CA1194463A - Propulsion system for a v/stol airplane - Google Patents

Abstract

Abstract of the Disclosure A propulsion system for an airplane to permit it to achieve vertical and/or short take-offs and landings. The propulsion system is integrated into a wing/nacelle unit and includes a thrust vectoring system.
A separate flow turbofan engine is mounted in each wing/nacelle unit. A
system of three flaps is located at the rear of each wing/nacelle unit for de-flecting the turbofan engine exhaust downward, rearward, or any angle in between. These three flaps are arranged to provide a main thrust nozzle in the horizontal flight position without any additional flaps between them.
One flap is located at the wing/nacelle upper surface trailing edge. Two slots are provided at the leading edge of this flap. The upper forward most slot is provided as an exit nozzle for the engine tubine exhaust, which is shrouded from the fan exhaust. The second of these two slots removes a por-tion of the high energy fan exhaust from the fan discharge duct and ejects is over the flap upper surface. The other two flaps are positioned such that, in the horizontal position they are both aligned with the wing/nacelle lower surface and in the vertical position, one is aligned with the wing/nacelle lower surface and the other is aligned with the wing/nacelle upper surface.
When the flaps are in the vertical position, the aft most slot in the upper flap and a slot formed between the upper flap and the lower aft flap provide a means of improving the turning efficiency of the fan exhaust stream.

Description

;3 This invention relates to vertical and/or short takeoff and land-ing ~/STOL1 airplanes and ;n particular to improved method, system9 and apparatus for vector;ng the aircraft engine exhaust flow with a system of trail;ng edge flaps to achieve vertical and/or short takeoffs and landings.
Several types of so called V/STOL aircraft have been proposed.
One type, exemplified in United States Patent 3J096a95~, Bauger et al, uses an articulated cylindrical duc~ through which a turbofan exhaust is discharged.
Thi.s type of system has relatively low efficiency due to large losses in turn-ing the exhaust. One loss occurs in the fan exhaust duct on the outsi.de of the turn, where the turning of the exhaust b~ the nozzle duct wall tends to generate contrarotating vortices. These vortices ~orm a blockage in the duct, causing a thrust loss. Also mixing o~ the fan exhaust with the hot core or turbine exhaust limits the augmentation ratio available because of a require-ment to match the pressures of the two streams.
Another proposal is shown in United States Patent 39330,500 ~.o Winborn. In this propulsive wing type, the fan discharge is vectored through lower surface flaps at approximately the mid cord of the propulsive wing, while the hot turbine exhaust is discharged at the upper trailing edge of the propulsive wing. The discharge of a high energy jet at mid chord on the ].ower surface of the wing will cause high suckdown forces on the wing and may even be large enough to prevent lit-of~.
Another disadvantage of designs such as the Winborn patent re~er-red to above is in the arrangement of the deflecting flaps for the ~an ex haust. Several flaps are spaced across the fan nozzle, forming a cascade and vertically dividing the exhaust stream into several layers. The flaps all pivot downwardly, turning the individual layers o:~ air. The several flaps in the mainstream create drag, causing a loss in thrus~ efficiency.

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;,3 Another disadvantage is that due to their positioning, the total noz7~1e area varies as the flaps move from the horizontal to downward poslt:ions. The variance can detrimentally affect the thrust during transition positions.
Another example of this cascade flap arrangement is shown in United States Patent ~,000~868, Gregor.
One manner in which certain types of airplanes have -improved the lift at low speeds is by bleeding a portion of the jet engine exhaus-t air or fan air over the upper surface of a wing trailing edge flap. An example of this system is shown in United States Patent ~,920,203 ~o Moorehead. The high energy sheet of air being discharged delays or prevents boundary layer air flow separation. Boundary layer separation as used in this context refers to the separation of an airstream flowing over an airfoil from the airfoil surEace. At and after the point of separation, a higher static pressure tur-bulent area exists between the airstream and airfoil, causing drag and re-ducing the lifting potentlal. The high energy sheet of air being ejected over the flap retards or prevents this separation. Also, the jet sheet can induce, by jet pumping action, additional flow over a wing to increase its circulation or li~t, this increased circulation being kno~l as super circula-tion.
Bleeding a portion of the exhaust over a trailing edge flap has been used, wit'n the energy level of the jet sheet at moderate levels, to successfully improve the low speed characteristics of conventional take-oEf and landing airplanes, as shown in the Moorehead patent.
One proposal, shown in United States Patent 2,879,957, Lippisch, proposes to utilize the propulsion system to create super circulation in a V/STOL airplane. One deficiency in the desig~ disclosed therein is that it îs unlikely tha-t the sheet of air could exit through the upper slot since ~2~

higher pressure air exis-ts on the upper surface of the nacelle.
Means would have to be provided -to scoop the airflow ou-t. The Lippisch design also utilizes the high drag cascade system of flaps, and has other disadvantages as well.
It is accordingly a general objec-t of this inven-tion to provide an improved propulsion system for a V/STOL airplane.
The invention provides the method of improving airp]ane fligh-t charac-teristics in a V/S~`OL airplane in which a higher than ambient static pressure flow of exhaust gas from a power means is turned to effec-t the change between flight modes respectively having greater horizontal and grea-ter ver-tical thrust vectors, wherein at least a major portion of said exhaust gas flow is directed through a closed conduit means to exi-t through a thrust producing main nozzle downstream of the power means for powering the airplane in all flight modes varying from horizontal to at least partly vertical; and wherein the exhaust gas flow is turned through an angle from a condition in which the exhaust gas flow is directed predominantly horizontally Eor horizontal thrus-t, -to a condition in which -the exhaust gas flow is direc-ted predominately downwardly -thereby forming a bend when at least partly vertical thrust is desired; said method comprising: bleeding-off -through a second nozzle a second portion of the exhaust gas flow from an outer portion of the bend in said closed conduit means upstrearn of the thrust producing main nozzle exit and downs-tream of the bend leading edge to reduce vortex formation in said conduit means dur-ing at least partly vertical thrust; and direc-ting a bled-off por-tion and said major portion of the exhaust gas flow adjacent each other and oriented towards the same general direction in all fligh-t .~
~-3-modes; whereby increased thrust is avai]able in all flight modes by recovering thrust potential of the bled-off por-tion and achieving high efficiency by eliminating contro-rotating vor-tices when said flow o:E exhaus-t gas is -turned to form a bend.
From another aspect/ the invention provides in a vertical and/or short takeoff and landing (V/STOL) airplane, a propulsion system providing enhanced thrust and airplane handling qualities through more efficient turning of its exhaust be-tween horizon-tal and upward directed flight modes which comprises: propulsion means for generating a higher than ambient static pressure flow of thrust producing exhaust gas; exhaust nozzle means forming a condui-t Eor containing and directin~ at least a portion of said exhaust gas flow from the propulsion means to the airplane exterior, and to turn the flow between substantially horizontal and downwardly direc-ted flow positions; said exhaus-t nozzle means comprising. primary thrust nozzle means for the exit of a major portion of said exhaust gas flow, and secondary thrust nozzle means for bleeding-off a minor portion of the exhaust gas flow; said secondary thrus-t nozzle means positioned in said primary -th.rllst nozzle means -to effect said bleed-off of exhaust gas flow downstream of the commencement of the -turn therein so as substantially to prevent formation of dynamic pressure-induced contra-ro-tating vor-tices in the outside of the turn; and said secondary -thrust nozzle means being directionally movable so as to direct -the bleed-off to flow closely parallel to the major portion of the exhaus-t flow a-t all positions thereof whereby the bleed-off is -turned -together wi-th the major portion of the exhaust flow, -to provide a subs-tantially coherent uni-tary-li.ke exhaust stream passing from said airplane at .~ 3a-all angles of flow from horizontal to downward flow; -thereby maximizing both the -thrus-t from said major por-tion of the flow and the recovery of thrust from said bleed-off flow and improving the handling qualities of the airplane at all positions of turning of -the exhaust gas flow.
The invention further provides a propulsion system for vertical and short take-off and landing airplanes, cornprising: a nacelle comprising a conduit, said nacelle having an upper surface and a lower surface forming an upper surface and a lower surface L0 of an airfoi1, respectively; a fan mounted in said nacelle for pro-viding a flow of propulsive fan exhaus-t; a turbine engine mounted in the nacelle behind the fan and connected to the fan for driving the fan; a fan nozzle and exhaust air turning means located in said nacelle downstream of the fan for discharging fan exhaus-t air at controllable angles between a generally horizontal direc-tion for forward thrust and generally downward direc-tions for vertical thrust, said turning means forming one or more bends; fan exhaus-t air bleed-off means positioned in said conduit for bleeding-off through a nozzle a por-tion of the fan exhaust air stream from an outer portion of the turning means downstream of the leading edge thereof to reduce vortex formation in -the -turned exhaust stream;
an engine nozzle and exhaust turning means located in said nacelle downstream of the engine for discharging engine exhaust downs-tream of a shroud means at a predetermi.ned desired angle between horizon-tal for forward thrus-t and generally downwards for vertical thrust, and forming one or more bends, said shroud means ex-tending from the rear of the engine to the engine nozz]e for separating the engine exhaust from the fan exhaust air un-til the engine exhaust ~-3b-passes through the engine nozzle and exhaus-t turning means and the fan exhaust passes -through the fan nozzle and exhaust air tuxning means; the fan nozzle and exhaust air turning means, the fan exhaus-t air bleed-off means, and the engine nozzle being positioned in close adjacency and oriented to direct all thrus-t in the same general directions in all flight modes to form the exhaus-t streams in a substantially unitary flow immediately downstrearn of -the fan nozzle so as to recover thrust poten-tial from both fan air and engine exhaust in all flight modes.
A propulsion system for a propulsion induced lif-t V/STOL
airplane is disclosed that has wing/nacelle units secured to each side of the fuselage. Each wing/nacelle unit con-tains a turbofan engine posi-tioned ahead of a system of three flaps. An upper flap is positioned at the -trailing edge of the wing/nacelle upper sur-face. Two slots are provided at -the leading edge of this flap.
The engine turbine discharge has a shroud leading to the most for-ward slot for separating its hot turbine exhaust from the fan exhaust and discharging it over the flap. The most rearward slot discharges high energy air from the fan exhaust duct ,;~ -'~`''`";'`"' `''~?i -3c-over the flap.
A lower .~lap is mounted to the trailing edge of the wing/nacelle lo~er surface. An intermediate flap is located behind and in alignmen~ with the lower flap as part of the airfoil lower surface during horizontal fligh~.
All three flaps pivot downwardly to vector the exhaust downward for vertical flight.
The n~ain fan discharge during horizontal flight is through the space between the intermedia~e flap and ~he upper flap, this space being free of additional flaps. For vertical flight, the intermediate flap pivots over to a position below the upper flap9 orming the trailing edge of the airfoil upper surface. A slot between the upper and intermediate flaps during -the vertical flight position bleeds off an additional amount of fan exhaust to improve turning efficiency and to provide additional external boundary layer control.
Accordingly it has been found that more efficient V/STOL aircraft fligh* can be achieved by providing a nacel~ forming an airfoil, wi~h an engine exhaust nozzle formed by a system of trailing edge flaps providing both main o~ primary and auxiliary or secondary exhaust nozzles in which one of the flaps is at the trailing edge of one of the airfoil surfaces ~e.g., lower) in one principal flight position ~e.g., horizontal) and is reposition-able to form the trailing edge of the other (e.g., upper) airfoil surface in the other principal flight position ~e.g., vertical) as the exhaust nozzles are directed between horizontal and vertical flight positions. Such flap can thus be shifted between positions in which it may optionally be a part of either the "upper" or "lower" surfaces of ~he airfoil depending on ~he direction of nozzle thrust with total nozzle area remaining substantial]y con~tant ~or all nozzle directions,or total nozzle area may be made variable according to predetermined aircraft operating requirements. In horizontal and vertical ~light conditions the nozzles can be fully open and unobstructed.
The inventlon will urther be described, by way o-E example only with reerence to the preferred embodiment illustrated in the accompanying drawings, wherein:
Figure 1 is a perspective view of an airplane constructed in accordance with this invention.
Figure 2 is a side elevational view of the airplane of Figure 1.
Figure 3 is a schematic cross-sectional view of the airplane of Figure 1, taken along the line III--III of Figure 6, with the propulsion system shown in the horizontal flight mode.
Figure ~ is a schematic view of the propulsion system, similar to Figu~e 3 but showing the propulsion system in a transistional flight mode.
Figure 5 is a schematic view of the propulsion system, also similar ~o Figure 3 to show the propulsion system in the ~ertical flight mode.
Figure 6 is a top view of the airplane of Figure 1.
Figure 7 is a fragmentary and schematic cross-sectional view o:E
the propulsion system of Figure 3, taken along the line VII-VII of Figure 3.
Figure 8 is a fragmentary and schematic cross-sectional view of ~0 the propulsion system of Figure 3~ taken along the line VIII-~III of Figure 3.
Figure 9 is a fragmentary schematic cross sectional view of the propulsion system of Figure 3, taken along the line IX~-IX of Pigure 3.
Airplane 11, shown in Figures l, 2 and 6, has a fuselage 13 cmd tail section 15 of general configuration common to many types of airplanes.
As shown in Figure 2, the main landing gear 16 folds inside a compartment 18 under each wing 17 during flight. Each wing 17 extends laterally from a pair of wing/nacelles 19 hereafter called nacelles. There are two nacelles, each mounted on a respective opposite side of the :Euselage 13. Nacelles 19 ha~e arl upper surface 21 and a lower surface 23. These surfaces are cur-vilinear when vie~ed in a longitudinal vertical section, as shown in Figures 3-5, but generally straight when viewed in a vertical lateral section, as shown partially in Figures 7~9. The ~Ipper surface 21 and lower surface 23 of each nacelle 19 serve as upper andlower surfaces of a ducted airfoil.
Within each nacelle l9, a vertical partition 2S separates the nacelle into -two compartments. Each compartment has a generally rectangular inlet 27. The nacelle outlet or no~le is also rectangular. The power means for forcing air through nacelle l9 comprises a turbofan engine, having a fan 29 and turbine engine 30 housed in each compartment. Each turhofan engine is a high bypass ratio, low fan pressure ratio engine of generally conventional design. The fan p-ressure ratio is preferably about 1.2 to 1.8 and the nozzle pressure ratio is approximately the same thus producing a higher than ambient static pressure flow of thrust producing exhaust gas.
Referring to Figures 3-5 and 7-9, a shroud 31 is attached to the rear of the turbine engine 30 and extends rearward. As shown also in Figure 6 in phantom, shroud 31 commences at the turbine engine exit as a cylindrical duct~ gradually flattening as it proceeds to the rear. At the trailing edge of the nacelle upper surface 21, the passage formed by shroud 31 is in a general rectangular shape of width greater than height. Shroud 31 contains all of the hot exhaust from the turbine engine 30, indicated in Figures 3-5 as 33. Exhaust air from the fan 29, indicated in Figures 3-5 as 35, passes through the interior 37 of nacelle l9. As shown in Figure 7, forward of the commencement of shroud 31, the fan exhaust 35 passes around the housing for turbine engine 30, being split at the top by a portion of the housing connected to the nacelle interior surface 37. Further downstream, as shown in Figure 9, the ~an exhaust 35 passes beneath the shroud 31.
Referring to Figures 3-5, a plurality of flaps are pivotally secured to the nacelle outlet ~or vectoring the exhaust by turning i-t between a hori-~ontal flight positî.on and a vertical flight position. An upper :Elap 39 is mounted adjacent the trailing edge of the nacelle upper surface 21. Flap 39 is pivotal from the position shown in Figure 3 to that sho~n in Figure 5, and is in the shape of an airfoil. Flap 39 includes a pair of vanes 41, 43 rigidly secured to the upper leading edge of flap 39. Vane 41 is considerably shorter in cord length than flap 39 and is sealed against the trailing edge of the nacelle upper surface 21. Vane 41 moves against this trailing edge while pivoting from the position shown in Figure 3 to that shown i.n Figure 5. Vane 43 is mounted between flap 39 and vane 41, and is also considerably shorter in cord length than flap 39. An upper nozzle or slot 45 exists between vanes 41 and 43. An intermediate nozzle or slot 47 exists between vane 43 and flap 39.
Vane 41 leads~zane 43 slightly~ and vane 43 leads flap 39. Shroud 31 terminates at the upper slot 45. Intermediate slot 47 receives a portion of fan exhaust 35, discharging it over the upper surface of flap 39. Engine turbine exhaust 33 is discharged from upper slot 45~ also over the upper s~rface of flap 39.
Vanes 41 and 43 should be considered as integral parts of flap 39 and pivot directly with it. Slots 45 and 47 should be considered to be found in the leading edge of upper flap 39. Vanes 41~ 43 serve to more efficiently turn a portion of the fan exhaust and engine turbine exhaust as it exits from slots 45 and 47 respectively and flows over the upper surface of flap 39.
A lower flap 49 is pivotally mounted to the nacelle lower surface 23. Flap 49 is in the shape of an airfoil and pivots from the position shown in Figure 3 to that shown in Figure 5. An intermediate flap 51 î.s pivotally mounted to the nacelle 19. Intermediate flap 51 is in the shape of an airfoil and is pivotal from the position shown in Figure 3 to that shown in Figure 5. In the position shown in Figure 5, a lower slot 53 is formed between the leading edge of intermediate flap 51 and the trailing edge of upper flap 39.
Fan flow out slot 53 tends to energize the flow over flap 39 and effect efficient flow turning over the external surface of flap 51.
Each compartment within each nacelle 19 has a separate and identical set of flaps. The width of the flaps and the vertical distance across the nacelle outlet are selected to provide a high aspect ratio opening at slots 45 and 47. That is, the width is much greater than the height.
In operation, in the horizontal flight position as shown in Figure 3, upper flap 39, along with its vanes 41, 43, is generally aligned with the nacelle upper surface 21. That is, flap 39 continues the airfoil upper surface at generally the same rate of curvature as contained on the trailing portion of the nacelle upper surface 21. Upper flap 39 forms the trailing edge of the airfoil upper surface in this position. Hot engine turbine ex-haust 33 is ducted through shroud 31 to the upper slot 45. A portion of the fan exhaust is discharged through the intermediate slot 47. The discharges through these slots retard boundary layer separation on the flap external surfaces and increase flow over the wing/nacelle by jet pumping action, as shown by the longer dashed lines 54 in the drawing. In this position, lower flap 49 and intermediate flap 51 are generally aligned with the nacelle lower surface 23. They continue the airfoil lower surface at generally the same rate of curvature that exists on the trailing portion of the nacelle lower surface 23. Upper flap 39 and intermediate flap 51 define a horizontal flight main thrust nozzle 56 through which the majority of the fan exhaust 35 is dis-charged. IN the horizontal flight position, no additional flaps are located in the horizontal flight main thrust nozzle 56, avoiding unnecessary drag.

In the horizontal 1ight position, the trailing edges of upper flap 39 and intermediate flap 51 are in approximately the same vertical plane. The height of the horizontal flight main thrust nozzle 56 is approximately one-half its width.
Figure 4 illustrates a ~.ransition and STOI, position. The pivoting of the flaps from the position shown ;n Figure 3 to that shown in Figure 5 is continuous with no automatic stop, thus the position sho~l in Figure 4 is one of an infinite number of transition positions. In the position shown - in Pigure ~, upper flap 39 has turned downwardly, turning along with it its vanes 4] and 43, as can be seen as referring *o reference pivok point 55.
Lower flap 49 has turned downward slightlyg although not noticeable by refer-ence to its reference pivot point 57. Intermediate flap 51 has moved away from the lower flap 49 and now splits the majority of the fan exhaust 35 into two separate flow streams, as shown by its reference pivot point 59. Lower flap 49 now becomes the trailing edge of the airfoil lower surace. ~oth the turbine engine exhaust 33 and fan exhaust 35 incline downward and combine aft0r passing through the flaps.
The vertical or upward flight position, used for vertical or sharply angled take-off and landing, is shown in Figure 5. In this position, upper flap 39 and its vanes 41, 43 remain i31 approximately the same position, as shown in Figure 4 with only a small amount of additional movement. Lower f]ap 49 turns downward to a greater degree. Note that the upper surface of lower flap 49 and the lower surface of the nacelle interior 37 form a large radius of curvature to promote turning efficiency. Intermediate flap 51 has pivoted downward further and now has positioned itself to become a part of the airfoil upper surface. Intermediate flap 51 and lower flap 49 define a vertical flight main thrust nozzle 55 that discnarges the majority of the fan exhaust 35. All of the engine turbine exhaust 33 continues to discharge ~hrough the upper slot 45. A portion of fall exhaust 35 discharges through the intermediate slot 47, and another portion through lower slot 53. Air flowing through these three slots or nozzles helps prevent separation of the stream of air 54 flowing over -the airfoil upper surface and induces super circulation or jet pumping of air over the wing. Discharge of a portion of the fan exhaust 35 at the outside of the turn through slots 47 and 53 pre-vents the internal formation of thrust destroying contrarotating vortices.
The thrust potential of the portion of fan exhaust 35 that is bled through slots 47 and 53, and the *urbine exhaust 33 through slot 45, is recovered by jet n~zzles formed cat the slot exits. The flaps are positioned so that the engine turbine exhaust 33 combines with the fan exhaust 35 after exiting through the upper slot 45. In the vertical flight posi~ion, the trailing edges of the intermediate flap 51 and lower flap 49 are substantially in the same horizontal plane. The height of the ver~ical flight mai.n thrust nozzle 58 is approximately one-half its wic7th.
The sum of the areas of slots 45, 47 and horizontal flight main thrust nozzle 56 equals the sum of the areas of slots 45, 47, 53 and vertical flight main thrust nozzle 58. Also, these sums equal all of the sums o:E the areas of slots 45, 47 and the streams of fan air 35 on both sides of i.nter--mediate flap 51 for all transition positions. The to~al nozzle area normally remains cons~ant through all positions, maintaining a constant power match between fan 29 and turbine engine 30. If desirecl, the total -fan nozzle area can be varied in flight according to a predetermi.ned schedule, however, by independently moving certain of the flaps, as a means for thrust control.
In the preferred embodiment, the engine turbine exhaust 33 will comprise only approximately 13% of the total exhaust flow. About 10% of the fan exhaust 35 is discharged through intermediate slot 47, regardless of the flap positi.ons. In the vertical flight position, an additional portion, approximately 5%, of the fan exhaust 35 is discharged through the lower slot 53.
The degree of pivot of the flaps may be determined with reference to the longitudinal axis 61 of the aircraft. For reference purposes9 the angle of inclination of the flaps with respect to the axis 61 is determined herein by drawing a line from the trailing edge of each flap through the approximate center of thickness of each flap. Angle x represents the angle between this center line and ~he longi*udinal axis 61 for upper flap 39.
Angle ~ represents the same angle measurement for the lower flap 49, and angle ~ represents the same angle measurement for the intermediate flap 51.
; In the horizontal flight posi~ion, sho~n in Figure 3, angle ~ is approxima~ely negative 23 degrees, angle ~ is approximately negative 3 degrees, and angle ~ is approximately positive 8 degrees. In the transition position shown in Figure 4, angle ~ has changed to approximately nega~ive 52 degrees, angle to approximately negative 8 degrees, and angle ~ to approximately negative ; 46 degrees. In the vertical flight posi*ion, shown in Figure 5, angle ~ is approximately negative 60 degrees, angle ~ i5 approximately negative 63 de-grees9 and angle ~ îs appro~imately negative 110 degrees. Consequently, be-tween the horizontal and vertical flight positions, the upper flap 39 pivots a total o:~ approximately 37 degrees, the lower flap ~9 pivots a total of approximately 60 degrees and the intermediate ~lap 51 pivots a total o approximatel~ 118 degrees.
It should be apparent tha~ an i.nvention having significant i~prove-ments has been provided. The propulsion system with its system of -flaps per-mits design of a highly efficient vertical and shorttakeoff and landing air-_11-6~3 plane. The discharge of high energy air over the upper surface Elaps retards boundary layer separation and induces super circulation around the airfoil.
The flaps are located so tha~ during horizontal flight and in vertical flight, the main thrust nozzles 56 and 58 are free of drag creating intermediate flaps.
The slots 47 and 53 provided in the vertical flight position bleed-off internal vortices formed by the fan exhaust air stream being turned by the internal noz-zle wall, making turning of the exhaust highly efficient. Separating the en-gine turbine exhaust from the fan exhaust promotes higher propulsion system augmentation ratio by avoiding the interaction of two streams of different pres-sures.
It will be apparent from the foregoing ~see especially drawingsFigures 3, 4 and 5) that the main or primary khrust nozzle means ~56 or 58; or the combination of the nozzles respectively between flaps 39-51 and 51-4~, i~e., between flaps 39 and 49, in transitional flight) discharge a primary vr major portion of the exhaust or exhaust gas flow. Likewise jet or thrust noz-zle means 47 in horizontal and transitional ~i.e.~ more upward or downward an-gled) flight and jet or thrust nozzle means 47 and 5~ in vertical or upward and downward flight are secondary in discharging a minor or bleed-off portion of the exhaust gas flow. Auxiliary nozzle 45, and the exhaust exiting from it that comes from the engine core or turbine, may be considered a part of the primary thrust nozzle means and the major portion of the exhaust gas flow res-pectively, all of the referred to nozzles together making up the exhaust noz-zle means for the exit of the exhaust from the airplane.
It can be seen that turning of the exhaust commences immediately downstream of the fan discharge. Thus, those skilled in the art, from at~ention to the drawings and text, will realize that an internal build-up of dynamic pressure will begin to occure in the vic;nity of the outside wall of the turn 12~

~9~3 due to impingement of the gas against the outer wa~ls of the turn, and that this build-up tends to cause the thrust reducing contrarotating vortices to form in the flow. These will be relieved or prevented, however, in that the slot or nozzle 47 is positioned to effect bleed-off downstream of the leading edge or commencement of the turn, i.e.~ where the obstruction to flow re-sulting from the build-up tends to occure, and will be relieved or prevented again by nozzle 53 downstream thereof where like obstruction may re-occur for like reasons.
It can also be clearly seen in the drawings that the auxiliary thrust nozzle 45 and secondary thrust nozzle means (slots 47 and 53) are tan-demly arranged along the turn and respectively direct the engine core (turhine) exhaust and the bleed-off exhaust substantially tangentially to and over the curved lifting surfaces formed by the flaps, with the core exhaust close a~ove the bleed-off, i.e., the bleed-off between the core exhaust and downstream flap surfaces. These flows individually and together induce supercirculation over the nacelle and retard boundary layer separation theref~m during horizontal and upward angled flight. It is ~rther apparent that such auxiliary thrust nozzle and secondary thrust nozzles are directionally movable so as to direct the core exhaust and bleed-off to flow generally parallel and close to the major portion of the exhaust flow at all positions of flow whereby the core exhaust and bleed-off are turned together with the rest oF the major portion o:F the eYhaust 10w to provide, in its effect, a substantially unitary or co-herent exhaust stream passing from said airplane horizontally and at all turning angles between horizontal and downward flow, i~e., between horizontal and upward flight positions. (See Fi~ures 3, ~ and 5.) As is clear from the drawings, each of the nozzles at all posi-tions of turning or to which directed for exhaus-t of the gas flow, has its noz-zle constriction or throat pos;tioned so as to be maintained at all times substantially at and forming (i.e., coincides with~ the nozzle exit plane unless purposely varied therefrom as indicated above. The effect is to pro-duce the maximum oE velocity and thus thrust from the exiting flow or stream of the exhaust gases and to cause t~rning of all of the exlting exhaust flow through the maximum angle with the maximum velocity thereby enhancing total thrust in all modes of f~ight and producing the coherent flow.
While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptlble to various changes and modifications without departing from the spirit thereof.

Claims (45)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of improving airplane flight characteristics in a V/STOL airplane in which a higher than ambient static pressure flow of exhaust gas from a power means is turned to effect the change between fight modes respectively having greater horizontal and greater vertical thrust vectors, wherein at least a major portion of said exhaust gas flow is directed through a closed con-duit means to exit through a thrust producing main nozzle down-stream of the power means fox powering the airplane in all flight modes varying from horizontal to at least partly vertical; and wherein the exhaust gas flow is turned through an angle from a condition in which the exhaust gas flow is directed predominantly horizontally for horizontal thrust, to a condition in which the exhaust gas flow is directed predominately downwardly thereby form-ing a bend when at least partly vertical thrust is desired;
said method comprising:

bleeding-off through a second nozzle a second portion of the exhaust gas flow from an outer portion of the bend in said closed conduit means upstream of the thrust producing main nozzle exit and downstrearn of the bend leading edge to reduce vortex formation in said conduit means during at least partly vertical thrust; and directing the bled-off portion and said major portion of the exhaust gas flow adjacent each other and oriented towards the same general direction in all flight modes;

whereby increased thrust is available in all flight modes by recovering thrust potential of the bled off portion and achieving high efficiency by eliminating contro-rotating vortices when said flow of exhaust gas is turned to form a bend.

2. The method of claim 1, further comprising directing said second portion over a portion of an airfoil upper surface substan-tially tangent thereto at all positions of turning of the flow for thrust recovery and to improve lift by supercirculation thereover, and reduce boundary layer separation.

3. The method of claim 1 in which the flow direction of said second portion is continuously changed concomitantly to the bend to effect supercirculation and reduce boundary layer separation of the air moving over the airfoil upper surface through all angles of bend.

4. The method of claim 2 in which bleeding-off of said second portion is effected at more than one tandemly arranged location along the outer portion of the bend.

5. The method of claim 3 in which bleeding-off of said second portion is effected at more than one tandemly arranged location along the outer portion of the bend.

6. The method of claim 2 in which the exhaust comprises fan exhaust and turbine engine exhaust and wherein the method further comprises:

maintaining the engine exhaust and the fan exhaust separate from each other until immediately after discharge from the thrust producing main nozzle.

7. The method of claim 1 in which the exhaust gas flow includes fan exhaust and engine exhaust and comprising:

directing the fan exhaust and the engine exhaust through separate thrust producing nozzles;
separating the fan exhaust from the engine exhaust until passing through their respective nozzles;
bleeding-off through a nozzle a portion of the fan exhaust flow from an outer portion of the turn downstream of the leading edge thereof to reduce vortex formation in the turned exhaust stream, and positioning the respective nozzles of the engine exhaust, bleed-off exhaust, and the fan exhaust in all flight modes closely adjacent each other and oriented in the same direction in all flight modes to direct the exhaust streams in a unitary flow in the direction of the thrust vectors so as to recover the thrust potential of all streams in all flight modes.

8. In a vertical and/or short takeoff and landing (V/STOL) airplane, a propulsion system providing enhanced thrust and air-plane handling qualities through more efficient turning of its exhaust between horizontal and upward directed flight modes which comprises:
propulsion means for generating a higher than ambient static pressure flow of thrust producing exhaust gas;
exhaust nozzle means forming a conduit for containing and directing at least a portion of said exhaust gas flow from the pro-pulsion means to the airplane exterior, and to turn the flow between substantially horizontal and downwardly directed flow positions;
said exhaust nozzle means comprising:

primary thrust nozzle means for the exit of a major portion of said exhaust gas flow, and secondary thrust nozzle means for bleeding-off a minor portion of the exhaust gas flow;

said secondary thrust nozzle means positioned in said primary trust nozzle means to effect said bleed-off of exhaust gas flow downstream of the commencement of the turn therein so as sub-stantially to prevent formation of dynamic pressure-induced contra-rotating vortices in the outside of the turn; and said secondary thrust nozzle means being directionally movable so as to direct the bleed-off to flow closely parallel to the major portion of the exhaust flow at all positions thereof whereby the bleed-off is turned together with the major portion of the exhaust flow, to provide a substantially coherent unitary-like exhaust stream passing from said airplane at all angles of flow from horizontal to downward flow;

thereby maximizing both the thrust from said major por-tion of the flow and the recovery of thrust from said bleed-off flow and improving the handling qualities of the airplane at all positions of turning of the exhaust gas flow

9. The propulsion system of claim 8 in which at least one of said primary thrust nozzle means and said secondary thrust nozzle means are in the form of elongated slot means.

10. The propulsion system of claim 8 in which at least one of said primary thrust nozzle means and said secondary thrust nozzle means are formed by at least one movable flap means.

11. The propulsion system of claim 10 in which said at least one movable flap is an airfoil.

12. The propulsion system of claim 9 or 10 in which said respective slot means and flap means are tandemly arranged at successive locations spaced apart along the turn in the exhaust gas flow so that internal vortex formation is avoided along sub-stantially the full extent of the turn at all positions of turning of the flow.

13. The propulsion system of claim 9 in which said slot means are formed by a tandemly arranged series of movable flap means providing lifting surfaces for said airplane and in which said bleed-off exhaust is directable over at least some of said lifting surfaces substantially tangent thereto to retard boundary layer separation during horizontal and transitional flight positions and to enhance the turning of said bleed-off flow together with said major portion of the exhaust gas flow.

14. The propulsion system of claim 13 in which said slot means are positioned adjacent at least one other lifting surface of said airplane whereby said bleed-off exhaust flow induces super-circulation over said other lifting surface for increased lift capability in said airplane.

15. The propulsion system of claim 14 in which said other lifting surface is a nacelle.

16. The propulsion system of claim 13 in which said propulsion means is a high by-pass ratio turbofan engine and the engine core exhaust is caused to exit from said airplane upstream of the exit of the exhaust from the engine fan.

17. The propulsion system of claim 16 in which said bleed-off issues from the fan exhaust of the turbofan engine and is directed over said at least some of said lifting surfaces between said surfaces and said core exhaust.

18. The propulsion system of claim 16 in which said nozzle means for exit of the core and fan exhaust are positioned closely adjacent one another to facilitate combining the flows so as to exit from the airplane as a coherent, unitary-like exhaust gas stream.

19. The propulsion system of claim 8 in which said exhaust nozzle means provides a constant nozzle area at the nozzle exit at all positions of nozzle turning.

20. The propulsion system of claim 8 comprising:
a nacelle having an upper surface and a lower surface forming an upper surface and a lower surface of an airfoil, respectively;

the exhaust gas being discharged between the upper and lower surfaces of the nacelle and out through said exhaust nozzle means;
said secondary thrust nozzle means comprising slot means for bleeding off a portion of the exhaust at the outer side of the bend, to reduce contra-rotating vortex formation, and for discharg-ing the bleed-off portion over a part of the upper surface of the airfoil to reduce boundary layer separation and effect super circulation.

21. A propulsion system for vertical and short take-off and landing airplanes, comprising:

a nacelle comprising a conduit, said nacelle having an upper surface and a lower surface forming an upper surface and a lower surface of an airfoil, respectively;

a fan mounted in said nacelle for providing a flow of propulsive fan exhaust;

a turbine engine mounted in the nacelle behind the fan and connected to the fan for driving the fan;

a fan nozzle and exhaust air turning means located in said nacelle downstream of the fan for discharging fan exhaust air at controllable angles between a generally horizontal direction for forward thrust and generally downward directions for vertical thrust, said turning means forming one or more bends;

fan exhaust air bleed-off means positioned in said conduit for bleeding-off through a nozzle a portion of the fan exhaust air stream from an outer portion of the turning means downstream of the leading edge thereof to reduce vortex formation in the turned exhaust stream;

an engine nozzle and exhaust turning means located in said nacelle downstream of the engine for discharging engine exhaust downstream of a shroud means at a predetermined desired angle between horizontal for forward thrust and generally downwards for vertical thrust, and forming one or more bends, said shroud means extending from the rear of the engine to the engine nozzle for separating the engine exhaust from the fan exhaust air until the engine exhaust passes through the engine nozzle and exhaust turning means and the fan exhaust passes through the fan nozzle and exhaust air turning means;

the fan nozzle and exhaust air turning means, the fan exhaust air bleed-off means, and the engine nozzle being positioned in close adjacency and oriented to direct all thrust in the same general directions in all flight modes to form the exhaust streams in a substantially unitary flow immediately downstream of the fan nozzle so as to recover thrust potential from both fan air and engine exhaust in all flight modes.

22. The propulsion system according to claim 21 wherein the fan nozzle and exhaust turning means comprises a plurality of flaps mounted to the nacelle, with one of the flaps being an upper flap positioned at the nacelle upper surface to form a part of the airfoil upper surface, the upper flap having fan exhaust slot means for discharging a portion of the fan exhaust over the upper flap in the horizontal and the vertical flight positions and all positions in between to increase induced circulation over the airfoil upper surface.

23. The propulsion system according to claim 22 wherein the engine nozzle and exhaust turning means comprises engine exhaust slot means adjacent the fan exhaust slot means for discharging the engine exhaust over the upper flap in the horizontal and the verti-cal flight positions and all positions in between to increase induced circulation over the airfoil upper surface.

24. The propulsion system according to claim 23 wherein the fan and engine nozzles are located at the trailing edge of the nacelle in all flight positions to minimize suckdown forces on the airfoil lower surface.

25. A propulsion system for a vertical and/or short takeoff and landing airplane, comprising: a duct having an upper surface and a lower surface respectively forming an upper surface and a lower surface of an airfoil;
means for forcing a flow of higher than ambient static pressure propulsion gas through said duct;
an upper flap located near the trailing edge of the duct upper surface and forming a part of the airfoil upper surface, the upper flap being pivotal from a horizontal flight position in which it is generally aligned with the duct upper surface to an upward flight position in which the upper flap points generally downward;
a lower flap adjacent the trailing edge of the duct lower surface and forming a part of the airfoil lower surface, the lower flap being pivotal from a horizontal flight position generally aligned with the duct lower surface to an upward flight position in which the lower flap points generally downward; and an intermediate flap operative with the duct and pivotal between a horizontal flight position in which the intermediate flap is rearward of the lower flap, generally aligned with the duct lower surface and forming a part of the airfoil lower surface and an up-ward, or vertical, flight position in which the leading edge of the intermediate flap is adjacent the trailing edge of the upper flap and in which the intermediate flap points generally downward, be-coming the trailing edge of the airfoil upper surface; in the horizontal flight position, the space between the upper flap and the intermediate flap defining a horizontal flight main thrust nozzle;
and in the upward, or vertical, flight position, the space between the lower flap and intermediate flap defining an upward, or vertical, flight main thrust nozzle.

26. A propulsion system for a vertical and short takeoff and landing airplane, comprising:
a nacelle having an upper surface and a lower surface forming an upper surface and a lower surface of an airfoil, respec-tively;
a turbo-fan engine mounted in the nacelle for providing a propulsive exhaust gas flow stream at higher than ambient static pressure;
said nacelle providing a conduit for containing and directing said flow stream;
fan exhaust nozzle means in said conduit downstream of the engine for discharging fan exhaust;
turbine exhaust nozzle means attached to the end of a second conduit and located at the discharge end thereof for discharg-ing turbine exhaust;
shroud means forming said second conduit extending from the rear of the turbine to the turbine exhaust nozzle means for separating the turbine exhaust from the fan exhaust until the tur-bine exhaust passes through the turbine exhaust nozzle means and the fan exhaust passes through the fan exhaust nozzle means for pre-venting undesired internal interaction between the two flows of exhaust gas;
said shroud means and turbine exhaust nozzle means posi-tioned to discharge said turbine engine exhaust to the exterior upstream of the discharge to the exterior of the exhaust from the fan; and said fan and turbine exhaust nozzle means each being directionally movable and adapted to effect turning of the exhaust from said nozzle means together as a coherent, unitary-like stream exiting from said airplane.

27. The propulsion system according to claim 26 wherein the fan and engine nozzle means are located at the trailing edge of the nacelle in all flight positions to reduce suck-down forces on the airfoil lower surface.

28. In a V/STOL airplane, a propulsion system for efficiently turning its exhaust between horizontal and upward or vertical light, the system comprising:
propulsion means located in the airplane; said propulsion means being capable of providing sustained super atmospheric pressure for propulsion;
flap means located in a portion of the airplane to form a thrust nozzle for the exhaust of the propulsion means and being movable to direct the exhaust between horizontal and upward or vertical flight positions; said flap means being capable of form-ing a thrust nozzle able to sustain said super atmospheric pressure upstream of its exit in all positions;
slot means formed adjacent leading edges of selected flap means to bleed-off a portion of the exhaust so as to minimize the formation of thrust inhibiting vortices in the turning exhaust during transitional and vertical flight, thus increasing the thrust efficiency of the vectored exhaust;
said flap means and slot means Forming a series of mov-able and directional thrust nozzles to vector a portion of the exhaust incrementally over upper surfaces of the flap means to induce super circulation over adjacent lifting surfaces and prevent boundary layer separation therefrom during horizontal and transi-tional flight;
said thrust nozzle flap means and said thrust nozzle slot means being effective to turn the exhaust progressively between desired positions from horizontal to vertical or upward flight.

29. The propulsion system of claim 28 in which the throat of each nozzle means is respectively maintained at the exit plane of each such nozzle means at all flight positions and at all positions of turning from horizontal to downward or vertically directed flow.

30. The propulsion system of claim 28 in which the total nozzle area remains constant through all positions of nozzle turning.

31. In a V/STOL airplane, a propulsion system for efficiently turning its exhaust between horizontal and upward flight, the system comprising:
a nacelle;
propulsion means located in the nacelle; said propulsion means being capable of providing sustained super atmospheric pressure for propulsion;
plural flaps located in a rearward portion of the nacelle to form a thrust nozzle for the exhaust of the propulsion means and being movable between horizontal and upward flight positions;
said plural flaps being capable of forming a thrust nozzle capable of sustaining said super atmospheric pressure upstream of its exit in all positions;
plural slots serially arranged along adjacent leading edges of selected flaps at least one such slot effective to bleed-off a portion of the exhaust over the upper surfaces of selected flaps to induce super circulation and prevent boundary layer separation during horizontal and transitional flight;
said slots during transitional and upward flight, due to bleed-off, minimizing the formation of counter rotating vortices in the turning exhaust thus increasing the thrust efficiency of the vectored exhaust;
the flaps and slots forming a series of movable and directional thrust nozzles to incrementally vector the bleed-off along the upper surfaces of selected flaps and turn the exhaust progressively downward for upward flight.

32. The V/STOL airplane of claims 28 or 31 in which the exhaust is turnable at least ninety degrees thus providing for said airplane to achieve substantially vertical flight.

33. The propulsion system of claims 28 or 31 in which a portion of said exhaust is turnable up to about 118 degrees.

34. In a V/STOL airplane, a propulsion system for efficiently turning its exhaust between horizontal and upward flight, the system comprising:
a nacelle;
a turbofan engine located in the nacelle; said turbofan engine being capable of providing sustained super atmospheric pressure for propulsion;
a shroud in the nacelle to contain the engine exhaust and separate it from the fan exhaust;
plural flaps located in series in a rearward portion of the nacelle to form a thrust nozzle for the exhaust of the turbo-fan engine and being movable between horizontal and upward flight positions; said plural flaps being capable of forming a thrust nozzle capable of sustaining said super atmospheric pressure up-stream of its exit in all positions;

slot means formed in series adjacent leading edges of the flaps to receive the engine exhaust from the shroud and bleed-off a portion of the fan exhaust over the upper surfaces of selected ones of the flaps to induce super circulation and prevent boundary layer separation during horizontal and transitional flight;
said slot means during transitional and upward flight, due to the bleed-off, minimizing the formation of counter rotating vortices in the turning exhaust thus increasing the thrust efficiency of the vectored exhaust;
said slot means and flaps forming a series of movable and directional thrust nozzles to vector the bleed-off exhaust along the upper surfaces of the selected flaps and turn the exhaust progressively downward for upward flight.

35. In a V/STOL airplane, a propulsion system for efficiently turning its exhaust between horizontal and vertical flight, the system comprising:
propulsion means located in the airplane; said propulsion means being capable of providing sustained super atmospheric pressure for propulsion;
flap means located in a portion of the airplane to form a thrust nozzle for the exhaust of the propulsion means and being movable to direct the exhaust between horizontal and vertical flight positions; said flap means being capable of forming a thrust nozzle capable of sustaining said super atmospheric pressure upstream of its exit in all positions;
slot means formed adjacent leading edges of selected flap means to bleed-off a portion of the exhaust over the upper surfaces of the flap means to induce super circulation over adjacent sur-faces and prevent boundary layer separation during horizontal and transitional flight;
said slot means during transitional and vertical flight, due to the bleed-off, minimizing the formation of counter rotating vortices in the turning exhaust thus increasing the thrust efficiency of the vectored exhaust;
said slot means forming a series of movable and direc-tional thrust nozzles to vector the bleed-off of the exhaust incrementally along upper surfaces of the flap means and turn the exhaust from the slot means progressively ninety degrees for vertical flight.

36. The propulsion system according to claim 21 wherein flaps are positioned apart from each other in the horizontal and vertical flight positions to define a main thrust nozzle, free of additional flaps, for discharging the majority of the exhaust from the fan.

37. A propulsion system for a vertical and short takeoff and landing airplane, comprising:
a nacelle having an upper surface and a lower surface forming an upper surface and a lower surface of an airfoil, respectively;
turbine driven fan means for forcing air through the nacelle;
an upper flap located near the trailing edge of the nacelle upper surface and forming a part of the airfoil upper sur-face, the upper flap being pivotal from a horizontal flight posi-tion generally aligned with the nacelle upper surface to a vertical flight position pointing generally downward;
a lower flap adjacent the trailing edge of the nacelle lower surface and forming a part of the airfoil lower surface, the lower flap being pivotal from a horizontal flight position general-ly aligned with the nacelle lower surface to a vertical flight position pointing generally downward; and an intermediate flap secured to the nacelle and pivotal between a horizontal flight position in which the intermediate flap is rearward of the lower flap, generally aligned with the nacelle lower surface and forming a part of the airfoil lower surface and a vertical flight position in which the leading edge of the inter-mediate flap is adjacent the trailing edge of the upper flap and in which the intermediate flap points generally downward, becoming the trailing edge of the airfoil upper surface;
in the horizontal flight position, the space between the upper flap and the intermediate flap defining a horizontal flight main thrust nozzle; and in the vertical flight position, the space between the lower flap and intermediate flap defining a vertical flight main thrust nozzle.

38. The propulsion system according to claim 37 wherein the upper flap is positioned from the trailing edge of the nacelle upper surface a selected distance so that a portion of the fan means exhaust flows over the upper flap.

39. The propulsion system according to claim 37 wherein a slot is located between the leading edge of the upper flap and the nacelle upper surface, wherein the turbine driven fan means com-prises a fan and a turbine engine in the nacelle, and further com-prising a shroud extending from the rear of the turbine engine to the slot for separating turbine engine exhaust from fan exhaust upstream of the slot.

40. The propulsion system according to claim 37 wherein the upper flap has a pair of vanes secured to the upper flap in a space between the upper flap and the nacelle upper surface, one above the other, the vanes being spaced apart from each other and from the upper surface of the upper flap, defining an upper slot and an intermediate slot and wherein the turbine driven fan means comprises a fan and a turbine engine in the nacelle, and further comprising a shroud extending from the rear of the turbine engine and terminating at the upper slot for discharging the engine turbine exhaust, the intermediate slot discharging a portion of the fan exhaust.

41. The propulsion system according to claim 37 wherein in the vertical flight position, the leading edge of the intermediate flap is separated from the trailing edge of the upper flap by a selected distance for creating a slot to discharge a portion of the fan means exhaust to improve turning efficiency.

42. A propulsion system for a vertical and short takeoff and landing airplane, comprising:
a nacelle having an upper surface and a lower surface forming an upper surface and a lower surface of an airfoil, respectively;
the nacelle having a generally rectangular inlet and out-let;

a turbofan engine, including a fan and a turbine engine, both mounted in the nacelle;
an upper flap pivotally secured adjacent the trailing edge of the nacelle and forming a part of the airfoil upper sur-face, the upper flap having a pair of vanes secured between the upper surface of the upper flap and the trailing edge of the nacelle upper surface; the vanes being secured to the upper flap and pivotal with the upper flap, the vanes being spaced vertically apart from each other and vertically from the upper surface of the upper flap, defining an upper slot and an intermediate slot, the intermediate slot discharging a portion of the fan exhaust, the upper flap being pivotal between a horizontal flight position generally aligned with the nacelle upper surface, and a vertical flight position pointing generally downward for vectoring fan and engine exhaust downward;
a shroud extending from the rear of the turbine engine to the upper slot for discharging the engine exhaust separate from the fan exhaust;
a lower flap pivotally secured to the nacelle lower sur-face and forming a part of the airfoil lower surface, the lower flap being pivotal between a horizontal flight position generally aligned with the nacelle lower surface and a vertical flight posi-tion, pointing generally downward to vector the fan exhaust down-ward; and an intermediate flap pivotally secured to the nacelle and pivotal between a horizontal flight position to the rear of the lower flap and forming a part of the airfoil lower surface, and a vertical flight position below the upper flap, pointing generally downward and forming a part of the airfoil upper surface; in the vertical flight position, the upper flap and intermediate flap being positioned with a lower slot between their trailing and lead-ing edges, respectively, for discharging a portion of the fan exhaust;
in the horizontal flight position, the upper and inter-mediate flaps defining a horizontal flight main thrust nozzle;
in the vertical flight position, the lower and inter-mediate flaps defining a vertical flight main thrust nozzle;
normally, the sum of the areas of the upper slot, inter-mediate slot, and horizontal flight main thrust nozzle being sub-stantially equal to the sum of the areas of the upper slot, inter-mediate slot, lower slot and vertical flight main thrust nozzle, and also equal to the sum of the areas of all the slots and the spaces between the flaps in all transition positions, and the flaps also may be actuated such that the sum of the areas of the slots and the nozzles vary according to a predetermined schedule in any flight position from horizontal to vertical.

43. The propulsion system according to claim 42 wherein in the horizontal flight position, substantially 10 percent of the fan exhaust is discharged through the intermediate slot, the remainder being discharged through the horizontal flight main thrust nozzle.

44. The propulsion system according to claim 42 wherein in the vertical flight position, substantially 10 percent of the fan exhaust is discharged through the intermediate slot J and substan-tially 5 percent of the fan exhaust is discharged through the lower slot, with the remainder being discharged through the vertical flight main thrust nozzle.

45. The propulsion system according to claim 42 wherein between the horizontal and vertical flight positions, a centerline drawn through the upper flap pivots substantially from a negative angle of 23 degrees to a negative angle of 60 degrees, and wherein a centerline through the lower flap pivots substantially from an angle of negative 3 degrees to negative 63 degrees, and wherein a centerline through the intermediate flap pivots substantially from an angle of positive 8 degrees to negative 110 degrees, all with respect to the longitudinal axis of the airplane.