The engine probably wouldn’t be able to give full power running a scale diameter prop, it may even stall if the prop is too big. The engine maker will specify the correct prop to use. Some flyers will swap the flying prop for a more realistic one for display on the ground.

Ah, the Reynolds factor… the correlation between airfoil shapes, air airdensity, airflow and speed. thats why scaling down the airfoil shape (in this case propellor shape and size does not work 🙂