Aircraft control system

(12) United States Patent (io) Patent No.: US 7,198,225 B2

Lisoski et al. (45) Date of Patent: Apr. 3,2007

(54) AIRCRAFT CONTROL SYSTEM 3,972,490 A * 8/1976 Zimmermann et al. .... 244/12.3 4,354,646 A 10/1982 Raymer ....................... 244/87 Inventors: Derek L. Lisoski, Simi Valley, CA (75) 4,375,697 A 3/1983 Visher 455/13 .........................

(US); Greg T. Kendall, Simi Valley, 4,415,133 A 11/1983 Phillips CA (US) (73) Assignee: Aerovironment, Inc., Monrovia, CA (US) (Continued)

( * ) Notice: Subject to any disclaimer, the term of this

FOREIGN PATENT DOCUMENTS patent is extended or adjusted under 35 U.S.C. 154(b) by 762 days.

DE 1 2 1 5 222 4/1966 (21) Appl. No.: 10/310,415 (22) Filed: Dec. 5, 2002 (Continued) (65) Prior Publication Data OTHER PUBLICATIONS US 200310141409 A1 Jul. 31. 2003 Flittie, K. and Curtin, B., “Pathfinder Solar-Powered Aircraft Flight Performance,” AIAA Paper 98-4446, Aug. 1998, pp. 618-632.

Related U.S. Application Data (Continued) Division of application No. 091527,544, filed on Mar.

(62) 16, 2000, now abandoned.

Primary Examiner-Tien Dinh (51) Int. C1.

ABSTRACT (57) B64D 2 7/00 (2006.01) (52) U.S. C1. ........................................................ 244/55 (58) Field of Classification Search .................. 244155, A solar rechargeable, long-duration, span-loaded flying 244134 R, 173, 13, 2,47, 35 R, 31, 49,45 R wing, having no fuselage or rudder. Having a two-hundred See application file for complete search history.

foot wingspan that mounts photovoltaic cells on most all of the wing’s top surface, the aircraft uses only differential (56) References Cited thrust of its eight propellers to turn, pitch and yaw. The wing U.S. PATENT DOCUMENTS is configured to deform under flight loads to position the propellers such that the control can be achieved. Each of five 1,288,384 A 12/1918 Coakley segments of the wing has one or more motors and photo- 1,815,341 A * 7/1931 Zaharoff voltaic arrays, and produces its own lift independent of the D137,938 S * 5/1944 Maycen 2,496,087 A 1/1950 Fleming other segments, to avoid loading them. Five two-sided 2,626,348 A 1/1953 Nobles photovoltaic arrays, in all, are mounted on the wing, and 2,969,933 A 1/1961 Vogt receive photovoltaic energy both incident on top of the wing, 3,161,373 A 12/1964 Vogt and which is incident also from below, through a bottom, 3,165,280 A * 1/1965 Lee transparent surface.

3,188,025 A * 6/1965 Moorehead 3,839,860 A * 10/1974 Martin 3,937,424 A 2/1976 Meier et al.

8 Claims, 28 Drawing Sheets

US 7,198,225 B2

Page 2 6,126,111 A * 10/2000 Burcham et al.

U.S. PATENT DOCUMENTS 6,364,251 B1 4/2002 Yim 4,492,353 A * 1/1985 Phillips 4,566,657 A 1/1986 Grow ....................... 244/90 A FOREIGN PATENT DOCUMENTS 4,568,043 A 2/1986 Schmittle ..................... 244/48 DE 43 O S 758 A1 9/1994 4,601,443 A 7/1986 Jones et al.

DE 296 16 989 U1 1/1997 4,697,761 A 10/1987 Long FR 1446609 9/1965 4,768,738 A 9/1988 Weinert FR 2 721 458 12/1995 4,781,341 A 11/1988 Kasper ........................ 244/13 GB 2 082 995 A 3/1982 4,907,764 A 3/1990 Long JP 04325395 11/1992 4,928,317 A 5/1990 Franchini .................... 455/601 JP 11-348894 12/1999 4,958,289 A * 9/1990 Sum et al.

wo WO 95/04407 2/1995

5,078,338 A * 1/1992 O’Neill et al.

wo WO 95/12237 5/1995

5,106,035 A 4/1992 Langford, I11

wo WO 97/33790 9/1997

5,131,605 A * 7/1992 Kress

wo WO 98/35506 8/1998

5,135,185 A * 8/1992 Adamson et al.

wo WO 99/13598 3/1999

5,356,094 A 10/1994 Sylvain

5,374,010 A * 12/1994 Stone et al. wo WO 99/23769 5/1999

5,379,969 A 1/1995 Marx et al.

..................... 359/159 5,465,170 A 11/1995 Arimoto OTHER PUBLICATIONS 5,518,205 A 5/1996 Wurst et al.

* 7/1996 Dah1 ........................ 244/75 R 5,531,402 A Djuknic, G.M., Freidenfelds, J., and Okunev, Y., “Establishing 5,652,750 A 7/1997 Dent et al. .................. 370/326 Wireless Communications Services via High-Altitude Aeronautical 5,678,783 A 10/1997 Wong Platforms: A Concept Whose Time Has Come?,” IEEE Communi- 5,710,652 A 1/1998 Bloom et al. ............... 359/152 cations Magazine, Sep. 1997, pp. 128-135.

........................ 324/671 5,808,472 A 9/1998 Hayes “Lockheed Studies Solar-Powered Surveillance Aircraft,” Aviation 5,810,284 A 9/1998 Hibbs et al. .................. 244/13 Week and Space Technology, Dec. 6, 1982, p. 120.

5,839,699 A 11/1998 Bliesner Aronson, Robert B., “Solar-Powered Planes,” Machine Design, Feb.

5,842,666 A * 12/1998 Gerhardt et al.

7, 1985, vol. 57, p. 32.

6,070,833 A 6/2000 Burke et al.

6,076,766 A 6/2000 Gmensfelder * cited by examiner

Apr. 3,2007

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FIG. 12B

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f~ SATELLITE EARTH STATION

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6 GROUND-TO-AIRPHONE EARTH STATION

-RADIO LINK

FIG. 15

U.S. Patent Apr. 3,2007 Sheet 21 of 28 US 7,198,225 B2

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FIG. 17A

U.S. Patent Apr. 3,2007 Sheet 27 of 28 US 7,198,225 B2

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CONNECTION TO OR CPE

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PHONE MODE

FIG. 17B

U.S. Patent Apr. 3,2007 Sheet 28 of 28 US 7,198,225 B2

FIXED

SUBSCRIBER PACS ANTENNA

WIRED CONNECTION TO

TATION/ FOR CORDLESS

IN-HOUSE DATA OR

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TELEPHONE WIRING 534

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FROM BASE STATION

FIG. 17C

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AIRCRAFT CONTROL SYSTEM aircraft, have been suggested for use in a variety of func- tions. As one example, a high altitude platform equipped The present invention relates to aircraft. More particu- with microwave communications equipment could provide larly, the present invention relates to aircraft having unique communication relay services between remote areas. In controls, and related uses thereof. The present application is 5 another example, high altitude platforms could measure and a divisional application of U.S. patent application Ser. No.

study winds, storms or pollutants in the atmosphere. Simi- 091527,544 filed Mar. 16, 2000 now abandoned, which is larly, governments could use these aircraft to monitor troop incorporated herein by reference for all purposes.

movements or narcotics production. Other types of aircraft This invention was made with government support under are not optimally suited to these tasks, because they are ERAST JSRA Contract NCC-04004 awarded by NASA. 10 limited by the amount of combustible fuels that they use, The United States Government has certain rights in the which are heavy, expensive and are consumed very quickly.

invention.

Typically, these other types of aircraft cannot remain over their desired location for any significant length of time, and BACKGROUND hence, are of limited utility in performing these tasks.

Aircraft are used in a wide variety of applications, includ- One way around these operational limitations is to use ing travel, transportation, fire fighting, surveillance and satellites as high altitude platforms. However, satellites are combat. Various aircraft have been designed to fill the wide expensive to launch, and typically remain in a permanent, array of functional roles defined by these applications.

fixed orbit. Some satellites can change their orbit to a limited Included among these aircraft are balloons, dirigibles, tra- degree; however, this is done only with great difficulty and ditional fixed wing aircraft, flying wings and helicopters.

expense, and there is a fuel limit to how many orbital One functional role that a few aircraft have been designed changes a satellite may make. For example, if it is desired to to fill is that of a high altitude platform. Operating from high, measure and study a hurricane that originates in Africa and suborbital altitudes, such aircraft can monitor weather pat- travels toward the Gulf coast of the United States, satellites terns, conduct atmospheric research and surveil a wide cannot, practically-speaking, be asked to follow and track variety of subjects. Most of these remarkable aircraft have such a storm.

limited flight duration due to fuel limitations. However, a The use of satellites is also disadvantageous for many number of aircraft have been proposed that are solar pow- types of measurement and surveillance as well, because ered, and that can sustain continuous flight for as long as satellites orbit outside the Earth‘s atmosphere. That is to say, sunlight is available, or even longer.

satellites as a practical matter cannot use many tools that Three such aircraft that have been constructed are the optimally require contact with the atmosphere. Photographic well-known Pathfinder, Centurion and Helios aircraft, which images taken by a satellite are also sometimes less than have set numerous flight records. The basic design under- optimal, since the target is usually a great distance from the lying these aircraft is discussed at length in U.S. Pat. No.

satellite. Finally, satellites are not easily brought back to 5,810,284, which is directed toward an unswept flying wing Earth and retrieved, e.g., for servicing, and so are typically aircraft having a very high aspect ratio and a relatively used only for one very expensive, special purpose task.

constant chord and airfoil. While these aircraft are quite Given the broad range of functions that a long-duration, noteworthy for their long term flight potential, they do have suborbital platform has the potential to perform, it is desir- limits in their available power and payload.

able to design such platforms to be capable of handling Such aircraft are designed as flying wings that include a larger payloads and power demands. The platforms could be number of self-sufficient wing sections, each having one or variations of existing platforms, such as the Pathfinder and more electric motors that are driven by power generated in Centurion aircraft, or they could be newly designed, high solar cells mounted in that section, and each generating altitude platforms.

enough lift to support its own weight. To minimize weight, Likewise, given a high altitude platform with expanded the aircraft structure is highly flexible, and is designed to payload and power capabilities, it is desirable to find new withstand only relatively small torsional loads along its uses for the platform. Such new uses can increase demand lateral axis. The aircraft’s wing has little or no dihedral while for the aircraft, and thereby cause increased production and on the ground. However, due to the high flexibility, the large lower production costs. Naturally, new uses also have the aspect ratio and the constant chord, in-flight wing loads tend potential for new advantages for the public.

to cause the wing to develop a substantial dihedral angle at the wingtips.

In sum, there exists a definite need for a multi-purpose To minimize the torsional loads, the aircraft wing includes aircraft that can remain airborne for long durations without elevators along a substantial portion of its trailing edge (i.e., the need to re-fuel. Preferably, such an aircraft should be the trailing edge of the flying wing). The aircraft does not able to operate up to very high, suborbital altitudes. Impor- include a rudder or ailerons, and the elevators are not 5 5 tantly, it is desirable for such an aircraft to have the capa- designed as elevons (i.e., they cannot move in contrary bility for larger payloads andor power supply requirements.

directions near opposite wingtips). Instead, the aircraft turns Furthermore, there exists a need for such an aircraft to be (and otherwise controls yaw) by using variable thrust inexpensive to build and operate and, furthermore, pollu- applied across the wingspan through the application of tion-free. Also, a definite need exists for such an aircraft to different power levels to different motors. Roll is passively 60 be able to perform surveillance, testing and measurement controlled by the dihedral of the wing, which is developed functions while being steerable, mobile, and able to perform in flight. Sideslip is also passively controlled, both by the varying missions of extended duration. Finally, with the dihedral of the wing, and by fins that extend down from a availability of the hardware of the present invention, it number of wing segments in a direction normal to plane of should be noted that a broad variety of communications the wing at the fin’s span-wise location. 6 5 needs exist that such a high altitude platform can fill. Various Long duration high altitude platforms that operate at embodiments of the present invention can meet some or all suborbital altitudes, such as the Pathfinder and Centurion of these needs, and provide further, related advantages.

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SUMMARY OF THE INVENTION Other features and advantages of the invention will become apparent from the following detailed description of the preferred embodiments, taken in conjunction with the The present invention solves the needs mentioned above accompanying drawings, which illustrate, by way of by providing a solar powered aircraft that is inexpensive to 5 example, the principles of the invention. The detailed produce and can remain aloft almost indefinitely, that is, at description of particular preferred embodiments, as set out least until its parts wear out. Thus, the present invention below to enable one to build and use an embodiment of the provides an aircraft that is perfectly suited to many appli- invention, are not intended to limit the enumerated claims, cations requiring a high altitude platform. For example, the but rather, they are intended to serve as particular examples aircraft could be guided to follow a hurricane, and using 10 of the claimed invention.

equipment on board, study how such storms originate and develop. Alternatively, the present aircraft provides a sub- BRIEF DESCRIPTION OF THE DRAWINGS orbital platform that can be used to convert radio wave signals from a ground station to optical signals directed to a FIG. 1 is an elevational view of a preferred embodiment satellite, or other spacecraft, that is above suborbital alti- 15 of an aircraft embodying the invention, in a zero stress tudes. Likewise, the aircraft can be coupled with a large position.

number of ground stations to create broadband andor wire- FIG. 2 is a plan view of the aircraft depicted in FIG. 1.

less networks. However, the present aircraft is not only far FIG. 3 is a perspective view of the aircraft depicted in less expensive to produce than satellites; it is retrievable and FIG. 1, in a flexed position typical of loading under flight may be reused for the same or different tasks. By using solar 20 conditions.

power, the present aircraft is completely pollution free, and FIG. 4 is a perspective view of the aircraft depicted in thus, provides potent promise for displacing the use of FIG. 1, in a flexed position typical of loading while the combustion-powered aircraft in many of these applications.

aircraft is at rest on the ground.

The aircraft of the invention typically includes a wing, FIG. 5A is a perspective, cutaway view showing the including a first wing portion and a second wing portion, 25 construction of one segment of the wing of the aircraft with a solar cell array mounted on the wing. The aircraft depicted in of FIG. 1.

preferably features a hinge mechanism that is connected to FIG. 5B is a cut-away plan view of the wing segment the first wing portion, and is configured to allow a pivoting depicted in FIG. 5A, with a regenerative fuel cell structured of the first wing portion relative to the second wing portion.

within the wing.

Each wing portion is preferably configured to generate FIG. 5C is a cross-sectional side view of the segment of enough lift to carry its own weight while the aircraft is in FIG. 5A, taken along lines C< of FIG. 5B.

flight, and the pivoting is preferably limited to a value that FIG. 6A is a front elevational view of the aircraft depicted generally allows each wing portion to continue to generate in FIG. 1, having five wing segments, the aircraft being enough lift to carry its own weight. The aircraft can also

depicted in a position typical of loading while the aircraft is

feature a hinge actuator configured to control the hinge 35 in flight.

mechanism such that the dihedral of the first and second FIG. 6B is a front elevational view of the aircraft depicted wing portions can be altered with respect to each other in FIG. 6A, having two hinge actuators that have rotated to during flight. Finally, a control system is preferably con- allow two wing segments on either side of the plane to nected to the hinge actuator, causing it to actuate the hinge increase in dihedral.

such that the dihedral is greater during time periods when a greater dihedral will increase the power generated by the FIG. 6C is a front elevational view of the aircraft depicted in FIG. 6A, having two hinge actuators that have rotated to solar cells.

allow one wing segment on either side of the plane to Preferably, the aircraft is a flying wing aircraft including increase in dihedral.

a plurality of sequentially connected, unswept, wing seg- FIG. 6D is a front elevational view of the aircraft depicted ments (most preferably five or more wing segments). Also, 45 .

in FIG. 6A, having six wing segments rather than five, and preferably the hinge actuator includes a mass actuator con- having one hinge actuator that has rotated to allow three figured to translate the center of gravity of a mass carried by wing segments on either side of the plane to increase in the wing, and wherein the wing and the mass are configured dihedral.

such that the location of the center of gravity of the mass can FIG. 6E is a perspective view of the aircraft depicted in drive the rotation of the hinge mechanism when the wing is FIG. 6B and the sun, wherein the sun is low on the horizon in flight conditions. To drive the rotation, the mass’s chang- and off one wingtip of the aircraft.

ing center of gravity location may deform the wing, creating FIG. 6F is a perspective view of the aircraft depicted in aerodynamic forces.

FIG. 6A, having four wing segments rather than five, having The aircraft may also feature a laterally extending wing 5 5 a varied vertical fin configuration, and having three hinge configured to have dihedral during flight, and a plurality of actuators rotated to allow the four wing segments to form a motors mounted on the wing. The wing’s dihedral is con- “W’ shape.

figured to cause at least one motor to produce thrust along FIG. 7A is an elevational, cross-sectional view of a hinge a line passing above the aircraft’s center of drag, and at least in the aircraft depicted in FIG. 6B.

one motor to produce thrust along a line passing below the FIG. 7B is an elevational, cross-sectional view of a first aircraft’s center of drag when the aircraft is in flight condi- 6o variation of the hinge depicted in FIG. 7A.

tions, the motors causing downward and upward pitching FIG. 7C is an elevational, cross-sectional view of a moments, respectively. The aircraft also includes a control second variation of the hinge depicted in FIG. 7A.

system connected to the throttle of each motor, and it FIG. 7D is an elevational, cross-sectional view of a third controls at least one of the throttles to control the pitch of the 65 variation of the hinge depicted in FIG. 7A, in a flexed aircraft. A remote pilot can control the aircraft through the use of redundant combinations of existing communications position, and including an attachment for a fin.

networks.

FIG. 7E is a plan view of the hinge depicted in FIG. 7D.

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FIG. 8 is a top, cut-away view of one section of the wing station in a broadband, wireless local loop or other commu- from a first variation of the aircraft depicted in FIG. 6B, nications system with subscriber base stations and sub- showing a hinge actuator that includes ailerons. scriber remote stations.

FIG. 9 is a top, cut-away view of one section of the wing FIG. 17B is a view of a subscriber base station for use from a second variation of the aircraft depicted in FIG. 6B, 5 with the communications system illustrated in FIG. 17A.

showing a hinge actuator that includes a laterally movable FIG. 17C is a view of a subscriber remote station for use mass. with the communications system illustrated in FIG. 17A.

FIG. 10 is a top, cut-away view of one section of the wing DETAILED DESCRIPTION OF THE from an alternative second variation of the aircraft depicted in FIG. 6B, showing tanks used for lateral mass movement. 10 PREFERRED EMBODIMENTS FIG. 11 is a side cross-sectional view of a third variation The invention summarized above and defined by the of the aircraft depicted in FIG. 5B, showing a hinge actuator enumerated claims may be better understood by referring to that includes a mass moveable in the fore-and-aft direction.

the following detailed description, which should be read in FIG. 12A is a perspective cross-sectional view of an 15 conjunction with the accompanying drawings. This detailed alternate third variation of the aircraft depicted in FIG. 6B, description of a particular preferred embodiment, set out showing a hinge actuator that includes a mass moveable in below to enable one to build and use one particular imple- the fore-and-aft direction, and showing a local area wing mentation of the invention, is not intended to limit the deflection resulting from the moving mass.

enumerated claims, but rather it is intended to serve as a FIG. 12B is a perspective cross-sectional view of another 20 particular example thereof.

alternative third variation of the aircraft depicted in FIG. 6B, showing a hinge actuator that includes a mass moveable in Introduction to the Preferred Aircraft the fore-and-aft directions, and showing a wing segment In accordance with the present invention, the preferred deflecting from the moving mass.

embodiment of an aircraft of the present invention is of a FIG. 13 is a perspective view of a variation of the aircraft 25 design similar to that of the Pathfinder and Centurion depicted in FIG. 1, in a position typical of loading while the aircraft, as mentioned above in the Background section.

aircraft is in flight, configured such that some motors are While the preferred aircraft embodiment’s design, and varia- located above the center of drag, and some motors are tions of it, are described below, further details useful for the located below the center of drag.

practicing of this invention are provided in U.S. Pat. No.

FIG. 14A is an illustration of a first idealized flexible 3o 5,810,284, which is incorporated herein by reference. Nev- aircraft having three axis flight control, according to the ertheless, it is to be understood that designs for other present invention.

embodiments of the invention can include apparatuses that FIG. 14B is an illustration of a second, and more general, differ substantially from the described aircraft.

idealized flexible aircraft having three axis flight control, The preferred embodiment is a solar-powered, flying according to the present invention.

35 wing with fuel cells to store energy for continuous day and FIG. 14C is a block diagram of a control system imple- night flight. The aircraft includes a plurality of laterally menting control laws form the aircraft illustrated in FIG.

connected, wing segments that each support their own 14B.

weight in flight so as to minimize inter-segment loads, and FIG. 15 is an illustrative view of an embodiment of an thereby minimize required load-bearing structure. In most aircraft control communications system for the aircraft 4o variations of the preferred embodiment, the segments have depicted in FIG. 1.

elevators, but not ailerons or rudders, further limiting inter- FIG. 16A is an illustrative view of the aircraft depicted in segment loads. While these features are preferred, they are FIG. 1, acting as a high altitude platform in a communica- not required in all possible embodiments of the invention.

tions system, to pass signals between a ground station using With reference to FIGS. 1-3, the preferred embodiment is radio wave signals and a satellite using optical signals. FIG.

45 a flying wing aircraft 10, i.e., it has no fuselage or empen- 16A further depicts a hand-off of communications from one nage. Instead, it consists of an unswept wing 12, having a satellite to a second satellite.

substantially consistent airfoil shape and size along the FIG. 16B is an illustrative view of the communications wingspan. Preferably, six, eight or fourteen motors 14 are system of FIG. 16A, where the satellite is at a significantly situated at various locations along the wingspan, each motor different latitude than the ground station.

50 driving a single propeller 16 to create thrust. Preferably, two, FIG. 16C is an illustrative view of the communications four or five vertical fins 18a-l8d, or pods, extend down from system of FIG. 16A, where the aircraft communicates with the wing, with landing gear at their lower ends.

multiple ground stations and the satellite is obstructed from The aircraft 10 is longitudinally divided into preferably one or more of the ground stations by a mountain.

five or six, modular segments sequentially located along the FIG. 16D is an illustrative view of the communications 5 5 wingspan. These include a center segment 20, left and right system of FIG. 16A, where the aircraft simultaneously intermediate segments 22, 24, and left and right wingtip communicates with three different satellites.

segments 26, 28. These segments range from 39 to 43 feet FIG. 16E is an illustrative view of the communications in length, and have a chord length of approximately eight system of FIG. 16A, where the satellite simultaneously feet. Thus, the aircraft has length of approximately eight communicates directly with two aircraft and a ground sta- 60 feet, and preferably has a wingspan of approximately 100, tion.

120, 200 or 250 feet.

FIG. 16F is an illustrative view of the communications The center segment 20 has a middle airfoil portion 30, system of FIG. 16A, where one satellite communicates with four motors 14 with propellers 16, left and right vertical fins multiple aircraft, each of which serves as a base station for 18b, 18c, and a solar array 32. The two intermediate communicating with multiple ground stations.

65 segments 22, 24 of the aircraft 10 each have two propeller FIG. 17A is an illustrative view of the aircraft depicted in motors 14 and a solar array 32, but each has only a single fin FIG. 1, acting as a high altitude, suborbital platform base Mu, 18d positioned at that segment’s outer end, adjacent to

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the wingtip segments. Finally, the wingtip segments 26, 28 nage, and therefore does not require such a relatively strong each mount three motors 14 with propellers 16 and one solar spar to maintain the structural integrity and dynamic stabil- array 32. ity of the wing.

The fins 1&-18d extend downward from the wing 12 at AS a result of the above design, the preferred embodiment the connection points between segments, each fin mounting 5 of the aircraft is light (less than 1 Pound Per square foot of landing gear front and rear wheels 34, 36. The fins are wing area), travels at relatively Slow air speeds (from 13 configured as pods to contain elements of the aircraft, such knots at low altitudes to 100 knots at high altitudes), and as electronics, andor various payloads. One of the pods, a needs relatively little electrical Power from the arrays of “control pod” is used to carry control electronics, including Solar cells in order to stay a i h x n e .

with reference again to FIGS. 1-3, the Preferred embodi- an autopilot principally embodied as software, to control the 10 motors and elevators, In addition, the pods carry sensors, ment of the invention derives its propulsion from the pro- including global positioning system (“Gps”) equipment, as pellers 16, driven by the electric motors 14, which are run on well as communications equipment, test equipment, surveil- electricity generated by the solar arrays 32. The aircraft lance equipment or a payload, depending upon the particular Preferably generates sufficient solar energy and contains 15 sufficient energy storage capacity, to fly continuously, i.e., task for which the aircraft is configured.

ne first embodiment is designed as a spanloader, with day and night. Preferably, it does so without polluting the environment, and without being encubered by the weight each of the segments designed to substantially support their own weight during flight, and thereby avoid significantly of stored fuels, such as fossil fuels, for propulsion. Altema- loading any other segment, This allows each segment to be tiveb, it can be designed to derive Some or all of its power quite flexible, and allows the joints between the sections to 20 from fossil fuels or other stored fuels, or combinations of include Some flexibility. Having low stiffness (i.e., high such as power by day and non- renewable Or partially renewable by night.

flexibility) requirements allows the aircraft structure to be Since each of the five segments supports its own weight, built at a minimum weight.

and not the weight of a fuselage, the wing 12 is designed Preferably, there are no rudders or ailerons on the pre- This ferred embodiment ofthe aircraft 10, thereby further allow- 25 with a ‘Onstant chord, rather than a tapered design permits even more solar cells to be mounted on the ing the wing to be flexible. The only active control surfaces solar arrays 32 ofthe aircraft 10 than would otherwise be the are elevators 38, which are situated along a large of case, and virtually the entire upper surface 42 of the wing is the wing’s trailing edge. In typical form, the elevators are used for conversion of solar energy to electricity. Present actuated in tandem to change the aircraft’s angle of attack.

30 day technology has produced some solar cells that exceed However, in other embodiments, some of the elevators could 20% in conversion efficiency, and it is expected that as the be configured for use as ailerons (i.e., configured as efficiency of solar cells increase, the required wingspan of elevons).

the aircraft to support a given load will decrease. Present yaw, and thereby turns, using The aircraft lo solar cells for a preferred embodiment include cells between differential thrust from varied motor torque on the propellers 35 14,5% and 1x,5%, 16. Other known methods or mechanisms for creating dif- is designed to be very power The preferred aircraft ferential thrust could also be used. The aircraft relies upon efficient and has a solar array 32 mounted proximately to its large wingspan and to avoid Yaw instabil- each propeller’s motor 14, It five solar arrays, one in ity. is passively by the wing being each of its five segments, such that solar arrays occupy most with a positive angle of dihedral. The vertical fins 18u-l8d, 4o of the surface 42 of the wing, The capacity of these which extend beneath the wing 12, Serve to prevent arrays far exceeds the motors’ instantaneous power require- unwanted sideslip and dutch-roll during the aircraft’s turns. ments, so that electrical energy than required by the FIG. 1 shows the preferred embodiment in an unstressed propeller motors 14 is generated each daylight period, position, with the central and intermediate segments 20, 22 T~ improve power generation further, the wing’s is and 24 being relatively level and coplanar, and the tip 45 transparent on both the upper and lower surfaces, and the segments 26, 28 having a natural 6 degree dihedral. The solar cells 32 are preferably two-sided. Thus, the solar arrays Perspective view of FIG. 3 illustrates the natural curvature can generate electricity from light that is incident upon both of the wing segments, as Occurring during flight. This the upper and lower surfaces of the wing. Additional power curvature causes an approximately 3-degree dihedral in the may thus be generated from light that is reflected off of the intermediate segments 22, 24, and an approximately 9 50 Earth, degree dihedral in the wingtip segments 26, 28, which With reference to FIGS. 5B and 5C, to provide power provides the passive roll stability for the design, and elimi- when sunlight is not available, e,g,, at night, the aircraft 10 nates the need for active roll control. FIG. 4, by contrast, stores excess electrical energy in an energy storage system Shows a view of the Preferred embodiment on the ground, including multiple regenerative fuel cells 44, preferably With the wingtip segments bent dOwnward by gravity. In 5 5 based on fuel cell elements such as water, hydrogen and either case, the Center segment 20 is substantially Symmetric oxygen, aboard the aircraft. This energy is used to keep the about its centerline.

aircraft continuously airborne. For the fuel cells, the spars 40 With reference to FIG. 5A, each of the five segments 20, in the center segment 20 and the intermediate segments 22, 22,24, 26 and 28 has a main spar 40 serving as its principal 24 each hold hydrogen and oxygen gases in hermetically structural member. The main spar provides the primary 60 sealed tanks 46 within the spars. All three of these segments structural connection to the other segments, carrying sub- have a spar that is approximately twelve inches in diameter stantially all of the loads between the segments. The present to contain the tanks. Unlike the middle three segments, the aircraft 10 is unlike both conventional aircraft structures, wingtip segments 26, 28 do not have their own regenerative and typical flying wings, which both use heavy main wing fuel cells, and they feature a main spar of reduced diameter.

spars to support either a fuselage or a large central section 65 However, they can optionally be used for fuel cell gas (in the case of a flying wing) during flight. It does not storage. For example, given that the fuel cell produces twice include large central structures, such as a fuselage or empen- as much hydrogen gas as oxygen gas from each unit of

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water, the outboard segments could be used for oxygen gas The aircraft 10 preferably features a hinge actuator con- storage while the inboard segments could be used for figured to control the rotation of the hinge mechanism 102, hydrogen storage.

thereby altering the dihedral of the first wing portion 100 In addition to the main spars 40, the aircraft 10 also with respect to the second wing portion 106. The hinge mounts a water tank 48 and other elements in close prox- 5 actuator is configured to deliver adequate torque to adjust imity to the Spar at the interface between segments. Each the dihedral during flight. Preferably, a control system 108, regenerative fuel cell 44 requires a combination fuel cell/ located within one of the pods, is to the hinge electrolizer 50, a water tank, thermal insulation 52, and a set actuator to the dihedral to be greater during tirne of Pumps and valves 54 to control storage and discharge of periods when the sun is close to the horizon with respect to the During hours, current from the lo the aircraft, Depending upon the heading ofthe aircraft with arrays 32 is used to form hydrogen and Oxygen gases respect to the sun, the greater dihedral can cause a significant from water. The gasses are produced at pressure, then stored increase in power generation. As seen in FIG. 6C, when the in their respective tanks within the main spar. At night, sun is appropriately positioned off to one side of the plane, electricity from the gases is derived by the fuel cell, which the lower surface of the wing on that side of the aircraft 114 allows the gases to recombine using proton exchange mem- 15 branes, The sole by-product, water, is pumped into the water can receive a substantial amount of incident light, while the upper surface Of the wing On the Opposite side Of the aircraft tank and stored there for use in a subsequent energy storage 116 can receive a significant amount of light, even while cycle.

In the alternative, the preferred aircraft, being highly Some Of the wing is shaded.

energy efficient, can be flown for extended periods of time 20 In order to optimize flight efficiencyby reducing drag, the by carrying stored fuels such as hydrogen for a fuel cell. control system causes the dihedral to be less when the sun Also, a combination of stored fuels and solar power tech- is high in the sky, or when it is night. This allows the aircraft nology can be used for extended flight. to optimize the tradeoff between power generation and flight The aircraft 10 is well suited for prolonged missions that efficiency. TOaccomplish this end, the control system deter- require an aircraft to station-keep at a high altitude over a 25 mines a dihedral configuration to increase the power gen- given location. Such missions include, for example, moni- erated by the solar cells. This can be done by simply reading toring weather, providing a mobile, reusable communica- a clock signal and adjusting the dihedral based on the tions platform, performing surveillance, testing atmospheric anticipated light conditions. More preferably, the control system can detect the light conditions, either through signals conditions, and other similar activities.

30 from light measurement devices, or from indications of the Features of the Aircraft power levels generated by one or more of the solar cells.

In order to carry out either the aforementionedmissions or As depicted in FIG, 7A, the hinge actuator preferably new missions, the aircraft must be able to derive as much includes a hinge motor 120 configured to actuate the hinge power as possible from its exposure to the sun. mechanism 102 and thereby control the rotation of the first Increased power generation allows for not only increased 35 and second wing segments with respect to each other, The power for the payload to use, but for more hinge actuator also preferably includes a rotational lock 122 motor and therefore a greater payload capacity. for the hinge mechanism, which can be either within the the aircraft must fly and weigh as hinge mechanism, or othemise controlling it, When the little as possible.

rotational lock is in an unlocked configuration, the hinge Aircraft the present invention preferably 40 actuator allows the rotation ofthe first wing portion 100 with include one or more of the following features to accomplish respect to the second wing portion 106, H ~ ~ ~ ~ ~ when the one or more of these ends.

rotational lock is in a locked configuration,the hinge mecha- nism is restrained, and the first wing portion is prevented Adjustable Dihedral With reference to FIGS, 6A, 6B and 7, one feature ofthe 45 from rotating with respect to the second wing portion, thereby maintaining the wing’s dihedral configuration.

aircraft that provides for a significant increase in the power derived from the solar arrays 32 involves the use of A Preferred hinge actuator can be designed with a motor particular, the wing 12 is 124 driving a pinion 125 enmeshed with a worm gear 126 adjustable wing dihedral, to (see the variation shown in FIG. 7C). A preferred rotational with a first wing portion 100 that is the remainder ofthe aircraft through a hinge mechanism 102 50 lock C a n be designed With disks 127 and calipers 128 (see the variations shown in FIGS. 7B and 7D). In alternative to allow the rotation of the first wing around a rotational axis 104, with respect to a second wing embodiments of the aircraft, some or all of the fins 129 can portion on the remainder of the aircraft. In the embodiment be mounted on the hinge% and OPtionallY geared to require depicted in FIG. 6B, the first wing portion includes the left both Wing segments 131 that are attached to the hinge to intermediate segment 22 and left wingtip segment 26, while 5 5 rotate by equal amounts relative to the fin (or by mounts of the second wing portion includes the center segment 20. Some Other ratio Or schema).

preferably, the hinge mechanism 102 is configured to It is preferable that there be a symmetric arrangement of allow alteration of the dihedral without changing the sweep hinge m ~ h a n i s m s 102 on the aircraft 10. Therefore, the of the wing 12 to a significant degree. The hinge mechanism aircraft Preferably has a third, symmetrically located wing preferably limits the rotation of the first wing portion 100 to 60 Portion 110 that COnnects to the remainder of the aircraft a value where the first wing portion can still generate enough through a second, symmetrically located hinge mechanism lift to carry its own weight while the aircraft 10 is in flight. 112.

Also preferably, the hinge mechanism allows adequate rota- While the preferred embodiment of the invention includes tion to develop enough dihedral to significantlyincrease the hinge mechanisms 102 between the center segment 20 and amount of electricity generated by the solar arrays 32 when 65 the intermediate segments 22,24, they could also be located the sun is located close to the level of the horizon with between the intermediate segments and the wingtip seg- respect to the aircraft. ments 26, 28, as depicted in FIG. 6D. Likewise, if the

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aircraft had an even number of segments, a single hinge states of the elements (i.e., whether they are combined as mechanism could be used to adjust the dihedral, as depicted water, or separated as hydrogen and oxygen gas). Further- in FIG. 6E. more, because the fuel cell will either be charging or Additional configurations, such as aircraft configured to discharging the majority of the time, functioning of the fuel deflect into W-shapes or M-shapes are also within the scope 5 cell can be used as a pump to relocate the mass. In addition, of the invention. Such configurations having alternating depending on the configuration of the aircraft, gravity may positive negative dihedral can reduce wing loading. As be used to feed fuel cell elements (or other masses) from one depicted in FIG. 6F, an embodiment configured to fly in a location to another. Thus, using this variation, the battery’s W-shape preferably has an even number of wing segments. control mechanisms can serve as a mass actuator to move the Preferably vertical fins 115 are located near hinge mecha- i o CG of the battery elements.

nisms that flex upward to form a positive dihedral 113, such With reference to FIGS. 11 and 12A, a third variation of that the fins extend below the rest of the aircraft. Further- the preferred embodiment has similarities to the second more, fins are preferably not located near the hinges that flex variation. In the hinge actuator of this variation, a mass is downward 117 to form a negative dihedral. Other aircraft translated such that its CG moves fore and/or aft. The mass designs incorporating adjustable dihedral are also contem- 15 can be located within the wing 12 (as depicted in FIG. 12A), plated within the scope of the invention.

or within some other aircraft component, such as the fin 18a With reference to FIGS. 6B and 8,in a first variation of the (as depicted in FIG. 11). While the mass and its actuator can preferred embodiment the hinge actuator is designed with be in many forms, the particular mass depicted in FIG. 11 is control surfaces 130, such as ailerons or elevons, that are a cable 146a that is moved between two spinning reels 148a, capable of producing the torque necessary to rotate the hinge 20 and the mass depicted in FIG. 12A is a cylinder 146b riding mechanism 102 during flight conditions. These control sur- on a screw 148b.

faces can be the same surfaces used for normal controlled The movement of the mass affects the CG of a local area flight, or they can be control surfaces specially configured within the wing around the mass, causing the local area’s for hinge actuation. While this option does require the wing CG to shift relative to the center of lift of the local area. The 12 to carry additional torsional loads generated by the 25 effect of this foreiaft CG shift is to cause a torque in the local control surfaces, it has the advantage of eliminating the area around the mass, from the forces of gravity and lift.

weight of the hinge motors. An additional advantage of this In this variation, the wing 12 is torsionally flexible enough system is that aircraft with typical flight computers will to respond to the torque significantly, and the structure of the already be configured to have the computers control the local area 150 around the mass 146 changes shape, as shown existing control surfaces, and thus the flight computer can 30 .

in FIG. 12A. In the shape change, the local area around the serve as the control system.

mass effectively pitches up or down, relative to the rest of With reference to FIG. 9, in a second variation of the the wing, in the direction of the torque. This controlled invention the hinge actuator is designed with a mass actuator pitching up or down of the local area causes an increase or 140 configured to laterally (Le., span-wise) translate the decrease in the lift generated in the local area, similar to the center of gravity (CG) of a mass 142 that is carried by the 35 actuation of a control surface. This change in lift is an first wing portion 100 to be rotated. The lateral movement of aerodynamic force that in turn applies torque to the hinge the mass’ CG changes the CG of the first wing portion, and mechanism. Thus, the mass and mass actuator can function thereby drives the rotation of the hinge mechanism 102 as a hinge actuator by changing the shape of the wing.

when the wing is in flight conditions. In particular, the mass Alternately, as depicted in FIG. 12B, in this variation the is moved such that the CG of the first wing portion is located 4o wing segments 20, 22, 24, 26 and 18 can be torsionally stiff in a position, relative to the center of lift of the first wing relative to the connections between the wing segments, portion, so as to cause a torque on the first wing portion.

which provides for the wing segments to rotate relative to Naturally, other forces and torques applied to the first each other. In this case, the entire left intermediate segment wing portion must be considered when attempting to analyze 45 22 pitches up or down to provide the aerodynamic forces this actuation. Other variations of the invention could necessary to actuate the hinge mechanism. In some designs, involve the mass being placed on portions of the aircraft both the wing segment and the connection between seg- other than the first wing portion to be rotated, so long as the ments can flex to a degree allowing significant aerodynamic moving of the mass’ CG causes a torque that rotates the results.

hinge mechanism.

In sum, the hinge actuator can be of a wide variety of While FIG. 9 depicts the mass 142 moving along a 50 designs both as a mass actuator and otherwise. Various rotationally driven screw 144, other actuators capable of actuators (e.g., linear actuators, motorized arm actuators, moving a mass are within the scope of the invention.

screwigear actuators, pulley actuators, hydraulic actuators, Furthermore, the mass can be an element designed solely for gas pressure actuators, aerodynamic actuators such as tabs, this purpose, or it can be a mass that serves some other purpose, such as a structural element or part of the payload. 5 5 and the like) are known for a variety of uses, and their potential use for the hinge actuator is contemplated within For example, with reference to FIG. 10, the fuel cell the scope of the invention. Furthermore, combinations of elements, which are stored in tanks and spars, can be hinge actuators can be used where desirable. For example, pumped between storage containers to move their CG lat- the fourth embodiment of the invention, being the pitching erally. In particular, by pumping hydrogen, oxygen, and/or 60 of local areas within wing segments, can be employed to the water from sealed spar-tank 46a to sealed spar-tank 46b, the extent allowed by wing torsion tolerances, and additional CG of the battery components can be moved laterally.

hinge actuation can be provided by a hinge motor.

Naturally, for this variation to work there needs to be appropriately located storage tanks, or dividers within the Furthermore, while the described embodiments of active storage spars, as well as appropriately configured battery dihedral control are employed on an aircraft having numer- system pumps to provide the ability to move the CG of the 65 ous, flexible, non-swept segments of constant airfoil and components. When the control system is configured to chord, they can likewise be employed on other aircraft control the pumping, it needs to account for the various designs including conventional aircraft, and even biplanes.

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The above mechanisms provide for a controlled dihedral pitching moment is applied to the aircraft. In particular, the that can be altered during flight. Under the control of a control system increases the throttle for the motors having a control system that is sensitive to the sun’s position in the line ofthrust 200 above the aircraft’s center of drag 202, and S k y , such as by having a S u n Sensor or by having time and decreases the throttles of the motors having a line of thrust latitude information, the aircraft can adjust the wing’s dihe- 5 204 passing below the aircraft’s center of drag, to a dral to optimize or improve the tradeoff between maximum downward-pitching moment when such a pitching moment Power generation (i.e.>by the toward the is called for. The change in thrust may be reversed to create sun) and maximum wing efficiency (i.e.> by minimizing an upward-pitching moment, Preferably, the control system dihedral to direct lift against gravity). Thus, the mechanism and motors are configured with a symmetry that allows the provides for a method of controlling the exposure of wing- i o pitching moment to be applied without causing undue torque mounted solar cells to sunlight at different times during the (i.e., the left side is a mirror image of the right side).

day.

Additionally, more limited throttle control can be used to Active Roll Control produce some pitch control. For example, the motor or A feature Of the aircraft lo that provides for increased 15 motors producing thrust along the line below the aircraft’s flight control with efficient power utilization is the provision central drag may be left with a constant level of thrust, while of active roll control without the use of active control the motor or motors creating thrust above the aircraft’s surfaces (or with reduced reliance on active control surfaces center of drag may be controlled to produce an upward or a for active roll control). In particular, using active roll control allows for controlled banking of the aircraft for efficient downward pitching moment’ turning, and allows for trimming out unwanted roll during 2o By forgoing active control surfaces such as elevators, the parts count, cost and weight of the aircraft are reduced, while normal flight.

Active roll control can be achieved using a mechanism the CG of the aircraft is likely favorably affected (Le., moved similar to that described above for adjustable dihedral. In forward along the wing). The reduced number of moving particular, the third variation of the preferred embodiment, parts provides for increased system reliability. The use of above, includes a mass actuator 14% configured to move the differential thrust provides for quick response time. For CG of a mass 146b in a fore andor aft direction, as depicted example, differential thrust avoids the effect of elevator slew in either of FIGS. 12A and 12B. Aportion of a flexible wing time. This is particularly true for aircraft having high dihe- 12 (either the local area around the mass or the entire wing dral angles, either natural, or those produced under flight segment) is configured to be pitched up andor down by the loads.

moving CG, thereby causing an aileron-like variation in lift.

Notably, this aileron-like action occurs without significantly Full Aircraft Control without the Requirement of Control changing the designed shape of the wing’s airfoil, such as Surfaces the deflection of an aileron would. This feature of the The above discussion of roll control is, in fact, a simpli- invention can be combined with a hinge mechanism to fication of a broader concept within one aspect of the present provide for both active roll control and adjustable dihedral. 35 invention. The idealization of an aircraft in flight, depicted in FIG. 14A, presents some of the more fundamental con- Pitch Control cepts of this aspect.

Just as the preferred embodiment of the present invention provides for an aircraft to be controlled without ailerons, it FIG. 14A is an idealization of a flexible aircraft 210 also can provide for an aircraft to be controlled without 40 having four engines 212, 214, 216 and 218, which be and which elevators, It is known that a rigid aircraft could theoretically referred to by their drawing reference In a control pitch if it had engines rigidly stationed above and produce thrust levels Of Ti, Tz, T3 and T4, below the aircraft,s center of drag, However, vertical strut- coordinate system based at the aircraft’s center of drag 220, tures add weight without contributing to lift, particularly the engines are located at distances Y1, Y2, z1 and z2 from the when they must both the weight of an engine and 45 center Of drag, as depicted in the figure, On the x=o plane, deliver its thrust to the rest of the aircraft, Therefore, and produce thrust in the positive x direction. Preferably, the structures such as engine pylons are designed as compact~y wing’s is formed principally by rather than on a heavy, rigid structure. Each engine’s line of thrust as possible.

through the wing spar (i.e~> the principal axis In the various embodiments described above, the laterally passes extending flexible wing typically develops a significant 5o of torsion). The aircraft has significant torsional flexibility in dihedral angle, even without the addition of dihedral from a center section 222.

the hinge mechanism. With reference to FIG. 13, the present yawing and Pitching ofthe aircraft 210 Can be achieved invention includes a laterally extending wing 12 configured through torques developed by differential thrust. In Padicu- to have significant dihedral during flight due to the wing lar, increasing Tz and T3, while decreasing Ti and T4 by a 55 like amount causes a nose up (-y) pitching torque while flexibility rather than due to rigid structural design.

Each of the aircraft’s motors 14 have a throttle to control maintaining the Overall thrust, rolling torque and Yawing the motor’s thrust. The dihedral of the wing causes one or torque. Likewise, increasing T3 and T4, while decreasing Ti, more of the motors to produce thrust along a line 200 and T4 by a like amount causes a kftward (+Z) Yawing passing above the aircraft’s center of drag 202 during typical torque while maintaining thrust, Pitch torque and roll torque.

flight conditions, thereby causing a downward pitching 60 Rolling of the aircraft 210 can be achieved through a moment. Furthermore, the dihedral causes at least one motor torsion of the center section 222. In particular, increasing T, to produce thrust along a line 204 passing below the air- and T4, while decreasing Ti and T3 by a like amount causes craft’s center of drag when the aircraft is in typical flight an upward (-y) pitching torque on the left side 224 of the conditions, thereby causing an upward pitching moment. aircraft, and a downward (+y) pitching torque on the right The aircraft also includes a control system configured to 65 side 226 of the aircraft, while maintaining the overall thrust, control each motor’s throttle, the control system being pitching torque and yawing torque. Because of the differing configured to control the throttles such that a controlled pitching torques between the right and left sides of the

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aircraft, the right and left sides pitch down and up, respec- direction, there are also net y and z forces to consider.

tively, with the center section twisting in torsion to accom- Partitioning this in matrix form, the control law equations modate them. can be solved for the magnitudes of each T,, the engine Because the left side 224 has pitched up, it has a greater thrust levels.

angle of attack, and therefore has both increased lift and a As before for the aircraft depicted in FIG. 14A, given the 5 portion of the thrust vector pointing in an upward direction. aerodynamics of the aircraft 230 and the torsional stiffness Likewise, because the right side 226 has pitched down, it has of each section of the wing 236, it is within the skill in the a lower angle of attack, and therefore has both decreased lift art to calculate or approximate the roll torque developed and a portion of the thrust vector pointing in a downward from a given twist torque zk on each section k. With the direction. With this differential in vertical forces, the aircraft 10 relationship between the twist torques zk and the roll torque has a right-rolling (+x) roll torque. The opposite roll torque established, the twist torque can be stated (or estimated) as can be achieved by reversing the increases and decreases in a function of roll torque: -ck(Roll Torque). Substituting this thrust. into the above described control laws for the thrust magni- Given the geometry of the aircraft 210, the net thrust, tudes provides a calculation of thrust levels required to meet yawing torque, pitching torque and center section 222 twist- 15 a set of flight requirements, including thrust, pitch, roll, and ing torque can be calculated by a person skilled in the art, as yaw, (along with vertical motion and side slip) as might be follows: received by a flight computer.

The above control laws can be implemented by a control system embodying the control block diagram depicted in 20 FIG. 14C. The block diagram further considers the well- Net thrust TI + T 2 + T 3 + T 4 known relationships between roll, yaw and heading, and Yawing Torque - T4)y1 + (T2 - T3)y2 between pitch and airspeed.

Pitching Torque + T4)z1 + (T2 + T3)z2 Midsection Twisting Torque (TI - T4)(z,+ z2) The description of the invention, provided with reference (Yielding wing tips at to FIG. 14B, can be further extended by adding the use of different angles of attack) 25 movable masses to further cause wing deformations. This type of procedure was described above in the sections entitled “Adjustable Dihedral” and “Active Roll control.” To Partitioning these equations out in matrix form yields con- analyze the aircraft of FIG. 14B, with the further addition of trol laws for the four engine thrust levels as a function of movable masses, each wing section 240 containing a mov- total thrust, yaw torque, pitch torque and (center section) 30 able mass can be considered a plurality of wing sections that twist torque, as follows: are separated by the movable masses. The deflection of each movable mass j can be quantized by a mass movement magnitude M,, and equations can be formed relating each movement M , with a resulting twisting torque T,. These 35 equations are combined with the thrust equations, above, and solved for a matrix containing the engine thrust levels T,and the mass movement magnitudes M,. This matrix equation forms the control laws for a control system, similar to that described above in FIG. 14C, with the addition of Given the aerodynamics of the aircraft 210 and the 40 mass movement commands and servos.

torsional stiffness of the center section 222, it is within the In sum, using this aspect of the present invention, full skill in the art to calculate or approximate the roll torque aircraft control can be maintained without the requirement developed from a given twist torque on the center section.

of active control surfaces as they are typically known.

Depending on the amount of deflection and the aerodynam- Flexible aircraft deformation can be achieved through the ics, the roll torque might not be linearly related to the center 45 use of differential thrust andor by the use of variable section’s twist torque. Nevertheless, with the relationship structural properties, such as mass. It is noteworthy here that between the (center section) twist torque and the roll torque a variable stiffness could be achieved using tubes of liquid established, the twist torque can be stated (or estimated) as pressurized to varying levels, could also serve a similar a z function of roll torque: z(Rol1 Torque). Substituting this function.

into the above control laws provides a calculation of thrust levels required to meet a set of thrust, pitch, roll and yaw Unmanned Control from a Distance flight requirements, as might be received by a flight com- Depending on the form of control system within an puter.

unmanned aircraft, it will typically need to be controlled by With reference to FIG. 14B, the above idealization of a skilled pilots, technicians, or other types of mission-control flexible aircraft within the scope of the invention can be 5 5 specialists. Typical radio-control is generally limited to 400 further generalized to a flexible aircraft 230 having n mile line-of-sight operations. Control of the above-described engines 232 carried by pylons 234 on a torsionally flexible aircraft, or indeed any unmanned aircraft, could frequently wing 236. For each engine i(i=l to n), there is a pylon mount need to be done from around obstacles andor at distances 238 position vector X,, a thrust location vector E,, and a greater than can be maintained through typical radio-signal thrust vector T,, as well as geometry, stiffness and aerody- 60 control. This is of particular significance to commercial or namic information for each section 240 of the wing, where military operators that wish to control a large fleet of each section extends between consecutive engines. high-altitude, long-endurance aircraft using a limited pool of skilled mission controllers.

Similar to the calculations done for the idealization depicted in FIG. 14A, the thrust vectors may be summed A dedicated network of satellites or other communication (now in all three directions) to yield net thrust, yaw torque, 65 equipment provides one solution to the problem of long pitch torque, and twist torque throughout each portion of the range control. However, this solution is very expensive, and wing. Because the engine thrust is not necessarily in the x can be subject to point failures in the network.

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The present invention provides a control communication passes packets of information from a first location to a system for highly reliable control over the above unmanned second location by any of a wide number of different paths aircraft, or any aircraft, at significantly lower cost than a using any of a wide variety of interconnected computer dedicated control system. Indeed, this aspect of the present systems. It therefore has some inherent redundancy. The invention has the potential for applications far outside the 5 failure of any one computer system, or failures that are only relevant art of aircraft inventions, and it could be used for regional, could affect traffic between one pair of locations communication andor control in a wide variety of situa- significantlymore than between another pair of locations. A tions. given computer within the network might not be critical (i.e., Most parts of the world are interconnected through a wide reducing the subsystem’s availability to a level that does not variety of competing and complementary communication i o allow adequate control) to both communications sub- systems such as the Internet, land line telephone networks systems. However, a system-wide failure of the Internet, (leased or public), terrestrial wireless networks, cable however unlikely, could equally affect Internet communica- modem networks, air phone networks, satellite networks, tions along seemingly separate pathways (such as one and other such systems. Such networks are themselves extending along the eastern states and another along the complex systems, and many are designed to provide on the 15 western states). Thus, two communications subsystems that order of 99.99% reliability, reliability being defined as the use the Internet through different portals are substantially, probability that the system is working during its lifetime. but not fully, redundant.

Nevertheless, any one of these systems is not likely to With the above consideration, the use of a single decen- provide the preferred level of reliability to operate the tralized network for more than one communication sub- aircraft.

20 system, which is a non-critical overlap, is within the scope In this aspect of the present invention, adequate reliability of the invention. Nevertheless, most preferably, the commu- is maintained by using a plurality of partially, substantially nications subsystems are entirely separate and distinct, i.e., or (most preferably) fully redundant communication paths, fully redundant, having no overlap whatsoever.

(i.e., redundant communication subsystems, to transmit a n d Additional communication subsystems can also be or receive signals between the mission controller and the 25 actively maintained andor monitored for availability.

aircraft). Preferably, the invention includes a controller that Indeed the controller preferably monitors the availability of controls the use of a first, primary communications sub- a plurality of available communications subsystems, the system and a second, alternate communications subsystem, controller preferably having access to reliability data on each typically made from a plurality of system components.

each such subsystem that it monitors. It preferably selects To be fully redundant, the subsystems cannot share any 30 whether to actually establish these additional links, and the critical link. Alternatively, the systems can be partially number of additional links to actively establish andor redundant, having only limited shared critical links that monitor, based on the anticipated reliability of each system preferably exhibit higher than normal reliability, or are at and the availability of the subsystem andor its components.

least under the control of an entity having an interest in the The communication subsystems can be preselected, end- aircraft. 35 to-end communication paths, such as the ones described Care must be taken to assure that seemingly different above, or they can be the much larger number of subsystems systems are not, in fact, sharing a common critical commu- that can be constituted from a plurality of available system nications link. For example, one long distance telephone components. In the later case, each system component is network might in fact lease lines from another network, and 4o preferably monitored for availability, while in the former thus share a critical link. Therefore, it is best to select service case, arrangements could more easily be made to simply providers that maintain their own communications back- monitor the full end-to-end functionality.

bone.

The overall reliability RS of the communications system Typically, there will be three classes of subsystem com- of the invention, having N communication subsystems, can ponents: backbone links (such as comprising fiberoptic 45 be calculated as: networks, microwave transmission networks, satellite net- works, coaxial cable networks, or copper wire networks), RS=l-(l-R,,)*(l-R,)* . . . *(l-RsN) aircraft access links (such as radio links between the back- bone links and the aircraft), and mission controller links where Rsl, Rs2. . . RsN, are the respective system reliabilities (such as land phone lines, cell phone connections, micro- of each of the N communication subsystems. This reflects wave links or direct satellite links between the backbone and 50 the fact that the system is functional so long as any one the mission controller).

subsystem is working. The reliability of each such commu- For example, as depicted in FIG. 15, a first communica- nication subsystem P, having I system components, can in tions subsystem could comprise a telephone link 400 from a turn be calculated as: pilot station 402 to an Internet gateway 404, which provides 55 R,=R,,*R,*. . . *R, an Internet link 406 to a ground-to-air phone broadcast station 408 that broadcasts to the aircraft 10. A second where R,,, R , . . . R , are the respective system reliabili- communications subsystem could comprise a cell phone link ties of each of the I system components. This reflects the fact 412 to a telephone switch hub 414 that connects with an that the subsystem fails if any component fails.

independent telephone system 416, which delivers the con- trol signal to a satellite ground station 418 that delivers the The controller preferably monitors the present status of 60 signal to a satellite network 420 that can directly commu- communication between the mission controller and the nicate with the aircraft. Notably and preferably, there are no aircraft. The controller preferably selects the communica- common links between the two communications sub- tions subsystems to be used by considering calculations of systems, making them fully redundant. the overall system reliabilities. The controller also prefer- When selecting system components, consideration should 65 ably takes into consideration the various costs involved in be made as to the extent of overlap with other systems. For using each communication subsystem, thus minimizing the example, the Internet is a decentralized network system that overall cost of operating the communications system.

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Advantageously, this communications system will typi- must have the ability to track its target. Furthermore, to the cally provide the ability to communicate with an aircraft extent that the signal strength can be increased, the increase almost worldwide using primarily existing communications broadens the geographic area that will experience significant infrastructure, which will likely simplifies the deployment interference from the signal, particularly if the signal has a and relocation of aircraft systems. Existing system compo- 5 wide beamwidth or is omnidirectional (such as is used for nents typically have established communication frequen- cellular communications). In sum, the communications cies, and generally have known reliability, providing for bandwidth is limited by the altitude of the satellite above the reduced startup and operational costs. The superior reliabil- ground station, by the maximum ground distance (Le., ity of the components will likely lead to efficient aircraft degrees latitude and longitude) between the ground station control, which in turn can provide for reduced power i o and the satellite, by receiver sensitivity (such as from requirements, thus leaving more power for use by an air- antenna size), by beamwidth, and by power level. Addition- craft’s payload. ally, for at least some applications, the communications bandwidth is limited by background noise levels and by Missions for the Aircraft limitations on the allowable interference with other loca- As noted above, the aircraft of the preferred embodiment 15 tion’s signals. Furthermore, if narrow beamwidth ground is ideally suited for certain types of prolonged missions.

station antennas are used to reduce the power requirements, These include monitoring weather, providing a mobile, significant costs can be incurred and additional risks of reusable communications platform, performing surveil- failure can occur due to the precision of the tracking lance, testing atmospheric conditions, and many other activi- requirements.

ties as well. For example, the preferred embodiment can be Satellite-to-satellite communication signals, or satellite to 20 used for to high altitude weather surveillance, and have its non-orbiting spacecraft uplinks, do not necessarily suffer course or flight pattern changed to follow a hurricane at high these types of constraints, as they can use high frequency altitudes, where the aircraft is well out of danger.

signals, e.g., lasers or other optical signals, to achieve a The aircraft is designed to fly continuous, unmanned broad bandwidth over large distances with limited power.

missions of 3000 hours, or longer, which is greater than the 25 Those signals can degrade rapidly when passing through mean time between overhauls for most aircraft. Therefore, atmospheric phenomena such as clouds. Therefore such high the aircraft is designed with reliability foremost in mind.

frequency communication signals are typically limited to This reliability is at least partially aided using redundancy, inter-satellite communication, or to communication between that is, by providing many back-up systems aboard the satellites and ground locations that do not tend to experience aircraft.

30 atmospheric phenomena such as clouds.

Satellite Downlink System The preferred embodiment of the present invention can With reference to FIG. 16A, one type of mission, for provide for a significant increase in ground-to-space com- which the aircraft 10 of the invention is well suited, is the munication bandwidths by providing a suborbital platform establishment of high bandwidth ground to space commu- 304 to transform a radio wave signal from a ground station nication system, from a spacecraft located at orbital altitudes 35 300, such as a microwave signal, to an optical signal directed or higher, such as a satellite, to a ground station. More toward a satellite, or other spacecraft. While this commu- particularly, the aircraft is particularly well suited to serve as nication link could be in either direction, preferably the part of a satellite downlink system, which would also communication link is bidirectional.

include a satellite 302, a ground station 300, and the signals For this function, the preferred suborbital platform, the traveling between them. This type of mission can be useful 40 aircraft 10 of the invention, includes a microwave trans- in the architecture of a wide variety of communication ceiver 310 with a downward-pointing antenna for commu- systems. nicating with a microwave transceiver 312 with an upward- Typically, communications between a ground station and pointing antenna at the ground station, and an optical a satellite use some type of radio wave signal, such as a transceiver 314 with an upward-pointing antenna for com- microwave signal, which can pass through various atmo- 45 municating with an optical transceiver 316 with a down- spheric phenomena, such as clouds, without interference. ward-pointing antenna in the satellite. The aircraft is pref- Some of these signals are omnidirectional, and some are erably elevated to an altitude above typical altitudes for directed toward a target with a given beamwidth. However, substantial atmospheric optical interference, such as from for a given level of receiver sensitivity and background clouds 318, and preferably low enough to maximize signal noise, the signal strength that is required to carry a particular 50 bandwidths between the ground station and the aircraft.

bandwidth increases substantially with the distance between Preferably the aircraft has a plurality of antennas for ground the ground station and the satellite, even if the broadcasting stations, each of these ground-oriented antennas preferably antenna has a relatively narrow beamwidth. Receiver sen- being aimable.

sitivity can be increased with antenna size, but that carries Most preferably the aircraft operates between the altitudes a mass tradeoff, which is costly for satellite systems. Fur- 5 5 of 50,000 feet and 70,000 feet, and does so for 200 hours or thermore, with the limited exception of geostationary satel- longer (and more preferably for 300 hours or longer). The lites, satellites follow a groundtrack crossing back and communications system created, using this aircraft, prefer- fourth over the equator that causes variation in their distance ably operates at a ground station microwave power level that and direction from the ground station and requires large would prohibit significant communication (i.e., communi- pointing adjustments in directional antennas (such as to 60 cation of a significant bandwidth) over the distance between periodically switch from satellite to satellite). Depending on the ground and low-orbit altitudes.

the ground track of the satellite (or group of satellites), Preferably, the aircraft is stationed in a relatively station- ground stations may require extensive amounts of power to ary position with respect to the ground, thus limiting or maintain a downlink with distant satellites. removing the necessity for the ground station to track the Therefore, the signal strength is typically a limiting factor 65 aircraft. In particular, the aircraft preferably operates within on the available bandwidth for the downlink, and, for a 7000-foot diameter circle, and with a 1000 foot altitude directional ground station, the directional antenna typically range, and more preferably substantially within or close to

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a 4000-foot diameter circle. Furthermore, the aircraft pref- overlap if the aircraft is somewhat north of the equator and erably operates within a 1000 foot vertical range, or more the ground station is farther north of the equator).

preferably within or close to a 100-foot vertical range. Likewise, as depicted in FIG. 16C, the system can be used Acting as a suborbital platform to relay radio wave signals to circumvent mountains 325 and other obstacles. This 306 from a ground station 300 through to a satellite 302 5 feature can be used for ground station to satellite linkups, using optical signals 308, the aircraft provides numerous and likewise used for ground station to ground station advantages, and can conduct various missions. For example, linkups. This is a particularly effective use of the system, such an aircraft can be quickly replaced if it develops since neither ground stations nor satellites are typically mechanical dificulties. Likewise, such aircraft can operate repositionable without great effort andor expense. One within a relatively close distance to each other, using fre- 10 potentially effective use for such a system is overcoming the quencies that could interfere with each other at higher power effect of obstacles on signals that are widely broadcast, such levels (for broad beamwidth or omnidirectional signals), as television signals. The source of these television signals because the radio wave signals to each of the aircraft are of could be a ground station, a satellite, or even another a substantially lower power level than would be required to aircraft. Another potentially effective use is frequency reuse provide a similar bandwidth to a satellite in orbit. This can 15 in broadcasting to multiple, geographically separated ground be further augmented with a closed loop signal-strength stations using the same frequency. This is advantageous in control system to minimize power usage to necessary levels that the satellite, being farther away, would require a nar- for the various signals. rower beam width to have separate communicationswith the By using upward-pointing ground antennas andor down- two ground stations using the same frequency.

ward-pointing satellite antennas having limited beamwidth, 20 Another related mission for one or more of the aircraft 10 the power usage can be further minimized. Each of these is in a communications system where the aircraft serve as aimable antennas delimits an area of airspace that the regional hubs, relaying communications between end users aircraft must remain within. If both an upward-pointing located in spot beams, and communications networks. The ground antenna and a downward-pointing satellite antenna communications networks can be either terrestrial based, are used, they must be aimed to mutually define an area of 25 accessed via ground antennas or space based, accessed via airspace that the aircraft can maintain a flight pattern within. optical or extremely high frequency microwave links.

To maintain station within the delimited airspace, the One such related mission, depicted in FIG. 16D, is as a aircraft will preferably be a slow flying aircraft. The flight communications hub, communicating simultaneously pattern will typically be aspirin shaped, being generally between a ground station 326 and a plurality of satellites circular, with a certain amount of vertical variation. How- 30 328. In this mission, the aircraft would require a larger ever, it should be understood that in high wind conditions, number of optical transceivers, and would need to generate the preferred flight pattern could vary from a zig-zagging additional power to operate the transceivers. Alternately, as pattern where the aircraft tacks back and fourth in a gener- depicted in FIGS. 16E and 16F, two coverage regions are ally upwind direction, to a straight upwind flight. shown with one airplane providing coverage over each one.

The aircraft can function to facilitate communication 35 In particular, one or more of such aircraft 10 can all between a single ground station and a single spacecraft, such communicate with a single satellite 330, thus connecting one as a geostationary (or other geosynchronous) satellite, or it or more ground stations with a single satellite that acts as a can communicate with a series of lower orbiting satellites communications hub. This potentially provides for fre- that sequentially pass within the aircraft’s range of optical quency reuse by each aircraft (i.e., each aircraft can use the communication, as depicted in FIG. 16A. Preferably, an 40 same set of available frequencies), increasing the available aircraft designed for switching between satellites will bandwidth between the satellite and the ground.

include two optical communications devices 314, 320, so as This scenario can provide for increased bandwidth to acquire a communication link with a second satellite 322 between a densely populated area and a satellite (see, FIG.

before breaking its communication link with the first satel- 16E), or between a satellite and two distant locations (see, lite 302. 45 FIG. 16F). The later scenario provides for extremely high As depicted in FIG. 16B, in one mission variation, the amounts of data to be passed between a satellite and a city.

aircraft 10 can be used at more northern or southern lati- It provides for different paths to reuse lower frequencies near tudes, where constant and direct access to communications the ground, and optical or extremely high frequency micro- satellites might not otherwise be readily available. By sta- wave links to communicate between the aircraft and the tioning the aircraft at adequate suborbital altitudes, the 50 satellite. That satellite can, in turn, act as a hub and com- aircraft can establish communications with satellites 324 municate with one or more other satellites 334, which can that are more than SO degrees latitude away, the satellite also use suborbital platforms for ground communication.

likely being closer to the Equator. Additionally, direct aircraft to aircraft communications can The aircraft can advantageously take advantage of most also be used. As these examples demonstrate, the aircraft can any non-equatorial station by using directional signals that 5 5 serve as part of the architecture of a variety of communi- reuse wavelengths that are dedicated to equatorial satellites. cations systems.

In particular, a particular ground station can directionally While the above-described preferred embodiment used broadcast two different signals using the same wavelength, microwave and optical signals, it should be understood that by directing one toward a geosynchronous satellite and the the system is operable for a wide variety of signals. In other toward the aircraft. Unlike non-equatorial satellites, 60 particular, it is known that atmospheric moisture interferes the aircraft is not required to cross the equator, and thus the significantly with radio wavelengths of approximately one ground station need not periodically switch to a new broad- millimeter or smaller (i.e., higher frequency signals, above cast direction (such as occurs when the ground station must twenty gigahertz), but not as much with greater wavelengths switch satellites). Naturally, for a given aircraft location, (i.e., lower frequency signals, below twenty gigahertz).

some ground stations will not be able to broadcast on the 6 5 Thus, the system can preferably be operated using a ground same frequency as is broadcast to the satellite because the station to aircraft radio signal having a wavelength greater two directional signals will overlap (e.g., the signals might than one millimeter, and an aircraft-to-satellite radio signal

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having a wavclength less than one millimeter. Furthermore, form is an aircraft 10, as described above, that circles or using the aircraft of the above invention to redirect andor holds position at or close to one location relative to the amplify a signal, power can be conserved even if the aircraft ground.

to satellite portion of the system operated with a signal that The aircraft serves as a suborbital platform base station would pass through atmospheric disturbances, such as a 5 that maintains preferably broadband communication signals signal identical to that used in the ground station to aircraft with and between a variety of ground stations 500, typically portion of the system. at fixed ground locations, potentially including the roofs of subscribers’ commercial buildings 502 and subscribers’ Broadband Distribution System residential buildings 504. At least some of the ground with reference to 17A, another type Of for 10 stations are preferably configured as base stations to distrib- which the aircraft of the invention is well suited, is as part ute data or voice channels to one or remote subscriber Of a local loop, broadband other communi- stations that are typically local fixed or mobile users, In cations network.

addition to buildings, the ground base stations can also be Various forms of communication, such as mobile and integrated within or mounted on street lamps 506, signs, residential voice telephony, mobile and residential Internet 15 stand-alone towers 508 or other ne subscriber access, and broadband data access, each have differing base stations (both commercial and residential) are prefer- transmission requirements. For example, voice telephony ably also lletworked to subscribers’ access ports on their requires a to 64 low level bandwidth (e.g.> premises, either by wired or wireless connection. Links to KBPs) for extended periods Of time (e.g.> 2 to 30 minutes), other networks, such as a PSTN (public switched telephone Internet access requires a larger bandwidth (e.g., 64 to 2000 20 network), PLMN (Public Land Mobile Network) or to the KBps) for limited periods Of time (e.!&>a few seconds), Internet, can be provided by separate ground stations 510, by and broadband access is based upon a large bandwidth (e%., satellite networks 512, or by access through existing sub- 1 MBit or higher) on a nearly continuous basis. scriber base stations, where access links to such networks To provide for such communication requirements, a vari- are available at the subscriber base stations, ety of network architecture are typically developed, leading 25 depicted in FIG. 17B, a subscriber’s ground base to various forms of networks. Included among these are station 500 typically is configured with an antenna 520 for land-line telephone networks, cellular networks, wireless maintaining a broadband or wireless loop link with the local loops, and various stratospheric satellite-based net- aircraft. Optionally, solar arrays 522 can be used to minimize works.

the power drawn by the subscriber base station through a Typically, different equipment is required to support each 30 power connection 524. The various forms of ground base of these technologies. However, in some cases, such net- stations to Serve either individual sub- be works can Serve more than one function. For example, scribers or large numbers of subscribers. To serve other broadband technology Can be brought to fixed location end subscribers, whether mobile, or fixed in the local area of the users by the use of ASDL (asymmetric digital subscriber ground base station, a wireless local loop is preferably used, line) technology delivered via terrestrial wires. Neverthe- 35 although a wired network can also be used to reach fixed less, most of these different types of networks tYPicallY locations. To communicate with the other, remote subscrib- require extensive and expensive infrastructures of wire to ers, the subscriber base station preferably has an antenna 526 interconnect either users or cellular towers.

appropriate to the selected wireless standard of the related If satellites are used in the network, they typically have remote subscriber stations. As an example, the remote difficulties Providing multiple access to users in h i ! & density 40 subscriber stations could be cordless telephones that are areas. Development of equipment meeting the strict weight possessed by subscribers that are otherwise unaffiliated with and Power requirements for use in a satellite is expensive. the subscriber base station, its associated subscriber, and the Furthermore, support is difficult due to limited frequency building oI1 which it resides, reuse and the excess power margin required for transmission A wide variety of communications standards, including to less than ideal locations where mobile users can choose to 45 wireless local loops, can be used in linking the subscriber go. Furthermore, SigifiCaIIt bands of frequencies are UnuS- base stations (or other ground base stations) to subscribers able due to their inability to penetrate atmospheric moisture having remote subscriber stations, Compatible wireless or other disturbances.

communication standards include AMPS (advanced mobile Cellular and PCS systems excel at penetration into build- phone service), TACS (Total Access Communications Sys- ings and hard to reach places through the use of excess 50 tem), NMT (Nordic Mobile Telephone system), IS-95 (code power and significant frequency reuse. However, these sys- division multiple access American digital cellular standard), tems require significant broadband connectivity between Is-54iIS-136 (USA cellular standard, also known as base stations andor transmission towers.

D-AMPS), B-CDMA (broadband code division multiple For reasons such as those above, it is difficult for a access), W-CDMA (wideband code division multiple communications company initially to deploy into regions 5 5 access), UMTS (Universal Mobile Telecommunications Ser- that lack an existing infrastructure, or regions having a vice), or other 3G, PHS (Personal Handyphone System), proprietary infrastructure that is not available for use. The DECT (Digital Enhanced Cordless Telephony), PACS (Per- present invention provides for an inventive network archi- sonal Advanced Communication System), PDC (Personal tecture that, in various embodiments, addresses one or more Digital Cellular), CDPD (Cellular Digital Packet Data), of these concerns.

60 Mobitex (Ericsson standard for wireless packet data net- As seen in FIG. 17A, this embodiment of the present works) and RD-LAP (Motorola-developed wireless packet invention includes the use of one or more high-altitude data network). A wide variety of services can thus be platforms, which could be aircraft (solar or conventional, transmitted to these subscribers, including voice telephony, manned or unmanned), or even balloons, to provide broad- e-mail, Internet Access, facsimile, video telephony and band point-to-multi-point connectivity between fixed 65 video conferencing.

ground locations. Alternatively, near Earth orbit (NEO) As depicted in FIG. 17C, a subscriber remote station 530 satellites could be used. Preferably, this high-altitude plat- would preferably include an antenna 532 appropriate to the

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wireless standard used by the subscriber remote station’s dihedral causes at least one motor of the plurality of related ground base station. These subscriber remote stations motors produces thrust below the aircraft’s center of would have wired or wireless networked connections 534 to drag, and thereby an upward pitching moment, when the individual devices of the subscribers. the aircraft is in flight; and As can be seen from the above description of this distri- 5 a control system connected to the throttles, wherein the bution system, this aspect of the invention provides for an control system is configured such that it controls the information distribution system without the installation of throttles to control the pitch of the aircraft.

an extensive infrastructure. Instead, the system requires only 2. The aircraft of claim 1, wherein the aircraft is con- individual subscriber base stations located with the subscrib- trolled without the use of elevators, ers, or other ground stations, and one or more preferably i o 3, The aircraft of claim 1, wherein pitching moments high altitude, suborbital platforms providing communication generated by the motors on a first side of the aircraft are links to and between the ground stations.

controlled relative to pitching moments generated by the While a particular form of the invention has been illus- motors on a second side of the aircraft to avoid torque trated and described, it will be apparent that various modi- between the first and second sides of the aircraft, fications can be made without departing from the spirit and 15 4, The aircraft of claim 1, wherein motors on a first side scope Of the invention. Thus, the invention has of the aircraft are controlled to produce the Same pitching been described in detail with reference only to the preferred moment as motors on a second side of the aircraft, embodiments, those having ordinary skill in the a r t will 5. The aircraft of claim 1, wherein the control system appreciate that various modifications can be made without controls pitch by actively adjusting only one set of motors departing from the invention. Accordingly, the invention is 20 from the group of: the set of motors above the center of drag not intended to be limited by the above discussion, and is and the set of motors below the center of drag.

defined with reference to the following claims.

6. The aircraft of claim 1, wherein the control system is We claim: further configured to control the throttles so as to control 1. An aircraft, comprising: a laterally extending, flexible wing, configured to develop 25 aircraft yaw.

7. The aircraft of claim 6, wherein the control system is dihedral during flight; further configured to control the throttles so as to control a plurality ofmotors mounted on the wing, at least aircraft of the plurality of motors having throttles that control 8. The aircraft of claim 1, wherein the control system is the thrust of at least some of the plurality of motors, wherein the dihedral causes at least one motor of the 30 further configured to control the throttles S O as to control roll plurality of motors to produce thrust above the air- of the aircraft.

craft’s center of drag, and thereby a downward pitching

* * * * *

moment, when the aircraft is in flight, and wherein the