Quantcast

Clone build: Centuri SR-71 Blackbird #5349

The Rocketry Forum

Help Support The Rocketry Forum:

GlenP

Well-Known Member
Joined
Oct 4, 2014
Messages
2,068
Reaction score
377
That will look great. Thanks for sharing.

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

Screen Shot 2020-10-19 at 9.00.42 PM.png
 

kuririn

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
5,004
Reaction score
2,616
Location
Hawaii
Got some CWF on all the exposed balsa.
It's 3:30 AM, calling it a night.
Next, sand, sand, sand.
1020200332a[1].jpg

1020200332[1].jpg
 

kuririn

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
5,004
Reaction score
2,616
Location
Hawaii
The inner wings were tack glued to the airframe.
1021200154[1].jpg


When dry they were then filleted and left to dry horizontally.
1021200447[1].jpg


Meanwhile the upper and lower rudders were attached to the ramjet tubes.
1021200522[1].jpg


TBC.
 

kuririn

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
5,004
Reaction score
2,616
Location
Hawaii
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. :D
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.

1022200928[1].jpg

1022201000[1].jpg


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

mbeels

Yes balsa
TRF Supporter
Joined
Feb 9, 2019
Messages
2,428
Reaction score
1,219
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

Well-Known Member
Joined
Oct 4, 2014
Messages
2,068
Reaction score
377
...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.
 

hermanjc

Well-Known Member
Joined
Jul 22, 2014
Messages
87
Reaction score
102
Location
Hudson, MA
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

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
5,004
Reaction score
2,616
Location
Hawaii
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.
1022202333[1].jpg

1022202334[1].jpg

1022202340[1].jpg

Calling it a night.
TBC.
 

kuririn

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
5,004
Reaction score
2,616
Location
Hawaii
Musings:
1023200634[1].jpg


Nah!

Here's a full shot:
1023200637[1].jpg


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.
 

hermanjc

Well-Known Member
Joined
Jul 22, 2014
Messages
87
Reaction score
102
Location
Hudson, MA
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

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
5,004
Reaction score
2,616
Location
Hawaii
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.:dontknow:
 

kuririn

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
5,004
Reaction score
2,616
Location
Hawaii
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:
 

GlenP

Well-Known Member
Joined
Oct 4, 2014
Messages
2,068
Reaction score
377
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

Builds Rockets for NASA
TRF Lifetime Supporter
TRF Supporter
Joined
Aug 27, 2011
Messages
6,748
Reaction score
1,895
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

Well-Known Member
Joined
Jul 22, 2014
Messages
87
Reaction score
102
Location
Hudson, MA
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.:dontknow:
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

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
5,004
Reaction score
2,616
Location
Hawaii
Launch lugs were glued on.
1024200712[1].jpg


Here are the instructions on the recovery rigging:
1024200722[1].jpg


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.
1024200715[1].jpg


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.
1024200716[1].jpg


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.
1024200716a[1].jpg


Next: assembling the harness and parachutes.
TBC.
 

kuririn

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
5,004
Reaction score
2,616
Location
Hawaii
Completed the harness and chutes.
1024201758[1].jpg

1024201800[1].jpg


Assembly is complete.
Finishing to be done whenevah.
I should finish and close my other nekkid builds first.
Before the end of December. (2021?).
1024201808[1].jpg

Ciao.
 

GlenP

Well-Known Member
Joined
Oct 4, 2014
Messages
2,068
Reaction score
377
Screen Shot 2020-10-24 at 11.15.45 PM.png

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

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
5,004
Reaction score
2,616
Location
Hawaii
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).
1024202035[1].jpg

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

Builds Rockets for NASA
TRF Lifetime Supporter
TRF Supporter
Joined
Aug 27, 2011
Messages
6,748
Reaction score
1,895
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

 

kuririn

BARGeezer
TRF Supporter
Joined
Oct 3, 2016
Messages
5,004
Reaction score
2,616
Location
Hawaii
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.
1024202332[1].jpg
 
Top