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drag is considered to act upward in the case of flight for instance...
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No it isn't:
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The four forces
When a well-trimmed aircraft is cruising (i.e. flying at a constant speed, and maintaining a constant heading and a constant altitude) in non-turbulent air, there are two sets, or couples, of basic forces acting on it. The two forces in each couple are equal and approximately opposite to each other otherwise the aircraft would not continue to fly straight and level at a constant speed; i.e. the aircraft is in a state of equilibrium where all forces balance each other out so there is no change in motion.
The couple that acts vertically is the lift, generated by the energy of the airflow past the wings and acting upward, and the weight acting downward. So, being equal and approximately opposite, the lifting force being generated must exactly match the total weight of the aircraft.
The couple that acts horizontally is the thrust, generated by the engine-driven propeller, and the air resistance, caused by the friction and pressure of the airflow, or drag, trying to slow the moving aircraft. The thrust, acting forward along the flight path, exactly equals the drag. The thrust provides energy to the aircraft and the drag dissipates that same energy into the atmosphere. The forces are not all equal to each other. In fact, an aircraft in cruising flight might generate ten times more lift than thrust.
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http://www.auf.asn.au/groundschool/index.html
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No intelligible explanation how you can tilt backward a running propeller in flight, which is necessary to make it go in a curve, without applying to it at least more than half of its total thrust...
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That's right, no explanation, because none is needed. This entire idea that you can't tilt a propeller without generating such huge forces is based on nothing but the pseudo-physics that lurks inside your addled brain, Gaston. Or if it isn't can you provide a link to a source that actually explains where this magical force is coming from? I'm not the slightest bit interested in you repeating your drivel about 'compound levers', 'stress risers' and whatever else you seem to think explains anything. Of course you won't provide a link, because you won't find one. You can't. It doesn't exist.
Try studying physics, and basic aerodynamics. You might learn something...