While I understand the mechanical part of the turbine which alternates the airway and redirects the sucked air back to the front via the reverser doors, physically it doesn’t make sense to me. Similarly with sea vessels that work with waterjet systems and reverse using a deflector which basically does the same thing (in marine propulsion systems).
The forces between the thrust from the propeller, and the deflector which the air hits should counteract each other. To me, it’s like you’re trying to stop a boat with sails, using a leaf-blower on board. The blower’s directed air hits the sails from the front, but the fan itself sucks air from the opposite direction (on a theoretical leaf blower that sucks air from the back, not the side).
Adding the forces from the propeller (which pulls the turbine) and the redirected air (which pushes the turbine back) should result in equilibrium (if not positive because the redirected air is going back to the front in an angle, not straight from the direction that was sucked).
This question arose after studying marine waterjet systems, and how they achieve reverse thrust, which reminded me of the airplane’s reverse system. Surely it is possible that I did not fully comprehend the principle of operation of both systems, or I wrongly thought they are similar, so please feel free to correct me if my understanding is incorrect 🙂
In: Physics
Follow the molecules; specifically the collisions. So long as they’re “in the system”, the force from the collisions is netting out to zero, like the air in a balloon. You’re interested in their delta-V from when they enter the system (first collision) to when they leave the system (last collision). That delta determines the net force each applied to the system. So a molecule enters the system at a very high speed (the engine is the frame of reference), but after it bounces off the deflector it leaves in the other direction. (Without the deflector it leaves in roughly the same direction it entered but faster.)
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