Research Paper on "Swept Wing Technology Is 75 Years Old"

Research Paper 5 pages (1656 words) Sources: 5

[EXCERPT] . . . .

Swept wing technology is 75 years old. But in that short amount of time it has been incorporated into nearly every aircraft design and played a major role in World War Two as well as in every other major air conflict in history. Its characteristics as a technological innovation are still being understood and future aircraft are being designed with both forward and rearward sweep. Many design considerations are taken into account when sweeping a wing and aircraft performance is directly influenced by shaping the wing and fuselage in this manner.

Swept Wing Design

The wing and wing structure play important roles in the limitations and characteristics of an aircraft. Wings that are swept have different performance characteristics than those that are not. Swept wing technology first appeared in the air over Europe during World War Two, when the Germans, eager to gain air superiority, incorporated the design into their jet fighter prototypes. There are many advantages that can be derived from sweeping the wing on an aircraft, but most notably are the superior maneuverability and handling characteristics at higher speeds.

This is most apparent at sub-sonic and trans-sonic speeds. The sound barrier wasn't crossed until after the war in 1947, but the information gained by the German and American efforts to experiment with wing sweep helped pave the way for super-sonic aircraft in the future. In fact, the swept-wing design concept was introduced by German engineer Adolph Busemann in 1935 and was not employed in earnest until later (Platzer, 2010).

Angle of Sweep

An aircraft's angle of sweep refers to the amount a wing is swept back or forward from a neutral position. Wing sweep can vary depending on where in the cord line it occurs. Some wings are swept back in segments and some are entirely swept. The angle of sweep can be influenced by many other design factors such as cockpit visibility and improved longitudinal stability. The former was employed in the DC-3 and the latter has been employed in many other aircraft designs that incorporate delta-wing or fuselage-as-wing designs (Platzer, 2010). This means that swept wing technology had a direct influence on super-sonic aircraft of the future, as it was first experimented with in a relatively meaningful way during World War Two.

Sub-Sonic Behavior

Speeds that are below the speed of sound are known as sub-sonic. Swept wing design at lower speeds yields an inherently inefficient and unstable aircraft. This means that the more a wing is swept back, the less efficient it becomes at lower speeds, where air needs to move forward to back to create lift on an airfoil (Seminov, Kosinov, and Yermolaev). Aircraft with swept wings can suffer from wing tip stalls much more commonly than those without due to the different pressure gradients and isobars associated with swept wing design and implementation. This means that the pressures on the wings that are created by the airflow as it is directed outward is less and less efficient as a component of lift creation the slower a swept wing aircraft flies (Hallion, 2011). This translates to higher stall speeds, especially at the wing tip, as well as poor handling characteristics at low speed.

Transonic Behavior

The speed zone right before the speed of sound is known as the sub-sonic zone. The transition from sub-sonic to super-sonic is quite complex aerodynamically due to the fact that air flowing over the wing tends to build up into a wave-like structure just before the sound barrier is passed (CFC, 2011). This wave actually adds drag to the wing and in some cases prevents certain designs from obtaining super-sonic status. Air compression upon a wing shape like this directly influences stability at high speeds as well if it is not dealt with through design features (Doig, Barber, and Neely, 2011). The aircraft requires more thrust to break the sound barrier since the shock waves associated with doing so, that have created drag, must be overcome by the wing and any other surface (canopy, nose, etc.). This means that the design of the wing influences the energy required to reach these speeds and also influences the fuel economy of the aircraft itself.

Once a wing or airfoil is supersonic, it generates lift through shock waves instead of pressure differentials associated with sub-sonic flight. Swept wing design is relatively inefficient unless it can smoothly transition from sub-sonic to super-sonic relatively quickly, or it incorporates design features that allow the wing to "feel" a part of the air as sub-sonic while reaching super-sonic speeds (Hallion, 2011). This means that the wing is shaped to control where the super-sonic shockwave forms and is carried by the aircraft, helping to further influence the energy and fuel requirements that the aircraft has.

Super-sonic Span-wise Flow

As a swept wing remains sub-sonic, it suffers from a span-wise flow. This is to say that without proper fuselage or cord line modifications, the wing has an inherent inefficiency. This sort of flow occurs due to the swept angle of the leading edge pushing the air to the sides of the wing, or span-wise (Doig, Barber, and Neely, 2011). This creates a major inefficiency at slower speeds because it does not allow for proper airflow over the wings to create lift. At higher speeds, the swept wing is more efficient because the air is moving almost straight back and does not have time to react and be pushed span-wise. This is a design feature of the swept wing that has influenced modifications that have appeared on the fuselage and on the wing to help increase wing efficiency (Doig, Barber, and Neely, 2011). Span-wise flow also creates the need for swept-wing aircraft to land at much higher speeds and be less stable at lower speeds than they are at higher ones.

Historical Advantages and Disadvantages

The swept-wing design that was incorporated into the late-war German fighters as well as Korean War era Mig 15's and other aircraft yielded specific tactical advantages (Platzer, 2010). These advantages included the ability to slip easily into super-sonic flight and increases in stability at higher airspeeds. These are major advantages in an era where air-to-air missiles were used to shoot down fighter jets from miles away. In lower speed dog-fighting scenarios, the aircraft were less efficient and the wings tended to stall at higher airspeeds than less swept or modified sweep designs. This was a major disadvantage for aircraft with this wing design in this era.

One aircraft design that worked to overcome the disadvantages and take advantage of the increase super-sonic efficiency and stability was the Grumman F-14 Tomcat. This aircraft had a swept wing design that could be modified in the cockpit. This is to say that the pilot could sweep the wings back for super-sonic flight and increased stability at high speeds and move the wings forward for increased lower speed handling characteristics and lower landing speeds. This meant that the aircraft had the best of both worlds. This aircraft, designed in the 1960's, flew in the U.S. Air Force from 1970 to 2006 (Hallion, 2011). It had a long and useful life in the military and also enjoyed the advantage of a swept wing design that could be modified on the fly.

Forward Sweep

Engineers have experimented with forward sweep wing designs since World War Two. The German Junkers JU 287 light bomber had them in fact, even before their performance characteristics were completely understood (Platzer, 2010). It has yielded interesting results which can be characterized in a similar manner to the rearward sweep results. This is to say that there are inherent advantages as well as disadvantages to the forward sweep. Aircraft equipped with rearward swept wings have good stability and super-sonic handling characteristics but also have improves low-speed handling characteristics as well (Hallion, 2011). This is due to… READ MORE

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