The nacelles are built of 1/8" lite ply with 1/4" ply firewalls. The accomodate a 10 oz tank and the throttle servo. The nacelles are removable and self contained such that I can work on the motor, throttle servo or fuel system without wrestling around with the wing. The nacelles are attached via 3/16" dowels in the leading edge of the wing and a 1/4" nylon bolt in the real of the nacelle that goes up into the wing.