Glasspacks' LVL II Build

[Glasspack]

Interesting idea. I normally just glue it to the ID of the airframe. In this case I'd have put it ahead of the FWD CR and installed it before inserting the MMT.

I didn't want it ahead of the FWD Ring to keep my Drogue recovery gear free from any possible snag.
If I was Smart...…… I would have only put the FWD centering ring on the tube without glue, as I secured the fins. Then I could have glued the ring in AFTER the Block and the Motor Tube Fin Can was in place. That action was long ago though, so I was going to slip it up and glue it in after the fin can was in position, BEFORE I attached the Middle Centering ring. **** ......… But THAT is why I am doing this !

 

[Glasspack]

Tried to get some more done before work today...……….. Sized up the tail cone and found the best place to position it, to minimize my fin slot errors from the previous marking and slotting. The AFT Rail Guide attachment block was final shaped and epoxied into position on the tail cone shoulder.
That was actually done Yesterday...……



I ended up not using the Centering ring that was for the AFT Fins. The very AFT centering ring is 1/2" thick, epoxied and screwed to the Tail Cone.
The Tail Cone shoulder is about 3" long Epoxied into the AFT Airframe.

I feel it has a good bit of construction design to transfer the motor thrust to the Airframe. I will find out on Launch day no doubt.


Some of the Proline 4500 was used to glue the cuts between Fin slots in the tube that allowed me to slide the fin can assembly up
from the bottom and into position. I have a lot of clean up and prep for finishing... I know.



So I applied a good bead of Proline 4500 inside the airframe and around the motor mount tube and carefully installed the Tail Cone assembly.
Twisting it around at least a full turn to spread the epoxy. Even used a bit to fill the tiny seam at the joint. Stood it up and weighted it down to dry.

 

[BrendanH69]

I've not had a build yet where the fin can is assembled and bonded up outside of the body tube. Will give this serious consideration on future builds for the benefits of good quality internal fillets and rail button hard points.

 

[Glasspack]

Brendan, It was easy for ME to make the decision to build it this way, as that is How my Public Enemy Kit was designed all those years ago.....
I was familiar with the idea and thought it would be easier. This one is just more complex. After this is all done, I don't think I will be convinced its any easier......… I will give it my all and also ensure its safe. There is a lot of reasons so many people build.... and THEN inject the internal fillets.


Installed the Rail Guides tonight...……. These are more difficult to do than the single screw Rail Buttons. More surface area...…. more Screws to install, all with a greater chance to get them just a wee bit crooked !!! I tell you though with the plywood anchor pieces inside; they are strong !!




Even though they may look ok in the above photos, ……. I Had to take them off, Re-align, and then drill again to get them as straight as possible. I was very disappointed with the initial friction on the rail....


I achieved a much better alignment this time using my heavier steel angle and the drill guide made for round stock.
It should come off the rail much smoother now !!




So I started sanding and prepping the lower part of the airframe.
I adjusted the Aft fin slots and made sure the Aft fins all fit.
(Remember me telling you about screwing up the alignment and cutting the one fin off and redoing it..? )


Had to stop for the night..... I hope to get them on tomorrow.

I know what your thinking........ This dam thing looks like its sliding into second base with a lot of duct tape and bondo !!
I feel like a Kit would have been easier for sure...…… But THIS is what I wanted to do for my LVL 2 model.

 

[Glasspack]

I had a chance ...… before work each day this week, to get down to the Rocketry Room and put the Aft Fins on.
They went pretty smoothly. First I had to adjust the front of the fin tab a little (1/16"). The fins would not sit exactly flat against the motor tube because the tip of the fin was on the airframe tube basically making the fin tab Just a TAD to short....…

Used my Dremel table and a spiral cutting bit, to take just a tiny bit off each fin...…

Mixed up some Pro Line 4500, and here they are...…… I wish I had thought to switch my Scale (before I started this whole thing), to read Grams instead of Ounces. Grams reading on the scale makes the epoxy mix easier to do ....math wise.



So I was hoping some of you would chime in ... I have been reading about "Coning" and over stable models. With the very long length of this model I am getting concerned about stresses and things like weather cocking and Coning. I could easily change the length of the model to closer match the original "Open Rocket" file I got from Sebastian in Argentina. Even shortening it form the original scale of 98", I could easily keep my stability margin closer to 1-1.5 for a fully loaded, ready to launch model. I have been playing with the overall length of my model on RockSim and Open Rocket ...… I am leaning closer to keeping it at 90" or less. That is still a High Ratio of ….What's the word? ….. "Fineness" Love it ! I am also shooting for a minimum rail exit velocity of 40-45mph. Apogee Rocketry, and Rocksim say that minimum safe speed is around 35mph..... I am not sure I am comfortable with that for a 10 pound model leaving the rail !!

Any way I would love to hear your thoughts and of course your experience.

 

[Glasspack]

No one has a thought on it ??

 

[Speaknoevil]

I have never experienced coning and have built quite a few long (L>>D) rockets. I think fin alignment is far more important to reduce any waggle on ascent. Example, this: https://www.rocketryforum.com/threads/estes-mean-machine-001295-gallery.159960/#post-2009847. If built right it does not cone.

 

[OverTheTop]

I agree with Speaknoevil. Get a good fin alignment (which helps get your rotational rate down) and you will hardly notice any coning that may occur. I don't think your rocket is excessively long, so don't lose any sleep over it .

 

[mbeels]

With the very long length of this model I am getting concerned about stresses and things like weather cocking and Coning.

I don't have as much experience with such large high power rockets, but I'd be willing to bet that the additional stresses due to weather cocking and coning are far lower than the stresses of a normal launch.

 

[Glasspack]

Thank you all...…. !!!

I really appreciate the feed back. I am looking at a total length of about 86-90" right now. The original math for the upscale would put it at about 98". I spent what little time I had Friday sanding the lower airframe assembly. I used a little bit of epoxy and filled a some of the gouges I had in the fins from the earlier posts about my router table mishap. Its going well so far despite all my building skill flaws and errors I had to correct. The prep work to get a nice finish is going to take me some time. For example: The tail Cone diameter is a tiny bit bigger than the Airframe. So there is a ridge at the seam. No big deal but again...…… All of that stuff affects the nice paint finish.

 

[Glasspack]

So I just saw the Email from Papa Elf..... I officially joined the Christmas In July celebration.
I made the dead line in time !!

 

[Glasspack]

Started the exterior Fin Fillets tonight. First, I experimented with the two PVC pieces I have for pulling the radius...…….
I quickly determined that the 3/4" piece is just to large to use for this model. The 1/2" piece will provide a nice looking fill radius along the root edge.

Once I had my tool picked out to pull the fillet, I sanded the whole thing and cleaned it all with alcohol. I used one of the pieces of my wifes' Drift Pattern transfer papers from her sewing warehouse. Its like this stuff: https://www.shabbyfabrics.com/traci...MI0abLitGA6gIV78uGCh3SUQBnEAQYDCABEgLg3fD_BwE Works great to transfer tape lines … just lay the paper, "dye" side down, and press down & pull the radius tool (what ever you use) from one end to the other. I used Blue during the testing; but had to clean it all off and do it again using the 1/2" piece of PVC. That's why it has blue lines in one photo and orange in the other. Old school carbon paper would work great as well.




I followed that up with Frog tape right on the transferred lines, I really like the Proline Epoxy; but boy its messy.
The tape was pulled as carefully as I could, about 10 minutes after laying the fillet. I don't want to attempt more than one set at a time, as this stuff is pretty runny compared to other fillet epoxies....

 

[Glasspack]

All I did tonight on my model was cut the Mid Airframe to 20". Then secured it temporarily to the fin can to mark the lines on it for shear pin placement.

The three pins will be in line with and about 2" below my altimeter air vents.
There will also be thin brass plates on the inside of the airframe to strengthen the airframe holes at the shearpoint.

Maybe get a chance to work on it tomorrow.


Hey.... I am well aware that the shearpins often are used to secure the nosecone. But...do most of you just friction fit the avionics bay to the lower section for drogue deployment....??
Or use shear pins on both ends that seperate?

 

[Glasspack]

Well I have planned to use pins on both ends but I Know a lot; if not most......D/D models use friction fit for the drogue.

 

[mbeels]

Hey.... I am well aware that the shearpins often are used to secure the nosecone. But...do most of you just friction fit the avionics bay to the lower section for drogue deployment....??
Or use shear pins on both ends that seperate?

I think it mostly depends on the anticipated drag separation forces. My two MD rockets have shear pins to the lower section, but my King Kraken does not.

 

[Glasspack]

Thank you for the responses. Found my (1800 lb. rated) 1/2" Tubular Nylon roll, so now I could use either material for my harness. I spent most of the day with my wife so I didn't work much on this today. I attached the 20" Mid Airframe tube to the Lower Airframe assembly and tried my best to ensure it is aligned as prefect as possible. Put 5lbs. of weight on it to keep the two pieces tight as the Tight Bond III dries. It is.... after all; two sections of Paper wound tubing.... Wood Glue will hold quite well !!! Tomorrow I will try to do more fill and sanding. The seam will have to disappear if I want a nice finish. I am already finding it difficult to make the seam at the tail cone disappear; the Tail cone has a slightly larger diameter.

 

[Glasspack]

I began the tedious task of filling and sanding, more filling and sanding...……. repeat.

 

[Glasspack]

Today I started to put together the upper airframe section. I have new tubes from Rocketarium.com (https://www.rocketarium.com/Build/Airframes/40) They are like 36" long and very nicely built & are all white and about 4.01" outer diameter so they are perfect for this project. If you remember from an earlier post I had destroyed one of the original airframe tubes when I cut the 3 fin slots a bit off from 120 degrees. So, I measured and marked the upper airframe and cut it at 20" length using my cutting jig.... looked like this:
Just imagine it was a white tube.
I also always coat the ends of the paper tubes with liquid CA and rub it in using baggies or Parchment/wax paper.

I planned to provide a secure strong place for sheer pin installation. There are a lot of cases where the card board tube gets worn out because the pin material is stronger than the tube. I had the thin brass stock already cut into 1" pieces and shaped each one to match the inner diameter of the airframe.
The 2-6 Pin location was marked at 2" down and 120 degrees apart, then I marked the inside of the tube for each plate. Carefully carved out the paper from inside, and fit tested.
The pieces were done one at a time and each one was sanded with 80 grit paper on the outside surface and cleaned with alcohol before gluing in with Gel type CA. My parchment paper keeps the glue from sticking parts together I don't want to get stuck.
I have a small section of tail cone shoulder to hold the brass pieces against the inside of the airframe until the glue sets.
My next plan is to lightly coat the inside of the tube with my Proline 4500 right over the brass pieces. Then, use the parchment paper to install the Nose cone for a snug fit without accidently gluing the nose cone in.

 

[mbeels]

Carefully carved out the paper from inside, and fit tested.

That's quite neat, how did you carve out from the inside? With a chisel?

 

[Glasspack]

I used each brass piece to guide my pencil...…………. Then slowly and carefully used my Xacto Knife to slowly carve out the square, one layer at a time.
Each one is about two layers of paper removed.

 

[Glasspack]

After all three brass shim pieces were in place and secured...I coated the interior of the tube with Proline 4500 Epoxy to cover all three shims.
The nose cone was installed with a single wrap of Parchment paper to ensure the epoxy forms to the shoulder, and to ensure that it doesn't get stuck !!

Here is the 90" model all assembled so you can see it.

All the Simulations I have run say it should fly just fine...…...

Please; Tell me if the fineness (Length to Diameter) ratio looks ok...…
Do you think the fins look to small for the size of the model ?

 

[OverTheTop]

Looks like a nice flyer to me. As long as it sims alright you will be fine . Boattail takes away a little stability.

 

[Glasspack]

OvertheTop,

Are you referring to the Stability Caliber ? I understand ANY weight aft of the CP is counter productive... but the length and the Avionics bay weight are all working to my advantage so far. I believe the Tail Cone does help with drag reduction though....... AND So far, at least, the actual model does seem to come in lighter than the Rocksim File says it is.... only like 1 - 1.5 lbs ... but that makes me happy

 

[OverTheTop]

Boattail reduces stability because it reduces base drag. Nothing to do with the mass. It shifts the CP forward a little. If you have a marginally stable rocket and you add a boattail to it beware .

If it sims good you are ok.

 

[Handeman]

So, how are you going to put the brass shims in the nose cone to match the BT?

 

[Glasspack]

So, how are you going to put the brass shims in the nose cone to match the BT?

Well, actually Handeman, I did not plan to install the brass shims on the nose cone. The Plastic is a little tougher than the cardboard and with a brass shim to shear each pin I thought that would be sufficient. Bonzai88's thread was my inspiration...…….

https://www.rocketryforum.com/threads/shear-pin-shear-plates-in-your-cardboard-tubes.136706/

Each one will be drilled and tapped for a 2-56 x 1/4" pin. I am using the short black ones form Apogee so I can see them easy on the White Airframe.
I plan to ground test it of course so I will look closely at the parts after separation to see how it performed. Am I sadly mistaken ??

 

[Handeman]

Well, actually Handeman, I did not plan to install the brass shims on the nose cone. The Plastic is a little tougher than the cardboard and with a brass shim to shear each pin I thought that would be sufficient. Bonzai88's thread was my inspiration...…….

https://www.rocketryforum.com/threads/shear-pin-shear-plates-in-your-cardboard-tubes.136706/

Each one will be drilled and tapped for a 2-56 x 1/4" pin. I am using the short black ones form Apogee so I can see them easy on the White Airframe.
I plan to ground test it of course so I will look closely at the parts after separation to see how it performed. Am I sadly mistaken ??

I've never used pins on any rocket that wasn't fiberglass.
I have seen some where they used pins with plastic nose cones and the holes did get chewed up some, even in the plastic. The shim might help. It will be interesting what your ground testing reveals.

 

[jd2cylman]

FWIW, I put shear plates in the plastic NC shoulders as well... It's a major PITA to do, but well worth it.

 

[Nytrunner]

Ive inly had plastic deformation issues with shear pins in the Pro Series II cones' thin plastic.

Basically if the plastic is thcker than 1mm, I dont worry

 

[Glasspack]

Thank you all for the feed back..... The nose cone is the "Pinnacle" model from Giant Leap. It was like $25.00 and seems like a very nice nose cone.

Handeman, I will take up close photos of the nose cone after recovery testing and post them here.