<< Page 23 Page 24: Page 25 >>   Wing Aspect Ratio The wing aspect ratio is THE most telling feature of an airplane’s purpose and performance. It is the easiest way to say whether a plane is built for transport, dogfighting, aerobatics, high-speed flight, or astronautic applications. Very High aspect ratio: This means that induced drag, a real problem at slower speeds, is minimized. In general, the higher the aspect ratio, the lower the drag. So airplanes with VERY high-aspect-ratio wings have very long range and especially a VERY long endurance, and are very fuel-efficient. They also cruise at slow speeds. Very high-aspect-ratio wings mean an airplane is supposed to stay in the air for a long, long time. Most spyplanes must act as aerial observation polatforms for as long as they can, as far into enemy territory as they can. So the U-2 and modern unmanned spyplanes (like the Predator and Global Hawk and the obscure, secret Boeing Condor, an early UAV) have very high-aspect-ratio wings, as do modern planes meant for distance records like the Voyager, and low-drag airplanes such as gliders and humanpowered airplanes. Very high-aspect-ratio wings are also ideal for high-altitude flight, so are found in planes made to fly really high – like the Helios solar-powered plane, Burt Rutan’s Proteus, the Myasishchev M55, the Grob 520 Egrett, the Grob 850 Strato, etc. Very few airplanes have “very high” aspect ratio wings. Other than for gliders, they are very rare and exotic, most are experimental and/or military. The ones pictured in the following couple pages are just about all the types with wings this thin. Above; Condor, U-2, RQ-1 Predator, RQ4 Global Hawk, Voyager and Proteus (and an F-18) Below; Grob 520 Egrett and Grob 850 Strato, and the Myasishchev M55 high-altitude research planes. Also, a glider, and the solar-powered Helios: High aspect ratio wings can be stiffer than those of very high aspect ratio, so they allow the airplane to fly faster (but not too fast, usually at subsonic speeds, as they are still not stiff enough to handle the loads of supersonic drag). Airplanes with high-aspect-ratio wings have long ranges and endurance times, even at faster speeds, especially if the wings are moderately swept, usually at around 30-35 degrees. (This amazingly optimal layout was pioneered by Boeing in 1947 for the Boeing model 450 (B-47), and was subsequently copied all over the world in almost every jet designed since. Therefore airliners (which are probably most of the planes most people ever see), bombers, transports and business jets have a very similar shape, with high-aspect-ratio wings mostly swept around 35 degrees). Above; the Airbus 380 (previously known as the “A3XX”) and Boeing B-52, The B-24 Liberator and C-130 Hercules, the Gulfstream 4 and the DC-3. Efficient (but practical) airplanes with high-aspect-ratio wings. Medium aspect ratio wings are stiff enough for dogfighting and aerobatics (not at extremely high g’s, but pretty high, as was the case in World War 2), and offer decent range, speed and fuel efficiency. Their low-speed induced drag is not too high, and they are stiff enough to fly at high subsonic or even slightly supersonic speeds. This larger range of speeds, coupled with agility and efficiency, means these planes are easy to fly, so most general aviation planes (Cessnas, Pipers and so on) have medium-aspect-ratio wings. World War 2 fighters, and modern trainers and aerobatic planes, also have aspect ratios like this. Above: A Van’s RV8 kitplane, and a Cessna. A P-51 Mustang and a Hawker Sea Fury. A T -2 Buckeye, a straight-winged F-84. And an Aero-vodochody L39. Low aspect ratio wings provide lower drag at supersonic speeds, and can be made VERY stiff to handle very tight turns. This is why they are used in modern jet fighters. However, they have very high induced drag, especially at low speeds, so they make for gas-guzzling airplanes with short range and short endurance (unless they carry a LOT of fuel, like the Concorde and Blackbird). But it’s the only way to fly very fast and pull 9g’s. Below: Built for speed: The Mirage 4 bomber, the Concorde and Tupolev 144 supersonic airliners, the Blackbird spyplane, and the X-3 and X-15 experimental high-speed record breakers. Below: Built for agility as well: The Lockheed F-104 Starfighter (fastest single-engine plane ever), the Eurofighter ,the MiG21, the Northrop F-5, the Sukhoi Su 27 and the Lockheed/Boeing F-22 all have low aspect ratio wings: Very Low aspect ratio wings can be made very, very strong. So they are used for very high-load applications, like extremely high-speed flight (as in the X-15, X-3, X-43, etc) and in space vehicle reentry (like the Space Shuttle, X-33, etc). Aircraft made to be space reentry vehicles have very stubby wings or no wings at all – their fuselages are shapes to generate lift, and are thus Lifting Bodies (like the M2-F3, HL-10, X-24, X-33, X-38, etc). Above; The HL-10, X-24, and M2-F1. A reentering X-38, and the failed X-33.