A Walk Along Glider (with CNC’d ribs!)

Posted: January 16th, 2010 | Author: Ian | Filed under: Flying Things | Tags: CNC, glider, MacCready | 1 Comment »

Through my contacts at the Owls Head Transportation Museum, I was introduced to a stick and tissue “Walk-Along Glider.”  What’s a “Walk-Along Glider”?  Essentially, it’s a very light aerofoil that flies on the air that is forced up over you as you walk.  The concept was patented by Tyler MacCready (early pilot of the Gossamer Condor, and son of it’s chief engineer Paul MacCready), and frankly it’s pretty neat.

The plans for the Club Racer 2007 plans I based my model off of can be found here.

Mine differs in that I didn’t feel like drawing and cutting the fuselage out of 1/32″ balsa sheet, so I substitute a 1/8″ square stick of balsa the same length of the original fuselage.  I wasn’t comfortable in my ability to glue two 1/32″ flat plates together at a 90 degree angle, so I made my tail out of 1/8″ sticks with a tissue covering.  Now, let’s get to builder her, shall we?

Ribs
The plan specified slicing the ribs out with a drafting curve.  I have no such tool, and tried cutting a few out freehand.  This was a total no go.  They are so thin (with spar depth of 1/16″) than any deviation from the curve simply cut the rib in half.  Not to be discouraged, my Dad is also a hobbyist, and built a CNC machine for kicks several years ago.  He uses it to make signs for gifts, and occasionally attempts something commercial.  (For those interested in home built CNC machines, I suggest www.CNCzone.com)

So, I drew a simple outline of the rib in NX6 and converted it into G-code using Vetric’s VCarve Pro.  Then it was off to the CNC machine, as can be seen to the left.  It took a few tries to get the cutting path right, as the material was so thin.  In the first pass all of the ribs broke, but during the second attempt we cut deeper into the backing material giving the piece a little more support, as well as placing a little support past the halfway point once the bit passed by.  This gave me 12 good ribs to use!

As you can see, the machine cut the spline (the curve), and then I removed them from the blank using a razor.  This also gave me the straight edges I needed to glue them to the spar.

This wing needed to be constructed in three segments because it has polyhedral (i.e. the flat center section and upward slanting outer sections).  To do this, I laid out a piece of parchment paper over some foam core board and drew two parallel lines 2″ apart.  The spars are held down with pins as can be seen in the picture, and it was relatively straightforward to drop the ribs in and glue them in place.  I used Loctite brand Super Glue Control Extra Time and was very pleased with the results.

At left is the end result of the center section.  Simply repeat with the additional two outer sections.  To attach the three sections as the original author drew would require lots of fancy cuts, though it would be the strongest method.  However, because I didn’t feel the need to calculate out the angles, I simply set the wing sections on the plans and sliced the spars of the outer sections such that they would nicely meet in the inner section at the correct angle, and glued them.  This results in less surface area in contact and a weaker bond, but it has worked reasonably well for me.  Should this joint break when the glider crashes (mine has) the tissue does a good job in keeping it in alignment so it is easy to glue back into the correct shape.

One outer section attached

Covering the wing is straightforward.  Simply cut a piece of tissue paper to about the size of the wing.  Coat the top of the wing lightly (glue is heavy stuff at this scale!) with Elmer’s glue.  Stick the tissue paper on, and allow it to dry thoroughly (if the tissue is still wet with glue, it will likely tear), then cut off the extra.  Do not use superglue for this task! It doesn’t stick nearly as well to the paper and wood, and is a general mess, as it is very good at sticking human flesh to paper.

Instead of cutting out the fuselage and vertical stabilizer per the plans, I modified it to take the lazy way out.  I used an 1/8″x1/8″ piece of balsa as my fuselage, and two struts covered with tissue paper as my tail.  This made it easier to glue the horizontal stabilier as well (which I did make per the plans, except I beveled the front edge as opposed to rounding it.

Once it was all set and done, my initial test flights were appalling.  It didn’t fly, it simply flipped over and looped to the ground.  I didn’t have any clay to use as a weight, but I did have some scotch tape and a penny, which served the purpose well.

Unfortunately, I don’t have a large enough space to test fly it at home.  It seems to require a pretty good clip to keep airborne, a nice run seems to do it.  Unfortunately, it requires very still air, so it’s almost impossible to do outside on the coast of Maine (it’s very windy here!).  So, I have yet to fly it as a walk along glider, but it’s made some pretty decent flights across my living room, and has survived a large number of crashes!

(See top of the post for finished craft!)
I also apologize for the lack of decent pictures/video, my camera is at school so these pictures were taken with my cell camera!

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