Good Morning Greg;

Don't know if you have a (US) AMA membership, but if you do you can log into the AMA site, and read the back issues in the archives.  Back in 2008/9 Bob Hunt did a 'build-along' series for his Hot Shot design and showed the various techiques he uses.  The September 2008 issue addressed the process he uses (used?) to cut his foam wing cores.

Direct link to that article (don't know if it will let you get there without authenticating a user name/password) is: https://library.modelaviation.com/ma/2008/9  Bob's column starts on page 139...

r/
Dave

You can cut perfectly good cores using 1/8 in. aircraft ply or formica as tempates.  Put a pin in the front for the lead in.  Most folks just use 3 in light nails through the tempates into the foam.  Or you can use a system where the templates have only one curve and rest on a board, to help maintain alignment.

You'll need a helper to get around the leading edge, although for just a couple of sets it can be done solo. Practice makes perfect.

lHollowing the cores is best done after sheeting, although folks have done it both ways.  If the cores are hollowed first you can press the cutouts back in before sheeting to help prevent warping the cores.  But ordinarily it doesn't take a lot of pressure to keep the sheeting down while the glue is drying.

Okay guys, I finally got around to trying to cut some cores on wednesday.

The results were appalling.

I think I might be doing it wrong.

Let me talk you through it and hopefully you can tell me where I'm going wrong.

I'm cutting cores using 4 templates, two upper two lower. I'm also trying to cut the leading edge as a part of this, by having a lower and higher lead in with a radius to get a decent shape.

The lower cut usually (not always) goes ok. If I don't haul on the bow too quickly (it's a automated weight driven bow) I can get it to follow the lower curve, but the upper curve turns into a disaster as the wire will usually catch on the radius as it's nearly vertical, and one side will usually climb the template first leaving a very funky looking trailing edge.

I'm cutting from LE to TE.

I'm now thinking that I might be better off cutting the upper surface backwards (from TE to LE) so that the bow doesn't have to climb over the LE radius, it goes down over it.

How is everyone else cutting their leading edge radius?

Curare- need to put wooden spools on the wire so they can be guided around the leading edge.  I assume this is something like the feather touch cutting system.  It will keep the wire on the right taper, but doesn't do anything to make it follow the templates, so you have to.

Wish I could be there in person to help you.   I have trouble putting into words the procedure of doing cores.   Really if you could get one of Bobby Hunts videos on cores would help a lot.   I have a video by icehockeydad, but it is a cassette and I have no way of looking at it any more.   But punching holes through the cores takes a jig and thought.   Need a vertical board to put eyelets in for the 1/8 music wire to slide through.   Then the cores are centered under it.   I use a clothes pin spring type to hold the rod just above the core.   Take the torch and heat the wire to red hot and release it.  Be sure you have clearance between the foam and the floor.   If everything is vertical the wire will melt through the core and hit the floor.  Then you start over again for the nest hole in the core. 

As I said,  I wish I could be there to help you.

Greg;

I think it is Phil Barnes' video on cutting cores for r/c sailplanes...  Those wings use a 1/2" ID tube for a spar/wing joiner, and I believe Phil simply has templates with a thin vertical slot leading down to the circular hole in the template.  He allows the wire to drop down through the top of the core, runs around the ID of the template cutout, and then lifts out the wire at the top (might even kill the current prior to doing so).

The kerf should be minimal, and you should be able to glue the gap closed and maintain airfoil integrity (I assume the cores will be skinned, and the outer beds will ensure the wing is the shape you want).

Possible solution?

r/
Dave