Composite airplanes are tough — easy to repair
Attend the Lancair composite repair and maintenance school and you'll get a good look into the future of airplane maintenance. Owners who are accustomed to the concerns that swirl around aluminum airplanes — metal fatigue, cracking, and corrosion — may feel like they're taking a big risk when buying a composite-airframe airplane. For those who are a little leery of composites, the November 12, 2001, crash of American Airlines Flight 587 in which the vertical stabilizer — an airfoil constructed largely of composite materials — departed the airplane during an encounter with wake turbulence may seem like enough evidence to dismiss this technology entirely. Other prospective composite-airplane shoppers may be worried about more mundane matters, such as the availability of qualified repair personnel for these new airframes.
At the Lancair school, our class learned about composite construction and repairs — scarfing; plies; honeycomb; tap testing; class 1, 2, 3, and 4 damage; room cures; and post cures. Although the technology was new for us, learning how to repair it wasn't difficult. By the end of that snowy week in December, the class had seen that the composite world of Lancair wasn't anything to fear.
Kitplane — what kitplane?
Some people may think that the certified Lancair 300- and 400- series airplanes are just beefed-up kitplanes — plastic airplanes, brittle toys that shatter like glass, and dumpster chow are among the derogatory comments heard from airport know-it-alls when composite airplanes are mentioned. Yet the speed and efficiency of contemporary composite airplanes make aluminum airplanes look like dinosaurs. Is it any wonder that potential composite-airplane buyers are confused? If I buy a Lancair, who's going to know how to repair it? None of the mechanics at my local FBO knows anything about working on or repairing a Lancair or any other composite airplane. After a week at the Lancair maintenance and composite repair school I can testify that none of these questions should slow down the prospective buyer of a composite airplane. The idea that a certified Lancair airplane is just a kitplane with an FAA stamp is folly.
Dieter Kohler, Lancair's vice president of engineering, dispelled this notion one hour into our first day when he said, "There's only one part in this airplane that's identical to the kitplanes, and that's the rudder pedal casting." The kitplane and certified airplane factories operate independently, although they are located only 16 miles apart.
The Lancair school is primarily for the mechanics who will service Lancairs in the field, and shops or A&Ps that are looking to become Lancair service centers. Our class had 12 members. Future classes, scheduled for every other month, will be limited to eight.
Jason Doscher and Paul Beck of Willmar Air Service in Willmar, Minnesota, came to Lancair to increase their knowledge of composites for their company's Lancair service center. Tim Tobey and Steve Betts of Winner Aviation in Vienna, Ohio, came to learn about setting up a Lancair service center. George Encinas of Southwest Flight Center in Scottsdale, Arizona, was also looking into the possibility of servicing Lancairs.
Other attendees included Layton Bennett, the 82-year-old owner of LAB Flying Service in Haines, Alaska, and his three sons, Lynn, Eric, and Bart. Layton is the proud owner of Lancair 300 serial number 10. David Sos of Herfi Aircraft in Orland, California, and Ken Bjork of Salt Lake City filled out the roster. Bjork, who had built a Lancair IV-P, was the only one of us with any real composite experience.
By the time the week was over, we had learned to make repairs that were undetectable by anyone except our instructors.
Jay shows us how
The Lancair production center is located in a clean, new red building on the Bend, Oregon, airport. This modern airplane-manufacturing plant (built in 1998) is quiet, well lit, and organized. It's a remarkably peaceful place for an airplane factory. After lunch on Monday, Sam Houston, Lancair's director of flight operations and customer training, gave us a tour of the facility. Each of us got a badge and were told that, with the exception of one off-limits area, we were free to wander the factory during our breaks and after work.
On Tuesday morning we met Jay Gilbert who was going to guide us through the hands-on composite repair section of the class. Unless the damage to a composite airplane falls into class 1, repairs can be done with very simple hand tools. An accomplished composite repairman's toolbox looks like something a painter would carry about. Cans of hardener and resin, a precision scale for getting the correct mix, microballoons, scissors, rollers, sanding blocks, and small air-driven grinders do the trick. Since the parts needed for small class 2-, 3-, and 4-type repairs we learned about are made on site, there's no need for any Lancair service center to stock small airframe parts, such as wing skins, stringers, or ribs.
The crash axe
It's hard to damage a Lancair wing. I tested the toughness of the wing skin by bashing down hard on a panel with the ball end of a ball-peen hammer. Based on how hard I had to swing the hammer to make a dent, I predict that "hail damage" will never be mentioned in a "for sale" ad for a Lancair composite airplane.
Gilbert trumped my test by slamming a sharp and sturdy Gerber crash axe into a wing skin. The crash axe penetrated through the inner and outer skins, creating class 2 damage. This is the most serious damage that can be repaired in the field.
Class 2 damage is defined as being less than six inches across and affecting both the inner and outer skins of the structure sandwich. Class 3 (the ball-peen hammer damage fit into this category) and class 4 damage is less serious, with class 4 being superficial or cosmetic. Every one of my 11 fellow composite-school graduates could conduct these repairs in the field if he worked in cooperation with a Lancair factory representative and used Lancair-approved procedures.
Class 1 damage is major structural damage and always requires a repair strategy that has been devised and approved by the manufacturer. A Lancair-authorized repair station must conduct these repairs.
Composite structure
A composite structure (in this case a wing leading edge) has an outer skin and an inner skin. The two skins are separated by a Nomex honeycomb interior, which is very strong despite its light weight.
Gilbert taught us how to use common sanding and grinding equipment to cut out the damaged materials and how to taper, or scarf, the skins that needed repairing. Techniques for repairing damaged inner skins, which often are not accessible from the back side, involve laying up a few plies of cloth in resin to form a backing plate, called a contour panel, and bonding it in place. Then we scarfed the inner skin plies and bonded in new plies of cloth to repair the inner skin. After this had cured, we filled the honeycomb area with a very lightweight putty consisting of resin and microballoons. When that was dry we finished off the structural repair by bonding a patch to the outer skin.
Since Lancair airplanes comply with the lightning-strike requirements for certification by embedding nonwoven aluminum or copper mesh over the entire airframe, we learned how to use a portable vacuum bagging procedure to install new mesh over the repaired areas. After Gilbert had shown us how to make class 2 and 3 repairs, George Burnett showed us how to make them virtually invisible.
George, the painter
It takes a great deal of experience and technique to make an aluminum repair that isn't noticeable to a savvy owner or mechanic. That's not true for composite repairs. They're invisible if the paint finish is applied correctly. George "you can always polish the shine back in" Burnett showed us how to clean and prepare the surface, and how to spot in new paint. One of Burnett's rules was KISS — keep it small, stupid. Any paint repair takes time, and the bigger it is the more time it takes.
Burnett shared his secrets, but you'll have to go to the class to learn them, because I was asked not to pass them on. We did learn to polish the shine in — 2,000-grit sandpaper was used for some of our work. That's about as rough as a sheet of newspaper. When we finished our test panels, the class 2 repairs and the lightning mesh we had worked in on top of them were invisible.
Repairing composite structures is a lot easier than repairing aluminum structures since the repairs don't require a large cash outlay for specialized tools and the technique is easy to learn.
Servicing the Lancair
On Thursday afternoon, we went back to the classroom where Mike Schrader, Lancair's director of sales and an A&P, talked us through the maintenance manual and procedures. When Schrader said that mechanics had been in on the design of the Lancair airplanes, you could have heard a pin drop as the 11 mechanics in the room — none of whom thought they would ever hear such words from an airplane manufacturer — gave thanks. We were told to wear our grubbies on Friday because we were going to be guided through a Lancair 300 annual.
"I used to work for the airlines and I knew metal airplanes," said A&P Mick Guinn. "The first week I was here I saw the wing stress tests and I was impressed. These things are so strong, and so light, and so easy to repair that I'll never go back to working on aluminum airplanes."
Guinn showed us how to do an annual on a Lancair. Since ease of maintenance was factored into the design, the cost of regular maintenance is quite low, especially when compared to other high-performance four-place general aviation airplanes.
"A 50-hour, which is an oil change and engine compartment look over, should take about four hours. A 100-hour inspection [which is the same scope and depth as an annual] takes two mechanics one day," said Guinn. We leveled and weighed a Lancair, and were taught timesaving tricks on how to service the brake system and nose gear strut, with its internal shimmy dampener. We were encouraged to ask questions — Guinn had a ready answer for everything.
The catch — and the proof
Amidst all this good news about the ease of repairs, there has to be one catch — and there is. The minimum ambient temperature must be 70 degrees Fahrenheit or the repairs will be brittle. And composite repairs must be heat cured before they can be certified as airworthy.
The first (and easiest) cure is a 24-hour room temperature cure. After the room temperature cure, the repair is still brittle and weak. The next cure, called a handling cure, can be achieved by heating the room-temperature-cured part to 100 degrees for eight hours, 120 degrees for six hours, or 140 degrees for four hours. This cure is only necessary if the part, or repair, is going to be moved, lifted, or sanded before the post cure.
No repair is airworthy unless it has been post cured. This process involves four steps. Ramp up the temperature surrounding the repaired area to 150 degrees over a two-hour period. Maintain 150 degrees for four hours. Then ramp the temperature up to 200 degrees over a two-hour period, and hold the temperature there for six hours. Then let the repair cool.
While this sounds difficult, it's not. The factory uses temperature-controlled forced-air heaters mounted on portable rolling carts that are pushed right up to the airplanes. Heated air is delivered via insulated ducting to cardboard enclosures fabricated out of boxes and duct tape.
Lancair's certified 300 and 400 are tough airplanes that were subjected to torture-chamber conditions before the FAA granted certification. During these tests, an entire airframe was mounted in a huge steel testbed and subjected to varying loads for 170,660 cycles. After passing all these tests, a worst-case-scenario test was conducted with load factors increased to 50 percent over the required 4.4 load factor for Utility category airplanes — while the airframe was baking in a 175-degree F oven. Think about it — any human aboard the airplane would be mummified in short order, but through it all the airframe would maintain 150 percent of design strength. The result is an airframe with tested strength margins. Yet, in true futuristic fashion, it's an airplane that is simple to repair and easy to maintain.
E-mail the author at [email protected].
