A Brief History of Flight
Human flight has gone through many transformations and is likely to go through more
How airplanes fly
The evolution of the airplane developed in lockstep with our understanding of the physics of flight. For eons, humanity admired birds and their freedom from the ground, but had no idea how they managed to keep airborne. The Greeks developed a steam powered toy bird that took flight during the golden age of Greece around 600 BC. The Chinese were among the first to achieve human flight by the use of tethered kites of many designs. Some were made large enough to house a person and were used for reconnaissance. Later, great minds such as Leonardo Da Vinci put their minds to the enigma of bird flight. It was Leonardo that some thought who developed human powered flight. If he did, it was likely with a device that was something like a hang glider. He also had ideas for parachutes and a helicopter like device. All of these exploited the principle of lift. Being passive machines, none exploited the principle of thrust. The Chinese kite however cleverly used the lift of the wind and the mass of the moving air to provide the drag and thrust to overcome gravity. All of Da Vinci’s devices used the force of drag, especially in the design of the parachute. All of the inventions, by those developing flight were influenced by gravity.
The next step in flight was the lighter than air balloon that relied on an altogether different force; buoyancy. Whether they were lifted by hot air, such as in the original design by Montgolfier or by hydrogen or helium that later became popular, the principle of lift through bouncy was the active principle. Among the later designs, some of which survived well into the 20th century, is the form of the dirigible like the ill fated Hindenburg.
With the successful flight of the Wright Brothers at Kitty Hawk, the age of heavier than aircraft began in earnest. In their design, these airplanes relied totally upon four dynamic interlinked principles being, lift, thrust, drag and gravity. The lift replaced buoyancy that was used in lighter than air aircraft. This was achieved through lightness of materials, design of the wings, the method used to generate thrust and ways to reduce drag and the influence of gravity.
Early designs tried a host of configurations, most of which failed miserably, but the basic design of the wings improved on the successful models. The design of the wing is such that an over pressure is created on the underside of the wing, while a partial vacuum or under-pressure is created on the top side. This differential caused lift as the greater pressure under the wing sought to fill the void above the wing. The wings and attached fuselage lifted off the ground against gravity as a result. But the effect was best achieved if the wing was tilted back slightly and was moving forward with sufficient speed to create enough lift to balance and overcome gravity. Thus a means of thrust was needed to create the lift necessary to attain flight. Thrust alone was not enough. A means to deliver thrust was necessary, so the idea of the wing was turned on its side to create the propeller and eventually the jet turbine or turbofan.
Drones, the latest in flying technology
Initially, human power was tried, but materials in the early days were just too heavy and drag due to the density of the atmosphere was too great and prevented enough lift from developing. Gravity and drag won the day. The Wright Brothers used an early internal combustion engine coupled with a propeller, which was barely sufficient to create enough lift for a short flight, but the result was so encouraging that improvements were pursued with vigor. The war years and competition between powers to win in war sped up design improvements in aircraft. Over the years, more powerful, lighter and reliable engines were created as well as airplane design. From the early bi-winged and tri-winged planes came the single wing design and the efficient and light rotary internal combustion engine. Speed and distance flights increased dramatically. Smother exteriors helped to decrease drag and allow for greater speed. Greater speed meant that fewer and smaller wings were possible for the same end result. Efficiency increased leading to better and better designs.
A dramatic change in delivering thrust came with the advent of the jet engine. Initially invented and developed in 1928 by the British RAF cadet, Frank Whittle, between WWI and WWII, the jet engine was pursued with vigor in Nazi Germany during WWII at the request of Adolph Hitler. By August 1939, the Germans were thus the first to fly the first sub-sonic jets capable of flying near the speed of sound and flying well above the 30,000 foot ceiling for standard internal combustion engines. It took a few years to develop the jets because Himmler was unimpressed at initial trials when the first flight did not prove much superiority over the Messerschmidt. The Nazis also used jet engines to power flying the thousand pound buzz-bombs that wreaked havoc on Britain. The British then rushed jets into development as the Germans began bombing mission using jets and shooting many Spit-fires out of the air from above where Spit-fires could not go. After WWII, the jet engine became standard for the military and commercial flying. Planes then could fly faster; well over the sound barrier. They have minimal surfaces incorporating new materials and small wings, reducing drag. Sometimes the jet engines were so powerful, that jets alone could create enough lift without relying on wings at all, despite the fact that the engines weighed in at a few tons. This fact was exploited in the Harrier Jump Jet and its successors. Wings became small enough that they could be incorporated as part of the fuselage such as in stealth jets, reducing their radar profile. Some speculate that jet engines of great power, provide the lift for some military flying saucers.
In any aircraft design, the four principles hold; lift, thrust, drag and gravity. All of these must be considered in the design. As we learn more about flying, we develop ever more efficient designs. In the modern era, materials are now designed to allow for human powered flight, such as in the flight of the Albatross, a human powered aircraft that was powered by a bicycle configuration operated by the pilot. The Albatross, though not gaining much height, stayed aloft for hours, something that Da Vinci could only dream of and the Wright Brothers failed to do with an internal combustion engine providing the thrust. Superior lightweight materials allowed a human being to create enough thrust to lift the aircraft for a substantial flight. The drag eventually tired the pilot enough that the craft eventually crash landed in open water; but the speed was so low, about the speed of a fast walk, that little injury resulted. This is due to the fact of the extra large lightweight wings providing more lift. The same basic design was then incorporated into a solar power aircraft that flew without a pilot for months on end, while it was used to study weather from a great height. The solar powered aircraft broke all distance and duration records, surpassed only by satellites in low Earth orbit. Aircraft are still going through evolution in design. Modern types include robot planes that can fly great distances by remote control with no pilot on board. The pilots fly them from the ground by remote control, just as a child does with a remote control toy plane.