Clone build: Centuri SR-71 Blackbird #5349

[GlenP]

That will look great. Thanks for sharing.

did you mean to put that one extra line in there?

 

[kuririn]

Got some CWF on all the exposed balsa.
It's 3:30 AM, calling it a night.
Next, sand, sand, sand.

 

[Saluki]

That will look great. Thanks for sharing.

did you mean to put that one extra line in there?

View attachment 435466

No. I'll go in and fix it and repost it. It's fixed.

 

[mbeels]

Next, sand, sand, sand.

That looks like it will be a lot of sanding. But really cool rocket, it'll be worth it.

 

[kuririn]

Sanded the ramjet inlet and tail nozzles.
Wanted to see how the "enhanced" ribs look so I started to glue them on.



I like it.

 

[kuririn]

The inner wings were tack glued to the airframe.


When dry they were then filleted and left to dry horizontally.


Meanwhile the upper and lower rudders were attached to the ramjet tubes.


TBC.

 

[kuririn]

Glued the outer wings on the jet tubes


And filleted the joints


TBC.

 

[kuririn]

The motor mount was glued into the airframe.
Next is the cardstock fairings.
This is the fun part.
It would be easier to glue these on now instead of after the jet pods and outer wings are attached.
At first I was going to diverge from the instructions and use Elmer's spray adhesive.
I swear I had a left over can somewhere but I couldn't find it.
Next I was going to paint it with watered down white glue.
Couldn't find that either.
They say the first thing to go is the memory.
I heard that once but don't remember where from.
So I used yellow glue thinned to a brushable consistency with water.
Use only enough water to get it brushable, not too thin.
I pre formed the fairing by conforming it to the tube and inner wings with both hands.
Sorry, no pics since I had to use both hands.
The instructions have you glue the center section first and the edges a few minutes later.
I did mine all in one step.
Brushed on the glue, burnished to the center line, and pulled in the edges and burnished.
More brushed on glue for the tips and done.




I'm considering painting the upper and lower fairings with thin CA.
Any opinions?
TBC.

 

[Cape Byron]

They say the first thing to go is the memory.

I thought the first thing to go was the spray adhesive?

 

[mbeels]

They say the first thing to go is the memory.
I heard that once but don't remember where from.

!!!!!

Ooh, this build is getting to the point where the major parts come together. Looking great, what a cool rocket!

 

[GlenP]

...I'm considering painting the upper and lower fairings with thin CA. Any opinions?

You might find the yellow glue dries pretty solid and you don't really need to coat the shroud with CA.

 

[NJRick]

looks awesome so far!

 

[hermanjc]

Since you aren't bringing the cardstock right to the front you probably won't need CA. I second what @GlenP said.

Looking really good!

 

[kuririn]

The jet pod and outer wing assemblies were glued to the inner wings using the cardstock alignment guides included with the fairing sheets. First tack glued, then when that was dry fillets were run.



Calling it a night.
TBC.

 

[kuririn]

Musings:


Nah!

Here's a full shot:


Recovery will be by dual 20" chutes and a horizontal recovery harness, keeping it true to the instructions.
Instructions say to use shroud line (!!!!!!) and elastic for the harness.
I will be changing that, more later.
TBC.

 

[neil_w]

Looks fantastic.

 

[hermanjc]

Recovery will be by dual 20" chutes and a horizontal recovery harness, keeping it true to the instructions.
Instructions say to use shroud line (!!!!!!) and elastic for the harness.
I will be changing that, more later.
TBC.

Dual 20" chutes? How big is this model? My estes upscale has a single 20" chute without horizontal recovery and the body of the SR71 provides significant drag, she comes down nice and slow (takeoff weight is ~270g with a D motor). I'd expect dual chutes coupled with horizontal recovery will lead to a lot of drift. I'll be interested your results

 

[kuririn]

No worries, my friends' initials are JLCR.
I set my releases at 200'.
Nice and slow on a grassy field on a calm day is what I'm shooting for.
With my luck the wings are still going to get damaged somehow.

 

[kuririn]

The Dynastar Firefox is heavier and comes down nice and slow on a single 32" chute.
So I may keep it simple and go for that, with the horizontal harness.
We'll see.
Video is here:
https://www.rocketryforum.com/threads/apogee-dynastar-firefox.157421/

 

[NJRick]

Musings:
View attachment 435874

Nah!

Here's a full shot:
View attachment 435875

Recovery will be by dual 20" chutes and a horizontal recovery harness, keeping it true to the instructions.
Instructions say to use shroud line (!!!!!!) and elastic for the harness.
I will be changing that, more later.
TBC.

this looks awesome! beautiful job so far!

 

[GlenP]

I lost mine when the nose cone popped off at ejection. Without that extra weight it just drifted away. Maybe it caught a thermal? But it went over the trees and just kept going. It had made many impressive flights, one of my favorites.

 

[BABAR]

Three point harness? One forward two just inside the pods? Your caudal fins are still at risk, but keeping the bird level adds the bird’s surface area to the descent drag

.

 

[hermanjc]

No worries, my friends' initials are JLCR.
I set my releases at 200'.
Nice and slow on a grassy field on a calm day is what I'm shooting for.
With my luck the wings are still going to get damaged somehow.

The JLCR seems likea rocketeers best friend What's the minimum size body tube you can fit one in?

I bet your build will come out unscathed on landing with the build process you have detailed so far.

Enjoying following this!

 

[kuririn]

Launch lugs were glued on.


Here are the instructions on the recovery rigging:


I decided to substitute kevlar thread for the shroud line in the instructions.
Not for flame resistance, since most of the shroud line would be outside the airframe.
But for tensile strength. Seems more robust than shroud line.


Tied to the engine hook but not yet glued or trimmed.
I was concerned about the thickness of the thread interfering with motor retention, but it looks OK.

The replica nose cone's shoulder was quite loose in the tube.
Turns out that was a good thing because with the kevlar between the shoulder and tube now it is a snug, just right fit.

Three point harness? One forward two just inside the pods? Your caudal fins are still at risk, but keeping the bird level adds the bird’s surface area to the descent drag

Good idea for stability coming down, but wondering if a couple of extra threads near the engine pods might pose a risk to the upper rudders with the chaos of ejection.
Also three threads outside the airframe instead of one might be less esthetically pleasing.

Cut two 20" canopies from my generi-pac hoard and added reinforcements.
They will be on swivels, can always switch to a single large chute if necessary.


Next: assembling the harness and parachutes.
TBC.

 

[kuririn]

What's the minimum size body tube you can fit one in?

BT-60, so this barely qualifies.

 

[kuririn]

Completed the harness and chutes.



Assembly is complete.
Finishing to be done whenevah.
I should finish and close my other nekkid builds first.
Before the end of December. (2021?).

Ciao.

 

[GlenP]

Tied to the engine hook

That one little spot on the body tube where the Kevlar wraps around the corner might be a good place to reinforce with a drop of CA.

 

[kuririn]

That one little spot on the body tube where the Kevlar wraps around the corner might be a good place to reinforce with a drop of CA.

Good observation.
Like they say, great minds think alike.
I cut a small notch there, will put a spot of CA to minimize wear and tear.
Also will swipe the inside lip on the other end of the airframe.
My standard anti-zipper protocol. (Along with no zip strips).

I was also considering alternatives to tying it to the engine hook but went with the instructions.
The acid test will be how it performs in flight.
BTW how did your original fly?
Any weathercocking with the big wings?

 

[BABAR]

Good observation.
Like they say, great minds think alike.
I cut a small notch there, will put a spot of CA to minimize wear and tear.
Also will swipe the inside lip on the other end of the airframe.
My standard anti-zipper protocol. (Along with no zip strips).
View attachment 436017
I was also considering alternatives to tying it to the engine hook but went with the instructions.
The acid test will be how it performs in flight.
BTW how did your original fly?
Any weathercocking with the big wings?

For the tail attachment, a loop around the extruded motor mount segment followed by by a knot on the hook might give you a bit more security and if done right, my prevent damage from yanking on the hook suddenly.
I am a bit concerned you are a setup for a zipper on the forward end as well, although a reinforcement of the outside of the tube has cosmetic consequences, and on the inside will cause nose cone and chute deployment issues. Maybe a shock cord buffer at the anticipated location of shock cord/tube contact, ala this from

@BlaineS

https://www.rocketryforum.com/threads/blaines-kevlar-anti-zipper-using-foam-ear-plug.154996/

 

[kuririn]

Maybe a shock cord buffer at the anticipated location of shock cord/tube contact, ala this from

@BlaineS

These no zip strips are very similar.
Basically foam padding.
They look like oversize eye glass nose pads.
These plus a swipe of thin CA at the tube end should do it.