Clone build: Centuri SR-71 Blackbird #5349

[kuririn]

Rummaging through my boxes of bagged parts last night, I came across these:


Specialty parts:
PNC-165 nose cone from Sirius rocketry Moldin' Oldies. Same nose cone used in the Quasar.
Custom turned balsa ramjet inlets and tail nozzles. By Gordon Agnello (aka sandman at YORF) from RoachWerks.
Other standard off the shelf parts not shown will be from my stash.
Need to scrounge up or order a 12" BT-60 tube.


BTW those of you with a 3D printer, there is a website that has free downloadable .stl files of the nose cone, inlets and tail nozzles:https://www.myminifactory.com/object/3d-print-centuri-sr71-nose-cone-113012
If you download these please consider a donation to the contributor via the "Support Me" button.

As luck would have it, I have some extra conduits from my Agni 1 kit. They were the wrong length and Boyce Aerospace sent replacements. Will use these for the ribs on the tail nozzles.

Oh, and plans are here:

https://www.spacemodeling.org/jimz/centuri/cen5349.pdf

Skin will be non embossed cardstock. Don't have the skill or inclination to even attempt embossing the pattern.
The nose cone and fuselage cross section are not true scale, so calling this sport scale.
TBC.

 

[GlenP]

One of my favorites, cool!

Any ideas for the white decals?

 

[kuririn]

White laser decal paper.
Will edit the scan with a black background.

 

[kuririn]

Here's a rough edit.
May do a little more clean up, may leave as is.
Cloners, this is for you.
Paying it forward.

 

[Ronz Rocketz]

You have a color laser printer?

 

[kuririn]

10-4 good buddy.

 

[Saluki]

Well, it's good to see someone is doing a build thread on this old SR-71 design. I was the one who sent JimZ this rocket to put up on his site. This was a big rocket and at the time it came out in 1981 it was the closest thing we had to an SR-71.

Centuri did a good job of making the ramjet inlets and tail nozzles and then combining them with nose cone from the Super Kit line to come up with the SR-71. I have never seen the ramjet or tail nozzles used in any other kits. This was near the end of the Centuri rocket life. The Centuri SR-71 showed up in the ESTES 1982 catalog for one year. In 1985 ESTES came out with their own SR-71 and that was the end of the Centuri one. This kit wasn't out there very long. If you notice you hardly see one of these kits for sale on eBay or anywhere else. They are rare. I liked the Centuri one because of its size. It's BIG. It's a good flyer on a D engine. I built one back when it came out. I wish I had taken pictures of it, but I didn't.

For those who have a 3D printer the nose cone offered is not quite the same as the one used on the Centuri SR-71. The canopy offered is a square design on it. The original Centuri SR-71 has a pointed canopy. The ramjet and tail nozzles are fine. A paper canopy can be made to work on the 3D printed one. The skin of the Centuri SR-71 could be made using Avery label paper cut into long narrow strips and laid down where the emboss area is. After you paint the skin you get the effect.

I have this rocket on my Winter build list. Glad to see this one come to life. If you search the rocket forums for this certain rocket you will come up with nothing because this kit is like I said, rare.

 

[GlenP]

That is a good idea to laminate the cardstock fairing with label paper instead of emboss it. You could also print up two of them from the scans on regular cardstock paper. Cut the strips from one sheet and glue stick them in place on their outlines on the other sheet. Might be slightly heavier, but not by too much.

Also, the original kit plastic nozzles had some ridges on them, you could add some laminated cardstock strips onto the balsa nozzles as well, maybe.

 

[kuririn]

Thanks guys, will give it a try.
Right now I've got to launch a few.
Laters.

 

[Saluki]

Here's a clean up of the skin patterns and tail nozzles pattern for adding ridges to the tail nozzles.

 

[kuririn]

Here's a clean up of the skin patterns and tail nozzles pattern for adding ridges to the tail nozzles.

Outstanding!
Hey, here's an idea: Fairing printed on cardstock. Strips cut out. then another fairing piece glued behind it. After assembly, paint with thin CA.
Thoughts?

 

[Saluki]

Outstanding!
Hey, here's an idea: Fairing printed on cardstock. Strips cut out. then another fairing piece glued behind it. After assembly, paint with thin CA.
Thoughts?

That sounds like a good idea. Give it a try and let us know how it goes.

 

[kuririn]

Problem: some of the templates, including the fairing do not fit on letter size paper when printing at 100%.
I will have to see if I can find some legal size cardstock at Office Depot tomorrow.
Laters.

 

[kuririn]

In the meantime the motor mounts were assembled.
Forgot to mention that this can fly on both 18 and 24mm motors.
So a permanent 24mm mount is glued into the airframe and an 18mm mount can slide into it.
Of course today we can just use a red Estes plastic adapter.
But I wanted to do it the old fashioned way.
Instructions say the assembly instructions for the 18 mm mount are at the end of the kit instructions, but I couldn't find it. So I winged it.
Recommended motors are C6-3, C5-3S, and D12-5.
Nice of Estes to bring back the C5 motor just in time for this build.
How thoughtful.
Good night.

 

[kuririn]

I remembered that I had a couple of packets of 11 x 14 poster board. It is about the same weight as cardstock, so I trimmed a few pages to 8 1/2 X 14 and printed the templates.
Balsa parts template

The scanned ruler verifies the right sizing.
And the fairing


Left, from JimZ's
Right, from Saluki. Same size, much cleaner
Thanks, buds.

The black strips look like the recessed embossed areas. The more I think about it, the less inclined I am to try simulating that. Overlaying adhesive strips would not give the right texture. And cutting the black strips away would be problematic for me. I don't think I could get clean cuts on the ends. Will mull this over, no final decision yet. But as Babar would say, the enemy of good is better.

I also used thin CA and painted the paper centering rings for the 18mm motor mount. They were delaminating after only a couple of trial fits inside the 24mm mount. Sanded smooth after drying.

Will try to cut and glue some balsa before calling it a night.
TBC

 

[GlenP]

I was mistaken that the stripes were raised, but seems like they are burnished inwards, so my earlier suggestion would raise the strip ridges in the wrong direction. Cutting them out with a sharp blade and a metal ruler might not be too hard.

 

[kuririn]

Proof of concept
(Aka giving it the old college try)
Using the spare fairing printout, I cut out a section of the embossed detail.


A piece of scrap paper that was Sharpied black was glued to the back.



White strips were then cut out of the extracted piece and glued back in.



Then a shot of gloss black paint.


The verdict:
While it does add texture, the paint also highlights imperfections in the process.
Perhaps someone with better skills (and more patience) can do a better job.
This clone's fairing will remain untextured.
Now I gotta check on the balsa.
TBC

 

[Saluki]

Kuririm, Give me a little time I may have what might work. Get it to you sometime tomorrow.

 

[kuririn]

One more try.
This time the black strips are cut out, backing paper is glued and the paint is shot.
Marginally better, but as I thought the end cuts are a little ragged.

 

[markg]

A laser cutter could do this very easily. My local makerspace has one, maybe you can find one near you?

Cheers

 

[mbeels]

One more try.
This time the black strips are cut out, backing paper is glued and the paint is shot.
Marginally better, but as I thought the end cuts are a little ragged.

Oh man, that's really close to looking really cool. It would add a nice bit of texture. Just thinking out loud, what if you cut only the long edges of the slots, pushed one side down slightly, and the other side up slightly (to twist them)? Perhaps that would give some of the surface texture without having to cut out the slot entirely.

 

[GlenP]

That looks really good. I think you are on to something with that method.

You could try to first lightly score a group of the adjacent short slot ends, use your metal ruler as a guide. Then cut them each individually all the way through by hand following the scored lines.

After the ends have been cut, then cut the long sides using the metal ruler as a guide. That might give you crisp slot edges.

 

[kuririn]

I'll let this percolate a while until I hear back from Saluki.
The texture is not important to me, I'm fine with a smooth skin.
In fact in the header pic you cannot even see the embossing.

Meanwhile.....
Traced and cut the parts for the inner wing, outer wing, rudders and ventral fins.
These will be aligned with a straight edge and glued together on wax paper.
Then covered with another sheet of wax paper and weighted down to dry overnight.


Used the Qualmann jig to mark 12 equally spaced tic marks around the ramjet motor tubes,
This will be to align the exhaust nozzle ribs.
The plastic spare conduits I'm using for the ribs are larger than the stock molded in ribs and are rectangular instead of round. Should be a more dramatic look (I hope).



Will be filling in the balsa before gluing on the ribs.
Want to make it easier on myself.

I scavenged another BT-60 tube from another bag of parts for a Super Starship Vega clone.
Cut to 12" and coupled with the shorter tube for the main airframe.
Slowly coming together.
TBC

 

[BABAR]

Outside the box thought for doing the embossing.

Lay down tape strips over the areas where you want the depressions to be.

I know this sounds backwards but stay with me.

Once you have the tape strips in place and burnished down in appropriate position go ahead and spray over that with high fill primer. You’ll want to do a test piece to figure out how many coats to put on.

After you get an adequate thickness of primer over the area go back and carefully remove the tape strips. You now have depressions relative to the High-fill primer.

You could adjust the depth of the depressions simply based on the number of coats of primer you use.

 

[Saluki]

OK, here's what I was thinking. Since you have a laser printer (lucky dog) anyway print out these decals I drew up and place them to represent the vent area. What do you think?

 

[kuririn]

Thanks for all the suggestions.
If I manually cut, laser cut, or overlay tape strips I would still have to do 106 narrow strips,
I'm a detail oriented person, but that takes the fun out of this.
Saluki, I like your suggestion. Will try that.
In the meantime will be rounding the leading and trailing edges of the wings and rudders.
Filler and sanding needs to be done before assembly, too difficult otherwise.
Update and pics later today.
TBC.

 

[hermanjc]

What about just taking a dull tool (i.e. rounded end of a popsicle stick) and running it down each "strip" on a soft backer like a mousepad? I considered this when building my SR-71, but was more anxious about completing the build than ensuring a perfect model appearance.

Love all the SR-71s of different vintages actively in process on TRF right now

 

[Saluki]

kuririn, I drew this up tonight. I think I will use this for my body skin cover when I build my SR-71.

 

[kuririn]

kuririn, I drew this up tonight. I think I will use this for my body skin cover when I build my SR-71.

Nice job! Are you going to clear coat it?

 

[Saluki]

Yes. Will start together up the parts tomorrow.