ORIGINAL: Joe Westrich
I'm not trying to rain on your idea, but a thrust reverser will really only work on a turbine not DF.
DF and turbines opperate differently in obvious ways and some not so obvious ways. With a DF you escentally have a prop turning in a housing. It pulls itself on the air deflection from the blades spinning. It does not move forward from the thrust of the air comming out of the tail. This air is strickly a byproduct of its function. Turbines, on the other hand, do not move forward from a spinning fan. The fan is strickly for compressing inlet air into the turbine. It move forward because of the expansion of gas in the chamber is forcing it forward. To recap, DF has an equal amount of air going in the inlet as it has coming out. The turbine has only a fraction of air going in as it has going out (20 to 1). This makes the difference when using a reverser.
At best, the reverser will only kill the efficieny of the DF and make it not go forward any faster, but it will never make it go in reverse. Obviously the reversing force is what slows the aircraft down.
I'm sure it will look cool, but I wouldn't expect it to slow the aircraft.
I would like to correct a few things here.
I think you are mixing up a few types of “jet engines.” The two most common types of jet engines are turbofans and turbojets or true jets. A turbofan, typical of a modern airliner, produces thrust both by the spinning fan on the front and exhaust from the turbine. The fan is connected to the drive shaft of the engine which is also connected to the compressor and turbine.
Air is drawn into the engine both by the fan and the compressor once inside it is mixed with fuel and ignited, which rapidly expands the mixture, then sent through the turbine blades at the rear which spin the compressor and fan. Air exiting the engine both from the fan and the exhaust creates the thrust.
Turbojets or true jets work on the exact same principle, minus the fan, and create all of their thrust from the hot gases exiting the exhaust.
In any jet the same amount of air (mass) exits as enters. There aren’t any non-Einsteinian processes going on in the engine, mass is not being created. It is true however that the volume of air exiting is much larger as it has expanded immensely, but the mass is the same.
According to Mr. Newton: F=MA, so the mass of the air and its acceleration is what is creating your thrust. It does not matter how that air is being moved, it can be a propeller, ducted fan, jet, fan, flapping wings, etc. Ultimately, if you can put something into the wind stream that directs the airflow in the opposite direction reverse thrust will be created. If you were so inclined, you could create some kind of louvers that redirected the wash from a prop to create reverse thrust.