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In a comment, John K points out that:

In any case, military fighter aircraft have to avoid icing, which is kind of odd for those that are considered "all-weather" interceptors..

This, to me, raises the question of "why would you omit wing anti-ice from a supposedly 'all-weather' aircraft?" Especially on a larger fighter like a F-15 or Su-27, it seems to me that the weight penalty for a couple of piccolo tubes, two butterfly valves, and a bit of extra bleed ductwork would be fairly minimal relative to the weight of the aircraft and payload, or am I wrong on that? Or are there aerodynamic or engine-performance reasons that prohibit fighter jets from using bleed-air anti-icing, or some other anti-ice system for that matter? I've also heard the saw that "fighters don't need anti-ice because they can simply fly fast enough to use ram rise to deal with icing", but could there be other reasons they couldn't fly in icing, such as not having heated pitot/static systems or inlet anti-ice functions?

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  • $\begingroup$ As you point out it would be easy enough, but fighters are designed to meet certain military specs. If the military doesn’t require anti-ice then building it in to the design simply adds cost and puts your bid at a competitive disadvantage. It might be a better question if you restated to ask why the military doesn’t require anti-ice. $\endgroup$ – Michael Hall Oct 28 '20 at 3:33
  • $\begingroup$ @Michael Hall But you would think that a fighter like an F-15 designed to do interceptions in all weather would need the capability to operate in know icing conditions, at least to be able to land in icing conditions. The only purpose built all-weather interceptor I've seen with the capability to operate in icing is the Canadian Avro CF-100, which had boots on the wings and tail. $\endgroup$ – John K Oct 28 '20 at 4:09
  • $\begingroup$ @John K - yeah, you might think that, but fighters can get through icing fast enough that there isn’t much time for it to build. Both climbs and descents... HI TACAN penetrations pegged the VSI down, not something you want to do with pax. $\endgroup$ – Michael Hall Oct 28 '20 at 5:39
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    $\begingroup$ @quietflyer the answers don't address the logical disconnect, that is, why don't "all weather interceptors" like the F-15 (as opposed to "day fighters" like the F-16) at least have the ability to operate in icing, at least through arrivals and departures. If your opponent incorporates that capability into their attack aircraft, that's quite a limitation for an all weather interceptor. $\endgroup$ – John K Oct 28 '20 at 13:09
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    $\begingroup$ Well even airliners with heated LEs have to leave icing if it's heavy enough. In the CRJs you're supposed to get out if ice is adhering to the cockpit side windows. What intrigues me is departures and approaches in icing where you are operating at low speed. I expect the answer is that they are considered capable of handling moderate ice loads at low speeds for approach and landing, same as lots of horizontal tails aren't anti-iced on jets because the surface is made a little bigger. During CRJ700 development tail anti-ice was considered to allow a smaller surface, but it was rejected. $\endgroup$ – John K Oct 28 '20 at 22:24
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Most fighters have enough thrust to power through icing conditions, so anti-icing or heat is limited to inlet(s) and pitot probe(s). That said, at least one F-16 flight manual, to use one example, says the following about flying in known icing conditions:

Flight in areas of icing should be avoided whenever possible. If icing conditions are anticipated or cannot be avoided, turn ANTI ICE switch to ON and PROBE HEAT switch to PROBE HEAT. Frequently check the aircraft leading edges for indication of ice buildup. Make all throttle movements slower than normal when in potential icing conditions to reduce possibility of engine stalls and/or stagnation. Consider diverting to an alternate field if required to avoid icing conditions.

The F-14 also had the same systems, engine inlets and pitot probe heat. No other anti-icing systems on the aircraft.

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