Tube Fin Profiles And Drag

[Arsenal78]

Does the drag from tube fins change depending on if the tube is not square on the ends? The Pemberton King Kraken has non-straight tube fin ends so would it have the same amount of drag as if it didn’t have cut tubes or would it have the same amount of drag as a wood fin in the same shape? OpenRocket can kind of do tube fins but not custom tube profiles like the Kraken.

 

[fyrwrxz]

I confess I do not understand the aerodynamics of tube fins. Obviously they work, but what changes to the airflow inside the tubes see during boost? Do they just become base drag after a certain speed? Looking for the reply to your question so I can learn something.

 

[DigBaddy]

I was recently reading some threads on the Kraken that mention groups of 3 fins where each of the three fins in the group are 7 degrees apart will simulate the shaped tube fins pretty accurately. Just make the profile of the fins in OR the same as the tube profile. I haven't tried this; but search a bit and you may find this being mentioned....

 

[dhbarr]

One of my favorite topics due to Larry Brand's article series. YES the drag changes fairly intuitively below about M 0.8. If your tubes are very long ( but still angled ) and you're above about M 1.2, they're going to choke up and act a lot more like a wedge.

In the transonic region, however, may the universe have mercy on your sim results.