Forward Swept Wing Fighter Needed For US

ME 363 Engineering Tools, Analysis, and Communication
Abstract
When looking for the next best thing in aviation, sometimes it is important to look back at old ideas that have not been used yet. A forward-swept wing provides better lift to drag ratios, compared to a swept-back wing of the same area, higher lift to drag ratio; higher capacity in dogfight maneuvers; higher range at subsonic speed; improved stall resistance and anti-spin characteristics; improved stability at high angles of attack; a lower minimum flight speed; and a shorter take-off and landing distance. Comparing the only U.S. forward-swept wing jet (X-29A) to contemporary fighters, the X-29A outperforms them in angle of attack and lift to drag ratios.
Forward Swept Wing Fighter Needed For US
Introduction
A forward swept wing design has been tested and dismissed by the United States, though it just might be the right configuration for the next United States fighter aircraft. NASA tested the X-29, a forward-swept wing jet, back in the early 90’s and submitted their data, but a fighter aircraft was never produced. Over the years since then certain areas of engineering have advanced and are now up to the task of supporting an aircraft featuring a forward-swept wing. This forward-swept wing configuration gives several advantages to a fighter aircraft which could be the deciding factor of a dogfight. “In 1936, a German aerodynamicist first postulated developing an airplane with its wings swept forward, but nobody built any actual models at the time.”[1]

Results and Discussion “Interest in forward-swept wings increased when some wind-tunnel tests in 1931 showed that [pic]of forward sweep provided a greater useful angle-of-attack range than did a corresponding amount of aft sweep. Later, as airplane wings began to experience the effects of local shock waves, A. Busemann and R.T. Jones independently recommended sweepback as a means of reducing transonic and supersonic drag. It was only natural, then, to consider using forward sweep for high-performance aircraft, because forward sweep offered the dual benefits of reducing compressibility effects at transonic speeds and providing high-lift advantages at lower speeds.”[2] The lift-to-drag ratio is higher on a forward-swept wing than on a regular wing and therefore gives you better fuel efficiencies at low speeds. At higher angles of attack maneuverability is higher on a forward-swept wing due to the direction of air flowing across the wings from root to tip. On a forward-swept wing surface stall occurs from the root of the wing out, versus the tip of the wing in like on a swept wing design. This allows the forward-swept wing to achieve slower speeds and use shorter runways for take off and landing. Most modern day fighter aircraft lose maneuverability input around an angle of attack of 40 degrees, though on a forward swept wing it is possible to achieve maneuverability at angles of attack close to 67 degrees. This is a huge leap in aerodynamic ability of fighter aircraft, which could be the difference of winning a dogfight.
[pic]
Better lift-to-drag ratios, reducing compressibility factors at transonic speeds, and higher angles of attack are three innate characteristics of a forward-swept wing. “The airflow over a forward-swept wing is reversed; wingtip vortices never appear, as the air travels inward to the fuselage. This creates much more lift than a conventional wing, particularly when combined with canards as on the X-29.” (fig 1) To stablize a forward-swept wing most models and designs produced over the years have had canards. These small wings allow for more input surface and they don’t cause drag like the tail of an F-15 but rather lift. There are some disadvantages that have been discovered with a forward-swept wing, unstable flight controls and wing strength (aeroelastically). With the wing setup the control surfaces become difficult to operate by hand and must have fly-by-wire controls. This is run by control equations that make many minute control surface changes that make flight stable even at high angles of attack and low speeds. When the X-29 was flown, it was noticed that this was not a perfected system, but now after all the testing that went into the F-22 this type of system has been refined through a process of testing and retesting. The wing strength was also cause for concern in early testing of forward-swept wings, but now with more advanced lightweight composite material the strength of the wings can be improved and for less weight and size. Using composites also makes it easier to mold the wing into specific shapes and sizes, getting better aerodynamic characteristics out of the wing. Supercritical wings can be made with the new composite materials, allowing for less drag and thus making the Lift/Drag ratio better. Data from the X-29A was compared with contemporary aircraft to show the difference in L/D ratio, keep in mind these aircraft are refined production models while the X-29A was a experimental aircraft with many rough edges such as hinges on the underside of the flaperons(flap and ailerons molded together in one structure), this means that redesigning a forward-swept wing it can reach even higher L/D ratios. (table 1) The X-29A was an experimental platform in which to test many different ideas and theories of aviation, not just the forward-swept wing.
[pic]
One way to compare the forward-swept wing concept to other aircraft is by looking at the coefficient of drag ([pic]) and the coefficient of lift ([pic]) in relation to each other. (equation 1 & 2) The dynamic pressure ([pic]), mach number (M) and ambient pressure (P) are all part of the equations. (equation 3)
[pic] equation 1
[pic] equation 2
[pic] equation 3
From this data we see what the X-29A is capable of without any new technology or being redesigned to fix some of the small areas of drag on the airframe. With thrust vectoring, new composite materials, stealth, and a forward-swept wing, an aircraft could become the top performer.
Conclusion
There is a difference of philosophies between the West and the East. Western fighter aircraft have become more stealthy and equipped with more high tech equipment in order to prevent dogfights, and fire and forget. Eastern philosophies such as Russia have adopted the philosophies of stealth and highly maneuverable aircraft. Russia has the Su-47 which is a forward-swept wing fighter; “The swept-forward wing, compared to a swept-back wing of the same area, provides a number of advantages: higher lift to drag ratio; higher capacity in dogfight maneuvers; higher range at subsonic speed; improved stall resistance and anti-spin characteristics; improved stability at high angles of attack; a lower minimum flight speed; and a shorter take-off and landing distance.”[3] These advantages in the new Russian fighter bring about the need for an aircraft on our end in order to combat the maneuverability of any such aircraft produced by another country. If one of the United States decided to build a production fighter with all the newest technology added, it would outperform all other proposed designs(without a forward-swept wing).
Recommendation
An aircraft like the Su-47 and X-29A could and should be built in the U.S. but ran through a much higher degree of testing to optimize it. This type of airframe would become a rival to the F-22 and Joint Strike Fighter, and then we could see which philosophy would win without gambling lives. If we begin designing now, when the Department of Defense start to ask for a new fighter concept, we will have it already in the works. At the moment the DOD will probably not want to build anymore aircraft but around the year 2015 they will be looking for the newest ideas in order to stay ahead. I propose with any new technologies acquired between now and then we add the forward-swept wing. I believe the wing alone could help our company outperform any others. We need to start designing and retesting these concepts, especially related to transonic flight, which is one of the DOD’s top priorities. Wind tunnel testing with 1/16 or larger size models will get us ahead of the rest of the aeronautical companies in designing the newest US fighter aircraft, which could mean a big contract.

airplane lifting efficiency (e). [pic]

The X-29A was an experimental platform in which to test many different ideas and theories of aviation, not just the forward-swept wing.

Works Cited
1. “Forward-Swept Wings.” U.S. Centennial of Flight Commission. 8 March 2006.
2. E. J. Saltzman and J. W. Hicks, “In-Flight Lift-Drag Characteristics for a Forward-Swept Wing Aircraft (and Comparisons With Contemporary Aircraft)”, NASA Technical Paper 3414, 1994.
3. “Sukhoi Su-47.” Wikipedia. 8 March 2006. 1. Nonlinear Wave Interactions In Swept Wing Flows, Nabil M. El-Hady., National Aeronautics and Space Administration, Washington, D.C, 1988

2. Natural Laminar Flow Flight Experiments On A Swept Wing Business Jet: Boundary Layer Stability Analyses, R.A. Rozendaal, National Aeronautics and Space Administration, Washington, D.C., 1986

3. Low-Speed Investigation Of Effects Of Wing Leading- and Trailing-Edge Flap Deflections and Canard Incidence On A Fighter Configuration Equipped With A Forward-Swept Wing, Thomas G. Gainer, Michael J. Mann, and Jarrett K. Huffman., Gainer, Thomas G., National Aeronautics and Space Administration, Washington, D.C., 1984

4. Pressure measurements of the leading edge of a swept wing at Mach 2.2, Russell B. Sorrells III, National Aeronautics and Space Administration, Washington, D.C., 1974