OR Trapezoidal fin set can not be attached to Transition, ignoring component.

mpitfield · Jul 3, 2015

I am trying to use OR for a rocket I designed in RS that has a boattail, which is where the fins attach. However OR does not like this configuration and throws the following error on import, which effectively produces a fin-less rocket. "Trapezoidal fin set can not be attached to Transition, ignoring component."

Any ideas on how to get around this?

Thanks

UhClem · Jul 4, 2015

Try attaching the fin to the body tube and use the offset to move the attachment point to the transition.

A more interesting question is about the aerodynamics: how well does Openrocket calculate the forces on fins attached to a transition? I suspect that the answer is not particularly well.

mpitfield · Jul 4, 2015

UhClem said:
Try attaching the fin to the body tube and use the offset to move the attachment point to the transition.

A more interesting question is about the aerodynamics: how well does Openrocket calculate the forces on fins attached to a transition? I suspect that the answer is not particularly well.

I Dave,

Thanks a bunch. The rocket design is not unique, it is essentially a 2X upscale of a 3" PML Bull Puppy with some modifications, but the aft fincan is the same. I will give your recommendation a shot and see what the result is.

markkoelsch · Jul 4, 2015

The issue traces back to Barrowman equations. Barrowman does not allow for fins on transitions. Rocksim gets around this by in essence creating an approximation that fits within Barrowman by defining the width of the fin at the midpoint of the transition as memory serves.

OR Trapezoidal fin set can not be attached to Transition, ignoring component.

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OR Trapezoidal fin set can not be attached to Transition, ignoring component.

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