Corona build questions

[Alex R]

I'm building a Fliskits Corona (and Corona-2, but haven't started the booster yet), and have a couple of questions...

The first, simple question:

The instructions say to leave the outside of the ring fin unpainted if it will be used with the booster... But can some painting be gotten away with? It'd be nice to fill the fairly deep spiral groove in the ring, but that would look really ugly without painting.

The second question is more complicated:

How well aligned do the upper and lower body tube sections need to be for straight flight? After a construction "oops", I found <a href="https://rocketryforum.com/printpost.php?s=&threadid=6922&postid=105281">this post</a> (toward the end of <a href="https://rocketryforum.com/showthread.php?threadid=6922"> this thread</a>) which emphasizes how important it is that the tubes be aligned for stability. When I check the alignment, the top tube is *just a little* out of alignment -- with lower tube section flat on a tabletop, I can rotate the rocket so the top end of the upper tube lifts about 1/4" above the tabletop -- this comes to a bit less than a 1 degree misalignment of the top with the bottom tube.

So, do the experts here think that this much misalignment is negligible, and I should go ahead and finish and fly it, or is this clearly so crooked that I should cut out the central coupler and start over? I could also do a test flight before finishing -- I think that the ring fin fits snugly enough over the radial fins that I could probably fly it without gluing it, allowing removal for finishing.

If anyone is interested, here is my "oops":

The instructions call for the Kevlar shock line to be knotted and then threaded outside the body tube coupler, but inside the body tube. When the upper section of the body tube is glued to the coupler, the Kevlar must be threaded through the tube *immediately* so that the Kevlar can be pulled tight and the tubes can be slid together.

I did a quick threading test before I glued, but when the time came to glue them together, the line picked up just enough glue from the inside of the body tube that it wouldn't slide up the tube with a push from the end. I scurried to find a heavy object to tie to the line to guide it through (as the glue was setting, tick, tick, tick...), found one (tick, tick...), guided the line through (tick, tick...) and shoved the tubes together. Alas, the glue had set up just enough that the tubes did not *quite* go all the way together. I also managed to very slightly "wrinkle" the upper body tube seams from the force I had to apply to slide the tube through the rapidly setting glue.

Due to the wrinkles, I couldn't tell how straight the tube was, despite my rolling it over the floor, but considering that there way *no way* I could have separated the tubes for another try, I decided just to move on, and fill and sand the gap (<1mm) and wrinkles...

If I were to do it again, I would modify my technique... Simple mod: thread first, then apply glue! However, I'd prefer some way of attaching the shock line that doesn't require it to deform the body tube or coupler -- the best one I've been able to think up would involve adding a single centering ring with a notch through which the Kevlar could be threaded...

 

[PunkRocketScience]

Hey Alex-

I am currently working on a Corona/Corona2 build myself and have had an identical experience! I am somewhat frustrated by the wrinkle that I've gotten in my tube joint.... and addressed it the same as you did.

I am going to fill and paint my Corona ring fin. I'd like to be able to fly it just single stage and not look bad. I've filled and primered it so far. I have sanded it down a bit so that the extra thickness shouldn't be an issue (hopefully). I'm going to sand out the inside of the forward booster ring as soon as I finish construction on it as well.

 

[Planet Andy]

I filled my ring and also sanded it down a bit and had problems with separation of the two stages however following a separation failure where the upper stage motor blew through the booster stage it seemed to loosen it all up and I've had about three successful 2 stage flights without failure since...As for the kevlar cord...you might get yourself a baffle and mount the kevlar cord through the bottom of that...

Andy

 

[jflis]

A 1-degree angle on the upper body tube may not be too bad, but to be honest I have no personal experience with that much of a discrepancy.

Corona's that I have seen go unstable due to an angle between the 2 tubes had well over 2 degrees of bend (you could see it just looking at the model), so it is hard to tell.

If it is doable, I would cut the tubes just above and below the coupler, strip the tube remnants from the coupler and sand it down so that you can re-use it and reconnect the tubes. Your Corona will be about 1.5 - 2" shorter. NOTE: The original FlisKits Corona was 2" shorter than it is today, so that won't be a problem

Also, any test flight you may do you REALLY need the tail ring glued securely in place. The most prevalent flight problems with the Corona have been cases where one or more of the glue points have come undone on the ring resulting in enough movement to cause instability. The Corona is very long and slender and the tail ring is a HUGE guidance force for such a rocket. Minor movement during flight can cause really bad things to happen...

However, gluing the tail ring on for a test flight should be fine as that end of the rocket wouldn't change even if you discovered that you had to operate on the tube joint.

Lastly, painting the outside of the tail ring should be ok if you follow these simple rules of thumb:

- Use as few coats of paint as possible to keep build up to a minimum
- Avoid primers as they are typically very thick (unless you sand them aggressively)
- Use paints that have little build up, such as silver or other light metalics or candy paints (they may not cover as well, but build up is the concern here)
- After the paint has completely dried, light sand the surface to give it a smooth, less sticky surface.
- You may also want to consider lightly sanding the INSIDE of the mating ring on the booster.

I have never done this, so I don't have firm information. These are just suggestions that I would recommend if you feel you really need to paint that ring.

Good luck and PLEASE keep us posted. All such information would be invaluable to other Corona owners!

jim

 

[PunkRocketScience]

Originally posted by jflis

- Use paints that have little build up, such as silver or other light metalics or candy paints (they may not cover as well, but build up is the concern here)


Good luck and PLEASE keep us posted. All such information would be invaluable to other Corona owners!

jim

Perfect! I was going to paint the ring silver anyway! I'll post my results once I have it complete!

 

[Alex R]

Thanks, Jim, for your input, and especially your caveats about a firm bond for the ring fin.

To be honest, given the tools I have available and my lack of experience cutting body tubes, I suspect that if I cut out the coupler and tried to reglue the shortened tubes, there's a good chance I'd end up with more misalignment than I started with... I've only built "3FNC" type rockets before this, so maybe I should have built a couple of easier models first, but I couldn't resist this beautiful design.

So I'll give it a try as is with a "heads up" launch -- and let you all know how it went.

 

[Blades]

Just completed mine as well and was thinking about the same problem of finishing the sustainer's ring. What about using some chrome Monokote? It might take a bit more sanding of the ring to get a decent fit, but it should also leave a nice smooth surface to prevent the booster from binding up.

Fliskits came up with a beauty here. There's an elegance to a simple design that puts me in mind of a fine Japanese Sword.

 

[tonypv]

I saw one at one of our launches this year where they used a black marker to color the ring and it looked good.
I left mine unpainted but I might color it with a silver marker.

 

[jflis]

A silver marker, like those new metalic Sharpie markers would probably be a great solution.

Blades, "Elegant" !
That's the word for the Corona. I love the design, shape and everything but never found a word that felt *right*.

Elegant.

Yeah, that does it

 

[GeorgiaRocket]

I never painted the ring on my Corona as it was a pretty snug fit as it was and paint would have made it impossible to fit the two rings together, and expect them to come apart. I had planned on using markers but I stuck mine in a tree and never got the chance. My next one I will use markers of some type.

The kevlar causes a bump out on one side where it slides under the coupler and that might what is causing your top end to raise up when you roll it. It did on mine, but the rocket was still straight.

I flew it with a C6-0 to C6-5 at Southern Thunder last year. It is a beautiful rocket.

 

[Blades]

Originally posted by jflis

Blades, "Elegant" !
That's the word for the Corona. I love the design, shape and everything but never found a word that felt *right*.

Elegant.

Yeah, that does it [/B]

Glad I could be of service.