Fin Sets Basics
Supported Fin Sets
Fins serve to stabilize a model rocket while in flight, and to guide the rocket on a safe and an intended trajectory. Most rockets, without the stabilizing forces acting on the fins, would tumble in midair soon after clearing the launch guide. Aside from their aerodynamic factors, fins are often what gives your rocket the character that others remember.
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So what's a trapezoidal fin . . . a quadrilateral having two parallel sides. Yes, but what it means to you is that the fin's root chord (the edge that's against the body tube) is parallel to the tip chord (the edge that is furthest away from the body tube). The leading and trailing edges can be at whatever angle or length you want and it will still be a trapezoid; in OpenRocket a triangle is considered a trapezoid too. OpenRocket allows you to change the leading and trailing edge angles and lengths quickly and easily. And, if you want, with the click of a button you can even convert trapezoidal shapes into freeform form fins for even more design flexibility. One thing to keep in mind is that, if you intend to verify the OpenRocket simulation results using RASAero II, then you can only use a trapezoidal fin set. |
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Limited Support and Unsupported Fin Sets
Ring Tail Fins
Although ring tail fins can easily be visually added to an OpenRocket model using a body tube, there's a catch, the ring tail must start at the exact aft-end of the component it visually surrounds, and the fins must trail to support it; this is because external airframe components in OpenRocket follow a strict linear pattern. You can also easily visually simulate a ring tail virtually at any point up or down the airframe using an inner tube. But, again, there’s a catch, inner tubes are aerodynamically ignored. OpenRocket does not support and simply WILL NOT accurately simulate ring tail fins at this time.
For a more detailed discussion about Ring Tail Fins, go to Advanced Rocket Design
Grid Fins
Fins, generally speaking, are aerodynamic control surfaces. Where grid fins differ from other fins is that they are not essentially just flat surfaces, but more of a frame with a grid inside. Usually made of metal (such as aluminum), not only can grid fins be light, they can be very strong (the very thin, spaced grid surfaces don’t generate much drag). Although OpenRocket doesn’t directly support grid fins as a single component, you can use the pod and fin set components can be used to create them; however, the simulated results with grid fins have not been verified and should not be relied upon without actual flight test verification and Cd adjustments of your own.