Why are swing-wing fighter jets obsolete?
Swing wings were also designed before computers were powerful enough to handle the aerodynamic simulations required to design modern wings. These improved aerodynamics have made swing wings all but obsolete, since the aerodynamic benefits of a swing wing can usually achieved now in a fixed wing. The added weight and complexity of a swing wing is thus unnecessary.
Variable-sweep wing are very good at what they do. Allow the plane to have increased maneuverability and efficiency in both high and low speed.
The problem is that, the modern fighter doesn’t necessarily need that increased maneuverability at low speed. No matter how cool it is, dogfights are a thing of the past. Missile technology have improve a lot and are not just too dominant and they shaped the tactics of pilots. Missile also made anti-air defense extremely difficult to fight over, staying as far as possible of heavy anti-air defense is extremely important. Flying at low-speed would be extremely risky anywhere where air dominance isn’t already acquired.
Stealth is becoming a major factor in fighter design and well for that you need specific shape. A variable sweep-wing would just be extremely inferior to current design in term of stealth. Stealth is not just about staying invisible, but also making it harder for the enemy to lock on you and shoot you down.
Some people talk about moving parts are vulnerable, added weight are complicity. They are right that those things exist, but they are not a factor in why sweep wing are not longer used. If sweep wing were providing an important capability, the designer would just work with the added weight and complexity. Look at the F-35B, the fan is extremely vulnerable, add a lot of weight and is complex, but it provide the F-35B with an advantageous capacity that made those drawback worth it. The advantage of sweep-wing are just not worth it in the current battlefield.
Why adjust wing sweep when they can just adjust thrust vectors?
The F-14 needed the low speed lift specifically for carrier landings and takeoff, the maneuverability was a bonus. The F-35 variants used on carriers today can just takeoff vertically.
There’s one basic problem that swing wings were intended to solve.
First is the ability to generate lift while moving relatively slowly. For example, when taking off from an aircraft carrier.
Second is the ability to minimize drag when flying supersonic. For fuel efficiency but also to enable them to go really, really fast.
The problem is that you want an aircraft that is able to take off from an aircraft carrier, but also travel really fast. It was a kind of “you can do A or B but not both” kind of problem.
So they invented a wing that could move. That solved the “you can’t do both” part of the problem because now you can move the wing so that it CAN do both.
And then computers got much more powerful and we were better able to model the forces involved in both slow speed and high speeds and we were able to figure out a single wing that is able to handle both kinds of flying.
So once we figured that out, having a moveable wing is just extra parts that can break. So there’s no point in doing it that way anymore.
At the time, variable geometry wings were a popular solution to the problem of wanting to reduce drag at transonic and supersonic speeds, whilst maintaining lift at low speeds. The trade-off is this moving part is vulnerable to wear and tear or failure, and is not good for stealth.
The modern focus is on stealth/low observability aircraft to protect the crew and increase mission success.