What is a Variable Sweep Wing aircraft?
A variable-sweep wing, colloquially known as a “swing-wing”, is an airplane wing, that may be swept back and then returned to its original position during flight. It allows the aircraft’s shape to be modified in flight and is therefore an example of a variable-geometry aircraft.
Typically, a swept wing is more suitable for high speeds, while an unswept wing is suitable for lower speeds improving field (take-off and landing) performance.
A variable-sweep wing allows a pilot to select the correct wing configuration for the plane’s intended speed.
The variable-sweep wing is most useful for those aircraft that are expected to function at both low and high speed, and for this reason, it has been used primarily in military aircraft.
A number of successful and experimental designs were introduced from the 1940s into the 1970s with the number of swing-wing aircraft numbering in the thousands. The Soviets developed the Su-24 and MiG-27 attack planes and the MiG-23 fighter, all with swing-wings. The European consortium Panavia developed the Tornado, produced in both ground attack and interceptor versions. It too had a variable-sweep wing. Aircraft designers also applied variable-sweep wings to large bomber-size aircraft. North American Rockwell began the B-1A bomber in the early 1970s as the U.S. Air Force’s new strategic bomber (it was cancelled in the late 1970s and revived a few years later). The Soviet design firm Tupolev also developed the Tu-22M Backfire naval attack bomber and the Tu-160 Blackjack strategic bomber.
By the 1980s, however, no one was designing variable-sweep aircraft and no new work on this technology has been incorporated into any new production military aircraft in at least the last 15 years, although work is still being carried out on wings that move in other ways. The technology of variable-sweep wings lasted little more than 20 years before being phased out, although hundreds of the aircraft continued to fly for years more.
There were several reasons for the move away from this technology, but the primary reason was that the large metal gearbox needed to move the wings was complicated and heavy. This increased maintenance requirements and decreased fuel performance. An aircraft capable of moving its wing forward for fuel-efficient flight could never be as efficient as an airplane equipped with a straight wing. The same was true for aircraft with swept-back wings; they would always be more efficient than aircraft with swing-wings. The B-1B Lancer, for example, has never been able to achieve its original range requirements and has to refuel in the air more often than planned. It also rarely flew at the high speeds that sweeping back the wings allowed it to do. Ultimately, aircraft designers decided that the flexibility of the variable-sweep wing was not worth the compromises it demanded.
Flying the Swing Wing MiG 23/27
The soviet tactical fighter was designed as single-engine, agile, and fast fighter which could accept and decline engagement by virtue of its high speed. Not designed to be engaged in long tuning dog fights with technologically superior western adversaries. Instead designed to suit large scale production and at the same time have the capability to be maintained and operated in extreme remote bases with standalone capability assisted by RSBN and PRMAG (Russian concept of mobile short-range navigation and precision landing system).
No other fighter have been so badly misunderstood as the MiG 23/27.
MiG-23/27 was faster in level flight and acceleration, and also had a much better range than the MiG-21, but not more maneuverable.
- Powered by one of the most powerful turbojet engine (Tumansky R -29 300) gave it unmatched capability to outrun any missile chasing it and quick acceleration on the ground for short take-off.
- The MiG-23/27 – had wings that could be swept to three pre-set positions (16, 45, and 72 degrees) in order to keep their construction simple and cheap. Thus providing a unique capability to take off and land from short fields as compared to MiG 21 and at the same time operating at very high speeds at a low level with increased ranges.
- With wing swept at 16 degrees, the aircraft offered good handling characteristics at low speeds required for take-off and landing. In this position, Pilots compared it to a glider with an excellent initial rate of climb away from the ground at low angles of attack as compared to other fighters. It also offered good glide characteristics and visibility on approach for landing. When compared with the approach for landing of MiG 21, MiG 23/27 almost came hugging the earth.
- The wing could be swept according to the flight regime, and when swept, the chord would increase as the wings moved back, thus reducing the thickness to chord ratio. At 45 degrees sweep, the aircraft offered a stable platform for weapons delivery which was suitable for ground attack and reasonable manoeuvrability to disengage from the fight and accelerate away like a fighter.
- With wing swept to 72 degrees and afterburners engaged the aircraft was a rocket. Once the weapons were delivered, wing fully swept and afterburners engaged, the aircraft had outmatched acceleration and high-speed performance with adequate handling.
- One platform and three aerodynamic variants. From straight wing to fully swept wing. It covered the entire regime of speed from subsonic to supersonic with reasonably blended handling qualities.
- The aircraft had powered controls and did not offer carefree handling. The pilot required a fair understanding of energy management as well as aerodynamics to be able to exploit the complete flight envelope. Due to this reason, it was not only exhausting but also immensely satisfying to fly the brute machine.
- I admire most of the pilots who have flown the swing-wing types. They had one more variable available which offered a formidable challenge to them as compared to others before entering a fight. They had to do more and plan it well as compared to fixed-wing types.
- I am fortunate and humbled after flying these swing wings ‘the wonderful machines’.
The future of Swing Wing
Though no new work is being undertaken on the swing-wing design platform, however in my opinion it offers a formidable solution for Supersonic transport. The new technological developments in material and controls for wing box design and handling characteristics may be able to overcome earlier problems encountered in the 50s to 70s. The effect of the sonic beam can be reduced by sweeping the wings. Further aircraft would be able to operate at high transonic speed over the continental areas with intermediate wing sweep and then subsequently accelerate to supersonic speed over water with a fully swept wing. This advantage could be unmatched and adoption of such design could drastically reduce the development and testing costs.
I hope to see the revival.
Be safe. Happy landing.
