When the two US Bombers dropped a-bombs on Hiroshima and Nagasaki, why didn’t the EMP knock out the engines and electronics on the aircraft?
Yes, I appreciate the irony of my screenname connected to this OP.
Seems Wiki has your answer:
The worst of the pulse lasts for only a second, but any unprotected electrical equipment — and anything connected to electrical cables, which act as giant lightning rods or antennas — will be affected by the pulse. Older, vacuum tube (valve) based equipment is much less vulnerable to EMP; Soviet Cold War–era military aircraft often had avionics based on vacuum tubes. There are a number of websites that explore methods for protecting equipment in the home or business from the effects of an EMP attack.
Many nuclear detonations have taken place using bombs dropped by aircraft. The aircraft that delivered the atomic weapons at Hiroshima and Nagasaki did not fall out of the sky due to damage to their electrical or electronic systems. This is simply because electrons (ejected from the air by gamma rays) are stopped quickly in normal air for bursts below 10 km, so they do not get a chance to be significantly deflected by the Earth’s magnetic field (the deflection causes the powerful EMP seen in high altitude bursts), but it does point out the limited use of smaller burst altitudes for widespread EMP.
If the B-29 planes had been within the intense nuclear radiation zone when the bombs exploded over Hiroshima and Nagasaki, then they would have suffered effects from the charge separation (radial) EMP. But this only occurs within the severe blast radius for detonations below about 10 km altitude. EMP disruptions were suffered aboard KC-135 photographic aircraft flying 300 km from the 410 kt Bluegill and 410 kt Kingfish detonations (48 and 95 km burst altitude, respectively) in 1962, but the vital aircraft electronics then were far less sophisticated than today and did not down the aircraft.
Atmosphere does much to slow down charged electrons. The EMP generated by any ground or low-altitude burst does not extend far enough beyond the thermal/radiation destruction. Essentially, your aircraft/vehicle is likely to be damaged by blast, thermal or (in case of passengers) radiation at the same distances that EMP could affect your vehicle. You don’t notice your watch has stopped when your arm is on fire :).
EMP becomes an operational and even strategic threat at very high altitudes-- tens to hundreds of kilometers.
D’oh, Whack-a-Mole beat me to it!
That Wiki article has the other reason: vacuum tubes, which aren’t nearly as affected by EMP.
One of the side perks of “old” Soviet technology-- for example, their then-modern MiG-25 high-altitude interceptor used vacuum tubes, much to the surprise of Western observers after they obtained a defector’s aircraft to examine.
The tubes gave the aircraft some resilience in an EMP environment.
The Mikoyan-Gurevich MiG-25 (Russian: Микоян и Гуревич МиГ-25; NATO reporting name: Foxbat) is a supersonic interceptor and reconnaissance aircraft that is among the fastest military aircraft to enter service. Designed by the Soviet Union's Mikoyan-Gurevich bureau, it is one of the few combat aircraft built primarily using stainless steel. It was to be the last plane designed by Mikhail Gurevich, before his retirement.
The first prototype flew in 1964 and the aircraft entered service in 1970. ...
So bitter that other posters beat me to this…
The only essential electrical components on B-29 engines would have been the magnetos. These are simple and probably not very susceptible to EMP.