NACA L-485 REPORT
The NACA L-485 REPORT is about a wind tunnel test of a model of World War II combat aircraft fuselage having a tail-mounted propeller. This design required an inside tunnel in the fuselage to provide air for the engine. In the tests, the airflow speed inside the tunnel was measured, and the raw data proves that air thermal energy was converted into kinetic energy, as Bernoulli stated in his energy conservation law.
Air entered the model engine tunnel through an inlet at the fuselage left side and flew toward the exit at right. The engine tunnel ended with two convergent nozzles, which accelerated the streams of air at the engine tunnel exits, to a speed ratio v/V=0.87, which was 1.58 faster than the air entering the engine tunnel inlet where v/V=0.55, see Fig. 7
This means increasing the air kinetic energy by a factor of 1.58 x 1.58=2.50!
Obviously, there must be a source of energy for this kinetic energy increment. However, there is only one available source of energy. This is the air's own thermal energy, i.e., air temperature.
Explanation: the air flew inside convergent nozzles, which accelerated its speed, i.e, increased the air kinetic energy at the expense of the air's own temperature, according to Bernoulli's energy conservation law.
Therefore, the temperature of the air exited the engine tunnel was colder than the temperature of the air entering the engine tunnel. Unfortunately, the air temperature is not mentioned in the report.
Jet Effect
The air exited the engine tunnel exit, generated a jet force effect because its exit speed was greater than its speed at the inlet. This jet force pushed the model forward, in the opposite direction to the airflows, thus reducing the fuselage measured drag.
TEST RESULTS- I
Compare CDF =0.0918 for case 1 in NACA Table No. 1 to case No. 9 where, CDF =0.0903!
*CDF is the drag coefficient of the model fuselage
The drag coefficient for case No. 9 should be greater than for case No. 1 due to additional drag generated by the flow through the model engine tunnel. HOWEVER, IT WAS SMALLER! how is it possible?
Answer: Due to the JET EFFECT, see the explanation above