ISON Tandem AirBike Builder's Log

The Great Aileron Sparcap Predicament

 

Let's start with two of the details from drawing no. 7 that led me down this path:

Now, the written instructions don't say anything about sanding these caps to match the airfoil (at the arrows), but these drawings suggest it to me.

 

I drew this detail in AutoCAD to help us (myself included) understand what's going on here. The details below are enlargements of the dashed area.

 

Here's the situation as I understand it. The upper cap has been installed with its front corner flush with the rib profile and its rear corner projecting outside of the rib profile. The 1/32" LE plywood is drawn here continuing its 1 3/4" radius to the back side of the cap. This shows two objects trying to occupy the same space at the same time (not a good idea when it comes to airplanes ;)

 

Here's what happens when the LE ply is glued to a cap installed thusly. The edges of the LE ply project outside of the airfoil more than 1/32" farther than they need to (not the end of the world, as your laminar flow has given up on this airfoil WAAAAAAAY before it gets back this far anyway).

 

This shows the LE ply continuing its 1 3/4" radius over a cap that has been sanded to match the rib profile. We can just force it down to the cap when we staple it, or...

 

...we can knock down the crown slightly with a sanding block for a smoother transition as shown here. To me this scenario best matches the intent suggested in Wayne's plans.

 

For argument's sake I'll mention the only other option obvious to me, which is to install the cap with its rear edge flush with the rib profile. Not a good solution to me, as the joint is too open and the staples will force the ply down when away from the ribs, producing a wavy seam.

If anyone has other suggestions or comments regarding this issue, I'll be happy to post them here.

 

 

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