NewComers

NewComers

Bob Underwood Box 40, St. Peters, MO 63376

Early in my modeling career, I recall someone asking me if I engaged in "trammeling." There was some reluctance to answer at first, since the initial impression was that it must be either fattening, immoral, or illegal! Then I discovered that the term simply refers to the process of careful measurement to see if the various parts of my model are in proper alignment with one another.

You might ask, "Is a properly aligned model important?" and receive answers all the way from "Who cares" to "Absolutely!" It's true that a sloppily aligned model will fly, but performance will suffer. You may find yourself forever fighting trim changes or inadequate trim to compensate.

Remember what went through your mind the last time you followed a car or truck down the interstate and noted that the rear wheels tracked several inches right or left of the front? You probably said to yourself, "That guy's fighting a problem and he's wearing tires like mad!"

So—let's trammel, or properly align, your model through the various stages of construction. It's not hard; the model will fly better; and the results will be aesthetically pleasing.

Two things should be noted:

1. Some models have parts purposely misaligned. For instance, more often than not, free-flight models will have the wing or stabilizer leaning to one side or another for a particular reason. In that case, the proper alignment is a degree of misalignment. There is a special reason for this — just as there is for some control-line models to have the inboard and outboard wing panels slightly different lengths.

1. Accurate measurement to determine alignment does not address the problem of warped or misshaped parts. Warped wings or stabilizers, though perfectly aligned to the fuselage and to one another, may still give you big problems.

Let's look at some alignment or trammeling procedures:

1. Engine to fuselage

• Usually (but not always) the first alignment will involve the engine relative to the fuselage. You may be able to mount the engine to the firewall and trammel it as it is glued permanently to the fuselage sides. For all practical purposes, however, that usually doesn't happen. Generally the fuselage is completed and the engine is then mounted.
• In that case, put a prop on the engine and place a pin on the fuselage centerline near the tail. Using a yardstick or tape measure, carefully measure the distance from the prop tip to the pin to determine proper alignment.
• Cautions: use the same prop blade for both measurements (just rotate the prop 180° for measurement on each side). Remember that some models call for right thrust in the engine; plans usually list right thrust in degrees. Generally, too much right is less of a problem than any left thrust. Finally, use the same relative position of the yardstick or tape to the pin and prop tip for both sides.

1. Locating the stabilizer and fin

• Move the pin from the fuselage centerline near the tail to the centerline at the firewall. Place the fuselage on your workbench and temporarily pin the stabilizer in its proper position. From a distance, sight down the fuselage to determine whether the stabilizer is level.
• You may also measure from the tip of the stabilizer to the workbench to determine whether it is level, assuming the fuselage was built true. Shim either side of the stabilizer saddle to bring it to a true, level position. Don't rely on glue to fill a gap.
• Now measure from the pin on the fuselage centerline to a common reference point on each half of the stabilizer — for instance, the end point (tip) of the stabilizer elevator hinge line. Shift the stabilizer back and forth until you come up with equal measurements. Glue it.

1. The fin

• The fin is generally glued along the centerline of the fuselage. Use a 90° angle across the fuselage and filler along the base of the fin. Once again, sight down the fuselage from a distance to visually determine the squareness of the three parts: fuselage, fin, stabilizer.

1. The wing

• If you've done your job well up to this point, you can align the wing using the stabilizer as a reference. Measure from a common reference point on the stabilizer tip to the wingtip, again establishing a common reference point. Build up the wing saddle on either side of the fuselage until the wing is level.
• Bear in mind that you are now working with dihedral. If the wing is on the workbench and the bench is large enough, you may be able to measure from the benchtop to the stabilizer and wingtips to establish levelness.
• Don't finalize the attachment of the wing until you've done additional sighting. Place the tentatively assembled model with its nose against the wall so you can look at it in plan view from the top. Closely study the alignment from a distance. Use the LAR — "Looks About Right" — method. With a little practice you'll be able to spot small amounts of misalignment.

One warning: be careful about noting an alignment problem on someone else's model unless asked for your opinion. Once I went to a local hobby shop and critiqued a model hanging on the wall. The stabilizer looked really crooked but the model was otherwise very nicely done. For reasons unknown I felt compelled to announce the error and, to my horror, the builder of the model turned out to be the shop owner; another customer; and someone who just happened to be standing nearby. So much for diplomacy.

Now, you experts who might be reading this may wonder why we didn't address measuring and setting the incidence of the stabilizer and wing. There are three reasons:

First, most trainers are either ARFs or kits, and the mounting saddles are already established on the fuselage sides. I know that sometimes you might find a model where the saddles are off a bit; but that leads to the second reason.

Second, most trainers are forgiving. Small amounts of incidence error can usually be trimmed out with the controls and by using thrust adjustments. Trying to make tiny incidence changes during the building process can sometimes create more problems than it solves.

Third, if you find after assembly that the incidence isn't quite right, it's generally easier and safer to correct it by trimming in flight or by minor adjustments than by rebuilding structural parts.

A final word: take your time when trammeling and use simple visual checks often. A well-aligned model will not only fly better, it will also look right — and you'll enjoy it more.

Generally, ARF or kit trainers don't list the incidence anyway. It's hard to measure what you don't know.

It really helps to have a meter to read incidence anyway. Robert would love to sell you one, and they really are great tools. In fact, they can be used not only to measure incidence, but also to check upthrust or downthrust in the engine as well. While you'd be well served to have one and use it, quite frankly your first effort probably won't require it. (Don't ever try to scratch-build without one.)

Some Dos and Don'ts

Do:

• Keep checking alignment at every step.
• Develop an eyeball technique by backing away 10 to 15 feet and sighting carefully.
• Use slower-setting adhesives to attach the stabilizer, fin, etc., so you have time to adjust.
• Use care!

Don't:

• Rush trammeling!
• Rely on glue to fill large gaps.
• Use the basement floor to measure stabilizer and wingtips. Basement floors are notoriously uneven!
• Build your fuselage with irregularly bowed sides.

You will learn some tricks as you gain experience. Spend more time than you think you need to just sight the model. Allow your eyes to focus on various parts.

For instance, when sighting from the nose, focus on the engine, then the wing, then the stabilizer. You'll form a sort of mental scan plan that may point out a problem.

Slowly move your head vertically and watch the alignment between surfaces as the angle changes. Does the stabilizer disappear behind the wing leading edge in an even manner?

Look straight down the wingspan from the tip. Is there a warp? Even a small amount can create an interesting takeoff the first time.

Maybe we could come up with some saying like, "A straight airplane is a happy airplane!" That's plain dumb. A straight, aligned model will certainly help your instructor — and you!

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