Q2 Plans Chapter 3 Page 3-3
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- Category: Q-2/Q-200 Plans
- Published: Sunday, 28 May 2006 03:05
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..... UNI cloth has 95% of the glass volume woven parallel to the selvage giving exceptional strength in that direction and very little at right angles to it. .....BID is generally used as pieces which are cut at a 45-degree angle to the selvage and laid into contours with very little effort. BID is often applied at 45 degree orientation to obtain a desired torsional or shear stiffness. UNI is used in areas where the primary loads are in one direction, and maximum efficiency is required, such as the wing skins and spar caps. .....Multiple layers of glass cloth are laminated together to form the aircraft structure. Each layer of cloth is called a ply and this term will be used throughout the plans. .....Marking and cutting the plies of glass cloth is a job that you will repeat often in the construction of your Q2. Glass cloth should be marked, cut, and stored in a clean area with clean hands and clean tools. Glass contaminated with dirt, grease, or epoxy should be discarded. A clean, smooth surface is needed for marking and cutting. The area used for storing and cutting glass cloth should be separated from the aircraft assembly area because otherwise it will be exposed to foam dust, epoxy, and other things which can contaminate the cloth. You will need a good sharp pair of scissors, a felt-tipped marker, a fairly straight board, and a tape measure for marking and cutting. The small amount of ink from marking and numbering plies has no detrimental effects on the glass cloth. .....In each step the size, type, and fiber orientation of each ply is given. Take the list to your glass cutting table, rollout a length of the appropriate cloth, straighten the selvage, mark all of the plies, and cut them. .....Now is a good time to stop reading long enough to go and cut a square ply of BID and see how easy it is to change its shape by pulling and pushing on the edges as shown in the sketches. Cut a square with the fibers running at 45° and pull on the edges to shape the piece.  ..... It helps if you make fairly stralght cuts, but don't worry if your cut is within 1 inch of your mark. As you cut BID, it may change shape, just as the square ply that you are experimenting with does when you pull on one edge. Plies that distort when cut are easily put back into shape by pulling on an edge. Rolling or folding cut plies will help keep them clean and make it easier to maintain their shape. If several plies are called for, it may help to number them before cutting. Save your clean scraps and make an effort to use them for smaller plies, If the cloth is spotted with epoxy, throw it away. .....When cutting long strips or large pieces of 45 degree BID, always roll or fold it so it keeps its shape when handled. When it's applied, it can be set on one end of the part and rolled onto it. If you pick up each end, it will distort and not fit the part properly. .....The fiber orientation called for in each lamination is important and shouldn't be ignored. UNI is characterized by the major fiber bundles running parallel to the selvage and being much larger than the small cross fibers which run at right angles to the selvage. In BID the cross fibers are the same size as those running parallel to the selvage, giving BID an even "checkerboard" appearance. BID is commonly used for plies cut at 45° to the selvage. Your tailor would call this a "bias" cut. The 45° cut makes it easy to work wrinkles out of a ply locally, without having to chase it to the far edge. The 45° cut also makes it possible to make a ply slightly longer than originally cut by pulling on the ends, or wider by pulling the sides. The 45° orientation isn't critical; you don't need to measure it. Your eyeball of a rough diagonal (45° ±10°) is adequate when either cutting or laying up the cloth. EPOXY ..... In recent years the term "epoxy" has become a household word. Unfortunately, "epoxy" is the general term for a vast number of specialized resin/hardener systems, the same as "aluminum" is a general term for a whole family of specialized metal alloys. Just as the "aluminum" pots and pans in your kitchen, the "epoxy" in your Q2 is vastly different from the hardware store variety. .....Epoxy is the adhesive matrix that keeps the plies of load-carrying glass cloth together. Epoxy alone is weak and heavy. It is important to use it properly so that the full benefits of its adhesive capability are obtained without unnecessary weight. A large portion of your education in composite structural work will be spent learning how to get the full strength of an epoxy/glass mixture with the minimun weight. This section will discuss the terminology and techniques for working with epoxy resin and its hardener. .....An "epoxy system" is made up of a resin and a hardener tailored to produce a variety of physical and working properties. The mixing of resin with its hardener causes a chemical reaction called curing, which changes the two liquids into a solid. Different epoxy systems produce a wide variety of solids ranging from extremely hard to very flexible. Epoxy systems also vary greatly in their working properties, some are very thick, slow pouring liquids and others are like water. Some epoxy systems allow hours of working time and others harden almost as fast as they are mixed. A single type of resin is sometimes used with a variety of hardeners to obtain a number of different characteristics. In short, there is no universal epoxy system; each has its own specific purpose and while it may be the best for one application, it could be the worst possible in another use. .....The epoxy systems used in the construction of your Q2 are tailored for a combination of workability and strength, as well as to protect the foam core from heat damage and solvent attack. These systems are very low in toxicity to minimize epoxy rash. The epoxies are not similar to the common types normally marketed for fiberglass laminating. Two different systems are used in the Q2: a normal curing system, and a 5-minute system. The very fast curing (5-min.) system is used much like clecos are used in sheet metal construction (or clamps in woodwork); for temporary positioning. Fiveminute is also used in some areas where high strength is not required, but where a fast cure will aid assembly. .....Safe-T-Pox will cure to a firm structure at room temperature within one day. Complete cure takes 14 days.
..... Any foam bonding where parts are small and the fast cure allows the next step to be done soon. Also used as a temporary joint for jigging.
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