Recent Patents on Mechanical Engineering 2010, 3, 000-000 1 Channel Wing as a Potential VTOL/STOL Aero-Vehicle Concept Zeki O. Gokce* and Cengiz Camci Turbomachinery Aero-Heat Transfer Laboratory, Department of Aerospace Engineering, The Pennsylvania State University, 223 Hammond Building, University Park, PA 16802, USA Received: June 10, 2009; Accepted: August 24, 2009; Revised: September 10, 2009 Abstract: Low-cost, high efficiency, multi-purpose and compact aircraft capable of Vertical Takeoff and Landing (VTOL) or Short Takeoff and Landing (STOL) flight have long been desired by the aerospace community. The channel wing concept, first proposed by Willard Custer in the late 1940s’, is a promising candidate for efficient V/STOL performance. A channel wing has an upwardly opening semi-cylindrical channel placed near the aircraft fuselage. A propulsion unit is mounted in the channel; usually a propeller located towards the rear. When the propeller is operated at static or low speed conditions, the speed of the air flowing through the channel is much higher than that of the air flowing below the wing. As a result, high lift is generated. The concept was brought to life in prototype airplanes manufactured by the Custer Channel Wing Corporation in the 1950s’ and the 1960s’, but these designs had a number of problems. The improvements in aerospace technology since then and recent developments in circulation control technology may facilitate the realization of a superior channel wing configuration. This paper presents a comprehensive review of the most significant patents on this subject and concludes with comments on possible future developments. Keywords: Channel wing, circulation control, boundary layer removal, tilting channel & curved wing. 1. INTRODUCTION within the channel, close to its trailing edge, air can be sucked over the channel surface. The reason for putting the Vertical Takeoff and Landing (VTOL) and Short Takeoff propulsion system near the trailing edge is to use the and Landing (STOL) flight has been one of the main maximum possible channel surface to generate lift. When the interests of both the civilian and military aviation engine is running, and the aircraft is standing still or is communities throughout the history of flight. Today, several moving with a low forward speed, the speed of the air aircraft capable of achieving V/STOL flight exist. The most flowing through the channel is high with respect to the speed common type of such aircraft is the helicopter. A fixed-wing of the air below the channel surface. Thus, a high pressure V/STOL capable aircraft is the Harrier jet, and the V-22 is a region below the channel and a low pressure region over the fixed wing airplane with a turboshaft engine that can be channel are created. Consequently, a high amount of lift is tilted. However, despite the advantages they possess, all generated that could not normally be produced by a these aircraft have setbacks that result from their operating conventional wing arrangement. At high speeds, the benefit principles. Helicopters are limited to a certain maximum derived from using the channel is eliminated but the aircraft speed due to compressibility effects and drag on their rotor can continue to fly unimpeded since the projected areas of blades, the Harrier consumes huge amounts of fuel, and the the channels and the fixed wing portions can generate V-22 is heavy due its mechanically complex engine enough lift. arrangement. All these aircraft perform well, yet their setbacks and/or limitations result in the need for a more efficient, all-around V/STOL aircraft. One possible solution to this issue is the channel wing design, first conceived by Willard Custer during the 1940s’. Custer proposed that it is the speed of the air flowing over the wing that creates lift, and not the speed of the wing through the air. Hence, he came up with the idea of the “channel wing”. As the name implies, the channel wing contains a semi-cylindrical or U-shaped channel. The channel wing is formed by merging the channel and a fixed wing portion that extends from one side of the channel. Figure 1 shows the arrangement in Custer’s final design. The channel surface is airfoiled, thus it can generate lift when air flows over it. With the placement of a propulsion system *Address correspondence to this author at the Turbomachinery Aero-Heat Transfer Laboratory, Department of Aerospace Engineering, The Pennsylvania State University, 223 Hammond Building, University Park, PA 16802, USA; Tel.: +1-814-321 7567; Fax: +1-814-865 7092; Fig. (1). The CCW-5 channel wing aircraft designed by William E-mail: [email protected], [email protected] Custer. 1874-477X/10 $100.00+.00 © 2010 Bentham Science Publishers Ltd. 2 Recent Patents on Mechanical Engineering 2010, Vol. 3, No. 1 Gokce and Camci If they achieve all the desired capabilities, channel wing engine, and they have a variable pitch configuration so as to airplanes could be beneficial for a number of applications. improve forward flight capabilities. The propellers could be They could be used by civilians as a personal aircraft, since placed behind or forward of the channel edges, as long as they require no runway or a very small one. In addition, they they are very close to the edge. This is done in order to can fly at speeds similar to other commercial, small size reduce tip losses. It is also suggested that the leading edge aircraft like the Cessna 172. Their hovering capabilities propeller's blades feather so as to cut back on speed during would make them very useful for other civilian purposes like landing. A way to control the feathering using the engine firefighting or rescue missions. Their properties described and/or other controls must be installed. above would naturally render them quite useful to the military as well. They could be stored within a very small area, like a small pocket camouflaged by trees, and take off whenever needed. They could easily depart from carriers and conduct similar missions to the V-22, while costing much less since they would not have the mechanical complexity of said aircraft. Custer took a number of patents on the channel wing concept. He and his company designed and produced prototype airplanes based on this design. The airplanes were effective at low speeds but a number of complications arose during cruise, high speed flight and landing. Recently, researchers from Georgia Tech proposed the idea of using pneumatic blowing slots to solve the problems of the basic channel wing design. Various modifications and solution methods have also been proposed by other inventors. This paper analyzes the patents obtained by Custer as well as by other inventors. To the best of the authors' knowledge, the patents chosen for inclusion in this review represent the most significant patent studies related to the subject, starting with the pioneering work done by Custer, and continuing with patents that are considered worthy of Fig. (2). Multiple propeller channel wing [1]. mention due to their contributions to the evolution of the basic channel wing concept. To honor his historical and scientific precedence, the paper begins with patents obtained A design having a movable channel has also been by Custer and continues with the patents of other resear- proposed [2]. The channels are arranged such that they can chers. Descriptions of each patent are provided to summarize be tilted (rotated about a lateral axis extending from one the development of the channel wing design until our time; wing tip to the other). The channels are tilted up during take- continued with a summary of previous articles on the subject off, and they're at a horizontal position during cruise. and concluded with suggestions on possible further improve- Vertical fins extend above the channel upper end and below ments. To the authors’ knowledge, this paper is the first the channel bottom surface. They isolate the stream within review article published on the subject. the channel (preventing outside air from entering the channel), and they contain rudders. Elevators are mounted 2. PHYSICAL PRINCIPLE behind the propeller discs so as to provide control and additional lift production. The propellers are located almost The basic idea of the channel wing concept is to make at the channel trailing edge; this is done in order to stop air use of the high speed of the air which flows over the channel flowing below the channel surface from entering the channel when air is sucked over the channel via a propulsion unit. stream, and make maximum use of the lift generated by the This situation is especially pronounced when the aircraft is channel. The aircraft's fuselage is rather short because the static or it is moving at a low speed, because there is a large author believes sufficient control is attained using the tail difference in the speed of the air which flows below and rudder and the rudders situated on the fins. The control above the channel. As a result, a high amount of lift is surfaces and tilting channels are controlled via conventional produced, even when the aircraft is moving slowly. methods through the cockpit. It is stated that good results in terms of lift production have been obtained when the 3. CHANNEL WING PATENTS & ARTICLES propellers are operated at 4000 revolutions per minute (rpms). This patent is the first to mention that the propellers 3.1. Patents by Custer on either side of the fuselage rotate in opposite directions. The aircraft design presented in Custer’s first patent has a A design based on a tailless fuselage employs the channel conventional fuselage with a conventional tail, and a channel wing concept so as to increase the overall efficiency of the wing superimposed on this structure [1]. The design can be aircraft, as seen in Fig. (3) [3]. Experiments have proven that seen in Fig. (2). A pair of propellers is located inside one this type of construction is indeed beneficial. Further goals channel; one fore and one aft. They're operated by the same are to increase the static and in-flight lift. The best results in Channel Wing as an Aero-Vehicle Concept Recent Patents on Mechanical Engineering 2010, Vol. 3, No. 1 3 lift production have been obtained with a channel chord Changing the tail arrangement to a single-vertical tail and smaller than the propeller radius, and when the propeller is modifying the channel setup so that the channel only extends placed very close to the rear end of the channel. This up to 50% of the wing chord, Custer proposes another design situation becomes more pronounced when the distance as seen in Fig. (5) [5]. This is done in order improve the low- between the propeller disk and the rear end is about 1.27 speed lift production capabilities of the aircraft without centimeters. It is noted that a 50% increase in lift is obtained compromising forward flight performance. The chord of the under static conditions and an important increase in in-flight channel is approximately equal to half of the propeller lift is attained. The channel may merge with the wing at the diameter. A different version of the design, seen in Fig. (6), leading edge, or extend beyond it if desired. Since there is no uses a single channel located at the mid portion of the wings. conventional tail on the airplane, in order to control it, it is An engine located inside the fuselage drives a propeller suggested to add a rudder to the rear part of the engine, and which is located at the rear edge of the fuselage. Fins which to put ailerons and elevators on the wing. are similar in construction to the ones described in previous patents protrude upwards of the channel sides, and they extend backwards along the aircraft's longitudinal axis in order to support a boom-tail structure. The rest of the aircraft's operational principles are similar to the first design. Fig. (3). Tailless channel wing design [3]. Custer obtained a patent for a modified version of the conventional fuselage, tail and channel wing combination in 1950 [4]. In this design, rudder-like devices can be attached to the fins that extend rearward from the side-walls of the channel. Two plates that connect the fuselage and the outboard wing portion extend over the channel, and they act as spars. The inner ailerons seen in Fig. (4), are used in Fig. (5). Channel wing airplane [5]. moderate to low speed range operations, whereas the outboard ones are used when the aircraft is approaching the runway and is in need of excessive lift. As a modification to the previous conclusion about the propeller disk – trailing edge gap, it is noted that this distance should be less than 1/6 of the propeller diameter. The depth of the channel should be almost constant when viewed from the front to the rear edge. The thickness of the airfoil is high at the mid portion of the channel, and it gradually decreases towards the side walls. Fig. (6). Boom-tail arrangement [5]. Boundary layer removal (BLR) can be extremely bene- ficial for aircraft, especially if turbulent conditions occur over the aircraft’s wings. Custer patented an interesting system that achieved this by using the flow conditions just before and after the propeller slipstream, as seen in Fig. (7) Fig. (4). Conventional fuselage, tail and channel wing combination & Fig. (8) [6]. BLR slots are located behind the maximum [4]. thickness point of the airfoil. This helps the process because 4 Recent Patents on Mechanical Engineering 2010, Vol. 3, No. 1 Gokce and Camci air pressure increases over the airfoil surface when air Another idea developed by Custer is to use an aircraft proceeds rearwards of that point. Two such slots extend over having multiple channels placed in tandem on their wings, as the top of the wing. When the propeller is operated in the seen in Fig. (9) & Fig. (10) [7]. This configuration produces channel, a low-pressure zone which draws the air (or large increases in lift production, when compared to the boundary layer) from the slots through the conduits is classical channel wing configuration with a single channel created. The air drawn is exhausted from openings located placed on either side of the fuselage. Custer mentions that just in front of the propeller disc. The air which passes over this conclusion has been drawn from experiments. The the openings of the ducts which are radially positioned on design comprises of a fuselage and tail of conventional the channel surface, behind the propeller disk, creates a low construction. The wings are also similar to previous Custer pressure at that region. As an additional BLR operation, air designs; however, this time there are multiple (a pair of) is drawn from the secondary slots located aft of the primary channels placed on either side of the fuselage. Ailerons are slots, into the conduits; then it is exhausted via the ducts. mounted on the fuselage between the channels to further The openings of the ducts have a triangular cross-sectional increase the amount of lift produced by the channels. Addi- shape which forces the flow to proceed rearward. The chan- tional control surfaces are placed on the tail and outboard nels have the previously mentioned vertical fins installed at wings. A pair of propellers is driven by a single engine their sides so as to prevent the air flowing over the outboard mounted on the aircraft. wings to mix with the channel flow. Fig. (9). Top view of the multiple channel wing design [7]. Fig. (7). Isometric view of the BLR system [6]. Fig. (10). Side/isometric view of the pair of channels [7]. Custer obtained a patent for a modified version of his basic design in which the fuselage, tail and channel wing arrangements are all the same; however, the outboard wing extending laterally from the channel outer wall is now made movable, for extended lift and control purposes [8]. Fig. (11) & Fig. (12) depict this concept. The movable wing is con- nected with a shaft which originates from inside the fuselage, continues through the channel and connects with the movable wing. The shaft supports the wing and controls its Fig. (8). Rear view of the BLR system [6]. rotation. The control mechanism for the movable wing is a conventional one and it is situated inside the cockpit. Channel Wing as an Aero-Vehicle Concept Recent Patents on Mechanical Engineering 2010, Vol. 3, No. 1 5 Fig. (11). Side view of the movable wing and the aircraft using such a system [8]. Fig. (13). Top and front views of the basic jet-propelled design [9]. design consists of a tubular fuselage having a channel inlet and channel exit. The jet tube contains a motor mounted inside. The third alternative has two tubes connected to the fuselage. The fore and aft portions of the tube are open so as Fig. (12). Close-up view of the movable wing [8]. to have the form of a channel. The jet tube has a motor mounted inside, and said tube has the classical curvature of a Custer’s first channel wing patent which involves jet jet engine. propulsion was obtained in 1952 [9]. Fig. (13) shows this jet Another method is to place the jet engines near the aircraft design. The upwardly opening semi-cylindrical chan- leading edge [10]. This way, the high exit velocity of the jet nel increases the take-off and landing stability of jet aircraft engine flows over the entire channel surface and the aircraft by making use of the increased lift capabilities of the channel makes maximum use of the channel wing concept. Fig. (14) wing. Decreasing the take-off/landing distance is also one of depicts said concept. the goals of the design. Multiple ramjets or jets can be placed within the channel At takeoff, a jet aircraft which is of conventional design at the middle [10]. The jets could also be embedded in the is oriented nose-up into the air, and it is not propelled in a channel structure, with their intakes located at the channel direction parallel to the ground. As a result, the engine does leading edge, as seen in Fig. (15). The multiple-jet concept not have sufficient mass inflow. This mass flow shortage can also be used with a flying-wing type arrangement. All results from the fact that most of the air travels over the these designs contain the vertical fins to isolate the channel engine nacelle (cowling), instead of flowing in through the flow. Note that the vertical plates designated as 42 seen in inlet. By using a channel wing, more mass flow is directed Fig. (14), form a rectangular channel which is the channel of into the engine and this liability is corrected. Furthermore, the flying wing design. the conventional aircraft is unstable at takeoff & landing because it relies on the engine thrust for stability. That is to The concept can be applied to missiles and rockets as say, the engine must provide high thrust and make the well. aircraft reach a high speed in a short time period. The high speed is necessary for producing lift because the wings' airfoils are of thin design, in order to create low drag at high speeds. If it cannot attain the necessary speed, it might overshoot the runway or crash. The channel wing concept provides extra lift at low speeds which alleviates the issue just stated, because the aircraft can now generate high lift despite its thin airfoil. The basic design consists of jet engines mounted on the middle of the channels, where the channels are similar to the ones used in previous patents. As before, wing portions that extend laterally outward from the channels are present. Three modifications to the basic setup are also presented: The first one has ducts placed at the middle of the channel. The duct extends from the fore end of the channel to its aft end. A motor is mounted inside each duct, and said motors provide mass inflow through the duct and channel. The second Fig. (14). Multiple jets used with a flying-wing like design [10]. 6 Recent Patents on Mechanical Engineering 2010, Vol. 3, No. 1 Gokce and Camci Fig. (15). Jets embedded within the channel airfoil [10]. Custer describes further details of his jet propelled channel designs in two additional patents [11, 12]. Fig. (17). The pressure balancing system [13]. A very clever method to stabilize the channel wing aircraft if one of the channels undergoes a decrease in lift or total loss of power during flight is obtained by establishing communication between the channels [13]. This commu- nication is achieved with the help of the tubes as shown in Fig. (16). The slots which are situated over the inner surface of the channel are connected with the tubes. When a pressure difference between the channels occurs, the valve designated as 14 which is placed inside the box designated as 12 in Fig. (17) shifts laterally so as to establish flow between the opera- tional and non-operational channel. Thus, the aircraft can still be controlled and can still continue its lift production. When the balance is re-established, the valve returns to its original vertical position. The box is situated inside the fuse- lage midway between the channels. The valve is balanced by a spring. This arrangement can also be used to generate unequal Fig. (18). The first concept [14]. lift and/or thrust on either side of the aircraft. If the conventional control surfaces are not adequate to perform a move or to control the aircraft under a certain condition, the pressure balancing system can be used to perform these operations. Fig. (16). The rear view of a connecting tube and channel [13]. Custer's 1964 patent focuses on a propeller tip spacing mechanism that will provide increased thrust and/or boun- dary layer control [14]. Custer has 3 alternative concepts that will deal with the issue at hand, which can be seen in Figs. (18), (19) & (20): Fig. (19). The second concept [14]. Channel Wing as an Aero-Vehicle Concept Recent Patents on Mechanical Engineering 2010, Vol. 3, No. 1 7 Fig. (21). Rear view of the contoured stack arrangement [15]. Fig. (20). The third concept [14]. The first one uses a shifting propeller design. That is to say, the propeller which is concentrically mounted on the shaft is shifted fore and aft by means of a mechanism (automatic or hydraulic control). When high thrust and lift are necessary, such as in take-off and landing, the gap between the propeller disk and channel trailing edge is very small and the propeller tip is kept very close to the trailing edge. During cruise, the propeller is shifted outwards to provide boundary layer control. The propeller is made up of stiff material. Fig. (22). Top/isometric view of the contoured stack arrangement The second and equally elaborate way of achieving this [15]. result is to employ a flexible propeller whose tips will approach the channel trailing edge at high lift requiring conditions. Since the suction is quite high at such conditions, directed in a parallel and flat manner over the channel- the centrifugal force can not straighten out the tip of the shaped exhaust stack, and then over the channel. Conse- propeller. As the rpm of the propeller is decreased, the tips quently, additional lift is generated. gradually move away from the channel trailing edge. The The exhaust stack is contoured such that it is elongated, flexible propeller should be constructed from flexible flattened and has the shape of a channel. It is placed slightly material like laminated wood or plastic. If this method is above the leading edge of the channel. In the case of a U- employed, the stiffness of the propeller should be scienti- shaped channel, the exhaust stack and the channel surfaces fically arranged from 50% radius to the tip such that the trace the same curved path. In the case of a rectangular flexibility just described could be achieved. Around 113 shaped channel, the contoured stack and channel bottom km/h, the tips usually assume their normal position with surface are not parallel, yet the plane passing from the respect to the channel and propeller shaft. The propeller bottom point of the stack and channel bottom surface are directs air flow effectively around 2400 rpm so as to provide parallel. boundary layer control. It is also noted that a gradual The design has various configurations. The exhaust of the decrease in chord length as one proceeds from the 25% radius to the tip will help to prevent stall. In addition, the engine might be placed slightly after or slightly before pitch of each section should decrease at a certain rate when (longitudinally) the channel leading edge. The exact location one proceeds from the 25% station to the tip. The airfoil of of the engine exhaust placement depends on the engine exhaust air and flame properties, as well as on aircraft size/ each section should be chosen accordingly. mission requirements. A third alternative is to use a mechanism mounted at the channel surface which is connected to the propeller tip. This When the propeller is rotated at high speeds, during take- mechanism will move the propeller tip longitudinally in off and landing for example, very low pressure is created just order to deflect it; eventually, the flexibility principle pre- ahead of the propeller tip. This causes a large amount of air spillback into the channel and a consequent decrease in lift viously described for the second alternative will be obtained. production. Thus, using a small tip gap (distance between the Custer patented an exhaust stack addition/improvement propeller tip and channel surface) is essential. In his 1972 to his designs in 1972, as seen in Fig. (21) & Fig. (22) [15]. and final patent, Custer introduces the idea of using a film of The basic idea of the design is to close the gap between the water flowing over the channel surface in order to seal that exhaust of the jet engine and the channel surface in order to gap when necessary, as seen in Fig. (23) [16]. Air com- maximize the lift produced by the channel. This is done by pressors (most likely those belonging to the engines) induce placing the discharge side of the engine’s contoured exhaust compressed air into the water storage tank through connector stack within that gap. The hot and fast exhaust air is being lines (pipes). Then, water is discharged through discharge 8 Recent Patents on Mechanical Engineering 2010, Vol. 3, No. 1 Gokce and Camci lines which are situated at the bottom portion of the tank. A two-way valve is the junction point for the discharge lines and the lines leading to the discharge manifolds. This valve dictates the water flow. The manifolds, designated as 24 in Fig. (24), transmit the water to jet tubes which are situated near the leading edge of the channel. The jet tubes direct water flow over the channel surface. The water evaporates once it passes the propeller tip. Fig. (23). Front view of a channel wing aircraft using the film of water jets to seal the tip gap [16]. Fig. (25). Taylor’s top mounted channel design [17]. Fig. (24). Water jets placed near the leading edge [16]. 3.2. Patents by other inventors The first patent including the channel wing concept obtained by someone else than Custer is Taylor's 1954 patent, which is visualized by Fig. (25) & Fig. (26) [17]. This invention incorporates the channel wing concept with a movable system so as to change the direction of the lift/thrust vectors as well as the orientation of the aircraft. Two variations are presented, where the first one is an aircraft having a quasi-conventional fuselage mounted with a channel on top, and ailerons on the side of the channel. A Fig. (26). Taylor’s notched-channel design [17]. rocker arm connects the control command and the propeller mount system. The propeller mount system's orientation can be modified with the use of the rocker arm, and this motion Fletcher's 1954 design consists of an aircraft having a will help to modify the lift/thrust capabilities of the aircraft. conventional fuselage and a pair of wings, mounted with 4 The propeller mount can be tilted up and down, as well as tilting channels at the end of the wings, as seen in Fig. (27) right and left. Therefore, it can be rotated in a 2D sense. The & Fig. (28) [18]. This patent contains an effective merge of aircraft relies almost solely on the channel for lifting some of Custer and Taylor's ideas. The channels contain a purposes, with the addition of small contributions by the turbo-prop engine. The channels are tilted in combination front portion of the fuselage and the ailerons. This design accordingly so that the lateral components of the lift and requires the careful arrangement of the aircraft's center of thrust vectors eliminate each other, and they provide a net gravity in order to have a stable aircraft. force which points upward, for hover or vertical climb/ descent situations. As the aircraft transists into forward The second design has a conventional fuselage and wing flight, the channels are tilted increasingly forward. In other combination. The wings are notched at their trailing edges. words, they have a near zero angle of attack. Note that the The notches house a channel plus propeller system which drag must also be accounted for while performing these can be rotated in a 2D sense, so as to vector the thrust and maneuvers. modify the orientation of the aircraft. Channel Wing as an Aero-Vehicle Concept Recent Patents on Mechanical Engineering 2010, Vol. 3, No. 1 9 Fig. (29). Shew's design [19]. Fig. (27). Fletcher's BLR design [18]. Taylor obtained a patent in 1960 which includes impro- vements to his previous patent as well as novel ideas [20]. Fig. (30), (31) & (32) contain details related to this patent. The basic aircraft design used has a cockpit/fuselage portion at the front; attached to the lower side of the nose is the frontal landing gear. A swept back conventional wing is superposed on the fuselage, towards the rear. A channel wing portion is mounted on the middle of the wing, towards the rear. The channel's lower surface smoothly blends with the airfoil structure of the wing. This provides an undis- Fig. (28). The tilting channel arrangement used by Fletcher [18]. turbed lifting section. A propulsion means is mounted inside the channel. The aircraft described does not have a tail, therefore the center of gravity of the channel wing must be The novel issue that the inventor sets forth is to use the placed forward of the c.g. of the wing section in order to turbo-prop engine's compressor as a high pressure pump to provide longitudinal stability to the aircraft. Vertical parts suck the boundary layer air (BLR) from the surface of the extend from the tips of the wings. The channel is of U shape, channel. BLR ducts which are placed near the trailing edge however rectangular channels are also proposed throughout are connected to conduits which transport the air flow to the the patent file. The wing might have a dihedral angle or it compressor. This action not only increases efficiency by might be straight. The patent also describes various methods preventing boundary layer induced separation, but it also on how to increase the lift-production performance of the increases lift because mass flow rate through the engine is aircraft via several additions/modifications to the channel increased. wing assembly. The channel could either be stationary, or it A modified version of the design has a second BLR could be tilted upon will so as to increase lift to a further stage, in addition to the system described for the basic extent. In this case, the bottom portion of the channel will act design. The channel surface contains orifices near the trailing as a flap. The author proposes 3 different flap designs: The edge, and these are connected to a series of holes placed near first one is connected to the main wing via a linkage situated the channel leading edge via a conduit. The engine exhaust at the bottom of the wing section. The second one is gases are ejected towards the trailing edge orifices; the connected at the mid-height of the airfoil. The third flap engine exhaust is bent so as to achieve this. These gases pro- comprises a slot-type flap, which is more productive in terms vide a low pressure zone while they pass over the orifices, of lift thanks to the smooth surface it provides after the and the boundary layer which forms over the holes are tilting of the wing. sucked through the conduit. Thus, a secondary BLR opera- tion is conducted. Note that directing the engine exhaust within the channel increases the thrust. Shew's 1960 patent incorporates two channels with a flying wing type surface [19]. The channels are placed at the front of the fuselage, as seen in Fig. (29). They are supported by side plates, which are placed on either side of the fuselage and extend along the entire length of the aircraft. The design has various control surfaces such as flaps and air brakes. There also are slots placed on the underside of the wing. These slots deflect the airflow to create high lift generating conditions. The plates also serve to constrain the high speed airflow over the wing. Fig. (30). Taylor's 1960 design [20]. 10 Recent Patents on Mechanical Engineering 2010, Vol. 3, No. 1 Gokce and Camci Fig. (33). The wings are tilted downwards to keep the tail at a low angle of attack [21]. can be rotated about a lateral axis so as to increase lift when necessary. If they're both tilted downwards at a positive angle of attack, the lower one is usually at a higher incidence than the upper one. Or they can both be tilted upwards to Fig. (31). Top view of the aircraft seen in Fig. (30). [20]. counteract the vector produced by the channels and airfoiled support struts, in order to take-off with a high angle of attack to create high lift during take-off. Spence's 1970 invention consists of an improvement in the cross-sectional profile of curved wings, especially of a semi-circular wing like the Custer channel wing [22]. Fig. (34) depicts the proposed cross-section. The lift generated by the classical channel wing cross section creates induced drag, and the resultant of the forces generated by the channel has a drag component. This situation is especially significant near the vertical sections of the channel, because they contribute little to the lift and still produce drag, as opposed to the central sections of the channel. It is suggested to use a crescent-like thickness profile for the channel, unlike the regular channel wing design which has a less varying thickness profile as one proceeded towards the channel sides. Decreasing the thickness reduces the drag created by the Fig. (32). One of Taylor's tilting channel arrangements [20]. vertical sections, and the author increases the incidence of the decreased-thickness sections in order to preserve the lift- Taylor proposes another design which comprises of a jet production capabilities of the channel. engine combined with a folding, rectangular channel wing. When extra lift is needed, parts on either side of a piece situated behind the wing section fold up, and form a rectangular channel combined with the lower portion. They can be folded back down when the extra lift is unnecessary. The rear end of the jet engine is of telescoping type so that it flexes and extends to maintain contact between the surface and the air flow. Similar to his 1960 patent, Shew's 1963 patent comprises of two channel wing structures placed at the front of the aircraft, as seen in Fig. (33) [21]. Two wings making up a bi- plane combination are situated at the back of the cockpit. Two vertical plates, or booms, extend from the channel wing portions all the way to two vertical stabilizers at the back, and all the aircraft structure is confined in between these booms. The booms support the aircraft structurally and also prevent the airflow generated by the propellers from being Fig. (34). Crescent shaped channel cross section [22]. propagated into the free-stream flow. The vertical stabilizers have airbrakes situated right in front of them. These De Angelis' 1988 patent comprises of an aircraft design airbrakes reverse the airflow so as to slow down the aircraft which uses a semi-venturi shaped channel fuselage to in situations where low speed is of the essence. The wings generate lift, as seen in Fig. (35) & Fig. (36) [23]. It derives