FlatCat Boost/Glider Build, Part 4 - Let’s Rustle Us Up Some Glider Wings.

Ah, there’s nothing like a full-sized, fresh chunk of balsa wood – just waiting to be butchered!

Taking the easy measurements off of the plans, the first job is to mark out the FlatCat wings.  For accuracy I like to use a straight-edge reference block and a small drafting triangle to mark the 90 degree cut lines.

A little precision slicing with a straight-edge and the ‘Sword of Exact Zero’ (Ref. The LEGO Movie) to produce a pair of wing blanks. 

Once the wings are cut out, it’s time to mark them with the high point of the airfoil.  I’m placing it parallel with and approximately 30% chord length aft of the wing leading edge.  For those of you who aren't quite up  on wing terminology, chord length is merely the dimension from wing leading to trailing edge, analogous to a standard rocket fin root edge.

IMPORTANT TIP:  It is rather important to keep the wing pieces oriented for left and right sides!  I don’t want to end up with two of the same wing – then I'd be forced to build two FlatCats!

In reading up on the history of the FlatCat, I learned that many of the earlier versions were built with non-air-foiled wings.  Even the plans and article from which I am working here show the model minus an airfoil.  In the last paragraphs of the article, Mr. Stine suggests sanding in an airfoil to optimize glide trim and performance.  Since I’ve done that with all of my past B/Gs, this FLatCat build will be no exception.

A piece of masking tape is set along the high point line to serve as a stop, preventing that point from being sanding down while forming the airfoil.

Back in the day, when I was more interested in building gliders for competition, I would have taken the time to sand a slight taper from the wing root edges to the tip, but since this is a sport bird, I will forego that step.

 To start the trailing edge of the airfoil, I place the wing parallel to the edge of the workbench and set it back about an eighth of an inch and hold it there during sanding.  I allow this little bit of clearance since I don’t want to sand the trailing edge to a sharp knife edge, as doing so might compromise the strength of the wing.

Using a sanding block equipped with 200 grit paper, I then sand a bevel into the trailing edge of the wing.  Doing so defines the final thickness of the trailing edge. Courser sandpaper is used because the idea is to hog off a substantial amount of wood while forming the airfoil.

 Now, still using the 200 grit block, the area between the wing high point and trailing edge is carefully sanded to define a gentle tapering curve (See the following illustration).

 Next, the masking tape strip is moved to the other side (aft)of the high point line. 

Again, using the 200 grit block, a gentle curve gets sanded into the fore part of the wing.

The leading edge now gets rounded over - top and bottom.

Once all is said and done, the finished wing profile should look like this:

 The next step involves smoothing out the wing.  This is done by lightly going over the entire wing surface with progressively finer grit sanding blocks.  I don’t sand very aggressively here, as it’s all about smoothing rather than further shaping.  300-400 grit paper works well here. 

It also doesn’t hurt to go over the flat bottom surface of the wings with fine grit block to smooth them out as well.

Next post will cover the wing glue-up.