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.