Newcomers

Newcomers

Bob Underwood Box 40, St. Peters MO 63376

"Let's get this straight!" No, this isn't a lecture on why you should accept my way of thinking or that you are out in left field. Rather, it is a set of suggestions on how to get things built straight.

So you've moved into the kit-building era of your newcomer program. You probably came home with a large box (or maybe small), opened it up, and found a zillion pieces of balsa, fittings, and "stuff"! Fortunately, you were smart enough to choose a kit that contains an excellent set of plans and illustrated step-by-step instructions, right?

Before you dive into the box, there are a couple of things you should be warned about.

• If you do not intend to start on the project for a while, don't take everything out of the box and try to put it back in. There's a law in packaging: things will fit into the box only once—at the time of initial packing. Beyond that point, it is futile to try to make it fit again.
• Don't unpack the box in the living room with your wife, dog, and kids present. The kids will break the wing main spar; the dog will grab the plans and shred them; and your wife will have interesting things to say about the balsa traces left on the furniture and rug.

Just take out the instruction book and read it several times; circle in red any terms that leave you clueless, such as "empennage." I will fast-forward to after you have made certain that all of the parts are there, after you have identified everything, and after you have built all of the major components. There they are: the fuselage, empennage, and wing panels. Now's the time to use the phrase, "Let's get this straight!"

I will assume that:

1. When you built the fuselage, you checked carefully to see that it didn't bow like a banana because one side was stiffer balsa than the other. You can check by placing a centerline or mark on each bulkhead, drawing a centerline on the plans, and lining everything up as you draw the tail end together. A little shift of the sides will help you create a straight, true fuselage. Don't forget to square up the firewall. (In some cases, a small amount of slant or offset is built into the firewall. Your plans and instructions will note this.)
2. When you built the wing and tail surfaces, you checked to see that the pieces were straight. Don't pretend that a wing built with a warped spar or leading edge will somehow straighten itself when you assemble it. Murphy's Law says, "The component will automatically take on the character of the worst piece used."
3. You built the parts on a flat surface; if it wasn't, your wing panel isn't. Bad building surface, bad wing panels; bad wing panels, bad model.

There will come the moment of truth when you must assemble all of these lovingly and exquisitely constructed pieces. The tail surfaces are glued to the fuselage. The wing panels are joined, then properly seated to the fuselage and aligned. Performing these steps is often referred to as "trammeling." Webster offers several definitions:

1. "a net for catching birds or fish"
2. "an adjustable pothook for a fireplace crane"
3. "a shackle used for making a horse amble"
4. "something impeding progress, or freedom of thought; government?"
5. "an instrument for drawing ellipses"

a. "a compass for drawing large circles" b. "any of various gauges used for aligning" — Bingo!

Leave it to Webster to get us there on the last shot: you need to be careful in aligning your model's parts. The "tools" to do it are easily obtainable:

• A ruler, tape measure, and/or yardstick (metric if you're inclined)
• A few pins
• A right triangle or carpenter's square
• A flat, straight building surface
• An incidence meter (such as Robart's) — not required, but very helpful

Because I'm writing this column, I'm going to start trammeling where I always start: at the back. The first piece I glue to the fuselage is the horizontal tail, or stabilizer (stab). You need to check two things.

First — level and tilt:

• Make certain the stab is not tilted relative to the fuselage vertical line. By sanding or using shims on the fuselage sides you can make it level. Most trainers have a flat bottom on the fuselage, so resting it on a straight building surface makes this easy.
• Measure each stab tip to the building surface to ensure the stab is level.
• After that, move away from the building board and sight down the fuselage. Does the tail look level? If not, correct it.

Second — elevator centerline:

• Make certain the elevator centerline is true (at right angles) to the fuselage centerline.
• Put a pin in the center top of the fuselage at the firewall, then measure from the pin to the stab at the elevator hinge line on each side.
• Shift the stab until the distance is equal on both sides, hold it tight and draw a pencil line on the fuselage side. This allows you to remove the piece, apply glue, pin it in place, recheck, and let it dry.

The vertical fin is easier. Often a slot in the fuselage top lines up with the centerline; scribe that line and use a right angle to make certain the vertical fin is truly vertical. Specialized tools have been developed to simplify much of this alignment work.

The wing is next. Gluing the two wing panels together is usually straightforward; the plans provide the proper dihedral. Watch one thing, however: sometimes the dihedral is expressed as a total amount. For example, "four inches" may mean the total dihedral (one tip elevated four inches while the other is flat) or it may mean a shallow V with both tips elevated two inches each. Most models have a plywood dihedral brace, and that gives you a choice as to the amount of dihedral to use.

• Make sure the panels are not twisted when you glue them. If you've built them straight and you line up the leading and trailing edges, there shouldn't be any twist.
• Fit the wing to the fuselage wing saddle. The wing can be aligned much the way the stab was: measure from the stab/elevator hinge line at the tip to the rear edge of the wing at the tip. This assures the wing and tail are aligned.
• Sight down the fuselage from the nose and make certain that the wing is not tilted in relation to the stab. By raising or lowering your line of sight you can superimpose the wing and stab to help with a visual check. You can also measure at the tips if you have a flat, level surface big enough. Beware of basement floors—they tend not to be level.

Checking the engine thrustline:

• With a propeller installed horizontally, measure from the vertical tip at the rudder hinge line to the propeller tip. Rotate the prop 180° and measure again. If there isn't any right thrust built in, the distances should be equal.
• An incidence meter can be used to measure the angle of incidence of the wing and stab relative to the fuselage thrustline and to each other. It can also check the wing between root and tip for twist. There is a fitting that allows attaching the meter to the engine crankshaft to check the engine thrustline.

Now you're trammeled: you have a straight model, and that should help make it easier to fly. However, many of us have seen models that were as crooked as sin and still flew fine—for a trainer, that is. I'm not suggesting you shouldn't try to build a straight model; you should. Just don't let perfection become an obsession in the early stages. Do your best, perfect your skills, be patient, and grow.

Illumination

• Empennage: The tail assembly—stabilizer and vertical fin—helps the model fly straight and true.
• Trammeling: The alignment process described above; various definitions were noted earlier.
• Saddle: The wing or stabilizer mounting area—do a good job on the fit here.
• "Stab": Short for stabilizer; the horizontal tail surface.
• "Carb": Short for carburetor. (If you're unsure, ask—I'll fuel your curiosity!)
• Incidence: The angle at which the wing and/or stabilizer is set relative to the fuselage centerline or thrustline.

Transcribed from original scans by AI. Minor OCR errors may remain.