Mig 21/Tejas/Delta Wing Fighter Aircrafts Operatinal Doctrine

[CONNAN]

The US Air Force has had several good delta wing warbirds …the F106 Delta Dart, the McDonnell Douglas A-4 Skyhawk, the North American XB-70 Valkyrie, Lockheed SR-71 Blackbird, the Convair B-58 Hustler…etc.

The best argument for the delta wing design is that the leading edge is behind the the shock wave made by the nose of that aircraft at supersonic speeds. This is a great improvement on other wing designs. Of course, this is also true of highly swept wings, but the delta wing design carries across the whole length of the aircraft, which then allows more structural rigidity and strength than a swept wing. The spar of the wing doesn’t have to be right in the vicinity of the center of gravity.

Another advantage of the design is easier manufacturing process while achieving structural strength plus a bigger amount of interior volume for fuel, not to mention the other equiptment that can be inserted in its mor capacious interior. And because of its inherent simplicity, it can be made very thin while maintaining rigidity and easier to build & manufacture. This is one of the main reasons for the commercial and military success of the Mirage aircraft design. As you can see, the Eurofighter is in the forefront now of the delta wing design.

 

[CONNAN]

One other advantage of th delta is the higher angle of attack that can be achieved because the leading edge of the wing generates a vortex which remains attached to the upper surface of the wing, giving the delta a very high stall angle. A normal wing built for high speed use is typically dangerous at low speeds, but in this regime the delta changes over to a mode of lift based on the vortex it generates.

Another example of a non US design that was very successful using the delta wing design is the British built Avro Vulcan strategic bomber.

It order to overcome the problems encountered at high angles of attack, some designs have replaced the tailplane with a close-coupled canard foreplane in front of the main wing. This design can be clearly seen in the Swedish Saab Viggen fighter design. This close coupling has been seen in high speed aerodynamic wind tunnel tests to actively and positively affect the airflow over the delta wing, especially during high angles of attack and sharp turns. With the incorporation of the close in canard design with the delta wing, it has been shown to improve maneuverability and significantly lowering landing airspeeds. This Viggen design was copied by many designers and as you can see, it is applied to the design of the Eurofighter Typhoon.

 

[CONNAN]

some other advantages like the wing's leading edge remains behind the shock wave generated by the nose of the aircraft when flying at supersonic speeds, which was a distinct improvement on traditional wing designs. Another advantage is that as the angle of attack

Angle of Attack is a term used in aerodynamics to describe the angle between the wing's chord and the direction of the relative wing, effectively the direction in which the aircraft is currently moving. The amount of lift generated by a wing is directly related to the angle of attack, with greater angles generating more lift. This remains true up to the stall point, where lift starts to decrease again because of airflow separation. Planes flying at high angles of attack can suddenly enter a stall if, for example, a strong wind gust changes the direction of the relative wind, an effect that is seen primarily in low-speed aircraft.

 

[CONNAN]

In military terminology, angle of attack is often referred to as alpha (&#945, the symbol used to denote it on most diagrams. Using a variety of additional aerodynamic surfaces (a.k.a. high-lift devices) like leading edge extensions, fighter aircraft have increased the potential flyable alpha from about 20 degrees to over 45, and in some designs, 90 degrees or more. That is, the plane remains flyable when the wing's chord is at right angles to the direction of motion.

increases the leading edge of the wing generates a huge vortex [ vortex is a spinning turbulent flow which resembles a tornado. Or, maybe it is better to say that a tornado is a well known example of a large vortex. ] which remains attached to the upper surface of the wing, making the delta have very high stall points. The combination of these two features is a dream come true, a normal wing built for high speed use is typically dangerous at low speeds, but in this regime the delta transitions to a mode of lift based on the vortex it generates.

Lippisch studied a number of ramjet powered (sometimes coal-fueled!) delta-wing interceptor aircraft [ An interceptor aircraft (or simply interceptor) is a type of fight aircraft designed specifically to intercept and destroy enemy air craftt, particularly bombers. A number of such aircraft were built in the period starting just prior to World War II and ending in the late 1960's, when they became less important due to the shifting of the strategic bombing role to ICBMs. ] during the war, one progressing as far as a glider prototype. After the war Lippisch was taken to the United States, where he ended up working at Convair. Here the other engineers became very interested in his interceptor designs, and started work on a larger version known as the F-92. This project was eventually cancelled as impractical, but a prototype flying test bed was almost complete by that point, and was later flown widely as the XF-92. The design generated intense interest around the world. Soon almost every aircraft design, notably interceptors, were designed around a delta-wing. Examples include the Convair F-102, F106 & B-58 Hustler, the Avro- Arrow and the MiG-21

 

[CONNAN]

Deltas fell out of favor due to some undesirable characteristics, notably flow-separation at high angles of attack (swept-wings have similar problems), and high drag at low altitudes. This limited them primarily to the high-speed, high-altitude interceptor roles. A modification, the compound delta, added another much more highly swept delta wing in front of the main one, to create the vortex in a more controlled fashion and thereby reduce the low-speed drag.

As the performance of jet engines grew, fighters with more traditional planforms found they could perform almost as well as the deltas, but do so while maneuvering much harder and at a wider range of altitudes. Today a remnant of the compound delta can be found on most fighter aircraft, in the form of leading edge extensions. These are effectively very small delta wings placed so they remain out of the airflow in cruising flight, but start to generate a vortex at high angles of attack. The vortex is then captured on the top of the wing to provide additional lift, thereby combining the delta's high-alpha "trick" with a conventional highly efficient wing planform.