Transitions

[Duncan.Byers]

So I've worked a lot to get transitions correct but I fight against rounding where the transitions meet the body sections. Any suggestions?

 

[David Schwantz]

Guess I am not sure what you don't like about ours. I think they came out great. Are you wanting a more square shoulder? I like to make a pattern on the rocket and then remove it to glass over.

 

[GlenP]

Well, that is kind of the point, aerodynamically, to make a smooth transition for lower drag. The paint is going to tend to fillet out the sharp edges. Mabye paint the model in different sections, and assemble it after painting? If you want to highlight the transition, then mask it off and paint it in a contrasting color for a sharper "edge" appearance? That will trick the eye into thinking it has a sharp edge at a color break. You can maybe split the model there for recovery instead of at the nose?

Excalibur breaks at the bottom of the transition for the sustainer stage. The top edge of the transition was masked of on parts of the upper tube. (Sting is a cardstock printed model, so that is kind of cheating, no paint fillet there, just a clear coat over the paper)


Cloudbuster has these transitions and a boat tail, since those are the most distinguishing feature, I painted them to highlight them, one of the designs from the Centuri Design Manual. The base coat did smooth out the sharp edges, but the paint job kind of gives the illusion of a sharp edge.


This Dr. Zooch kit had a balsa cone with a base transition that was very smooth. I added a little cardstock wrap to give it a sharp edge, and painted the transition a shade of gray to help it stand out more, on a smaller model that helps it create a shadow to highlight the transition too, otherwise it is not very apparent.


if you don't want to change the color, what would it look like if you masked it off, and painted it again the same color. When you pull off the masking tape, will that take off part of the paint fillet that you don't want? I have not tried that before, but it might pull off part of the paint and leave you with a little bit of a sharper edge there?

 

[neil_w]

So I've worked a lot to get transitions correct but I fight against rounding where the transitions meet the body sections. Any suggestions? View attachment 527039View attachment 527040

Those look fantastic. What is your technique?

 

[Duncan.Byers]

Those look fantastic. What is your technique?

Maybe I'm just being too picky. This is a one-off designed from the nose down. The only "stock" parts are the nose cone and the top BT. It's a Nike Spartan built to scale; the bottom two BTs are cut-down to size. The transitions are paper (made with Bristol Board paper) then hardened with a good
soaking with ultra-thin CA. This is what the real deal looks like. The build is pretty big - it's 3 1/2 feet tall. Made this one a single stage but will likely build a 2 and (maybe) 3 stage.

 

[Duncan.Byers]

Well, that is kind of the point, aerodynamically, to make a smooth transition for lower drag. The paint is going to tend to fillet out the sharp edges. Mabye paint the model in different sections, and assemble it after painting? If you want to highlight the transition, then mask it off and paint it in a contrasting color for a sharper "edge" appearance? That will trick the eye into thinking it has a sharp edge at a color break. You can maybe split the model there for recovery instead of at the nose?

Excalibur breaks at the bottom of the transition for the sustainer stage. The top edge of the transition was masked of on parts of the upper tube. (Sting is a cardstock printed model, so that is kind of cheating, no paint fillet there, just a clear coat over the paper)
View attachment 527041

Cloudbuster has these transitions and a boat tail, since those are the most distinguishing feature, I painted them to highlight them, one of the designs from the Centuri Design Manual. The base coat did smooth out the sharp edges, but the paint job kind of gives the illusion of a sharp edge.
View attachment 527042

This Dr. Zooch kit had a balsa cone with a base transition that was very smooth. I added a little cardstock wrap to give it a sharp edge, and painted the transition a shade of gray to help it stand out more, on a smaller model that helps it create a shadow to highlight the transition too, otherwise it is not very apparent.
View attachment 527043

if you don't want to change the color, what would it look like if you masked it off, and painted it again the same color. When you pull off the masking tape, will that take off part of the paint fillet that you don't want? I have not tried that before, but it might pull off part of the paint and leave you with a little bit of a sharper edge there?

These are custom built paper transitions. And with the original rocket's color scheme it's mostly white.

 

[GlenP]

If you don't like the results with paper transitions, maybe try to get some 3D printed parts. Most of the smoothing is probably a result of painting, so painting it separately then assembling the model after paint might help. Good luck!

 

[Duncan.Byers]

Guess I am not sure what you don't like about ours. I think they came out great. Are you wanting a more square shoulder? I like to make a pattern on the rocket and then remove it to glass over.

I'm assuming you meant to say "yours." I'm just thinking looking at the real rockets that the transition is a lot sharper at the edge.

 

[GlenP]

I'm assuming you meant to say "yours." I'm just thinking looking at the real rockets that the transition is a lot sharper at the edge.

Those full scale rockets probably have the same paint fillet radius in them, it just looks so much smaller in comparison. So, this suggests another option, UPSCALE!

On the other hand, those full-scale rocket designers might look at your model with those lower drag and smoother transition edges and take note, so they can make a better rocket next time!

 

[Duncan.Byers]

Those full scale rockets probably have the same paint fillet radius in them, it just looks so much smaller in comparison. So, this suggests another option, UPSCALE!

On the other hand, those full-scale rocket designers might look at your model with those lower drag and smoother transition edges and take note, so they can make a better rocket next time!

This is pushing upscale for LP, at least on black powder. I'm sure I could make it bigger, but...it's a single stage that's about 3.5 feet tall. On an E16 OR gives it an apogee of 227m. I won't be winning any altitude contests. I can use bigger composite motors of course. The plan is to do it again with 2 or (maybe) 3 stages as the original Spartan was. I might upscale it some at that point......

Engineers take note!

 

[Woody's Workshop]

Well, this is my take on it. I've used plastic, balsa and paper transitions. They all have a unique way of dealing with different body tubes from different manufacturers. I always coat balsa with several coats of thinned TiteBond 3 glue and sand until it meets the BT's that I coat with glue and after sanding. For plastic, I use Tamiya White putty to smooth out imperfections. With paper transitions I coat the underside with thinned TiteBond 3, and glue it in place while still wet. Once it sets I coat the outside with thinned TiteBond 3 and let dry, then use Tamiya White Putty to smooth things out.
Couple coats of primer and some sanding (I always wet sand by dipping the paper in water, never saturate the sanding sutface and wipe clean when necessary with a paper towel) and it's ready to go for paint.
What you have to remember is what a Real Rocket looks like, and if your flying the rocket or building it for show. I don't know too many people that build for show, so it's going to fly.
What you want to come out of this is something that will handle the flight and the recovery without showing signs of cracking at the transitions so it looks good for the next flight.
You can spend as much time as you want and after the first flight it's a disaster. Build smart, think things out and make them structurally strong for what it is, yet looks good from 10 feet away. And you will be in the groove.
BTW, Pachie is NOT for sale at any cost!!!
I now return to our regularly scheduled kits for sale posting, break time is over...

 

[Duncan.Byers]

Well, this is my take on it. I've used plastic, balsa and paper transitions. They all have a unique way of dealing with different body tubes from different manufacturers. I always coat balsa with several coats of thinned TiteBond 3 glue and sand until it meets the BT's that I coat with glue and after sanding. For plastic, I use Tamiya White putty to smooth out imperfections. With paper transitions I coat the underside with thinned TiteBond 3, and glue it in place while still wet. Once it sets I coat the outside with thinned TiteBond 3 and let dry, then use Tamiya White Putty to smooth things out.
Couple coats of primer and some sanding (I always wet sand by dipping the paper in water, never saturate the sanding sutface and wipe clean when necessary with a paper towel) and it's ready to go for paint.
What you have to remember is what a Real Rocket looks like, and if your flying the rocket or building it for show. I don't know too many people that build for show, so it's going to fly.
What you want to come out of this is something that will handle the flight and the recovery without showing signs of cracking at the transitions so it looks good for the next flight.
You can spend as much time as you want and after the first flight it's a disaster. Build smart, think things out and make them structurally strong for what it is, yet looks good from 10 feet away. And you will be in the groove.
BTW, Pachie is NOT for sale at any cost!!!
I now return to our regularly scheduled kits for sale posting, break time is over...

I appreciate the info. Haven't used the White Putty - my default generally has been to use gap filling CA and usually get a sharp transition - until priming, etc. I've looked back at what images I've got of the Spartan and have to say maybe the transition edges aren't quite as sharp as I'd thought. They are where the stages separate, though, so there's bound to be more there I think.

All that being said I'm not building to win awards. To your point, I'm building to fly. And fly it will.

thanks!

 

[Duncan.Byers]

Those look fantastic. What is your technique?

And to reply further, it's generally the technique described by the folks at Apogee. Here: https://apogeerockets.com/education/downloads/Newsletter136.pdf; and here: . The video is part 1. Watch all 4 and it's pretty close to what I've been doing.

 

[neil_w]

And to reply further, it's generally the technique described by the folks at Apogee. Here: https://apogeerockets.com/education/downloads/Newsletter136.pdf; and here: . The video is part 1. Watch all 4 and it's pretty close to what I've been doing.

I'm familiar with the general technique, and have made many, many of them. However, I don't think I've ever been able to get the seams that perfect, either at the large or small end of the transition. Would love to know your filling and sanding regiment to achieve those results.

 

[Duncan.Byers]

I'm familiar with the general technique, and have made many, many of them. However, I don't think I've ever been able to get the seams that perfect, either at the large or small end of the transition. Would love to know your filling and sanding regiment to achieve those results.

Happy to. I'll see if I have photos. But in general it's fairly straightforward. Once the transition is in place, it's glued with gap-filling CA at both the top and the bottom. Sanding using a block that I made by gluing two pieces of basswood about 2" x 4" together, and taping sandpaper onto it of desired grit. After the CA and sanding using 120grit, really really liberal coat of primer. Sanding with 220grit. Primer again, repeat sanding. Last coat of primer to hit any remaining holes/etc., sand with 220 then 600 grit. First coat of gloss white. Sanding with 600 then another coat. Sand with 600 last time and final coat. When sanding, I used the block to sand vertically over the bottom transition and around the transition keeping it as flat on the slope of the transition as possible. The top transition was sanded without a block using basically the space between the thumb and forefinger to conform the sandpaper to the bend at the meeting of the transition and tube.

That's about it. Next one I'll take photos of each step. This is the primer I used:

 

[Duncan.Byers]

Happy to. I'll see if I have photos. But in general it's fairly straightforward. Once the transition is in place, it's glued with gap-filling CA at both the top and the bottom. Sanding using a block that I made by gluing two pieces of basswood about 2" x 4" together, and taping sandpaper onto it of desired grit. After the CA and sanding using 120grit, really really liberal coat of primer. Sanding with 220grit. Primer again, repeat sanding. Last coat of primer to hit any remaining holes/etc., sand with 220 then 600 grit. First coat of gloss white. Sanding with 600 then another coat. Sand with 600 last time and final coat. When sanding, I used the block to sand vertically over the bottom transition and around the transition keeping it as flat on the slope of the transition as possible. The top transition was sanded without a block using basically the space between the thumb and forefinger to conform the sandpaper to the bend at the meeting of the transition and tube.

That's about it. Next one I'll take photos of each step. This is the primer I used:
View attachment 527331

Oh - and I also sand by wrapping sandpaper around the body and rotate the body within the sandpaper. I do this for all sanding from rough to finish.

 

[GlenP]

Oh - and I also sand by wrapping sandpaper around the body and rotate the body within the sandpaper. I do this for all sanding from rough to finish.

You maybe could print the transition template and glue stick it to the back of your sandpaper sheet as a cutting guide and form the sandpaper sheet into a transition sanding wrap, similar to how you sand a body tube. You could oversize it a little.

 

[Duncan.Byers]

You maybe could print the transition template and glue stick it to the back of your sandpaper sheet as a cutting guide and form the sandpaper sheet into a transition sanding wrap, similar to how you sand a body tube. You could oversize it a little.

I basically the same thing but without cutting it. Just wrap the sandpaper as a cone.

 

[Duncan.Byers]

Fins on and masked for painting.

 

[Duncan.Byers]

Still have final sanding and clear coat left but it's not terrible. Still trying to figure out the best way to keep the edges sharp on the paint. And ordered the decals from Stickershock23 so should be done done later this week I would think.

 

[Duncan.Byers]

So I finally got the thing off the ground. Sort of. First launch a month and a half ago it took a nosedive into the ground. Not a massive amount of damage. I head scratched about it until I realized that I had skipped over the velocity off the rail and it was WAY too low. Not enough umph. So I repaired and set out for a decent launch on an Aerotech f-67 I believe it was. More than enough umph off the rod and projected altitude of something like 1000ft. This is what it looked like prior to launch:



aaaaaaand after it did the same damned thing off the rail only a LOT faster lawn darting this time:




So either I did something way wrong in the sim or - as I suspect - I had a structural failure that caused it to cock over just enough to start the death spiral. This time I'm going to scratch trying to get perfect scaling (which requires modifying tube diameters) and go with sport scaling and leave the tube sizes alone. Back to the drawing board.

That's why it's called "launching" and not "recovering" right?

 

[jmasterj]

Bummer, that was a beautiful rocket!

 

[tsmith1315]

I hate to see the rocket damaged like that, but your attitude is great!

Did you get a favorable CP/CG with the design?

 

[Duncan.Byers]

I hate to see the rocket damaged like that, but your attitude is great!

Did you get a favorable CP/CG with the design?

No point in getting upset right? Just an opportunity to do a better job and fix the things I didn't get right the first time around.

And yes, the sim had the CP about a third up from the bottom and the CG about two thirds. I did fudge a little with the weight distribution but not enough to explain this I don't think. As I said I think I had a structural failure but I'm going to pay closer attention to the actual component weights this time just in case that was the problem and/or contributed to it.

I also didn't video it because I don't like having a phone in front of my face when launching but from now on I think I'm going to use a tripod so that future hiccups can be identified. At least that sounds good in my head as I write this.

 

[lakeroadster]

Oh man... aarrgghh! Beautiful rocket, what a bummer.

My mind sim thinks the flight issue are those fins on the nose. Sometimes folks will make them so they are allowed to pivot /swing during launch.

 

[Duncan.Byers]

Oh man... aarrgghh! Beautiful rocket, what a bummer.

My mind sim thinks the flight issue are those fins on the nose. Sometimes folks will make them so they are allowed to pivot /swing during launch.

They were immovable. I never even considered making them swivel.

That being said, you're not the first person to suggest that.

 

[lakeroadster]

They were immovable. I never even considered making them swivel.

That being said, you're not the first person to suggest that.

But.. I'm not sure. I write that because I started a build thread for the scratch design rocket shown below, folks stated early on when I was 1st building it that it likely wouldn't be stable, but it was. Sometimes the Gods of Stability are fickle.