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Does anyone know, why the eurofighter does have a variable engine inlet while similar aircraft such as for example the rafale or the f-16, which also has an underslung engine inlet, do not employ any kind of variable geometry in their engine inlet?

My two own theories are, that it is either to primarily help with inlet performance at high angles of attack or to optimize the capture area of the intake for the wide range of possible airspeeds of the aircraft. Sadly I haven't been able to find any concret evidence to underpin either theory.

Given that the variable inlets bring with them quite a bit of added technical complexity, I would expect strong arguments to justify their incorporation in the design.

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It is a design choice as the intended missions of both aircrafts differed slightly.

The inlet of the Eurofighter Typhoon features variable geometry, to improve the performance at high angle-of-attack and performance at transsonic and supersonic speeds. This design choice was made because the Eurofighter Typhoon is intended to be used as a top of the line, hyperagile aircraft which outstanding dogfight and interceptor performance. The twin-egine design, canards, relaxed stability/unstable design and the originally envisioned thrust vectoring engines were to help in this mission profile. The expensive and complex variable geometry inlet is therefore only a logical choice when you put in other equally complex systems to enable this use profile.

The F-16 on the other hand was designed to be relatively cheap, easy to maintain and to have a low operating cost. This was partially achieved by installing only a single engine with a straight inlet and no complex variable inlet duct. The disadvantage in the transsonic and supersonic regime as well as drawbacks at high angle-of-attack were accepted in order to keep the aircrafts cost low. Other fighters such as the F-15 or F-22 should fill the role of higher-cost aircraft.

See also this post about the inlet of the F-16.

In hindsight, the F-16 has obviously aged better. The Eurofigher Typhoon while being remarkably agile, probably the most capable Dogfighter ever, has never been in a real dogfight (at least to my knowledge). Instead, missiles have taken over this aspect of air-to-air combat. The F-16 on the other hand is a very cheap still very capable aircraft which is cheap to operate while it still can execute todays mission reasonably well. The Eurofighter can fullfill the same mission, however operating costs are significantly higher.

P.S. Do not get me wrong, the Eurofighter is a remarkable piece of engineering. Especially the flight control system is an absolute beast!

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    $\begingroup$ Additionally, the "state of the art" in aerodynamics and engineering has improved significantly. When both of these aircraft were designed, it was thought that the only way to prevent supersonic shock waves from disturbing the flow at the compressor was with a variable geometry inlet. Since then, we have learned how to use fixed geometric shapes on the inside of the inlet that have the same effect. See this: aviation.stackexchange.com/questions/68320/… $\endgroup$
    – Charles Bretana
    Commented Jul 28 at 17:03
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    $\begingroup$ > In hindsight, the F-16 has obviously aged better. The Eurofigher Typhoon while being remarkably agile, probably the most capable Dogfighter ever, has never been in a real dogfight (at least to my knowledge). Can you elaborate on that more? As far as I know, the countries operating Eurofighter haven't really been in an air superiority war since it exists, what do missiles have to do with it? It's not like other modern air superiority fighers like F-22s were ever in a dogfight - it's a function of history, not design or "aging". $\endgroup$
    – Mavrik
    Commented Jul 28 at 17:06
  • $\begingroup$ @Mavrik I think we both mean the same thing. All I want to say is that the specific design advantage of the Eurofighter (its high agility) is not needed anymore on todays battlefield because of modern long-range and/or highly agile missiles. The F-16 on the other hand is still cheap. Therefore, in the end, the Eurofighters agility was never really needed but the F-16 "cheapness" was always a important factor. This is why I say, perhaps the F-16 proofed to be a more "successful" design. Of course, if history were different, this conclussion would also be different. $\endgroup$
    – U_flow
    Commented Jul 28 at 21:01
  • $\begingroup$ Also, for the downvoters: Please indicate why you are unhappy with this answer so that I can improve it. Thank you! $\endgroup$
    – U_flow
    Commented Jul 28 at 21:02

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