CONTROL LINE AEROBATICS
Frank McMillan, 12106 Gunter Grv., San Antonio TX 78231
FOR SEVERAL YEARS, we modelers have been seeing the term "laser-cut" applied to an increasing number of kits. Naturally, we implied an accuracy equivalent to the cutting medium: a laser. So I thought I would take a closer look at laser-cut parts as they apply to Control Line Aerobatics models. Let's take a look at the process.
The laser has to be controlled by a computer. The next logical question is, How does the information to cut the part get into the computer?
If the situation requires duplication of a specific part, such as fuselage formers, a scanner can be used as an input device.
Wing ribs can be handled a couple ways, and both require software to generate ribs. You can scan root and tip profiles or you can use the computer to develop the rib set. Within the last few years, programs have become readily available to work these problems, so all the elements were in place to make dramatic leaps.
There are factors that can make progress happen or significantly slow it. The first is cost and access to equipment. The second is a willing and interested individual who will work with you to develop your project. The cost is beyond most individuals unless there is a commercial application, so let's consider how you might look at a laser-cut project.
Accuracy and clean wood cuts are but two of the advantages. The laser cut actually burns the wood and the cut is clean, but the edge will be slightly charred. The smoothness of the cut depends on the digital step rate used. The smoother the cut, the more steps used, but the more expensive it is because of the increased computer time. I've seen both speed cuts (I'm sure there can be more than just two), and it doesn't seem to make much difference, practically.
Accuracy will be what is in the computer. If a program generates the ribs, the accuracy will be there. If the patterns are scanned, the accuracy depends on the pattern.
Now we get to the crux of the generic laser parts. No matter how accurate the parts are, there must be an approach to assembly. As you evaluate building or developing a project, you need to consider how you're going to build the part.
The reason I'm focusing on this was the occasion I had to be involved with Al Rabe's quick-build Bearcat project. The thrust of the project, aside from producing an enlarged version of Al's original model from the original 1969 design, was to assemble the
CL Aerobatics
in the center-section. The wing center, gear to gear, is assembled as a unit, with integrated plywood control-system mounts. The completed unit, with controls, could then be transferred to complete the wing.
The fuselage had been engineered to take advantage of the laser-cutting capability. Plywood formers and stress plates assemble like a jigsaw puzzle. This was possible only because of the best-cut accuracy. The additional formers were cut in two mediums: 1/32 plywood and 1/32 balsa, glued together. Corresponding pockets to hold the formers were produced at the same time. This was an extension of Al’s time-proven system. However, the laser-cut parts made possible a much more accurate model.
To answer potential questions, the laser parts are available from the gentleman who helps Al with his projects. Contact Kyle Tankersley at (817) 831-1406. Check out Kyle’s Web site at www.ajlaser.com. Among the items you might find interesting are Classic legal wing-rib sets for the Mustang II and Bearcat III, which incorporate the latest building technology from the quick-build Bearcat the parts follow the plans available from PAMPA Products.
The quick build Bearcat and Mustang parts packages, which include all the necessary parts except sheet wood and molded shells, are for sale. However, plans are not currently available. Check out the Web site because there are other interesting subjects in production, such as the French Champion Berringer’s four-stroke designs.
New items: I started this column with the intent to review a laser-cut design, but I got diverted!
When I went to the Vintage Stunt Championships in Tucson in 2, I expected to see only Old-Time and Classic-design Stunters. But there was this slick, .25-powered, nonflapped model named Primary Force. I recognized the shape from one of his earlier designs, so I asked Mike Pratt what he did was. Basically, he liked the way this model flew, so he decided to do a laser-cut kit as an experiment. So I thought, why not?
This is not a kit in the sense of many commercial kits. Some sheet wood and all the hardware must be purchased. Everything is commonly available, so there is no problem. Mike has produced an excellent set of step-by-step instructions which are logical and well thought-out. Complementing the instructions are two plates of full-size plans. The smaller of the two has all the full-size templates that are laser-cut. The second has a complete full-size layout of the model.
Remember when we were discussing alignment and how to set up the wing? Mike uses a system whereby the ribs are assembled on a central main spar. The assembly is pinned to the plan over a flat building board. Tabs on the rib support the wing in alignment while the trailing edge sheeting and 1/8-inch square leading edge is positioned and glued. It is a simple wing with a high aspect ratio.
To take advantage of the laser-cutting, the major parts such as the fuselage are laminated for strength. Precise interlocking parts can be glued directly without further preparation. For additional stiffness, carbon veil can be sandwiched between the layers with an epoxy glue.
Overall, this is a well-engineered design by Mike, who was with Sig for many years. It fits a niche in available designs in that it is a simple, nonflapped design for the inexpensive .25-.35 engines. It is capable of excellent performance; so it is suitable for Intermediate- and Advanced-class competition. I like it and will use it in local Formula 40 profile events.
Contact Mike Pratt directly at Mikey’s Models, 109 Glenn Roe Dr., Pueblo West CO 81007; Tel.: (719) 547-0541; E-mail: [email protected].
Transcribed from original scans by AI. Minor OCR errors may remain.
