CONTROL LINE AEROBATICS
Frank McMillan 12106 Gunter Grove, San Antonio TX 78231
Early experiences
Many years ago, when I started building models, Veco kits and Sterling Ringmasters and Flying Clowns were the popular designs. In those days, the most difficult part for me was the control system; the Veco kits had the best representation of how to do it and included many of the components.
The Veco kits were expensive for the time at $6.95—about double the price of the profile kits, the Ringmaster and the Flying Clown. I recall the mystery of each new airplane's first flights. I thought that was just the way things were: sometimes they flew well, sometimes not. There wasn't much in print about how to trim airplanes, much less the modern technology on the trim devices.
I wonder how I could have built things straight at the time; I basically built those kits "in the air" (not on a bench), which accounts for the "wonder" of the good-flying airplanes.
The first real successes I had were two Veco Chiefs—the second version. Both flew well, with a string of successes.
A friend's question about alignment has prompted me to get into some history, and to think about techniques and procedures.
Design and construction lessons
I believe Joe Wagner designed the Veco kits, and many features promoted accurate assembly, such as interlocking formers in the fuselage. The die-cutting was accurate, to go along with good wood selection.
Even in those days, both of my models were 37-ounce airplanes. I'm making the assumption that the Chiefs went together well; I built both in an average of 10 days, purchase to flying. That's something I wouldn't even think about today.
But the thing that really makes me cringe, even today, was that I would build essentially without any references. That the models flew was more luck and coincidence than building skills.
After the Chiefs I started a string of originals, and as I worked through the design and construction, I saw the obvious need for alignment procedures. At about that time, I learned that balsa was "alive," and moved when long, straight cuts relieved stress in the wood. I also learned that without a good straightedge, everything I did was going to end up crooked.
At about this stage, I found out that when I put on the fuselage sides, the top edge would bow unless I was careful. (I still didn't have a building board to frame up the structure.) I tried, with some success, to slide the one-piece sides over the wings and assemble the fuselage over the wings.
These were some of my early approaches to procedural assembly, which provided the accuracy.
Although far more sophisticated than what I was doing, the Detroit I-beam construction can be classified as a procedural accuracy technique. The concept is to engineer the assembly so that the parts are located precisely and accurately. I was trying to do the same thing with simpler means.
From watching Bob Hunt's and Windy Urtnowski's construction videos, I came to the conclusion that there are individual methods for assembly techniques. Bob and Windy use techniques that result in extraordinary models, but I don't do everything they do; I use what I like and what I feel comfortable using. Sometimes I combine their approaches, sometimes I use one, and sometimes neither.
However, I thoroughly recommend both videos for instruction, if you really want to learn how to build well and competitively.
Facilities and tools
A point that ties in to being comfortable with your technique are the facilities you have at your disposal. Do you have the workshop of Tom Morris, or a modest apartment where you have to put everything up after your building sessions? Some builders in our end of the hobby share space and equipment with friends.
Also, finances may not permit elaborate fixtures or power tools; you have to adapt approaches to suit what you can do. Careful work can produce first-rate results; if you really know how to use sandpaper, you can do work as good as anyone. I built many of my first models with rudimentary tools such as razor blades, pliers, screwdriver, sandpaper, and a brush. You can do it!
Fuselage sides and doublers
Back to the discussion I had with my friend on fuselage assembly:
The way I do it may have some flaws, but I've evolved it with time, and the airplanes that use it have all flown well. The final test in anything you do is consistency and good performance.
I'll deal with the fuselage sides separately from the engine crutch. First, I lay out the sides after making a stress-relief cut on each long edge. The sides will ideally be closely matched and oversized; typically 40–48 inches long and four inches wide. The sides are available from Lone Star Models, Rt 9 Box 437, Lubbock TX 79423; Tel.: (800) 687-5555.
At this point, I make the doubler laminations with epoxy glue, under pressure. I use 1/32" plywood for the nose and 1/64" doubling in the stabilizer area. Later, after the wing is in the fuselage, I slip in a large U-shaped 1/64" plywood doubler around the trailing edge of the wing to lock the flap horn and strengthen the bottom cutout.
The next point is to cut the top of the fuselage with an accurate straightedge. Then I clamp the sides together and sand them straight. At this time, I do a rough cutout of the wing and stab openings.
Engine crutch and firewall assembly
The engine-mount system borrows from many other designs in detail. Basically, mounts, which are notched 1/8" to permit tank shimming, are epoxied to a 1/8" plywood plate that serves as the top of the basic fuselage.
There is a 1/4" glass/balsa end-grain laminate that serves as the main firewall at the leading edge of the wing. A 1/8" engine-mount plate bridges a piece of engine mount material at the front, behind the engine. Cross-grain balsa bridges the gap between the two mounts and forms a tank floor. This assembly is put together on thick plate glass as an accurate base.
Adjustments and reference surfaces
Now for the adjustments: the materials you work with are not always cut square, and you have to account for that; I do it after assembly. I sand the 1/8" plywood base as flat as I can, then I take reference measurements from the glass plate with a dial caliper.
Remember that the plywood surface is the reference for thrustline and incidence lines, the top of the fuselage. I measure the surfaces and remove material until the engine-mount surfaces are equal and the notched tank floor is equal. This is not an easy or short process, but it guarantees that you have an accurate base for adjustment and alignment.
If the tank floor was not true to the thrustline, the tank could not be trimmed properly. The new power plants can "sense" a twisted tank.
Now you have a straight set of fuselage sides and a dead-true engine crutch.
Fuselage assembly methods
I can suggest two options for assembling the fuselage:
- Use the fuselage jig, available through Bob Hunt (Box 68, Stockertown PA 18083; Tel.: (610) 746-0106).
- Use a method I first saw in a Windy Urtnowski video: use cyanoacrylate (CyA) glue to attach the fuselage components to a level glass-top table.
Both methods have a flat surface as the reference point, so you have the engine mount flat, the fuselage sides flat, and the table flat. Now go to work with formers, which are accurately cut from your plans. Make sure that they are placed accurately within the sides.
If you are using the Hunt jig, the sliders are positioned and secured to hold all of the pieces in place. There should be no forcing; that will induce stress.
When everything is correct, start the gluing process by setting up the front end with slow-set epoxy, then tack the rest with CyA.
Final alignment and setting references
After you have allowed the front end to cure, set the reference lines on the fuselage. Measure from the surface for the wing and stab references; use your plans for the exact distance. When you mark the fuselage, make sure that the points are deep enough that you will not sand them off in the finishing process. Mark the aft points for use in aligning the control surfaces.
Now you have an accurate basic fuselage that will serve as the heart of a great-flying airplane. Note the sequence that uses measurements from a reference surface; this is the basis for accuracy. It will serve you well.
Next time I'll discuss getting the wing in the fuselage.
Transcribed from original scans by AI. Minor OCR errors may remain.
