Why has the rest of the world gone after delta wings while not the USA?

Question

JAS Gripen, Eurofighter, HAL Tejas, Mirages, all are delta winged fighter jets.

We don't see any delta-winged fighter jets in the US inventory.

Why is that difference?

Answer 1

The Gripen and Eurofighter are canards with a delta wing (as is the J-37 Viggen). This, coupled with relaxed stability, gives the first two unmatched maneuverability, and good transsonic and short-field performance. While the Viggen is a stable design, it too has very good short-field performance.

The Mirage III (and the F-102, F-106, B-58, J-35 Draken and Concorde) were first-generation Deltas from the mid-1950s which were optimized for supersonic speed. By using a highly swept delta wing, low supersonic drag could be combined with short take-off and landing distances.

So it is not true that the US "never went after delta wings"; they just outgrew that configuration when they shifted their priorities away from high supersonic performance.

Note that the more modern Mirage F1 is an unstable conventional configuration while the last Dassault design is also an unstable canard.

Regarding the Tejas: It is designed for the specific requirements of the Indian Air Force. One of the unusual design requirements was the low vulnerability to bird strikes, because Indian airfields have a high birdstrike rate. Therefore, no leading edge devices were allowed, and to give the Tejas still a respectable short-field performance, a delta wing was the best choice. Full disclosure: This was actually the requirement which led to the LCA having a delta wing, and the Tejas, which resulted from the LCA, does have leading edge flaps after all.

Answer 2

'Rest of the world' hasn't gone towards delta- only the previous generation European combat aircraft have (along with India). Also, none of the fifth generation aircraft have anything resembling delta wing. In fact, there are few 'pure' delta wings aircraft anymore- most of them are modified delta or have canards.

Delta wings have a few disadvantages- the wing shape increases drag (especially at low speeds) and reduces maneuverability- this requires addition of canards to overcome. The delta shape is optimized for high speed something which made sense when speed was the main requirement (USAF last operated delta aircraft in a dedicated interceptor role in Century Series, which is telling); however, as speed has given way to other aspects (like maneuverability, stealth etc), USAF has moved on.

Delta wings are not exactly stealthy, which is a major factor in them not being considered for fifth gen aircraft. USAF has invested heavily in stealth, so delta is out of the question. Boeing tried it in X-32, but had to change it later on.

One advantage of delta wing is its high internal fuel load, which is of less consequence for the USAF with its unparalleled refueling capabilities.

Also, don't underestimate institutional inertia- most companies would go with tried and tested designs rather than entirely new ones- this reduces risk and they have significant data available. Saab and Dassault have, for example, haven't made anything other than delta for quite sometime now. Boeing's T-X wing, for example, is strikingly similar to the Hornet.