Launching and recovering aircraft from ship flight decks is very challenging because of the small size of the flight deck and the movement (pitch, roll, etc.) of the ship as it travels through the water. This is especially true for smaller ships like frigates and destroyers that launch and recover rotary wing aircraft. In addition, most of these ships have superstructures, functioning has aircraft hangars, in front of the flight deck. The ship's geometry, along with the combined effect of prevailing winds and the forward motion of the ship, creates an air flow over and around the ship's superstructure resulting in an air wake behind the superstructure on the ship's flight deck. This air wake is often a turbulent and unsteady vortex on the flight deck creating difficulties with aircraft maneuverability on and around the flight deck.
The ship's superstructure is essentially a combination of bluff bodies. The air flow separates from the sharp edges of the hangar forming shear layers and low-speed recirculation zones leading to large spatial and temporal velocity gradients in the airflow over the flight deck. Vortical flow structures are shed from the hangar and other large-scale features on the superstructure. These vertical flow structures typically have length scales similar to a helicopter's fuselage and main rotor. Therefore, as the pilot moves the helicopter through the air wake during take-offs and landings, the highly unsteady airflow causes large fluctuations in the aerodynamic loading on the rotor and fuselage that adversely affect the helicopter's lift and thrust on take-offs and landings. The air vortex can also significantly disturb the aircraft's flight path as the aircraft responds to the influence of the ship's air wake. These factors, combined with poor visibility and water spray can significantly increase pilot workload. Consequently, the margins for pilot error can be significantly reduced, which increases the frequency and severity of accidents and crash landings.
The impact on flight decks and pilot workload, caused by these superstructure air wakes has not been fully appreciated in ship design. Although studies have shown benefits of placing flow control devices on ship superstructures to control the air flow around the vessel and increase aircraft maneuverability during takeoff and landing, these studies have only examined modifications applied to the rearmost edges of the ships hangar to mitigate the effect of superstructure vortices to the front of the carrier flight deck as shown in FIGS. 1 and 2. These types of flow control devices have had only a slight to moderately positive, and sometimes negative, effect on the reduction of flight deck air wake.
FIG. 1, shows several configurations, where air flow control structures extended upward from the top, aft edge of the hangar. In these locations, the structures obstruct views of the flight deck and also interfere with radar and radio communications signals to the aircraft. In other configurations, the flow control structures extend from the ends of each side of the hanger toward the flight deck. These configurations offer little to no airflow break-up and also reduce the usable area around the flight deck. Moreover, these structures are fixed in their positions, making them permanent obstructions to the radar and radio communications signals, as well as the usable flight deck area.
Flow control structures have also been placed along the top edge, starboard side of the superstructure, as shown in FIG. 2. These structures extend out parallel to the air flow along the side of the ship, offering little to no resistance as a streamlined airflow field passes over and around them. Therefore, air vortexes typically form on the ships flight deck with the same intensity as they would have without these flow control structures in place. Consequently, a more effective flow control device is desired.