aerodynamics What exactly keeps airplanes in the air? The popular explanations are basically wrong. The first airliner patent was issued mid-nineteenth century. Its wing was a flat plate set at an angle, designed to push the air down as it pulled itself forward. This design would work better if the wing was slightly curved, the trailing edge still lower than the front. That's not how modern wings are usually illustrated. They appear almost flat at the bottom and curved on top. In these pictures the air appears to bypass the underside, while 'squeezing' over the top and seemingly pushing it down. One explanation involves boundary layers, regions of air partially dragged along with the wing. The wing influences all the air around it, parallel lines curving from high to low pressure, through drag and turbulence. Pressure waves reach all the way to the ground. Whether they describe actual reality or not, the computerized equations undeniably work well (even if they don't account for drag well). It's an example of how even elementary things don't need to be fully understood.

Wing Designs canards Small wings are sometimes found near the nose of fighter jets. Normally, elevators are part of the tail. They control the pitch (making the plane go up or down). To maintain the center of gravity, delta wings are rear-mounted, making it hard to have separate elevators. One solution is 'elevons'. Instead of a separate tailplane, all moving surfaces at the back help regulate lift, roll, pitch and yaw. This works well for high-speed flight, but not landing and rapid turns. To improve handling, separate elevators known as canards can be placed near the front. Usually the entire canard is movable, without separate flaps. During the 1980s, canards were considered the wave of the future, but newer American stealth fighters don't have them (a Chinese one does, the Russian has a hybrid version). Instead, the F-22 has 'cut-outs' to accommodate conventional elevators in the back. Even better maneuverability could be achieved by having control surfaces at the front and the back. Canards may also appear on future airliners operating from short fields. winglets The airflows over the top and bottom of the wing merge at the trailing edge. Usually this goes smoothly, but at the wingtips the airflow may slip off the sides entirely, causing the streams to mix in wasteful spiral vortices, instead of pushing the wing up and forward. For this reason and others, the Spitfire and other early high-speed aircraft had oval wings. Another solution is to put barriers at the wingtips, keeping the top and bottom airflows separate. These are called winglets. They also provide some directional stability. Winglets induce a different type of drag at high speeds, so they are mostly found on subsonic planes, including airliners. Large, low-speed winglets could become common. swept wings Swept wings have a larger area, but less high-speed drag than straight wings of the same width. To interact with low-pressure/high altitude air, they are streamlined for high velocity in a way quite unrelated to low-speed streamlining. Their shape is said to prevent or delay sonic shockwaves from forming. Once the air moves at supersonic speed relative to the wing, it won't flow smoothly. High-speed air is like a confined explosion. Energy is carried away by shockwaves instead of the airflow itself. To function at low speeds, swept wings need complex arrangements of leading-edge slats, flaps and spoilers. delta wings Triangular wings have a large surface area. A low-pressure vortex forms over them to generate lift at low speed. This helps with slow turns at altitude, and for final approach. Delta wings can also ride supersonic shockwaves up to Mach 3, quite unlike straight wings. They are not as popular as they used to be. Modern high-speed wings are whittled-down hybrids between traditional deltas and swept wings. One compromise is bell-shaped. forward swept wings Swept wings work whether they are swept back or forward. In the latter case, shockwaves from the wingtips and fuselage can interfere. They have good low speed maneuverability, but are less stable. Forward swept wings were demonstrated on the X-29, the Russian S-37 Berkut, and the German Hansa business jet. They may become useful on regional airliners to help them rapidly climb from small airports. ring wing This design from the 1930s has yet to be demonstrated on an actual plane. It would have the advantages of the box wing (a biplane with both sets of wings connected by oversized winglets) and the related diamond wing. Without edges, there is no drag at the wingtips. It would confine the airflow and speed it up, generating lift by lowering air pressure. A wing with both anhedral and dihedral can be unstable. An unrelated benefit could be its ability to capture and 'reflect' the shockwave from the front of the fuselage downward at transonic speeds. circular wing Not to be confused with the ring wing, it's basically a flying disk with a big hole in the middle, which may increase some types of stability. This wing type supposedly works at a wide range of speeds and angles of attack. It could almost fly sideways. Some designs are hybrids of the above two variants. swing wings The most common type of variable geometry airfoil. By changing the wing sweep in flight, a constant airflow can be maintained at different speeds. The earliest examples could only be adjusted on the ground. The largest swing-wings are found on the Russian Tu-160 'Blackjack' bomber. Swing-wings have lost favor because of the heavy hinges required, while conventional wings and flight controls have improved dramatically: good compromises exist for different speeds. These are very unstable (unlike swing-wings), but improved sensors and software could almost keep a brick flying, and the inherent instability actually makes them more maneuverable. Future improvements in lightweight materials may make swing-wings fashionable again. They could even sweep forward. scissor wing A long, straight wing mounted on a single pylon over the fuselage. At high speed the wing rotates around the axis to adjust its sweep angle. One half of the wing then points forward into the airflow, the other half is swept back. A single hinge makes this wing lighter and simpler. One disadvantage: the airflow around the plane is not symmetrical. flying wing Perhaps the most efficient aircraft design. Considered by the Nazis during WW2, it has always had stability problems. The flying wing is optimized for level flight, with less drag, more range, and greater fuel economy. One issue is the lack of internal space; the wing has to be thicker than ideal to accommodate the engines and cabin. Today's only known examples are the B-2 and B-21, but one day they may be joined by a fleet of long-range airliners and cargo planes. lifting body Some experimental aircraft had no wings at all. Shaped like eggs or bullets, they did have control surfaces. Most lift was generated under the fuselage. They had more 'camber' than other aircraft, but were stable at high speeds. Lifting bodies couldn't even take off under their own power. Their compact shapes are good for re-entry vehicles. blended body A compromise between the previous two variants: conventional outer wings, but the fuselage also provides some lift. More expensive to build because of the complex shape, and harder to modify. A 'stretch' version would be out of the question. It wouldn't fit at most airport gates, and even taxiways would need to be modified. The canceled A-12 light bomber had a blended body. Propulsion engine locations The VFW-614's turbofans were mounted on pylons above the wings, causing less noise on the ground. A disadvantage was the increased weight of heavier pylons and stronger engine casings. The 'Coanda' design diverts the exhaust flow over the wing to generate low speed lift. Drag could be reduced by installing the engines conformal with the wings, or even inside them. The De Havilland Comet's engines were installed in the wing roots. Engines mostly hang below and ahead of the wings to prevent shrapnel from an engine explosion from damaging the flight controls. Keeping them from the wings also reduces drag by separating airstreams. Most jet fighters have their engines near the centerline. Future airliners may also have engines mounted inside the fuselage, reducing total drag. S-curved air intakes could provide some lift. propfans The ultimate in high-bypass turbofans, propfans are a cross between jet engines and propellers. Single crystal turbine blades spin at near-sonic speeds around a jet engine core, and provide most of the thrust. They are very noisy, and passengers have an irrational dislike for what appear to be propeller aircraft. They aren't mentioned much anymore, but rising fuel prices in the 2020s may give propfans a second chance. ramjet Basically a hollow tube through which air passes at high velocity. The incoming air is slowed by a cone or a plate to subsonic speeds. Fuel is injected, and spontaneously ignites as it flows out. The pressure increase pushes the ramjet forward. Ramjets only work at high speeds; at low speed the exhaust bleeds out the front as well as the back. Miniature ones can be mounted at the tip of helicopter rotors. Since the 1950s they have fallen out of favor. The noise level is a factor, along with poor fuel economy. Most airframe materials also melt or crumble at ramjet speeds. scramjet The engine for the now forgotten 'Orient Express' proposed spaceliner. Like in a ramjet, adjustable plates compress the incoming air. Here, fuel is injected and combusts at supersonic speed, at relatively high pressure. Speeds above Mach 5 are possible, but eventually even a scramjet can't keep up with the airflow. Even more powerful engines will be needed to reach orbit. paddle wheel engine There's no reason why a propeller has to face the airflow. In theory a fast spinning 'paddle wheel' with individual air scoops would also work. Such an engine could also divert the airflow to provide direct lift. It would be powered by a conventional jet turbine. ornithopter The entire wing flaps up, down, and backwards in a rather complex variable curve, generating lift like birds and insects do. This design can power tiny unmanned aircraft. Someday, lightweight wings may be covered with thousands of small electrically powered 'motivators', a blur of transparent flaps moving huge volumes of air every second. nuclear power A nuclear reactor could heat liquid hydrogen to high temperature, and blast it from a variable nozzle. Alternatively, the heated fluid could directly drive propeller turbines. Since the reactor can only generate heat, most of its power output would be wasted. electromagnetic propulsion Also known as 'magnetodynamics'. A very advanced future engine could strip electrons off the incoming air, and accelerate air molecules electrically. The energy could come from a chemical reaction as the air combines with fuel. Or the thrust might come from the fuel being injected at high speed into the hypersonic airstream, so it can combine with the incoming air. The combustion energy would then be captured and used to expel more fuel, in pulses or continuously. In either case, the combustion would not provide direct thrust, but energy for the thrust. Less complicated would be a purely electrical system driven by a separate powerplant. The outer surface of the aircraft could be electrically charged. Then the familiar rules of aerodynamics would no longer apply. VTOL tilt rotor or tilt wing These operate like regular aircraft or helicopters by moving the powerplant or the entire wing to a horizontal or vertical position. The problem is the added complexity of making these systems move, which triples maintenance. There were many V-22 Osprey crashes before most kinks were worked out. This only makes sense when vertical flight has to be combined with long range, otherwise helicopters are cheaper. convertiplane A few experimental rotorcraft were built with both propellers and helicopter-style lifting rotors. They usually had short wings also. The design's weight penalty over tilt rotors is compensated by an increased safety margin. During forward flight the rotor can be left unpowered, providing lift by spinning in the airflow like a gyroplane. With more advanced versions, the rotor can be stowed or fixed in place. flying cars Will we have personal sky-cars someday? The odds are minuscule. Progress has actually been negative in that direction. The problems are energy and safety: since runways are scarce, flying cars must operate from normal roads, with short or vertical take-offs and landings, requiring ultralight airframes with narrow wings. Current lifting engines are wasteful for that purpose. It would take a radical new lightweight rotor of a type not seen before: perhaps spinning wires or even a corkscrew, suitably covered to protect pedestrians. Developing powerful new software to navigate airborne traffic jams could be easy by comparison. Lighter Than Air heavy lifters Around 2000, a German company planned to build a fleet of giant airships to lift modestly heavy loads, like lumber and oil drills. Ducted fans would have swiveled for extra stability and lift. The giant hanger they built was eventually converted into a waterpatk. There has always been military interest in the concept, which could fill the gap between large cargo planes and small ships. Be among the first to read Infinite Thunder by Jack Arcalon. The book that took a quarter century to plan and write. With more original scientific, sociological, and technical ideas than any science fiction novel ever published. Original source of the Anonymous meme. Buy the book Read chapters for free 01-08-10-3/12-16-8/18-12/22