You can get down in the weeds and start arguing about boundary layers,
shock effects, etc. but for the purpose of analysis by rocket software, yes
the brackets are part of the fins for aerodynamic purposes. And the sheet
part is what’s going to flutter first.
Yours looks good to go, but channeling one of Charles Pooley’s favorite
ideas for tank construction, I wonder if you could weld two hexagonal
sheets of metal together along all their edges and then inflate it a little
bit hydraulically, same as how a pita is inflated by steam. Then saw it in
a half and you have a stiffer fin than the equivalent thickness in flat
sheet, and a vaguely aerodynamic shape.
On Thursday, October 15, 2020, Robert Watzlavick <rocket@xxxxxxxxxxxxxx>
wrote:
When modeling fins in software such as RasAero or OpenRocket, what's the
best way to handle the fin bracket? Does it contribute as much
aerodynamically as the fin does? For example, I have fin brackets that are
the same length as the fins but are 1 inch tall. The fins themselves have
a 5 inch span with 1 inch gripped by the brackets. It seems from a flutter
standpoint that the span is only the 4 inches that are protruding from the
bracket but from an aero standpoint, the fin span is 5 inches. Is this
correct? Or is there some diminished effectiveness of the fin since part
of it is gripped by a much wider bracket? The fins are 0.090 thick and the
bracket width where it grips the fin is about 0.35 inches. Body OD is 6
inches.
I'm about to trim the fins down to make them smaller but I don't want to
cut off too much. Here is a "before" picture with larger fins and longer
brackets:
http://www.watzlavick.com/robert/rocket/rocket1/photos/dsc_8310m.jpg
-Bob
