01) Sanded all the fin roots, entire outer surface of MMT and the inside back end of the airframe with 220 grit sandpaper. Then wiped everything down with isopropyl alcohol.

02) Placed MMT and fins back into the airframe. Then using a mechanical pencil placed hash marks on the MMT where the fins roots rested. I also marked where the MMT protruded passed the fwd CR. Then I pulled the MMT out, and using a fine point Sharpie drew out guide lines for the root of each fin. Then using the mark for the CR, drew a line around the circumference of the MMT.


03) Drilled holes in airframe for rail buttons and glued the anchors in place with BSI 15 epoxy.
04) Mixed up some Aeropoxy with a nice dose of colloidal silica.
05) Applied a fillet of epoxy to the back side of the fwd CR/airframe joint. Also applied lines of epoxy where the front end of each fin will butt up against the fwd CR.
06) Applied epoxy over the guide lines on the MMT for the fins and CR.
07) Next I slid the fins loosely in place in the airframe, then I applied epoxy to the root of each fin. With that accomplished, I installed the MMT alligning the lines of epoxy with the roots of the fins, and then carefully nudged each fin into place against the MMT.
08) After triple checking that the fins and MMT were all properly positioned, I snugged up the 3D printed fin guides against the leading and trailing edges of the fins to help maintain fin alignment.
09) After I was satisfied everything was lined up, I checked all my glue joints.




10) Last but not least, I temporarily installed the aft CR and added some rubber bands around the leading edges and tips of the fins.



I am sorry I did not take more pics. I did not want to risk the epoxy setting up before I had all the parts in place and properly aligned.

That's all for today.

 

[Hobie1dog]

thanks for the pictures

 

[Tobor]

Welp, I made another boo boo....

The 3D printed forms I made for the internal fillets cannot be used on this build. When I installed the MMT and fins I was a little too sloppy with the epoxy and now the forms will not sit flush with the fwd CR... ooops

So last night I reverted to doing the internal fillets the old school way.

Fillet #5 applied this morning (R-hand side)



Each fillet consists of 1 pump of West System 105/206, 2 level tea spoons of colloidal silica and 1-1/2 teaspoons chopped carbon fiber. Overkill? Most likely, but this my first 6" rocket and I'd rather it not re-kit itself on it's first flight. Besides the second set of internal fillets (airframe/fin joints) will be much smaller.

One comment. West System 105 is the thinnest epoxy I have ever used. Unmodified, it flows like hot syrup. Imo it's like water compared to Aeropoxy or Rocketpoxy. Because it behaves as it does, I had a tad bit of trouble after I laid down my first fillet. Even though the rocket as level, the epoxy wanted to flow pass the back end of the fin. I realized I needed to add some sort of dam. It took me a moment before it dawned on me to just use the GLR motor retainer as the raised flange on the front of the retainer acts like a retaining wall, albeit a short wall.

I've also started applying Frog tape to the external fin/airframe joints. This will prevent epoxy from seeping through when I lay out the second set of internal fillets.

 

[jd2cylman]

Welp, I made another boo boo....

The 3D printed forms I made for the internal fillets cannot be used on this build. When I installed the MMT and fins I was a little too sloppy with the epoxy and now the forms will not sit flush with the fwd CR... ooops

So last night I reverted to doing the internal fillets the old school way.

Fillet #5 applied this morning (R-hand side)

View attachment 536518

Each fillet consists of 1 pump of West System 105/206, 2 level tea spoons of colloidal silica and 1-1/2 teaspoons chopped carbon fiber. Overkill? Most likely, but this my first 6" rocket and I'd rather it not re-kit itself on it's first flight. Besides the second set of internal fillets (airframe/fin joints) will be much smaller.

One comment. West System 105 is the thinnest epoxy I have ever used. Unmodified, it flows like hot syrup. Imo it's like water compared to Aeropoxy or Rocketpoxy. Because it behaves as it does, I had a tad bit of trouble after I laid down my first fillet. Even though the rocket as level, the epoxy wanted to flow pass the back end of the fin. I realized I needed to add some sort of dam. It took me a moment before it dawned on me to just use the GLR motor retainer as the raised flange on the front of the retainer acts like a retaining wall, albeit a short wall.

I've also started applying Frog tape to the external fin/airframe joints. This will prevent epoxy from seeping through when I lay out the second set of internal fillets.

View attachment 536531

More colloidal…

 

[Tobor]

Welp, I made another boo boo....

More colloidal…

Roger that. What amount do you add per pump of 105?

 

[jd2cylman]

Roger that. What amount do you add per pump of 105?

I use the West mixing cups. So one pump cup of West and one mixing cup full of Colloidal. Basically, enough Colloidal to make it peanut butter consistency.

 

[pathtouch]

Roger that. What amount do you add per pump of 105?

Similarly I use Total Boat epoxy but it’s all the same. I use two heaping teaspoons per pump usually. Chuck a popsicle stick in a cordless drill for mixing.

 

[Tobor]

Weekend was really stressful. Early Friday evening my mother-in-law fell while walking to my sister-in-law's house and fractured her hip. Saturday she spent 3+ hours in surgery. Doctor implanted several steel pins in her femur and ball joint. Yesterday they gave her a blood transfusion.

Amazingly, she has been in high spirits throughout her ordeal, even witnessing to hospital staff (she is Evangelical). If I were in her shoes, emotionally I would not have fared nearly as well.

Thankfully, she is steadily improving.

---------------------------------------------------------------------

On Friday morning I worked on the 2nd set of internal fillets.



My cardboard dams worked okay but cleanup was pesky. Lesson? If I use this technique again, I will add a layer of packing tape or mylar to the epoxy facing side and use hot glue to affix the dams in place.

Saturday evening I had time to flesh out the design for the LiPo holders and Sunday afternoon I started printing parts. Around midnight all the PETG bits were in place.





Had a design error with the small LiPo holder. If you look closely, you can see my "fix".

 

[Tobor]

Welp, it's been a short spell since my last post...

2 weeks ago I ordered a 6-position barrier strip for terminating E-Match wiring and designed and printed a conformal base to mount the strip on. (See 2nd pic below)
After I epoxied the base in place I completed all the wiring within the AV Bay.
About 8~9 days ago I updated the firmware on my ET Proton.
Last Tuesday I fleshed out my ideas for sealing the AV Bay against ejection charge gases.
*Outer perimeter of AV Bay: I will use a 5.77" x 0.21" silicon O-Ring that will be sandwiched between the fwd FG bulkplate and the fwd plywood CR.
*E-Match pass-through: I designed and printed a block style cover (See 1st pic below)

 

[Tobor]

More Progress...

3D printed a "Stop" block for the bottom end of the AV Bay. Tacked in place with 5-minute epoxy.



The gap filled with West System & silica



This morning I worked on beveling the AV Bay's fwd CR to accept a 0.139" Dia. silicone O-Ring I picked up at McMaster-Carr. The o-ring I listed in a previous post was decidedly too large for this application.



The o-ring will hopefully keep the ejection charge gasses away from the electronics.

 

[Tobor]

Still making progress, doing this and that as time, life/wife and will permit. I'll post more pics soon.

Also, I've decided on a motor, it will be an AeroTech J615ST.

 

[Tobor]

Almost there... This bird might just be ready in time for MWP!

From last week:

Finished fiddling with the AV Bay internals

3D printed holders for 1/4-20 Nylock hex nuts and epoxied them onto repurposed CR. CR + 1.5" wide coupler tubing make up the "anchor block" for the AV Bay assembly.


AV Bay carriage finished. The 3D printed "nozzle like thingies" are just alignment guides for the 1/4-20 allthread rods.


Last weekend:

3D printed a "bulkplate block ring" for the nosecone (NC). The fwd bulkplate (BP) will rest against this ring. When the ejection charge fires, the ring will take the load from the BP and transfer it to the NC, thus preventing the BP from getting rammed further up into the NC. The ring had a 2.5mm thick x 13mm wide gap between it and the NC that was filled with West Systems epoxy.


This week:

All vents holes drilled out, 3 for the AV Bay and 1 for the airframe. Also added an indexing key (6-32 socket head cap screw) to the AV Bay housing that engages at the seam of the airframe and NC. Installed rail buttons


From several weeks ago:

Display stand and 3D printed adapter (used together in the pic right above). The display stand is actually oversized for the Stinger. When I get around to building my L3 rocket, this stand will be used for that rocket. I will then make a smaller stand for the Stinger.

 

[Tobor]

Today I fleshed out the recovery rigging. Going with 24" WM Recon Drogue and a 50" WM Recon Main.



All up weight sans J615 is 17lbs-2oz.

 

[Tobor]

Hmmmm, looks like I never posted a pic of the Stinger painted...



I plan on repainting it after it's maiden flight this spring at MMWP. And btw, when I took this rocket to MWP last year, I purchased an AT 75/54 adapter from Wildman. When I tried to use it in the Stinger, I discovered that the adapter was not compatible with the GLR 75mm Slim-Line retainer I used in the rocket.

So I will either try to fabricate an adapter or buy a DMS motor at MMWP.