Control Line: Aerobatics
Frank McMillan 12106 Gunter Grove San Antonio, TX 78231
FLASH NEWS
Tom Dixon is working with the current world champion, Zhang Xian Dong, to import his models and engines. This would be a great opportunity to see, evaluate, fly and collect championship-quality equipment, including perhaps finished airplanes! Contact Tom for information at 1938 Peachtree Road, Suite 401, Atlanta, GA 30309. I'm excited about this one and hopeful that I'll be reporting on the engines soon.
Tech Tip: Repairing airplanes is a fact of life
There are many times I think I'd rather build a whole new plane than undertake a major restoration. But when you look at the time and money involved in constructing a new one, you'll find that it's often more economical to get that old ship airworthy again. Before you get into the actual repair work, there's one thing you'd better do now or you're going to run into major problems down the road: get the plane clean.
You must free the surfaces of all accumulated oil, dirt and wax. I hope you will have done some cleaning after your mishap, because it's necessary in order to prevent oil soaking unprotected wood. But if you're like me, you didn't, and you'll have to take other steps to prepare your plane for reincarnation.
Before you start anything, take a thorough look at what you have to do and plan your approach. Wipe off as much dirt as you can, and be careful to keep any accumulation of grime away from bare wood. Examine all the mating fractured surfaces and determine if any oil has soaked into the wood. If it has, spray all the affected areas with Texize K2R. Do this outdoors if possible or in a well-ventilated room; wear a mask until the fumes have dissipated. The spray contains a cleaning solvent and will form a gel on the surface. The gel dries quickly to a white powder and draws oil to the surface. Dust the surface and see if any oil remains. It may require repeated applications, but it will work eventually.
Once you have the serious oil removed, it's a good time to think about what's on the surface that you can't see. There's probably some oil, wax and dirt still left that will have to go before you can refinish or repair. Automotive degreasers should do the trick. Prep-Sol and Pre-Kleaner are two good ones. These are both slow-drying clear liquids which dissolve the oils and must be wiped off before drying. Several applications will get painted surfaces super clean. That's cleanup. Now you have to put your puzzle together again.
Good technique while preparing and reassembling will save headaches later. Clean mating surfaces, test-fit parts dry, and make sure you have correct adhesives and clamps before final assembly.
I'd like to pass along a solution to a problem that has plagued me for more years than I care to admit. On most of the dope-finish planes I've built in the last ten years there has been a spot or two that would crater on the last clear coats. Sometimes there would be some spots that when sanded would show as black pinheads. The problem was so serious on my last plane that it would crater no matter what I did and I was ready to lock it in a box for a week with a slow leak to see if the solvent would outgas without further showing the trouble.
I knew it was time the problem got solved, so I tried to test all of the suggestions I'd collected over the years. The first coats with a very slow thinner to allow any trapped air to escape and to level the coat worked the best. The coat must be dry before you apply the next coat. One good approach is to spray a light coat every ten minutes until the build is complete, then let it sit 48 hours before wet sanding. Another approach is to brush the first coats and then spray the final coats. I have found that good ventilation is very important; dope in a confined area will form bubbles in the finish.
Sanding sealer works better than sanding dope for eliminating pinholes and small surface defects. The sealer fills and levels and then the final coats of dope can be applied. Often you'll find that the last coat needs to be thinned to avoid crater formation. Straining the dope before use and keeping the spray area clean of oil, wax and lint will prevent many finish problems. Use tack rags and wipe surfaces with a good degreaser such as Prep-Sol or Pre-Kleaner just before spraying.
Another source of finish trouble is moisture or temperature change. Blanching or a milky appearance will occur if moisture condenses on the surface during or after spraying. Avoid spraying when humidity is high and keep parts warm and dry. If you must spray in marginal conditions, increase flash time between coats and use slower reducers. Hand oils and contaminants can be removed by wiping with solvent; when mixing and handling dope, strain it through cheesecloth and use brushes reserved only for finishing.
Good technique, clean materials, proper thinning and patience will take you most of the way toward flawless finishes. Good advice from one and all, but I'd done all of these things. The problem still showed up during the final coats. Strangely, the problem didn't appear every time, and it showed up at different spots on the airplane. On several of the ships it popped up on the elevators, so I began to search there. I'd used one of the elevators to test the weather to see if I was getting a blush before laying on a clear coat over the whole plane. Sometimes I'd used retarder or more thinner on a following coat shortly after the first coat. Nothing unusual, but I did remember that, on occasion, the ink lines faded after three coats.
I felt sure the secret was hidden here, so I focused on what was different in this situation. Beginning with the basics, I looked at my spray setup. I was using 25 psi regulated at the gun and carrying more pressure from the regulator at the compressor—this to account for the drop in the twelve-foot hose. And suddenly a light bulb flashed.
As I played with the setup I noticed that I was regulating to 25 psi but only after the first surge of high pressure air. I was blasting the surface with 50 psi as I made repeated short passes while loading a thick coat on certain pieces. Unknowingly, I was creating the worst possible condition: high pressure air on a thick, wet layer of color or clear. The undercoats were softened, and the air dislodged the unstable surface. Simple, and right under my nose.
To test my theory I refinished the new ship. After I got the color stabilized, I set the regulator on the compressor to just above 25 psi and left the gun regulator set at 25 psi. Everything worked very well: nice finish, no fading, no craters and good gloss.
Vintage Stunt Championships
Mark your calendars and start building! It's time to get ready for the third edition of the Vintage Stunt Championships. Jo Ann and Mike Keville have announced that the next edition will occur March 23 and 24, 1991. Like last year, the event will be held in Tucson, AZ at Silverbell Park — a super flying facility.
The times have been changed though. Old Time Stunt will be flown on Saturday and Nostalgia will be flown on Sunday — two rounds in each category. This year ignition—OTS—may separate into a class if there are enough entries. Jo Ann will again be CD for the contest and can be reached at 6109 E. Ivyglen, Mesa, AZ 85205. Don't miss this one.
New Products
Those of us who sheet our foam parts know how difficult it is to get good joints on the wing skins. I've tried all sorts of techniques and they all worked OK but I was never completely satisfied with the consistency or the ease it took. Then I was watching one of the Pro Stunt building tapes and saw Windy Urtnowsky using a fixture that was just the ticket.
The fixture is composed of two 1/4-in. x 2-ft. x 4-ft. sheets of Corian aligned at each end with steel pins. The edges are milled straight and square. To use them, sandwich a set of skins between the sheets with the edges overlapping the milled surface. Then run a long sanding block over the sheeting edges until they are all flush with the true fixture surfaces. This automatically gives straight edges with the surfaces perpendicular to the sheet surface. Super joints and beautiful skins.
This is not a cheap item (around $100!) but it does the intended job superbly. Contact Windy at Pro Stunt Products, 9 Union Ave., Little Ferry, NJ 07645.
Transcribed from original scans by AI. Minor OCR errors may remain.
