Enerjet by Aerotech Strong Arm Build, Part 3, Strakes

Here I'm cutting the back of the strake.

Notice I'm cutting a little outside the pencil line.

The top picture shows the rough cut using a knife.

Here's the same cut after sanding with 220 grit on a block, followed by 400 grit on a sanding block.

Another before and after picture - 

220 to take down the rough cuts then 400 grit to smooth.

This inside angle is tough to smooth out.

Mark the side with a pencil and use a finger to block the block edge from cutting in too deep.