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Stewart Systems vs Other Systems

Posted: Monday, November 4, 2013 10:57 PM Quote

I asked a local IA his thoughts on the Stewart Systems.  He said he was taking a "wait and see" attitude, siting the following issues:

-  He wanted to see if the process holds up for 30 years.
-  The fabric "falls apart" when there is a fuel leakage.
-  The fabric is subject to worm holes.
-  The system has not been subjected to extreme colder temperatures for an extended period of time.
-  Superflite was a passing fad and fears the Stewarts will be the same.
-  Thinks Stewarts is a "water born" process and has concerns about the "water" causing erosion.

Please share your thoughts on his concerns.

Posted: Tuesday, November 5, 2013 1:19 PM Quote
Most importantly all solvent based paints and covering systems have been changing over the last few years as the EPA has restricted the use of chemicals that were previously available in an effort to reduce the VOC's of coatings.  Nothing that you can buy today to cover and paint an airplane has a 30 year track record because it's not the same stuff that it used to be.  To my knowledge Dope and Polytone are the only coatings that have had very little change.  Superflite is going to faze out their dope process over the next few years and I suspect Randolph will disappear within the next 5-10 years too.  Just like 80 octane av gas disappeared so will Dope.  

When you talk about "fabric" I believe you mean the coatings applied to the fabric.  The only thing that will destroy fabric is fire, UV light, excessive heat when shrinking the fabric, and sharp objects.  We have multiple customers with cover jobs over 10 years old that have had to make repairs and they all say that the fabric and finish when cut of the airplane is just as flexible and shiny as the day it was applied.  You can wad up a piece of fabric into a ball without cracking the finish.

The only systems that are comparable to Stewart Systems would be ones that use a Polyurethane type catalyzed paint.  Dope and Polytone do not have the performance that you get from a catalyzed paint and require regular maintenance with rejuvenator to maintain the flexibility and gloss.  Rejuvenator is supposed to be applied before ringworm or cracks not after. Single part coatings do not have the solvent and stain resistance that catalyzed paints do either.  So now we are comparing Aerothane/Randathane, Air-tech, Superflight VIII, and Stewart Systems as what is available for an STC'ed covering process.  The only system tested and approved under the newer and more stringent FAR part 43 standards is Stewart Systems.  Stewart Systems has the best UV protection and the lightest weight finishing system.  According to our customers that have been using all the various systems they feel that the performance and longevity of the process over the last 5 years looking at various aircraft covered with the different systems all done at about the same time is showing SS to be equal or better than all other systems in use.  

Car gas is nasty stuff with additives designed to clean carbon and sludge from automotive engines. It's basically a mild paint stripper and yes if you continuously and heavily soak fabric covered with SS from the inside with car gas you will see blistering from the inside out.  Other finishing systems will do this too but SS reacts faster to the car gas.  I have repaired multiple aircraft covered with dope and polyfiber that have suffered finish defects from leaky fuel tanks.  100LL does not have the additives that affect paints like car gas.  You shouldn't be operating with a massive fuel leak anyway.  From the outside fuel does not effect the paint.  Catalysed paints are solvent resistant.  All coatings are subject to staining dependent on multiple factors but soaking the finish from the outside with fuel does not blister the finish.

SS coatings resist the cold just as good as the other catalyzed paints and better than most.  We do not use flex additives that disappear over time like the solvent based systems do.

There are no problems with corrosion when using waterborne coatings.  We have not seen or heard from any customers any problems related to corrosion.  I can tell you that if you aggressively sand blast steel and when priming it you do not apply a thick enough layer of primer the tiny peaks of steel that protrude through the thin coating of primer as it flows and dries become exposed to the atmosphere and will rust.  That will happen with solvent based coatings too.  And we highly recommend that you always top coat steel parts with paint and not leave them in primer.

Again the most important thing to remember is that NO covering system in use today for fabric aircraft has a 30 year track record because the chemicals have changed over the last few years.  

Posted: Thursday, November 1, 2018 7:55 AM Quote
I am building a wooden aeroplane and am at the painting stage. At this point I have all components covered and painted with PolyBrush and PolySpray, with only the wing needing another PolySpray coat before colour coats.
Can I use Stewart Systems colour coats over the PolySpray, and your aluminum filler over PolySpray?
There is no legal issue here in Oz as the aircraft will be non certified.
Posted: Wednesday, November 7, 2018 4:44 PM Quote

I'm sorry I didn't respond sooner.  Our website does not notify me when something is posted.  Yes, you can go over Poly Fiber products with our products on experimental.  Make sure the surface is clean and scuff sanded.

Andy Humphrey A&P
Stewart Systems Tech Support