Jim.Thompson's blog View Details
Archive for May, 2019
Posted by Jim.Thompson | May 04, 2019 @ 07:02 PM | 1,529 Views
I have adopted the routine of modifying the templates for hot wire cutting from that produced by (in my situation) Profili2.
Profili2 template print outs show a sharp change of gradient from the airfoil to the chord line at both the leading edge and the trailing edge.
I shape the LE with a curved, smooth entry to facilitate easy starting of the wire transit. It is inclined to get stuck with a sharp change of template shape here (or anywhere for that matter).
The very small extra foam can be quickly sanded off after the cut is done. If care is taken with the shaping of this curved starting section, little or no extra foam is left uncut.

At the TE, I continue the airfoil contour gradient beyond the TE, as distinct from sharply changing the contour to the chord line. This minimises or avoids any "scalloping" (loss of foam mid panel) of the TE and provides a faithful result.

One other practice that I am at variance with Phil Barnes vac bag instructions is in the type of top template used. If I recall correctly, he advised the use of a bottom template with a full airfoil template sitting on top of that to do the top cut.
Not only does this obviate the above advantages, but also can result in the wire slipping between the two template parts and completely ruining the foam blank.
This at least, was my experience, and I now only use a separate top cut template.
A typical one can be clearly seen in the foam rib hot wire cutting video posted in this blog below.

Jim.