Tips for modeling a dorsal fin

[Grant Hiller]

Hi folks,

I am looking to model the dorsal fin of the B1900D, and I am wondering if any of you have any tips or suggestions on how to best go about it?

I have tried creating a multi-section wing (see screenshot), but it is quite challenging to get it all to line up and look right.

Then, it becomes an issue of thickness, albeit which can be adjusted via the airfoil i.e. using a NACA 0002 at the root.

Would it be worth rotating the wing about Y to try and line it up with the slope of the top of the fuselage?

Creating another wing altogether just for the dorsal?

Any suggestions are welcome!

Thanks,

Grant.

[Brandon Litherland]

https://upload.wikimedia.org/wikipedia/commons/f/f4/Beechcraft_1900D_Tail.jpg

Always go to the source and take a look at how the feature is implemented on the aircraft.  Three views often lie to you.

The dorsal transition to the vertical tail has a ~sharp edge rather than a smooth, continuous blend to the tail.  Consider the best approach to recreate this shape in VSP.  My recommendation would be to use a Stack with either a triangular or diamond cross-section.  Accomplish this with either a General_Fuse section with T/B/U/L Strength set to 0.01 to avoid collapsed edges or a superellipse with M and N set to 1.0 (better and exactly linear).  If you want to get more advanced, you can use Edit Curve and put control points at X and Y = 0.5 in a diamond shape, set your desired height and width, then put a corner radius at the top so it's not exactly sharp.  This method will be the most reflective of reality, I feel.  Probably looking at a corner radius of only 1/4 inch or less with the sharpness of that edge.

The type acceptance below has better line drawings and dimensions for the D variant.  It also illustrates the intersection of the dorsal fin with the tail.

https://www.aviation.govt.nz/assets/aircraft/type-acceptance-reports/Beech_1900C_and_D.pdf

[Grant Hiller]

Hi Brandon,

Thanks for your reply and suggestions.

I used a Stack with a diamond cross-section as you suggested, and it has worked really well, however, I noticed that there is some bulging of the surface on the upper edge between section 1 and 2. I have played around with the skinning strength to try and reduce/remove, but it's still noticeable. Any suggestions on how to resolve this, or is it just an artifact of the skinning controls? I've attached the vsp3 file of the fin (with reduced skinning strength) for reference.

Cheers,

Grant