How could an airplane defend against an electromagnetic pulse attack from another airplane?

Question

Two nations are at war over something rather trivial, but offenses have been perpetrated here and there such that the conflict has escalated from a couple of guys shooting each other to massive bombing runs by both sides which can kill thousands.

The bombing runs are a la the strategic bombing campaigns of Britain and Germany during World War II:

• Wings of bombers set out in groups of four, flying four abreast. They're not quite heavy bombers, but more like the Heinkel He 111:

  

  There are a few squadrons of heavy bombers, though, like the Avro Lancaster:

  

• The bombers are protected by fast, single-seat fighters armed with four front-facing machine guns and two rear-facing machine guns. They're similar in speed and size to the Supermarine Spitfire:

  

  There are about ten fighters per four bombers - enough heavy defenses to hold off most attacks.

Technologically, all of the aircraft have systems similar in technology those of the 1960s. The one significant difference is that the engines are not jet engines. On this world, electric engines have been developed, making anything running on oil obsolete. The jet engine was never developed.

However, one side has developed technology that can emit electromagnetic pulses. Concentrated pulses can travel about fifty feet before dissipating. Each of the enemy fighters has been modified so that it only carries two (forward-facing) machine guns but has turrets above and below the cockpit that can fire an electromagnetic pulse. The one below the cockpit is weaker so that it can be fit in without causing inconvenience to the landing gear.

With proper aim, one of these fighters can render part of a bomber useless. Targets depend on the bomber type; on two-engine bombers the main target is one of the engines, in an attempt to knock out the power and control. One four-engine bombers, the strategy is to take out the rear gunner with the machine guns, then fly overhead and deliver two pulses in the general area of the cockpit, hopefully destroying instruments and potentially killing crew members.¹

The other side (non-EMP guys) are not too pleased about this, and they'd like to figure out a mechanism that can protect all the critical components (e.g. engines, fuselage, bomb bay, etc.) of the bombers from EMP attacks. They've hit on the idea of a Faraday cage, which can be really effective . . . but it's been found that holes from bullets can inadvertently cause considerable damage to the cage, which drastically reduces its ability to stop the EMP pulses (hence the strategy used when attacking heavy bombers). They've also read this pdf, but they're not at all convinced that any of the shielding ideas could remain uncompromised after machine gun attacks. Bullet-proof walls have proven to be ineffective, because of certain (as-yet unknown) characteristics of the enemy's bullets.

What can the bomber crews do to protect themselves and their airplanes?

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¹ _{Bombers now are designed with escape routes and landing gear doors that do not involve electricity and can be operated manually. Same goes for fighters.}

Answer 1

Of the two bombers you mention, one is fuel-injected and the other is carbureted. Neither of them use sensitive electronics (the first fly-by-wire/ECM system appeared in the Concorde in the late 60s). To see how much protection they need, let's look at some real-world examples of EMPs.

These guys have developed a car-stopping EMP 'gun' that, at first, seems to operate like you describe. However, the video neglects to show you the (undoubtedly large) capacitor bank used to power the EMP. They also pull the car up to point-blank range, suggesting that the impressive-looking helical antenna isn't able to focus the broadband pulse (they certainly have no qualms about firing it out towards the parking lot!). Lastly, they mention that they are disabling the car's microprocessors, which is not a feat, since without their protective circuitry, complex integrated circuits can be destroyed by accidental static discharges far too small to feel. Also note that their claimed timeframe is five years: but it's 2015 and no one's using EMP cannons on cars.

This video shows another example of disabling a car with an EMP. The important thing to notice is that the electric windows still work. The alternator, starter motor, and spark plugs are built to handle far more current than the window motor, so they are undoubtedly still working too. The reason the car doesn't start is most likely that the computer is damaged. An engine without a computer (see 1960s planes, above) would be undamaged.

Even if your EMPs are powerful enough to cause damage to an unprotected alternator, shielding such a small target is relatively simple. The only other target is the spark plugs (the starter could be external to the plane), which are already well-protected due to their placement between the head and valve covers, which form a very thick shell.

All the other parts can be mechanical, and in fact on WWII bombers like the ones you mention (developed in the 30s and 40s), they were! If powerful, long-range EMPs were developed in the 60s, likely the only change the Air Force would have to make is to switch from the B-29 (which used, among other things, electronic fire control) back to the B-17.

Finally, unless your EMP fighters are equipped with some really, really heavy shielding, they're going to fry themselves when they fire. Since they're closer to the focal point of the pulse, their shielding requirements scale faster than the defender's requirements, meaning that an offensive, non-kamikaze EMP is wholly impractical.

Answer 2

Using aircraft technology as in World War 2, I believe EM weapons wouldn't actually do much damage. The controls are complete mechanical and work without electric power and I think the electronics in the engine spark plugs are so simple that they can deal with pretty strong EMP before being damaged. Radio and gun turrets are probably the most vulnerable components on a bomber of that era and lightbulbs might fail, but otherwise I think they would be fine.

The damage of EMP is caused by the wires experiencing an energy surge that is high enough to cause the components to heat to a point where they are destroyed. The efficiency of EMP depends on the length of electronic circuits and the diameter of the the wires. Modern electronics have microscopically thin circuits that are very sensitive to getting too hot and their total length can be many kilometers. Especially when connected to power grid landline the length of circuits become mind boggling. An airplane is not connected to the power grid so all the cables to be affected are limited to those on the plane itself. And 1940s electronics are very primitive with comperatively thick wires and not actually a great length of wires. The strength of the power surge would be pretty low and the equipment be quite robust to withstand it. I wouldn't be surprised if a bomber of that era would be unscratched by an EMP that completely fries a modern cell phone.

And no, bullet holes don't actually have any effect on a Faraday Cage.

That is not to say you can't get ahead with your idea, but it probably needs to be handwaved sci-fi magic and does not actually work with real physics.

Answer 3

EMP works against electronics, by inducing electric pulse of voltage far exceeding the flimsy ratings of 5V or so in wires nanometers thick, breaking through diodes, transistors and capacitors, damaging the components. It's a very low power, capable of micrometer scale damages, but applied to microscopic structures the effect destroys them.

High-power electronic and electric circuits experience a short surge of high-voltage current, but the power delivered wouldn't change a thing.

In internal combustion engines you might experience a minor glitch, the spark going off at a wrong moment etc, the engine skipping one cycle without a burn, but they would not be damaged. Diesel engines would be entirely unaffected; once started they can run without any electricity at all.

If the bombers have some on-board electronics: radio, radar etc, these would possibly be damaged, though if made in discrete parts and not in integrated circuits, that's a rather low possibility.

The worst that could happen is triggering a spark in the ignitor of a bomb on board. They vary in construction, but some may use wire constructions that could spark with enough voltage induced. Of course that would be fatal for the airplane, and of course constructing an ignitor entirely immune to EMP is perfectly viable, providing they realize the requirement.

Also, though quite improbable, some construction quirks (e.g. of fuel level sensors) may cause a spark in the fuel tanks of the airplane.

Answer 4

What about changing the design of the aircraft instead?

Rather than protecting against it directly - which as you've noted is somewhat unfeasible - you could decentralize your systems and add additional redundancies. The enemy's tactic only works if they can disable the bomber in a fairly short period of time, so anything that makes it take significantly longer to disable your bombers makes the EMP fighters less useful.

Use 8 smaller engines instead of 4, and insulate them from each other. This mitigates any single attack, and isn't incredibly hard to do with electrical engines. Have two cockpits, with parallel controls. The second cockpit will still be connected to some systems and can do most of what a co-pilot normally does, and in the case of an attack on the primary cockpit they can hit a manual control and connect fully to take over. Do something similar with your bomb bays and other critical systems.

Another tactic presents itself - controlled shutdowns. Design your bombers with the expectation that they'll need to glide for significant distances. If a fighter gets close (and 50 feet is really close), go into a special shut down mode and glide for 20-30 seconds. This mode completely isolates all electrical systems, putting the controls back on a temporary, manual setup and cutting all power. EMP attacks may do some damage, but that damage can't spread and will be reduced and contained. I find it unlikely that a fighter will be able to stay close for a long period, so you don't need to stay that way for long.

Answer 5

Well, unless the EMP plane is a suicide plane, it needs to have protection from EMP just to stay up and use its weapon more than once.

So the other side just needs to steal that technology itself.

Answer 6

You could use a redundant electronic system, one of its part is normally on while other(s) is(are) off keeping "well-grounded" to an accessible "mass". In the case of a success EMI attack, the first part will be dis-operated (got harmed), after that, the second part (so called cold reserve) could start to operate that give your plane a second chance.

This is a real technique, the Satan ICMB used such a surviving concept in each of its warheads.

Answer 7

EMP isn't magic. It's little more than what is experienced by a generator. The plane is passing through a dense magnetic field just as the generator's wire is passing through a (locally) dense magnetic field. The theoretical threat of an EMP is that it carries so much energy that things are damaged.

But that doesn't change the physics of delivery. If the plane is sheeted in conductive metal, then the fusalage skin is getting all (100%) of the energy. That's what's passing through the field first, and it has by far the largest conductive path to absorb the energy.

So the real question is, what is the skin connected to? Modern automobiles, for example, connect the chassis, frame, skin (if metal), etc., to the negative pole of the battery. It makes the car's electronics easy to reference (voltage reference or ground reference). I'd be surprised if airplanes didn't do the same thing for the same reason.

This means the first (and likely only) thing damaged is the battery. And the easiest way to protect against EMP is to add more battery, or to create some electricity-consuming device (like an arc generator) that could dump overvoltage energy.

I have not looked into the effect of EMP on automobiles, but I'm willing to bet that cars that survive are metal-skinned cars and cars that don't are fiberglass/plastic skinned cars. Further, the chassis/frame, motor, etc., are all so large that they'll absorb the energy long before wires or computers. The only way the computers would be damaged is if they're not begind something large and metalic (referenced from the direction of the emp source) or not shielded (encased) in metal.

Solution: build the planes with metal skin, connect the negative post of the battery to the skin with thick cables, use a lot of batteries or design an over-voltage shunt that dumps excess energy to an electricity-consuming device like an arc generator.