Aircraft flying round a spherical shape

hello please I am trying to make an air craft fly over a spherical world . i use a pawn were i set an add force for the movement( which is alright ). now the physics I set to keep the aircraft orbiting the sphere is not working properly, only keep flying upward after a given time. I have watch several tutorials online for that, and the problem was not solved. below is the blueprint for the orbiting . thank you in advance