DESCRIPTION 
In the NRAP (fig 3), a low-power, efficient, de series-wound electric motor drives 
one or more pistons by means of an adjustable linkage system. The pistons all operate to- 
gether to change the projector’s volume in the breathing mode of oscillation. Up to six or 
eight pistons can be accommodated on a single rocking cross arm, and several such arms can 
be ganged on a single shaft. The unit described here, however, employs only two opposed 
pistons. Since the operating frequency of the rotor and pistons varies with the voltage ap- 
plied to the motor, the source can be made to generate either a constant frequency or a 
frequency-modulated signal as desired. Applying voltage to the screw adjustment motor 
moves the amplitude adjustment link to control piston oscillation amplitude. 
If point F on the amplitude adjustment link is fixed at the location shown in figure 
3, point C is forced to oscillate along arc G as the rotor turns. This makes point D oscillate 
along arc I, which is centered on the fixed point E. Since the rocking cross arm is forced to 
rock with near-sinusoidal angular motion about its fixed point E, the pistons are driven in 
and out at the rotor turning frequency. If the amplitude adjustment motor is actuated to 
drive point F into coincidence with point D, are G swings into coincidence with arc H, which 
is centered on point D, and both D and the rocking cross arm become stationary even 
though the rotor continues to turn. If the amplitude adjustment motor is actuated to drive 
point F to a location between point D and that shown for point F in figure 3, arc G swings 
OCEAN 
PROJECTOR at 
HOUSING 
PISTON (TYPICAL) 
_ LINEAR BEARING 
(TYPICAL) APAPLITUDE 
=a 
ROCKING ADJUSTMENT 
CROSS ARM 
TO PISTON 
(NOT SHOWN) 
; ——> 
AMPLITUDE 
ADJUSTMENT 
LINK 
ROLLING 
SEAL 
(TYPICAL)- 
AIR INSIDE | 
HOUSING 
he »” OCEAN 
OUTSIDE 
HOUSING 
Figure 3. Third conceptual design for NRAP. 
