Reading Plans

"Things I Didn't Know I Didn't Know"
By AnnMarie Cross

As the manager of product support at Great Planes, I have to know how to read our plans in detail, right? Well, if you'd asked me a year ago, I would have said I had a good working knowledge of our plans. And I thought I did. Last year my husband Michael designed the Great Planes Giles G202, and I had the pleasure of working with him on the AutoCAD files, learning about the small stuff, and learning more than I ever thought there was to know about the information provided on a set of Great Planes plans. I mean, how much can there be? There are lines for some parts, a servo here, a pushrod there... no big deal! Right? Well, I'd like to share with you some of the things I didn't know I didn't know.

(Please note that these thoughts are specifically about Great Planes plans. While many of the conventions are true across most manufacturer's plans, some may not apply. When in doubt, talk to your kit's manufacturer about information which is unclear to you.)

An Overview of Plans

Every plan view has a label such as "Top View", "Left Side", etc. Be sure to read these carefully and think about how a finished aircraft looks as a bottom view rather than a top view. This is important to be sure you're not accidentally building upside down. Issues such as right thrust, and servo placement can get really sticky if you're misreading the plans! The case where this comes up most frequently is wing assembly. For example, a wing which is built with retracts is often built upside down so the retract support structure can be installed while the structure is still pinned down. The the wing is drawn, however, right side up. Therefore, wing plans often have a label similar to: "Right Wing Panel Top View—Build The Left Wing Upside Down Over This View". As long as you remember how your wing is oriented as you're building, and you follow the instructions, your wing should go together just fine.

Illustration 1

Most plan sheets also have large labels, such as "Left Side Sheeting Removed For Clarity". By removing the sheeting, stringers, fuselage side, or whatever part would be closest to you when looking at the model, it allows you to get a much better view of the less obvious... a view of what's going on inside. One such example is seen in Illustration 1. Notice how you can see the leading edge stick of the fin, and the fin's ribs, yet you still see random vertical lines? Those random vertical lines are the grain of the sheeting on the far side of the fin, which are visible behind the sticks of the fin once the near side fin sheeting is lifted out of the way.

Plans will sometimes have a cut away. The wing sheeting, for example, is shown on a portion of the wing. Then there's a very wavy edge to the sheet part way out the wing, and the sheet is not shown from there. What does the wavy line mean? It's telling you that the sheeting actually goes the whole length, but has been 'cut away' at that point, allowing you to see what's underneath.

Illustration 2

Another example of a cutaway is Illustration 2, showing you the wing panels joined, but not re-drawing the entire left panel. (The left panel by itself is drawn elsewhere on the plan sheet.)

Do you know why there's a ruler on the side of most plans? Well, it sure is helpful when you're building, but it has a second purpose as well. Paper is very susceptible to temperature and humidity changes, and by using a good ruler you can check your plan sheets to be sure they haven't been distorted before building on them. It's amazing how much damage a single day sitting out in a humid garage can do to the accuracy of your plans.

And what about two-sheet plans? We've had many modelers comment that they don't understand why large models have two plan sheets which need to be aligned and taped together for use. Well, the first reason may seem obvious, but its bigger than most people think. The cost to print one single sheet that's larger than the standard printer's press is far more than the cost to print two sheets that fall within the standard paper size. The increase in kit cost for a single plan sheet would be significant for those that could be printed that way. For some of the largest kits, there are very few printers with a press large enough to print these plan sheets at all. The only alternative would be blue line instead of printed plans, which is not as accurate or economical. Plans that are as perfect as possible for you to build over are important to all manufacturers. Two-piece plans that you have to splice is a good compromise that keeps them affordable, readily printable and still of excellent quality and accuracy.

A Closer Look At What's Overlooked... Cross Sections

From the conversations I've had with many modelers, it appears the cross sections are the most underutilized tool provided on plans, and boy, did I learn just how much work it takes to create them (Whew!) So let's look at a few cross sections to help demonstrate some of what I learned. The best advice I have to share is to use the cross sections as a reference tool every chance you get. Study them before you begin building, and refer back to them frequently. There are lots of things which neither a top nor side view can show you clearly, from landing gear mounting configurations to stringer positioning on a turtle deck, from flap mounting configuration to servo pushrod bends on a wing plan.

Illustration 3

Let's start by looking at a wing cross section. Illustration 3 is the cross section of the Giles' wing at rib R3. The first thing I notice looking at this cross section are all the labels. On a quick glance, it can be confusing. But if you take the time to really look it over, there's tons of valuable information here. Need to replace the aileron leading edge material? The part # is right here for you, GIL6W18. You may notice the hardware isn't labeled on this cross section, because the hardware is labeled clearly on the wing top view and more labels would only clutter this cross section further. Parts generally are not labeled in every view. It would only clutter the plan and make it harder to read. But items that need clarification, such as the webs, are labeled as needed. A quick glance at the leading edge sheet on Illustration 3 shows that the labels even go to such detail as to tell you the size stick a piece is cut from to help you know what piece to use.

The biggest thing this cross section provides when I'm trying to assist a confused consumer is a view of this kit's unusual four full span webs. There are four webs running from root to tip in this wing, but that's not clear from a top view. Take a careful look at this wing cross section, and you can see the leading edge, main, trailing edge and aileron webs clearly. See how the main web is captured between the spars, making an I-beam structure? And how the rib sits on the balsa spar and the support jig off the aileron web to keep it positioned during assembly? From this view, the modeler can easily visualize how the four webs run through each rib and make this wing snap together much like the interlocking fuselage construction. The graining of the rib vs. the web helps to clarify just what's going on. How? Take a careful look at the arrow that points to "leading edge web". See the dotted upper part and then the white part just below? What that shows is that the rib has a notch cut out there and the web is coming through that notch. The dashed line down from the notch is showing that the web goes down to the bottom sheeting behind the rib. The web and rib are both notched and interlock together. The graining and the cross section make this visible and explainable, whereas from a top view, you can't really tell how the ribs and the webs are related.

This rib cross section also provides information not only about the wing at this location during assembly, but upon completion as well. For example, see how the support jig is dashed and says "(REMOVED)"underneath it? This helps show not only what is holding the aileron during assembly but also how the assembly is finished. Another such example is the sheeting going below the building surface. Why is it like that? Because that way, the modeler can see both how the rib is positioned during assembly, flat on the building surface, and how the rib will look upon completion. The top side gets sheeted once the wing is removed from the building table.

Cross sections also show you final shapes of items, such as the aileron leading edge on this wing, or the final sanded shape of a fin or stab. This information can be invaluable to getting a flying surface as intended and may affect how the model snaps, spins, etc.

Illustration 4

Probably the most critical and the least used cross section is the example given in Illustration 4, the firewall or "F1". These cross sections provide some really critical information about engine placement, pushrod and fuel tube routing, nose gear steering setup, and more. For example, notice in Illustration 4 that the cross hairs drawn on the firewall are off center. These marks provide the proper crankshaft placement out the front of the cowl after compensating for engine thrust offset built into the model. If you're not using the supplied engine mount, this information tells you where to center your own mount on the model to get proper engine placement. (And important information such as those thrust angles and wing/stab incidences are provided on the top/bottom and side views to double-check your building and to aid you when repairing a damaged model.)

"Graining", or "What Wood Is That Anyway?"

Graining is enormously helpful information I never really saw before. I mean, of course you see the grain lines on the plans, but have you ever thought about what they're trying to show? Lets look at the rib cross section again. The short random lines on the rib show that this rib is balsa; the dotting of the spar, leading edge and webs shows that all these are balsa, as well,looking into the end of the stick, not at the side. The curved grain of the spar doubler represents basswood. The straight lines of the servo tray represent plywood, again looking into the grain, not at the flat side. (Flat ply graining can be seen in Illustrations 1 and 2. The random curved lines do look like a sheet of ply, don't they?) This information can be enormously helpful when you're trying to identify pieces, understand a confusing section of a manual, and is especially when making repairs to a damaged model. Another place graining clarifies steps is turtle and front deck sheeting. For example, this design requires the specific strength of the sheeting as support for the fin. Running the grain parallel to the fuselage side instead of the top of the turtle deck would compromise that support. While a good instruction manual will point this out clearly, understanding the drawing really helps to clarify what the writer is telling you.

What About All Those Dashes?

One place where the cross sections vary from side or top views is dashed lines. When you look at a side view, for example, those parts which are closest to you are shown with solid lines. Anything hidden behind a visible part is shown in dashed lines. Any item which is more than one layer deep is usually not shown (unless its something unique or unusual where the designer felt showing you would be helpful). This idea wasn't new to me, but the nuances and exactness of it, and the hours of effort needed to be sure every inch of it is right, amazed (and entertained) me! Since coming to understand the exactness of this concept, I've come to use plans to answer consumer's questions about certain portions of assembly more easily than manuals. A quick look at the right area of the plans can tell me that part A is part of the model's inside or outside, or that a certain stringer runs behind part A but in front of part B., etc. Not sure if a doubler goes to the inside or outside of a certain rib? Look to the dashed lines. (This rule usually does not hold for cross sections, however. A cross section would get terribly busy and confusing trying to show everything behind it, so cross sections are just what the name implies... a slice of the aircraft at that specific location, usually without additional items shown behind.)

Did you know dashed lines can show a lot of other things, too? For example, a portion of a stick is dashed to show it will be removed or sanded down to the solid line, such as both the support jig in Illustration 3 and the turtledeck stringer shown in Illustrations 1 and 2. Certain types of optional items, like the optional rear-mounted rudder servo shown in Illustration 2 are also shown dashed so that location and installation are clear, but it is also clear that you don't want to install two rudder servos. A similar example would be showing an optional scale tail wheel location or optional retractable tail wheel, in dashes to provide the information for those modelers who wish to use it.

Why Don't the Views Always Agree?

Major and complex options are often shown on just one view of the model. For example, retracts or flaps are often shown on one wing panel with fixed gear or no flaps on the other. This gives complete detailed information to modelers building either configuration. Another example is showing a 4-stroke engine on one sheet, and a 2-stroke engine another.

An example where a top and side view may appear not to match would be when the side view is a true, flat side view on which you build a fuselage side. Now you go to the top view, and it is noticeably shorter than the side view. Why? Because your fuselage side is curved on your final model. Take that fuselage side you just assembled, and place it over the top view, curving it to its final shape. Guess what? It's a perfect match! These views are designed to be exactly right for the specific steps and processes used to build the model. Trust the information provided, and you'll be pleased with your end result.

There's a ton more information I could ramble on about, but these are the main issues that I've learned and, where I spend a good deal of time sharing with consumers, hobby shop owners and technicians alike. Any questions? Drop me an email: Otherwise, go have some fun on the flight line, and put in a nice smooth flight for me, okay?

     -AnnMarie Cross

Reprinted with permission.
March 2000 R/C Report
Editor: Gordon Banks