What are the differences between pre-transistor and transistor era jet engines? Towards the end of the second world war, most of the air powers had started development on jet engines. From what I understand, all of this predated any practical application of transistors. The transistor era obviously gave way to integrated circuits and microprocessors. On any piston engine I can usually spot the evolution of components because I'm well versed in the operation of piston engines. For jet engines it is less obvious to me, there are for example differences between turbofan and turbojet engines. I superficially understand the difference between them but I've never even operated one, much less been hands on with it.

What are the significant changes from pre-transistor to transistor-era jet engines? I've never seen vacuum tubes used on jet engines so it doesn't seem like it is just a matter of "they replaced the tubes".


2 Answers 2


The vibration levels on jets preclude the use of vacuum tubes. They may work if everything is fine and all rotating parts are well balanced, but once you have a defect and an out-of-balance condition, the electronics would fail quickly, just when you need their help the most. Especially the afterburner adds a lot of vibration when it works as designed already.

Earlier jet engines used hydraulics for adjusting things like compressor vane angles (litte stationary "wings" positioned between the rotating discs of the compressor, which help to convert rotational flow energy into compression) and the nozzle size. Like on piston engines, the amount of adjustment was much lower back then, and all adjustments were done mechanically.

  • $\begingroup$ Vacuum tubes can be build to withstand vibrations. The proximity fuse works with vacuum tubes inside a projectile shot from a cannon. $\endgroup$
    – Lenne
    Mar 6, 2022 at 17:21

The primary advance in the transistor era is the FADEC. It's essentially a fly-by-wire throttle, incorporating rate limiters to key engine inputs such as fuel flow rate, and performing automated monitoring tasks to reduce flight crew workload. Prior to the FADEC system, sufficiently complex jet aircraft required a crew member, the flight engineer, whose primary task was monitoring and maintaining engine performance in flight. Additionally, jets without a FADEC require particular attention paid by the pilot(s) to the rate at which the throttle is adjusted; you can't just firewall it for a takeoff as that will cause a compressor stall.

  • $\begingroup$ So, FADEC would have prevented accidents like this one involving an F-14? youtube.com/watch?v=prEFjYrAJuw $\endgroup$
    – Eric Urban
    Jul 10, 2015 at 17:58
  • $\begingroup$ Probably not. The F-14 was notorious for compressor stalls, especially with its original TF30 engines (however only the F-14As had these; Bs and Ds in service by 1995 used more reliable GE F110-400 engines). You'll notice transonic shockwaves developing several times as the plane flies by, which indicates to me the aircraft is holding near Mach 1, and that's a very dangerous place for fighters with large rectangular intakes to be as leading-edge shockwaves can enter the engine and cause wide variations in compressor pressure, thus causing wide swings in fuel-air mixture. $\endgroup$
    – KeithS
    Jul 10, 2015 at 18:36

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