The WWII fast battleships were immense machines with nine guns, each of which could throw a projectile the size of a Volkswagen a distance of 23 miles. A photo of the port propeller from the USS Missouri (the surrender of Japan took place on its’ deck) is shown. It looks quite different from the very earliest steam ship propellers, such as the one on the SS Great Britain (Isambard Kingdom Brunel's first great ship), which were simply twisted in a flat plane. The primitive propeller, when turning counter-clockwise, would “push” the ship forward. However, the blades on the propeller from the Missouri are not only twisted, but curved into the shape of an airfoil
The curvature in the battleship’s propeller takes advantage of Bernoulli’s Principle which states that faster moving air exerts less pressure than slowly moving air. This can be demonstrated with a spoon under a faucet. The best known application of Bernoulli’s Principle is the airplane wing. The shape of the airfoil forces air to take a longer path over the top of the wing. Since it is moving faster, there is less pressure on the top of the wing than the bottom, which creates the “lift.
However Bernoulli's Principle applies to any curved object, and explains among other things, why tennis balls and baseballs can be made to curve, Beckham can bend it, golfers can hook or slice, and roofs are exploded off houses in hurricanes and tornadoes, even though the walls may still be standing.
Water is a fluid, just like air, and so the same principle works with ship’s propellers like the “Big Mo’s”. If the photo of the Missouri's propellor is viewed carefully, each blade is also an airfoil which works in exactly the same way as an airplane wing. As this propeller turns counter-clockwise, it will “push” the ship forward, but the curvature also creates a hydrofoil with the “lift” vectored in the forward direction. The “pull” is even more effective than the “push” in driving the battleship. The Iowa class battleships could steam at 37 mph. Later, during the Cold War, U.S. preeminence in Fluid Dynamics theory and engineering of propellers is what made U.S. submarines faster and quieter than the Soviets.
The top blade of “Big Mo’s” propeller looks a bit like a fruit fly wing, which as a former Genetics teacher in college, I have seen thousands of times. The interesting thing is that at rest, a fruit fly wing is flat, like the early propeller, and would be aerodynamically inefficient. Googling around to explain this, it turns out that insect wings take on much different shapes in flight than when they are motionless. In fact the shape of the wing, and the patterning of the veins, cause the wings to flex into various aerodynamic shapes appropriate to the insect, as the wings are moved, and air pressure forces are generated. It is no coincidence that Dragonflies, the helicopters of the insect world, have much different wing shapes and venation patterns than Horse Flies which are built for speed (they can reach 40 mph), or Bumblebees which are built for heavy lifting.
One of the interesting things about fruit fly genetics is that there are many developmental mutations which effect the development of the wing veins. According to the ideas above, the precise locations and strengths of the veins are what determine how the wing flexes into an aerodynamic shape in flight. When the wing venation patterns are changed by developmental mutations, this very likely stiffens or weakens the wing in various planes, leading to changes in shape, and reducing aerodynamic efficiency, which may explain why these mutants don’t exist in the wild.
Another interesting idea is that the fruit fly mating ritual consists of the males attracting females by singing and dancing. The fruit fly "song" consists of different pulse patterns and ‘humming sounds which are produced by wing vibration (unlike the whine produced by mosquito wings, it is inaudible to humans) while keeping the wing tipped forward. Listen to "Duo for Bass Flute and Fruit Fly". The wings of males cross-vein mutations may not flex correctly to produce the ideal song - they may sound more like Adam Sandler than Frank Sinatra!
Air and water are both fluids, so do the same Physics apply to marine creatures? It turns out that whale fins are also foil-shaped. Especially surprising has been the epiphany that Humpback whales have bumps (tubercles) on the LEADING edges, not the trailing edges. However whales have been evolving for a long time - DNA evidence reveals that they diverged from Hippos 50 million years ago. Evolution proceeds by trial and error, but even so, stupid mistakes can lead to a high degree of perfection if given 715,000 human lifetimes! The solutions of evolution have sometimes given clues to better engineering of machinery. In this case, computer models showed that the tubercles actually increase lift and decrease stall speeds of the whale fin.
So this takes us back to machines again. Engineers are currently using this new theoretical understanding to design more efficient windmill blades, with bumps on the leading edges, to mimic whale fins!
It is the visual lines which give beauty to a race horse, a ship or a car. It is the lines of explanation, meaning and connection which give beauty to Science.
William S. Barnes