SB2C Dive Flap Mechanism

Pat Donahue wondered how the same hydraulic actuator could position both the upper and lower Curtiss SB2C flaps for dive bombing as well as only open the lower flap for takeoff and landing. He thoughtfully provided pictures so I could puzzle it out. Here is how it works, in the unlikely event that anyone else wants to know.

Basically, the key is the positioning of what I call the Dive Flap Position Link. If it was locked in the bottom of a slot in a bracket mounted on the aft wing spar, then the "Upper Flap Actuator Link" functioned as an idler, i.e. the upper flap didn't move when the flap actuator extended.

If the Dive Flap Position Link was free to move in its slot, then the Upper Flap Actuator Link functioned as a driver and the actuator extension opened both the upper and lower flaps.

Note that the two pictures above are taken from opposite sides of the mechanism. I think that the rods running along the bottom of the wing spar locked and unlocked the Dive Flap Position Link at the bottom of the slot.

The pilot was provided with two flap-control levers. One selected Diving Flaps or Landing Flaps, which locked or unlocked the Dive Flap Position Link. The other extended or closed the flaps, with a neutral position to be selected when the desired angle of the flaps had been reached.

Note that the SB2C-3/4 Pilots Manual required the pilot to make sure that the flaps were closed before folding or spreading the wings because "Flap selector forces at the wing fold are transmitted through bell cranks which disengage when the wings are folded."