By Lisa Turner, EAA Lifetime 509911
This piece originally ran in Lisa’s Airworthy column in the July 2023 issue of EAA Sport Aviation magazine.
“Where do I get this covered?”
Tom was in the flight school office showing off pictures of the tube and fabric kit he’d just brought home.
“The owner did some assembly but wasn’t quite to the covering stage,” he said. “I’m going to need some advice.”
“There’s nothing to it; just call the manufacturer and have them ship you what you need,” said Pete, one of the flight instructors. “There’s a manual that goes with it. I’ve walked past the forums on covering, and they say it’s the simplest thing in the world.”
“How can it be that simple if the shops charge thousands of dollars to re-cover a Cub?”
Tom realized he was asking the wrong person.
“I’ll find someone who knows something about it,” Tom said.
Tom called around at the small airport and got some names. No one seemed to know anything about fabric covering. He ended up talking to a restoration shop about an hour away.
“Yes, what they say in the forums is that it’s easy,” the shop owner told him. “What goes unsaid is that it’s not simple but can be learned by you and me. My advice is to go to a workshop on covering before you begin. If you enjoy working on things, you’ll love it. But no, it is not necessarily easy or simple.”
The Top Six Myths
Fabric covering is fun and not hard to do. However, that doesn’t mean there aren’t traps and pitfalls. Here are the top six myths about fabric covering based on what I’ve seen. Whether you are new to the world of fabric or an old hand, these may surprise you.
Myth 1: There’s Nothing to It
There’s a lot to it. While some of the systems are simpler, such as Oratex, fabric covering spans pre-cover inspections and repairs through correct tape application and attachments to spray coatings and final paint.
It can take months for a new technician to learn all there is and gain the experience necessary to turn out an airworthy basic level job. Learning the fine details that mark advanced craftsmanship takes much longer.
There are many traps for the unwary. Mixing systems, using the wrong weight fabric, not understanding spacing on attachments, and not calibrating tools (like the iron) are some of the biggest problems. Then there is paperwork and logbook entries.
If you’re new, take workshop classes and find someone to work with until you gain confidence. Since most of us have day jobs in addition to our building or restoration activities, this may be hard to do. At a minimum, attend a workshop and review the resources available online via EAA.org/Extras.
Myth 2: You Can Use Any Method You Wish to Shrink the Fabric Around the Structure
When I get a call about fabric problems, I still hear about techniques that aren’t in the instructions. “Shrinking is shrinking,” I hear from the misinformed using hair dryers. I’m talking about Poly Fiber and Ceconite systems since these are the systems used on 70 percent of aircraft. With other systems, it’s also important to follow the directions to the letter.
If you are using Oratex, the instructions will specify a calibrated heat gun and the technique to shrink the material, which has a higher melting point. This is not the same gun you use to loosen the ice around your frozen HVAC condensate line in the winter.
Typically, a finely calibrated iron is used in stages for shrinking the Dacron cloth used in most systems. Errors at this stage will adversely affect the entire production.
Myth 3: The Most Difficult Job in Fabric Covering Is the Attachment to Structure, Particularly the Rib Lacing
When we show students the knot (a modified seine knot) to attach fabric to the aircraft, they throw up their hands and say they will never learn it. But after a little bit of practice, they help the other students.
Once you get the muscle memory for it, it may never leave you, even when you haven’t done it in a while. It’s like the moment when you balance a bicycle.
The toughest job in fabric covering is sanding the silver coats. This procedure takes finesse and patience. With large surface areas, it’s easy to under sand or over sand. If you under sand, the final product will be rough. If you over sand, exposed fabric will fuzz up, causing angry blemishes in the surface later.
When you get to the sanding stage, slow down and find a bucket of patience. The time you take now will pay you back in a beautiful, smooth finish.
Myth 4: You Have to Replace the Cover With Exactly What Came Off the Airplane
When you read the regulations, it sounds like you’ll need to put exactly what came off the airplane back on. But there is a catch — and it’s an important one. When a fabric-covered aircraft is certificated, the aircraft manufacturer uses materials and techniques to cover the aircraft that are approved under the type certificate issued for that aircraft.
What if the material was Grade A cotton, and we can’t get Grade A cotton? The FAA says we can use an approved alternate. Good. Now we know we can use an STC, a field approval (Form 337), or a manufacturer’s type certificate data sheet for a different set of materials as long as we follow all the procedures and directions for that system.
Confused? Don’t worry, you and your A&P/IA mechanic will have this settled before you begin. The thing to remember is that there must be a legal and approved avenue for the materials and methods you use in the cover/re-cover.
While you will see many showplanes covered in the Ceconite system, the difference between Ceconite and Poly Fiber is small. They both use the same Dacron polyester fabric with different identity stamps. The Poly Fiber materials are less flammable than Ceconite because Poly Fiber uses vinyl coatings rather than nitrate and butyrate coatings.
Myth 5: Mix and Match Systems to Get the Best Result
This is the biggest issue when things go wrong. The materials used for a specific system play well together. If they are mixed with other systems, it is entirely possible that all that work could peel right off the structure.
Unfortunately, there are plenty of structural failure accidents illustrating this error. Follow instructions and procedures to the letter, and don’t mix system materials.
Let me repeat that. Don’t mix system materials.
Myth 6: An Advantage of Fabric Is That You Can Use Any Kind of Paint You Wish
Once again, we should stick to the specific materials and the specific instructions for the system we are using to ensure it’s airworthy. The important thing about fabric paint is that it is designed for fabric, meaning that it will have a flexing agent — an additive — that allows the finish to move and flex with the cover, lowering the chance the finish will peel or crack.
The STC you use to re-cover your aircraft only applies through to the silver coatings with many systems. The paint may be up to you. I’d follow the recommendations for the system you’re using. Aircraft surfaces are subjected to vibration and an assortment of loads in flight, so using a coating without flex additives will cause both adhesion and cracking issues over time.
Finally, I hear you saying that since you are covering/re-covering an experimental, none of the regulations matter. However, the materials follow the laws of chemistry and physics in the same way that materials on a certified aircraft do. That means you are every bit as susceptible to crashing as the certified aircraft is. Choose to be airworthy and follow the instructions in the same way you would if you were working on a certified aircraft.
Overall, remember to get some hands-on experience, have the manual and checklists available for reference, and follow the procedures to the letter. Throw in patience and time, and you’ll be very happy with the result. Also, remember to check out EAA.org/Extras for additional resources.
Lisa Turner, EAA Lifetime 509911, is a manufacturing engineer, A&P mechanic, EAA technical counselor and flight advisor, and former designated airworthiness representative. She built and flew a Pulsar XP and Kolb Mark III and is researching her next homebuilt project. Lisa’s third book, Dream Take Flight, details her Pulsar flying adventures and life lessons. Write Lisa at Lisa@DreamTakeFlight.com and learn more at DreamTakeFlight.com.