QuickTalk 27 - Q-TIPS
- Category: Q-Talk Articles
- Published: Wednesday, 30 April 1986 07:11
- Written by Jim Masal
- Hits: 1270
You mentioned a tri-ply cloth used in the Dragonfly. I have used this and other woven industrial fabrics. This is no doubt the Nytex DB 120, Diagonal Bias 12.0 ounce Tri-Axial cloth which is heavy, woven and takes a great deal of epoxy and micro to fill the surface due to the knitted fabrics which protrude. It is not cost effective in the homebuilt marketplace, but some will sell it to you in order to make a killing on your lack of knowledge of this product and its proper use.
Be safe and use only designer selected raw materials.
T. J. Wright, Friedens, PA
ED. NOTE: On close inspection of this cloth and some layups, I noticed some very subtle and small waves in the cloth along its length. This is bothersome as our original instructor in layups, Rutan, seems to take care to stress that orientation of fibers should be as absolutely straight as humanly possible - a straight fiber is stronger than a wavy one.
From Canard Pusher
Getting silicone lubricant (e.g. WD-40) onto any glass surface will absolutely guarantee that you will never be able to get anything to stick to that area again. Epoxy will not stick, nor will primer or paint. In short, you have a major problem on your hands.
From SHAP Talk
Painting fiberglass: If the homebuilder experiences a paint adhesion problem on fiberglass parts, it may be due to silicone contamination. A good solution that may be used to cure the problem is Dupont Fisheye Eliminator. It is available at auto paint stores that sell Dupont finishes and it is conveniently packaged in capsules that are mixed one per pint of finish material. You will discover that the finish flows out better, which leads to a smoother, glossier finish.
From Mitch Strong #2835
I've finished both wings up to the primer in my heated attic over the winter. To keep the dust down, I gray taped an old sheet to the exhaust side of a 20" box fan to form a dust bag. It worked well after I created a "ducted fan" with a large piece of cardboard cut to fit the O.D. of the blades. A fan is also useful for drawing away vapors when epoxying.
For filler I use NAPA brand micro-light with more balloons mixed in for a thicker consistency and easier sanding.
From Mike Peay
When leveling a wing tip to tip with a long plastic tube water level, a few drops of liquid dish soap in the water will take away the surface tension and make both ends of the water column look level instead of a "dish" one end and a "dome" on the other. Any bubbles can be easily floated out one end of the tube. (ED. NOTE: a few drops of India ink or food coloring added to the water also makes it easier to read.)
From T. J. Wright
Do not use wax paper for any laminating. The wax WILL migrate into the epoxy and will NOT be removed during sanding. Instead, use polyvinyl plastic (PVC) sold in big rolls at most building supply or hardware stores.
On areas to be re-laminated under the glass skin, place a Peel-Ply strip on the foam surface then laminate. After cure, remove foam, remove Peel-Ply, and you have a surface ready to glass.
About a month before Rex Taylor went for my jugular over Quigley's Dragonfly canard failure report. I visited him at Eloy, AZ, his home base and learned some interesting things. We got talking about the angle of incidence problems some builders are having. Taylor dragged out a carpenter's level and set it out on a desk. He asked me to make it level and I started stacking business cards under one end until I got it just where I wanted it. Taylor than placed a well-used but high dollar vernier angle measuring device on top of it, whirled the dial and pointed out that I was 34 minutes (a tad over a half degree) off. Now if I happened to be off a half degree in different directions on each wing, I'd have a total error of 1 degree and it would likely be significant.
Now there are those of you out there using cheap $5 levels, string levels, 89 cent bubble levels and God knows what all to do an extremely critical job of aligning your flying surfaces. And then, before you fly, you do not check this piece of work. Ask yourself how much risk you'll take to save a buck here.
Get the best level you can, and the longer the better. When checking a level line, always set your level, adjust your part and then swap ends on the level. The bubble may not read the same from each end so you should at least average the readings from both ends.
From Mike Bergen
I mentioned to you about setting the angle of attack on the wing and canard with a device called an inclinometer. Aircraft Spruce handles the very device I was going to recommend on page 257 of the new catalog. All one needs to do is fabricate a little platform for it to sit on and use it while installing both flying surfaces.
The pedestal/platform mating surface may be constructed using the templates for the wing/canard.
FOAM TEMPLATES AND FOAM CUTTING
From Tom Gordy
My foam cutting templates were made from thin sheet metal found in my hardware store's rain gutter department. Cut out the paper patterns, glue them to the metal (not too much glue or they will pull up and wrinkle as it dries - I used plain old Elmer's Glue-All), cut out the templates, and make sure you carefully file the edges of them smooth so the hot wire does not catch and hang up on you as you cut the foam. I think it is harder to get wooden templates free of splinters, which can cause hangs, and they are heavier - which makes it easier to damage the foam as you mount them to it. Also, they can burn. Transfer all talking numbers to the opposite side of your templates (you will want one left and one right part).
I used two headed 'forming' nails to hold the templates to the foam - not being pushed in all the way made them easier to pull out. Any hole drilled in the templates for the mounting nails should be tight. I drove the nails through the templates into a piece of scrap wood to make the holes. If you place some nails along the template's level line, you will have that line well marked in the foam by the set of holes which will be left long after the templates are removed when you need to refer to it. You might get too busy while cutting foam and forget to mark these important references. The first mounting nail should be inserted at the center of the level line to make one handed adjusting and leveling of the template easier. It is important to hold the foam blocks firmly in place as you are cutting the cores out. I used 15-20 lb. sandbags for this and believe they are a better, more flexible, less dangerous to the foam weight than bricks or scrap metal pieces. They will not cause any damage to the foam if a helpful neighbor happens to toss one on the wrong piece of 'scrap'. I made mine out of the legs of blue jeans - this explains why I wear shorts so much of the time while I'm working on my project.
In general, it is a good idea to label the ends of the cores as they are cut (e.g. lt. wing, BL 50) and put the foam billet back together with the newly cut cores being well protected in the center until you are ready for them later. A few wraps of masking tape and your storage problems are greatly eased.
MISSING KNIFE TRIM TIME
For me, it was hard to catch a layup at knife trim time. Cutting (scissors trim) excess glass off a layup as close as practical to the edge left 1/4" to 1/2" extra glass which I removed from the green cured layup with a Surform shaver (#21-115). By green cured layup, I mean a layup which is hard and dry to the touch, but which is not yet fully cured -- about 12 hours old at 75-80 degrees. In other words, I got a good night's sleep and did it in the morning.
From Jim Masal:
SANDPAPER! Once again (while sanding on a QBAers Q-2), I was abruptly reminded about some of the very basic basics that we fail to pass on. In fact, I remember 3 years ago encountering a fellow working on a Q-2 who actually didn't know how to use sandpaper (if you can imagine that!).
I started out using some old flint and garnet papers that I had accumulated. Bad news. This is not a place to try and save money! Sandpaper is just a layer of abrasive mineral particles glued to paper, but like a knife, the particles will cut faster and longer if they hold their edge sharpness. Flint paper is cheap but does not keep its cutting ability as long as garnet. You'll also lose cutting if the glue doesn't bond well to the particles. I lucked onto a "fire sale" early on where I bought a couple sleeves of 80 and 100 grit aluminum oxide paper. This stuff was the best and is longer lasting, especially if you slap the paper frequently on your hand or a board to shake out a lot of the accumulated dust.
Sandpapers (more technically, coated abrasives) are called open-coat if the surface mineral grains are spaced to cover only a portion of the surface while closed-coat means the abrasive covers the entire area. Closed-coats naturally provide maximum cutting but will clog faster. Paper "grade" or grit refers to the coarseness or fineness of the mineral, ranging from a very coarse 4 1/2 to super fine 600 in common use. "Grit" actually means the number of grains which, when set end to end, would equal one inch.
When I sand, I start with the coarsest grit for the job (36 or 40 is my coarsest), usually taking down gross high spots with the straight or curved Stanley Surform blades (tungsten or regular blade) first. Some of the very best sanding stuff I've found in coarse grades is the aluminum oxide coated cloth used for sanding belts (presumably for floor and commercial uses). This stuff is expensive but try a couple belts and you'll find it worth the money. Belts are in 4-6" widths, just cut 'em up in the pieces you need. Watch this stuff, though, and check your work every few strokes to be sure you don't go sanding through anything important.
After using the approx. 36 grit belt, I go to my 80 or 100 grit paper and then stop for Feather Fill. The body shop boys recommend always folding your sandpaper in thirds with the end thirds over lapping so that the sandpaper won't slip around in your hand.
SANDING BLOCKS: Sandpaper will last longer if it has some sort of backing or block behind it to distribute the abrasive pressure evenly across its face, furthermore, most sanding has to be done with a block of some sort to achieve a good contour. I recently saw a Glassair wing being sanded with a 6-foot long 3x3 rectangular steel tube to which sandpaper sheets had been glued (you can use rubber cement). I've heard also from some Long-EZ guys who believe they are getting better wing contours by using the 18" pneumatic straight line sanders, described here before, but with a twist: they adapt a 1/8" aluminum plate to the sander as a sandpaper backing plate instead of the normal felt or foam pad. The thinking is that if you are bridging two high spots, the soft pad may "give" before you've brought them to level thus leaving some waviness seen after paint. Sometimes I don't want a hard block so I have a hard rubber block (about $2) or I wrap paper around a stiff sponge. I also bought a couple of grit covered foam blocks sold for use in sanding woodwork in the house. Grit's long gone but I wrap my own paper and I like the feel. Also handy: a piece of radiator (or other) hose for curves, a rolled up magazine or cardboard or a deck of cards (push it into the curve then grip the deck tightly and it will hold shape), or back the paper with kid's modeling clay. Visit a good hardware store or auto paint store and take a gander at the sanding tools they offer the professionals.
The object of this exercise is to get the nicest finish you can while minimizing your experience with sandpaper. Start with the coarsest grade first. Use SHARP paper...and don't be slogging away for 15 minutes with a piece of paper that is no longer cutting! Throw it away and stop wasting your time (unless you're a masochist)...and don't throw it away too early either. Pay attention, if dust is still beading up in front of the paper, it's still cutting.
When using a sanding tool, especially a power sander, don't get mesmerized by your work! Frequently pick up the tool and look at your progress so that while grinding away at one trouble spot you don't go right on through the material at the other end of the sander. The coarser your sandpaper, the more frequently you should inspect. Always stay alert, even during this boring job.
Now, a related matter. Ever get itchy after a session of grinding away on the ol' fiberglass? That sensation is caused by microscopic, real glass needles pricking the nerve ending of your skin. Eventually they break off into shorter segments that you can't irritate so easily and get shed. But what about the thousands of these needles that you inhale and wind up sticking in all up and down your respiratory tract? As a former Respiratory Therapist, I am compelled to mention that these things are not so easily removed. Like inhaled smoke particles, much of this glass becomes part of you...forever. (You are what you build, so to speak). Invest $20 in a comfortable mask...and USE it. IF YOU HAVE YOUR HEALTH, YOU CAN ALWAYS MAKE MONEY.
AAMWELL TECHNOLOGY offers both 2 and 4 place intercom systems, which come either as kits or fully assembled ranging from $89.50 (bare bones 2 place kit) to $195.50 (fully assembled 4 place). The company also offers two dual light nav/strobe wingtip systems for $250 and $285 and most recently a single unit strobe for $125.50. For further information, write RTX Ltd., P O Box 20334, Dallas, TX 75220.
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