I’ve been particularly interested in fish pectoral fin shapes as, unlike mammals, their tails are vertically oriented, so lift to rise or fall in the water is a strong function of pectoral fin foil action. The Monterey Bay Aquarium has a four footer in captivity (for now), and this pic ran in our local paper today.
Very interesting pic. when I look at the Pectoral Fin it looks like the trailing edge down towards the base has bumps. Does it look like that to anyone else? Also can anyone tell me what that is on the tail, up towards the tip, looks like a bump, or is it just a fish that was in the shot? My montor is not all that good so I can’t tell. Maybe you are on to something here.
Hey Blakestah,
I completely agree with you about the function of the the pectoral fins on a shark. They act very much like wings and with trailing edge detached from the body that portion of the fin acts like aerlerons (spelling?) The use them to change depth and to maintain the swimming attitude.
Al, I think the back lighting in the photo shows the slight undulations in the thinned trailing edge of the fin. It would be easy to misinterpret the visual and think they were bumps.
I blieve that little extra flare at the tip of the tail, though subtle gives the fins a big boost in swimming power.
Sharks use ther pectoral more like wings than any of the other fishes. They have a very specialized anatomy and demonstrate how very important the subtle break in a line or change in a curve is to performance.
Mahalo, Rich
Aileron (looked it up) “a moveable part of an airplane wing or a movable airfoil external to the wing at the trailing edge for imparting a rolling motion and thus providing lateral control” Webster’s 9th New Collegiate Dictionary.
Hm. We don’t use fins for rolling, but we do use 'em for controlling lateral motion in another way, more like the tail of a plane, or the tail of the shark.
I suggest we not call surfboard fins “ailerons”
BUT, what strikes me about the shark pic is the similarity between the outline of the pectoral fin and the upper part of the tail. Same base/height ratio, and NEARLY STRAIGHT edges. What do we make of that?!
Aileron…“a moveable part of an airplane wing or a movable airfoil external to the wing at the trailing edge for imparting a rolling motion and thus providing lateral control” …
Hm. We don’t use fins for rolling, but we do use 'em for controlling lateral motion in another way, more like the tail of a plane, or the tail of the shark.
I suggest we not call surfboard fins “ailerons”……
I agree with not calling surfboard fins “ailerons”; I partially agree that they’re like the vertical foils on the tail of an airplane; I disagree that they’re like the tail of a shark. There are typically two components to the vertical foil(s) on the tail of an airplane. The forward part is fixed; the rear part swivels around an (approximately) vertical axis. The function of the forward part is to keep the longitudinal axis of the plane aligned with the airflow past the plane (particularly in instrument flying conditions); the function of the swiveling portion is to do the same plus create optional side forces to create moments that rotate the plane about it’s yaw (vertical) axis. The latter foil is the “rudder”, and most closely corresponds in function to the tail of a shark (although a plane does not use it to also provide forward thrust). The fixed vertical foil portion most closely approximates in appearance and in function a surfboard fin…and guess what? …in aeronautical terms it’s referred to as the (vertical) “fin”.
BUT, what strikes me about the shark pic is the similarity between the outline of the pectoral fin and the upper part of the tail. Same base/height ratio, and NEARLY STRAIGHT edges. What do we make of that?!
The more agile marine animals have pectoral fins with a near 2-1 aspect ratio (give or take a little fudge factor) from sharks like the mako and white to whales like the orca and dolphins too.
Ailerons are indeed a sub-wing that changes in its AOA. Watch the wing on a commercial airplane sometimes. Tiny sub-wings move up (in the rear) on the inside wing and down in the rear on the outside wing to make a big sweeping turn. The tiny sub-wings are the ailerons.
Fins with straight edges - what will they think of next…
Snap! (Or nearly) . . . Various 1997 2/1 ratio ‘spitfire’ cutaway upright singlefins.
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I noticed an article in Science News (sept 3, '04 I believe) about the dynamics of fins. One thing pointed out were the tubercules on the leading edge of the gray whales. It was hypothesized that the tubercules created mini-vortices along the top edge of the whale’s pectoral fin, allowing for a much tighter turning radius without having the fin breaking away from its track due to turbulent flow. Whitey doesn’t need to do the tight circular turns that a whale does to catch krill, so maybe the leading edge is faster for being smoother.
I work under the supposition that vicious predators are the most maneuverable marine animals…
Dolphins…
Orcas…
Great Whites…
Makos…
Bull Sharks…
Humpback fins are neat also, but they are substantially different. Much longer much higher aspect ratio fins. Not the gymnasts these others are.
The sneakiest, maybe. The most manuverable? I bet the seals win out on that one. The fastest, supposedly the Orca, at 40mph.
As far as lift goes, sharks don’t have swim bladders, so they need that attitudinal control that the pectoral fins supply.