# Rocsim Question

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#### cdma77

##### Well-Known Member
I am new to Rocsim and it is asking for the slope angle for the fin. Could somebody please explain how to get this ? I can calculate the slope with a simple formula, however this can't be what the program is asking for. I am doing this as a scratch build, so I don't have the number in my hands. Are they asking for the delta between the angle and 90 degs ?

Thanks,

Jeff

#### Elapid

##### Well-Known Member
i think if you have a point in the middle of the root edge of the fin and connect it to a dot in the center of the tip edge, that will give you the sweep angle relative to the body tube...

#### cdma77

##### Well-Known Member
Originally posted by Elapid
i think if you have a point in the middle of the root edge of the fin and connect it to a dot in the center of the tip edge, that will give you the sweep angle relative to the body tube...

Wouldn't that be 90 degs ?

#### Stymye

##### Well-Known Member
Jeff, the sweep angle is simply the angle of the "leading" edge of the fin in relation to the body tube. zero would be square to the body tube , a negative value would be forward swept.

Elapid, what you describe sounds like the mid- chord. tho I'm not positive

#### Elapid

##### Well-Known Member
of sweep angle would give you the entire FIN sweep, which may or may not be the same as the leading edge angle.

take a theoretical fin with a jagged leading edge... which angle do you choose? How about a cloverleaf shape?
heart shape?

#### Stymye

##### Well-Known Member
I know what your saying but it doesn't seem to work that way in rocksim.

I grabbed a tube and went to the fin designer screen (simple or eliptical fin)

I see that when I change the tip cord or the root cord the sweep angle number(and the leading edge angle) never changes...nomatter what shape I make the fin
the leading edge remains the same unless I change the sweep angle
If a line runs from the center of the tip cord to the center of the root cord to determine the sweep angle. this can't be true.

what am I missing?

#### Elapid

##### Well-Known Member
looks like rocksim really means leading edge sweep angle rather than fin sweep angle/