What is the minimum speed of an airplane and the average speed of an airplane?

Answer 1

Simply put, the minimum speed for all aircraft is Vs, the speed below which the wings cannot produce sufficient lift for level flight. You can further refine the answer by discussing Vmcg and Vmca which relate to multi-engine aircraft. These are the minimum controllable speeds on the ground and in the air (respectively) with an engine out and the other engines at maximum power. As for average speed, I'm not sure what you're after here, but one might say that the "average" speed of an aircraft would be the best speed at which it cruises. Cruise speeds are a function not only of aerodynamics, but of cost efficiencies as well and are determined by each operator according to its needs.