ID: Tony Bingelis •

ILT Parti Preparing It For Painting perfectly dimpled holes. You might be able to complete your NO MATTER who will paint your 6. Misdrilled holes. preparations for painting the airplane in airplane - or where or under what condi7. Rivet gun marks and other dents. as little time as a week or so - but I tions - the final results can only be as 8. Irregular or unfinished edges, doubt it. good as your own pre-painting preparajoints and gaps. There is good reason for my skeptitions will make it. 9. Poorly fitted covers, plates and trim cism. Although the paint may cover the When you first begin thinking about strips. surfaces uniformly, it does a very poor getting your airplane ready for painting, 10. Inadequately cleaned surface you, like many of us, will probably underjob of concealing surface imperfections. (ink markings, etc.). estimate the size of the job. It will reDoes seeing scratches and sanding marks under a paint job bother you? If Unfortunately, the crowded confines quire more than a little bit of sanding of our workshops, as well as the relentso, you'd be much happier to see your here and there and a coat of primer to less passage of time (two, three or more airplane free from that sort of eyesore. prepare it for its final top coat. years for most projects) often subjects We soon learn that simple jobs often If uneven or rough edges seem to jump a project to a variety of cosmetic mishave a way of mushrooming into fullout at you when you examine other haps that can best be described as fledged time consuming projects. Unairplanes, resolve that your own project "hangar rash." will not suffer from like problems. All it fortunately, preparing an airplane is a takes is a little extra time and a lot of simple enough task but it seems to go Useful Preparation Tips on and on. That being the case, it is elbow grease to eliminate these and similar blemishes. advisable to begin your pre-paint prepThe so-called hangar rash notarations somewhat sooner than you withstanding, unless you are an excepmight have anticipated. Look For These Surface tional builder, a fuddy duddy as it were, A good time to start preparing your Imperfections you will certainly be surprised by the airplane would be coincident with the number of previously unnoticed little Here are 10 of the most common initial assembly of the airplane. blemishes that detract from an otherblemishes and skin problems you are Typically, an initial assembly of the finding. wise beautiful finish: homebuilt is made soon after all of the major components have been com1. Sanding scratches, swirls, and file If a beautifully finished surface is important to you, everyone of these flaws marks. pleted. will have to be corrected somehow. 2. Pin holes in fiberglass compoThis preliminary assembly effort is A few suggestions follow. primarily for the purpose of rigging the nents. 1. Reworking Unsightly Blemishes 3. Bumps, lumps and buckles in the controls and assuring yourself that evand Damaged Areas surface metal. erything fits. 4. Poorly driven rivets. a. Sanding - Thoroughly examine all As you install each of the control sur5. Poorly countersunk holes and imof the external surfaces, inch by inch, faces, for example, you will have to establish that it connects properly, has the required range of movement and that sufficient clearances are maintained. While doing all this, you may find that you have to adjust clearances by cutting away more metal, enlarging openings, and smoothing and fairing some of the edges. Small details like this affect the finished appearance of the airplane considerably and are best corrected on the spot lest you forget them later on. These distracting little chores of sanding, filing, trimming and patching can develop into a lot of work but they have to be done to assure yourself that everything looks good, fits good and works good. As you get further into the preparation of the external metal surfaces, the details requiring attention sometimes seem to be endless as one blemish after another is discovered. Unfortunately, you cannot rush the work or You can prepare, prime and paint both sides of a wing panel this way . . . without any slight the smallest detail. Yes, it will take help. Suspend the wing from its aileron bracket with a wire to a screw hook screwed into the garage door frame. Rest the spar end on a saw horse or stand. time, a lot of time . . . maybe weeks. SPORT AVIATION 29

for deep scratches and file marks. Having used too coarse a grit sandpaper may also have contributed to some scratches. These will certainly show through the painted surface unless you remove them. If the scratches are fairly deep, fair them out with No. 240 grit paper. Then, sand the affected areas with No. 320 grit wet/dry sandpaper followed by the smoother No. 400 grit wet/dry sandpaper. Do not remove any more of the Alclad finish than is necessary to remove the scratches and other blemishes. Water sanding is the fastest, cleanest and easiest way to sand. If you can, use a water hose adjusted to provide a tiny trickle of water at all times. If that is not possible, a pail of water and a sponge will serve almost as well. Wet the surface thoroughly before you start and work in the shade, if you can. The correct sanding technique calls for the sanding to be done in straight strokes. That is, sand with straight strokes in one direction (back and forth) or alternate with cross hatch strokes. Never sand with circular motions. The swirl marks are more likely to show through the final finish. b. Rivets - Examine each rivet for fit. Rivets should be seated solidly in their countersunk or dimpled holes. If a rivet head is slightly cocked or protruding, you should file it down, or dress it flush with a rivet shaver set in your Micro Adjustable Stop Countersink tool. To do a good job of inspecting rivets, run your finger tips over each rivet to see if it needs special attention. You will be surprised. Your finger tips can tell you a rivet head is protruding or otherwise needs attention when your eyes alone won't even see the need. Replace poorly fitted solid rivets if you can. If the rivet is sound but poorly driven,

A fiberglass fairing at the base of a windshield should be faired and primed with a sandable primer. Any pin holes that become apparent can then be filled by smudging over them with your finger wetted with primer.

leave it be and fill around the blemish with a filler (lightweight Bondo or similar) after roughing the spot with a coarse grit sandpaper. Hammered dents and depressions adjacent to rivets (known as 'smilies') should be similarly filled and leveled (after roughing the area with coarse sandpaper). After filling the ding, dress the Bondo filled area roughly with a coarse file (clean the file frequently) before the filler sets too hard. After the filler cures completely it becomes so hard that sandpaper cannot do a good job of leveling it and feathering the filled edges. Finally, scrub around the rivet heads with a toothbrush dipped in acetone, MEK or lacquer thinner, especially if your rivet holes have been primed and the wings and other metal components have been laying around for a year or two. If you don't, the finish coat may not flow properly around inadequately

Sanding and scuffing the fuselage bottom is tiring work. It helps to have a creeper to lie on ... but don't stop to rest or you just might doze off. 30 SEPTEMBER 1990

cleaned rivet heads. c. Lumps and Bumps - Carefully remove all previously overlooked hardened glue and resin drips. These lumps and similar drippings cannot usually be dissolved by solvents, so you may have to remove them mechanically with a sharp wood chisel or a single edge razor blade. Be careful not to gouge the soft metal surface. If a particular lump cannot be sheared off, work the lump down flush with a shop file. Finish the clean up with sandpaper wrapped around a sanding block. Never try to dress down a lump with sandpaper backed only by finger tip pressure. You will find that the sandpaper will tend to override the blemish and cause you to inadvertently sand off more material surrounding an offending lump than from the lump. A small protruding bump in the metal is best left alone. You can't file or sand it down without cutting through the metal. If you want to risk it though, you could try hammering it down and changing that bump into a depression. A depression can be filled and leveled. However, this won t work if the bump is directly over some underlying rib or structure. Anyway, think hard . . . is it worth the risk? d. Fiberglass Parts - Most metal homebuilts use a number of prefabricated fiberglass components. Some of these are beautifully finished, others are not. Anyway, these fiberglass parts are notorious for harboring countless pinholes that seem to show up only after the parts have been primed and painted. What to do? I would suggest you first make any necessary repairs for extensively gouged areas, separated joints, or other imperfections, using fiberglass cloth and resin.

If the area being treated is not large, only a filler is required. You can use microballoons (Q-Cells) or preferably a lightweight Bondo filler for small areas. Next, sand and smooth all of the fiberglass seams and edges (wing tips, cowling, fairings, wheel pants, etc.) with a sanding block. Finish with No. 320 grit sandpaper. Blow off the sanding dust and wipe the surfaces down with a solvent. Follow this by spraying the entire fiberglass component with a sanding primer like "Fill 'n Sand" (DuPont) or some other similar brand. That primer coat will, magically, cause pinholes and other imperfections to stand out in stark relief, making them more visible. Unfortunately, no matter how much primer or paint you spray over these tiny rascals, you cannot hide them. All you will be doing is to cause a heavy build up around the pinholes, making them show up worse than ever. The only practical way to fill pinholes is by smearing primer on your finger and rubbing it over and into the holes to seal them. When you think you have covered all the pinholes, sand the treated area, blow off the dust, and wipe the part with a clean rag dampened with an enamel solvent. Make another inch by inch inspection and again try to fill the newly discovered pinholes. Although you may carefully check and check again, don't be surprised if you discover a few more pinholes . . . AFTER you have painted everything. e. Metal Edges and Clearances - Be sure the clearances around your control surfaces are adequate and there is no danger of them rubbing or binding against adjacent structure. Smooth and slightly chamfer the edges with a smooth cut file to finish them. Your gaps and joints will look much better when their adjacent edges are uniformly parallel to each other. Working a hand held hacksaw blade down, along and through each joint will help even their edges. For example, the joint between the cowling and the firewall, as well as the space between the upper and lower cowling halves, can be noticeably enhanced by running a hacksaw blade between the edges to even them up. Careful . . . don't saw into the underlying piano hinge or adjacent parts. All metal edges, particularly those forming the ends of the flaps and ailerons, should be dressed with a file to make them smooth and straight. At the same time slightly round the edges. Sharp square edges and corners do not hold paint well and chip easily.

After you have filled, filed, sanded and otherwise repaired whatever dings and unsightly gouges and scratches you can find, your wings, fuselage, control surfaces and tail assembly can be readied for priming. 2. Preparing Metal Surfaces For Priming As you know, primers are undercoats applied to metal surfaces to inhibit corrosion and to provide a good base for the application of paint (polyurethane, lacquer, enamel, etc.). NOTE: Never ever spray paint (or for that matter, primer) directly over an unprepared Alclad aluminum surface. The paint (or primer) will peel or flake off. Before you can prime Alclad aluminum surfaces and be assured that the primer (or paint) will not peel off, they must at least be: a. Scuffed with Scotch Brite (3M) pads, or b. Sanded lightly with No. 400 grit wet/dry sandpaper. The purpose of the scuffing, or sanding, is to de-glaze the Alclad skin. This will provide a slight "tooth" and the primer will adhere better. This procedure is considered to be the first step in preparing new aluminum surfaces for priming. This scuffing or sanding can be done wet or dry. Some builders use the Scotch Brite pads dipped in water although you may prefer to use them dry. To speed up your scuffing work and to cut down on the manual labor, try affixing a Scotch Brite pad to your jitterbug (vibration) sander. After the entire surface of a wing (or whatever) has been dulled, blow off the dust with an air hose while wiping the surface with a clean rag. Following the dulling process, you have two alternatives:

Method 1 - The low cost minimum effort method. a. Wash the scuffed skin surface with soapy water. Then, rinse, wipe and blow dry the joints and corners with an air hose. b. Spray on a coat of zinc chromate primer, preferably a self-etching primer like Variprime (DuPont product) and the surface is ready to receive its finish color coat. This is considered to be the minimum preparation method. So much for the bare minimum preparation. Method 2 - The 2-step Method. This is a more expensive preparation. It is also considered to be the aviation industry standard for preparing aluminum surfaces for priming. For example, the DuPont paint folks recommend using their 2-step cleaning/ etching preparation. Step 1 - Clean the surfaces with their 225-S Cleaner. Step 2 - Apply their 226 Conversion Coating to the cleaned surface. After that, the surface is primed, making it ready for painting. The Ditzler paint folks also recommend a similar 2-step preparation treatment of their own. That is, after the basic scuffing, the aluminum surface is to be treated with their DX-53 Alumiprep cleaner and then given a DX-503 Alodine conversion coating. Actually, other well known paint companies have their own 2-step procedure for preparing the bare aluminum skins for priming and painting. Use whatever brand you like, but for the best results stay with their products all the way . . . and follow their instructions to the letter. It could keep you from Part 1, botching your paint job. For example, did you know that paint manufacturers usually stipulate that a

Rest the propeller hub on a saw horse and you will have easy access for preparing the priming the bottom of the fuselage. Don't forget to chock the wheels. SPORT AVIATION 31

The engine mount finish suffers unbelievable abuse during the installation and hook-

up of the engine. Use a good epoxy primer. Enamel or lacquer finishes scrape and chip easily. By the time you finish, the mount will look like it has been hit by shrapnel.

The primer and paint will not adhere very well to an Alclad surface unless it is first dulled by scuffing with a Scotch Brite pad or with #400 grit wet/dry sandpaper.

primed surface be given its finish coat within so many hours or days after their primer is applied? Many builders prime their completed components and store them for months before they can be painted. These old primer coats need to be freshened by a light sanding with No. 400 grit wet dry paper and wiped down with an enamel reducer, or be given a seal coat. It all depends on the type of primer used and the manufacturer's instructions. After all those long drawn out days of surface preparations, it is nice to know that the whole airplane can be painted in a mere day or two. However, that, of course, depends on the complexity of the color scheme and the type of paint system to be used. You know the rule. When all else fails, read and follow the instructions. More next month.

If you wish to contact the author of this column. Sportplane Builder, for additional information, please write to Tony Bingelis, 8509 Greenflint Lane, Austin, TX 78759.

BOOKS BY TONY

The following books by Tony Bingelis are available from the EAA Aviation Foundation, EAA Aviation Center, Box 3086, Oshkosh, Wl 54903-3086,1 -800/843-3612, in Wl 1-800/

236-4800. Major credit cards accepted. - Sportplane Builder (Aircraft Construction Methods. 320 pages) - $17.95. - Firewall Forward (Engine Installation Methods, 304 pages) - $19 95

- Sportplane Construction Techniques (A Builder's Handbook. 350 pages) - $20.95.

Add $2 40 postage and handling for each

publication ordered

If you have to prime and paint your airplane in the driveway, pick a cloudy day. Painting in the sun is not recommended. The surfaces get overly hot, and shadows make it difficult to get even coverage with the primer or paint. 32 SEPTEMBER 1990

. o r order all three for

$52.97 plus $6.95 postage and handling Wisconsin residents add 5% sales tax.