Fins on a tailcone in Open Rocket?

[DGBrown]

I recently picked up a 4" Loc R2/Canadian arrow kit. The fins on this kit are on the tailcone, basically being a stretched V2. Is there a good way to model this in OR?

 

[neil_w]

A standard approach would be to create a "phantom body tube" at the end of the rocket. Make it length 0 and the same diameter as the end of the tail cone. Put fins on that tube and you're good to go. You can either try to actually shape the root edge to track the curve (if it's curved) of the tail cone, or just let the root sit flat and just make the exposed part match the actual fin shape.

For an example look at the Black Brant II file over here: https://www.rocketryforum.com/showthread.php?123564-K-Tesh-s-Open-Rocket-files&p=1575364#post1575364.

 

[Kruegon]

The ability to add fins to a tailcone is the single biggest feature I'd like to see added to OR. Been hoping for it for the past two builds.

 

[rocketguy101]

^^^^ +1

 

[DGBrown]

Thanks for the tip, I'll see what I can come up with.

 

[UhClem]

I haven't tried this in Openrocket but it imports Rocksim files just fine...

I attach the fins to the body tube in front of the tail cone then adjust their position appropriately.

The downside is that the program likely uses a value for the fin area that is too small. The result being an overly conservative CP location. If you attach the fins to a zero length piece the size of the back of the tail cone it is likely that too large of a fin area will get used. Leading to an optimistic CP location.

The portion of the fin inside the main body tube diameter likely has reduced effectiveness as well. Depending on the tail cone angle and airflow details.

 

[K'Tesh]

I haven't tried this in Openrocket but it imports Rocksim files just fine...

I attach the fins to the body tube in front of the tail cone then adjust their position appropriately.

The downside is that the program likely uses a value for the fin area that is too small. The result being an overly conservative CP location. If you attach the fins to a zero length piece the size of the back of the tail cone it is likely that too large of a fin area will get used. Leading to an optimistic CP location.

The portion of the fin inside the main body tube diameter likely has reduced effectiveness as well. Depending on the tail cone angle and airflow details.

However, unless you have a fin tab, your fin will be floating in air where the transition is on the -Y plane.

I created a quick tutorial on this topic... You can find it here: https://www.rocketryforum.com/showt...-s-OpenRocket-Tutorials&p=1595653#post1595653