Need Input on my 3" Min Diameter Project

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Oct 22, 2018
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Hey everyone,
I'm working on a 3" min diameter rocket, and overall I'm feeling pretty good about the design, but I have a few questions. A screenshot of the rocket is below, and I'll attach the OpenRocket file as well.


1. A friend suggested that I move the fins a bit forward to maybe 1" or 2" forward of the end of the body tube (they are currently 0.5" forward from the end of the body tube). The idea is that this will provide the airflow over the fins time to re-attach before the flow reaches the end of the body tube. Any thoughts on this? It hurts my stability, but I have some margin to play with. Does anyone know if this provides significant benefits for flights in the Mach 1 to Mach 2.5 range?

2. I currently have 3/16 fiberglass fins modeled. I'm debating whether or not to add a few layers of tip-to-tip carbon fiber for reinforcement, and also debating going down to thinner fins with tip-to-tip. This will be my first-ever attempt at doing any composite work. I'm confident I can mount 3/16" fins straight and they'll *probably* survive a Mach 2.6 flight without carbon fiber reinforcement. Adding tip-to-tip will obviously make them stiffer and more likely to survive, but since I've never done tip-to-tip, I'm concerned that imperfections in the layup that I'll do by hand will actually result in a worse outcome than no tip-to-tip at all. For example, if the layup is a little thicker or located a little bit more forward or aft on one set of fins than the others, I suspect this could create a worse condition than if I didn't apply any carbon at all. I'd really appreciate your thoughts on this.




Crazy Jim's Gone Banana's
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Jan 18, 2009
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Savannah Ga
My 3in min. has carbon plate ]Dragonplate] 3/16th fins just glued on with Hysol epoxy. Flown on full M's no issue with fins staying put.M-2.8
If I do it again I will go down to 1/8 fins [carbon plate] 3/16 was overkill in carbon.

If you do T-T [which I never do] go down to 3/32 or 1/8th the overlay will add thickness and drag.
Just put a killer bevel and make sure fins are absolutely straight!
I usually put fins 1in from rear.
I use 4 smaller fins rather than 3 for more stability.