Can you explain the biomechanics of more complicated movements such as rolling and relate these to the pilot’s control of a fighter airplane? This topic is covered in an article titled “Three-dimensional kinematics and wake structure of the pectoral fins during locomotion in leopard sharks Triakis semifasciata” (Wilga and Lauder, 2000).
In reference to simple flight dynamics, and aerodynamics, there are three movements that are required to maintain control or the aircraft (Schmidt, D.K. 2011). Those movements are roll, pitch and yaw. Rotation around the front-to-back axis is called roll. Ailerons control roll. On the outer rear edge of each wing, two ailerons move in opposite directions, up and down, decreasing lift on one wing while increasing it on the other. This causes the airplane to roll to the left or right. To turn the airplane, the pilot uses the ailerons to tilt the wings in the direction desired. The elevator controls the pitch of the aircraft. Pitch is the rotation around the side-to-side. On the horizontal tail surface, the elevator tilts up or down, decreasing or increasing lift on the tail. This tilts the nose of the airplane up and down. Yaw, or the rotation around the vertical axis, is controlled by the rudder (Schmidt, D.K. 2011).
The three of these can be used together to change direction of the aircraft, make it go up and down and remain steady hold. When the ailerons and rudder are used together, they can turn the direction of the aircraft.
In more advanced flight dynamics, some fighter jets are tail-less, or delta wing aircraft, and have combined elevator/ailerons are called elevons. The space at the trailing edge of the wing is at a premium. The F-117 had elevons as well, as did Concorde. In the 1970’s era prior to the F-15/16, fighter jets or high-performance aircraft had problems attempting to roll the aircraft using ailerons. If at a higher angle of attack, or AOA in the aviation world, adverse yaw would produce yaw in the opposite direction. This in short created a roll in the opposite direction than intended.
Hydrodynamics and aerodynamics follow the same laws of physics. The main difference is the property of incompressibility. The better term to relate these movements we are discussing is fluid dynamics.
Simply stated, the pectoral fins work the same as ailerons; in the natural world, we can replace the ailerons with pectoral fins. The elevator is replaced by the pelvic fins. The upper lobe of the caudal fin replaces the rudder. Dorsal fins increase directional stability. There are more parts to the shark that further precise movements, control trim, increase acceleration and reduce drag. The shark is the fighter jet of the natural world.
However, there is a much more complex case with Triakis semifasciata. According to Wilga and Lauder, 2000, “during steady horizontal locomotion, the pectoral fins are cambered, concave downwards, at a negative angle of attack that we predict to generate no significant lift”. The shark is holding position. Wilga and Lauder (2000), further state that “Leopard shark pectoral ﬁns are also oriented at a substantial negative dihedral angle that ampliﬁes roll moments and hence promotes rapid changes in body position. Vortices shed from the trailing edge of the pectoral ﬁn were detected only during vertical maneuvering. Starting vortices are produced when the posterior plane of the pectoral ﬁn is actively ﬂipped upwards or downwards to initiate rising or sinking, respectively, in the water column. The starting vortex produced by the pectoral ﬁn induces a pitching moment that reorients the body relative to the ﬂow. Body and pectoral ﬁn surface angle are altered signiﬁcantly when leopard sharks change vertical position in the water column.” They said that locomotion in leopard sharks is not completely similar to flight in fixed-wing aircraft. “Instead, a new force balance for swimming leopard sharks is proposed for steady swimming and maneuvering. Total force balance on the body is adjusted by altering the body angle during steady swimming as well as during vertical maneuvering, while the pectoral ﬁns appear to be critical for initiating maneuvering behaviors, but not for lift production during steady horizontal locomotion (Wilga and Lauder, 2000).”
In conclusion based on this topic, the biomechanics of sharks can be easily understood by the movements of aircraft; however, we must treat each shark as a custom engineered design, which have unique combinations tailored to their specific, most efficient needs within its environment. Over time, environments change, and evolutionary radiation could have an impact on each shark’s individual locomotion.