In the 1980s, I worked as an avionics supervisor at Hayes International Aircraft Corp. in Birmingham, Ala. A Boeing KC-135 test pilot on return from a test flight told me in a debriefing that they had been struck by lightning during the flight, and all of the compass instruments, and some of the other flight gauges, were now not working correctly.
We checked and found that the compasses were pointing in all different directions -- except the correct one.
We started the repair by replacing the simplest part -- the cockpit whiskey compass. The new one pointed in the wrong direction, as well. My crew and I were dumbfounded. We thought that maybe we had a bad part, so we replaced it again. This one also performed the same as the first replacement.
I went to my truck and got my trusty Boy Scout hiking compass. As I entered the cockpit, it too was pointing in the wrong direction. Something had to be magnetized. We brought the aircraft engineers out to try to help figure this out. When they looked at the cockpit blueprints, they found that there was a steel shield buried under the aircraft skin just above the cockpit to reduce damage from bird strikes.
That was it, and it was huge -- nearly six feet long and 11 feet across. Now the question was: How do we demagnetize something this big? We used a TV demagnetizer coil and went over every square inch of the top of the cockpit, hanging on a strap from a crane.
It actually worked! We towed the plane to a compass rose, checked the headings using a sextant, and found it was back on target. We calibrated the compass and everything was back to normal. I've heard of aircraft being struck by lightning before, but I never knew something like this could happen. I definitely think it could happen to a steel car, as well.
This entry was submitted by Dan Clark and edited by Rob Spiegel.
Dan Clark designs RF imaging coils for the highest magnetic field MRIs in the world at the National High Magnetic Field Laboratory in Tallahasse, Fla., Gainesville, Fla., and at Los Alamos, N.M.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
Dan, you mention that this could happen to a steel car, and that is may be correct. There is a bit of a difference, since the car is typically a cage, or enclosed structure, while the plate you mention is not.
Cars are said to be a safe place to ride out a lighting storm since they create this Faraday cage effect and becuase the rubber tires insulate the vehicle from the ground. This helps protect the passengers. With all the talk about cars made of composites to save weight, we may loose this safety feature.
My convertable (an older, mostly metal vehicle) has a cloth roof and a flimsy metal frame (hardley a cage) and I think about this every time I'm caught in a thunder storm. For me this isn't just a statistic, as my father was protected in a metal car that was hit by lightning in a freak tornado (and yes, his car was not touching the ground when it was hit).
I doubt the insulation the tire's provide has a measureable effect on a lightning strike (the electrical arc has already travelled thru 10's of miles of insulation, the extra few inches of rubber are negligable).
I used to design warning equipment for cranes and the equipment was frequently damaged by lightning strikes. I had a small collection of artifacts and was amazed by the strange paths the charge would follow. I had one unit with a neat 1/8" hole blown through a filter capacitor so that you could see through to the other side. The capacitor still tested good, but the chassis behind the capacitor had a 1/2" hole of melted steel.
Ever see the movie "Sweet Home Alabama"-? Reese Witherspoon and Josh Lucas's characters put steel rods (like 10' rebar) standing upright in the sand on the beach before a lightning storm. The result was a twisted root-like structure of glass resulting from the instant crystallization of the sand. I always wondered if that was real or just Hollywood.
Yikes!! I viewed those sites on FULGURITES, and the natural result of lightning strike is a far-cry from what was depicted in the Movie! Real Fulgurites look like crusty, porous rock. The movie depicted beautiful shimmering curves of crystal, like a swan's neck. Kind of as I suspected; Hollywood dresses up reality.
However the UF site had some awesome images of actual lightning strikes. Definitely worth the click. Thanks!
At an office where I worked, lightning struck a tree very near to where I park. A few days later I noticed a very awful smell near the area. This particular location often is tested for groundwater contamination from benzine. Anyway looking around on the ground, I found a fulgarite in the sandy soil. One of those weird things.
This is fortunate that the planes are designed with compass redundancy. If there had been only one compass and the plane was flying at night, the pilot could have been flying in the total wrong direction for a long time before seeing the error.
Actually, the KC-135 had three double airline-type seats and, across the aisle, some fold down bunks to accomodate a second crew for very long missions. Also there was a freezer, refrigerator, and microwave oven for the in-flight meals. In addition, there were some fold down troop transport type seats. There were windows in the escape doors above the wings.
I had a long ride in such an aircraft at AFROTC summer camp in 1963. We got to watch refueling of a B-47 from the boom operator's compartment in the tanker.
The Airforce KC-135 is a version of a Boeing 707 passenger plane. Neither are being manufactured any longer. The KC abreviation is the Airforce initals for an in-air-refueling plane. It mostly carrys cargo but the ones I worked on also had hammocks strapped to the walls for hitchikers. I would imagine it's still in service at a very greatful general. We had originally thought it might be removed from service till a fix had been found.
That was a very interesting scenario - which also hits home as to why pilots need to be trained how to fly when losing instrument orientation - those guys knew what to do!
I really appreciated the solution they came up with - an obvious fix because they related it to similar problems with a known solution and out of the box thinking to make it work for their particular situation. I would have liked to seen it implemented!
Presumably they took all the compasses out of the aircraft before they degaussed it. Otherwise they could demagnetize them and weaken or destroy perfectly good compasses.
This would be even more likely if they had built a huge coile and passed the entire aircraft fuselage through it. That would do a more thorough job of demagnetization.
This is not so far out as it seems. During World War II, submarines were degaussed (so as to eliminate vulnerability to nmagnetic-homing torpedos and mines with magnetic triggers by passing them through a huge degaussing coil.
Good point about the compasses, Larry. That is very interesting about the submarines. I would think if the airplane design was such that this was a frequent problem then building a huge coil for degaussing would make sense. But then if the problem was frequent and caused instrumentation loss at critical times - a redesign is probably a better solution...
Not only Submarines.. but more importantly: WW-II Minesweepers! Those had large degaussing coils BUILT into their hulls. Later designs (Vietnam era) were made with some non metal sections to avoid magnetization. It is not generally known that mines have sunk more ships than other weapons along history. Magnetic ones were perfectioned quite a bit during WW-II. Another thing that can be magnetized in ships, are the twin iron balls installed on an adjustable slide bar just under the magnetic compass, used to correct the compass reading by adjusting the distance of each ball to the compass, which modifies the magnetic field around the compass (in order to compensate for any asymmetry in the ship construction).
Having a 1976 Ford Pinto that was struck by lightning, seemingly nothing happened. Although, after about a month or so (memory does not recall time lapse but it seemed short) the charging system quit working and then the electronic spark module quit working. The radio never seemed to tune in stations very good. Then when I thought I had everything fixed, the engine started knocking due to a cracked piston skirt. Coincidence?
1) The PINTO wasn't a "bright star" in the heavens for FORD! I'm surprised that these maladies were the only ones with that vehicle!
2) IF y'all wanna see some KC-135 tanker planes, take a trip to Tampa, FL and visit MacDILL AFB. You'll see MORE of them than you can count on your fingers & toes!
3) VERY god point about the new "compoosites" being used for vehicle bodies. But, maybe they'll add some carbon fibre or lampblack to keep the Faraday Cage effect alive.
Some ships and submarines have on-board magnetism-control equipment. The magnetic signature of the vessel can be adjusted to help avoid magnetic detection and ensure proper operation of magnetically-sensitive equipment.
The KC-135 has been in service for a long time (over 50 years), so it is not surprising that some of its design features are not too clever by today's standards. Placing a large piece of steel near compasses in an aircraft just isn't smart at all. There are other (non-magnetic) materials that could have been used instead.
Fortunately, with modern electronic navigation equipment, it is not absolutely necessary to rely heavily on a compass for navigation anymore.
Steel-hulled ships have used compasses for a long time. Compasses can be compensated (historically using obvious compensating balls) for the hull magnetism, and must be adjusted periodically if accuracy is important.
Several effects cause ship hulls to become magnetic. Some occur at construction time, like hammering and riveting of hull plates.
Others occur in operation including cables carrying DC currents, wave motion lapping at the hull, and even the motion of the ship through the earth's magnetic field. These are compensated by running calibrated DC currents through cables provided on the hull for this purpose.
The US Navy used to have a destroyer degaussing site in Newport R.I. Periodically the destroyers would steam to this site and slowly maneuver through the range. As I remember, most radio and radar was turned-off and occasionally there were some eddy-current issues that created some interesting folklore. I've seen several boats struck by lightening and while some had obvious physical damage from both the heat of the lightening and the heat of the current flowing through stainless rigging, others had no damage at all. Every single electronic component that I found damaged as a result of a lightening strike on the water was from current coming up through the negative (ground) and overstressing protection as well as parasitic diodes. Making the engine block and the entire negative side of the electrical system charged to several hundred/thousand volts cause all kinds of damage, some of which didn't appear for several months after the final insurance check had been cashed. Airplanes and cars really appear as conductive air and the current usually just passes through the skin and out the opposite side. BTW car tires are not a very good insulator (the black part of the tire is mostly carbon) and you can see photo's of cars that had energized high-tension lines draped across them where the tires are on fire.
There is an (much used and abused) old saying: "good ol' KC-135's never die, they just get new bigger and better engines and continue flying, just don't tell em how old they are"
And that is probably true of many old Boeings (the 707 and 727) specially. New much more powerful, higher By-pass engines give the 707 design new life and awesome performance compared to the original 60's design. Could the 727 by fitted with those newer engines (not easy given number 2 engine location), it would still be an outstanding model.
Dan--Very interesting post. Several years ago my wife and I were coming back from a visit to a friend of ours now living in Spain. We were in-bound over the Atlantic, about 45 or 50 minutes from NY, when our 747 was struck by lightning. The pilot indicated we had just experienced a "static discharge" and there were no issues with arriving safely. The sudden "hit" sounded like cannon had gone off inside the cabin and there was a tremendous flash that illuminated the entire right wing. After 30 minutes, the captain came on line and told us we had been cleared for immediate landing and would be on the ground in15 minutes. I always wondered what, if any, damage had been done to the instruments and the air frame. Of course the airlines would never let you know but it was an interesting moment.
You were on an international flight, which means all systems must work 100% including the duplicate backup systems or you land and have them repaired immediately. I could imagine a wing strike might have affected the fuel guage readings from that wing, engines readings or even the compass.
Hopefully that was just a precaution, to declare a lightning strike and get pushed to the front of the line for the landing. In any case you are safe and sound and I can relate to that!
You should probably grateful you were flying in an old-design 747 that has mostly aluminum and metallic construction, with some composites, but not much compared to most Airbus designs or the B-787 Dreamliner... which make increased use of non-metallic composites.
I've seen ugly holes burned trough the fiberglass reinforced fairings of the tail feathers of several airliners. I specially remember one which entered in that area, to leave though the rear tip of the right horizontal stabilizer. On that flight I was riding inside the Flight Deck, and just after the hit, one Stewardess came into the Flight Deck asking confirmation that we were struck by lightning, as she started to feel the odd "taste" of the amalgams in their teeth... She was somewhat familiar with these events and learned to recognize them! After landing at the next scheduled stop at Minatitlan, I was invited to "walk the plane" (a visual inspection around the airplane). Surely enough, there was an oval hole burned in the base of the fairing where the fairing meets the vertical stabilizer, about two and a half inches by two inches, and the outermost static dissipator on the right stabilizer was damaged, only the stem remained attached to the elevator. What the lightning rod did, was to enter the underlying metal structure and exit at the elevator tip. The old aircraft mechanic that helped us carry the inspection, said such impacts were not too uncommon, but that the size of the burned hole was on the larger size.
I honestly don't think so. Although it could probably have been done with a non-magntic material as hard as steel, Titanium maybe. It would be quite expensive! I use titanium tools around our MRI magnets and most pieces cost around $300.00 each just for box wrenches. You think the government pays a lot for a hammer? Check out this web site:
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