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Bavar - Wing In Ground-effect (WIG)

Irans claims are often exaggerated. The Iranian Defense Ministry in a ceremony on 28 September 2012 delivered three squadrons of upgraded, radar-evading flying boats named 'Bavar-2' (Belif-2) to the Islamic Revolution Guards Corps (IRGC). The ceremony was attended by Iranian Defense Minister Brigadier General Ahmad Vahidi and Commander of IRGC Naval Forces Ali Fadavi, during which Vahidi elaborated on the features of the new home-made flying boats.

Iranian Defense Minister Brigadier General Ahmad Vahidi announced on Sunday that his ministry is due to equip the Islamic Revolution Guards Corps (IRGC) with new flying boats. "The ceremony to deliver the flying boats to the IRGC Navy will be held this week," Vahidi told reporters in a ceremony to commemorate the Week of Sacred Defense, marking the country's resistance against the 8-year-long Iraqi invasion in 1980.

"Bavar 2 is a surface-moving flying boat and performs patrol and reconnaissance missions on the sea," Vahidi said, adding that the vessels are equipped with machine gun, night goggles and reconnaissance equipment to record and send the desired images and data. Noting that Iran is among the few countries of the world, which has designed, manufactured and used flying boats in a short period of time, he boasted that Tehran is now a member of the club of designers and producers of the vessel. The development comes after Iran in 2009 said it had successfully tested the domestically-made craft.

Built by Iran Shipbuilding and Offshore Industries Complex shipyard located near Bostanu, their small size and light weight suggest the Bavar WIGs are trailerable or transportable. If so, they could be maintained well in-shore - within some broadly-dispersed array of hardened, underground shelters where they would be difficult to locate and strike but from which they could be brought to their operating areas fairly quickly and easily. Alternatively, such surface-effect vehicles can ride their aircushions both over land and over water, they might be brought-up quickly from shelter, launched from suitable locations close by, then directed towards the sea across some relatively flat and straight, pre-planned course.

The examples seen in Iranian photographs do not appear to be armed, though they problably have some armament scheme. It was reported that the Bavar-2 featured surveillance cameras and a machine gun. Speculation that "weapons include Iranian-produced anti-ship guided missiles, as well as the Russian Shkval, a super-cavitating (250 mph) torpedo" would seem to be little beyond heavy breathing.

A flying boat is a fixed-winged seaplane with a hull that allows it to land on water. In general, when a fixed-wing aircraft flies near the earth's surface, an air cushion is created between the underside of the wing and the ground. In this flight environment, the air cushion imparts lift to the aircraft, while at the same time reducing drag on the aircraft. In actuality, the air cushion effect results from two physical phenomena often respectively referred to as "chord-dominated ground effect" and "span-dominated ground effect". In particular, chord-dominated ground effect acts to increase the lift of the aircraft, while span-dominated ground effect acts to reduce the induced drag on the aircraft. The combined effect of the two phenomena is to increase the lift to drag, or L/D ratio, thereby allowing for more efficient flight on the "cushion of air".

As can be appreciated by the skilled artisan, the span-dominated ground effect is most apparent in aircraft with a high aspect ratio wing. Specifically, the higher the aspect ratio, which is the wingspan divided by the average chord length of the wing, the lower the induced drag will be. Notably, as the wing gets closer to the earth's surface and the wing vortices are constrained and weakened at the wing tips, the "effective" aspect ratio of the wing increases beyond the geometric aspect ratio. As a result of the increase in this "effective" aspect ratio, the induced drag is reduced. Also, a reduction in drag is most pronounced when the ratio of the aircraft operational altitude to the length of the wingspan is on the order of 1:10.

The wing-in-ground-effect craft, which is alternatively known as a wing-in-surface-effect craft, was first successfully developed in the early 1960's in the former USSR where it was known as "ekranoplan". Subsequent developments in other parts of the world have experimented with varying degrees of success, with different configurations. Russian development work culminated in the 1970's with the development of large waterborne ground-effect craft capable of the rapid deployment of masses of military equipment and personnel in and around the Caspian Sea.

A key distinctive feature of wing-in-ground effect craft operation consists in that main operating height, i.e., height of flying in ground effect mode, is less than length of wing mean aerodynamic chord (MAC) in actual flight (0.1-0.3), while airspeed varies from 150 to 600 km/h that corresponds to aircraft speeds. Besides, aerodynamic forces and moments affecting pitch control feature somewhat complicated nature of dependence on flight parameters and, what is more important, they boast higher gradients of change.

For longitudinal stability nearly all known wing-in-ground-effect craft have relied on a relatively large horizontal tail plane, when compared with aircraft. This horizontal tail plane is nearly one third the size of the main wing in many craft, and sometimes larger. Another design originating in Russia used two equal sized wings in tandem, and in-line, effectively the rearward wing replacing the horizontal tail plane.

Widely-used methods of providing longitudinal stability in tight time flight nearby water or ground surface minimizing decision-making interval may and, in fact, do cause crashes. This is due to development of emergent conditions in fractions of seconds at external disturbances or in faulty control over craft. Most known emergencies and crashes of wing-in-ground effect craft, both in flight tests and in service, both light and heavy craft, have been in some way related with longitudinal stability and controllability. Wing-in-ground effect craft designed by widely-known designers A. Lippisch and R. Alexeyev match the situation.

Another factor detrimental to flight safety, seaworthiness performance and fuel efficiency directly related to pitch control is the flight control method. Basically, the method used for WIG craft operations is the same as for airplanes, i.e. in order to take off a WIG craft should accelerate to liftoff speed and at the same time vary its pitch angle so as to gain the required lift. Further, during all flight phases up to and including landing, relevant variations of pitch angle are still required. The challenge is high risks in maneuvers involving pitch angle variations at heights comparable to length of the aerial vehicle. This is confirmed by both accidents with WIG craft and numerous airplane crashes and emergencies that have occurred in take-off and landing.

Another important characteristic of WIG craft is seaworthiness. On the one hand, it is limited by emergence of high impact loads during take-off and landing in heavy sea conditions which may lead to damage and disruption of structure, and also to development of forces and moments that prevent the craft from reaching liftoff speed and disrupt hydrodynamic conditions that are necessary for safe completion of take-off or landing. On the other hand, seaworthiness is limited by effective relative height of ground effect flight which depends on WIG craft geometry, that is, overall length and width of its airfoil (length of MAC). That is, solution to both the problems of seaworthiness and that of longitudinal stability consists in selecting methods of generating hydrodynamic forces and selecting aerodynamic configuration.

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Bavar - Wing In  Ground-effect (WIG)




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Page last modified: 08-07-2019 18:52:29 ZULU