I build this propeller-powered car (in image). The propeller pushes air backwards and the car moves forward.
I observed something weird. While I place my palm behind the propeller (about 2-3 cm from it) such that the air pushed by the propeller hit my palm, the car moves significantly faster.
My palm was placed facing the propeller's rear side and was parallel to the rotational plane of the propeller. My palm was not in contact with the car. Please refer to the image I have attached. (P.S. it is not a perfect illustration, however, it will give you an idea about the car)
Can anyone please help me with why this happens?