US3656723A - Multiple helicopter lift system - Google Patents

Multiple helicopter lift system Download PDF

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US3656723A
US3656723A US885400A US3656723DA US3656723A US 3656723 A US3656723 A US 3656723A US 885400 A US885400 A US 885400A US 3656723D A US3656723D A US 3656723DA US 3656723 A US3656723 A US 3656723A
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helicopter
control
helicopters
pitch
units
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US885400A
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Frank N Piasecki
Donald N Meyers
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Piasecki Aircraft Corp
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B64AIRCRAFT; AVIATION; COSMONAUTICS
    • B64CAEROPLANES; HELICOPTERS
    • B64C37/00Convertible aircraft
    • B64C37/02Flying units formed by separate aircraft
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B64AIRCRAFT; AVIATION; COSMONAUTICS
    • B64CAEROPLANES; HELICOPTERS
    • B64C27/00Rotorcraft; Rotors peculiar thereto
    • B64C27/04Helicopters
    • B64C27/12Rotor drives
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B64AIRCRAFT; AVIATION; COSMONAUTICS
    • B64CAEROPLANES; HELICOPTERS
    • B64C27/00Rotorcraft; Rotors peculiar thereto
    • B64C27/04Helicopters
    • B64C27/12Rotor drives
    • B64C27/14Direct drive between power plant and rotor hub
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B64AIRCRAFT; AVIATION; COSMONAUTICS
    • B64DEQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLYING SUITS; PARACHUTES; ARRANGEMENTS OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
    • B64D1/00Dropping, ejecting, releasing, or receiving articles, liquids, or the like, in flight
    • B64D1/22Taking-up articles from earth's surface

Abstract

A multiple helicopter lift system of two or more helicopters of the conventional type normally operating independently that are rigidly connected together in a spaced relationship by structural beam members to form an integral unit with the rotor drive systems of the attached helicopters interconnected so that the engines of each of the interconnected helicopters rotate at the same speed, as do the rotors. If desired the flight controls of all helicopters in the system are interconnected so that the rotational path and pitch of the rotors of all helicopters in the system are controlled from a single master pilot''s station in a manner to establish the necessary forces and moments required to effectively control the movement of the entire system of connected helicopters.

Description

[151 3,656,723 51 Apr. 18,1972

United States Patent Piasecki et a1.

[54] MULTIPLE HELICOPTER LIFT SYSTEM [72] Inventors: Frank N. Piaseckl, Haverford; Donald N.

Primary Examiner-Milton Buchler Assistant Examiner-Carl A. Rutledge Attorney-Beveridge &' De Grandi Meyers, Philadelphia, both of Pa.

[73] Assignee: ABSTRACT A multiple helicopter lift system of two or more helicopters of Piasecki Aircraft Corporation, Philadelphia, Pa.

[22] Filed: Dec. 16, 1969 the conventional type normally operating independently that are rigidly connected together in a spaced relationship by structural beam members to form an integral unit with the rotor drive systems of the attached helicopters interconnected that the engines of each of the interconnected helicopters 'ght controls of all helicopters in the system are interconnected so that the rotational path and pitch of the rotors of all helicopters in the system are controlled from a single master pilots station in a manner to establish the necessary forces and moments required to effectively control the movement of the entire system of connected helicopters.

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SHEET 10F 8 INVENTORS FRANK N. PiASECKI DONALD N. MEYERS BY t W' ATTORNEY:

PATENTEDAPR 18 I972 SHEET 2 [IF 8 PATENTEDAPR 18 m2 SHEET 3 [1F 8 INVENTORS FRANK N. PIASECKI DONALD N. MEYERS ,4 Q: A BY in ii MB Ml not ATTORNEYS PATENTEDAPR 18 I972 13. 656.723

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SHEET 8 BF 8 IEFI HELICOPTER RIGHT HELICOPTER g' ENGINE ENGINE ..I.- ..E GOVERNOR GOVERNOR COMPARATOR FUEL CONTROL 7 FUEL CONTROL- COMPARATOR ENGINE ENGINE fir TORQUE SUMMER I INVENTORS FRANK N. PIASECKI DONALD N. NEYEIIs BY wag Z W' ATTORNEYS BACKGROUND OF THE INVENTION This invention relates to a system of connected helicopters that will provide a platform having a lifting capacity considerably exceeding that of a single helicopter. Regardless of what the lifting capacity produced by the latest and largest helicopter that comes off the production line may be, requirements always exist to lift loads beyond the capacity of that helicopter. This requirement for an increasing lifting capacity has resulted in the design and construction of ever larger machines but the capacity of these new machines has never caught up with the ever increasing requirement for a larger lifting capacity.

Much larger loads could be lifted if two or more helicopters were tov be used in combination to lift more than either could lift alone. A scheme of this nature has been attempted wherein each of several helicopters have lifted one end of a spanning structure with the payload suspended or attached at the center of the structure. A further extension of this idea is to be found in U.S. Pat. No. 3,008,665 in which a further increase in lifting capacity is achieved by using a balloon in combination with the multiple helicopters. In this case the buoyancy of the balloon supports most of the empty weight of the helicopters so that all of the lifting capability can be applied to lift the payload rather than the structure weight.

In these examples each helicopter is operated as an individual entity. This system has a serious drawback in that, if any of the helicopters has a partial power failure, the entire systems lift capacity is drastically reduced because of the requirement for static equilibrium. For example, consider two helicopters, each with two engines. Assume that each helicopter operating at full power can lift 20 tons, including its own weight which may be tons. The two, acting jointly, could lift 40 tons, tons of which would be useful load. If one engine of one helicopter fails, however, that helicopter can only lift approximately one-half its normal amount or 10 tons. Its payload capability would now be zero, instead of 10 tons. The other helicopter, in order to maintain equilibrium of the combination, would have to reduce to one-half power so that a safe useful load for the entire system, if engine failure is to be considered, is zero. Another disadvantage of having each helicopter operate individually, is that each must be controlled by its own pilot and obtaining the necessary degree of coordination between the pilots of the separate helicopters is most difficult, requiring an exceptional degree of pilot skill and flawless communications.

An object of this invention is to provide an assembly of two or more helicopters that operate as an easily controlled integral unit to provide a lifting capacity greater than the individual helicopters.

Another object of this invention is to provide an assembly of interconnected helicopters in which the failure of one or more engines of the various helicopters will not adversely effect the maneuverability or stability of the assembly nor disproportionately decrease the lifting capacity.

Yet another object of this invention is to provide an assembly of connected helicopters in which the attitude and vertical position of the entire assembly may be controlled from a single station.

Yet still another object of this invention is to provide an integral assembly of connected helicopters having a large lifting capacity and being controllable from a single station in which all helicopters are of the conventional variety and upon being detached from the assembly can continue operating independently in a normal fashion.

SUMMARY OF THE INVENTION These objects have been achieved by providing a rigid structure for interconnecting two or more helicopters in a fixed, spaced-apart relationship, interconnecting the rotor drive merely results in the loss of power of the one engine, and superimposing on the basic control system of a designated master helicopter a coordinating transducer system that drives the actuators of various rotor control systems of all helicopters in such a manner that the rotational path and pitch of the individual rotors of each helicopter are coordinated to control 7 the complete assembly of rigidly interconnected helicopters.

Unlike the example discussed above of two jointly acting but independently operating helicopters, the lift system of this invention of two interconnected helicopters having three of the four engines operating could lift three-fourths of the original 40 tons, or 30 tons, of which 10 tons would be useful load.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic perspective view of one embodiment of the invention showing three tandem rotor helicopters rigidly connected together into an integral assembly to form a typical high lift system.

FIG. 2 is a plan view of a portion of the assembly shown in FIG. 1.

FIG. 3 is a front elevation of that portion of the assembly shown in FIG. 2.

FIG. 4 is a schematic plan view illustrating the interconnection of the power trains of the embodiment shown in FIG. 1.

FIGS. 5A and 5B are schematic diagrams of a typical manner of interconnecting the flight controls of the helicopters forming the embodiment illustrated in FIG. 1.

FIGS. 6A, 6B and 6C are schematic front elevations of several embodiments of the invention illustrating various load hoisting arrangements for high lift systems.

FIG. 7 is a perspective view illustrating another embodiment of the invention utilizing two interconnected, tandem rotor helicopters.

FIG. 8 is a plan view illustrating still another embodiment of the invention involving two interconnected, tandem rotor helicopters.

FIG. 9A is a view taken along section line 9-9 of FIG. 2.

FIG. 9B is a cross sectional view of a variation of one of the struts shown in FIG. 9A.

FIG. 10 is a schematic diagram of a manner of interconnecting the engine controls of a two helicopter lift system.

FIG. 11 is a view similar to FIG. 7 but illustrating a multiple helicopter lift system utilized in a towing operation.

DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 is a schematic drawing illustrating a typical embodiment of the multiple helicopter lift system of this invention in which three tandem rotor helicopters I0, ll, 12 of conventional type and having conventional rotor, engine and power train and control systems are rigidly connected together into an integral assembly unit by the rigid beam structures l3, 14 of which the ends are each affixed to the fuselage structure of the respective helicopters by suitable attaching connections, such as bolts or the like. The individual interconnecting beam structures l3, 14 can be of any convenient construction, such as the illustrated arrangement comprising the four struts 15 which attach to the fuselage structures of the respective helicopters through fittings (not illustrated) and separated by opposite pairs of horizontal and vertical struts I6, 17 extending transversely of the beam structure at spaced intervals along its length with structural bracing or wires 18 connected between points where the vertical and horizontal struts join. The beam structure is so configured and attached to the helicopters that there is clearance for the rotors, as may be seen in FIG. 3 in which the center of the beam 13 is lower than each of the ends, as is the line of interconnecting power shafts 34. As illustrated in FIG. 9, the structural members of the beam, such as the struts 15 can be of a streamline shape and their chords aligned such that the angle of attack of the streamline shape to the air flow during forward cruise speed would be a positive angle so as to add to the lift of the assystems of all helicopters so that the failure of any engine sembly in forward flight and also add to the span effect on the over-all lift to drag ratio of the assembly. Instead of being fixed, the streamlined struts can be made mounted in a manner that the direction of their chord is adjustable so that in towing or low speed operations the chord of the strut can be aligned with the air flow or at a small angle to the direction of air flow. Still another variation would be to make the rear portion of the streamlined strut rotatable with respect to the other portion in the manner of a single flap arrangement on an airplane wing in the general manner illustrated in FIG. 9B in which the trailing edge portion a of the streamlined strut is hinged at 15b. Of course, the front portion of the strut could also be mounted in a manner to be pivotable and further change the direction of the effective chord of the strut. Each beam structure with the drive shafting (to be subsequently described) attached thereto should be constructed in a manner to be readily transportable and easily attached and detached from the helicopter fuselage structure. Preferably the beam structure should be erectable in the field.

Each of the three helicopters 10, ll, 12 is a conventional type, tandem, rotor helicopter having a front rotor system 19 and a rear rotor system 20 rotating in opposite directions and interconnected by a drive shaft 21 of the main rotor drive system which connects through a gear box 22 and cross shafts 23 to the two turbine engines 24, 25 that are each mounted opposite sides of the after section of the helicopter fuselage. Each helicopter is capable of operating independently in normal flight and, except for certain minor modifications involving beam structure attachment fittings, additional flight and engine control units and rotor drive system interconnecting gear boxes to be subsequently described, are standard helicopters capable of normal operations. I

A minor modification to the rotor drive system of each helicopter is required to make it adaptable for use in the multiple helicopter system of this invention so that the rotor drive systems of all helicopters of the lift systems are interconnected causing the rotors of all connected helicopters in the assembly to rotate at the same speed and the engines to do likewise. Thus, if the engine of any of the helicopters should fail, it would cease to contribute power and merely result in a redistribution of the required power among the remaining operating engines. In each tandem rotor helicopter of the embodiment of FIGS. l-3 an extra gear box may be installed in the manner illustrated in FIG. 4 wherein the rotor drive shaft 21 of the center helicopter 11 is modified to install a supplementary gear box 26 in which thebevel gear 27 connecting to the rotor drive shaft 21 meshes with two bevel gears 28 each affixed to the end of a cross connecting shaft 29 extending outwardly on each side of the supplementary gear box. A supplementary gear box 30 is installed in the rotor drive system of each of the outboard tandem rotor helicopters 10, 12 with the gear box containing a bevel gear 31 connected to the rotor drive shaft 21 of each of the outboard helicopters and meshing with a bevel gear 32 connected to the end of a cross connecting shaft 33 that extends outwardly from the gear box in the direction of the center helicopter. Lengths of shafting 34 attach to and interconnect the cross connecting shafts 29 of the center helicopter l1 and the cross connecting shafts 33 of the outboard helicopters 10, 12 through flexible couplings 35. The interconnected lengths of shafting 34 are supported at spaced intervals in bearings mounted in brackets 36 that are supported at intervals along the top rear strut 15 of each of the beam structures 13, 14. As can be seen from FIG. 4 the arrangement of the bevel gears in the gear boxes 26 and 30 is such that the rotor drive shafts 21 of all three helicopters rotate in the same direction. The gear box arrangement of FIG. 4, which is a schematic illustration only, shows the center helicopter 11 to have a supplementary gear box 26 that difiers from the configuration of the gear boxes 30 of the outboard helicopters 10, 12. A standard supplemental gear box for all helicopters could be designed in which the gearing arrangement could be adjusted to suit any position that the helicopter might occupy in the lift system assembly.

The engine controls of each of the three helicopters are preferably interconnected so that they are all operable from a common master pilots control station in one of the helicopters, to be discussed in more detail later with respect to flight controls, and the power output of all engines is equalized. FIG. 10 represents one manner of interconnecting the engine controls of a lift system comprising two helicopters each having a single engine. Expansion of such an arrangement, or an equivalent arrangement, to the embodiment of three tandem rotorhelicopters illustrated in FIG. 1 is obvious to anyone skilled in the art. In the illustration of FIG. 10 the right helicopter is the master helicopter from which the assembly of two helicopters is controlled from the pilots station. A servomotor 6 or similar driving unit of a transducer system is connected to arid actuated by the RPM control 5 of the right helicopter which also connects to and controls the engine speed of that helicopter through the usual engine governor and fuel controls, as illustrated. The servomotor 6 in the right helicopter has a suitable connection to a servo receiver 7 in the left helicopter, which receiver connects to and drives the RPM control 8 of the left helicopter, which also has the normal connections to control the engines of the left helicopter through its engine governor and fuel control units. Thus movement of the RPM control 5 in the master control, right helicopter not only establishes the RPM of the engine in the right helicopter but it also moves the RPM control 8 a similar amount, which movement is passed on to the governor and fuel control of the left helicopter. However, to overcome any slight amount of slack or variation in the transducer system and in the RPM control system of each helicopter, an arrangement that automatically equalizes the power output of the respective engines in the two helicopters is indicated in FIG. 10. A unit that adds the sum of the torques of all engines and determines the average torque output for each engine is installed in the right, or master, helicopter and a torque output signal from the engine of each of the helicopters is fed to this unit that is labeled a Torque Summer. A Comparator" unit is installed in each of the two helicopters and connections are made to the engine of that helicopter as well as to the Torque Summer with these connections, respectively, feeding to the Comparator from the engine a signal representing the engine output torque and a signal representing the average engine torque of all engines as measured by the Torque Summer. Each Comparator then compares the two torque signals that are received and, if not the same, then feeds a signal through a connection to the fuel control of the helicopter in an amount to change the power output of the engine to match that of the other engine. The line diagram of FIG. 10 is schematic only and it is to be understood that suitable feed-back and other necessary connections as are required to establish a fully operative system are visualized and considered to be part of the system which a normally skilled power plant engineer can produce. Although, such an interconnected engine control system as the one briefly described, or an equivalent, would make operation of the lift system more effective and easily controllable, the power output of the engine of the connected helicopters could probably be synchronized through the flight engineers or pilots in the respectivehelicopters adjusting the governor settings on the engines of the respective helicopters until the torque readings on each engine are the same. This would require constant communications are careful attention to the torque readings of the engines in order that no engine not contribute power to the system.

Since the interconnected helicopter system comprises a substantially single rigid structuralassembly, preferably features are added to the flight control system that are additional to those found in the conventional system of each helicopter. These added features permit the flight path of the entire assembly of interconnected helicopters to be controlled from a single master station and also provide for actuating selected rotor control actuators that are not normally actuated by the normal movement of the conventional controls of the helicopter so as to generate a rotational path and pitch of selected rotors that will establish the additional moments and forces that are required to provide an adequate aerodynamic control for the entire assembly of connected helicopters. The conventional cyclic pitch and rudder controls of each helicopter produce the necessary moments and forces required to control the attitude of the helicopter in roll, pitch and yaw. Although the forces exerted by the rotors of each of the three helicopters 10, 11 and 12 through the normal functioning of the cyclic pitch and rudder controls would, in general, be in a direction to establish the desired roll, pitch or yaw attitude of the entire assembly, these moments and forces in some instances would be of insufiicient magnitude to effectively control the assembly of interconnected helicopters if the respective cyclic pitch and rudder controls of the three helicopters were merely interconnected and operated the respective rotor actuators of all three helicopters in the conventional manner. Therefore, it is proposed that the attitude control forces that are normally provided by movement of the attitude controls, i.e., the cyclic pitch control and the rudder control, be supplemented as indicated in the description to follow.

Table l, following, indicates the nature of control movement that may be applied to each rotor of each of the three tandem rotor helicopters of the embodiment of FIGS. l-3 in executing the various indicated maneuvers that comprise the basic maneuvers required for flight control of the entire assembly of conventional helicopters and should be reviewed in associa tion with the schematic diagrams of FIGS. 5 and 6 that illustrate the manner in which the flight controls are interconnected:

are increased. The normal lateral cyclic pitch forces produced in each of the separate helicopters upon lateral movement of the cylic pitch control is retained to provide a greater pqsitioning precision in airborne operations.

The normal yaw forces produced in each of the helicopters by the rudder controls in establishing left and right cyclic con- The pilot's station of one of the helicopters is chosen to be' the master control station for controlling the flight operations of the integral assembly. This master control station can be the pilots station of any of the three helicopters but in the embodiment of FIG. 1 the master control station is indicated to be in the left helicopter 10. The reason for this choice, which is an arbitrary one, is that the pilot in the left hand helicopter would have a good overall view of the assembly of connected helicopters and the load L being supported by the lifting cable 37 from the center helicopter, as indicated by the two arrows extending from the window in the pilots compartment of the left helicopter. As indicated, this choice of the master control station is an arbitrary one and could be in any of the three helicopters illustrated in FIG. 1. Ifdesired for safety purposes, a co-pilots station could be incorporated in a helicopter other than the one in which the master control station is installed,

TABLE I Control interconnections for multiple helicopter lift system (tandem rotor helicopters) Increase Pitch Yaw Maneuver total lift nose down Roll left nose left Front Increase Fwd. longitudinal Left lateral cyclic and Left lateral cyclic and] rotor. collective cyclic pitch and decrease collective or aft longitudinal pitch. decrease collecpitch. cyclic. Left helitive pitch.

copter(s). Rear Increase Fwd. longitudinal Left lateral cyclic and Right lateral cyclic and/ rotor. collective cyclic and indecrease collective or aft longitudinal pitch. crease collective pitch. cyclic. Front Increase Fwd. longitudinal Left lateral cyclic Left lateral cyclic.

rotor. collective cyclic and pitch. decrease collec- Ccnter helitive pitch.

coptcr. Rear Increase Fwd. longitudinal Left lateral cyclic Right lateral cyclic.

rotor. collective cyclic and inpitch. cr iaie collective p1 c Front Increase Fwd. longitudinal Left lateral cyclic and Left lateral cyclic and/or rotor. collective cyclic and deincrease collective Fwd. longitudinal pitch. crease collective pitch. cyclic. Right helipitch.

copter(s). Rear Increase Fwd. longitudinal Left lateral cyclic and Right lateral cyclic rotor. collective cyclic and inincrease collective and/or fwd. longipitch. cigpaksle collective pitch. tudinal cyclic.

Table 1 indicates the control output required for each of the front and rear rotors, 19, 20 of each of the three tandem rotor helicopters, 10, l1 and 12 of FIGS. 1-3 in changing the lift of the helicopter or establishing the indicated attitude in roll, pitch and yaw. The major difference in the action of each ofv the controls, as compared to that of an individual helicopter in independent flight, is in the roll axis. The attitude of a single helicopter in roll is controlled by the lateral cyclic pitch. However, when three helicopters are connected together in the manner illustrated in FIG. 1, the lateral moment of inertia of the rigid assembly of helicopters is so high that the moments established by the normal lateral cyclic pitch of the three individual helicopters would be insufficient for good control of the assembly of three helicopters about its roll axis. Superimposing a differential collective pitch change in the rotors of the outboard helicopters onto the usual lateral forces produced by moving the cyclic pitch control laterally creates a moment of the required magnitude about the roll axis of the assembly. Thus, for a roll to the left, the collective pitch of the rotors of the left helicopter 10 of the assembly are decreased and the collective pitch of the rotors of the right helicopter 12 To make maneuvers in the reverse direction, each control motion in the chart is reversed.

such as either the center helicopter 11 or the right helicopter 12, or two co-pilot 5 stations could be incorporated so that one control station is installed in each of the three helicopters of FIG. 1.

FIG. 5A shows a typical manner of interconnecting the collective pitch controls and the lateral phase of the cyclic pitch controls of all helicopters and FIG. 53 illustrates a typical manner of interconnecting the longitudinal cyclic pitch controls and the rudder controls in which all controls are actuated from the single master control station of the left helicopter of the assembly. If a co-pilots station is to be incorporated, a servo system substantially duplicating that illustrated for the master pilots station would have to be provided and con-' nected into the control system along with an interlock so that only the pilots station or the co-pilots station would feed an input into the controls of all helicopters at one time.

In FIG. 5A the master cyclic pitch control and master collective pitch control of the left helicopter are shown in the top portion of the figure and the corresponding slave controls of the center and right helicopter are shown in the center and .9 P -e ere i q yt ilq- Ihe sensatio servomotor 40 or equivalent transmitting unit of a transducer system which in turn through a connection 41 of the servo system connects to and drives the servo receivers 42 and 43 in the center and right helicopter control stations, respectively.

The servo receiver 42 of the center helicopter 11 connects through suitable linkages 44 or equivalent hydraulic, pneumatic or electrical connections to the cyclic pitch control 45 of the center helicopter which has its normal connection to the actuators establishing lateral cyclic rotor control in the center helicopter, as indicated by the arrow and box labeled Lateral Cyclic System. Similarly the servo receiver 43 of the right helicopter 12 connects through suitable linkages 46 or equivalent connection devices to and drives the cyclic pitch control 47 of the right helicopter which has its normal connections to the actuators establishing lateral cyclic rotor control in the right helicopter, as illustrated by the arrow and box labeled "Lateral Cyclic System. Thus lateral motion of the cyclic control pitch stick 38 in the master control station of the left helicopter, not only establishes lateral cyclic pitch in the rotors of the left helicopter 10, but also establishes the same lateral cyclic pitch in the rotors of the center and right helicopters 11, 12.

In a similar manner the collective pitch control 48 at the master control station in the left helicopter has suitable connections represented by the linkages and connections 49 to a servomotor 50 of a servo or transducer system with connections 51 to the servo receivers 52 and 53 which connect through suitable linkages 54, 55 or other type connections to the collective pitch controls 56 and 57 of the center and right helicopters 11, 12, respectively. I

The collective pitch control 56 of the center helicopter 11 has its normal connection to the actuators establishing collective pitch rotor control in the left helicopter, as indicated by the arrow and box labeled Collective Pitch System." However, in the left and right helicopters the motion of each of the respective collective pitch controls 48, 57 is transmitted to the rotorcollective pitch actuators of these helicopters, of which the normal connections are represented by the arrows and boxes labeled Collective Pitch System," through a motion integrating unit 58, 59. The motion integrating unit 58 of the left helicopter control system adds the motion produced by a servo receiver 60 connected by the servo system line 61 to the servomotor 40 in the servo system of the lateral cyclic pitch control to the normal control motion fed to the collective pitch system of the left helicopter by the linkages 65 from the master collective pitch control 48. Thus the collective pitch of the rotors of the left helicopter is established by motion of either or both the master collective pitch control 48 and lateral movement of the master cyclic pitch control 38. Similarly, the motion integrating unit 59 in the right helicopter has an output to the actuators in the collective pitch control system of the right helicopter that reflects both any motion imparted by the servo receiver 62 driven by connections 63 from the output of the lateral cyclic pitch servomotor 40 and the normal control motion fed to the collective pitch control system and motion integrating unit 59 by the linkage 64 of the master collective pitch control 48. The motion integrating units 58 and 59 can be of any conventional type of device, mechanical, electrical, hydraulic or otherwise in which motion from one source is added to that of another source such as any conventional extensible link arrangement, a differential worm gear arrangement, a whiffletree, etc. To comply with the requirements of Table I, the direction of movement induced in the servo receiver 60 of the integrating unit 58 in the left helicopter-10 by movement of the lateral cyclic control 38 must be opposite that of the movement induced in the servo receiver 62 of the integrating device 59 of the right helicopter 75 12 so that lateral motion of the master cyclic pitch control 38 will establish an increase in collective pitch of the rotors of one outboard helicopter and a decrease in collective pitch of the rotors of the opposite outboard helicopter.

The placement of the controls of each of the three helicopters in FIG. 5B is the same as in FIG. 5A, the controls at the master pilot station in the left helicopter being at the top of the figure. The conventional rudder control 66 of the left helicopter has its nonnal connection to the actuators establishing yaw control in the left helicopter as indicated by the arrow and box labeled Yaw Control System. In addition the left helicopter rudder control 66 connects through a linkage 67 or other suitable hydraulic, electrical or other type connections to a servomotor 68 which in turn connects through the connection 69 of a servo or transducer system to and drives servo receivers 70 and 71 in the center and right helicopters, respectively. The servo receivers 70, 71 each are connected through suitable connections 67 67 to drive the rudder controls 72 and 73 in the respective center and right helicopters, which in turnhave their normal connections to the actuators establishing yaw control in the helicopters as indicated by the arrow and box labeled "Yaw Control System. Thus the various actuators of the rotors in all helicopters that establish normal yaw control in the helicopters in their normal, independent flight mode follow the rudder control 66 in the master station of the left helicopter.

Control of the assembly in pitch is exercised through the cyclic pitch control 38 in the master helicopter. A servomotor 74 connects through suitable linkages and other type connections 75 to the cyclic pitch control 38 of the left helicopter (master station) in a manner to be actuated by longitudinal motion of the left helicopter cyclic control 38 in the same manner as the servomotor 40 is actuated by lateral motion of the cyclic control 38. The longitudinal cyclic servomotor 75 connects to and drives servo receivers 76 and 77 through a suitable connection 78 and the servo receivers 76 and 77 operatively connect through linkages 79 and 80 or other type connections in the respective center and right helicopters to the cyclic pitch controls 45 and 47 of these helicopters in a manner that the slave" cyclic pitch controls 45, 47 of thecenter and right helicopters have the same longitudinal motion as that of the master cyclic control 38 in the left helicopter.

In the particular embodiment illustrated in FIG. 5B the iongitudinal phase of the cyclic pitch control 45 in the center helicopter has its normal connections to the actuators establishing normal longitudinal cyclic rotor control in the center helicopter but the output of the longitudinal phase of the left and right helicopter cyclic pitch controls 38 and 47 does not directly connect to the normal longitudinal cyclic rotor control systems of these helicopters but connects to these control systems through motion integrating units 81 and 82 in a manner similar to the arrangement of the collective pitch controls 48 and 57 of the left and right helicopters. The motion integrating units 81 and 82 each respectively incorporate a servo receiver 83 and 84 that respectively connect through suitable connections 85 and 86 to the output connection 69 from the rudder control servomotor in the left 60 helicopter so that the servo receivers 83 and 84 receive signals 70 cyclic pitch controls. The arrangement of the motion integrating units 81 and 82 and the associated servo receivers and connections is such that the respective servo receivers 82 and '84 feed oppositely directed signals or motions to the respective integrating units so that movement of the master rudder control 66 in a given direction will establish oppositely directed longitudinal cyclic pitch in the rotors of the left and right helicopters, respectively, thus establishing oppositely directed longitudinal cyclic pitch in the rotor systems of the left and right helicopters in the alternate manner indicated in the last column of Table I. In other words the rotor system of the left helicopter 10 would establish a longitudinal cyclic pitch force in one direction and the rotor system of the right helicopter 12 would establish a longitudinal cyclic pitch force in the opposite direction upon actuation of the master rudder control 66. If the yawing moment produced on the entire assembly of interconnected helicopters by the normal yaw forces that would be established by the individual helicopters.

upon actuation of their individual rudder controls would be adequate, the longitudinal cyclic motion integrating units 81 and 82 and respective associated servo receivers 83 and 84 and connections 85 and 86 could be eliminated, so that the connections of the longitudinal phase of the cyclic pitch controls of the left and right helicopters would be the same as shown for the center helicopter in FIG. 5B.

Although the diagrams of FIGS. 5A and 5B illustrate stick type flight controls and mechanical link connections, it should be understood that electrical type controls or equivalent arrangements could be utilized. The servo or transducer system and connections are also schematically indicated with no feed back connections shown. However, it should be understood that any type transducer or servo system could be utilized to accomplish the control interconnections indicated in Table I and that suitable feed back and other types of necessary or desirable connections are contemplated. Although the interconnection of controls herein described is desirable and permits the multiple helicopter system to be controlled by a single pilot, it is probably possible for a team of well trained pilots to control such a system from the normal pilots station in each helicopter, if provided with adequate communications.

Tandem rotor helicopters are not necessary for practicing this invention and single rotor helicopters or any other types could also be rigidly interconnected by a beam arrangement similar to that illustrated in FIGS. 1-3 for providing a lift system. However, tandem rotor helicopters appear to be somewhat more adaptable for use in this invention than single rotor helicopters or other types as the drive shaft arrangement of the tandem rotor helicopters presents less of a problem in interconnecting the rotor drive systems of the helicopters. The manner in which controls of single rotor type helicopters could be interconnected in order to achieve satisfactory aerodynamic control of the entire assemblage of interconnected single rotor helicopters from a single pilots station is outlined in Table II to follow. The arrangement of servo system and interconnection of the controls to achieve the rotor control forces outlined in Table 11 could be generally similar to the arrangement illustrated in FIG. 5 modified to a single lifting rotor configuration for each helicopter and will not be described since it would be obvious to one normally skilled in the art. Therefore, it should be understood that TABLE 11 whenever this specification or claims refer to the term rotor the plural is also intended where appropriate.

Although the previous discussions and the illustrations of FIGS. 1-5 relate to an assembly of three interconnected helicopters, the multiple lift system could obviously comprise two helicopters or four or more interconnected helicopters. FIG. 7 illustrates an arrangement wherein two tandem rotor helicopters and 91 are interconnected by a single beam structure unit 92 which can be of the same general type as the beam structures 13, 14 previously briefly described with respect to the arrangement of FIG. 1. The rotor drive systems of the two helicopters, of course, must be interconnected through a suitable shafting arrangement 93 in a manner generally similar to that previously discussed relative to the embodiment of FIG. 1 and the controls of the two helicopters must be integrated in a manner somewhat similar to that of the three helicopter embodiments illustrated in FIG. 1 with the controls in one of the helicopters driving the rotor controls of both helicopters and an interconnection being provided between the lateral cyclic control and the collective pitch control so that differential collective pitch control is established to provide for effective control of the entire assembly about its central roll axis. Differential longitudinal cyclic pitch control can also be tied into the rudder controls, if necessary, to augment the control of the assembly about its yaw axis, as in the case of the embodiment of FIG. 1. In the two-unit multiple lift system illustrated in FIG. 7 the hoist cable 94 attached to the load L cannot be supported from the fuselage structure or a winch in one of the helicopters but must be supported from the beam structure 92 at a midpoint between the two helicopters 90 and 91.

Another possible arrangement of two helicopters is illustrated in FIG. 8. In this embodiment two tandem rotor helicopters and 101 are arranged in a side-by-side relationship but facing in opposite directions, the fuselage structure of the respective helicopters being rigidly interconnected by an X beam arrangement 102 or any other type of rigid beam structure arrangement. As in the previously described assembly of tandem rotor helicopters, the rotor drive shafts 103 of the two helicopters are interconnected by suitable gear boxes 104 and interconnecting lengths of shafts 105. This particular embodiment of FIG. 8 has an advantage in that the separation between the two helicopters 100, 101 can be less than that for the previously described embodiments of tandem rotor helicopters. In the embodiment of FIG. 8 the span of the front rotor of one helicopter can overlap the span of the rear rotor of the other helicopter since the blades of the overlapping rotors are moving in the same direction so that they can intermesh like the blades of an egg beater. The span of the front rotor 106 of helicopter 100 in FIG. 8 overlaps the span of the rear rotor 107 of the other helicopter 101 in FIG. 8 and the span of the rear rotor 108 of the helicopter 100 in FIG. 8 overlaps the span of the front rotor 109 of the other helicopter 101 in that figure, the arrows on the circular arcs representing Control interconnections for multiple helicopter lift system (single-rotor type helicopters) Pitch Maneuver Increase total liit nose down Roll left Yaw nose left Left heli- Increase collective Fwd. Left lateral Conventional single copter(s). pitch increase tail longicyclic and rotor yaw control rotor pitch to tudinal decrease and/or aft longitud. balance torque. cyclic collective cyclic pitch. pitch pitch. Center heli- Increase collective Fwd. Left lateral Conventional single copier. pitch increase tail longicyclic. rotor yaw control.

rotor pitch to tudinal balance torque. cyclic pitch Right heli- Increase collective Fwd. Left lateral Conventional singlecopter(s). pitch increase tail longicyclic and rotor yaw control rotor pitch to tudinal increase and/or fwd. balance torque. cyclic collective longitud. cyclic.

pitch. pitch.

To make maneuvers in the reverse direction, each control motion in the chart is reversed.

isliml by the Home nl'mngolnont ol' dillorontiul longitudinal cyclic control of the outbonrd helicopters or by connecting the outboard helicopters to ollsnt the rotors from the vertical in opposite directions.

the respective rotor spans indicating the direction of blade movement. In this embodiment the minimum separation between the two helicopters 100 and 101 is such that there is blade clearance between the front rotors 106 and 109 and the rear rotors 107 and 108 of the respective helicopters. Although the interconnection of the controls of the two helicopters in the embodiment of FIG. 8 is not quite as simple as that in the embodiment of FIG. 7, interconnection of the controls of the two helicopters through transducer systems in establishing the necessary forces and moments to control the entire assembly in roll, pitch and yaw is obvious from the descriptive matter relating to the interlinkage of the controls in the embodiment of FIGS. 1 and 7. For example, in interconnecting the longitudinal cyclic controls of this embodiment, a reversal of control movement directio would have to be incorporated since the two helicopters e facing in opposite directions. However, this could be easily incorporated when installing the transducer system.

Although all discussions have related to a multiple helicopter lift system in which the helicopters are arranged in a side-by-side arrangement, the helicopters could be interconnected with each other in a tandem arrangement, a V-type arrangement or any other geometrical pattern that might be considered to be advantageous. Of course, the manner in which the rotor controls are interconnected to provide for an integration of collective pitch control into cyclic pitch control or possibly the integrating cyclic pitch control into rudder control in establishing the required moments and forces to control the entire assembly in roll, pitch and yaw would be different than the interconnections indicated in Tables I and II if the helicopters were not connected in a side-by-side arrangement. For example, if the helicopters were connected in a tandem arrangement, differential collective pitch control would have to be integrated into the longitudinal cyclic pitch control to establish the necessary moments of the entire assembly in pitch and the normal lateral cyclic pitch control of the individual helicopters would be adequate for controlling the attitude of the assembly in roll.

Since the multiple helicopter lift system is visualized as being essentially a flying crane, provisions should be included for attaching to the load to be lifted. FIGS. 6A, 6B and 6C are schematic diagrams indicating possible ways for controlling the load lifting arrangement of the assembly of helicopters. FIGS. 6A and 6B relate to the embodiment of FIG. 1 in which the three helicopters 10, 11 and 12 are interconnected by the beam structures 13 and 14 previously described. In the embodiment of FIG. 6 winches 110 are installed in each of the three helicopters 10, 11 and 12. Lifting cables 111 for each of these three winches can be reaved through a suitable pulley system with a suitable load limiting device on each to converge at the center helicopter 11 for attachment to a single lifting hook 112 so that a load to be lifted by the entire assembly is shared by the lifting cables of the three winches l 10.

-In such an arrangement provisions can be made for interconnecting the controls for the three winches so that one control would operate all three winches. In the arrangement of FIG. 6B but a single winch 113 is installed in the central helicopter 11. FIG. 6C shows an arrangement for a single winch 114 installed in the connecting beam structure 92 of the dual helicopter arrangement of FIG. 7. In such a dual arrangement it would also be possible to utilize individual winches installed in the respective helicopters 90 and 91 with the winch cables reaved through a suitable pulley system, similar to that illustrated in 6A, to converge at the center of the beam structure 92 for attachment to the load lifting hook or structure.

Although the various illustrated embodiments indicate a multiple helicopter lift system that is operating in the general nature of a flying crane in which the load from the helicopter assembly is supported by a cable extending vertically below the center of the assembly, many other arrangements for supporting a load could be provided. A load could be hoisted onto and aflixed to the lower part of the helicopter interconnecting frame structure or could even be integrated into the connecting structure itself. Many variations of attaching the "road the assemblies of helicopters comprising the multiple lift 'system could be adopted. Helicopters are used, not only for lifting and transporting loads by air, but also for towing vehicles or objects on land or water. As an example, they are used '11. In this drawing, the two helicopters and 91 are interconnected by an arrangement similar to FIG. 7 and a tow line leads from the center of the connecting beam 92 to the device which is being towed beneath the water. Obviously the equivalent towing arrangement could be utilized to tow items across the surface of the water or on land.

It should be understood that the foregoing disclosure relates only to typical embodiments of the invention and that numerous modifications or alternations may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims.

What is claimed is:

l. A multiple helicopter lift system comprising a plurality of helicopters, the flight control system of each helicopter including a collective pitch control operatively connected to actuators controlling the pitch of the blades of the main rotor system and attitude controls operatively connected to actuators controlling the pitch of each of the rotors of the helicopter for establishing the desired attitude of the helicopter,

means attachable to the structure of each said helicopter for rigidly interconnecting said helicopters and securing them together in a fixed, spaced-apart relationship to form an integral unit,

means interconnecting the rotor drive systems of all said helicopters, whereby the engines and rotors, respectively, of all helicopters are interconnected for operation at their same respective speeds,

collective pitch control transducer means connected to the collective pitch control of one of said helicopters and to the collective pitch actuators of each of the other of said helicopters for establishing equivalent control movement in the collective pitch actuators of said other helicopters as is established in the collective pitch actuators of said one helicopter upon movement of the collective pitch control of said one helicopter,

attitude control transducer means connected to each attitude control of said one helicopter and to selected rotor pitch control actuators of said helicopters for controlling said selected actuators in establishing a pitch of the rotors of all connected helicopters that produces an attitude of said integral unit similar to the attitude that would be produced in said one helicopter upon similarly positioning its attitude controls when operating independently in a normal configuration, said one helicopter attitude controls including a cyclic pitch control for controlling roll and pitch and the attitude control transducer means of said one helicopter cyclic pitch control being operatively connected to the collective pitch actuators of each of at least two connected helicopters located on opposite sides of a mid-point between the most widely spaced of said connected helicopters, said cyclic pitch attitude control transducer means and connections being arranged such that movement of said one helicopter cyclic pitch control in a given direction causes control movement in opposite directions of the respective collective pitch actuators of each of said two oppositely located helicopters, thereby increasing the pitch of the blades in the main rotor system of a helicopter on one side of said mid-point and decreasing the pitch of the blades in the main rotor system of a helicopter on the other side of said mid-point to establish a moment about a horizontal attitude control axis of said integral unit.

2. The lift system described in claim 1 wherein said one helicopter conventional attitude controls additionally include a rudder control for controlling yaw and the attitude control transducer means of said one helicopter rudder control is operatively connected to selected cyclic pitch actuators of said two oppositely located helicopters, said rudder attitude control transducer means and connections being arranged such that movement of said one helicopter rudder control in a given direction causes said selected cyclic pitch actuators of each of said two oppositely located helicopters to move oppositely in a direction that establishes a moment about the yaw axis of said integral unit.

3. The lift system described in claim 2 wherein said attitude control transducer means establishes in the respective attitude control actuators of each said other helicopter the equivalent control movement as is established in the corresponding attitude control actuators of said one helicopter by movement of said one helicopter attitude controls.

4. The lift system described in claim 3 additionally comprising means interconnecting the RPM controls of all said helicopters for causing the engine control of each said other helicopter to follow the engine controls of said one helicopter and means connected to the engines and engine control units for establishing the same torque output in all engines of said helicopters.

5. The lift system described in claim 1 wherein said helicopters are connected by said interconnecting means in a side-byside arrangement with said one helicopter cyclic pitch control including a lateral and a longitudinal phase for controlling roll and pitch, respectively, and the attitude control transducer means connected to the lateral phase of said one helicopter cyclic pitch control has operative connections to the collective pitch control actuators of said two oppositely located helicopters, whereby lateral movement of said one helicopter cyclic pitch control establishes an increase in collective pitch of the main rotor blades of one of said two oppositely located helicopters and a decrease in collective pitch of the main rotor blades of the other of said oppositely located helicopters.

6. The lift system described in claim 5 wherein the attitude control transducer means connected to the longitudinal phase of said one helicopter cyclic pitch control has operative connections to the longitudinal pitch actuators of the rotor of each said other helicopter and establishes the same rotational path and pitch in the blades of the rotors of each said other helicopter as is established in said one helicopter upon longitudinal motion of said one helicopter cyclic pitch control, whereby longitudinal movement of said one helicopter cyclic pitch control establishes in each helicopter the normal pitch control forces present in normal independent flight of that helicopter.

7. The lift system described in claim 6 additionally comprising means interconnecting the RPM controls of all said helicopters for causing the engine control of each said other helicopter to follow the engine controls of said one helicopter and means connected to the engines and engine control units for establishing the same torque output in all engines of said helicopters.

8. The lift system described in claim 7 wherein said one helicopter conventional attitude controls additionally include a rudder control for controlling yaw and the attitude control transducer means of said one helicopter rudder control has operative connections to the longitudinal cyclic pitch control and actuators of said two oppositely located helicopters, said rudder attitude control transducer means and connections being arranged such that movement of said one helicopter rudder control in a given direction causes said longitudinal cyclic pitch actuators of each of said two oppositely located helicopters to move oppositely, whereby aft longitudinal cyclic forces are established in the main rotor of one of said two oppositely located helicopters and forward longitudinal cyclic forces are established in the main rotor of the other of said oppositely located helicopters.

9. The lift system described in claim 8 wherein said attitude control transducer means establishes in the respective attitude control actuator of each said other helicopter the equivalent control movement as is established in the corresponding attitude control actuators of said one helicopter by movement of said one helicopter attitude controls.

10. The lift system described in claim 5 wherein said helicopter interconnecting means includes horizontally extending structural members connecting between adjacent helicopters, said structural members being streamlined in shape and being positioned at such an angle as to establish a. positive angle of attack to the airflow during forward motion of said integral unit at cruise speed.

11. The lift system defined in claim 1 wherein said conventional one helicopter attitude control includes a yaw control, the attitude control transducer means of said one helicopter yaw control is operatively connected to the pitch actuator of a tail rotor such that movement of said one helicopter yaw control causes the pitch actuator of said tail rotor to change pitch establishing a moment about the yaw axis of said integral unit.

12. A multiple helicopter lift system comprising at least two independently operable helicopters of the conventional type, the conventional flight control system of each helicopter including a collective pitch control operatively connected to actuators controlling the pitch of the blades of the main rotor system and a cyclic pitch control and rudder control each operatively connected to actuators controlling the rotational path and pitch of each of the rotors of the helicopter for establishing the desired pitch, roll and yaw attitude of the helicopter when operating in independent flight,

at least one beam structure having connections at each end adapted for being connected to the fuselage structure of one of said helicopters, attaching means for rigidly connecting said connection at each end of said beam structure to different helicopters for interconnecting said helicopters together through said beam structure in a side-by-side, spaced-apart arrangement, said beam structure having a span such that the rotating rotor blades of adjacent helicopters will not come into contact,

drive shafts supported on said beam structure and con nected to the rotor drive system of each helicopter connected to said beam structure, whereby the engines and rotors, respectively, of all helicopters are interconnected for operation at their same respective speeds,

means interconnecting the RPM controls of all said helicopters for causing the engine control of each said other helicopter to follow the engine control of said one helicopter,

transducer means connected to the collective pitch control of one of said connected helicopters and to the collective pitch controls of each of the other of said connected helicopters for causing the collective pitch controls of said other helicopters to follow the movement of the collective pitch control of said one helicopter,

an integrating means connected into the collective pitch control system between the collective pitch control and the actuators controlling the collective pitch of the rotor blades of each of at least two helicopters located on opposite sides of a midpoint between the most widely spaced of the connected helicopters for superimposing in said collective pitch control system of each said oppositely located helicopters an input additional to that established by the collective pitch controls of each of said oppositely located helicopters,

transducer means connected to the lateral phase of the cyclic pitch control of said one helicopter and to the lateral phase of the cyclic pitch control of each of said other helicopters for causing the cyclic pitch controls of said other helicopters to follow any lateral actuation of the cyclic pitch control of said one helicopter,

said transducer means connected to the lateral phase of the cyclic pitch control of said one helicopter additionally connecting to each said collective pitch integrating means in said two oppositely located helicopters for feeding said additional input to each said integrating means upon the I cyclic pitch control of said one helicopter being laterally actuated, said lateral cyclic pitch control transducer means and associated integrating means in said oppositely located helicopters being arranged such that lateral actuation of said cyclic pitch control of said one helicopter increases the collective pitch of one of said two oppositely located helicopters and decreases the collective pitch of the other of said oppositely located helicopters, transducer means connected to the longitudinal phase of the cyclic pitch control of said one helicopter and to the longitudinal phase of the cyclic pitch control of each of 'said other connected helicopters for causing the cyclic pitch controls of said other helicopters to follow any longitudinal actuation of the cyclic pitch control of said helicopter, and transducer means connected to the rudder control of said one helicopter and to the rudder controls of each of said other connected helicopters for causing the rudder controls of said other helicopters to follow the movement of the rudder control of said one helicopter. 13. The multiple helicopter lift system described in claim 16 wherein an integrating means is connected into the cyclic pitch control system between the cyclic pitch control and the cyclic pitch actuators controlling the cyclic pitch of the rotor blades of each of said two oppositely located helicopters for superimposing in said cyclic control system of each said oppositely located helicopters an input additional to that established by the cyclic pitch control of each of said oppositely located helicopters,

and said transducer means connected to the rudder control of said one helicopter additionally connects to each said cyclic pitch integrating means of said two oppositely located helicopters for feeding said additional input to each said cyclic pitch integrating means upon the rudder control of said one helicopter being actuated,

said ruddercontrol transducer means and associated integrating means in said oppositely located helicopters being arranged such that actuation of said rudder control of said one helicopter establishes a forward longitudinal cyclic pitch component in one of said two oppositely located helicopters and a rearward longitudinal cyclic pitch component in the other of said oppositely located helicopters.

14. A method of providing a load transportingv capacity greater than the transporting capacity of a single, conventional helicopter operating independently comprising the steps of rigidly connected together in a fixed, spaced-apart relationship a plurality of helicopter units each having a flight control system that includes a rotor collective pitch control system operable through a collective pitch control means and an attitude control system operable through 50 an attitude control means that includes a cyclic pitch control means, thereby establishing a rigidly connected assembly of helicopter units,

applying the load to said assembly of helicopter units,

operating the rotor drive systems of said connected helicopter units as a single system at the same RPM by interconnecting the rotor drive systems of all said connected helicopter units,

controlling the flight control system of each said helicopter unit of the assembly by operating the collective pitch control systems of all said helicopter units through the collective pitch control means of one of said connected helicopter units, by operating the attitude control systems of all helicopter units through the attitude control means of said one helicopter unit to include operating the pitch control means of said one helicopter unit, and by causing the collective pitch of the rotor system of one of at least two of the connected helicopter units located on opposite sides of a midpoint between the most widely spaced of said units to increase and the collective pitch of the rotor system of the other of said oppositely located helicopters to decrease upon actuation of the cyclic pitch control of said one helicopter unit in controlling attitude along the direction of alignment of said oppositely located helicopter units. 15. A method of aerial towing comprising the steps of connecting the towing load to an assembly of more than one helicopter units which are rigidly connected together in a fixed, spaced-apart relationship,

each helicopter unit having a collective pitch control system operable through a collective pitch control means and an attitude control system operable through an attitude control means that includes a cyclic pitch control means,

causing the rotors of each of said helicopter units to rotate in synchronism at the same speed by interconnecting the rotor drive systems of all said helicopter units and controlling the flight path of said assembly from the pilot's station of one of said helicopter units by operating the collective pitch control system of all said helicopter units from the collective pitch control means of said one helicopter unit, by operating the attitude control system of all said helicopter units from the attitude control means of said one helicopter unit and by causing the collective pitch of the rotor system of one of at least two of the connected helicopter units located on opposite sides of a midpoint between the most widely spaced of said helicopter units to increase and the collective pitch of the rotor system of the other of said oppositely located helicopter units to decrease upon actuation of the cyclic pitch control of said one helicopter unit in controlling attitude along the direction of alignment of said oppositely located helicopter units.

16. Aerial lift apparatus comprising in combination,

a plurality of individual helicopter units each having a flight control system and rotor drive system,

means rigidly interconnecting said helicopter units in fixed,

spaced-apart relationship to form an integral assembly of rigidly interconnected individual units,

means interconnecting the rotor drive systems of each of said units for operation of all said drive systems at the same synchronous speed,

means operative between the flight control systems of all said units whereby all said flight control systems are controlled conjointly and stably by operation of any one of said flight control systems,

said helicopter interconnecting means comprising a beam structure having connections at each end adapted for connecting to the structure of one of said helicopter units and attaching means for rigidly connecting said connection at each end of said beam structure to a different helicopter,

said beam structure including horizontally extending structural members having a streamline shape and positioned such that the chord of said streamline shape is positioned so as to establish a predetermined angle to the airflow during the forward flight motion of saidassembly, and

at least some of said attaching means being adapted for adjusting the direction of the chord of said streamline structure members. 17. Aerial lift apparatus comprising in combination, a plurality of individual helicopter units each having a flight control system and rotor drive system,

means rigidly interconnecting said helicopter units in fixed, spaced-apart relationship to fonn an integral assembly of rigidly interconnected individual units,

means interconnecting the rotor drive systems of each of said units for operation of all said drive systems at the same synchronous speed,

means operative between the flight control systems of all said units whereby all said flight control systems are controlled conjointly and stably by operation of any one of said flight control systems,

said helicopter interconnecting means comprising a beam structure having connections at each end adapted for connecting to the structure of one of said helicopter units and attaching means for rigidly connecting said connection at each end of said beam structure to a different helicopter,

said beam structure including horizontally extending structural members having a streamline shape and positioned such that the chord of said streamline shape is positioned so as to establish a predetermined angle to the airflow during the forward flight motion of said assembly, and

at least some of said streamline structural members being divided into at least two segments and include means for changing the relative alignment of said two segments.

18. In a multiple helicopter unit comprising a plurality of separate conventional helicopters each normally capable of independent, controlled flight and interconnected by structural members to fonn a plural helicopter assembly, the improvement of rigid connecting means attaching said structural members to each said helicopter for rigidly connecting said helicopters together in a fixed relationship to one another, means connected to the rotor drive systems of all said helicopters for causing the main lift rotors of all said helicopters to rotate at the same velocity, and means for connecting the flight control system of all said helicopters together for actuation by the pilots flight controls of one of said helicopters, the conventional flight control system of each said helicopter including a rotor collective pitch control system operable by the pilots collective pitch control, a rotor cyclic pitch control system operable by the pilots cyclic pitch control and a yaw control system operable by the pilots rudder control, and said flight system connecting means including means connecting to the pilots collective pitch control of one of said helicopters and the collective pitch control systems of all other of said helicopters for operating the collective pitch control systems of all said helicopters by actuating the collective pitch control of said one helicopter, means connecting to the pilots cyclic pitch control of said one helicopter and the cyclic pitch control systems of each of the other of said helicopters for operating the cyclic pitch control systems of all said helicopters by Ill-I actuating the cyclic pitch control, of said one helicopter, means connecting to the pilot's rudder control of said one helicopter and the yaw control systems of each said other helicopter for operating the yaw control systems of all said helicopters by actuating the rudder control of said one helicopter, and means connecting to the cyclic pitch control of said one helicopter and the collective pitch control systems of each of at least two connected helicopters located on opposite sides of a mid-point between the most widely spaced of said connected helicopters for causing the collective pitch of the rotor system of one of said oppositely located helicopters to increase and the collective pitch of the rotor system of the other of said oppositely located helicopters to decrease upon actuation of the cyclic pitch control of said one helicopter in controlling an attitude direction.

19. An aerial lifting system comprising, a plurality of separate aircraft vertical lifting units each having a powered rotor lifting system and a flight control system having a collective pitch control system actuated by a collective pitch control and an attitude control system actuated by at least one attitude control, means for rigidly connecting said units together in a rigidly fixed, spaced-apart relationship, means interconnecting the flight control systems of all said units for actuating the collective pitch and the attitude control systems of all units by actuating the collective pitch and attitude controls of one of said units and means operable upon actuation of an attitude control of said one unit for causing a differential actuation of the collective pitch control systems of two units oppositely located with respect to said connecting means. 7

201 The combination of claim 19 additionally comprising means mechanically interconnecting the lifting rotordrives of all said connected units to cause the lifting rotor of all connected units to rotate at the same speed.

21. The combination of claim 20 wherein said connecting means connects said units in tandem and said differential col-- lective pitch actuation means is operable to establish a differential collective pitch in the rotors of said oppositely con-

Claims (22)

1. A multiple helicopter lift system comprising a plurality of helicopters, the flight control system of each helicopter including a collective pitch control operatively connected to actuators controlling the pitch of the blades of the main rotor system and attitude controls operatively connected to actuators controlling the pitch of each of the rotors of the helicopter for establishing the desired attitude of the helicopter, means attachable to the structure of each said helicopter for rigidly interconnecting said helicopters and securing them together in a fixed, spaced-apart relationship to form an integral unit, means interconnecting the rotor drive systems of all said helicopters, whereby the engines and rotors, respectively, of all helicopters are interconnected for operation at their same respective speeds, collective pitch control transducer means connected to the collective pitch control of one of said helicopters and to the collective pitch actuators of each of the other of said helicopters for establishing equivalent control movement in the collective pitch actuators of said other helicopters as is established in the collective pitch actuators of said one helicopter upon movement of the collective pitch control of said one helicopter, attitude control transducer means connected to each attitude control of said one helicopter and to selected rotor pitch control actuators of said helicopters for controlling said selected actuators in establishing a pitch of the rotors of all connected helicopters that produces an attitude of said integral unit similar to the attitude that would be produced in said one helicopter upon similarly positioning its attitude controls when operating independently in a normal configuration, said one helicopter attitude controls including a cyclic pitch control for controlling roll and pitch and the attitude control transducer means of said one helicopter cyclic pitch control being operatively connected to the collective pitch actuators of each of at least two connected helicopters located on opposite sides of a mid-point between the most widely spaced of said connected helicopters, said cyclic pitch attitude control transducer means and connections being arranged such that movement of said one helicopter cyclic pitch control in a given direction causes control movement in opposite directions of the respective collective pitch actuators of each of said two oppositely located helicopters, thereby increasing the pitch of the blades in the main rotor system of a helicopter on one side of said mid-point and decreasing the pitch of the blades in the main rotor system of a helicopter on the other side of said mid-point to establish a moment about a horizontal attitude control axis of said integral unit.
2. The lift system described in claim 1 wherein said one helicopter conventional attitude controls additionally include a rudder control for controlling yaw and the attitude control transducer means of said one helicopter rudder control is operatively connected to selected cyclic pitch actuators of said two oppositely located helicopters, said rudder attitude control transducer means and connections being arranged such that movement of said one helicopter rudder control in a given direction causes said selected cyclic pitch actuators of each of said two oppositely located helicopters to move oppositely in a direction that establishes a moment about the yaw axis of said integral unit.
3. The lift system described in claim 2 wherein said attitude control transducer means establishes in the respective attitude control actuators of each said other helicopter the equivalent control movement as is established in the corresponding attitude control actuators of said one helicopter by movement of said one helicopter attitude controls.
4. The lift system described in claim 3 additionally comprising means interconnecting the RPM controls of all said helicopters for causing the engine control of each said other helicopter to follow the engine controls of said one helicopter and means connected to the engines and engine control units for establishing the same torque output in all engines of said helicopters.
5. The lift system described in claim 1 wherein said helicopters are connected by said interconnecting means in a side-by-side arrangement with said one helicopter cyclic pitch control including a lateral and a longitudinal phase for controlling roll and pitch, respectively, and the attitude control transducer means connected to the lateral phase of said one helicopter cyclic pitch control has operative connections to the collective pitch control actuators of said two oppositely located helicopters, whereby lateral movement of said one helicopter cyclic pitch control establishes an increase in collective pitch of the main rotor blades of one of said two oppositely located helicopters and a decrease in collective pitch of the main rotor blades of the other of said oppositely located helicopters.
6. The lift system described in claim 5 wherein the attitude control transducer means connected to the longitudinal phase of said one helicopter cyclic pitch control has operative connections to the longitudinal pitch actuators of the rotor of each said other helicopter and establishes the same rotational path and pitch in the blades of the rotors of each said other helicopter as is established in said one helicopter upon longitudinal motion of said one helicopter cyclic pitch control, whereby longitudinal movement of said one helicopter cyclic pitch control establishes in each helicopter the normal pitch control forces present in normal independent flight of that helicopter.
7. The lift system described in claim 6 additionally comprising means interconnecting the RPM controls of all said helicopters for causing the engine control of each said other helicopter to follow the engine controls of said one helicopter and means connected to the engines and engine control units for establishing the same torque output in all engines of said helicopters.
8. The lift system described in claim 7 wherein said one helicopter conventional attitude controls additionally include a rudder control for controlling yaw and the attitude control transducer means of said one helicopter rudder control has operative connections to the longitudinal cyclic pitch control and actuators of said two oppositely located helicopters, said rudder attitude control transducer means and connections being arranged such that movement of said one helicopter Rudder control in a given direction causes said longitudinal cyclic pitch actuators of each of said two oppositely located helicopters to move oppositely, whereby aft longitudinal cyclic forces are established in the main rotor of one of said two oppositely located helicopters and forward longitudinal cyclic forces are established in the main rotor of the other of said oppositely located helicopters.
9. The lift system described in claim 8 wherein said attitude control transducer means establishes in the respective attitude control actuator of each said other helicopter the equivalent control movement as is established in the corresponding attitude control actuators of said one helicopter by movement of said one helicopter attitude controls.
10. The lift system described in claim 5 wherein said helicopter interconnecting means includes horizontally extending structural members connecting between adjacent helicopters, said structural members being streamlined in shape and being positioned at such an angle as to establish a positive angle of attack to the airflow during forward motion of said integral unit at cruise speed.
11. The lift system defined in claim 1 wherein said conventional one helicopter attitude control includes a yaw control, the attitude control transducer means of said one helicopter yaw control is operatively connected to the pitch actuator of a tail rotor such that movement of said one helicopter yaw control causes the pitch actuator of said tail rotor to change pitch establishing a moment about the yaw axis of said integral unit.
12. A multiple helicopter lift system comprising at least two independently operable helicopters of the conventional type, the conventional flight control system of each helicopter including a collective pitch control operatively connected to actuators controlling the pitch of the blades of the main rotor system and a cyclic pitch control and rudder control each operatively connected to actuators controlling the rotational path and pitch of each of the rotors of the helicopter for establishing the desired pitch, roll and yaw attitude of the helicopter when operating in independent flight, at least one beam structure having connections at each end adapted for being connected to the fuselage structure of one of said helicopters, attaching means for rigidly connecting said connection at each end of said beam structure to different helicopters for interconnecting said helicopters together through said beam structure in a side-by-side, spaced-apart arrangement, said beam structure having a span such that the rotating rotor blades of adjacent helicopters will not come into contact, drive shafts supported on said beam structure and connected to the rotor drive system of each helicopter connected to said beam structure, whereby the engines and rotors, respectively, of all helicopters are interconnected for operation at their same respective speeds, means interconnecting the RPM controls of all said helicopters for causing the engine control of each said other helicopter to follow the engine control of said one helicopter, transducer means connected to the collective pitch control of one of said connected helicopters and to the collective pitch controls of each of the other of said connected helicopters for causing the collective pitch controls of said other helicopters to follow the movement of the collective pitch control of said one helicopter, an integrating means connected into the collective pitch control system between the collective pitch control and the actuators controlling the collective pitch of the rotor blades of each of at least two helicopters located on opposite sides of a midpoint between the most widely spaced of the connected helicopters for superimposing in said collective pitch control system of each said oppositely located helicopters an input additional to that established by the collective pitch controls of each of said oppositely located helicopters, transducer means Connected to the lateral phase of the cyclic pitch control of said one helicopter and to the lateral phase of the cyclic pitch control of each of said other helicopters for causing the cyclic pitch controls of said other helicopters to follow any lateral actuation of the cyclic pitch control of said one helicopter, said transducer means connected to the lateral phase of the cyclic pitch control of said one helicopter additionally connecting to each said collective pitch integrating means in said two oppositely located helicopters for feeding said additional input to each said integrating means upon the cyclic pitch control of said one helicopter being laterally actuated, said lateral cyclic pitch control transducer means and associated integrating means in said oppositely located helicopters being arranged such that lateral actuation of said cyclic pitch control of said one helicopter increases the collective pitch of one of said two oppositely located helicopters and decreases the collective pitch of the other of said oppositely located helicopters, transducer means connected to the longitudinal phase of the cyclic pitch control of said one helicopter and to the longitudinal phase of the cyclic pitch control of each of said other connected helicopters for causing the cyclic pitch controls of said other helicopters to follow any longitudinal actuation of the cyclic pitch control of said helicopter, and transducer means connected to the rudder control of said one helicopter and to the rudder controls of each of said other connected helicopters for causing the rudder controls of said other helicopters to follow the movement of the rudder control of said one helicopter.
13. The multiple helicopter lift system described in claim 16 wherein an integrating means is connected into the cyclic pitch control system between the cyclic pitch control and the cyclic pitch actuators controlling the cyclic pitch of the rotor blades of each of said two oppositely located helicopters for superimposing in said cyclic control system of each said oppositely located helicopters an input additional to that established by the cyclic pitch control of each of said oppositely located helicopters, and said transducer means connected to the rudder control of said one helicopter additionally connects to each said cyclic pitch integrating means of said two oppositely located helicopters for feeding said additional input to each said cyclic pitch integrating means upon the rudder control of said one helicopter being actuated, said rudder control transducer means and associated integrating means in said oppositely located helicopters being arranged such that actuation of said rudder control of said one helicopter establishes a forward longitudinal cyclic pitch component in one of said two oppositely located helicopters and a rearward longitudinal cyclic pitch component in the other of said oppositely located helicopters.
14. A method of providing a load transporting capacity greater than the transporting capacity of a single, conventional helicopter operating independently comprising the steps of rigidly connected together in a fixed, spaced-apart relationship a plurality of helicopter units each having a flight control system that includes a rotor collective pitch control system operable through a collective pitch control means and an attitude control system operable through an attitude control means that includes a cyclic pitch control means, thereby establishing a rigidly connected assembly of helicopter units, applying the load to said assembly of helicopter units, operating the rotor drive systems of said connected helicopter units as a single system at the same RPM by interconnecting the rotor drive systems of all said connected helicopter units, controlling the flight control system of each said helicopter unit of the assembly by operating the collective pitch control systems of all said helicopter units through the collective pitch control means of One of said connected helicopter units, by operating the attitude control systems of all helicopter units through the attitude control means of said one helicopter unit to include operating the pitch control means of said one helicopter unit, and by causing the collective pitch of the rotor system of one of at least two of the connected helicopter units located on opposite sides of a midpoint between the most widely spaced of said units to increase and the collective pitch of the rotor system of the other of said oppositely located helicopters to decrease upon actuation of the cyclic pitch control of said one helicopter unit in controlling attitude along the direction of alignment of said oppositely located helicopter units.
15. A method of aerial towing comprising the steps of connecting the towing load to an assembly of more than one helicopter units which are rigidly connected together in a fixed, spaced-apart relationship, each helicopter unit having a collective pitch control system operable through a collective pitch control means and an attitude control system operable through an attitude control means that includes a cyclic pitch control means, causing the rotors of each of said helicopter units to rotate in synchronism at the same speed by interconnecting the rotor drive systems of all said helicopter units and controlling the flight path of said assembly from the pilot''s station of one of said helicopter units by operating the collective pitch control system of all said helicopter units from the collective pitch control means of said one helicopter unit, by operating the attitude control system of all said helicopter units from the attitude control means of said one helicopter unit and by causing the collective pitch of the rotor system of one of at least two of the connected helicopter units located on opposite sides of a midpoint between the most widely spaced of said helicopter units to increase and the collective pitch of the rotor system of the other of said oppositely located helicopter units to decrease upon actuation of the cyclic pitch control of said one helicopter unit in controlling attitude along the direction of alignment of said oppositely located helicopter units.
16. Aerial lift apparatus comprising in combination, a plurality of individual helicopter units each having a flight control system and rotor drive system, means rigidly interconnecting said helicopter units in fixed, spaced-apart relationship to form an integral assembly of rigidly interconnected individual units, means interconnecting the rotor drive systems of each of said units for operation of all said drive systems at the same synchronous speed, means operative between the flight control systems of all said units whereby all said flight control systems are controlled conjointly and stably by operation of any one of said flight control systems, said helicopter interconnecting means comprising a beam structure having connections at each end adapted for connecting to the structure of one of said helicopter units and attaching means for rigidly connecting said connection at each end of said beam structure to a different helicopter, said beam structure including horizontally extending structural members having a streamline shape and positioned such that the chord of said streamline shape is positioned so as to establish a predetermined angle to the airflow during the forward flight motion of said assembly, and at least some of said attaching means being adapted for adjusting the direction of the chord of said streamline structure members.
17. Aerial lift apparatus comprising in combination, a plurality of individual helicopter units each having a flight control system and rotor drive system, means rigidly interconnecting said helicopter units in fixed, spaced-apart relationship to form an integral assembly of rigidly interconnected individual units, means interconnecting the rotor drive systems of each of said uniTs for operation of all said drive systems at the same synchronous speed, means operative between the flight control systems of all said units whereby all said flight control systems are controlled conjointly and stably by operation of any one of said flight control systems, said helicopter interconnecting means comprising a beam structure having connections at each end adapted for connecting to the structure of one of said helicopter units and attaching means for rigidly connecting said connection at each end of said beam structure to a different helicopter, said beam structure including horizontally extending structural members having a streamline shape and positioned such that the chord of said streamline shape is positioned so as to establish a predetermined angle to the airflow during the forward flight motion of said assembly, and at least some of said streamline structural members being divided into at least two segments and include means for changing the relative alignment of said two segments.
18. In a multiple helicopter unit comprising a plurality of separate conventional helicopters each normally capable of independent, controlled flight and interconnected by structural members to form a plural helicopter assembly, the improvement of rigid connecting means attaching said structural members to each said helicopter for rigidly connecting said helicopters together in a fixed relationship to one another, means connected to the rotor drive systems of all said helicopters for causing the main lift rotors of all said helicopters to rotate at the same velocity, and means for connecting the flight control system of all said helicopters together for actuation by the pilot''s flight controls of one of said helicopters, the conventional flight control system of each said helicopter including a rotor collective pitch control system operable by the pilot''s collective pitch control, a rotor cyclic pitch control system operable by the pilot''s cyclic pitch control and a yaw control system operable by the pilot''s rudder control, and said flight system connecting means including means connecting to the pilot''s collective pitch control of one of said helicopters and the collective pitch control systems of all other of said helicopters for operating the collective pitch control systems of all said helicopters by actuating the collective pitch control of said one helicopter, means connecting to the pilot''s cyclic pitch control of said one helicopter and the cyclic pitch control systems of each of the other of said helicopters for operating the cyclic pitch control systems of all said helicopters by actuating the cyclic pitch control, of said one helicopter, means connecting to the pilot''s rudder control of said one helicopter and the yaw control systems of each said other helicopter for operating the yaw control systems of all said helicopters by actuating the rudder control of said one helicopter, and means connecting to the cyclic pitch control of said one helicopter and the collective pitch control systems of each of at least two connected helicopters located on opposite sides of a mid-point between the most widely spaced of said connected helicopters for causing the collective pitch of the rotor system of one of said oppositely located helicopters to increase and the collective pitch of the rotor system of the other of said oppositely located helicopters to decrease upon actuation of the cyclic pitch control of said one helicopter in controlling an attitude direction.
19. An aerial lifting system comprising, a plurality of separate aircraft vertical lifting units each having a powered rotor lifting system and a flight control system having a collective pitch control system actuated by a collective pitch control and an attitude control system actuated by at least one attitude control, means for rigidly connecting said units together in a rigidly fixed, spaced-apart relationship, means interconnecting the flight control systems of all said units for aCtuating the collective pitch and the attitude control systems of all units by actuating the collective pitch and attitude controls of one of said units and means operable upon actuation of an attitude control of said one unit for causing a differential actuation of the collective pitch control systems of two units oppositely located with respect to said connecting means.
20. The combination of claim 19 additionally comprising means mechanically interconnecting the lifting rotor drives of all said connected units to cause the lifting rotor of all connected units to rotate at the same speed.
21. The combination of claim 20 wherein said connecting means connects said units in tandem and said differential collective pitch actuation means is operable to establish a differential collective pitch in the rotors of said oppositely connected units upon actuation of said one unit cyclic pitch control in the pitch phase.
22. The combination of claim 20 wherein said connecting means connects said units in juxtaposition and said differential control pitch actuation means is operable to establish a differential pitch in the rotors of said oppositely connected units upon actuation of said one unit pitch control in the roll phase.
US885400A 1969-12-16 1969-12-16 Multiple helicopter lift system Expired - Lifetime US3656723A (en)

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Cited By (14)

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US3743214A (en) * 1971-08-02 1973-07-03 United Aircraft Corp Direct lift, drag and heading improvement for multi-lift aircraft control system
DE2640433A1 (en) * 1975-09-09 1977-04-14 Piasecki Aircraft Corp Vectoring thrust airship
US4591112A (en) * 1975-09-09 1986-05-27 Piasecki Aircraft Corporation Vectored thrust airship
US20090299551A1 (en) * 2008-05-27 2009-12-03 Wilfred So System and method for multiple aircraft lifting a common payload
US20140374532A1 (en) * 2013-06-24 2014-12-25 The Boeing Company Modular Vehicle Lift System
US9043052B2 (en) 2008-05-27 2015-05-26 Wilfred So System and method for multiple vehicles moving a common payload
US9079662B1 (en) * 2012-10-01 2015-07-14 The Boeing Company Co-operative, modular, unmanned, vertical lift cargo vehicles
US9205922B1 (en) * 2013-07-17 2015-12-08 The Boeing Company Systems and methods for implementing a payload distribution system
US9469394B2 (en) * 2015-03-10 2016-10-18 Qualcomm Incorporated Adjustable weight distribution for drone
US9501061B2 (en) 2015-02-24 2016-11-22 Qualcomm Incorporated Near-flight testing maneuvers for autonomous aircraft
US9902496B2 (en) * 2013-01-24 2018-02-27 The Boeing Company Multi-directional elastomeric dampened ball joint assembly
US10310501B2 (en) 2017-02-15 2019-06-04 International Business Machines Corporation Managing available energy among multiple drones
US10538323B2 (en) * 2015-11-06 2020-01-21 David Rancourt Tethered wing structures complex flight path
US10773799B1 (en) * 2017-02-03 2020-09-15 Kitty Hawk Corporation Vertically-tethered multicopters

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US2721044A (en) * 1952-12-18 1955-10-18 Raymond A Young Cargo helicopter assembly
US3008665A (en) * 1958-03-17 1961-11-14 Frank N Piasecki Helicopter and balloon aircraft unit

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US2721044A (en) * 1952-12-18 1955-10-18 Raymond A Young Cargo helicopter assembly
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Cited By (20)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3743214A (en) * 1971-08-02 1973-07-03 United Aircraft Corp Direct lift, drag and heading improvement for multi-lift aircraft control system
DE2640433A1 (en) * 1975-09-09 1977-04-14 Piasecki Aircraft Corp Vectoring thrust airship
US4591112A (en) * 1975-09-09 1986-05-27 Piasecki Aircraft Corporation Vectored thrust airship
US20090299551A1 (en) * 2008-05-27 2009-12-03 Wilfred So System and method for multiple aircraft lifting a common payload
US8761968B2 (en) 2008-05-27 2014-06-24 Wilfred So System and method for multiple aircraft lifting a common payload
US9043052B2 (en) 2008-05-27 2015-05-26 Wilfred So System and method for multiple vehicles moving a common payload
US8370003B2 (en) 2008-05-27 2013-02-05 Wilfred So System and method for multiple aircraft lifting a common payload
US9079662B1 (en) * 2012-10-01 2015-07-14 The Boeing Company Co-operative, modular, unmanned, vertical lift cargo vehicles
US9902496B2 (en) * 2013-01-24 2018-02-27 The Boeing Company Multi-directional elastomeric dampened ball joint assembly
US20140374532A1 (en) * 2013-06-24 2014-12-25 The Boeing Company Modular Vehicle Lift System
EP2818406A1 (en) * 2013-06-24 2014-12-31 The Boeing Company Modular vehicle lift system
US9457899B2 (en) * 2013-06-24 2016-10-04 The Boeing Company Modular vehicle lift system
US9205922B1 (en) * 2013-07-17 2015-12-08 The Boeing Company Systems and methods for implementing a payload distribution system
US9501061B2 (en) 2015-02-24 2016-11-22 Qualcomm Incorporated Near-flight testing maneuvers for autonomous aircraft
US20170021915A1 (en) * 2015-03-10 2017-01-26 Qualcomm Incorporated Adjustable Weight Distribution for Drone
US9469394B2 (en) * 2015-03-10 2016-10-18 Qualcomm Incorporated Adjustable weight distribution for drone
US9908618B2 (en) * 2015-03-10 2018-03-06 Qualcomm Incorporated Adjustable weight distribution for drone
US10538323B2 (en) * 2015-11-06 2020-01-21 David Rancourt Tethered wing structures complex flight path
US10773799B1 (en) * 2017-02-03 2020-09-15 Kitty Hawk Corporation Vertically-tethered multicopters
US10310501B2 (en) 2017-02-15 2019-06-04 International Business Machines Corporation Managing available energy among multiple drones

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CA943935A (en) 1974-03-19
IL35864A (en) 1973-11-28
IL35864D0 (en) 1971-02-25

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