Procedure Manual No. 1

Rib Lacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31 Let’s Tie Some Knots! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36 Inspection Hole Reinforcements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44 Finishing Tapes and Gussets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 Drain Grommets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53 Heat Smoothing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54 6. Control Surfaces & Fuselage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57 Ailerons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57 Tailfeathers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57 Fuselage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59 Final Steps! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62 7. Spraying Poly-Brush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65 First Spray Coat of Poly-Brush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65 Second Spray Coat of Poly-Brush . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68 Revision 21: pg. iii Revision 21: pg. iv POLY-FIBER AIRCRAFT COATINGS Mailing Address: P.O. Box 3129, Riverside, CA 92519-3129 Shipping Address: 4343 Fort Drive, Riverside, CA 92509 Phone (951) 684-4280 Fax (951) 684-0518 • Toll Free: 800-362-3490 COPYRIGHT 2006, Consolidated Aircraft Coatings. All rights reserved. No part of this publication may be reproduced in any form or by any means without permission. 8. Poly-Spray UV Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69 Silver Poly-Spray Performs Two Important Functions . . . . . . . . . . . . . . .69 How about Those Chemical UV Blockers? . . . . . . . . . . . . . . . . . . . . . . . .69 Get Ready to Spray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70 Mixing and Straining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71 1st Coat of Poly-Spray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72 Top Two Imperfections and How to Fix Them . . . . . . . . . . . . . . . . . . . . .73 2nd Coat of Poly-Spray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74 Sanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74 3rd Coat of Poly-Spray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75 9. Color Coats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77 The Basics: Equipment, Cleanliness, and Mixing . . . . . . . . . . . . . . . . . .77 Gloss, Temperature, and Drying Time . . . . . . . . . . . . . . . . . . . . . . . . . . .79 Reducers, Retarders, Accelerators, and Rejuvenators . . . . . . . . . . . . . . .80 Do Not Use These Paints Over Fabric! . . . . . . . . . . . . . . . . . . . . . . . . . . .81 What About Flex Agents? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82 Clear Coats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82 What Paint Do We Recommend? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83 Poly-Tone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83 Polishing Poly-Tone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84 Waxing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85 Taping for Trim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85 Poly-Tone Over Metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85 If You Don’t Want to Use Poly-Tone Over Metal, Then What? . . . . . . . . .86 Using Our Two Polyurethanes – Aero-Thane and Ranthane – Over Fabric, Metal, or Fiberglass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88 Mixing & Thinning Aero-Thane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89 Mixing & Thinning Ranthane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90 Common Aero-Thane and Ranthane Errors . . . . . . . . . . . . . . . . . . . . . . .91 Appendices Appendix A: Ultralight & Very Light Aircraft . . . . . . . . . . . . . . . . . . . . . . .93 Appendix B: Envelopes & Sewing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95 Appendix C: Concave-Bottom Wings . . . . . . . . . . . . . . . . . . . . . . . . . . . .99 Appendix D: Covering Plywood Surfaces . . . . . . . . . . . . . . . . . . . . . . . .100 Appendix E: Airworthiness Limitations . . . . . . . . . . . . . . . . . . . . . . . . .102 Appendix F: Inspecting Fabric a& Coatings . . . . . . . . . . . . . . . . . . . . . .103 Appendix G: Rejuvenating Fabric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106 Appendix H: Dealing with Stains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107 Appendix I: Making Repairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108 Appendix J: Product Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111 Reference Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131 Poly-Fiber STC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131 Poly-Fiber PMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .132 Poly-Fiber Installation Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133 Approved Model List (Aircraft on the STC) . . . . . . . . . . . . . . . . . . . . . . .134 Material Estimates by Aircraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .148 Poly-Fiber Test Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .154 Whenever there’s an important point that needs to be discussed before going on with the job, we’ll pause and take a Coffee Break… Whenever we need to make a short point of information during the project, you’ll see this Note… This means, “Take notice of this!” If there’s a point that’s really important or that deals with basic safety, you’ll see one of these Warnings… It means, “Read and heed, Jim! This is MAJOR important!” Revision 21: pg. v A Better Manual How Tight Should That Fabric Be? Let’s talk about how tightly you should be attaching the fabric. How taut you pull the fabric as you… etc etc. The only authorized heat source for accurate control of the tem- perature transferred to fabric is a CALIBRATED CLOTHING IRON. Period. NEVER APPLY AN IRON HOTTER THAN 250° TO A CEMENTED AREA. DOING SO COULD RELEASE THE SEAM OR THE BOND! We’ve all been frustrated by instruction manuals that don’t instruct, so we tried very hard to create one that instructs, inspires, and entertains. Throughout this manual you’ll see some special little sections that stand apart from the main text. They will look like these: Meet LeRoy… You know LeRoy. He lives someplace out near the airport, and he likes to come around and share his wisdom about cov- ering tube and fabric airplanes. He does this with the greatest of ease, because he’s an expert. Just ask him! There’s a LeRoy at just about every small airport. Why, he’s been covering airplanes for years, and he knows all there is to know about it. He’ll show you his own secret recipes and shortcuts. Shucks, it was good enough for Wilbur and Orville, and that gangly kid from Minnesota… I guess it’s good enough for you. Right? Wrong! You MUST follow the Basic Rules to the letter! Maybe LeRoy used to use his old blowtorch to tighten up his fabric, or maybe he liked to add a little castor oil to his cement before he slathered it on… but you’d better not! You’ll see LeRoy from time to time through- out this manual. He’ll show up whenever we hit a point where there have been some off-the-wall “short cuts” suggested in the past. Look for LeRoy… but DON’T LISTEN TO HIM! About the Other Cartoons… Here and there you’ll see cartoons like this, rescued from pilot training manuals of World War II. For those of you who were there, we think they’ll be delightfully nostalgic. For younger builders, they’re a humorous glimpse into what was perhaps the richest, most patriotic part of Ameri- ca’s past. Revision 21: pg. vi LEROY SAYS you need to buy at least a gross of sandpaper to have a good dope and fabric job. NOT SO. You can do gorgeous work in preparing your Poly-Fiber covering job for a big trophy at Oshkosh with an iron, and skip lots of sanding. How to Speak “Poly” Here’s a quick “dictionary” of some of the products we’ll be talking about. POLY-TAK This is our own special proprietary fabric cement. It’s used to cement fabric together, and to cement fabric to the airframe. POLY-BRUSH This is our fabric sealer. It’s used for closing the “pores” of bare fabric and prepare it for subsequent coatings. It’s also used to attach finishing tapes. POLY-SPRAY Applied just before the final color paint, this silver coating protects the fabric against ultra violet (UV) rays. POLY-TONE Here’s the final color paint. It has a nice satin-gloss finish. Used over fabric, it is easy to repair. Not the best when used over metal, but it works OK with proper preparation. VINYL This is the basic stuff all four products above are made from. All four are chem- ically compatible, meaning they won’t separate over time. MEK The universal “fixer” solvent that cuts the four vinyl products above. It’s used to “unglue” fabric-to-fabric and fabric-to- airframe bonds. It’ll also remove any of the four products at any point in the process, and it’s handy during repairs, too. However, it’s too harsh to be used as a reducer. R 65-75 REDUCER (Thinner) The stuff used to thin Poly-Brush, Poly- Spray, and Poly-Tone at “normal” tem- peratures, between 65 and 75°F. RR 8500 REDUCER Serves the same purpose as 65-75, but works at temperatures above 85°F. AERO-THANE If you want a high-gloss high-tech “wet- look” finish, this is the colored paint to use. It’s a two-part product that uses it’s own U-865 catalyst and UE-820 reducer. MEK doesn’t cut it. It works great over fabric and metal, but it’s more difficult to repair than Poly-Tone. RANDOLPH RANTHANE Ranthane is an addition to the Poly-Fiber STC from the our sister line of Randolph Products. Like Aero-Thane, Ranthane is a two-part polyurethane, but it has it’s own AU-2X1 catalyst and G-4200 reducer. It also works great over fabric, primed metal or composites. DOPE Not understood in polite Poly. This word does not exist in our language. There is no dope in Poly-Fiber. EP-420 EPOXY PRIMER This is our two-part catalyzed epoxy primer for use on steel and aluminum. It’s the only consistently successful primer you can use in the Poly-Fiber system. Famil- iar zinc chromate and other one-part primers will peel off after contact with the Poly-Fiber products. Not a good idea. EV-400 EPOXY VARNISH Serves the same purpose as EP-420 above, except this one’s for wood. BR-8600 BLUSH RETARDER Used to slow down the drying time of our coatings to reduce the possibility of “blush” in high-humidity environments. It also makes Poly-Tone paint glossier. Revision 21: pg. vii Revision 21: pg. viii Revision 21: pg. 1 1. Getting Ready The Goal of This Manual We hate to see builders shy away from fabric-covered aircraft projects because they don’t think they can handle the covering and finishing. They’re depriving themselves of a very satisfying experience, and for no good reason. Fabric covering is not hard to do. Today’s methods and materials are huge improvements over what was available back in the ‘30s. All it takes today is careful work and some patience. There’s no magic required. Really. This manual can take even a complete novice through the entire process of cov- ering a newly-constructed homebuilt or re-covering a restored classic. The steps are the same. In either case, we’ll assume you’re familiar with the construction of the aircraft you’re covering. If you don’t really know your way around your air- craft, we strongly suggest you get some experienced help before you begin. The Poly-Fiber System Certified Aircraft and STCs The Poly-Fiber STC (Supplemental Type Certificate) SA1008WE allows you to replace the original covering that was on your aircraft when it rolled off the assembly line, probably Grade A cotton and cellu- lose dope, with the Poly-Fiber system. It does not license you to get creative and depart from this manual in any way. In order to fly a safe and legal aircraft, you must follow these Basic Rules. The Basic Rules For certified aircraft, you must follow these rules without substitution. For experimental aircraft, we encourage you to stay with these rules for a safe cover job with proven performance.  Products applied to a certified air- craft must have a Parts Manufactur- er Approval) PMA. Poly-Fiber fabrics, tapes, cements, coatings, and paint all have PMA.  You must use only Poly-Tak, Poly- Brush, and Poly-Spray. You can’t use any amount of either nitrate or butyrate dope in the build-up process.  You must use only Poly-Tone, Aero- Thane, or Ranthane topcoat paint over fabric components. Poly-Tone, Aero-Thane, and Ranthane have a PMA and have established track records over Poly-Brush and Poly- Spray. Using any other topcoat paint voids the STC.  You must heat tighten with a cali- brated household iron only. Heat guns may not be used.  You must not cover critical inspec- tion ports. For example, some air- craft have inspection ports in the aft portion of the wing, aileron, or flap wells that allow inspection of the spar. These holes must not be per- manently covered. If in doubt refer to the original aircraft maintenance manual. SUBSTITUTIONS WILL VOID THE STC AND YOUR AIRWORTHINESS CERTIFICATE IF DISCOVERED BY A SAVVY INSPECTOR AT ANY TIME DURING THE SERVICE LIFE OF YOUR AIRCRAFT. DON’T RISK IT! When you have finished your re-cover job, an A&P with an IA must complete an FAA Form 337 to certify that the air- craft was re-covered according to the Poly-Fiber STC. He must also make the appropriate entries in your logbook. A list of the aircraft eligible for re-cover- ing under the Poly-Fiber STC appears in the back of this book. If your certified aircraft is not included (but most have been during the 40 years the STC has been in effect), you can have it added to the Approved Model List on page 134 of this manual. A Poly-Fiber installation report form for adding aircraft not on the AML is included in the back of this manual on page 133. An A&P can fill this out and mail it to us for processing. Amateur-Built Aircraft If, on the other hand, you’re covering or re-covering an amateur-built aircraft with an Experimental Airworthiness Certificate, our STC doesn’t apply as gospel. However, it’s a good idea to follow the steps in this manual just as though you were working with a certified air- craft. AC 43.13 can also serve as an excellent guide. You can get a copy of it from one of the homebuilders’ supply companies. Simply passing an airworthiness inspec- tion is no guarantee that what you have done is safe. Don’t second-guess the experts. Follow the instructions carefully and completely. The Fabric to Use Poly-Fiber Heavy and Medium fabrics are manufactured under our PMA and are included in our STC. Remember, you MUST use either our Heavy and/ or Medium fabrics to comply with the STC. Both of these fabrics are marked with a stamp like the one shown here. These stamps appear on our fabrics and are a sure-fire way to identify a genuine Stits Poly-Fiber job. Our Heavy and Medium fabrics may be mixed or matched on every aircraft included on our STC. UNCERTIFIED LIGHT is an uncertified fabric and is not approved for certified aircraft. It is recommended for covering plywood surfaces on any aircraft, certified or uncertified. It may be used for any uncertified ultralight. UNCERTIFIED LIGHT fabric is not stamped. We publish a Fabric Product Data Sheet (currently 2004-1) that presents and explains test reports on all three of our fabrics. We’ll be happy to recommend a fabric style to fit your airplane. Just call our Poly-Fiber Tech Support Line, 800- 362-3490. Health Issues Protect Your Skin! Serious allergic reaction to some chemi- cals can show up years after exposure to them, so protect yourself now. Start with one of the barrier hand creams, like Invisible Gloves, available from all the supply houses. Then top that off with some of those dis- posable latex surgical gloves. They’re cheap so you can don new ones whenever solvents begin attacking the ones you’re wearing. 1. Getting Ready Revision 21: pg. 2 POLY-FIBER ACFT. MEDIUM - 2 F.A.A. P.M.A. 2.6 oz./sq. yd. Over 102 lb./in. Protect Your Lungs & Body! Some of the materials you will be using can do nasty things to you if you inhale them for any length of time. The first thing you should buy is a good, effective respirator. Don’t begin your project without one! Those paper masks won’t do. You need the real thing, one rated for lacquers and enamels. Check with homebuilders’ supply companies. They have respirators in their catalogs. You might even find a local source in your yellow pages. If you feel yourself getting nauseous while working with solvents, wear a respirator rated for organic solvents. Wear a Tyvek spraying suit, or old clothes with long pants and a long-sleeve shirt. If you spill solvent on yourself, remove the clothes, wash your skin well, and put on fresh work clothes. Wash the first outfit promptly. Protect Your Eyes! At some point in your project you’re bound to spill or slosh or spatter something. Wear safety goggles in any situation where that might occur. Don’t take chances. Fire Prevention Work in a Well-Ventilated Area Some of the products used in the Poly- Fiber system are highly flammable! While they are being used, potentially explosive vapors accumulate. Make sure there are no open flames, such as gas water heater or furnace pilot lights, any- where near your work area. Outlaw all smoking. Lay down the law to visiting kibitzers. Be aware that even a sparking electric motor or a light switch could trigger a no-fun afternoon. Seek out all potential sources of flame or spark. Have the right kind of fire extinguisher on hand, one designed for petroleum fires, and make sure it is fully charged. Under certain circumstances, especially in warm weather with low humidity, the action of sanding or spraying can generate static electricity. When this static charge is transferred to the fuse- lage or other part, the resulting spark could ignite solvent vapors explosively. Ground the structures being sanded or sprayed. Some builders even ground their spray guns. 1. Getting Ready Revision 21: pg. 3 There’s a right way and a wrong way to dress for spraying. Can you tell which is which up above? A Practical Work Area Make sure you have enough room to work. You not only need room for the fuselage, wings, and other structures but you also need plenty of room to walk and work around them without knocking things over or backing into fresh paint. Basements are poor choices due to lack of ventilation and potential fire hazards. Not only that, but the sol- vent vapors will rise right up in to the house above. Garages are better. Empty hangars are best. Just make sure you have plenty of room and that the area is as clean as you can make it. Dust and junk floating in the air will wind up in your nice new finish, guaranteed. Ventilation fans are very desirable. They will help with vapors, sanding dust, and spraying mist. Under no circumstance should you work in a closed room with no ventilation! During the sanding it will occasionally be necessary to flush the surface with water. That means the floor of your work area should be able to stand getting wet. It also means you’ll need a source of running water within hose distance. Atmospherics and Spraying In a perfect world, your work area would always remain at 77°F with 0% humidity, the accepted laboratory standards. Fat chance. The best tool you have for climate control is your calendar. Temperature. Remember: the glossiness of a paint finish is determined by drying speed; the drying speed is determined by temperature. The slower paint dries, the glossier it becomes. As the temperature goes up, drying time goes down. In a perfect world, you’d always spray at 77°. If the temperature is 87°, the drying time will be cut in half. At 97°, the drying time is even shorter. If the temperature is 67°, the drying time is doubled. At 57°, though, drying time may be endless. Humidity. The ideal humidity for spray- ing is anything between 0% and 70%. Since there are lots of places that never see humidity as low as 70%, we need to look at what humidity does to coatings. As an aircraft coating dries, the rapidly evaporating solvents lower the tempera- ture at the surface. Any water vapor in the surrounding air condenses on the surface. If the humidity is 80% or more this condensed water vapor gives the coating a milky appearance called blush. It also weakens the coating. Blushed coatings MUST be wiped off with some MEK or reducer and resprayed. If you are stuck with high humidity, you can still spray with good results by using blush retarder. This is a special solvent that slows down the drying of the coat- ing, therefore minimizing the chance of blush. Face it: if you spray on a 95° day with the humidity at 99%, you’re going to have problems. Period. Use common sense when spraying. Always wait for moderate temperatures and the lowest humidity. If you live in a normally hot humid area, make sure you have lots of blush retarder on hand. Work in the cool of the early morning, or wait until a front has just blown through. Don’t wet the floor in an attempt to keep dust down. You’re just increasing the humidity. Sweep and vacuum the floor thoroughly before spraying, and give the dust in the air plenty of time to resettle. If you want to wash the floors, let them dry for a few days before you start spraying. 1. Getting Ready Revision 21: pg. 4 Tools You’ll Need Let’s Start With an Ideal List • Fuselage holding and turning jig. We’ll talk about this in a minute. • Sturdy sawhorses, about 3' high; pad the tops with carpet scraps; great for wings and tail surfaces. We’ll go into detail about this later. • A nice big sturdy snag-free table will make handling and cutting fab- ric much easier. • Drop cloths to protect floor, cover airframe parts, etc. • An electric clothing iron. Don’t use your wife’s! • A small “sealing” iron. Great for tapes, patches, and hard-to-reach areas. • Thermometers to calibrate irons. • Heat sink compound. • An effective respirator, plus extra replacement filters. • Brushes: 1˝, 2˝, 3˝, and 4˝. • Glue brushes, 1 ⁄2˝ wide (acid brush- es are good). • Sandpaper: 400-grit wet or dry. • Two 12˝ straight and two 12˝ curved rib lacing needles. • Sharp scissors; polyester fabric dulls them quickly, so buy several pairs of cheap ones. • Pinking shears. Buy a good pair and wear them on a cord around your neck while using them; if you drop them, they’re ruined. • Sharp X-ACTO or other knife. • Paint spray gun and accessories. • Cotton rags. Do NOT use shop rags; they aren’t clean enough and resid- ual silicon will ruin your work. • Paper towels. • Scotch-Brite pads, ultra fine. • Single-edge razor blades. Big box. • Chalk snap line. • Measuring tape. • Paint stirring paddles. • Paint filter cones, 60x48 mesh. • Soup ladle. • Lots of clean soup and coffee cans with tight lids. • Small wide-neck container to use as a glue pot. • Craft masking paper (don’t use newspaper). • Six spring clamps with 2˝ throats - for holding fabric. • Wooden spring clothespins. Great for fabric work. • T-head pins. • Tack cloths - for cleaning just before painting. Fuselage Holding & Turning Jig You can make a simple jig from two-by- fours, as shown here. The center square of the two-by-four “tic-tac-toe” grid bolts to the front of the fuselage using the engine mount bolt locations. Make the legs long enough for the fuselage to sit level with the tail resting on one of your sawhorses. You and your helper can then turn the fuselage whenever needed. 1. Getting Ready Revision 21: pg. 5 About Spray Guns Don’t skimp here! After all your careful and patient preparation, this is where “the rubber meets the road.” You can ruin your entire job by trying to pinch pennies and using “bargain” spraying equipment. Don’t do it. You’ll hate yourself. Most spraying is done with a compressed air system capable of at least 40 pounds of pressure AT THE GUN. Measurements taken at the compressor tend to be high- er than the actual pressure delivered at the gun itself. Don’t get fooled. If you use a compressed air system: • You must have filters and a water trap on the air line. • Cleanliness is everything. The spray gun must be disassembled and thor- oughly cleaned after EACH USE. Borrowed guns are never clean enough, and rented guns are usually junk. • Pressure pot lines become coated inside with whatever’s been sprayed. Solvents in subsequent spraying can loosen this old material which then contaminates your job. Replace pres- sure pot lines often. The newer turbine-powered high- volume, low-pressure (HVLP) sprayers are terrific. They’re expensive, but well worth it. Consider buying one with a few friends or have your club or chapter buy one for everyone to use. When you fac- tor in the cost of the compressor, tank, lines, filters, water traps, and standard guns of a compressed air system, the cost of an HVLP isn’t really that high at all. And the HVLP systems are self contained, more or less turnkey. All you need is 110 volts. Use two lengths of hose with turbine- powered HVLP systems. HVLPs heat the air delivered to the gun, sometimes up to 90°. The extra length of hose solves this problem. Regardless of the system you use, use the needle, aircap, and nozzle combina- tion recommended by the manufacturer for the type of paint you’re spraying. You’ll need one combination for Poly- Brush, Poly-Spray, and Poly-Tone, and probably a smaller one for enamel and urethanes. Be sure to read the instruction very carefully. Sorry, but those inexpensive airless sprayers designed for latex house paint won’t work for aircraft. Materials You’ll Need We’ll use a J-3 Cub as our example. Naturally, your list depends upon what you’re covering, and you can scale things up or down as needed. Here’s our list. • 45 yards of Poly-Fiber Med-2 fabric • 1 roll of 1˝ Med-2 finishing tape • 7 rolls of 2˝ Med-2 finishing tape • 2 rolls of 3˝ Med-2 finishing tape • 1 roll of 4˝ Med-2 finishing tape • 1 roll of 4˝ Bias finishing tape • 1 roll of rib lacing cord • 2 rolls of 1 ⁄2˝ reinforcing tape • 2 rolls of inter-rib brace tape • 1 roll of cloth anti-chafe tape • 100 plastic drain grommets • 30 inspection rings 1. Getting Ready Revision 21: pg. 6 • 30 inspection ring covers • 1 gallon Poly-Tak • 10 gallons Poly-Brush • 11 gallons Poly-Spray • 6 gallons Reducer • 10 gallons Poly-Tone color Other Things You Should Know There’s No Dope in Poly-Fiber! The term “dope” refers to cellulose-based coatings, and goes back to the earliest days of aviation. Nitrate dope was first used, then was gradually replaced by buty- rate dope during World War II. Because butyrate was somewhat less flammable than nitrate, it soon became the predom- inant product used over Grade A Cotton and Irish Linen. Heat-tightened polyester fabric was intro- duced in the late ‘50s. This fabric was a big time saver when it was glued rather than sewn to airframes before tightening. Ceconite soon became the predominant polyester covering system, and flammable nitrate dope was resurrected as an initial coat over the slick polyester fabric. Butyrate dope would not stick to raw Ceconite, so a combination system of nitrate/butyrate dope with Ceconite was introduced in the ‘60s, and remains unchanged today. By the early ‘60s, Ray Stits had designed, produced, and kitted 16 original sport aircraft. He’d used nitrate and butyrate dope most of his professional life, even though he knew they had serious draw- backs when used with either cotton or Ceconite: • Dope burned readily. • Dope shrank over the years, even “non-tautening” dope. • As dope shrank, it delaminated from polyester fabric and deformed light- weight structures. • Dope could become brittle, crack, and “ringworm” within years. • Dope was extremely sensitive to humidity in application. In 1965, Ray introduced a whole new process that started with his own spe- cially-designed polyester fabrics. The Stits Poly-Fiber system was similar to the nitrate/butyrate/Ceconite system in the initial step of cementing rather than sewing of fabric to the airframe. However, there the similarities ended. In fact, there is no dope in Ray’s system. All the liquid products in the Poly-Fiber system are made from vinyl, not from cellulose dope. All the reducers and other coatings are also from the same chemical family, so they all “melt” together. Chemical fire suppressors have been intro- duced to insure that the system does not support combustion. Vinyl has real advantages over dope: • Poly-Fiber vinyl coatings never shrink or make fabric get tighter. • They remain flexible, similar to the vinyl on the dashboard of your car. • They don’t support combustion. • The are easily removed from the fabric with MEK, which makes repairs a snap. The Poly-Fiber system was awarded its STC in 1965. Forty years of service expe- rience have proven its ease of application and longevity. 1. Getting Ready Revision 21: pg. 7 Notes Revision 21: pg. 8 Revision 21: pg. 9 Removing Old Fabric Old fabric should be removed with care. Use razor blades or an Exacto knife to cut the old fabric away, and if necessary, soak cemented areas with MEK to loosen the old cement. Take care not to splash MEK into your eyes or onto your skin; wear protective equipment and goggles. Cut old rib laces before pulling fabric from ribs. If rib rivets are installed, carefully drill them out, insuring that the drill does not slip and damage ribs. If Martin or Cessna fabric clips were used, do not rip the fabric off of the ribs without releasing the clips, or severe damage can result to thin aluminum cap strips. Note positions of inspection rings, fairleads, and drain grommets. A photographic record of the old installed fabric is always helpful. Take Your Time The hours you spend preparing for the minutes you’ll spend spraying will bring you years of enjoyment. Keep that in mind. There is no shortcut to thorough, meticulous preparation. The Right Stuff: Epoxy Whether you’re preparing a steel, alu- minum, or wood structure, do not use any of the familiar one-part zinc chro- mate primers or “spar” varnishes, the type you find in hardware stores. The fabric cements and dopes used in cov- ering aircraft will wrinkle and lift them. Use only two-part epoxy primers or var- nishes. They are unaffected by cements and dopes. Two-part epoxy products may also be sprayed right over old zinc chro- mate or varnish for a safe attachment surface and additional protection from the elements. Wood Surfaces Dry-sand old flaking varnish scale. You needn’t remove all the old varnish, just the loose parts. After sanding, wipe the surface with Poly-Fiber C-2210 Paint Cleaning Solvent to remove any grease and contamination. Then wipe with a clean dry rag. Now apply Poly-Fiber EV-400 Epoxy Varnish directly to the surface. Use our E V - 4 1 0 C a t a l y s t , a n d t h i n a s instructed with E-500 Epoxy Reducer. Steel Tubing If you are re-covering a tube-and-rag air- plane, you must first remove ALL the old fabric. Once you do that, you’ll be pre- sented with tubing structures loaded with old primer and cement. There may also be some rust. If the rust is extensive, you are probably facing some metal repair. Examine the structure carefully, marking areas that will need fixing. Make all needed struc- tural repairs now, replacing damaged tubing or other members in accordance with accepted standards and practices. 2. Airframe Preparation Now you must remove the old cement, paint, primer, and rust WITHOUT pitting or damaging good metal under it. The best way to do this is by blasting it with one of the many media available. Test a painted tubing scrap first. Find the combination of air pressure and media that will remove the paint and leave everything else. Once the structure has been repaired and stripped, the metal must be protected as soon as possible. Letting more than an hour or two go by between blasting and priming invites new rust to begin forming. Be sure to have everything you need – cleaner, primer, catalyst, reducer, spray equipment, and spraying area ready to spray – BEFORE you start blasting. Immediately before priming, wipe the bare areas with Poly-Fiber C-2200 Metal Surface Cleaner to remove all traces of oil, grease, and contamination. Wipe dry with a clean rag, NOT with a shop towel. Finally, prime with Poly-Fiber EP-420 Epoxy Primer. Use EP-430 Catalyst, and thin according to the directions with E-500 Epoxy Reducer. If the metal is in good shape, just deal with the few spots of rust and let it go at that. If the areas are small, you can remove them with dry sandpaper and elbow grease. You need not remove all the old paint and/or primer from the rest of the structure. Just before priming, wipe the entire structure with Poly-Fiber C-2200 Metal Surface Cleaner to remove all traces of oil, grease, and contamination. Wipe dry with a clean rag. Finally, prime with Poly-Fiber EP-420 Epoxy Primer. Use EP-430 Catalyst, and thin according to the directions with E-500 Epoxy Reducer. This two- part epoxy primer will encapsulate any old paint and primer, giving you a safe, sound surface to which new coatings will safely adhere. Fiberglass Many fiberglass parts are pretty rough. Fill big holes or seams with SuperFil, our epoxy filler. Sand until smooth with 180-grit sandpaper. Fill pinholes with our UV Smooth Prime. Apply in light coats with a fine cell foam roller, or spray it on. Dry sand with 320- grit until smooth. Once the UV Smooth Prime has dried for 4 days, spray our white EP-420 Epoxy Primer to seal the surface. Poly-Tone or Aero-Thane can then be sprayed over the primer. If you are using Poly-Tone, spray it directly into the tacky EP-420 for best adhesion. See the section on Painting Poly-Tone for more on this. Aluminum Old Aluminum After stripping, inspect carefully for corrosion. If there is any corrosion present, it all must be removed before you go any further. Use fine sandpaper (not emery), Scotch-Brite pads, or alu- minum wool. Do NOT use steel wool or a steel brush! These just introduce tiny bits of steel into the aluminum which will promote even worse corrosion. Avoid blasting. It is very hard on alu- minum sheet. 2. Airframe Preparation Revision 21: pg. 10 Old aluminum must now be acid etched, treated with a conversion coating, and then primed for best results. Thoroughly wash all the aluminum parts with E-2310 Phosphoric Acid Etch and Brightener, diluted with two parts water. Use an ultra-fine Scotch-Brite pad. Rinse thoroughly with clean water to insure that no etch is trapped in seams or under rivet heads. For best results, blow seams dry with compressed shop air nozzle. Next wash with E-2300 Conversion Coating, diluted with two parts water. Wash and keep wet with a sponge for at least five minutes. Rinse with clean water and allow to dry completely. Prime with epoxy primer. We recommend using EP-420 White Epoxy Primer over aluminum. Remember that there are three components to our epoxy primer systems; you must also have EP-430 Catalyst and E-500 Epoxy Reducer to get the job done. See a complete explanation of epoxy primer in our Product Profiles section at the end of this manual. New Aluminum There is no need to use Phosphoric Acid Etch on new aluminum. First wipe the new aluminum surface with MEK, Acetone, or Toluene to remove packing oils. If the new aluminum has an Alclad surface, gently scuff the entire surface with an ultrafine Scotch-Brite pad or 320-grit sandpaper to impart some tooth adhesion. Be careful not to leave any noticable scratches in the Alclad, go easy. Next wash with E-2300 Conversion Coating, diluted with two parts water. Wash and keep wet with a sponge for at least five minutes. Rinse with clean water and allow to dry completely. Prime with epoxy primer. See the direc- tions in the paragraph above on Old Aluminum. Dealing With Dents and Imperfections Nothing looks worse than a new cov- ering job with dents and old damage showing through. Maybe you taxied into a hangar door, or a hail storm tattooed your airplane, or maybe there are some low spots in those plywood fairings. Take the time now to smooth or correct them. Once the new fabric is installed, it’s too late. Here are some suggestions. Replace Badly Damaged Areas If the damage is severe or extensive, you might be better off just biting the bullet and replacing the material. The time you take installing nice smooth new aluminum or plywood will pay for itself later in the praise your airplane will get from jealous onlookers. Fill With Poly-Fiber’s SuperFil SuperFil works great on wood, fiberglass, steel, and aluminum. It really grips the surfaces, and stays flexible enough over its service life to keep from cracking. DON’T USE BONDO! Bondo is heavy! Bondo will shrink over time and separate from the surface. Bad news. And Bondo is made from polyester. You need epoxy products. Apply SuperFil with a squeegee, and 2. Airframe Preparation Revision 21: pg. 11 work it into the basic shape you want. After 12 hours, SuperFil will be ready to sand and smooth. Apply primer to SuperFil used on aluminum; apply var- nish to SuperFil used on wood. Make a point of reading the SuperFil instructions. Remember to thoroughly stir each of the two parts before mixing them. Mix them carefully, by either weight or volume. “TLAR” mixing (“That Looks About Right”) doesn’t fly when you’re working with epoxy. Use Polyester Padding Poly-Fiber polyester padding is a special thick “cloth” that hides minor dents and glitches. It is most commonly used on wing leading edges, and is sandwiched between the leading edge aluminum or plywood and the Poly-Fiber fabric itself. The padding fills the dents and levels the surface. There are a few drawbacks. Padding can collect Poly-Brush in areas where it tends to pool with gravity. The result is a permanent mottled effect. Also, you must not construct any cemented seams over padding. We’ll get into cemented seams a little later. If you use leading edge padding, you must use a sewn seam over it, or use an envelope. More about these later. Only Poly-Fiber polyester padding is compatible with the Poly-Fiber system. Don’t substitute felt or some cheap padding purchased from a fabric store. Many non-Poly-Fiber paddings will melt or produce strange results when they come into contact with Poly-Tak and Poly-Brush. You don’t need this. Cement the padding around the perime- ter of the leading edge fairing with Poly-Tak. Then cover the rest of the wing normally. Inter-Rib Bracing This bracing keeps the ribs straight up and down when the fabric is heat tightened over them. It is nothing more than twill tape to provide stability for the ribs while covering. As the drawing shows, the tape is looped around the top capstrip of the first rib halfway between the front and rear spars. Then it loops the bottom capstrip of the next rib, and then back to the top capstrip of the next rib, and so on until the whole wing is braced. When complete, the inter-rib brace looks like a series of “Xs” in each rib bay. It is important to only loop the inter-rib brac- ing without tying it to each rib, except at the very ends. If you tie it, the ribs won’t be able to move and readjust their posi- tions during the tightening process. This bracing is not removed. Anti-Chafe Tape Any sharp edge or structural feature that might cut or poke through the fabric should be covered with cloth sticky-back anti-chafe tape. It is self adhesive and easy to use. 2. Airframe Preparation Revision 21: pg. 12 There’s no hard and fast rule about where to put the tape. Obviously, it should go over rivet heads, metal seams, and sharp edges that could cut the fabric. You don’t need it over smooth ribs or well-prepared wood or aluminum. Let your sense of touch be your guide. If you feel something sharp or pointy, put some tape on it. CAUTION: Don’t go crazy with anti-chafe tape and make your airplane look like the mummy’s revenge. Keep tape off places where you need a good Poly-Tak bond. Wherever you cement something to anti-chafe tape, the bond is only as strong as the sticky adhesive on the underside of the tape! NEVER use paper masking tape, duct tape, or aluminum-faced tape instead of genuine Poly-Fiber anti-chafe tape. All of these retain water and will bring about rust or corrosion on metal under them. Also, paper masking tape turns brown with age, and will show through light-colored paint. Very ugly! 2. Airframe Preparation Revision 21: pg. 13 Notes Revision 21: pg. 14 Revision 21: pg. 15 From this point on you will be using your iron to install fabric and smooth out any wrinkles that appear. Now’s the time to prepare your iron for use. The only authorized heat source for accurate control of the temperature transferred to fabric is a CALIBRATED CLOTHING IRON. Period. Heat Guns? No! How come you can’t use your heat gun? Because there’s no way to calibrate it, and the temperature changes as the gun’s distance from the fabric changes. You run a tremendous risk of permanently loos- ening your fabric and ruining all your nice work. Leave the heat gun for removing paint and for emergency corn popping. The Right Iron Avoid Any Iron With an Automatic Shutoff! Understand that individual irons vary. It helps if your iron is rated at 1100 watts or higher. There may be some non-load carrying areas that can’t be reached with a stan- dard size iron, places where exact fabric tension is not important as long as the wrinkles are removed. For these areas we recommend a small 165-watt heat sealing iron. It’s available through Poly-Fiber distribu- tors. It should be calibrated the same as your large iron and used only to smooth the edges of trim tapes and patches and in areas not subjected to flight loads because these little irons can’t maintain their temperature in contact with a large heat sink area. Why Calibrating Your Iron Is So Important Polyester fabric does different things at different temperatures, and we take advantage of this to make the fabric do what we want when we want it.  225° is used to smooth the edges of finishing tapes and patches, heat form fabric around corners, and remove fold creases.  250° is used for the initial tightening and to smooth wrinkles from seams before final heat tightening.  350° is for the final tightening.  Above 350° the fabric gets looser, permanently looser! 3. Tune Up Your Iron! At about 375° polyester filaments start to thermo-soften and lose all measurable tension. At 415° they start to disintegrate. Not good at all. You can see why calibra- tion is so important. Don’t just guess or assume your iron’s dial is accurate. How to Calibrate Your Iron Correctly You need an accurate thermometer with a stem that can be placed in contact with the plate of your iron, plus some silicone heat sink compound, available from Poly-Fiber distributors. An accurately calibrated low-cost glass thermometer is available through Poly- Fiber distributors. A deep fry, candy and jelly thermometer, available at hardware stores, is another economical choice. Remove the protective glass shell, check the calibration in boiling water (212° at sea level), then secure the cali- bration card with cement.  Put a nice big glob of heat sink compound on the bulb end of your thermometer.  Build a 1 ⁄2˝-thick stack of dry paper towels on your workbench.  Lay the thermometer bulb in the center of the paper towels. Place your iron on top of the thermometer bulb and the towels. Make sure the bulb is in contact with the plate of the iron.  Advance your iron’s heat control knob and watch the thermometer. Give your iron time to change tem- perature, and give the thermometer time to react.  When the thermometer has settled down at 225°, mark your iron’s dial. Use something visible and removable. You’ll probably have to change your calibration marks at some future time.  Now do 250° and 350°. Your iron should hold the desired tem- peratures, ±10°. It should be recalibrat- ed at the start of each new covering pro- ject or if it is dropped. Always use the same extension cord. SUPER IMPORTANT! After calibrating is finished and your iron has cooled, carefully remove all traces of silicone heat sink com- pound from the sole of your iron! The latest and quickest (although more costly) way to calibrate your iron is with a temperature sensing gun, avail- able through Poly-Fiber distrib- utors. You simply point the laser beam at the sole plate of the iron for a quick and accurate read- ing of the iron’s tempera- ture. Then record 225°, 250°, and 350° temperatures on the tape-covered dial. 3. Tune Up Your Iron! Revision 21: pg. 16 Revision 21: pg. 17 Cemented Seams Our fabric is attached with Poly-Tak cement, using cemented seams. A cemented seam is a place where Poly- Tak is used to join two pieces of fab- ric where they contact an airframe structure, as when covering a wing, for example. There is virtually no sewing to do, unless you want to. In our STC, cemented seams are approved for any airspeed and any wing loading if you follow these rules: • All seams require at least a 1˝ over- lap of the two pieces of fabric. • Wing leading edge seams require a 2˝ fabric overlap. • Wing trailing edge seams require a 1˝ fabric overlap. • All cemented seams must be covered with a finishing tape at least 2˝ wide. You can use wider. • All cemented seams must lie over a structural part of the airplane, and that structural part must be at least as wide as the cemented seam. So what’s a structural part of the airplane? On wings, it’s the leading edge, trailing edge, the tip bow, and the butt rib. Ribs are not considered structural. On control surfaces, it’s leading and trailing edge or the perimeter tubing. On fuselages, it’s the longerons or main cross tubes that are part of the load- bearing structure. Wooden formers or stringers that are there just to give shape aren’t considered structure. All fabric edges that will over- lap as part of a cemented seam should be cut with STRAIGHT SCISSORS. Here’s a great way to make a sharp cut with no loose thread or ravels: 1. Draw your cut line with a #2 lead pencil. 2. Coat the line with a thin coat of Poly- Tak Cement. 3. When dry, cut with straight scissors. 4. Voila! A crisp, sharp cut! 4. Attaching the Fabric NOTE: The structure over which these seams are created has been left out of the illustrations to make them easier to understand. The Cementing Process Use a soup can for the Poly-Tak with a 1˝ wide gluing brush. If the Poly-Tak gets thick in the soup can, add pure MEK to get it back to the original consistency. If you spill or have a messy area with excess ooze or drips, clean it up with MEK. MEK will clean up even dried Poly-Tak. Poly-Tak cement dries fast… real fast. In hot weather it can dry in five minutes. It normally dries in about 15 to 20 minutes. Because Poly-Tak dries so fast, you have to brush it on a little at a time, then stop and press the fabric into it while it’s still wet. Normally, you only cement about 12˝ to 18˝ at a time to keep it from dry- ing. The trick is to keep the cement liq- uid when the fabric is placed into it. If it dries, that’s no good. You must do it again. The best cement bond is accomplished by brushing about a 1˝ wide strip of wet Poly-Tak onto the area where fabric is to be attached, then immediately laying the fabric wrinkle-free into the cement. Force the cement up through the fabric until it wets out the surface. Use your fingers (you do have on your barrier cream or latex gloves, don’t you?) to smooth the fabric into the wet strip of cement, making sure it penetrates the fabric. If you make a mistake, you can uncement any seam. Simply wet the seam with MEK on a rag, pull the seam apart, and imme- diately re-cement it correctly with fresh Poly-Tak. You can’t make a mistake here that MEK can’t fix. Don’t brush more Poly-Tak over the top surface of a drying ce- mented seam. Resist this temptation! Doing so could hurt the bond. The top coat will dry before the original bottom coat, impeding drying of the bottom. 4. Attaching the Fabric Revision 21: pg. 18 Before setting out on a night flight, check your airplane’s lighting system. Revision 21: pg. 19 You’re going to cover a wing from start to finish, right up to where you’re ready to begin building up the final coating. Once you understand the steps involved, you’ll be ready to tackle the rest of the airplane. Basically, the steps are… 1. Cement the new fabric to the wing. 2. Heat-tighten the fabric in stages. 3. Brush on the 1st coat of Poly-Brush. 4. Rib-lace the fabric to the wing. 5. Apply finishing tapes and inspection rings. 6. Smooth rough tapes and imperfec- tions with the iron. All the prep work discussed earlier, prim- ing, varnishing, inter-rib bracing, anti-chafe tape, etc., is done, right? If you have control cables installed, or electrical wire for lights, pull them all normally taut and secure them that way with clamps or tape or whatever. You’ll use the blanket method to cover this wing. A blanket is simply a rolled- out length of fabric cemented to the wing. Poly-Fiber Heavy and Medium fabrics are about 70˝ wide, so they can easily cover almost any normal wing. If you have an unusually wide chord, two pieces of fabric can be sewn together to make a wider blanket. Or you might be able to use three pieces of fabric with an insert, as long as you follow the basic rules for cemented seams. If you think you’ll need to sew fabric together, see the appendix on sewn seams. Handy Sawhorses The best way to hold the wings for covering is to rest them upon specially modified sawhorses. Two pieces of wood, typically 2-by-4s long enough to reach across at least two ribs, are fastened perpendicular to the top beam of each sawhorse. Space them the same distance apart as the spars. Cover the whole shebang with scrap car- pet. Position the sawhorses beneath the wing, with the padded pieces parallel to the spars and directly under them. Covering the Wing, Step by Step The game plan for this wing is simple. You’ll use one long piece of fabric applied spanwise to cover the bottom of the wing, and another for the top. Following our basic rules on cemented seams, you’ll join the top and bottom pieces with a 2˝ overlap at the leading edge, and 1˝ overlaps at the trailing edge, tip bow, and butt rib. You won’t cement fabric to the ribs themselves, since later you’ll use rib lacing or some 5. Let’s Do a Wing! other mechanical means to hold the fab- ric to the ribs. Other common mech- anical attachments are pop rivets, PK screws, and fabric clips. More about them later. We’re assuming your wing has an essentially flat bottom surface. However, if it’s con- cave, you MUST instead go to Appendix C, “Concave- Bottom Wings.” You’ll start with the bottom of the wing first, although it doesn’t matter. First, the Leading Edge  Mix up some thinned Poly-Brush. The recipe is 3 parts Poly-Brush to 1 part Poly-Fiber Reducer.  Brush two coats of this thinned Poly-Brush onto the leading edge to provide a “bedding” that will help adhesion and reduce the pos- sibility of pinholes in the finish coat. Actually, all large metal, wood, or fiberglass parts that will be covered with fabric should get these two coats of Poly-Brush.  Let this dry for about 15 minutes.  Get out your chalk line and snap a line along the center of the leading edge. Then measure 1˝ above the center line and 1˝ below that cen- ter line and snap parallel lines at those marks. By the way, regular blue carpenter’s chalk lines will disappear later and won’t bleed through. These chalk lines will be your guide lines. Cement bottom fabric to this line. Cement the top fabric to this line. If you use these lines when cementing, you are assured of straight seams with a legal 2˝ overlap.  Roll out a piece of fabric to cover the bottom of the wing. Trim off any selvage (built-up edges where threads are doubled over during looming). They may show through the finishing tape. Trim it off care- fully with sharp straight scissors. Take care to make a straight, clean cut with no raveled threads. Flaws and ravels will show through later. If the selvage is straight and is not noticeably raised, you may choose to leave it on. The fabric has no top or bottom. There’s no special orientation to the weave. Attach it with the stamp in or out. Doesn’t matter. Scallops Scallops are troughs that form between the ribs, more so with modern polyester fabrics than classic Grade A Cotton. Although they present no aerodynamic problems, for cosmetic reasons, some prefer fabric that is more level to the ribs with little scalloping. To avoid scallops: 1. Use Poly-Fiber Medium fabric; its weave pattern results in little or no scalloping. 5. Let’s Do a Wing! Revision 21: pg. 20 Center Line 2. If you use Poly-Fiber Heavy Duty fabric, consider purchasing a pre-sewn wing envelope with the seams run- ning chord-wise. This chord-wise orientation also prevents scalloping. However, you can always use heavy duty fabric with the blanket method; the aircraft will fly the same, it will just show a bit deeper trough between wing ribs. OK… back to work.  Allow about an extra foot at the wing- tip and the butt, and cut it off the roll. Clamp it in place with spring clamps or clothespins. Don’t be afraid to remove the clothespins and move the fabric as necessary throughout the cementing process.  Starting at the butt rib, brush a strip of Poly-Tak about 2˝ wide (1˝ each side of the cen- ter line) and 12˝ to 24˝ long along the leading edge where the fabric will be attached. Line up the fabric edge with the appropriate cement line.  Lay the fabric onto the wet cement. Work the fabric into the cement with your fingertips or the brush to force the cement up through the weave. Work in short sections, applying tension to the fabric as necessary to keep the wrinkles out. Think ahead though. Make sure the whole piece of fabric is aligned and lying where you want it to be. Stop every now and then and look at the whole job. If you’re unhappy with an area, un-cement it with MEK and do it again.  Continue this process, working 12˝ to 24˝ at a time, until the entire bottom section of fabric is attached to the leading edge. Let this dry for about 15 minutes. How Tight Should That Fabric Be? Let’s talk about how tightly you should be attach- ing the fabric. How taut you pull the fab- ric as you cement it at the trailing edge has a big effect on the final tension of the fab- ric when it is eventually tightened with the iron. Final tightening will shrink the fabric about 10%. On a wing 60˝ wide, that means it will shrink about 6˝. If for some reason you left 6˝ of slack in the fabric (and you certainly wouldn’t want to do that) the fabric would pull up and conform to the shape of the wing, but would be far too loose. On the other hand, if you pull the fab- ric as tight as a bedsheet in boot camp (remember bouncing a quarter off it?) and cement it down, and then tighten it, the resulting tension can warp or bend light structures. Stamped ribs or thin tubing can be deformed when the fabric is applied too tight. As a good rule of thumb, the fabric should look like a bed sheet with the big wrinkles pulled out of it... snug, but not tight. OK… back to work. 5. Let’s Do a Wing! Revision 21: pg. 21 Uh Oh… Protrusions! Strut fittings and other attachment points can work like tent poles under the fabric. If the protrusions are less than 2˝ above the surface of the wing, you don’t need to cut the fabric to make a hole for the protrusion before heat tightening. Leave the fabric intact and tighten it right around the protrusion. Don’t worry, they won’t rip through. More on this later. If they are 2˝ or more, you’ll have to make a cut to let the protrusion through. Brush some Poly-Brush over the area of the protrusion before you cut to keep the fabric from raveling around the cut. Make the smallest possible cut you can. Make sure the fabric is as close to it’s final position as you can before you cut anything. When you tighten the fabric, the hole will get a lot bigger, so take care. Next, the Trailing Edge  Pull the bottom fabric gently toward the trailing edge to remove wrinkles. Rough-trim it to overhang 6˝ mini- mum, and secure it with spring clamps. Rough-trim the fabric so it will fold at least 1˝ down into any control surface recesses. Industrial single-edge razor blades are good for this. Inside corners of flap and aileron recesses are cut at a 45° angle to allow the fabric to fold down at the sides.  Cement the fabric to the BOTTOM surface of the trailing edge ONLY. Work from the butt rib to the wing- tip in short sections, keeping the wrinkles out just as you did on the leading edge. Now, before cementing the fabric to the TOP surface of the trailing edge, you’re going to heat-form the fabric around it. It’s much simpler to pre-shape the fabric than to use clothespins, spring clamps or fingers to hold it in shape around the edge of the trailing edge while the Poly- Tak dries. Warm up the iron to 225°. You DID calibrate it, didn’t you? It’s VERY important!  With your iron, roll the fabric around the trailing edge, working from the bottom surface around to the top. Apply pressure so it permanently creases and takes the shape of the trailing edge. If you stay with it, the fabric will not only crease around the corner, but will lay flat on the top surface of the trailing edge with- out using clamps. It should end up like this: The reason you are wrapping the fab- ric entirely around the trailing edge is to make sure you wind up with a real overlapped cemented seam. Later, when you attach the top fabric, it will over- lay this bottom fabric. That’s where the required overlap comes in. If you simply trimmed the fabric flush with the trailing edge and then cemented it down, you would have no fabric-to-fabric overlap. 5. Let’s Do a Wing! Revision 21: pg. 22 1ß Bottom Fabric REMEMBER, you must always have an overlap.  Once the fabric has been heat-formed to assume the shape of the trailing edge, cement it down and trim it off. Take care trimming. Uneven lines or raveled threads will show later. Now for the Butt Rib  With the wing still top side up, start heat-forming (225 to 250° iron) the extra fabric at the butt rib. You want to cover the entire butt rib with fabric. Heat-form carefully to make the fabric bend around the corners and edges to assume the shape of the rib. Heat-forming is best done by pulling the dickens out of the fabric (you can’t tear it) and applying heat with the iron on the area to be formed. Stay with it; you can make the fabric take any shape you wish with enough practice and patience. Heat forming gets rid of all potential wrinkles and keeps you from having to cut “darts” in the fabric. Darts are those ugly 45° slits we used to have to cut in cotton to make the fabric conform to curves. With pressure and patience, you can even form polyester fabric around a bowling ball with no wrinkles. True.  When you’ve successfully formed the fabric, cement it to the butt rib. You may need to make some cuts for cables or wires. Never mark on fabric with any- thing but a soft lead pencil or a chalk line. Pens, magic markers, etc. will bleed right through your final paint. V E R B O T E N !  Trim the fabric even with the top edge of the butt rib. Later you will heat-form at least an inch of the top wing fabric around the corner and down onto the butt rib to make our 1˝overlap. Aileron and Flap Recesses  For aileron and flap recesses, heat- form the fabric into the recess and cement it securely. Put your fabric overlap inside the recess as shown. The Curved Wingtip Bows You should have plenty of excess fab- ric left at the wingtip, hopefully about a foot. This excess gives you a good “handle” to pull on while heat-forming.  Make a small “ironing board” out of cardboard, about 5˝ x 3˝. 5. Let’s Do a Wing! Revision 21: pg. 23 Note the 45° slit in the corner  Place the ironing board under the fabric about a foot in from the bow. Tighten this area first at 250°. This will help the heat-forming of the fabric at the tip. If you tighten the center of the radius, it makes it easy to make the curve at the bow.  Now start rolling and heat-forming the fabric around the tip bow with the iron set at 225 to 250°. Roll and form the fabric as far as you can to the inside of the bow. Yes, sharp-eyed readers! This IS the TOP of our wing, just to show how the curvature is smoothed out. You should start with the BOTTOM of the tip bow.  Pull hard on the fabric around the bow and apply heat. The trick is to get the fabric wrapped around the bow at least an inch. More is even better. Whenever you can, wrap all the way around to the inside of the tube so the seam won’t show. At some point, you’ll have to turn the wing right side up to wrap the bottom fabric around the bow tubing.  When you have the fabric well formed to the inside of the bow, cement it down. Try to cement it in one appli- cation, rather than in short sections. You have to work fast, but you’ll get fewer wrinkles. A neat way to trim is to use single edge razor blade. Hold it firmly on the surface, and pull the fabric into the blade. Don’t slice with the blade; you could cut the primer or fabric below. 5. Let’s Do a Wing! Revision 21: pg. 24 “Ironing Board” under fabric  Let the Poly-Tak dry for about 15 minutes after the bottom fabric is cemented all the way around the perimeter of the wing. OK, now the bottom piece is on, and most of the basics have been done.  Before you attach the top fabric, go over all the cemented areas with an iron lower than 250°. Use enough pressure to take out all wrinkles. The idea is to iron out all wrinkles or imperfections in the cemented areas of the bottom fabric before you cement the top piece over it. The smoother you can make the cemented areas, the bet- ter they will look later when covered with the top piece of fabric. You are using the iron on JUST THE CEMENTED AREAS now. You’ll heat tighten the whole wing later, after the top piece is applied. Patience. Notice how the iron can take out all the wrinkles that occur during the cementing process. Work carefully and stay with it until all the wrinkles are gone. Use pres- sure and the tip of the iron. The iron also softens the Poly-Tak below the fabric, allowing you to re-smooth any lumps. Use the little sealing iron in tight places. NEVER APPLY AN IRON HOTTER THAN 250° TO A CEMENTED AREA. DOING SO COULD RELEASE THE SEAM OR THE BOND! Now for the Top Fabric  Roll out the top piece of fabric. Clamp and trim it as before, with a foot extra at the tip and butt.  Cement the leading edge, aligning it to the lowest chalk guide line. That line is now covered by the bottom fabric and may be hard to see. If so, re-chalk it.  Cement the trailing edge as before. For the best overlap seam, heat- form the top fabric around both sides of the trailing edge, and cement it to both sides. That will give you more than the required 1˝ overlap and a very strong seam. If your trailing edge fairing is at least 1˝ wide, you can simply cement the fabric to the top of the trailing edge and trim the fabric off flush without wrapping it around. That would make a legal 1˝ overlap also. 5. Let’s Do a Wing! Revision 21: pg. 25 1ß Bottom Fabric Top Fabric  Heat-form the top fabric over the edge of the butt rib until the fabric is smooth and flat. Keep forming until at least an inch of formed fabric lies flat over the butt rib. Trim this neatly and cement it to the fabric below making sure you have a legal 1˝ overlap.  At the wingtip bow, heat-form the top fabric the same way you did the bottom. Make sure you have a 1˝ overlap where the top piece overlies the bottom. Trim the top piece with scissors as neatly as you can. Razor blades are danger- ous here, you could inadvertently cut the bottom fabric while trim- ming the top. Before You Start Ironing… OK, now the fun part. You’re about to tighten the wing fabric with your carefully cali- brated iron. The iron is ready, and the untight- ened wing is on the sawhorses. But first, a few important points. Remember, a calibrated iron is the only approved source for tighten- ing. Heat guns or uncalibrated irons are the surest way to damage your project or invalidate your STC. If you ignore this and use a heat gun or an uncalibrated iron, you could wind up with permanently loose fabric! At best, this means cracked paint. At worst, it causes fabric floppy enough to seriously deform the airfoil in flight! Bad news. Remember that unlike dope, neither Poly-Brush nor Poly-Spray will tighten the fabric any further. What- ever you do with the iron is the fin- ished product. LeRoys who use heat guns might get away with loose fab- ric now because the dope they put on later will pull the fabric tighter. OK… back to work. 5. Let’s Do a Wing! Revision 21: pg. 26 Regardless of what LeRoy says, you can’t tell how tight your fabric is by feel. Thumping and bouncing quarters are old aviation wives’ tales. You must know the exact temperature applied to the fabric to know how much it has been tightened. Do not attempt restart if engine stopped because of obvious mechanical failure. Heat Tightening Start With 250° The idea is to spread the increasing ten- sion evenly and symmetrically across the surface. To do this, start at one end of the wing, say at the tip.  Hold the iron in the center of the fab- ric near the tip bow. See the fabric pull up tight around the iron? Move the iron slowly around the fabric to take out the big wrinkles. Don’t try to remove all the wrinkles on this first pass. They’ll come out later with the next heat setting. Iron over the hard surfaces too, like the leading edge. Don’t start at one end of the wing and work toward the other. This can exert enough asymmet- rical force to bend light struc- tures. You could put unwant- ed dihedral in your wing (or maybe you always wanted a “bent-wing” Corsair), or you could wind up with deep troughs in the fabric between ribs as the fabric is pulled spanwise in one direction only.  Now go out to the opposite end of the wing, by the butt rib, and do the same thing. Alternate your tightening at opposite ends of the wing, working toward the middle. Don’t be afraid of letting the iron pause on the fabric. It won’t scorch the fabric like it does your cotton shorts. Nor will the fabric get any tighter. The amount of tightness depends upon temperature, not time.  Turn the wing over and tighten opposing areas at 250°, as you did on the top side of the wing. Protrusions Remember those strut fittings sticking up like tent poles 2˝ or less under the fabric? Iron right around them; they won’t break through. Later, when the whole wing has been tightened at 250°, cut the fabric just enough to let the protrusion pop through, and cut no more. The idea is to make the smallest cut you can. Now the Big One, 350° Crank up the iron to 350°. This takes the fabric to peak tightness. Anything over 350° starts permanently loosening the fabric. Be sure of your calibration! This is the IMPORTANT one!  Iron the fabric in opposing areas at 350° the same way you did at 250°. You may see steam coming off the fabric at 350°. This is mois- ture in the fabric boiling out. It’s normal and is nothing to worry about. Make sure you iron every inch of the fabric. If you get distracted and skip an area, it will forever be looser than the rest. This is not a good idea. To make sure, do the whole wing twice at 350°, or make check marks with your lead pencil (no pens or magic markers) in each area as you final-tighten it. 5. Let’s Do a Wing! Revision 21: pg. 27 CAUTION: NEVER IRON OVER A CEMENTED SEAM AT ANY TEMPERATURE OVER 250°! A 350° iron can pop cemented seams. Use caution and stay away from glue bonds at the higher tem- peratures. The trick is to make sure you tighten the whole fabric surface at 350°. Don’t forget the fabric that lies over hard surfaces like leading edges, tanks, or walkways. Very Lightweight Aircraft If you’re covering an ultralight or very lightweight experimental aircraft, tight- en at 250° and see how the structure holds up. Calibrate the iron at 300° and try that next, again monitoring for struc- tural deformation. You may get all the way to 350°. If you must stop at 250° or 300° because of the lightweight structure, so be it. The fabric will not be at full tension, but the slow speeds of your ultralight or very light aircraft will keep the paint from cracking and keep in-flight airfoil defor- mation to a minimum. Always try for the maximum tightening you can get, however. Remember, however, that on a certified aircraft you must tighten to 350° with a calibrated iron. This is an inescapable part of the STC. 1st Brushed Coat of Poly-Brush Applying Poly-Brush does two things: 1. It seals the fabric. 2. It acts as a cement that soaks through the fabric and further secures the fabric to the airframe. Poly-Brush should ALWAYS be thinned 3 parts Poly-Brush to 1 part reducer. Normally, you should use Poly-Fiber R 65-75 Reducer. Above 85°, use our RR 8500 Reducer. Poly-Brush has a pink tint so you can see where it has been applied. It also comes untinted for use on open cockpit aircraft where you may not want the pink tint to show.  Thoroughly scrub the fabric with MEK or reducer. Use a clean rag. Don’t flood the cement joints! A NOTE ABOUT RAGS: Use only new rags. Cotton is best, but watch the lint. NEVER USE INDUSTRIAL SHOP RAGS OR LAUNDERED RAGS. They’re full of some- body else’s silicone and impregnated grease that never really comes out. Rub a shop towel on your fabric and you may ruin it. Go to a builders’ supply store and buy fresh painters rags. It’s worth the expense. Or go to a fabric store and buy cheap 100% cotton cloth.  After scrubbing the fabric with MEK or reducer, follow by passing a tack rag lightly over the surface to pick up any dust or lint. Cut an old rectangular can (like a reducer can) to make a nice Poly-Brush applica- tion bucket. The handle at the top makes it easy to hold while you are brushing. 5. Let’s Do a Wing! Revision 21: pg. 28 Stick a piece of rigid wire or welding rod through the side to wipe the brush on or hold it out of the liquid. A WORD ABOUT BRUSHES: Natural-bristle brushes are best for Poly-Brush. You can use high-quality polyester brushes, but avoid foam or nylon. They dissolve in Poly- Brush. Buy a good 3˝ brush for applying Poly-Brush to fabric, and a good 2˝ brush for apply- ing finishing tapes later on. Ok, get your bucket of thinned Poly-Brush (3 to 1), a good 3˝ brush, and a can of MEK or reducer with a rag.  Brush Poly-Brush liberally over all the fabric. Brush all open fabric areas and fabric over the hard sur- faces. The idea is to turn the fabric pink, make it look glossy wet, and leave no dry starved areas. This is no time to skimp. You need to really wet the fabric to fill the weave. Notice that over the leading edge the Poly- Brush soaks through and further bonds the fabric to the hard surface below. Don’t leave any dry areas or places where the surface doesn’t look trans- lucent when you’re through brushing. This would mean the weave isn’t suffi- ciently filled, and it leads to big problems with pinholes later. We’ll talk about pin- holes further on. The idea is to brush on a wet coat, and then make only one more pass with the brush to level any small bubbles that may have formed. Look at the wet surface glare area to check for bubbles. Work fast, quit brushing, and get your brush out of there before the Poly-Brush dries. Poly-Brush dries in about 15 minutes. In hot weather, it can dry in as little as 5 minutes. You have to brush it on and quit fiddling with it. If you continue to brush while it is drying, you can leave serious brush marks. If you’re putting enough Poly-Brush on, you’ll see runs on the inside of the fabric. This is perfectly normal. On the other hand, if these runs pool together on the underside of the top fab- ric and drip down onto the inside of the bottom fabric, you’re brushing on too much Poly-Brush. These drips seal the bottom fabric where they fall on the inside, the wrong side. If you let these drips stay, they’ll show up as a difference in gloss in your final paint. Simply wipe these drips away with MEK and a clean rag. As you brush the top surface, keep monitoring for drips on the bottom and clean if necessary. 5. Let’s Do a Wing! Revision 21: pg. 29 Welding rod or stiff wire, poked through holes in can, with ends bent over. Tape over sharp edges.  When the Poly-Brush is dry on the top of the wing, turn it over and do the bottom. Drip-throughs are not a problem now since the top of the wing has already been properly sealed, and the drips won’t show. “Can’t I spray on this first coat of Poly-Brush?” We don’t recommend it. Brushing does a much better job of filling the weave. If you don’t fill the weave sufficiently, you get pinholes later. Brush marks are not a problem if you follow the instructions above. Ray Stits didn’t name it Poly-Brush for nothing. “Can’t I just sand the drips or flaws in Poly-Brush?” Nope. Poly-Brush doesn’t sand. It’s too rubbery. Remove wet or dried drips and runs with some reducer on a rag. Or, you can smooth them out with a 225° iron. 5. Let’s Do a Wing! Revision 21: pg. 30 LeRoy will tell you this is a mistake, cause this ain’t the way he brushes on nitrate dope. Sorry, LeRoy, but that’s just not true here. These runs tell you Poly-Brush is penetrating, and they will not be visible in the final product with vinyl coatings. Revision 21: pg. 31 Rib Lacing Fabric on wings needs to be mechanically secured to the ribs rather than just cemented. The standard mechanical attachments are: rib lacing, PK screws, pop rivets, and fabric clips. On certified aircraft, the method you use to secure the wing fabric to the wing ribs should be the same one used at the factory when your airplane was manu- factured. If you want to use a different method, you have to get a field approval from an FAA Field Service District Office. On some aircraft, the tail feathers and occa- sionally some fuselages were rib laced. Again, replicate the way the factory did it. Using cement alone is a recent idea that came out of the ultralight movement. The theory was that since the speeds and wing loadings were low, you didn’t need mechanical attachments. However, many kit planes have evolved from enclosed ultralights to high-horsepower firebreathers. Some have 180 HP! They need to be rib laced! Additionally, any ultralight or very light aircraft you plan on keep- ing for more than just a couple of years needs RIB LACING. Aircraft fabric cement is made for shear loads, not peel. But in flight, an aircraft is subjected to constant peel loads from the center of lift on the top of the wing. The giant vacuum cleaner called lift is always trying to peel your wing fabric off the top surface. Aircraft fabric cements were never designed to resist this peel force. And certainly not for the long service lives fabric covering jobs can last today. If you’re covering an experi- mental aircraft for which there is no rule or prece- dent, WE STRONGLY REC- OMMEND RIB LACING OR SOME OTHER MECHANICAL ATTACHMENT. Fabric cements were never meant to be the sole means of attaching fabric to ribs, even to 1˝ ribs. Incidentally, we call it RIB LACING rather than rib stitching. We are lacing around the whole rib, not just stitching it to the top or bottom rib caps. How Far Between the Laces? Let’s start with how to plan and lay out rib lace spacing. This works for screws and rivets, too. Take a look at this chart: This same chart is also in the FAA’s AC 43.13, and should be used if you don’t know the rib lace spacing of your air- craft as it was manufactured. The bottom of the chart shows the plac- ard maximum speed of aircraft in miles per hour. The left side shows the dis- tance between laces (or screws or rivets). 5. Let’s Do a Wing! Notice that there are two lines, one for spacing in the propwash areas, and one for spacing in other than propwash areas. Propwash area includes all the wing ribs included within the diameter of the propeller, plus one more rib. Using the Chart We’ll use our J-3 Cub as an example. Position the wing right side up. We’ll mark the top of the wing first. On the chart, you draw a vertical line up from the Vne speed of the Cub, which is 115 mph, until it reaches the line marked “Propwash Area Spacing.” Then you draw a horizontal line from that point of inter- section over to the scale on the left side of the chart. That gives us a spacing of 21 ⁄2˝ inside the propwash area. Then you extend the vertical Vne line to the “Non- Propwash Area Spacing” line, and turn left again to the left side of the chart. This gives us a rib lace spacing of 3 1 ⁄2 ˝ outside the propwash area. Perform these same steps for your airplane, Most sport aircraft work out to 21 ⁄2˝ in propwash and 31 ⁄2˝ out of propwash. These are MAXIMUM spacings. The faster the aircraft, the tighter the spacing. You can pretend you’re doing a P-51 if you wish and use 1˝ spacing. No problem in using tighter spacing anytime. Aerobatic aircraft should always have tighter spacing. So what you get out of this drill is that on an average wing the first three or four ribs out from the butt rib require 2 1 ⁄2 ˝ spacing since they are in the propwash area. The remaining ribs get rib laces every 31 ⁄2˝. The chart gives us two sets of spacing, but you don’t really have to lay out two sets of laces if you choose not to. Remember, the spacing you get from the chart is the MAXIMUM spacing between laces. Since there is no restriction on using narrower spacing than the maxi- mum, it’s just as easy on most airplanes to use the propwash spacing (21 ⁄2˝) for the whole wing. It looks neater, it’s easi- er to lay out, and you’ll only end up doing a few more laces in the bargain. So in our discussion on how to mea- sure and layout the laces, we’ll go with 21 ⁄2˝ laces for the whole wing. Tailfeather Spacing: If your aircraft requires you to lace the tailfeathers, and you don’t know the original spacing, use twice the wing propwash spacing. Marking Rib Lace Locations Now that you know the spacing, you’ll measure, lay out, and mark the posi- tion of the individual rib laces. This will result in evenly spaced, neat looking laces. Once you mark the lace positions, you’ll pre-punch the lacing holes with a nee- dle to give us guides to lace through. Not only does this give us a good look- ing job, but saves lots of time by not having to measure while lacing. Pre- punched holes save lots of fumbling. Put the wing top side up on the sawhorses. Get a ruler or a tape measure and a soft lead pencil. 5. Let’s Do a Wing! Revision 21: pg. 32 Remember, no pens or magic markers. They will bleed all the way through the paint. You begin measuring rib lace spacing at the butt rib, working from aft edge of the leading edge fairing, where it meets open fabric, toward the trailing edge. The first rib lace is always placed at half the re- quired distance of the others. Since our required distance is 21 ⁄2˝, half of that is 11 ⁄4˝.  Place the tape on the top of the butt rib and start measuring and marking. The first mark goes 1 1 ⁄4˝ back from the leading edge fairing (half the chart distance). The next mark goes 21 ⁄2˝ beyond that. Keep marking in 2 1 ⁄2˝ segments all the way to the trail- ing edge. Make sure the last mark is no greater than 2 1 ⁄2˝ from the trailing edge.  Now lay the measuring tape on the rib closest to the tip bow and do the same thing. Then, to be safe, pick a rib in the middle of the wing and do it again.  Get the chalk line out and line up the marks made on all three ribs. Snap lines on the top of the wing. You should have parallel lines every 21 ⁄2˝ spanwise on the wing. Every place the chalk line intersects a rib is where the rib lace will be. This is a nifty way to get nice even laces at the required spacing. Rib laces go through the entire wing, and must be parallel to the spar face, or in other words they should go straight up and down and all be parallel if you looked at them in cross section inside the wing. The bottom surface is different. If your wing was symmetrical, you could flip it over and measure and chalk the bottom as you did the top. The resulting laces would all be straight up and down and parallel. But most wings have an airfoil shape; that is, the top surface has a greater curve than the bottom surface, which is almost flat. Therefore, the top surface is longer than the bottom. So, if you measured the bottom exactly as you did the top of airfoil, the resulting rib laces would certainly not be straight up and down and parallel. In fact, they would look like a sunburst! Not to worry. The Magic Template You can keep the laces straight up and parallel by making a simple cardboard template. 5. Let’s Do a Wing! Revision 21: pg. 33  Hold a piece of cardboard up to the butt rib and trace the shape of the rib. Also mark on it the position of the main (forward) spar. Cut out the shape of the butt rib to make a template. Put the template against the butt rib and transfer to the tem- plate the spacing marks on the top of the butt rib.  Lay the template on something flat. At each lace position along the top of the airfoil, draw a line parallel to the main spar face, extending down through the bottom of the airfoil template. This gives you the proper positions for the rib laces on the bottom.  Now transfer these lace positions, both top and bottom, to the other side of the template. This gives you a tem- plate for both wings.  Place the template back on the butt rib and transfer the marks from the bottom of the template to the bottom of the butt rib. Turn the wing bottom side up.  Use the bottom edge of the template to mark the lace positions onto a middle and outboard bottom rib. Snap your chalk lines as before, and you are done. All the rib lacing locations are marked. If you absolutely want to have both in-propwash spacing and out-of-propwash lace spacings, just make two templates. Use them as above. 5. Let’s Do a Wing! Revision 21: pg. 34 Reinforcing Tape Reinforcing tape is an adhesive-backed polyester twill material that is stuck to the fabric over the rib cap before rib lacing. It reinforces the fabric so that rib laces, screws, or rivets don’t cut right through the fabric when mechanical attachments are snugged down. Poly-Fiber reinforcing tape comes in 1 ⁄4˝, 3 ⁄8˝, and 1 ⁄2˝ widths. Use the width of tape that exactly matches the width of your rib cap. Tape that is too wide will leave puckers when the laces are snugged down. Tape that is too narrow will allow fabric cuts where the rein- forcing tape ends. Use two parallel 1 ⁄2˝ tapes to cover a 1˝ rib.  Simply peel off the paper backing and press the tape into position over the bottom ribs. Align the tape precisely with each rib cap. Extend the tape a minimum of 1˝ beyond the first and last laces on each rib. For cosmetics, it looks better to extend the reinforcing tape all the way to the leading and trailing edges of the wing. Position the wing right side up on the sawhorses.  Apply reinforcing tape along the top rib caps, just as you did for the bot- tom rib caps. Take care when cutting reinforcing tape. Uneven cuts will show through. Keep everything nice and square. CAUTION: Don’t use anything but genuine Poly-Fiber poly- ester twill reinforcing tape. Sub- stituting fiberglass strapping tape, or any other tape, is not approved. Strapping tape fails easily in shear, and falls apart in a few years. Rib laces can fail if you use strapping tape! It also negates your STC.  Once all the reinforcing tape is in place, pre-punch the top rib lace holes with a rib lacing needle. Punch holes where the chalk lines intersect the ribs, as close to the rib caps and tape as you can. Turn the wing over again, upside down on the sawhorses.  Pre-punch the holes on the bottom of the wing, same as on the top. 5. Let’s Do a Wing! Revision 21: pg. 35 Leading Edge Fairing Reinforcing Tape Punched Holes Chalk Lines Fabric Let’s Tie Some Knots! There are two kinds of Poly-Fiber poly- ester rib lacing cords, round and flat. It is your choice. Flat rib lacing cord, like a shoelace, takes some untwisting at times. Round cord is faster and only slightly thicker than flat. Rib lacing cord is impreg- nated with a special wax. Only two knots are approved with the Poly-Fiber STC: 1. The modified seine knot as shown in AC 43.13. After tying, this old standby stays on the exterior surface. The cord that runs between knots (the continuous cord) also runs on the surface. Leaves a lot of drag on the outside of the wing, but that’s the way it was done from WW1 on. Tie this knot with a 12˝ straight needle. 2. We recommend, and will show you, the hidden modified seine knot. This “hidden” knot winds up on the inside of the wing. So does the con- tinuous cord. So all you see with this knot is one small stitch across the rib. Much cleaner. You’ll need a 12˝ curved tip needle to tie and hide this knot. The video “Aircraft Fabric Covering,” produced by EAA SportAir, shows you a differ- ent way to tie the knots than is illustrated in this manual. The video is available in either VHS or DVD from your Poly-Fiber distributor. You can rib lace with the wing on saw- horses and spend a lot of time exer- cising your knees, or you can put the wing in a vertical stand and pass the needle back and forth with a helper. Wings can be laced while positioned horizontal or vertical, usually leading edge down. Exceptionally wide-chord wings are easier to lace when posi- tioned vertically, with the needle being returned by a helper. You can start at the leading edge and work aft, or vice versa. You can begin on either the top of the wing or the bottom. It doesn’t matter – all the knots will be concealed inside the wing. To save time untangling long lengths of rib cord and to prevent wearing off the wax coating and fraying the cord by pulling through the fabric too many times, use shorter lengths of rib lacing cord. Six to eight feet is plenty, depend- ing on the rib thickness. Tie off the last knot in each length with a half- hitch. Make sure all cables are temporarily secured taut, in their normal runs. If you rib lace with them in a loose con- dition, they could destroy adjacent rib laces when you pull them back to their normal runs as you assemble the airplane.  Set up a floodlight so it shines through the wing to reveal structure and obstacles within.  Thread a curved tip needle with about six feet of cord. 5. Let’s Do a Wing! Revision 21: pg. 36 A. Start by inserting the threaded needle into the prepunched hole on the right side of the reinforcing tape. Guide the needle through the wing and out the bottom prepunched hole directly below the top hole. B. Leaving a tail of thread on the top of the wing, pull the needle out the bot- tom. Cross to the left of the bottom reinforcing tape, insert the needle into the prepunched hole on the left side of the tape. Push the needle and thread all the way back up inside the wing and out through the prepunched hole on the left side of the top rein- forcing tape. C. Pull the needle out with thread attached, but don't pull all of the thread out. You will have a short end of the thread (about 4 to 5 inches) on the right side of the top reinforcing tape and a lace of thread running from the top through to the bottom on the right of the rib and back up to the top on the left as illustrated. Now you’re ready to tie the Starter Knot. 5. Let’s Do a Wing! Revision 21: pg. 37 The Starter Knot. This handy knot is used when you start a sequence of rib lacing. It is simply a square knot with a half-hitch on each side. 1. Tie a square knot by passing the short end of the cord through the folded-back loop. 2. Lock the tightened square knot with a half-hitch on each side. The starter knot can also be used as a single lace in places where you can- not tie continuous seine knots. If you have a lot of time, you could lace your entire airplane with starter knots. 5. Let’s Do a Wing! Revision 21: pg. 38 3. Route the needle back through the starting hole. Bring it back out through the next hole aft on the same side of the rib cap. Pull the square knot inside the wing. 4. Route the needle back in through this same exit hole, and then out again through the corresponding hole on the opposite wing surface. Leave about a 3˝ loop when the needle is pulled clear. 5. Cross over the rib cap, and return the needle. As the needle emerges, orient the loop as shown and pass the needle up through it. This is the beginning of the modified seine knot. 5. Let’s Do a Wing! Revision 21: pg. 39 6. Pull the needle clear. Use the tip of the needle to reach under part B of the loop, hook part A, and pull it toward your starting point. 7. Rotate the needle clockwise, twisting the captured part A. Route the needle tip over part A, then under part B. 8. Now pass the needle over cord part C and pull it through. Hold part C per- pendicular to the fabric while you pull, to keep the cord from getting tangled. 5. Let’s Do a Wing! Revision 21: pg. 40 9. Pull part C perpendicular to the fabric to remove all slack in the lacing cord back to the last rib lacing knot, while working the loose knot over to the right side. Do not pull on part D. 10. With all slack removed by pulling part C, hold the loosely formed knot with your thumbnail. Pull firmly on part D, perpendicular to the fabric surface, to secure the finished knot. GO BACK TO STEP 3 - Repeat Steps 3 through 10 until you’ve completed the entire rib or you’ve come to the end of your length of lacing cord. In either of these cases, go to Step 11. 5. Let’s Do a Wing! Revision 21: pg. 41 11. After completing an entire rib, tie off the last modified seine knot with a half-hitch. What if you run out of cord halfway through the rib? Tie it off with a half- hitch, and start again at the next set of holes with a starter knot and a new length of cord. Sometimes you can’t get through the entire wing to rib lace normally. Hidden structure, fuel tanks, etc. may preclude lacing around the whole rib. In this case, you can lace to just the cap. Use a curved needle to tie a single starter knot. A. Go in on one side of the rib cap, and come out on the other. B. Go back in through the exit hole, then come out opposite the first entry hole. C. Now you can tie a starter knot, 5. Let’s Do a Wing! Revision 21: pg. 42 Other Mechanical Attachments: Pop Rivets Fabric pop rivets are special broad head rivets sold by aircraft supply houses specifically for use on metal ribs. DO NOT attempt to use the hardware store variety! Start with the reinforcing tape, as with rib lacing, and use the same spacing. If an existing rivet hole is wallowed out or damaged, drill a new hole half an inch or so away. For best results use a 1 ⁄2 ˝ diameter .016˝ aluminum washer under each rivet. Plastic washers tend to crack and fail with age. Pop rivets are easy to install, but they’re a real pain to drill out at re-covering time. PK Screws These are small self-tapping stainless steel sheet metal screws. You’ll find them in a variety of certified aircraft that have metal ribs. As with the pop rivets, start with the reinforcing tape and use the standard spacing. If an existing screw hole is wal- lowed out or damaged, drill a new one half an inch or so away. For best results use a 1 ⁄2˝ diameter .016˝ aluminum washer under each PK screw. Don’t use PK screws on wooden ribs. They can create a path that introduces moisture into the rib over the years. Fabric Clips Fabric clips are pieces of wire formed into a row of self-locking “barbs” that snap into holes or slots in metal ribs. Taylorcraft and Cessna use them, and they’re avail