The sound is caused by the twin propeller design. You don't hear this from modern versions of the UH-1 or more modern choppers because they use a 4 prop design and make a "smoother" sound that doesn't have a "chop chop chop" sound resonating from the air. 4 propeller helicopters are also more stable in the air and that is why most are like that now. Smaller helicopters still use a 2 prop design but the blades are a lot smaller and don't have as much of a loud sound as the UH-1.
Yo he montado en el Uh1, la batería para dar electricidad al motor esta en un panel que esta en el morro de la nave, se abre se conecta la batería y ya tienes corriente para el motor y todos los instrumentos de vuelo.
