Patent Publication Number: US-2022212772-A1

Title: Airframe localized keel structures

Description:
FIELD OF THE DISCLOSURE 
     This disclosure relates generally to aircraft, and, more particularly, to airframe localized keel structures. 
     BACKGROUND 
     Aircraft sometimes encounter situations that endanger the thrust capabilities of associated propellers, such as when a fan blade of a propeller is released from an associated retention disk (e.g., a fan blade out condition). A thrust capability of the aircraft is vital to the functions of the aircraft and the safety of its passengers. As such, aircraft are able to fly using the thrust of a single propeller in case another propeller is compromised. 
     BRIEF DESCRIPTION 
     Localized keel structures for wings and/or airframes are disclosed. 
     Certain examples provide an example aircraft including an airframe, a first engine mounted on a first side of the airframe, a second engine mounted on a second side of the airframe, and an airframe keel positioned on at least one of a lower portion of the airframe or an upper portion of the airframe between the first engine and the second engine, the airframe keel to prevent an object from exiting the first engine and impacting the second engine. 
     Certain examples provide an example aircraft including an airframe, engines mounted on opposite sides of the airframe, the engines not including containment systems, and a keel disposed between the engines on an upper surface of the airframe or a lower surface of the airframe, the keel to deflect objects traversing a portion of the airframe. 
     Certain examples provide an apparatus including a body, a first means for propulsion positioned on a first side of the body, a second means for propulsion positioned on a second side of the bod opposite the first side, the second means for propulsion aligned with the first means for propulsion, at least one of the first means for propulsion or the second means for propulsion not including a containment system, and means for deflecting extending from a lower surface of the body or an upper surface of the body between the first means for propulsion and the second means for propulsion, the means for deflecting to deflect objects traversing at least a portion of the body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-B  illustrate prior art aircraft. 
         FIG. 2  illustrates a fan blade out condition analysis of the prior art aircraft of  FIGS. 1A-B . 
         FIGS. 3A-B  illustrate an aircraft including an example airframe localized keel structure. 
         FIGS. 4A-C  illustrate example cross-sections of the aircraft of  FIG. 3A . 
         FIGS. 5A-B  illustrate a frontal view of the aircraft of  FIG. 3B  including a first implementation the airframe localized keel structure. 
         FIG. 6  illustrates a fan blade out condition analysis of the aircraft of  FIGS. 3 and 5 . 
         FIG. 7  illustrates an aircraft including a second implementation of the airframe localized keel structure of  FIGS. 5A-B . 
         FIG. 8  illustrates an example 4-engine including wing keels and the airframe localized keel structure of  FIGS. 3A-B ,  4 ,  5 A-B, and/or  6 . 
     
    
    
     The figures are not to scale. As used herein, unless otherwise stated, the term “above” describes the relationship of two parts relative to Earth. A first part is above a second part, if the second part has at least one part between Earth and the first part. Likewise, as used herein, a first part is “below” a second part when the first part is closer to the Earth than the second part. As noted above, a first part can be above or below a second part with one or more of: other parts therebetween, without other parts therebetween, with the first and second parts touching, or without the first and second parts being in direct contact with one another. As used in this patent, stating that any part (e.g., a layer, film, area, region, or plate) is in any way on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, indicates that the referenced part is either in contact with the other part, or that the referenced part is above the other part with one or more intermediate part(s) located therebetween. As used herein, connection references (e.g., attached, coupled, connected, and joined) may include intermediate members between the elements referenced by the connection reference and/or relative movement between those elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and/or in fixed relation to each other. As used herein, stating that any part is in “contact” with another part is defined to mean that there is no intermediate part between the two parts. 
     Unless specifically stated otherwise, descriptors such as “first,” “second,” “third,” etc. are used herein without imputing or otherwise indicating any meaning of priority, physical order, arrangement in a list, and/or ordering in any way, but are merely used as labels and/or arbitrary names to distinguish elements for ease of understanding the disclosed examples. In some examples, the descriptor “first” may be used to refer to an element in the detailed description, while the same element may be referred to in a claim with a different descriptor such as “second” or “third.” In such instances, it should be understood that such descriptors are used merely for identifying those elements distinctly that might, for example, otherwise share a same name. 
     DETAILED DESCRIPTION 
     Federal Aviation Administration (FAA) regulation 33.94 requires a turbofan engine of an aircraft to safely demonstrate a blade release from an associated retention disk (e.g., a fan blade out condition). For example, the blade cannot pierce a fuselage (e.g., an airframe, a body, etc.) or interfere with operations of another component of the aircraft, such as a second engine. Aircraft can continue to propel their flight using a single functioning propeller even if another propeller on the aircraft is inoperative (e.g., defective, broken, unable to produce thrust, etc.). However, if all propellers of the aircraft are inoperative, the aircraft is unable to produce thrust, which forces the aircraft to pursue an emergency landing. As such, it is essential that a failure of a first engine of an aircraft does not affect a second engine of the aircraft. 
     In some examples of an engine with a containment system (e.g., closed rotor engines, ducted engines, etc.), a detached and/or broken blade may be held within a case that surrounds the engine. In other words, the detached and/or broken blade does not penetrate the case, which addresses the risk of the loose blade affecting another component outside the damaged engine. However, in some examples, the blade penetrates the case and ejects from a first engine (e.g., a damaged engine). In some such examples, the blade launches towards a second engine in line with the damaged engine. Specifically, a trajectory of the blade towards the second engine is in response to a rotation of the blade when it was attached to the first engine and a point of release (e.g., a break and/or detachment) of the blade during the rotation. In some examples, the trajectory of the blade impacts the second engine ingests the blade in response to the trajectory impacting or approaching the second engine. In some such example, the second engine also becomes inoperative leaving the aircraft without any means for propulsion. 
     Aircraft today typically utilize engine propellers with closed rotor configurations. However, implementations of engines without containment systems (e.g., propfans, open rotor engines, unducted engines, etc.) has become increasingly desirable as they address some of the concerns associated with closed rotor engines. For example, engines without containment systems provide a better fuel efficiency and produce reduced emissions compared to closed rotor engines. As such, engines without containment systems address some concerns associated with closed rotor engines, such as fuel prices, energy security, and/or the environment. 
     In an engine without a containment system, there is no case, shield, or other restraint to retain a loose fan blade, or a portion thereof, after it is released from the retention disk (e.g., due to stress, foreign object, other failure, etc.). Further, the rotation of the retention disk can propel the loose fan blade towards another engine on the aircraft. As a result, the loose fan blade can contact exposed rotor blades of the other engine, rendering both engines inoperative, which presents a catastrophic risk to the aircraft. 
     To address the risks presented by the fan blade out condition, examples disclosed herein include airframe localized keel structures (e.g., a keel, an airframe keel, a wing keel, a keel apparatus, etc.). In some examples, engines (e.g., engines including containment systems, engines not including containment systems, etc.) of an aircraft are mounted on an airframe and/or on opposite sides thereof. In some such examples, the keel is disposed between the engines to prevent objects from traversing between them. Specifically, the keel deflects objects, such as loose fan blades and/or portion(s) thereof, that travel between the engines. For example, if a first engine loses a fan blade, the keel can prevent the fan blade from crossing the airframe and impacting a second engine. Further, if the first and second engines are mounted on a same wing, the keel can be positioned on the wing to obstruct objects traveling between the engines. As a result, when a fan blade is released from the first or second engine, the keel can block the fan blade from impacting the other engine. 
     In some examples, the keel is integral to a portion of an aircraft, such as the airframe and/or the wing. In some examples, the keel is a separate part that is mounted onto the airframe and/or the wing via mechanical fasteners (e.g., screws, bolts, etc.) and/or adhesives. In some examples, the keel includes one or more openings through which the mechanical fasteners can be inserted. Further, the airframe can include openings on a surface thereof that correspond with the openings of the keel. As such, the mechanical fasteners can couple the keel to a surface of the airframe. In some examples, the mechanical fasteners and associated openings are countersunk into the airframe to minimize drag. 
     In some examples in which at least a portion of the engines are positioned below the airframe, the keel is positioned on a lower surface of the airframe in response to at least a portion of the engines being positioned below the airframe. In some examples in which at least a portion of the engines are positioned above the airframe, the keel is positioned on an upper surface of the airframe. For example, the keel can be positioned on a lower portion of the airframe and/or the wings when the engines are mounted on a bottom surface of wings of the aircraft. Further, the keel can be positioned on an upper portion of the airframe and/or the wings when the engines are mounted on a top surface of the wings. Although examples disclosed herein describe engines mounted on opposite sides of the airframe, the keel can be positioned between engines mounted anywhere on the aircraft, such as the top and/or bottom of the airframe. 
     In some examples, the keel is aligned with a plane of rotation of fan rotors of the engines. In some such examples, a length of the keel extends along the airframe at least 15 degrees from each side of the plane of rotation of the fan rotors. In some examples, a height of the keel is less than or equal to a diameter of the fan rotors of the engines to minimize unnecessary drag forces on the aircraft. In some examples, the keel is foldable, collapsible, retractable, and/or detachable from the aircraft. As such, the keel does not interfere with a landing of the aircraft that may occur when landing gear cannot be deployed due to a failure and/or malfunction. 
     The keel provides shielding that prevents cross-engine damage. As a result, the keel maintains the functionality of one engine even if another engine were to lose a fan blade, which further addresses FAA regulatory requirement 33.94. In some examples, the keel prevents other objects besides fan blades from traversing the airframe and colliding with one of the engines. In some examples, the airframe includes additional shielding to prevent the fan blade from piercing it as described in U.S. patent Publication Ser. No. 17/071,114, U.S. patent Publication Ser. No. 17/071,379, and U.S. patent Publication Ser. No. 17/071,308, which are hereby incorporated as references in their entirety. 
       FIG. 1A  illustrates a first example prior art aircraft  100  that utilizes a first engine (e.g., a right engine)  104  and a second engine (e.g., a left engine)  106 , which both include containment systems. In  FIG. 1A , the aircraft  100  includes an airframe (e.g., a fuselage)  102 , a right wing  108 , a left wing  110 , a vertical stabilizer  112 , horizontal stabilizers  114 , and a blade rotation plane (e.g., a plane of rotation of fan rotors of the first engine  104  and the second engine  106 )  116 . In  FIG. 1A , the first engine  104  and the second engine  106  include containment systems. However, in some examples, the containment systems of the first and second engine  104 ,  106  are unable to prevent a loose blade from slicing through and/or ejecting therefrom. In  FIG. 1A , the first engine  104  is mounted on a bottom surface  109  of the right wing  108  and the second engine  106  is mounted on a bottom surface  111  of the left wing  110 . In some other examples, the right and left engines  104 ,  106  are mounted on a top surface of the right and left wings  108 ,  110 , as discussed further in association with  FIG. 7 . In some other examples, the right engine  104  and the left engine  106  are mounted on the airframe  102  and/or a bottom surface of the horizontal stabilizers  114 . 
     In  FIG. 1A , the blade rotation plane  116  aligns with the fan rotors of the first and second engines  104 ,  106 . Further, the blade rotation plane  116  spans across a bottom surface  118  of the airframe  102 . In other examples, the blade rotation plane  116  spans across a top surface  120  of the airframe  102 . The aircraft  100  can include more than one of the blade rotation plane  116 , as discussed further in association with  FIG. 1B . In  FIG. 1A , the blade rotation plane  116  is unobstructed, which allows objects (e.g., loose blades, debris, etc.) to traverse the bottom surface  118  of the airframe  102  between the first engine  104  and the second engine  106 . 
     As a result, if either the first engine  104  or the second engine  106  is struck by an object and/or loses a fan blade, both the first engine  104  and the second engine  106  can lose propulsion (e.g., thrust) capabilities. For example, a rapid rotation of the fan blades of the first engine  104  can launch a loose fan blade, or a portion thereof, through the containment system of the first engine  104 , across the blade rotation plane  116 . Further, the loose fan blade of the first engine  104  can travel through the containment system, or in the proximity, of the second engine  106  causing the second engine  106  to ingest the loose fan blade. As a result, the loose fan blade of the first engine  104  causes damage to the second engine  106 . In  FIG. 1A , both the first engine  104  and the second engine  106  may be unable to provide thrust and propel the aircraft  100  in response to the first engine  104  or the second engine  106  losing a fan blade or a portion thereof (e.g., a fan blade out condition). 
       FIG. 1B  illustrates a prior art aircraft  150  including a first engine  152  and a second engine  154  that do not include containment systems (e.g., open rotor engines, propfans, unducted engines, etc.). In other words, blades (e.g., rotor blades, fan blades, etc.)  156  of the first engine  152  and blades  158  of the second engine  154  are exposed. Further, a first row of the blades  156 ,  158  of the first engine  152  and the second engine  154  are aligned along a first blade rotation plane  160 , and a second row of the blades  156 ,  158  are aligned along a second blade rotation plane  162 . In  FIG. 1B , the second blade rotation plane  162  is disposed aft the first blade rotation plane  160 . 
     In  FIG. 1B , the first engine  152  and the second engine  154  are both at risk of losing thrust capabilities, and being unable to propel the aircraft  150 , if either the first or second engine  152 ,  154  is impacted by an object and/or loses one of the blades  156 ,  158 , or a portion thereof. Specifically, rotation of the blades  156 ,  158  of the first engine  152  and/or the second engine  154  can propel one of the blades  156 ,  158 , or a portion thereof, that has detached from an associated retaining disk on a trajectory across the first or second blade rotation plane  160 ,  162 . Further, the detached one of the blades  156 ,  158  can traverse the bottom surface  118  of the airframe  102  and strike the blades  156 ,  158  of the opposite engine  152 ,  154  rendering both the first engine  152  and the second engine  154  inoperative (e.g., broken, ineffective, defective, etc.). 
     In some other examples, the first engine  152  and/or the second engine  154  does not lose one of the fan blades  156 ,  158  in response to impact from an object. However, collision between the object and one the fan blades  156 ,  158  can propel the object towards the opposite engine  152 ,  154 . As a result, the object can break off one of the fan blades  156 ,  158  of the opposite engine  152 ,  154 , which again puts the aircraft  150  at risk of losing propulsion from both engines  152 ,  154  as the object and/or a detached one of the fan blades  156 ,  158  launch across the first or second blade rotation plane  160 ,  162 . 
       FIG. 2  illustrates a fan blade out condition simulation  200  of the first and/or second example prior art aircraft  100 ,  150  of  FIGS. 1A  and/or B. In  FIG. 2 , the fan blade out simulation  200  includes a first engine (e.g., the first engine  104 , the first engine  152 )  202  and a second engine (e.g., the second engine  106 , the second engine  154 )  204 . In  FIG. 2 , the fan blade out simulation  200  further includes an airframe (the airframe  102  of  FIGS. 1A  and B)  206  and a blade rotation plane (e.g., the blade rotation plane  116 , the blade rotation plane  160 )  208 . In  FIG. 2 , the fan blade out simulation  200  includes a blade (e.g., a fan blade, a rotor blade, etc.)  210  and a retention disk  212  of the first engine  202 . Further, a release of the blade  210  from the retention disk  212  of the first engine  202  was simulated to determine a trajectory  214  that the blade  210  follows. 
     In  FIG. 2 , the blade  210  of the first engine  202  launches on the trajectory  214  across the blade rotation plane  208  below the airframe  206 . For example, an external object may contact the blade  210 , during a rotation thereof, causing the blade  208  to detach from the associated retention disk  212 . In some other examples, wear and tear during operations of the first engine  202  causes a crack and/or other imperfections in the blade  210  and/or the retention disk  212 , which eventually causes the blade  210  or a portion thereof to rupture and eject from the first engine  202 . Further, the first engine  202  is unable to provide sufficient thrust in response to losing the fan blade  210  or a portion thereof. 
     In the example simulation  200  of  FIG. 2 , the blade  210  travels across the blade rotation plane  208  on the trajectory  214  in response to detachment from the retention disk  212  of the first engine  202 . As a result, the blade  210  impacts the second engine  204 , which can render the second engine  204  inoperative and remove thrust capabilities of the aircraft  100 ,  150 . In some examples, fan blades of the second engine  204  are exposed, as shown in  FIG. 1B . In some such examples, the blade  208  impacts the fan blades of the second engine  204  causing them to break and/or dislodge from the second engine  204 . In some examples, the blade  208  pierces a containment system of the second engine  204 , as discussed in association with  FIG. 1A . In some such examples, the blade  208  and/or a portion of the pierced containment system can obstruct a rotation of the fan blades of the second engine  204 , which results in an insufficient and/or nonexistent thrust being provided by the first engine  202  and the second engine  204 . In other words, loss of the fan blade  210  of the first engine  202  jeopardizes propulsion capabilities of the aircraft  100 ,  150 . 
       FIG. 3A  illustrates an aircraft  300  including an airframe localized keel structure (e.g., a keel)  302 . In  FIG. 3A , the aircraft  300  includes a first engine (e.g., a right engine)  306  mounted on a first side  305  of an airframe  304  and a second engine (e.g., a left engine)  308  mounted on a second side  307  of the airframe  304 . Specifically, the first engine  306  is mounted on a bottom surface  309  of a right wing  310  and the second engine  308  is mounted on a bottom surface  311  a left wing  312 . In  FIG. 3A , the aircraft  300  further includes a vertical stabilizer  314  and horizontal stabilizers  316  positioned on an aft portion of the airframe  304 . 
     In  FIG. 3A , the first engine  306  and the second engine  308  include containment systems that are unable to prevent penetration by a fan blade. In  FIG. 3A , the keel  302  is positioned on a lower portion (e.g., a lower surface, a bottom surface, etc.)  320  of the airframe  304  between the first engine  306  and the second engine  308 . In some other examples, the keel  302  is positioned between engines on an upper portion  322  of the airframe  304 , the right wing  310 , and/or the left wing  312 , as discussed further in association with  FIGS. 7 and 8 . That is, the keel  302  can be positioned anywhere on the aircraft  300  in response to a location of the first engine  306 , the second engine  308 , and/or any other engines. 
     In  FIG. 3A , the keel  302  is positioned in line with a plane of rotation  318  of fan rotors of the first engine  306  and the second engine  308 . In  FIG. 3A , the keel  302  extends longitudinally along a bottom surface  320  of the airframe  304  at least 15 degrees from each side of the plane of rotation  318  of the fan rotors of the first and second engine  306 ,  308 . In other words, the keel  302  extends toward a fore end  324  of the airframe  304  at least 15 degrees from the plane of rotation  318  and also extends toward an aft end  326  of the airframe  304  at least from the plane of rotation  318 . In  FIG. 3A , a height of the keel  302  is equivalent to a diameter of the fan rotors of the first and second engine  306 ,  308 . In some examples, the height of the keel  302  is less than the diameter of the fan rotors of the first and second engine  306 ,  308  in response to a portion of the blade rotation plane  318  intersecting the airframe  304 . 
     In  FIG. 3A , the keel  302  prevents an object (e.g., a fan blade) from exiting the first engine  306  and impacting the second engine  308 . For example, if a fan blade of the first engine  306  exits the containment system thereof and traverses the plane of rotation  318 , the keel  302  deflects the fan blade and prevents it from crossing the airframe  304  to protect the second engine  308 . As such, the keel  302  provides shielding to allow the second engine  308  to propel the aircraft  300  regardless of if the first engine  306  loses a fan blade. 
       FIG. 3B  illustrates an aircraft  350  including a first engine (e.g., a right engine)  352  and a second engine (e.g., a left engine)  354  mounted on opposite sides of the airframe  304 . In  FIG. 3B , the first engine  352  and the second engine  354  do not include a containment system. In other words, the first and second engines  352 ,  354  are open rotor engines with fan rotors (e.g., fan blades, rotor blades, etc.)  356 ,  358  that are exposed to the outside environment. In  FIG. 3B , the first engine  352  is mounted on the right wing  310  and the second engine  354  is mounted on the left wing  312 . In  FIG. 3B , the aircraft  350  further includes the vertical stabilizer  314  and the horizontal stabilizers  316  of  FIG. 3A . 
     In  FIG. 3B , a first row of the fan blades  356 ,  358  of the first and second engines is aligned along a first plane of rotation  362 , and a second row of the fan blades  356 ,  358  is aligned a second plane of rotation  364 . In  FIG. 3B , the second plane of rotation  364  is disposed aft of the first plane of rotation  362 . In  FIG. 3B , a keel  360  is positioned on the bottom portion  320  of the airframe  304  between the first and second engines  352 ,  354 . In some examples the keel  360  is foldable, collapsible, and/or retractable, as discussed further in association with  FIG. 5B . In  FIG. 3B , the keel  360  intersects the first and second plane of rotation  362 ,  364  of the first and second rows of the fan blades  356 ,  358 . In  FIG. 3B , the keel  360  extends along the bottom portion  320  of the airframe  304  at least 15 degrees from the first plane of rotation  362  towards a fore end  366  of the airframe  304  and at least 15 degrees from the second plane of rotation  364  towards an aft end  368  of the airframe  304 , for example. 
     In some examples, the keel  360  is substantially perpendicular (e.g., plus, or minus 10 degrees) to the first and second planes of rotation  362 ,  364  to prevent objects from crossing a portion of the airframe  304 . As a result, when the second engine  354  or the first engine  352  loses one of the respective fan rotors  356 ,  358 , the keel  360  protects the first engine  352  or the second engine  354 , respectively, from being obstructed. As used herein in the context of describing the position and/or orientation of a first object relative to a second object, the term “substantially perpendicular” encompasses the term perpendicular and more broadly encompasses a meaning whereby the first object is positioned and/or oriented relative to the second object at an absolute angle of no more than ten degrees (10°) from perpendicular. For example, a first axis that is substantially perpendicular to a second axis is positioned and/or oriented relative to the second axis at an absolute angle of no more than ten degrees (10°) from perpendicular. 
       FIG. 4A  illustrates a first example cross-section A-A of the aircraft  300  of  FIG. 3A  to more clearly illustrate the airframe localized keel structure  302 . In  FIG. 4A , the cross-section A-A can also be representative of the keel  360  of the aircraft  350  of  FIG. 3B  as the difference between the keel  302  of  FIG. 3A  and the keel  360  of  FIG. 3B  is the size thereof. In  FIG. 4A , the keel  302  includes a first aerodynamic section  402  and a protection section  404 . In  FIG. 4A , the first aerodynamic section  402  and/or the protection section  404  includes an energy absorbing material, such as a foam honeycomb with a composite skin. In  FIG. 4A , the protection section  404  of the keel  302  is disposed aft of the aerodynamic section  402 . In  FIG. 4A , the protection section  404  includes a rectangular cross-section. In  FIG. 4A , a first end (e.g., a trailing edge, an aft end, etc.) of the first aerodynamic section  402  is fixed to a leading edge of the protection section  404 . In  FIG. 4A , a second end (e.g., a leading end, a fore end, etc.) of the first aerodynamic section  402  includes a reduced height relative to the protection section  404 . In  FIG. 4A , a contour of the first aerodynamic section  402  includes an arc between the first end and the second end. As a result, the first aerodynamic section  402  reduces a drag force on the aircraft  300  caused by the keel  302 . In some examples, the second end of the first aerodynamic section  402  includes a smaller thickness than the protection section  404  to further reduce the drag force on the aircraft  300  caused by the keel  302 . For example, the keel  302  can be tapered to include a smaller width (e.g., thickness) at a leading edge (e.g., a fore end of the keel  302 ) compared to a trailing edge (e.g., an aft end of the keel  302 ). In some examples, the keel  302  is tapered to include a width that decreases away from the airframe  304  (e.g., towards a bottom edge of the keel) to reduce the drag force on the aircraft  300  caused by the keel  302 . 
     In  FIG. 4A , the protection section  404  extends along the airframe  304  at least 15 degrees from each side of the plane of rotation  318  of the fan blades of the first and second engine  306 ,  308 . Further, a uniform height of the protection section  404  relative to the airframe  304  is equivalent to a diameter of the fan blades of the first and second engine  306 ,  308 . As a result, the protection section  404  prevents objects from traversing a portion of the airframe  304  to protect the first and second engines  306 ,  308  and, thus, the propulsion capabilities of the aircraft  300 . In other words, the protection section  404  prevents a fan blade from exiting the first engine  306  and impacting the second engine  308 . Damage to the second engine  308  can be avoided, and the second engine  308  can continue to operate, sustaining lift and velocity of the aircraft. 
       FIG. 4B  illustrates a second example cross-section A-A of the aircraft  300  of  FIG. 3A  to more clearly illustrate the airframe localized keel structure  302 . In  FIG. 4B , the cross-section A-A can also be representative of the keel  360  of the aircraft  350  of  FIG. 3B . In  FIG. 4B , the keel includes the protection section  404  of  FIG. 4A  and a second example aerodynamic section  406 . In  FIG. 4B , the second aerodynamic section  406  includes a first end fixed to a leading edge of the protection section  404  and a second end extending away from the protections section  404 . In  FIG. 4B , the second aerodynamic section  406  includes more than one arc between the first end and the second end resulting in a double inflection contour that reduces the drag force on the aircraft  300  caused by the protection section  404 . That is, a first arc of the second aerodynamic section  406  extends past a height of the protection section  404  and a second arc of the second aerodynamic section  406  extends a length of the second aerodynamic section  406  away from the protection section  404  at a reduced height compared to the protection section  404 . As a result, the second protection section  406  reduces the drag force on the aircraft  300  caused by the protection section  404   
       FIG. 4C  illustrates a third example cross section A-A of the aircraft  300  of  FIG. 3A  to more clearly illustrate the airframe localized keel structure  302 . In  FIG. 4C , the cross-section A-A can also be representative of the keel  360  of the aircraft  350  of  FIG. 3B . In  FIG. 4B , the keel  302  includes the protection section and a third example aerodynamic section  408 . In  FIG. 4C , the third aerodynamic section  408  includes a first end, a second end, and at least one arc therebetween. In  FIG. 4C , the at least one arc of the third aerodynamic section  408  extends toward the protection section  404  to reduce the drag force on the aircraft  300  caused by the protection section  404 . 
       FIG. 5A  illustrates a frontal view of the aircraft  350  of  FIG. 3B . In  FIG. 5A , the keel  360  extends from the bottom portion  320  of the airframe  304  to a lowermost position  502  of the fan rotors  356 ,  358  of the first engine  352  and the second engine  354 . In  FIG. 5A , the aircraft  350  further includes landing gear  504  in a deployed position. In  FIG. 5A , a height of the keel  302  is less than a diameter of the fan rotors  356 ,  358  of the first and second engine  306 ,  308 . Specifically, a top of the fan rotors  356 ,  358  of the first and second engines  306 ,  308  is aligned with the airframe  304  and, thus, is above a top of the keel  360 . As a result, the airframe  304  shields the first and second engines  352 ,  354  if a release of one of the fan rotors  356 ,  358  is on a trajectory above the keel  360 . As such, if one the fan rotors  356 ,  358 , or a portion thereof, detaches from the respective engine  352 ,  354 , the detached fan rotor  356 ,  358  is unable to obstruct the opposite engines  352 ,  354 . In  FIG. 5A , the keel  360  extends from the bottom portion  320  of the airframe  304  to align with the lowermost position  502  of the first and second engines  306 ,  308 . In some examples, the keel  360  extends from the airframe  304  to align with an uppermost position of the first and second engines  306 ,  308 , as discussed further in association with  FIG. 7 . In some examples, the first engine  352  and the second engine  354  are positioned on the airframe  304  and/or the horizontal stabilizers  316 . In some such examples, the first and second engine  352 ,  354  are at least partially external to a cross-sectional area or the airframe  304 . Further, the keel  360  is positioned on the aircraft  350  in response to a position of the first and second engines  352 ,  354 , for example. 
     In some examples, the keel  302  includes an energy absorbing material, such as a foam honeycomb with a composite skin. As a result, the keel  302  absorbs the impact of the rotor blades  356  and/or any other object traversing between the first engine  306  and the second engine  308 . Further, the energy absorption of the keel  302  prevents the rotor blades  356  from traversing the airframe  304  and/or affecting the opposite engine  306 ,  308 . 
       FIG. 5B  illustrates a frontal view of the aircraft  350  of  FIGS. 3B and/or 5A  with the keel  360  in a collapsed (e.g., folded, retracted, etc.) position  506 . In some examples, the aircraft  350  lands without utilizing the landing gear  504  due to a failure or malfunction thereof. As such, the landing gear  504  of  FIG. 5A  is not shown in  FIG. 5B  to illustrate the failure thereof. In some such examples, the keel  360  folds, retracts, and/or collapses into the collapsed position  506  to avoid interfering with a landing and inflicting damage on the aircraft  350 . In some other examples, the keel  360  detaches from the airframe  304 . 
       FIG. 6  illustrates a fan blade out simulation  600  of the aircraft  300  of  FIG. 3A  or the aircraft  350  of  FIGS. 3B and/or 5A . In  FIG. 6 , the fan blade out simulation  600  includes a first engine (e.g., the first engine  306 , the first engine  352 )  602  and a second engine (e.g., the second engine  308 , the second engine  354 )  604  disposed on opposite sides of an airframe (e.g., the airframe  304 )  606 . In  FIG. 6 , the fan blade out simulation  600  further includes a keel (e.g., the keel  302 , the keel  360 )  608  extending from a lower surface  609  of the airframe  606  and a blade rotation plane (e.g., the plane of rotation  318 , the first plane of rotation  362 , the second plane of rotation  364 , etc.)  610  of rotor blades of the first and second engine  602 ,  604 . In  FIG. 6 , the first engine  602  further includes a retention disk  612  and a fan blade (e.g., one of the fan blades  356 )  614  that detaches from the retention disk  612  and follows a trajectory  616 . 
     In  FIG. 6 , the trajectory  616  of the fan blade  614  is similar to a beginning portion of the trajectory  214  of  FIG. 2 . However, in  FIG. 6 , the keel  608  interferes with the trajectory  616  as the fan blade  614  traverses the airframe  606 . As a result, the keel  608  preserves thrust capabilities of the second engine  604 . Specifically, the keel  608  obstructs the blade rotation plane  610  and extends at least 15 degrees from each side thereof to prevent objects, such as the fan blade  614 , from traversing a portion of the airframe  606  that may otherwise lead to impacting the second engine  604 , for example. As a result, the keel  608  deflects the fan blade  614  and, thus, prevents the fan blade  614  from exiting the first engine  602  and impacting the second engine  604 . 
       FIG. 7  illustrates an aircraft  700  including a keel  702  positioned on an upper portion  703  of an airframe  704 . In  FIG. 7 , the aircraft  700  further includes a first engine  706 , a second engine  708 , a right wing  710 , a left wing  712 , and a vertical stabilizer  714  mounted to an aft portion of the airframe  704 . In  FIG. 7 , the first engine  706  is mounted on a top surface  716  of the right wing  710  and the second engine  708  is mounted on a top surface  718  of the left wing  712 . In  FIG. 7 , the keel  702  is positioned on the upper portion  703  of the airframe  704  between the first engine  706  and the second engine  708 . In  FIG. 7 , the keel  702  is disposed closer to a fore end of the airframe  704  than the vertical stabilizer  714 . In other words, the keel  702  is positioned upstream of the vertical stabilizer  714 . 
     In  FIG. 7 , the keel  702  extends from the upper portion  703  of the airframe  704  above an uppermost point  720  of the first and second engine  706 ,  708 . In some examples, a fan blade  722  of the first engine  706 , or a portion thereof, is released on an upwards trajectory that traverses the airframe  704  towards the second engine  708 . As such, the keel  702  extends to the highest point of a trajectory of the fan blade  722  that impacts the second engine  708  and, thus, obstructs the trajectory as it traverses the airframe  704 . Further, a trajectory of the fan blade  722  that launches above the uppermost point  720  of the first and second engine  706 ,  708  can avoid contact with the second engine  708  due to a velocity of the fan blade  722  upon release. Additionally, air resistance on the fan blade  722  after release and continued propulsion of the aircraft causes the fan blade  722  to travel slower than the aircraft  700  if the fan blade  722  takes more than about 3 seconds to cross the airframe  704 . As a result, the fan blade  722  falls behind the second engine  708  and avoids impact therewith. In some examples, the highest point of the trajectory of the fan blade  722  that impacts the second engine  708  is determined based on simulated blade releases similar to the simulations illustrated in  FIGS. 2 and 6 . As a result, the keel  702  prevents an object from exiting the first engine  706  and impacting the second engine  708 . 
       FIG. 8  illustrates an aircraft  800  including a first keel  802  positioned on a first wing  816  between a first engine  804  and a second engine  806 , a second wing keel  808  positioned on a second wing  818  between a third engine  810  and a fourth engine  812 , and a third keel  814  positioned on an airframe  820  between the second engine  806  and the third engine  810 . In  FIG. 8 , the first wing keel  802 , the first engine  804 , and the second engine  806  are mounted on a bottom surface  822  of the right wing  816 . In  FIG. 8 , the second wing keel  808 , the third engine  810 , and the fourth engine  812  are mounted on a bottom surface  824  of the left wing  818 . In  FIG. 8 , the airframe keel  814  extends from a bottom surface  826  of the airframe  820 . In some other examples, the engines  804 ,  806 ,  810 ,  812  and the keels  802 ,  808 ,  814  are positioned on a top surface of the right and left wings  816 ,  818  and/or the airframe  820 . 
     In  FIG. 8 , the first wing keel  802  and the second wing keel  808  deflect objects that traverse a portion of the right wing  816  and the left wing  818 , respectively. In some examples, the first wing keel  802  prevents objects, such as fan blades, from exiting the first engine  804  and impacting the second engine  806 . In some examples, the second wing keel  808  prevents objects, such as fan blades, from exiting the third engine  810  and impacting the fourth engine  812 . Further, the airframe keel  814  deflects objects, such as fan blades, that traverse a portion of the airframe  820 , which prevents objects from exiting the second engine  806  and impacting the third engine  810 . 
     In some examples, rotor blades of the first, second, third, and fourth engines  804 ,  806 ,  810 ,  812  are positioned within different planes of rotation. In some such examples, the keels  802 ,  808 ,  814  extend along the wings  816 ,  818  and/or the airframe  820  between the different planes of rotation and at least 15 degrees towards an aft end of the aircraft  800  from a trailing plane of rotation and at least 15 degrees towards a fore end of the aircraft  800  from a leading plane of rotation. In  FIG. 8 , a height of the keels  802 ,  808 ,  814  is less than or equal to a diameter of the engines  804 ,  806 ,  810 ,  812  (e.g., a diameter of the rotor blades of the engines  804 ,  806 ,  810 ,  812 ). 
     “Including” and “comprising” (and all forms and tenses thereof) are used herein to be open ended terms. Thus, whenever a claim employs any form of “include” or “comprise” (e.g., comprises, includes, comprising, including, having, etc.) as a preamble or within a claim recitation of any kind, it is to be understood that additional elements, terms, etc. may be present without falling outside the scope of the corresponding claim or recitation. As used herein, when the phrase “at least” is used as the transition term in, for example, a preamble of a claim, it is open-ended in the same manner as the term “comprising” and “including” are open ended. The term “and/or” when used, for example, in a form such as A, B, and/or C refers to any combination or subset of A, B, C such as (1) A alone, (2) B alone, (3) C alone, (4) A with B, (5) A with C, (6) B with C, and (7) A with B and with C. As used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. Similarly, as used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. As used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. Similarly, as used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. 
     As used herein, singular references (e.g., “a”, “an”, “first”, “second”, etc.) do not exclude a plurality. The term “a” or “an” entity, as used herein, refers to one or more of that entity. The terms “a” (or “an”), “one or more”, and “at least one” can be used interchangeably herein. Furthermore, although individually listed, a plurality of means, elements or method actions may be implemented by, e.g., a single unit or processor. Additionally, although individual features may be included in different examples or claims, these may possibly be combined, and the inclusion in different examples or claims does not imply that a combination of features is not feasible and/or advantageous. 
     From the foregoing, it will be appreciated that example airframe localized keel structures have been disclosed that deflect an object, such as a fan blade or a portion thereof, traversing between engines of an aircraft. In other words, the airframe localized keel structures prevent the object from exiting a first engine and impacting the second engine. As a result, the disclosed airframe localized keel structures protects a first engine in response to a second engine losing a fan blade, which, in turn, maintains propulsion of the aircraft. 
     Although certain example methods, apparatus and articles of manufacture have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent. 
     The following claims are hereby incorporated into this Detailed Description by this reference, with each claim standing on its own as a separate embodiment of the present disclosure. 
     Further aspects of the invention are provided by the subject matter of the following clauses: 
     1. An aircraft comprising: an airframe, a first engine mounted on a first side of the airframe, a second engine mounted on a second side of the airframe opposite the first side of the airframe, and an airframe keel positioned on at least one of a lower portion of the airframe or an upper portion of the airframe between the first engine and the second engine, the airframe keel to prevent an object from exiting the first engine and impacting the second engine. 
     2. The aircraft of any preceding clause, wherein the airframe keel includes a protection section and an aerodynamic section, the aerodynamic section including an arc that diminishes in height towards a fore end of the airframe to reduce drag forces on the airframe keel. 
     3. The aircraft of any preceding clause, wherein the airframe keel is at least one of collapsible, retractable, or detachable. 
     4. The aircraft of any preceding clause, further including a wing keel positioned between the first engine and a third engine on the first side of the airframe. 
     5. The aircraft of any preceding clause, wherein the airframe keel is positioned in line with a plane of rotation of fan rotors of the first engine and the second engine. 
     6. The aircraft of any preceding clause, wherein the airframe keel extends longitudinally along the airframe at least 15 degrees from each side of the plane of rotation of the fan rotors. 
     7. The aircraft of any preceding clause, wherein a height of the airframe keel is less than or equal to a diameter of fan rotors of the first engine and the second engine. 
     8. The aircraft of any preceding clause, wherein the first engine and the second engine do not include containment systems. 
     9. An aircraft comprising: an airframe, engines mounted on opposite sides of the airframe, the engines not including containment systems, and a keel disposed between the engines on an upper surface of the airframe or a lower surface of the airframe, the keel to deflect objects traversing a portion of the airframe. 
     10. The aircraft of any preceding clause, further including a vertical stabilizer mounted to an aft portion of the airframe, the keel disposed upstream of the vertical stabilizer. 
     11. The aircraft of any preceding clause, wherein a height of the keel is less than or equal to a diameter of the engines. 
     12. The aircraft of any preceding clause, wherein the keel includes a first section disposed aft a second section, the first section including a uniform height and the second section including a height that diminishes towards a fore end of the airframe. 
     13. The aircraft of any preceding clause, wherein the keel is at least one of collapsible, retractable, or detachable relative to the airframe. 
     14. The aircraft of any preceding clause, wherein the keel is mounted onto the upper surface of the airframe or the lower surface of the airframe via fasteners. 
     15. The aircraft of any preceding clause, wherein the engines include fan rotors, the keel aligned with a plane of rotation of the fan rotors. 
     16. The aircraft of any preceding clause, wherein a length of the keel extends along the airframe at least 15 degrees from each side of the plane of rotation of the fan rotors. 
     17. The aircraft of any preceding clause, wherein a leading edge of the keel includes at least one of a smaller width or height compared to a trailing edge of the keel. 
     18. A keel apparatus comprising: a protection section including a rectangular cross-section, the protection section to be fixed to a body, the protection section to deflect objects traversing at least a portion of the body, and an aerodynamic section including a first end and a second end, the first end of the aerodynamic section fixed to a leading edge of the protection section, the second end of the aerodynamic section including a reduced height relative to the protection section, the aerodynamic section including at least one arc between the first end and the second end, the second end of the aerodynamic section including a smaller thickness than the protection section to reduce a drag force on the protection section. 
     19. The keel apparatus of any preceding clause, wherein at least one of the protection section or the aerodynamic section includes an energy absorbing material. 
     20. The keel apparatus of any preceding clause, wherein the energy absorbing material is a foam honeycomb with a composite skin. 
     21. An apparatus comprising: a body, first means for propulsion positioned on a first side of the body, second means for propulsion positioned on a second side of the body opposite the first side, the second means for propulsion aligned with the first means for propulsion, at least one of the first means for propulsion or the second means for propulsion not including a containment system, and means for deflecting extending from a lower surface of the body or an upper surface of the body between the first means for propulsion and the second means for propulsion, the means for deflecting to deflect objects traversing at least a portion of the body. 
     22. The apparatus of any preceding clause, wherein the first and second means for propulsion include a plane of rotation, a length of the means for deflecting to extend longitudinally along the body at least 15 degrees from each side of the plane of rotation. 
     23. The apparatus of any preceding clause, wherein the means for deflecting is collapsible. 
     24. An apparatus comprising: a first engine including at least one blade rotation plane, a second engine including the at least one blade rotation plane, and a keel positioned between the first engine and the second engine, the keel aligned with the at least one blade rotation plane of the first engine and the second engine, the keel to deflect objects traversing the at least one blade rotation plane between the first engine and the second engine. 
     25. The apparatus of any preceding clause, wherein a length of the keel extends at least 15 degrees from opposite sides of the at least one blade rotation plane. 
     26. The apparatus of any preceding clause, wherein the keel includes a height that is less than or equal to a diameter of the first engine or the second engine. 
     27. The apparatus of any preceding clause, wherein a leading edge of the keel includes at least one of a smaller width or height compared to a trailing edge of the keel. 
     28. The apparatus of any preceding clause, wherein the keel is at least one of collapsible or retractable. 
     29. The apparatus of any preceding clause, wherein the first engine and the second engine do not include containment systems.