After Ralph puts on the stabilizers, he then takes off, but in the footage, he is missing those parts until he lands.
The way they show Aircraft that are invisible to radar is incorrect. Stealth aircraft show up on screen as a duck or similar type of bird. The design is a single wing aircraft whose shape deflects the radar signal. The plane is also coated with a special material that absorbs radar signals. Simply having a "gizmo" can't be used to block radar.
When Maxwell returns to the desert with the fire fighters, his car makes "tires screeching on pavement" sounds when he brakes, but he is driving on sand.
Ralph develops the power to see into the future. When he and Max go to the "crash site" he not only can see the plane crash, but he also can touch parts of the plane. He shouldn't be able to touch something that isn't there.