Arcturas 1

[Pem Tech]

What do you do with a pile of leftover/unloved parts, 3" and 4" mailing tubes, a sudden surplus of BT5, BT20 and BT55 tubes as well as a hand full of Honest John nose cones?

Of course, you throw them together to create a cool as beans spaceship!
With a couple of wraps of tape a 29mm MMT will fit nicely inside a BT55, and the overall weight should be low enough to allow flights on 24mm E's and F's. JUst wonder if the BT55 will hold up to a full bore 29mm F40.


OK, here is the Parts Pile, before the idea had fully developed.

 

[Pem Tech]

The original idea was to build a double tube-fin but RockSIm was giving some pretty sorry numbers...

A couple of centering rings took care of the first ring....
As for the second, I cut the larger (4") tube in fourths and mounted the pieces on some scrap ply that just happen to be lying around.
TA DA!
Instant solar panel fins!

(sorry about the inserted images, for some reason I can't attach them from work)
(Work? Did I say work? I'm not at work! And you can't prove otherwise)

 

[Pem Tech]

Now to attach the Solar Panels

 

[Pem Tech]

The completed propulsion unit....

 

[Pem Tech]

Here is a quartering shot with the BT55 dry fitted into the 3" tube.
You may notice that those BT5's and BT20's mentioned ealier have been attached.

 

[Pem Tech]

And finally her maiden flight..



Not really, but it looks good..

 

[TeenRocketNerd]

do I smell a new kit release?

In any event, a very neat rocket; thanks for sharing Layne!

 

[Stormbringer]

awwwwwsome

let us know how it flies.

 

[sandman]

Very very nice!

I would either lose or move back the ring of BT-5's at the front, they may be problematic. I can see the shock cord tangling on them or them being damaged very easily.

But I could be wrong...it's happened before.

 

[Pem Tech]

Originally posted by TeenRocketNerd
do I smell a new kit release?

Hmmmm..
Actually this was one of those "Stay up all night till I get the idea worked out" build, for myself. No kit was planned, but if any interest is expressed I may consider it.

In any event, a very neat rocket; thanks for sharing Layne! [/B]

You are quite welcome...
It is great to be able to show your work to people who appreciate the hobby. Heck, all the people at work run when I try to show them pics of my builds.

 

[Pem Tech]

Originally posted by Stormbringer
awwwwwsome

let us know how it flies.

Fly?!
These things are supposed to fly??

 

[Pem Tech]

Originally posted by sandman
Very very nice!

I would either lose or move back the ring of BT-5's at the front, they may be problematic. I can see the shock cord tangling on them or them being damaged very easily.

But I could be wrong...it's happened before.

You know..
That wasn't even remotely considered when building this thing.
However, I don't believe it will be a problem, since the recovery system deploys from Center of Gravity and the entire rocket remains intact. But I am a bit concerned about how the BT55 will take the stresses of recovery. Maybe a KEVLAR thread anchored past the mid-point?

 

[BobCox]

I'd be more concerned about the BT-5's acting as tube fins. The ones near the nose will detract from the stability margin. Adding another section of tubing right below the nose cone would move the CG forward and improve the stability.


BTW, I love the curving solar panels and the angled propulsion section.

 

[Pem Tech]

Originally posted by BobCox
I'd be more concerned about the BT-5's acting as tube fins. The ones near the nose will detract from the stability margin. Adding another section of tubing right below the nose cone would move the CG forward and improve the stability.

RockSim gives it a clean bill of health, even with the BT5's and 20's. But the plan is the cap all of them to create mock storage pods along the airframe. Think that would help?

BTW, I love the curving solar panels and the angled propulsion section. [/B]

Thank you....

 

[BobCox]

Originally posted by Pem Tech
RockSim gives it a clean bill of health, even with the BT5's and 20's. But the plan is the cap all of them to create mock storage pods along the airframe. Think that would help?

Yes. If the air can flow through the tubes, they will act like fins.

If you post your RockSim file, I can modify it to show the effect of the tube fins. I use a method similar to Bruce Levison's, which appears to be much more accurate than the tube-fin model built into RockSim 8.

 

[Pem Tech]

Originally posted by BobCox
Yes. If the air can flow through the tubes, they will act like fins.

If you post your RockSim file, I can modify it to show the effect of the tube fins. I use a method similar to Bruce Levison's, which appears to be much more accurate than the tube-fin model built into RockSim 8.

Cool, I'm very interested in hearing about your computational method.
PM me....

The Rocksim will be posted when I get home, in a couple days.

Any ideas on the Estes strength BT holding up to 29mm reloads?

 

[Stormbringer]

My ripper rocket has flown on a G77 a couple of times and the MMT looks fine. But it has CR's about every 6 inches for 18 ins. Its a tube from apogee.

 

[BobCox]

Originally posted by Pem Tech
Cool, I'm very interested in hearing about your computational method.

Here is a link to Bruce Levison's article about simulating tube fins. Despite the banner across that top that says it is not necessary in RockSim 8, I still think that it gives better results than the version built into RockSim 8.

My method is similar to Bruce's method #5. Each tube fin is modeled as three flat fins with span the same as the tube diameter, chord that matches the length of the tube fin, and thickness that matches the tube wall thickness. For a model with 6 tube fins, I model them as three sets of 6 flat fins, each spaced about 10 degrees apart. Material is unimportant, since I do a mass override to set the weight to 0.0001 oz. I account for the mass separately. I also set the opacity of the fins to 0.01 so that they are nearly invisible on the 3D model view. These flat fins should have restoring force and drag similar to the real tube fins.

To account for the mass and the appearance, I do a few tricks. First I temporarily increase the airframe diameter so that it surrounds the tube fins. I then use the cluster wizard to install internal tubes that are identical to the real tubes. I then shrink the airframe back to its original diameter. This leaves the tube fins exposed. These tubes will have the same mass distribution and appearance as the real ones, but because RockSim thinks they are internal, they have no effect on the airflow.

For beveled tube fins, I make a small tweak to the shape of the flat fins. Yours has square tube fins, so I won't go into that here.

Your propulsion section is beveled but has no airflow through it so it does not qualify as a tube fin.

 

[SwingWing]

I'm a little concerned about the grain direction on those fins/solarpanel mounts. It looks like a real weak point to me....

 

[TeenRocketNerd]

Originally posted by SwingWing
I'm a little concerned about the grain direction on those fins/solarpanel mounts. It looks like a real weak point to me....

Posted by Pem Tech

As for the second, I cut the larger (4") tube in fourths and mounted the pieces on some scrap ply that just happen to be lying around.

He used ply, so he's safe.

 

[Pem Tech]

Originally posted by Stormbringer
My ripper rocket has flown on a G77 a couple of times and the MMT looks fine. But it has CR's about every 6 inches for 18 ins. Its a tube from apogee.

Cool!
Thanks for the info.....
May have to try a full length liner.

 

[Pem Tech]

Originally posted by TeenRocketNerd
Posted by Pem Tech

He used ply, so he's safe.

Yeah, Drake broke me of the Basswood habit and turned me on to the wonders of Ply. And I be soooooooooooo happy about it.

Actually started experimenting with Craft Ply instead of Aircraft Ply on my scratch builds after reading the thread concerning said material.

 

[Pem Tech]

Originally posted by BobCox
Yes. If the air can flow through the tubes, they will act like fins.

If you post your RockSim file, I can modify it to show the effect of the tube fins. I use a method similar to Bruce Levison's, which appears to be much more accurate than the tube-fin model built into RockSim 8.

Better late than never...
Here is the RockSim file.

Let us know what effect the Levison Model has on the simulation.

 

[BobCox]

Layne,
I replaced the RockSim8 tube fins with tube fins simulated using the modified Levison method. (I used RockSim8 for both, but manually entered the fins for the Levison method rather than using the built-in tube fin calculations.)

Method        RockSim8 Tube Fins   Modified Levison    
------       -------------------   -----------------           
Mass               14.834  oz         14.836  oz 
CP                 33.058  in         32.640  in
CG (empty)         25.6355 in         25.6351 in
Stability Margin  (F52 loaded) 
                    1.18   cal         1.05   cal
Drag Coeff          1.65               0.576
Altitude (F25-5)     606   ft          1212   ft

Changing from the default RockSim8 tube fin calculation method to the modified Levison method resulted in a small change in CP (~.4 inches) resulting in 0.13 calibers less stability margin. These differences are pretty minor.

However, the differences in drag coefficient are HUGE. The RockSim8 version has 4x as much fin drag, resulting in 3x as much overall drag. This cuts the simulated altitude in half!

Based on actual flight performance with the Quest Totally Tubular and other tube-fin rockets I have built, I am convinced that the Levison method is a closer match to reality than the native RockSim8 tube fin calculator.

The modified file is attached.

 

[Pem Tech]

Bob,
Thanks for the rework, I agree with you on the RockSim tube and ring fin miscalculations. From experience I have found them to be a bit off.
Next step is to rip off the fins increase the fin area. Tried to do the "Twirl it around on a string" thingy this weekend and she failed.
The interesting bit is that it flew sideways, not backwards.

On well...
Just means more time at the work bench.
OH THE AGONY!

Originally posted by BobCox
Layne,

Changing from the default RockSim8 tube fin calculation method to the modified Levison method resulted in a small change in CP (~.4 inches) resulting in 0.13 calibers less stability margin. These differences are pretty minor.

However, the differences in drag coefficient are HUGE. The RockSim8 version has 4x as much fin drag, resulting in 3x as much overall drag. This cuts the simulated altitude in half!

Based on actual flight performance with the Quest Totally Tubular and other tube-fin rockets I have built, I am convinced that the Levison method is a closer match to reality than the native RockSim8 tube fin calculator.

*snip*

 

[BobCox]

Originally posted by Pem Tech
Next step is to rip off the fins increase the fin area. Tried to do the "Twirl it around on a string" thingy this weekend and she failed.

The interesting bit is that it flew sideways, not backwards.

Read this paper by Pete and Bob Alway. It explains how the CP moves when the angle of attack get far away from zero. This effect can be harnessed to make a rocket that is stable in forward flight but can also become a glider without changing geometry or moving mass at ejection. It also can explain why your rocket flies sideways in a swing test.

 

[roadkill]

Hey Layne,

Take a peek here:

https://www.drsuesrocketworks.com/Solaris.html

...its all your fault...

 

[Stormbringer]

hey, the solaris is neat looking. do you have a build thread (hint, hint)?

 

[roadkill]

Originally posted by Stormbringer
hey, the solaris is neat looking. do you have a build thread (hint, hint)?

Sorry,

Between finishing four upscale Vipers, balancing my Crayon X3 for
AMW I-315 Skiddy, new XB project and tinkering with Solaris
(read = whimsically changing the plans a million or so times thru the build until it looked and balanced right) I kinda sorta forgot to take pix....

Got something new and different coming up soon thou...

 

[Pem Tech]

Originally posted by roadkill
Hey Layne,

Take a peek here:

https://www.drsuesrocketworks.com/Solaris.html

...its all your fault...

Sorry for the delay...
I'm out of town attending training courses.

SWEET!
That rocket radiates much coolness....
Glad I could inspire you to create such a beauty.
What are the stats? If it flies on G's you had to save weight in some way.
Details!
We demand Details!