Tips on Painting a Challenger

Painting the Challenger Using Stewart Systems Waterborne Paint

When I was first considering building my first Challenger, the idea of using aircraft paints with their powerful solvents was really holding me back from even starting the project. I knew that I couldn’t stand to use that kind of paint. Just getting a few drops on my skin or a few whiffs of that odor would give me powerful headaches. Painting an entire aircraft would be very unpleasant if not fatal. Then I discovered Waterborne paint for aircraft supplied then by a company called AFS or Aircraft Finishing Systems. It has since been purchased by another company and goes by the name Stewart Finishing Systems.

While this waterborne paint is very environmentally friendly and painter health friendly, it does present some unique challenges and I had somewhat of a learning curve using it. So this section is presented to help others with using the Stewart Systems Paint and has general tips useful in painting a Challenger or any other ultralight aircraft. Using this paint has been an overall positive experience. If not for it, I would likely have had to contract out the major painting portion of the build to a professional paint shop.

TIPS ON PAINTING:

1. Have a well lighted work area. I installed extra lights in my shop. They were not enough. So I bought cheap 4 foot portable fluorescent lights at Canadian Tire when they were on sale and strung them up with extension cords. You need a lot of light to see the surface as you paint to make sure you don’t miss any spots or put it on too thick and get runs in the paint.
2. The air compressor should be big enough to do the job. The wings on a Challenger are such a large area and they require a lot of continuous spraying which will drain a small compressor. You do not want to run out of air in the middle of a wing as it will ruin the finish. I bought my compressor on sale at Canadian Tire. It is the Campbell Hausfield 5 HP 120 volt with 13 gallon tank rated at 6.9 scfm @ 40psi. When I spray the wings (the biggest paint job on a Challenger is the wings) it runs continuously. I have a fan that I set up to blow on the compressor to keep it cool as it really heats up when it runs hard like that. A bigger compressor & tank would be better if you can afford it but that unit does work. I used it with an Apollo HVLP spray gun running at between 35 and 40 psi. Other spray guns may require more air volume and thus a larger compressor.
3. You will need a nice air filter combination unit to clean the compressed air before it gets to your spray gun. A particulate filter to clean out particles and water droplets. Then an oil removal filter to make sure no oil from the compressor gets sprayed on the paint surface. Even the tiniest amount will ruin a paint surface. I have a Wilkerson unit. Another top notch brand is Norgren. These two are the industry leaders. I use the Wilkerson 18 series F18-02-SH00 particulate filter and an M18-02-CH00 oil removal filter. Then I have a pressure regulator R18-02-RG00. They have a nice joiner bracket #GPA-96-603 that joins them together and allows you to easily mount the whole assembly to the wall. They are distributed by industrial automation companies. They are also often available through hardware chains. I haven’t checked but similar stuff may be available at Sears, Home Depot, Canadian Tire, Princess Auto or an automotive garage supply type company.
4. Drain the filters of water before you spray. They will remove some of the water from the air and hold it in the filter bowl. If you don’t empty it, the bowl will over fill and then water will get picked up by the compressed air stream and splatter all over your paint surface causing light coloured blotches. Yes. It happened to me. Another step, if you can afford it, is a compressed air dryer. There is one at Princess Auto for $79.99 . It is a chamber full of water removing desiccant pellets. It would be placed in the air line after the filters mentioned above. Then another particulate air filter is placed after the desiccant dryer to remove any desiccant dust from being carried down the line. Also drain the compressor’s receiver tank weekly as it too will fill with water.
5. I found that the HVLP spray guns were amazing. HVLP sprayers have much better performance than a standard sprayer. I use a unit made by Apollo. It produces a nice fine spray mist with very little over spray. It uses less compressed air too. I first tried using the cheap Campbell Hausfield spray gun from Canadian Tire but they use a lot of air and spray so hard that most of the paint or primer is floating in the air, on the shop walls, or on the floor. The HVLP gun puts the paint and primer on the surface where you want it. You use less paint too. They are sold at Princess Auto for a good price, around $140.00 .
6. Check your sprayer setting before you spray every time. Especially after cleaning. A few times I caught myself spraying a coat on the wrong setting and as a result did a poor job. Follow the instructions on the video. I found that it works well. The one thing I did find is that the number of turns required for spraying volume varied on my spray gun from the one used in the video. Of course, we were using two different guns, so the settings would naturally be different. Remember that these are cross coats. One coat sprayed horizontal and one coat sprayed vertical = a cross coat. I did find that to cover the dark gray Ceco-Fill primer, that I had to double up on the number of covering coats in order to fully cover up that dark grey primer. It needed about 6 cross coats, not the 3 shown on the video. Then it was ready for the final gloss coat.
7. I found that the Stewart Systems paint was good for about 45 minutes life in the cup after mixing, not the 1 hour quoted in the book or the video. Any more and it would be settling out in the bottom of the paint cup and would tend to run on the surface being painted. Or it would spit nasty globs on the surface. It also made cleaning up more difficult. For the final gloss coat, I recommend spraying it all within a ½ hour if possible for best results.
8. Don’t order the paint until you have the fabric on and are getting close to be ready to paint. It settles out in the bottom of the paint jugs and hardens. Then it takes a long time to re-mix and you never get all the solids fully re-mixed if it’s been left a long time. Stir the paint often when using as the solids settle to the bottom very quickly.
9. I used the special chain mixer that Stewart Systems sells. It was a very effective mixer. I had purchased my paint well in advance of painting and much of the solids had settled and hardened on the bottom of the jug by the time I used it. I mounted the chain mixer on the end of my cordless drill. It saved a lot of laborious hand mixing with a stick. However, it does create a foam which has to settle before using. When the paint and primer is fresh from the factory it only requires a standard paint stick to mix it.
10. The mixing ratio for the Stewart Systems paint is 1 part epoxy, 3 parts paint and about ¾ to 1 part distilled water. But here’s the tricky part. When adding in the distilled water to get that 20 second viscosity, be very careful as you get closer to the right viscosity. As you get closer, just a little bit of water makes a really big change in viscosity. So when you are close but not quite there, just mix in a tiny bit of extra water. You’ll see what I mean when you do it yourself.
11. Don’t take any short cuts on the Stewart Systems procedure. At one point someone, somewhere, suggested that it wasn’t necessary to seal the weave of the fabric with the glue thinned 10%. They promoted going directly to the Ceco-fill. That is wrong. Skipping the sealing results in a paint surface that is prone to cracking and pealing. The procedure is:
    • Glue the fabric.
    • Shrink the fabric in 3 temperature stages (250, 300, 350ºF).
    • Wick up the extra glue before it hardens. If it does harden into any blobs, use an iron at 200ºF to soften and remove or smear flat. Any blobs will show up during final painting.
    • Seal the whole fabric surface with the glue thinned 10% with distilled water.
    • Then prime with Ceco-fill until the weave is filled. A close inspection should show a surface that is flat and not like a fabric.
    • Paint.
12. Clean your spray guns after each use. The paint will tend to build up inside the internal passages. If left uncleaned, the spray tip will clog and give an uneven pattern and the needle will stick and not close. (When you go to release the trigger, the paint spit out in a small stream. Been there. Done that.) Remove the spray nozzle and needle and also clean the suction tube and the paint bowl. Clean using Lacquer Thinner. I bought a can at Canadian Tire. I use rubber coated cotton gloves for spraying and cleaning to keep the paint and thinner off my hands as much as possible. I found them at Princess Auto. I also found a paint gun cleaning kit at Princess Auto. Only $5. Comes with lubricant for the paint needle so it won’t stick. And they have a nice 1 Litre stainless steel measuring cup with Metric and Imperial volumes stamped on the side. It’s great for measuring the paint mixtures and easy to clean. I picked up a painting hood to cover my head when spraying to minimize the amount of primer or paint left in my hair and the back of my neck. Always where a breathing mask when spraying or working in the area after spraying. The paint and primer are not toxic but you don’t what the tiny particles suspended in the air to enter your lungs and harden there. I bought a proper spray paint breathing mask at Canadian Tire for $50.
13. Always sand and prime aluminum and fibreglass before painting. Make sure the all ink marks on the aluminum are removed as they will seep through the primer and paint. Use MEK solvent to remove the ink and then sand it. Wear a breathing mask and gloves when working with MEK or you will likely get the mother of all headaches. Then prime the aluminum and fibreglass with the Stewart Systems primer. Otherwise the paint will peel off after a short life. Lightly sand the Ceco-fill to remove any rough spots before painting. If you sand it too hard you’ll take it back down to the glue level again. I used 320 or 600 grit for that stage.
14. I really recommend building the wing stands. The first Challenger I built and painted, I didn’t use wing stands. I just hung the wings by the spars on wires from the ceiling. This made it very difficult to spray the leading and trailing edges and other hard to reach places (such as near the floor and ceiling). As a result, my paint and primer was a little thin in some places. With the wing stands you are able to rotate the wings and easily paint the leading and trailing edges. It also enables you to bring those hard to reach places into the light to check your work. I built mine out of 8 foot 2×4 lumber, some metal angle brackets and a few 1” and 3” long #8 wood screws. The wings have an extra 1/8” thick aluminum flange riveted to the wing box at each end at the center of gravity with a ½” pivot hole drilled in the centre of the flange. Then the wings pivot on 6” long ½” diameter bolts. I always thread on the nut to the bolt for safety to make sure the wing can’t ever slide off the bolt while I am rotating it. That would be a disaster! Anyway, this set up is inexpensive ($30-$40) and easy to build and disassemble.
15. You may want to paint the aluminum tubes in the cockpit to give fully finished look. The first step is to sand them to remove the ink markings and give a clean surface for the coatings to stick to. If you paint these with canned spray paint such as Tremclad or Armor-Coat, always prime the aluminum first with “galvanized metal primer”. Then spray the Armor-coat or Tremclad. Otherwise the paint will peel off the aluminum after a couple of years.
16. Quantities Required for Covering and Painting a Challenger:
    If you are painting the plane all one colour, about 3-4 gallons of paint, 2 gallons of Ceco-Fill, 1 gallon of Glue, 1 quart of Fibreglass Primer.
    If you are doing two colours, more will likely be required. On my latest plane, I have painted the wings and tail yellow, and the fuselage, mid wing gap covers, nose cone, wheel pants and struts are blue. I ordered 3 gallons of yellow and 2 gallons of blue. I will have a fair bit left over, but it’s better than trying to stretch the paint.

    Other Supplies Needed:
    

    • Viscosity cup.
    • Chain mixer.
    • Cordless screw gun to spin the chain mixer.
    • 1 litre MEK. This is a powerful solvent. I wore a breathing mash and gloves when using this stuff.
    • 1of 4 litre (1 gallon) jug of Lacquer thinner.
    • 1 of 4 litre (1 gallon) jug of distilled water.
    • Measuring cup for mixing paint. (the stainless 1 quart one from Princess Auto is great)
    • Miscellaneous tins or cups for solvents and water – I use yogurt containers, icecream containers, and the large 1 Kg coffee tins.
    • A few rolls 1 inch masking tape.
    • Paint strainers – about 15 or 20.
    • Garbage bags for masking off parts of the plane you don’t want to paint such as the instrument panel and cockpit. Don’t use fabric – the paint spray will seep through.
    • Sand paper: 15 sheets of 220, 15 sheets of 320, 5 sheets of 600.
    • Lots of rags and paper towel.