VTOL AIRCRAFT

Be it known that I, William P. Strumbos, citizen of the United States of America, and resident of Northport, in the county of Suffolk, in the State of New York, am the inventor of the above-entitled invention of which the following is a Specification:

Field of the Invention

This invention relates to vertical take-off and landing (VTOL) aircraft and, more particularly, to an aircraft that uses upper surface blowing of the lifting surfaces to generate lift coupled with a modulation or reaction of the propulsor thrust to achieve vertical flight.

Background of the Invention VTOL aircraft of all types in use today have on

_* thing in common: the propulsion efflux is directed' downward to produce lift by a consequent reaction to-' the downwash momentum. However, it is also known in the prior art that lift can be produced by yet another means which may be conveniently termed "upper surface blow¬ ing." Upper surface blowing comprises the acceleration of the flow over the upper surface of a body to create a drop in pressure thereover relative to the pressure on the under surface of the body, producing lift forces on that body. Upper surface blowing produces lift without

a requirement for a turning downward of the flow that has passed over the body being lifted.

In the VTOL aircraft of this invention, the propul¬ sor fans provide propulsion thrust to accelerate the aircraft for conventional flight in which the forward velocity of the aircraft produces an airflow over the lifting surfaces that generates lift for flight. Ring and channel wings are efficient airfoils, thus the air¬ craft possesses the flying characteristics of a normal fixed wing aircraft both in engine-on and engine-off conventional flight. It can, therefore, be flown as a conventional aircraft with the propulsion fans providing the required propulsion thrust. For VTOL flight, the propulsor fans operate to induce a flow over the lifting surfaces to generate lift and, at the same time, the fan slipstream that has induced lift is reacted by the thrust vectoring means in the empennages to stop forward travel by the aircraft. The generating of lift without forward travel results in a lift vector that is straight up; i.e., hovering or vertical flight. The spoilers or similar aerodynamic control means in the wings and em¬ pennages provide pitch, roll, and yaw control in conven¬ tional flight. The thrust reacting and vectoring means in the ring empennages vector propulsor fan slipstream for pitch and yaw control and react propulsor thrust such that fully controlled hover and vertical flight is achieved. A coordinated operation of the spoilers in conventional flight and of the wing spoilers and thrust

-3- vectoring means in VTOL flight produces control moments transverse to the normal line of flight.

Description of the Prior Art

As discussed previously herein, the upward force producing flight in conventional heavier-than-air VTOL aircraft is usually generated by moving a mass of air downward. Or in terms of impulse and momentum: an upward impulse is the result of changing the downward momentum of a mass of air. In the case of a wing, it is the downwash produced by the wing that generates the lift. In the case of the rotor in helicopters and the like, it is again the downwash produced by the rotor blades. And in the case of a rocket or downward pointing or vectored jet engine, it is the momentum of the downward blast that produces the upward force. In each of these cases, the principles are the same; only the mechanism is different.

However, the prior art also shows that it is known to generate lift solely by upper surface blowing.. The prior art teaches that it is not required to provide an upward impulse on the aircraft to produce ^{^} lift as the result of changing the downward momentum of a mass of air. There are also designs shown in the prior art in which it is proposed, not only to generate lift by upper surface blowing, but also to react the horizontal forces produced by the propulsion means such that vertical flight capabilities are obtainable. Designs of that

-«_ -. type are disclosed by D.W. Wells, (U.S. patent No.

1,824,250), R.W. Davis (U.S. patent No. 1,987,607), L.F. Jordan (U.S. patent No. 2,419,780), and W.S. Miller (U.S. patent No. 3,360,218). However, because these prior art designs do not provide positive control, difficulty will be experienced in all phases of flight, particularly during the criti¬ cal transition phase between vertical and horizontal flight. Thus, it is a principal object of the invention to provide a VTOL aircraft having the propulsors thereof blowing the wings to generate lift by upper surface blowing, the slipstream from the propulsors that is producing lift also reacting with a ring tail empennage system to provide positive control during all phases of flight, with thrust vectoring means in the empennage reacting horizontal travel of the aircraft such that fully controllable vertical flight and transition thereto or therefrom is achieved.

Description of the Drawings FIG. 1 is a perspective view of a preferred embodi¬ ment of the VTOL aircraft of the invention in a conven¬ tional flight configuration;

FIG. 2 is a fragmentary perspective view of the aircraft embodied in FIG. 1 showing the aircraft on the ground;

-5"- FIG. 3 is a fragmentary perspective view partially i in section of the aircraft embodied in FIG. 1 showing another view of the aircraft on the ground;

FIG. 4 is a fragmentary perspective view partially in section of the aircraft embodied in FIG. 1 in the VTOL configuration;

FIG. 5 is a fragmentary perspective view of one of the empennages of the aircraft embodied in FIG. 1 in the VTOL configuration; i FIG. 6 is a fragmentary cross-sectional view of the peripheral door system of the empennage of the aircraft embodied in FIG. 1 in the conventional flight configura¬ tion;

FIG. 7 is a fragmentary cross-sectional view of the peripheral door system of FIG. 6 in the ^J VTOL configura¬ tion;

FIG. 8 is a diagram of a flight >control-system for the VTOL aircraft of the invention;

FIG. 9 is a perspective view of the flight controls for conventional flight of the aircraft of FIG. 1;

FIGS. 10 and 11 are diagrammatic side elevations partially in section showing the action of the pitch controls of the aircraft of FIG. 1 in conventional flight; FIG. 12 is a perspective view of the flight con¬ trols for VTOL flight of the aircraft of FIG ^" . ^* !;

- C_~

FIGS. 13 and 14 are diagrammatic side elevations partially in section showing the action of the pitch controls of the aircraft of FIG. 1 in VTOL flight;

FIGS. 15, 16 and 17 are fragmentary side elevations partially in section of the peripheral door system of the empennage of the aircraft of FIG. 1 in different phases of propulsor thrust modulation;

FIG. 18 is a side elevation partially in section of a further embodiment of the VTOL aircraft of the inven- tion in the VTOL flight configuration;

FIG. 19 is a top plan view partially in section of the aircraft embodied in FIG. 18;

FIG. 20 is a front elevation of the aircraft embod¬ ied in FIG. 18; FIG. 21 is a side elevation of another embodiment of the VTOL aircraft of the invention in a conventional flight configuration;

FIG. 22 is a top plan view of the aircraft embodied in FIG. 21; and FIG. 23 is a front elevation of the aircraft embod¬ ied in FIG. 21.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference now to FIG. 1 in particular of the drawings, a preferred embodiment 10 of the VTOL aircraft of the invention has a fuselage 12; fixed ring wings 14, 16 on either side of the fuselage; nacelles 18, 20 asso¬ ciated with the ring wings; propulsion means 22 and 24

- 7- in the noses of the nacelles; and a ring tail empennage system 26 and 28 at the after ends of the nace_J.es. It will be recognized that ring wing 14 and its associated nacelle 18 and other components are substantially a mir- ror image of ring wing 16 and its nacelle 20 and other components; thus, in the interest of brevity, tϊ^e fol¬ lowing detailed description of one ring wing and its associated components will be understood to apply with obvious variations to the other ring wing and its asso- ciated components.

Each ring wing has a series of deployable spoilers 30 encircling the inside periphery of throat 32 of the wing parallel to the leading edge 34 thereof. A second series of deployable spoilers 36 are located parallel to the leading edge 34 on the outside periphery"3 ^* 8 of the wing at least in the upper 40 and lower 42 sectors of the wing. Although the spoilers 30 and 36 are shown located near the leading edge of the wing, it ill he understood that their location will be governed by aero- dynamic considerations and can differ from that shown.

In addition, deployable circulation control slats _, 44 are provided in the lower outside quadrant of the wing lead¬ ing edge. As is known, means such as chord-wise fences 45 can be fitted on the wings for circulation control. The nacelle is suitably mounted in the wing with appro¬ priate means such as struts 46 and 48. The propulsor fan 24 is mounted for operation in the nose of the na¬ celle and means such as a spinner 50 can be provided to

streamline the installation. As shown in FIG. 2, the wing and the propulsor fan can be sized and positioned such that the tips 52 of the fan in their upper arc of travel operate to "suck" the flow from the top sector of the wing. An annular groove 54 can be provided in the inside of the wing to accommodate the tips of the fan to counter problems with clearance, tip losses, vibration, and the like.

Any suitable power plant can be used to drive the fan 24; FIG. 3 shows a turboprop type installation hav¬ ing a gas turbine engine 56 driving the fan through a propeller shaft 58 and gear box 60 arrangement. As is well known, the power plant could also be located in the fuselage 12 instead of in the nacelle and appropriate shafting, gear boxes, and a suitable drive train can be used to drive the fans in the nacelles. As is also well known, cross shafting 62 can be provided for operation in an engine-out condition. The turbine engine can have air intakes 64 and the tail pipe nozzle 66 can be pro- vided with a clamshell door type thrust reverser 68.

The ring tail empennage system is mounted co-axially on the after end 70 of the nacelle by an appropriate tail strut 72 arrangement. (See FIGS. 4 and 5.) Each ring tail has a series of spoilers 74 encircling the inside periphery or throat 76 of the tail in any aerodynamic suitable location parallel to the leading edge 78 of the tail. Around the after end 79 of the ring tail is a thrust vectoring door system 80 which has an operative

-<f ~ relationship with a tail blocker door system 82. A suitable linkage system 84 connects the blocker door system 82 for operation with the thrust reVerser 68.

The leading edge 86 of the doors 88 of the blocker door system 82 are hinged on suitable pivots 90 spaced around the nacelle in the tail region 70 thereof.^ In their stowed condition, the doors are folded down in close streamlined proximity to the nacelle surface. When deployed, they are rotated about their pxvots 90 by a suitable actuating lever arrangement 92 such that their trailing edges 94 are erected into contact with the inside periphery 76 of the ring tail near the trail¬ ing edge thereof to close off longitudinal flow through the ring tail. In their stowed condition, each door 96 of the thrust reverser 68 fits in close streamlined

M proximity against the tail pipe nozzle 66. When ring tail blocker doors 88 are deployed to "close off the flow through the ring tail, linkage system 84 swings the thrust reverser doors 96 about their vertical pivots 98

^■ ' t on the upper and lower end surfaces of nozzle 66 to a i position across the nozzle. With the doors 96 in this position, the efflux from the gas turbine engine is split and deflected laterally to opposite sides such that the reaction forces of the efflux, as indicated by directional arrows 99, are cancelled.

In keeping with common usage, the clamshell door system 68 is referred to herein as a thrust reverser; however, it will be understood that the clamshell doors

-ιo - are used mainly as thrust attenuating means in this in¬ vention rather than thrust reversers as in conventional practice and the thrust reversing function in this invention is served mainly by the blocker door system 82 in conjunction with the thrust vectoring door system 80 of the ring tails.

As shown in FIGS. 4-7, system 80 comprises a series of pairs of doors 100, 102 around the periphery of the ring tail parallel to the trailing edge thereof. Each door has an outside surface 104, and inside surface 106, and side walls 108 and 110 joining the outside and in¬ side surfaces such that an open-ended box-like configur¬ ation results. Doors 100 and 102 are pivotally mounted on pivots 112 and 114 respectively. Suitable actuators 116 are provided to selectively swing the doors between their opened and closed positions and intermediate set¬ tings therebetween by means of a suitable actuator link 118 pivotally connected to the doors by pivots 120, 122. When the thrust vectoring doors 100 and 102 are closed as shown in FIG. 6, their outside 104 and inside 106 surfaces form a continuation of the outside and in¬ side surfaces of the ring tail. This is their configur¬ ation in conventional horizontal flight. In this con¬ figuration, the lateral empennage forces required for control purposes are produced by a selected actuation of the spoilers 74 in the throat of the ring tail. In VTOL flight, however, longitudinal and lateral thrusts for control purposes are produced by a selective actuation

-/ '- of the thrust vectoring doors 100 and 102. For-VTOL flight, the tail blocker door system 82 is deployed to close off the after end of the ring tail and the doors 100 and 102 are opened selectively by the actuators 116 to a position in which the propulsor slipstream which is deflected by the blocker doors 88 is directed out the thrust vectoring doors as indicated by directional ar¬ rows 117 to produce radial control thrusts for VTOL flight. In this invention in conventional powered fLight, the propulsor fans 22 and 24 provide thrust to pxopel the aircraft in a normal manner during all phase's of flight. In VTOL flight, the fans provide a flow* over the airfoils to create lift and the fan slipstream is acted upon by the empennage to modulate horizontal trav¬ el and to supply full positive directional control. The ring wings and tails are efficient airfoils; thus, in unpowered conditions, the aircraft-will glide ^' efficient¬ ly with the wings generating lift and the tails provid- ing directional control such that a controlled forced landing can be made.

The pilot's controls in this aircraft (See FIG. 8) comprise a control stick 124; rudder pedals 126, 128; engine throttle levers 130, 132; and a thrust reverser lever 134. In addition to these more-or-less conven¬ tional controls, the pilot is provided with a tail pe¬ ripheral door vector lever 136 and push buttons 138, 140 and 142, 144 on the control stick for commanding direct

upward and downward vertical forces and direct starboard and port side forces respectively.

Control inputs by the pilot to provide three- dimensional guidance of the aircraft are transmitted by any suitable linkage arrangement to the control means or surfaces to activate them. Preferably the linkage is by a known "fly-by-wire" system in which electrical cir¬ cuitry is connected to electrical actuators at the con¬ trol means or surfaces such that command input signals by the pilot produce the desired control response. (See FIG. 8.) Such control systems are well known and it thus is not believed necessary to go into greater detail with respect thereto.

Engine speed and power are controlled by the throt- tie levers 130-, 132. The thrust reverser lever 134 is used to activate the tail vectoring door system 80, and to deploy and stow the blocker doors 88, the clamshell doors 96, and also the leading edge slats 44. Vector lever 136 controls the collective setting of peripheral doors 100 and 102 of the tail vectoring door system 80 about their pivots 112 and 114 to vector propulsion slipstream in VTOL flight for governing the thrust act¬ ing on the aircraft along its longitudinal axis. In both normal level or in VTOL flight, the control stick 124 commands pitch and roll moments; the rudder pedals 126 and 128, yaw; the vertical side forces buttons 138 and 140 command direct upward or downward forces respec¬ tively in a vertical direction normal to the longitudi-

nal axis of the aircraft; and the side force buttons 142 and 144 command direct starboard and port transverse forces respectively in a direction normal to the longi¬ tudinal axis of the aircraft. When the thrust reverser lever 138 is actuated for VTOL flight, the control stick 124 actuates the vector doors 100 and 102 in the upper or the lower sectors of ' the ring tails to command pitch moments; the ^" rudder ped¬ als 126 and 128 actuate the vector doors in ttie side sectors of the ring tails to command yaw moments; the vector lever 136 commands the modulation of the vectored thrust with respect to the longitudinal axis to hover the aircraft and to produce forward (or backward) motion along that axis. In conventional aircraft, the pilot can exert inde¬ pendent direct control over four degrees of freedom; thrust/drag, pitch, roll, and yaw; In the aircraft of this invention, seven degrees of freedom are afforded; in addition to the conventional four degrees, the..pilot can command a direct vertical upward or .downward force and a direct side force; in addition, in hovering flight, a retrograde motion is available. Ring wings basically have no preferred direction of lift ^" -- tzhe aircraft of this invention can be inverted and the pilot will still retain direct control over the seven degrees of freedom.

The flight control surfaces used to control the aircraft in normal cruise flight are shown in FIG. 9.

In normal cruise flight, the control stick commands pitch moments by actuating the spoilers 74 in the upper and lower sectors in the inside periphery 76 of the ring tails. It may be useful to give a brief exposition of how the actuation of a spoiler in a ring structure such as a ring tail or ring wing results in the generation of transverse forces on the structure. In operation, the propulsor fan (or the forward velocity of the aircraft) moves fluid at a higher velocity across the inside sur¬ face of the ring structure than fluid moves across the outside surface thereof due to any motion of the vehi¬ cle. The differences in relative fluid velocities re¬ sult in pressures that are lower on the inside surface than the pressures on the outside surface. Actuating a spoiler in a sector in the bore of the ring causes a separation of the flow that effectively diminishes the lift in that sector. Diminishing the lift in one inside sector of the ring causes a pressure rise in that region with respect to the lower pressures existing in the other sectors in which the flow over the ring surface is undisturbed. A pressure rise in a particular sector in the throat of the ring airfoil relative to the lower pressure in the other sectors, coupled with the rela- tively higher pressures prevailing circumferentially on the outside of the shroud, produces an unbalance in the forces acting on the ring. Because of this pressure unbalance, there will be a net force acting on the ring

- /y- structure, the vector of the force passing radially out¬ ward through the sector in which the spoiler is acti¬ vated. This force acts normaj. to the longitudinal axis of the fluid flowing through the ring. To roll the aircraft in normal cruise~'flight, the control stick activates the spoilers 30 in the lower sectors in the throats of the ring wings. For yaw mo¬ ments in normal cruise flight, the rudder pedals actuate spoilers 74 in the side sectors in the throats of the ring tails.

A direct lateral force in normal cruise flight without aircraft rotation is by means of spoilers 30 commanded by the side force buttons 142, 144 located on either side of the hand grip of the control stick. The rudder pedals are used to stop or modulate yaw rotation at such time the side forces are being generated by the wings. A direct vertical force without aircraft rota¬ tion in normal cruise flight is by means of spoilers 30, 36 commanded by depressing selectively the vertical side buttons 138, 140 on the front and back of the hand grip of the control stick. The modulation or prevention of rotation in pitch is controlled in the usual manner by the control stick. It will be appreciated that the spoilers that have been actuated are extended into the flow over the wing surfaces opposite those that are pro¬ ducing the forces that are lifting the aircraft. The spoilers will, therefore, disturb the flow thereover and will stagnate that flow. This increases the pressure on

the surfaces over which the flow is disturbed, adding to the lift being generated on the opposite upper surfaces. Thus, although there will be an increase in drag, the added lift will produce a direct vertical force that augments the lift that has maintained the aircraft in cruise flight. Again, the prevention or modulation of rotation in pitch is controlled in the normal manner by use of the control stick.

To initiate the VTOL mode of flight, the thrust reverser lever 134 is actuated, deploying the blocker door system 82, the thrust vectoring door system 80, the clamshell door system 68, and the leading edge slats 44. Flow due to the travel of the aircraft and the propulsor slipstream through the empennages is blocked by the blocker doors 88 and is directed through the thrust vec¬ toring doors 100 and 102. The tail door vector lever 136 is set to adjust collectively the thrust vector of the flow through the vectoring doors to bring the air¬ craft into the hover mode and to control travel in the forward or rearward direction along the longitudinal axis. Selective adjustment of individual pairs of the vectoring doors are mediated by the control stick and rudder pedals for directional control. Extending the leading edge flaps reduces or stagnates possible flow across the under surfaces of the wings to induce to the greater extent possible static pressure conditions thereunder such that the pressure differential between

- n- the upper and lower surfaces of the wings are accentu¬ ated.

The flight controls used to control the aircraft in VTOL flight are shown in FIG. 12. To produce control moments in pitch and yaw in the VTOL mode, the peripher¬ al doors of vectoring door system 80 in tie ring tails are closed selectively by commands generated by move¬ ments of the control stick and rudders to thereby unbal¬ ance the forces on the tails. For yaw control in the VTOL mode, the rudder pedals actuate the peripheral doors 80 selectively in the side sectors of each of the ring tails. "Roll moments in the VTOL mode are controlled as in cruise flight by lateral movements of the control stick. Direct side forces in the VTOL mode of flight as in cruise flight are command¬ ed by depressing the buttons 142 and _144 on the sides of the hand grip of the control stick. However, in VTOL, commands initiated by the rudder pedals actuate tfee pe¬ ripheral doors 80S or 80P rather than spoilers in the ring tails as in cruise flight, to stop or modulate air¬ craft yaw rotation during the generation of direct side forces.

In the VTOL mode, the aircraft travels directly upwards or downwards with control in pitch and yaw being governed as in conventional flight by the control stick and rudder pedals respectively. To take off, the thrust reverser lever 134 is moved to deploy the blocker doors, the clamshell doors, and the leading edge slats, and the

-/f- engine throttles are advanced to generate an airflow over the lifting surfaces. When the propulsor fans move air over the lifting surfaces at a rate sufficient to generate a lift force greater than the weight of the aircraft, it begins to ascend. Whenever there is a change in the engine throttle settings, the tail door vector lever 136 is adjusted accordingly to stop or mod¬ ulate travel along the longitudinal axis of the air¬ craft. If it is desired to increase the rate of ascent at a specific throttle setting, the vertical force but¬ ton 138 on the front of the control stick is depressed. This action causes spoilers 30U and 36U in the upper sector in the throat and the lower sector on the outside of each of the ring wings respectively to be actuated to slow or stagnate the flow over those surfaces, thereby increasing the pressure thereon such that greater lift is produced. Increases in the rate of ascent are also produced by further opening the throttles to provide added lift due to the heightened blowing effect of the propulsors. Horizontal translation along the longitudi¬ nal axis of the aircraft is stopped or modulated by mov¬ ing tail door vector lever 136 to adjust the thrust vec¬ tor of the propulsor efflux issuing from the ring tail peripheral doors to obtain the desired vertical flight path.

The thrust vector of the wing tail peripheral doors has an angular range that will selectively permit rear¬ ward translation of the aircraft; that is, it can be

"backed up" in vertical flight or while hovering (See FIGS. 15-17). Direct downward travel in the VTOL mode is regulated either by throttling back the propulsion engines to reduce the lift generated by the propulsor efflux over the lifting surfaces, or by pressing the vertical force button 140 on the rear of the hand grip of the control stick. Actuating the vertical force but¬ ton causes spoilers 36D on the top sector on the outside of the wings and the spoilers 30S and 30P in- he bottom sector in the throat of the wings to deploy to thereby spoil controllably the lift of the wings. Use of the vertical force button thus permits vertical landing ap¬ proaches to be made using full engine power. Lift is decreased smoothly by the spoilers such that a con- trolled vertical descent is made to a landing. However, the spoilers can be retracted at any time during the descent and the lift being continuously generated by the flow induced over the lifting surfaces by the propulsors will arrest downward motion and the aircraft will hover or can be caused to ascent vertically. Because of the continuous induction of flow by the propulsors oveif. the lifting surfaces, transition to normal cruise flight from the VTOL mode of flight can be made at any time by simply moving the thrust reverser lever 134 to stow the blocker doors, the clamshell doors, and the leading edge slats. The transition from VTOL to conventional flight (and vice versa) is made without a change in the flight attitude of the aircraft and without a loss in altitude.

- Zø-

In addition to the twin wing and propulsor aircraft embodiment described previously herein, the invention can be embodied in an aircraft 150 having a single wing and propulsor. As shown in FIGS. 18-20 illustrating the aircraft in its VTOL mode, such embodiment has a fuse¬ lage 152 with a single ring wing 154 and a single ring tail 156 fixed coaxially there-around by suitable strut arrangements 158 and 160 respectively. Propulsion is provided by a suitable engine 162 driving a propulsion fan 164. The engine has an air intake 166 and a tail pipe 168 which is provided with a clamshell door type thrust attenuator 170. Aircraft 150 is provided with the usual appurtenances such as landing gear and the like (not shown) and has a cockpit with a pilot's posi- tion and controls identical with those of aircraft 10. To avoid prolixity herein, reference should be made, therefore, to the drawings and description of the air¬ craft 10 embodiment for an understanding of the controls and control system of the aircraft 150 embodiment. With respect to the single ring wing 154 of this embodiment, its design and construction is identical to ring wing 14 or 16 of the FIG. 1 embodiment and deploy¬ able inside spoilers 172, outside spoilers 174 and cir¬ culation control slats 176 are provided. An annular groove 178 which extends about the lower 180 and side 182 sectors in the throat 184 of the wing can be pro¬ vided to accommodate the tips of the fan to counter problems with clearance, tip losses, and vibration. The

- ^■ 2.1 - e pennage system 156 of this embodiment also is identi¬ cal in design, construction, and operation to that of the aircraft 10 of FIG. 1. Thus, the empennage system 156 will have spoilers 186, a thrust vectoring door sys- em 188, and a tail blocker door system 190. Actuation of the various elements of the ring wing and the empen¬ nage system by means of the pilot's controls to control the aircraft will be readily understood, with variations that will be obvious in light of the single wing and tail of aircraft 150, if reference is made to the expo¬ sition of the operation of aircraft 10 embodied in FIG. 1. It will also be understood that the spoilers used

•- 4 _< « for control of the aircraft, particularly in the side sectors of the wing and, if need be, the tail, will be properly segmented such that they can be used to produce roll moments.

It will also be appreciated that the invention can be embodied in a channel wing or a wing having an arcu¬ ate configuration less than a closed ring wing. A . - craft 200, as shown in FIGS. 21-23, has a channel wing 202 mounted on its fuselage 204 by a suitable strut ar¬ rangement 206. In this embodiment, the propulsion sys¬ tem has counter-rotating fans 208 and 210 and ring-foil flow straightening means 212 to insure proper flow to the empennage 214, but in every other respect it is identical to aircraft 150 embodied in FIGS. 18-20 except for variations in construction and control incidental to

a channel wing. It will also be appreciated that chan¬ nel wings can be fitted to aircraft 10 instead of wings 14 and 16.