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 Sailplane Construction Project Session #54

Comet Sailplane Project
 
I have been concerned about the silk covering "bridging" or wanting to pull away from the fin's bottom concave fillet at the bottom near the front. So I added some balsa fill wood above the bottom fillet to give the silk a surface to stick to that is in line with the fin's ribs. A discussion and pictures have been included herein. ........................Tandy
 
The bare fin primary structure shown below requires ribs, spars, and all sorts of fill wood to give it its final shape.
 
The four symmetrical fin ribs along with the internal spar were glued into the primary structure. A soft balsa block was then carved and sanded to the top contour of the stab to make the fin's root rib. With fin mounted in the stab slot, this contoured block was glued to the base of the fin as shown below.
 
Next soft balsa fill strips were glued to the trailing edge as shown below.
 
 
Then soft balsa fill strips were glued to the leading edge as shown below.
 
When everything was dry, the fin's leading edge, trailing edge, and root rib block were carved and sanding to shape. The fin's resulting foot print is shown below.
 
This shows the fin mounted in the stab slot. Notice the shape of the fin's forward fillet now.
 
This is a nice close up of the fin/stab interface juncture.
 
This is more of a frontal view of the fin/stab interface juncture.
 
In the picture above, you can see that when I try to cover the fin, the silk will want to "bridge" or pull away from the fin's bottom concave fillet, which I have been worrying about. So I decided to add some balsa fill wood above the bottom fillet to give the silk a surface to stick to that is in line with the ribs above the fillet as shown below.
 
This balsa fill wood was then sanded and contoured to shape as shown below.
 
In the picture below, I have drawn on a series of vertical lines. Think of them as straight lines of silk covering that stop at the point where the fin's bottom fillet starts to increase in thickness. If I have explained this right, you will see that the silk will now some flat surface to stick to and should not pull away from the bottom fillet near the front of the fin...................Tandy
 

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