Imagine swinging a weight attached to a rope around in around in a horizontal circle. It's swung at such a speed the angle of the rope is about 60 degrees from vertical. The ball experiences gravity and a put from the string. If you sat on the ball you would feel twice as heavy.
Let's assume we make the rope long enough that the ball moves at 60 miles per hour, and we swing the ball on a truck that moves at 60 miles per hour. If you stand on the truck the ball moves in a circle. To someone standing by the side of the road it .makes the same movement that would be made by a point on the wheel of the truck: ome to a stop, and leap forward, come to a stop and leap forward with dramatic changes in horizontal velocity and strong acceleration forces. The ball doesn't feel that, because it's frame of reference moves at that steady speed of 60mph. It still feels that same constant 2g pull from the rope.
Now change ball into airplane flying in circles, and truck into the air the plane is flying in.