Q1 Plans Chapter 3 Page 3-9
- Category: Quickie Plans
- Published: Tuesday, 11 November 2008 00:00
- Written by Dan Yager
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The correct set-up is just as important as using the correct tools and materials. Foam is a fairly flexible material and an improper set-up can cause deflection. The foam block should be well supported at each end, so that it doesn’t sag and doesn’t move around while being cut.
You need clearance for the hot wire cutter to pass by the table and the weights used to hold the foam steady.
Foam is manufactured in sizes that are often too small to get a solid core from a single block. It is necessary to use two foam blocks to get the size required for the wing cores. These blocks have to be joined using an epoxy/ microsphere mixture. The hot wire won’t cut through the micro joint, so all of the hot wire cutting is done with the blocks temporarily joined. Nails or blobs of 5-min epoxy are used for temporary foam joints, but the hot wire won’t cut through these. Thus they have to be placed carefully so that the wire doesn’t have to pass through them.
Don’t be overly concerned if you don’t make perfect foam cuts: ridges on the foam core from inadvertently lifting the hot wire off the templates are easily faired in with a sanding block. A less-than-perfect leading edge can be blended in by sanding after the foam core is assembled. Gouges in the foam can be smoothed and filled with dry micro to contour after applying the glass skins. The foam is too expensive to throw away because of a minor gouge.
A finished foam core may warp out of shape after it is removed from the original block. This is due to internal stresses in the foam from the manufacturing process,and is no cause for concern.
A warped core is simply weighted into the jig blocks and shimmed straight. Once the skin has been installed, the foam is held firmly in position.
URETHANE FOAM SHAPING
One of the real treats in the construction of your Quickie will be shaping and contouring urethane foam. Urethane is a delightful material that shapes with ease using only simple tools. A butcher knife, old wire brush, sandpaper, and scraps of the foam itself are the basic urethane working tools. A vacuum cleaner is convenient to have handy since working urethane producee a large quantity of foam dust. The knife is used to rough cut the foam to size. The knife needs to be kept reasonably sharp; a sander or file is an adequate knife sharpener since it’s a frequent task and a razor edge isn’t necessary. Coarse grit sandpaper (36 grit) glued to a board as shown on page 3-1 is used for rough shaping outside contours.
Inside contours or “dishing” is done by using a ragged old wire brush to rough out the bulk of the foam and following up with a scrap foam piece to smooth the surface. The foam scrap conforms to the shape of the surface resulting in a very smooth contour.
Outside contours are roughed out with a sanding block and finished using a foam scrap. Dry micro and flox are used to fill voids and pot fasteners in a number of places. All foam shaping should be finished before any micro filling is done, because the filler is much harder than the foam and this makes smooth contouring very difficult. Your best carving template is your eyeball, an occasional check on the depth of a contour is about the only measurement necessary.
Keep your shop swept reasonably well. The foam dust can contaminate your glass cloth and your lungs. Use a dust respirator mask while carving urethane. Try not to aggravate the better half by leaving a green foam dust trail into the house.
The glass layup techniques used in your Quickie have been specifically developed to minimize the difficulty that glass workere have traditionally endured. Most of the layups that you will do will be on a flat horizontal surface without the molds, vacuum bags, and other special equipment that are common in glass work. The layups that you do will all cure at room temperature, no ovens or special heating is required. If you have suffered through a project that requires you to build more molds and tools than airplane components, then you are in for a real treat.
The techniques that you will use are easy but they still need to be done correctly. 90% of the work that you will do is covered in the next few paragraphs, so make sure that you read and understand this section very well. If you learn these basics, your airplane will be Quickie indeed. If you skip over this information, you will probably end up frustrated.
Step 1: Personal Preparation
Before you get atarted with a layup, plan ahead. Some major layups take several hours and before getting your hands in the epoxy, it’s a good idea to make a pit stop at the restroom.