It seems that trapezoid wings are used by all fifth generation fighters (although the wing of J20 looks quite like delta wing), but why? What made a trapezoid wing so attractive? Why don't they use other forms, like the swept wing on SU27?
Trapezoidal wings have advantages and disadvantages:
- Better performance than delta wings at transonic speed
- Good stealth performances
- Flaps can be easily used.
- drag reducing
- better Lift/Drag ratio than delta wings
The problem is that they stall at much lower angles of attack than delta wings.
Edit:this problem is overcome using leading edge,LERX,and/or canards