ORIGINAL: Ram Jet
If you have access to a belt sander mount the sander upside down in a vice or device of your choosing, draw a center line down your trailing edge and sharpen it like they manufacture knife blades.
Bill
Sounds safe, I use a 12" radial Drum Sander with a larger piece of hardwood that is notched out to hold balsa stock in. Takes some time to make the jig, however once that is done it has been good for many airplanes.