Filling and sanding the wings

This job can be a pleasure or a nightmare depending on whether or not you follow a few basic rules:

1) Do not EVER use sanding blocks shorter than 1m (apart from the flex board shown below - explanation to follow). Sanding blocks remain aligned with the longitudinal axis always!

2) Change the sandpaper after 400 strokes! Yes the sandpaper might still feel rough to the touch but it is not - grit your teeth and throw it away - you are saving money by doing so!

3) Do not change to anything smoother than 40 grit until you are 100% happy that all profiling / contouring is complete. With your eyes closed run your hand fore/aft over the spar area. If you can sense where the spar is you are not finished with profiling yet!

4) Ignore the micro picture and focus on the macro picture - do not try and sand away a localised scratch as you are causing a hollow. Concentrate on getting the overall profile right. The small scratches and voids are easy to do later.

5) Do not "over sand". A few hard strokes with fresh paper are worth much more than a days sanding with blunt paper. Fresh paper cuts away the crests and leaves the hollows.

6) Use the flex block sparingly and only over the spar area. Use the long block for 90% of the time and the flex block for a few strokes in between. It's paper MUST be brand new. 3mm plywood with the grain at 45 dgrees seems to be just stiff enough for this block. The flex block is orientated chordwise and moved at 45 degrees to the wing - use sparingly as it can cause flat spots.