- Email: [email protected]
Effective WIG-Craft – Large Ekranoplane with Facilities of Automatic Control
Copyright © IFAC Control in Transportation Systems, Tokyo, Japan, 2003
ELSEVIER
IFAC PUBLICATIONS www.elsevier.com/localelifac
EFFECIlVE W1G-CRAFf - LARGE EKRANOPLANE WITH FACD....ITIES OF AUTOMATIC CONTROL
Alexander Nebylov·, Nobuyuki Tomita··
•State University ofAerospace Instrumentation. 67. Bolshaya Morskaya. St. Petersburg. 190000. Russia email: [email protected] •• Musashi Institute of Technology. 1-28-1. Tamazutumi. Setagaya-ku. Tokyo. 158. JAPAN email: [email protected]
Abstract: The effectiveness of large ekranoplanes with automatic control facilities development and commercial application is reasoned l . The requirements to motion control systems are analyzed. The statement of the main problems of equipment and software design for flight control at small altitude above the disturbed surface is given. The aim of investigation is to define the way for operational performance improving of the vehicles of advanced design. This way is implementation of modem navigation and motion control systems. The facilities of ekranoplanes with perfect control systems double application are studied. One of such options consists in assist of aerospace plane horizontal launch and landing. Copyright©2003IFAC. Keywords: flight control, low altitude flight, autopilot, sea waves, traffic control.
required passengers and goods traffic quickly, reliably and cheaply, and desirably having not very complex and expensive infrastructure. But ekranoplane looks well from different sides of the integrated problem of optimal transportation and has some additional attractive functioning abilities (aerodrome is not required, possibility to sail as a ship in stormy sea, amphibious ability, safety at engine failure, ... ). That is why the attempts to develop commercial ekranoplanes were undertaken in different countries, but not rather successful yet (Nebylov, 1994; Murao, 1997; Tailor, 2000).
I. INTRODUCTION
Wing-in-ground machines (WIGs) perform flight at extra low altitude where the lift/drag ratio grows due to the effect of supporting surface. The greatest up to present time WIGs with the mass 140 ton (Orlyonok) and 400 ton (Lun) were created at the former USSR, and Russian name ekranoplane is widely used in the world for such kind of high-speed marine vehicles. Analysis of different transportation means shows that weight-to-drag ratio K"could be nearest to theoretical maximum values only for several kinds of vehicles: for displacement ships at speed around 10 m/s, ordinary trains at speed 20-40 m/s, ekranoplanes at speed of 70-150 m/s and planes at speed about 250 m/so Hovercraft, hydrofoils, cars, helicopters and other existing vehicles are not so successful on this index. Of course, the ratio K"is not a single index of transport effectiveness, i.e. the ability to realize the 1 The
As a rule, the recently constructed vehicles were designed for 5-10 passengers' transportation at rivers, lakes and calm seas and have not any means of control automation. The main failures at their meeting the requirements of market are: low seagoing ability, difficulties with stability of flight, too high specific cost, problems of certification.
work was supported by the Russian Foundation for Basic Research under the project 02-01-00031
107
in operation and has good place for location, many catastrophes in the sea can be staved off. In this case the instructive experience of great WIG-craft exploitation will also be obtained, which is necessary for perfection the WIGs of different kinds and mass. The paper is devoted to reasoning the idea of developing the large WIGs with perfect automatic control before creation the commercial small and middle-sized WIGs.
2. ADV ANTAGES OF LARGE COMMERCIAL EKRANOPLANES AGAINST THE SMALL ONES Fig.l. Amphibian ekranoplane "Orlyonok" The evolution of planes, hovercraft, hydrofoils and many other kinks of transport vehicles went "from small to large". But in the case of WIGs the inverse way could be more successful. Several reasons could prove up this thesis. I. Wing-in-ground effect is especially effective when the altitude of flight is less then IO-IS% of the wing chord value. In this case the lift-to-drag ratio may be almost two times more comparably the case of great altitude of flight. If the wing chord for small vehicle is around 2-3 m, the altitude of flight must be 30 cm, but it is impossible even at small wave disturbances at the water surface. At the wing chord around 10-20 m (as "Orlyonok" and ''Lun'' have) and flight altitude 2-3 m the disturbed sea of number }OS will be quite good for operation, if the perform automatic stabilization of vehicle motion is available. If the wing chord is 30-S0m and the vehicle configuration is "flying wing", such ekranoplane practically will not have any limitations for flight at stormy sea.
Fig.2. Combat ekranoplane "Lun"
2. Only rather large WIG-craft can perform take-off and landing at stormy sea, and also float as a ship among the great sea waves. 3. Only rather large WIG-craft can have the range of operation in 2000 km and more. 4. The price of perfect autopilot for WIG-craft could be approximately 70-100 thousands US$ (Ambrosovski and Nebylov, 2000), and it increases slowly with increasing the vehicle mass (mainly at the account of more developed actuators). If the reasonable for market price for simple in construction 6-8 seater WIG-craft is 200-300 thousands US$, it is impossible to involve good autopilot in this frame. So, automatically controlled WIG-craft has to be rather large. But as the digital electronics and mechatronic devices become cheaper, after some years the autopilots developed for large WIG-craft will be possible to apply also at smaller vehicles.
Fig.3. Design ofS&R ekranoplane "Spasatel" At the same time the leadership of Russian Navy lost the interest to ekranoplanes as the naval doctrine has been changed strongly. The largest for nowadays ekranoplanes "Orlyonok" (Fig. I) and "Lun" (Fig.2) with rather perfect automatic systems for motion control and stabilization (Diomidov, 1996) are locked up in storage at the Caspian Naval Base and not used. Moreover, the construction of the second "Lun" which was established in 1991 as search-and-rescue ekranoplane "Spasatel" (Fig.3) with take-off mass 400 ton, cruise speed SOO km/h and ability to take-off and land at stormy sea is not finished due to finance cutting. In 96% readiness this unique vehicle is staying at assembly jig at Volga plant. If it would be
Certainly, it is more difficult to provide a full load for passenger or cargo large ekranoplane. It is necessary to find the adequate lines with permanent rather great density of passenger traffic. The necessary seagoing
108
ability and the available number of passengers must be taken into account first of all at determining the optimal ekranoplane dimension and mass applying for a certain line. The ekranoplane of 400 ton mass could be acceptable for sorre routs in different regions, especially in Southeast Asia and Pacific countries. It could carry up to 500-550 passengers with the cruise speed 450 kmlh and perform takeoff and landing at sea waves in 3.5m height. The cost of such machine may be approximately US$60M The minimal mass of large (in above-mentioned sense) ekranoplane could be estimated in 100-\10 ton and its carrying capacity - in 200 passengers at twostoried passenger salon. It could easy perform takeoff and landing at sea waves in 2m height. The cost estimation gives approximately US$24M. Such machine could meet the cost-effective requirements of more various passenger lines. Even at half average load along the year and half cost of ticket against the airplane one, the pay back term may be about 4 years at effective management. Of course, it requires the computerization and optimization of time schedule development, tickets booking and other elements of automation.
- rising of the seagoing ability of a vehicle, i.e. its capability to move in given direction and to decide another functional tasks at the largest number of sea conditions; - reducing of fuel consumption; - depression of vehicle rocking for creating the favorable conditions for crew and passengers or for functioning of on-board equipment. Naturally, it is impossible to reach the extremum of all these criteria simuhaneously and each concrete case requires appointing the only main criterion of control effectiveness, transforming other ones to the rank of limitations. In the number of limitations is necessary to denote also the necessity of economical expenditure of control elements resource.
4. ALGORITHMS OF COM BINED CONTROL ON ERRORS AND WA VE DISTURBANCES The effect of wave disturbances on the vehicle moving at small altitude along the bound of water surface is complex and can have the following consequences: - appearance of periodical forces and moments exciting trajectory of motion (rocking, the reduction of speed, the deterioration of the indexes of fuel saving); - likelihood of the appearance of abnormal situation or catastrophe due to the impulsive exposures of too large value (the hazard of destruction or overturning of a vehicle); - creation of significant interference for sensors (radar, sonar and others) of the parameters of low altitude motion of vehicle due to tracking by them of the profile oflarge sea waves.
3. AUTOMATIC MOTION CONTROL PROBLEMS FOR LARGE FKRANOPLANES Trouble-free m>tion at the altitude of I-Srn close to disturbed sea surface may be guaranteed by the application of special methods and means of navigation and control capable to solve the following specific problems (Nebylov and Wilson, 2002): - the precise control of 1he altitude of motion with error not above 5-10 cm; - restriction the angles of airframe inclination for the preventing of undesirable tangency of water by the extreme points of body or wing; - the ensuring of the vehicle stability as control plant in the circumstances of the action of flake non-linear aerodynamic effects attributed to nearness of water surface; - non-eontact measurement, tracking and prediction of ordinates and biases of the field of sea wave disturbances for the rising of motion control effectiveness.
It is necessary to allow for all these factors at the optimization of motion control laws and the ensuring of the potential characteristics of the seagoing ability of the vehiclc.
The models of sea wave disturbances have a principal significance at the examination of the similar algorithms of estimation and control. The methods of calculation of spectral and correlation characteristics of wave disturbances on the base of the three-dimcnsional irregular model of sea waves are described in (Nebylov, 1994; Nebylov and Wilson,2002).
Most of these problems were reasonably solved applying to ekranoplanes "Orlyonok" and "Lun" in the 70's - 80's (Diomidov, 1996). These outcomes together with modern facilities of digital integrated control systems, satellite navigation and communication systems, new mechatronic devices are the base for development of new generation of ekranoplane on-board equipment. Some initial steps in this direction have been already done (Ambrosovski and Nebylov, 2000; Nebylov, 2001).
It is also shown, that at the large speed of motion the recalculation of wave disturbances characteristics in moving coordinate system can be lawfully fulfillcd with the application of the spatial spectra of "frozen" surface with simplified elements motions. This enables the speedy calculation of the characteristics of disturbances in real time and expands the possibilities of increasing the intelligence of control complex.
It is advisable k> consider the following criteria of control quality at motion above disturbed sea surface:
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Obtained current data on the field of wave disturbances can be used (I) for the adaptation of the main motion control loops and (2) for the realization of the principle of combined control. This lets arise the quality of motion control as to each criterion, mentioned in the item 3. However, main difficulty in the building of the channel of control on wave disturbances is the complexity of the calculation of disturbing forces and moments, attached to the vehicle, based on measured ordinates and the biases of wave field. At two-dimensional sea waves this task is solved enough successfully, but in general case of three-dimensional waves it is necessary to use approximations. But positive effect may be guaranteed in any case.
6. PROSPECTS OF LARGE EKRANOPLANES MULTIOBJECTIVE APPLICATION It is important the parallel development of some types of large ekranoplanes with different properties and opportunity of common use of positive experience saved in each line of development. The ekranoplanes competitiveness would be essentially raised also with a possibility of double application of any their type in different areas that would Jlow more effectively use of financial and other resources at their development and construction.
At present several ideas of large ekranoplanes effective civil application are exist [Nebylov, 2002; Nebylov and Wilson, 2002). Among them: Passenger routes along the coast or between the islands having several runs in 300-900 km length each; transportation of fruits and other perishable goods from far islands without aerodromes. aerospace plane horizontal landing on moving ekranoplane and horizontal launch for prospective aerospace planes; creation of the world naval search-and-rescue system;
Notice, that for displacement ships the distdrbing effect of sea waves is practically impossible to !ower using the facilities of control. But the undisplacement vehicle has the considerably larger possibilities to parry the disturbances from sea waves at the expense of creating the powerful controlling forces, including vertical ones. This appertains not only to ekranoplanes and hydro-airplanes, but also to hovercraft, controlled hydrofoils and other undisplacement vehicles.
The main distinctive of ekranoplanes which provide their marketability are: • air flying speeds at the greater safety of exploitation because of small altitude of flight and capability of immediate landing in an emergency; absence of requirement in cost intensive aerodromes or quay buildings; • the potentials ability to carry a freight of large mass and dimensions are higher than for airplanes; • the level of comfort for the passengers can be close to cruise ship one; • the potential high transport profitability on midranges (about 1000 km) in matching with aircraft because of absence of necessity of energy consumption for rise on a high altitude; • the potential cost of construction, equipment and exploitation below aviation.
5. COLLISION AVOIDANCE PROBLEM At the high speed of motion, proper to ekranoplanes (similar to planes), the problem of collision avoidance with conflict vehicles in the circumstances the time scarcity for maneuvering also originates, which is not characteristic of displacement ships. Low altitude of ekranoplane flight gives point to this problem, as the obstacle could be determined only at rather small distance. From the other side, the task of going round an obstacle became easy as it becomes the single-agent one against the multi-agent approach, which is demandable for relative motion control of ships. Another JX:culiarity of collusion avoidance problem for ekranoplanes consists in possibility of maneuver not only by course and velocity, but also by altitude of flight. In critical case of numerical obstacles at sea surface when the avoidance maneuver in horizontal plane is impossible, ekranoplane with perfect motion control system could jump over the obstacle. This maneuver is not desirable due to additional fuel consumption and complexity, but it could increase the flight safety in general case. The decision for any maneuver has to be automatically produced at analyzing the radar and other kinds of navigational information.
The project of ekranoplane use for horizontal launch and landing of aerospace plane (ASP) was offered by N. Tomita, Yo. Ohkami and A. Nebylov in 1995 (Tomita and Ohkami, 1995), and since that time it has been developed in a view of detailed reasoning and feasibility studying (Nebylov, Ohkami and Tomita, 1999; Tomita et ai, 1999;). The goal of investigations is the creation of space transportation system with reduced specific cost of payload injection at near-Earth orbits and extended functional capacity.
Some special regulations are necessary to be adopted by IMO and ICAO for juridic providing of traffic control for WIG-craft and other high-speed undisplacement marine vehicles in the areas of maritime traffic, and this work was already initiated.
ASP launch by use of heavy airplane is well known and deeply analyzed idea with definite advantages and drawbacks. The basic lacks are limitations on the
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take-off mass makes 375 ton, and landing mass - 51 ton. However, it is essential that the great mass and corresponding dimension provide not only payload capacity of ekranoplane but its seaworthiness at the rough ocean, as well. The account that ekranoplane will have take off and landing in the closed bay with obviously weak sea disturbance, and at the open ocean will make only non-stop flight, would strongly narrow the tactical opportunities, reliability and safety of launch system. For this reason, economy of mass of ekranoplane used for ASP landing is rather challengeable. The digital automatic complex of relative motion control for two craft at approach and docking has been synthesized and investigated. It consists of four coupled multidimensional closed loops: for ASP proper motion control, for ekranoplane proper motion control, for relative motion control of two vehicles on the base of precision short-range navigation system readings, and for exact positioning of mating elements by a special quick-response automatic system. The correct interaction of these four coupled multidimensional loops and control algorithms optimization in each controlled linear and angular coordinate is a complicated problem of analysis and modeling. It is shown ( ebylov. Ohkamy and Tomita, 1999) that at the final stage of approach the errors of relative positioning may be within :Bm, and the local positioning of matting elements (especially, the nose element) could reduce the errors up to 30 cm.
Fig.4. General configuration of ekranop:ane "combined wing" and ASP available ASP starting mass, on accessible parallax, the impossibility to place onboard plane the bulky cryogenic equipment and tanks for ASP filling by fuel components directly before its start, necessity for the specially prepared runway. Three main reasons of ekranoplane use as a component in space transportation system (Fig.4) could be pointed. I. ASP can be supplied with simplified landing gear when landing on moving ekranoplane. Large saving of mass will be provided if all equipment for docking is an accessory of ekranoplane. The mass of gear for landing on runway may be 3% of empty mass or 25-30% of payload. Ekranoplane assist can permit to increase the payload of ASP up to 30% and to decrease correspondingly the specific cost of launch. 2. The launch and landing points can be chosen at any area of ocean. 3. The specially prepared runway is not required that also decreases the operational cost.
Notice, that the most unfavorable external disturbance for a loop of lateral deflections depression would be a pulse rush of wind in a cross head direction. But even in this case the error will be acceptable due to the following reasons: - high landing velocity of ASP will make this impulse short and its influence will be decreased; - high landing velocity of ASP will increase the effectiveness of its aerodynamic rudders essentially; a pulse of wind will influence both ASP and ekranoplane that decrease their relative shift.
A heavy ekranoplane is likely to be the unique transport means that can realize the idea of docking with the stage, which would allow completing the ASP landing without heavy gear.
Objectively, the accuracy of ASP relative motion control at landing on moving ekranoplane may be higher than one of ordinary plane motion control at landing on a runway at half as much velocity. Optimization of ASP landing speed is a special problem under consideration, and this optimal speed lies in the interval Mach 0.45-0.6 depending on many factors.
At the stages of ASP takeoff and landing a single ekranoplane or two different ekranoplanes can be used. The first version is possible at ASP launch with the purpose of fulfilling the certain mission on an near-Earth orbit, when the moments of takeoff and landing are separated with rather large interval of time. This version is preferable both for simplification of preparing to the following ASP start, and for funds saving for ekranoplanes construction. The advantage of the second version is a possibility to use a comparatively light ekranoplane for ASP landing, as ASP mass is less almost the order at landing than at takeoff. For example, in described in (Tomita et ai, 1999) project the ASP
7. OUTLOOKS OF EKRAI\OPLANES EFFECfIVENESS RlSE AT THE EXPE SE OF IMPROVING THE FAOUTIES OF MOTIO CONTROL Returning to comparison between different types of transportation means, it is necessary to emphasize the
I11
certain advantages of craft development functioning on the base of their being closed to the supporting surface without direct contact with it. Different dynamic or static air-cushion craft and vehicles with other principles for the narrow altitude corridor creation for moving at a high speed allow the combination of the advantages of wheeled, floated means of transportation and aviation means, and are likely to satisfy the requirements for economical, safe and ecologically clean high speed mass transport of the future. Some time later it can become the central line between two extremes: the first one includes the extra economical trains, vessels, tracks, dirigibles, pipelines, the second one consists of extra high speed aviation and space transport means.
ekranoplanes chances for evolution, as the opportunity of common use of positive experience saved in each line of development exists.
It must be admitted that the separation of transport means into land and water ones is given to mankind by the nature and an artificial differentiation caused by this fact makes, in certain sense, the perfecting of transport processes difficult. The development of transport craft with no restrictions to the kind of supporting surface can substantially simplify the transport structure organization. A great deal of our planet surface covered by water or ice will become the perfect transport space for such vehicles. For their motion by the land one may allot certain narrow zones where extra large unevenness are excepted. Those zones will not be lifeless like asphalt roads or railways - for instance, they can be used to grow vegetables or corns. Having finished a flight above water, transport craft can continue it along considered land corridor and deliver the passengers and cargo directly to the required point. However, such mode of vehicle motion at the extra low altitude above the supporting surface could be feasible only at perfect functioning of automatic flight control systems. Development of such systems has to be considered as the very important part of WIG-craft construction.
Ambrosovski,V.M. and A.V. Nebylov (2000). Flight Parameters Monitoring System for Small WIGCraft In: Ifl International Conference on Ground-Effect Machines / The RSME, Russian Branch. Saint-Petersburg, pp. 15-25. Diomidov, V.B. (1996). Automatic Control of Ekranoplanes Motion. CSRJ "Elektropribor", St. Petersburg, 204 pp. (in Russian). Murao, R. A study on a WIG with upper-surface blowing (USB) PAR. RINA International Conference on WIGs. London, UK. 1997. .Nebylov, A.V. (1994). Measurement of Parameters of Flight close to the Sea Surface. Monograph. SAAI, St. Petersburg, 307pp., in Russian with summary in English. Nebylov, A.Y. (2001). Wing-in-Ground Flight Automatic Control Principles, Systems and Application Advantages. In: 15,h IFAC Symposium on Automatic Control in Aerospace. Forli, Italy, M. 542-547. Nebylov A.V.(2002). Controlled flight close to rough sea: Strategies and means. In: 15th IFAC World Congress. Barcelona, Vol. 8a. Nebylov, AV., Y. Ohkami and N. Tomita (1999). Control Strategies and Means of Spaceplane Landing with Ekranoplane Assist. In: 14th IFAC World Congress. Beijing, P. R. China,. Vol.P , pp. 395-400. Nebylov, A.V. and P. Wilson (2002). EkranoplaneControlled Flight close to Surface. Monograph. WIT-Press, UK, 320 pp.+CD. Tomita, N., et al. (1999). Performance and Technological Feasibility of Rocket Powered HTHL-SSTO with Take-off Assist. Acta Astronautica. 45, No. 10, pp. 629-637. Tomita, N. and Y. Ohkami (1995). A study of the application of take-off assist for SSTO with rocket propulsion, IAF-95-V.3.06. Tailor G.K. (WOO). Wise or Otherwise? The dream or Reality of Commercial Wing in Ground Effect Vehicles. GEM-2000 Intern. Conf Proceedings, St.-Petersburg, pp. 249-262.
7.
The demanded characteristics of large ekranoplanes can be achieved only at use of the new capabilities of perfecting the systems of navigation and motion control. At improvement, cheapening and lightening of the on-board automatic control equipment the small ekranoplanes for several passengers would also become automatically controlled and increase their marketability.
REFERENCES
CONCLUSION
The possible effectiveness of the development and commercial application of large ekranoplanes for 200 or more passengers with automatic control facilities was stated. The control algorithms and some hardware of automatic control systems of ekranoplanes differ essentially from airborne ones and require the special research and design. Some new results in this field have been already achieved. Several fields of large ekranoplanes application besides passengers and cargo transportation are available. Among them the integrated space transportation system in which heavy ekranoplane assists aerospace plane in horizontal launch and landing. For realization of this project the application of the entire conceptual resources of modern navigation and automatic control systems is required. Such different application abilities expand
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ELSEVIER
IFAC PUBLICATIONS www.elsevier.com/localelifac
EFFECIlVE W1G-CRAFf - LARGE EKRANOPLANE WITH FACD....ITIES OF AUTOMATIC CONTROL
Alexander Nebylov·, Nobuyuki Tomita··
•State University ofAerospace Instrumentation. 67. Bolshaya Morskaya. St. Petersburg. 190000. Russia email: [email protected] •• Musashi Institute of Technology. 1-28-1. Tamazutumi. Setagaya-ku. Tokyo. 158. JAPAN email: [email protected]
Abstract: The effectiveness of large ekranoplanes with automatic control facilities development and commercial application is reasoned l . The requirements to motion control systems are analyzed. The statement of the main problems of equipment and software design for flight control at small altitude above the disturbed surface is given. The aim of investigation is to define the way for operational performance improving of the vehicles of advanced design. This way is implementation of modem navigation and motion control systems. The facilities of ekranoplanes with perfect control systems double application are studied. One of such options consists in assist of aerospace plane horizontal launch and landing. Copyright©2003IFAC. Keywords: flight control, low altitude flight, autopilot, sea waves, traffic control.
required passengers and goods traffic quickly, reliably and cheaply, and desirably having not very complex and expensive infrastructure. But ekranoplane looks well from different sides of the integrated problem of optimal transportation and has some additional attractive functioning abilities (aerodrome is not required, possibility to sail as a ship in stormy sea, amphibious ability, safety at engine failure, ... ). That is why the attempts to develop commercial ekranoplanes were undertaken in different countries, but not rather successful yet (Nebylov, 1994; Murao, 1997; Tailor, 2000).
I. INTRODUCTION
Wing-in-ground machines (WIGs) perform flight at extra low altitude where the lift/drag ratio grows due to the effect of supporting surface. The greatest up to present time WIGs with the mass 140 ton (Orlyonok) and 400 ton (Lun) were created at the former USSR, and Russian name ekranoplane is widely used in the world for such kind of high-speed marine vehicles. Analysis of different transportation means shows that weight-to-drag ratio K"could be nearest to theoretical maximum values only for several kinds of vehicles: for displacement ships at speed around 10 m/s, ordinary trains at speed 20-40 m/s, ekranoplanes at speed of 70-150 m/s and planes at speed about 250 m/so Hovercraft, hydrofoils, cars, helicopters and other existing vehicles are not so successful on this index. Of course, the ratio K"is not a single index of transport effectiveness, i.e. the ability to realize the 1 The
As a rule, the recently constructed vehicles were designed for 5-10 passengers' transportation at rivers, lakes and calm seas and have not any means of control automation. The main failures at their meeting the requirements of market are: low seagoing ability, difficulties with stability of flight, too high specific cost, problems of certification.
work was supported by the Russian Foundation for Basic Research under the project 02-01-00031
107
in operation and has good place for location, many catastrophes in the sea can be staved off. In this case the instructive experience of great WIG-craft exploitation will also be obtained, which is necessary for perfection the WIGs of different kinds and mass. The paper is devoted to reasoning the idea of developing the large WIGs with perfect automatic control before creation the commercial small and middle-sized WIGs.
2. ADV ANTAGES OF LARGE COMMERCIAL EKRANOPLANES AGAINST THE SMALL ONES Fig.l. Amphibian ekranoplane "Orlyonok" The evolution of planes, hovercraft, hydrofoils and many other kinks of transport vehicles went "from small to large". But in the case of WIGs the inverse way could be more successful. Several reasons could prove up this thesis. I. Wing-in-ground effect is especially effective when the altitude of flight is less then IO-IS% of the wing chord value. In this case the lift-to-drag ratio may be almost two times more comparably the case of great altitude of flight. If the wing chord for small vehicle is around 2-3 m, the altitude of flight must be 30 cm, but it is impossible even at small wave disturbances at the water surface. At the wing chord around 10-20 m (as "Orlyonok" and ''Lun'' have) and flight altitude 2-3 m the disturbed sea of number }OS will be quite good for operation, if the perform automatic stabilization of vehicle motion is available. If the wing chord is 30-S0m and the vehicle configuration is "flying wing", such ekranoplane practically will not have any limitations for flight at stormy sea.
Fig.2. Combat ekranoplane "Lun"
2. Only rather large WIG-craft can perform take-off and landing at stormy sea, and also float as a ship among the great sea waves. 3. Only rather large WIG-craft can have the range of operation in 2000 km and more. 4. The price of perfect autopilot for WIG-craft could be approximately 70-100 thousands US$ (Ambrosovski and Nebylov, 2000), and it increases slowly with increasing the vehicle mass (mainly at the account of more developed actuators). If the reasonable for market price for simple in construction 6-8 seater WIG-craft is 200-300 thousands US$, it is impossible to involve good autopilot in this frame. So, automatically controlled WIG-craft has to be rather large. But as the digital electronics and mechatronic devices become cheaper, after some years the autopilots developed for large WIG-craft will be possible to apply also at smaller vehicles.
Fig.3. Design ofS&R ekranoplane "Spasatel" At the same time the leadership of Russian Navy lost the interest to ekranoplanes as the naval doctrine has been changed strongly. The largest for nowadays ekranoplanes "Orlyonok" (Fig. I) and "Lun" (Fig.2) with rather perfect automatic systems for motion control and stabilization (Diomidov, 1996) are locked up in storage at the Caspian Naval Base and not used. Moreover, the construction of the second "Lun" which was established in 1991 as search-and-rescue ekranoplane "Spasatel" (Fig.3) with take-off mass 400 ton, cruise speed SOO km/h and ability to take-off and land at stormy sea is not finished due to finance cutting. In 96% readiness this unique vehicle is staying at assembly jig at Volga plant. If it would be
Certainly, it is more difficult to provide a full load for passenger or cargo large ekranoplane. It is necessary to find the adequate lines with permanent rather great density of passenger traffic. The necessary seagoing
108
ability and the available number of passengers must be taken into account first of all at determining the optimal ekranoplane dimension and mass applying for a certain line. The ekranoplane of 400 ton mass could be acceptable for sorre routs in different regions, especially in Southeast Asia and Pacific countries. It could carry up to 500-550 passengers with the cruise speed 450 kmlh and perform takeoff and landing at sea waves in 3.5m height. The cost of such machine may be approximately US$60M The minimal mass of large (in above-mentioned sense) ekranoplane could be estimated in 100-\10 ton and its carrying capacity - in 200 passengers at twostoried passenger salon. It could easy perform takeoff and landing at sea waves in 2m height. The cost estimation gives approximately US$24M. Such machine could meet the cost-effective requirements of more various passenger lines. Even at half average load along the year and half cost of ticket against the airplane one, the pay back term may be about 4 years at effective management. Of course, it requires the computerization and optimization of time schedule development, tickets booking and other elements of automation.
- rising of the seagoing ability of a vehicle, i.e. its capability to move in given direction and to decide another functional tasks at the largest number of sea conditions; - reducing of fuel consumption; - depression of vehicle rocking for creating the favorable conditions for crew and passengers or for functioning of on-board equipment. Naturally, it is impossible to reach the extremum of all these criteria simuhaneously and each concrete case requires appointing the only main criterion of control effectiveness, transforming other ones to the rank of limitations. In the number of limitations is necessary to denote also the necessity of economical expenditure of control elements resource.
4. ALGORITHMS OF COM BINED CONTROL ON ERRORS AND WA VE DISTURBANCES The effect of wave disturbances on the vehicle moving at small altitude along the bound of water surface is complex and can have the following consequences: - appearance of periodical forces and moments exciting trajectory of motion (rocking, the reduction of speed, the deterioration of the indexes of fuel saving); - likelihood of the appearance of abnormal situation or catastrophe due to the impulsive exposures of too large value (the hazard of destruction or overturning of a vehicle); - creation of significant interference for sensors (radar, sonar and others) of the parameters of low altitude motion of vehicle due to tracking by them of the profile oflarge sea waves.
3. AUTOMATIC MOTION CONTROL PROBLEMS FOR LARGE FKRANOPLANES Trouble-free m>tion at the altitude of I-Srn close to disturbed sea surface may be guaranteed by the application of special methods and means of navigation and control capable to solve the following specific problems (Nebylov and Wilson, 2002): - the precise control of 1he altitude of motion with error not above 5-10 cm; - restriction the angles of airframe inclination for the preventing of undesirable tangency of water by the extreme points of body or wing; - the ensuring of the vehicle stability as control plant in the circumstances of the action of flake non-linear aerodynamic effects attributed to nearness of water surface; - non-eontact measurement, tracking and prediction of ordinates and biases of the field of sea wave disturbances for the rising of motion control effectiveness.
It is necessary to allow for all these factors at the optimization of motion control laws and the ensuring of the potential characteristics of the seagoing ability of the vehiclc.
The models of sea wave disturbances have a principal significance at the examination of the similar algorithms of estimation and control. The methods of calculation of spectral and correlation characteristics of wave disturbances on the base of the three-dimcnsional irregular model of sea waves are described in (Nebylov, 1994; Nebylov and Wilson,2002).
Most of these problems were reasonably solved applying to ekranoplanes "Orlyonok" and "Lun" in the 70's - 80's (Diomidov, 1996). These outcomes together with modern facilities of digital integrated control systems, satellite navigation and communication systems, new mechatronic devices are the base for development of new generation of ekranoplane on-board equipment. Some initial steps in this direction have been already done (Ambrosovski and Nebylov, 2000; Nebylov, 2001).
It is also shown, that at the large speed of motion the recalculation of wave disturbances characteristics in moving coordinate system can be lawfully fulfillcd with the application of the spatial spectra of "frozen" surface with simplified elements motions. This enables the speedy calculation of the characteristics of disturbances in real time and expands the possibilities of increasing the intelligence of control complex.
It is advisable k> consider the following criteria of control quality at motion above disturbed sea surface:
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Obtained current data on the field of wave disturbances can be used (I) for the adaptation of the main motion control loops and (2) for the realization of the principle of combined control. This lets arise the quality of motion control as to each criterion, mentioned in the item 3. However, main difficulty in the building of the channel of control on wave disturbances is the complexity of the calculation of disturbing forces and moments, attached to the vehicle, based on measured ordinates and the biases of wave field. At two-dimensional sea waves this task is solved enough successfully, but in general case of three-dimensional waves it is necessary to use approximations. But positive effect may be guaranteed in any case.
6. PROSPECTS OF LARGE EKRANOPLANES MULTIOBJECTIVE APPLICATION It is important the parallel development of some types of large ekranoplanes with different properties and opportunity of common use of positive experience saved in each line of development. The ekranoplanes competitiveness would be essentially raised also with a possibility of double application of any their type in different areas that would Jlow more effectively use of financial and other resources at their development and construction.
At present several ideas of large ekranoplanes effective civil application are exist [Nebylov, 2002; Nebylov and Wilson, 2002). Among them: Passenger routes along the coast or between the islands having several runs in 300-900 km length each; transportation of fruits and other perishable goods from far islands without aerodromes. aerospace plane horizontal landing on moving ekranoplane and horizontal launch for prospective aerospace planes; creation of the world naval search-and-rescue system;
Notice, that for displacement ships the distdrbing effect of sea waves is practically impossible to !ower using the facilities of control. But the undisplacement vehicle has the considerably larger possibilities to parry the disturbances from sea waves at the expense of creating the powerful controlling forces, including vertical ones. This appertains not only to ekranoplanes and hydro-airplanes, but also to hovercraft, controlled hydrofoils and other undisplacement vehicles.
The main distinctive of ekranoplanes which provide their marketability are: • air flying speeds at the greater safety of exploitation because of small altitude of flight and capability of immediate landing in an emergency; absence of requirement in cost intensive aerodromes or quay buildings; • the potentials ability to carry a freight of large mass and dimensions are higher than for airplanes; • the level of comfort for the passengers can be close to cruise ship one; • the potential high transport profitability on midranges (about 1000 km) in matching with aircraft because of absence of necessity of energy consumption for rise on a high altitude; • the potential cost of construction, equipment and exploitation below aviation.
5. COLLISION AVOIDANCE PROBLEM At the high speed of motion, proper to ekranoplanes (similar to planes), the problem of collision avoidance with conflict vehicles in the circumstances the time scarcity for maneuvering also originates, which is not characteristic of displacement ships. Low altitude of ekranoplane flight gives point to this problem, as the obstacle could be determined only at rather small distance. From the other side, the task of going round an obstacle became easy as it becomes the single-agent one against the multi-agent approach, which is demandable for relative motion control of ships. Another JX:culiarity of collusion avoidance problem for ekranoplanes consists in possibility of maneuver not only by course and velocity, but also by altitude of flight. In critical case of numerical obstacles at sea surface when the avoidance maneuver in horizontal plane is impossible, ekranoplane with perfect motion control system could jump over the obstacle. This maneuver is not desirable due to additional fuel consumption and complexity, but it could increase the flight safety in general case. The decision for any maneuver has to be automatically produced at analyzing the radar and other kinds of navigational information.
The project of ekranoplane use for horizontal launch and landing of aerospace plane (ASP) was offered by N. Tomita, Yo. Ohkami and A. Nebylov in 1995 (Tomita and Ohkami, 1995), and since that time it has been developed in a view of detailed reasoning and feasibility studying (Nebylov, Ohkami and Tomita, 1999; Tomita et ai, 1999;). The goal of investigations is the creation of space transportation system with reduced specific cost of payload injection at near-Earth orbits and extended functional capacity.
Some special regulations are necessary to be adopted by IMO and ICAO for juridic providing of traffic control for WIG-craft and other high-speed undisplacement marine vehicles in the areas of maritime traffic, and this work was already initiated.
ASP launch by use of heavy airplane is well known and deeply analyzed idea with definite advantages and drawbacks. The basic lacks are limitations on the
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take-off mass makes 375 ton, and landing mass - 51 ton. However, it is essential that the great mass and corresponding dimension provide not only payload capacity of ekranoplane but its seaworthiness at the rough ocean, as well. The account that ekranoplane will have take off and landing in the closed bay with obviously weak sea disturbance, and at the open ocean will make only non-stop flight, would strongly narrow the tactical opportunities, reliability and safety of launch system. For this reason, economy of mass of ekranoplane used for ASP landing is rather challengeable. The digital automatic complex of relative motion control for two craft at approach and docking has been synthesized and investigated. It consists of four coupled multidimensional closed loops: for ASP proper motion control, for ekranoplane proper motion control, for relative motion control of two vehicles on the base of precision short-range navigation system readings, and for exact positioning of mating elements by a special quick-response automatic system. The correct interaction of these four coupled multidimensional loops and control algorithms optimization in each controlled linear and angular coordinate is a complicated problem of analysis and modeling. It is shown ( ebylov. Ohkamy and Tomita, 1999) that at the final stage of approach the errors of relative positioning may be within :Bm, and the local positioning of matting elements (especially, the nose element) could reduce the errors up to 30 cm.
Fig.4. General configuration of ekranop:ane "combined wing" and ASP available ASP starting mass, on accessible parallax, the impossibility to place onboard plane the bulky cryogenic equipment and tanks for ASP filling by fuel components directly before its start, necessity for the specially prepared runway. Three main reasons of ekranoplane use as a component in space transportation system (Fig.4) could be pointed. I. ASP can be supplied with simplified landing gear when landing on moving ekranoplane. Large saving of mass will be provided if all equipment for docking is an accessory of ekranoplane. The mass of gear for landing on runway may be 3% of empty mass or 25-30% of payload. Ekranoplane assist can permit to increase the payload of ASP up to 30% and to decrease correspondingly the specific cost of launch. 2. The launch and landing points can be chosen at any area of ocean. 3. The specially prepared runway is not required that also decreases the operational cost.
Notice, that the most unfavorable external disturbance for a loop of lateral deflections depression would be a pulse rush of wind in a cross head direction. But even in this case the error will be acceptable due to the following reasons: - high landing velocity of ASP will make this impulse short and its influence will be decreased; - high landing velocity of ASP will increase the effectiveness of its aerodynamic rudders essentially; a pulse of wind will influence both ASP and ekranoplane that decrease their relative shift.
A heavy ekranoplane is likely to be the unique transport means that can realize the idea of docking with the stage, which would allow completing the ASP landing without heavy gear.
Objectively, the accuracy of ASP relative motion control at landing on moving ekranoplane may be higher than one of ordinary plane motion control at landing on a runway at half as much velocity. Optimization of ASP landing speed is a special problem under consideration, and this optimal speed lies in the interval Mach 0.45-0.6 depending on many factors.
At the stages of ASP takeoff and landing a single ekranoplane or two different ekranoplanes can be used. The first version is possible at ASP launch with the purpose of fulfilling the certain mission on an near-Earth orbit, when the moments of takeoff and landing are separated with rather large interval of time. This version is preferable both for simplification of preparing to the following ASP start, and for funds saving for ekranoplanes construction. The advantage of the second version is a possibility to use a comparatively light ekranoplane for ASP landing, as ASP mass is less almost the order at landing than at takeoff. For example, in described in (Tomita et ai, 1999) project the ASP
7. OUTLOOKS OF EKRAI\OPLANES EFFECfIVENESS RlSE AT THE EXPE SE OF IMPROVING THE FAOUTIES OF MOTIO CONTROL Returning to comparison between different types of transportation means, it is necessary to emphasize the
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certain advantages of craft development functioning on the base of their being closed to the supporting surface without direct contact with it. Different dynamic or static air-cushion craft and vehicles with other principles for the narrow altitude corridor creation for moving at a high speed allow the combination of the advantages of wheeled, floated means of transportation and aviation means, and are likely to satisfy the requirements for economical, safe and ecologically clean high speed mass transport of the future. Some time later it can become the central line between two extremes: the first one includes the extra economical trains, vessels, tracks, dirigibles, pipelines, the second one consists of extra high speed aviation and space transport means.
ekranoplanes chances for evolution, as the opportunity of common use of positive experience saved in each line of development exists.
It must be admitted that the separation of transport means into land and water ones is given to mankind by the nature and an artificial differentiation caused by this fact makes, in certain sense, the perfecting of transport processes difficult. The development of transport craft with no restrictions to the kind of supporting surface can substantially simplify the transport structure organization. A great deal of our planet surface covered by water or ice will become the perfect transport space for such vehicles. For their motion by the land one may allot certain narrow zones where extra large unevenness are excepted. Those zones will not be lifeless like asphalt roads or railways - for instance, they can be used to grow vegetables or corns. Having finished a flight above water, transport craft can continue it along considered land corridor and deliver the passengers and cargo directly to the required point. However, such mode of vehicle motion at the extra low altitude above the supporting surface could be feasible only at perfect functioning of automatic flight control systems. Development of such systems has to be considered as the very important part of WIG-craft construction.
Ambrosovski,V.M. and A.V. Nebylov (2000). Flight Parameters Monitoring System for Small WIGCraft In: Ifl International Conference on Ground-Effect Machines / The RSME, Russian Branch. Saint-Petersburg, pp. 15-25. Diomidov, V.B. (1996). Automatic Control of Ekranoplanes Motion. CSRJ "Elektropribor", St. Petersburg, 204 pp. (in Russian). Murao, R. A study on a WIG with upper-surface blowing (USB) PAR. RINA International Conference on WIGs. London, UK. 1997. .Nebylov, A.V. (1994). Measurement of Parameters of Flight close to the Sea Surface. Monograph. SAAI, St. Petersburg, 307pp., in Russian with summary in English. Nebylov, A.Y. (2001). Wing-in-Ground Flight Automatic Control Principles, Systems and Application Advantages. In: 15,h IFAC Symposium on Automatic Control in Aerospace. Forli, Italy, M. 542-547. Nebylov A.V.(2002). Controlled flight close to rough sea: Strategies and means. In: 15th IFAC World Congress. Barcelona, Vol. 8a. Nebylov, AV., Y. Ohkami and N. Tomita (1999). Control Strategies and Means of Spaceplane Landing with Ekranoplane Assist. In: 14th IFAC World Congress. Beijing, P. R. China,. Vol.P , pp. 395-400. Nebylov, A.V. and P. Wilson (2002). EkranoplaneControlled Flight close to Surface. Monograph. WIT-Press, UK, 320 pp.+CD. Tomita, N., et al. (1999). Performance and Technological Feasibility of Rocket Powered HTHL-SSTO with Take-off Assist. Acta Astronautica. 45, No. 10, pp. 629-637. Tomita, N. and Y. Ohkami (1995). A study of the application of take-off assist for SSTO with rocket propulsion, IAF-95-V.3.06. Tailor G.K. (WOO). Wise or Otherwise? The dream or Reality of Commercial Wing in Ground Effect Vehicles. GEM-2000 Intern. Conf Proceedings, St.-Petersburg, pp. 249-262.
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The demanded characteristics of large ekranoplanes can be achieved only at use of the new capabilities of perfecting the systems of navigation and motion control. At improvement, cheapening and lightening of the on-board automatic control equipment the small ekranoplanes for several passengers would also become automatically controlled and increase their marketability.
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CONCLUSION
The possible effectiveness of the development and commercial application of large ekranoplanes for 200 or more passengers with automatic control facilities was stated. The control algorithms and some hardware of automatic control systems of ekranoplanes differ essentially from airborne ones and require the special research and design. Some new results in this field have been already achieved. Several fields of large ekranoplanes application besides passengers and cargo transportation are available. Among them the integrated space transportation system in which heavy ekranoplane assists aerospace plane in horizontal launch and landing. For realization of this project the application of the entire conceptual resources of modern navigation and automatic control systems is required. Such different application abilities expand
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