Internal tube fins?

[Rocketbuilder]

I was trying to think of interesting and unique elements to incorporate into a rocket design, and I was wondering if it would be possible to construct a rocket with internal tube fins. I was thinking that the exterior opening could be either in a transition, or you could just have the tube fins be at an angle.

Would this work?

 

[Scotty Dog]

Ya never really know the final answer till you light the candle...:y:
What size tubes?

 

[Rocketbuilder]

What size tubes?

Well, If I did design a model with internal tube fins, if that's even possible, than it would probably be a cardstock model... so anything that a C6-5 can get off the ground.

 

[stealth6]

I'm not sure exactly what you mean by "internal tube fins", but perhaps you're thinking something like this?

First off, please excuse the build/finish quality on this - this is just a prototype. I did not put a lot of time/energy into quality on this, it was just to test out how this might work. I plan to build a nicer version of this at some point.

Basically, the tube fins pierce the airframe. There are no centering rings, as the internal portions of the tube fins anchor the motor tube. As well the airframe itself tapers down (sort of a boat-tail) along the length of the fins. And finally, I heavily tapered the leading/trailing edges of the tubes.

btw - the prototype worked; I test fired this just a short time ago and it flew great.

 

[Rocketbuilder]

I'm not sure exactly what you mean by "internal tube fins", but perhaps you're thinking something like this?

Sort of. I was thinking of tube fins that are entirely within the body tube. Sort of like this, if you can make any sense out of it:

 

[[POW]Eagle159]

Sort of. I was thinking of tube fins that are entirely within the body tube. Sort of like this, if you can make any sense out of it:

Yeah, it looks like it could work, just make sure the tube fins are a large enough diameter... pretty neat idea!

 

[Larry Curcio]

Sort of. I was thinking of tube fins that are entirely within the body tube. Sort of like this, if you can make any sense out of it:

Anything that's wider toward the aft end will have a modicum of stability. Question is whether the thing will tend to cone, as it would with a simple transition.

 

[dixontj93060]

This can certainly be done--maybe something like this... Here is a ducted cone rocket where the openings at the aft end drive the stability.

 

[powderburner]

This is purely qualitative, not one bit quantitative

I would expect some small 'stabilizing' contribution but not nearly as much as the aerodynamic stabilizing effect of a more normal ('external') tube fin.

Reason: Tube fins generate stability the same way conventional fins do: they use the airflow moving over the surface to generate a force (roughly) perpendicular to the airflow when the fin is placed at a small angle of attack (that is, when the rocket's axis is tilted a few degrees). This works with conventional fins because they see the 'full' airflow velocity (ignoring boundary layer effects, forebody effects, etceteras for sake of simplifying this example).

When you bury tubes inside the contour as you have shown I expect you will get reduced airflow through those tubes. Most of the airflow will likely flow around the exterior of the transition and aft BT. I do not think your internal tube fins will be as aerodynamically effective as normal external tube fins.

My two cents.

 

[powderburner]

Here is a ducted cone rocket where the openings at the aft end drive the stability.

I am no expert on BenJarvis' rocket design, but those aft ports (scoops? vents?) appear to me to be mostly to vent the aft fuselage to 'kill' the Krushnic effect. They might add a little stability effect.

We need Ben back here, to explain his design.....

 

[luke strawwalker]

Sort of. I was thinking of tube fins that are entirely within the body tube. Sort of like this, if you can make any sense out of it:

Transitions arranged like this also move the CP aft, much like rockets that use cones or funnels in place of fins... of which there have been a few built and flown... much like a saucer.

Later! OL JR

 

[jdbectec]

Here's a link to an old issue of Model Rocketry Magazine that contains a plan for a ducted rocket by Grant Boyd. I believe he did some R&D work for Centuri.

It will take a while to load:

https://www.ninfinger.org/rockets/ModelRocketry/Model_Rocketry_v02n03_12-69.pdf

 

[chrisudy]

That's kind of like the Augie II just without fins...

 

[paul.nortness]

That's kind of like the Augie II just without fins...

COOL! I was just looking at that today thinking it would be a cool project to add to the list...now I know for sure!