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Old 05-23-2019, 11:14 PM
teflonrocketry1's Avatar
teflonrocketry1 teflonrocketry1 is offline
Join Date: Aug 2007
Location: Whitehouse, Ohio
Posts: 264

There is some new data about the aerodynamics of fins below a wider transition section. Check out the article titled "Increasing Rocket Aerodynamic Performance" by Thomas Salverson on page 42 in the May/June 2019 edition of Sport Rocketry. Essentially (on the right side of page 48) the portion of the fin inside the turbulent wake of the airflow behind a reducing transition doesn't do anything for the rockets stability. It is suggested that while a transition section below a wider payload section decreases the aerodynamic drag on a rocket, it induces a wake that interferes with and decreases the effectiveness of the rockets fins, and these fins should extend out beyond the rockets body until they are in the laminar airflow region beyond the diameter of the transition. I am working on a RockSim fix for this effect.

Also mentioned is that rail buttons create an asymmetric wake behind the rocket causing it to fly in an arc. Did you use launch lugs on your design that might have a similar effect? The original 1340/20 used a thin loops of wire for launch lugs visit:
Bruce S. Levison, NAR #69055
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