graylensman
Well-Known Member
- Joined
- Feb 24, 2009
- Messages
- 949
- Reaction score
- 1
If the fins are forward of the BT end by x, do you calculate that aft area as a "zero change" conical transition?
Yes, it is a very useful tool and is fine for the 'average' rocket.Originally posted by powderburner
But the Barrowman approach only gives an estimate, and I doubt it was ever intended to address every peculiar design that we could think up.
thats right ,a big difference.. a fin that has a blunt leading and trailing edge will create base drag behind the fin.. much like a straight body tube will...well over 200% increase over a fin with a rounded leading edge tapering to a knife edge.I have also always wondered at the way fin effectiveness is analyzed. Barrowman gives absolutely no credit for fins with a good airfoil section, and treats all fins as though they are flat plates with sharp edges. Theoretically, well-airfoiled fins would be *much* more effective than flat plates.
If you are strictly following the Barrowman equations the answer is no; the body tube (and for that matter any part of it) is not taken into account by this method. Barrowman used a few simplifications to make a tenable thesis out of his project. One of the main assumptions is that the pressure along the body tube remains more or less constant at small angles of attack; so the body tubes contribution to the CP can be left out of the static stability estimation.Originally posted by graylensman
If the fins are forward of the BT end by x, do you calculate that aft area as a "zero change" conical transition?