The hydraulically operated cowl flaps are attached to the aft edge of each engine cowling. The center flap of the top segment is stationary. A hydraulic actuating cylinder, installed on the lower part of the engine cowling, is connected to each movable cowl flap by a series of tie rods and operating levers. Movement of the cowl flaps is controlled by the cowl flaps hydraulic controls in the cockpit.
Two cowl flap handles, attached to hydraulic valves, are located on the side of the cockpit to the right and forward of the co-pilot's seat. Each handle has CLOSE, OFF, TRAIL, OFF, and OPEN positions.
In the CLOSE position, hydraulic fluid pressure is directed to one side of the actuating cylinder and the cowl flaps move towards the close position.
In the OPEN position, hydraulic pressure is directed to the other side of the actuating cylinder and the cowl flaps move toward the open position. In the OFF position, the hydraulic fluid is trapped in the actuating cylinder to hold the cowl flaps in any desired position.
In the TRAIL position, both sides of the actuating cylinder are manifolded together, allowing the cowl flaps to move in either direction depending on the balance of the air loads on the cowl flaps.
Note: In the current version of the VSKYLABS DC-3, the cowl flap interaction is simplified and has 3 available positions: CLOSED (fully closed), OPEN (fully opened) and TRAIL (in between, fixed position).
