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.
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.
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.
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.
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.
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!
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.
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