Electromagnetic Machine "Pulls" Dents In Place, Leaves Finish Intact

A guy at our field owns a beautiful Cessna Cardinal that got caught in the Midwest in the summer hail season. Its upper surfaces look like an army of vandals attacked it with ball-peen hammers. Now I'm debating whether to tell Andy that there's a machine that can fix his airplane, and leave the surface not only looking like new, but relieved of the stress paths that dents put in aluminum. It's truly a wondrous machine, but I hate to get his hopes up -- because he can't afford it. At this time, it's for planes that cost a thousand times what he spent. But many novel technologies are costly at first.

The machine in question is made by Fluxtronic, a Bothell, Washington company headed by Rob Olsen. Olsen is a tall, young man of serious mien. Perhaps he's a cutup in private, but in business -- such as at the NATA/PAMA/GSE Aviation Industry Week show where I met him -- he's professionally serious. That doesn't matter; engineers aren't supposed to be exotic, their technology is. And on that score, Rob definitely delivers.

Robert Heinlein famously said, through his fictional character Lazarus Long, that "Any technology sufficiently advanced is indistinguishable from magic." That statement absolutely, positively applies to the Fluxtronic Electromagnetic Dent Repair unit.

First, consider what happens when a piece of sheet metal is dented. Something strikes it, applying a force greater than the deformation threshold of the material, causing it to be displaced. If the part was structural -- and in most metal aircraft, skin bears considerable loads -- the stress paths in the metal reroute around the dent, treating it like a hole, weakening the metal. There can be aerodynamic consequences to a dent, depending of course on where the dent is on the airplane. And one of the customary repair methods -- fill and refinish -- is one of the causes of creeping weight gain in older airframes.

But you can't just put a dented pieces of metal back in the status quo ante. Or can you?

One example that Olsen shows is instructive. His machine was flown to the location of a Falcon 50 -- an expensive, sleek bizjet, and beloved of its pilots (don't get our cartoonist Wes Oleszewski started on Falcons... you might get the idea that he flew them for fun and didn't cash his paychecks). The Falcon in question had suffered a wrench dropped into the intake ring... an annular, compound-curved structure of polished aluminum; a metalworker's masterpiece and a repairman's nightmare. Removing a dent from this thing. Rob Olsen gleefully shows before and after pictures -- and in the "after" picture, you need to rely on some unrelated scratches as a landmark to see where the dent was.

The machine is simple in concept, but has been difficult and costly to manufacture in practice. By applying very high electric power to a coil near the surface of the metal, the Fluxtronic device induces an electromagnetic field on both the near and far side of the metal part. Suddenly, the outboard field is cut off -- in the split-second that the inboard field remains, it pushes against the inside of the metal, and pops the dent out. Usually, this restores the part's original contour, while preserving its original finish (whether painted or polished). Sometimes it takes several applications, and operators get better with experience.

The bulk of the machine is housed in a nondescript grey rotomolded case, and it can be shipped anywhere as cargo. From the machine, a thick cable runs out and terminates in the unit's head, which houses the all-important electromagnetic coil, an LCD control panel, and operating switches, mounted in a framework with spade-grips like those a B-17 waist gunner hung on to. The operator "points" this device at the dent and actuates the trigger, basically.

"What if there was a partially-filled fuel tank on the far side of the metal. Is there any danger of igniting it?"

Rob thought that that was a reasonable question, but that the danger, if any, was not in the fuel tank. "If you had a lot of vapor on the outside of the tank, that might be a hazard. This shouldn't be used on a tank with any fuel in it indoors. But if you open the hangar doors, or work on the plane outside, no problem."

Rob takes a piece of alloy honeycomb that has a bunch of dents, energizes the machine -- which plugs into a wall outlet! -- and applies its head to the dent. Zap! Actually, the noise it makes is a sharp metallic sound, almost like a carpenter's nail gun. The dent is not completely removed, and Rob scowls at it. "See, it's mostly gone. In some cases, you need a second shot." And the dent is, indeed, mostly gone, and it's easy to imagine that a second shot would cure it entirely.  Magic!

There are limits to the uses for the machine. A very large dent, or one that compromised internal structure, calls for parts replacement instead.

Now, about the cost? That's what keeps the unit out of the hands of smaller Repair Stations -- it's in the hundreds of thousands of dollars. "If you have a fleet of aircraft, it pays for itself. One big hailstorm and you have paid it off."

What do the manufacturers think of the technology? They are, at best, ambivalent. "They make money from the sales of service parts, too," Olsen points out. But in the end, this technology stands to benefit the manufacturers as well. Boeing, in fact, offers electromagnetic dent removal as a service using an earlier machine that works on the same principle as this one.

FMI: www.fluxtronic.com