Patent Application
20210122461
This disclosure relates to the field of aircraft landing gear.
Typical aircraft include landing gear having either a nose wheel or a tail wheel. Tailwheel aircraft have two (left and right) main landing gear assemblies that are spaced apart in the lateral direction (e.g. one on each side of the fuselage or one on each main wing), with the tailwheel (or other support, such as a skid) located behind the main landing gear. This configuration is commonly referred to as a “conventional” landing gear arrangement. In contrast, nose wheel aircraft have a nose wheel located in front of the two main landing gear assemblies. This is commonly called a “tricycle” or “tri-gear” landing gear arrangement.
Each type of landing gear arrangement has advantages and disadvantages.
Conventional gear typically perform better on rough terrain, where the distribution of the main landing gear helps stabilize the aircraft on rough terrain or soft surfaces. Conventional gear also typically hold the main wings at a greater angle of attack relative to the ground, thus making them more suitable for short takeoff and landing (“STOL”) operations. However, conventional gear are less stable during landings in crosswinds, during which high lateral loads can cause the aircraft to enter a “ground loop” in which the aircraft pivots horizontally around the main gear, risking contact between the wing and the ground and other damage. Aircraft with conventional gear are also more likely to nose over during sudden heavy braking, and can potentially flip entirely over.
Tricycle gear have three significant advantages over conventional gear. First, the nose wheel provides longitudinal stability during landing, thus virtually eliminating the possibility of entering a ground loop. Second, the nose wheel reduces the likelihood of nosing over during braking. Third, greater breaking force is generally available. Despite these advantages, tricycle gear are much less useful on rough terrain and softer surfaces, in which the single nose gear is more likely to dig into the surface and potentially collapse or lead to a nose over.
As a consequence of these advantages and disadvantages, conventional gear are typically favored for off-runway use, and tricycle gear are typically favored for on-runway use.
Historically, landing gear on aircraft are configured either as conventional gear or as tricycle gear, but not both. The reason for this is that the location of the main wheels relative to the center of gravity must be selected to establish proper stability for the selected configuration. Thus, main landing gear are not positioned appropriately to allow the aircraft to alternate between tailwheel operation and tricycle operation. Despite this, a small number of aircraft are known to include both forward and rearward supports. For example, the BAC “Concord” supersonic transport (introduced in 1976) was configured with tricycle landing gear and operated with the nose gear on the ground during normal takeoff and landing, but included a small retractable tail wheel as protection against ground strikes between its elongated tail cone and the ground. As another example, the Royal Aircraft Factory F.E.2 fighter (introduced in 1915) was configured with conventional landing gear and normally operated during takeoff and landing with the back of the aircraft supported by a tailskid, but included a small forward wheel to prevent nose overs when landing in soft terrain (the wheel was often removed by aircrews). Finally, the Ilyushin IL-62 transport (introduced in 1963) was configured with a tricycle gear and operated during takeoff and landing with the aircraft supported on the nose gear, but included a retractable “tail prop” to prevent the aircraft from tipping backwards when unloaded on the ground. It has also been suggested to provide a conventional gear aircraft with a movable main landing gear to allow the main wheels to move forward to help prevent nose-overs, as seen in U.S. Pat. No. 1,493,022, but such aircraft is not known to have a forward landing gear and thus the main gear would have been configured to operate as a conventional gear aircraft under all circumstances. Furthermore, such a configuration would increase the effect of cross-wind side loads on the aircraft, making it more likely to experience ground loops.
This description of the background is provided to assist with an understanding of the following explanations of exemplary embodiments, and is not an admission that any or all of this background information is necessarily prior art.
In a first aspect, there is provided an aircraft having: a fuselage extending in a longitudinal direction from a nose to a tail; a nose wheel located at the nose; a tail support located at the tail; and a main wheel assembly located between the nose wheel and the tail support in the longitudinal direction. The main wheel assembly is positioned such that the aircraft is operable to selectively land in: a first operating mode in which the main wheel assembly and the nose wheel support both the aircraft during the landing process, and the tail support does not support the aircraft during the landing process, and a second operating mode in which the main wheel assembly and the tail support both support the aircraft during the landing process.
In some examples of the first aspect, the nose wheel does not support the aircraft in the second operating mode.
In some examples of the first aspect, in the second operating mode, the tail support supports the aircraft during one portion of the landing process, and the nose wheel supports the aircraft during another portion of the landing process.
In some examples of the first aspect, the main wheel assembly comprises a first main wheel spaced in a transverse direction from a second main wheel, the transverse direction being perpendicular to the longitudinal direction, and the first main wheel and second main wheel are movable to at least two fixed operating positions in the longitudinal direction.
In a second aspect, there is provided a method for operating an aircraft having a fuselage extending in a longitudinal direction from a nose to a tail, a nose wheel located at the nose, a tail support located at the tail, and a main wheel assembly located between the nose wheel and the tail support in the longitudinal direction. The method comprises landing the aircraft in a first operating mode in which the main wheel assembly and the nose wheel support both the aircraft during the landing process, and the tail support does not support the aircraft during the landing process, and landing the aircraft in a second operating mode in which the main wheel assembly and the tail support both support the aircraft during the landing process.
In some examples of the second aspect, landing the aircraft in the first mode comprises applying down elevator to move the nose wheel into contact with the ground, and landing the aircraft in the second mode comprises applying up elevator to move the tail support into contact with the ground.
In some examples of the second aspect, landing the aircraft in the second operating mode further comprises: applying up elevator to move the tail support into contact with the ground; decelerating the aircraft; and applying down elevator to move the tail support out of contact with the ground and move the nose wheel into contact with the ground.
In a third aspect, there is provided an aircraft comprising: a fuselage extending in a longitudinal direction from a nose to a tail, and a main wheel assembly comprising a first main wheel spaced in a transverse direction from a second main wheel, the transverse direction being perpendicular to the longitudinal direction. The main wheel assembly is movable between a first fixed position with the first main wheel and the second main wheel in a first longitudinal position behind a center of gravity of the aircraft, and a second fixed position with the first main wheel and the second main wheel are in a second longitudinal position behind the center of gravity of the aircraft.
In some examples of the third aspect, the aircraft also includes a cross-member connecting the first main wheel to the second main wheel, and a cross-member mount. At least one of the cross-member and the cross-member mount is configured to selectively and alternately fix the cross-member to the fuselage in a first configuration with the first main wheel and the second main wheel in the first longitudinal position behind a center of gravity of the aircraft, and in a second configuration with the first main wheel assembly and the second main wheel assembly in the second longitudinal position behind a center of gravity of the aircraft. The cross-member mount may have a first mounting position configured to hold the cross-member in the first configuration, and a second mounting position spaced longitudinally from the first mounting position and configured to hold the cross-member in the second configuration. The cross-member may be slidably connected to the cross-member mount. The cross-member may be reversible relative to the cross-member mount between a first orientation in which the cross-member is in the first configuration, and a second orientation in which the cross-member is in the second configuration.
In some examples of the third aspect, the aircraft fuselage has an airframe, and the cross-member mount is formed integrally with the airframe.
In some examples of the third aspect, the aircraft also has a nose wheel located adjacent the nose and a tail support located adjacent the tail, with the main wheel assembly between the nose wheel and the tail support with respect to the longitudinal direction. The tail support may be a wheel or a skid. At least one of the nose wheel and the tail support may be removable.
In some examples of the third aspect, the main wheel assembly may be attached to the fuselage by one or more pivots having a rotation axis extending in the transverse direction such that the main wheel assembly is pivotable between the first fixed position and the second fixed position.
In some examples of the third aspect, the first main wheel and the second main wheel may be separately movable between the first longitudinal position and the second longitudinal position. The fuselage may have one or more forward mounting points configured to hold the first main wheel and the second main wheel in the first longitudinal position, and one or more rearward mounting points configured to hold the first main wheel and the second main wheel in the second longitudinal position. The one or more forward mounting points may include a respective front clevis and a respective rear clevis for the first main wheel, and a respective front clevis and a respective rear clevis for the second main wheel; and the one or more rearward mounting points may include a respective front clevis and a respective rear clevis for the first main wheel, and a respective front clevis and a respective rear clevis for the second main wheel.
In a fourth exemplary aspect, there is provided an aircraft landing gear assembly having: a main wheel assembly having a first main wheel, a second main wheel spaced from the first main wheel in a transverse direction, and a cross-member connecting the first main wheel to the second main wheel; and a cross-member mount configured to fix the cross-member to an aircraft frame. At least one of the cross-member and the cross-member mount is configured to selectively and alternately fix the cross-member to the cross-member mount in a first configuration with the first main wheel and the second main wheel in a first longitudinal position relative to the cross-member mount, and in a second configuration with the a first main wheel and the second main wheel in a second longitudinal position relative to the cross-member mount, the first longitudinal position and the second longitudinal position being spaced in a longitudinal direction that is perpendicular to the transverse direction.
In some examples of the fourth aspect, the cross-member mount may have a first mounting position configured to hold the cross-member in the first configuration, and a second mounting position spaced in the longitudinal direction from the first mounting position and configured to hold the cross-member in the second configuration. The first mounting position may have a first plurality of connector locations, and the second mounting position may have a second plurality of connector locations, wherein the first plurality of connector locations is identical to and spaced from the second plurality of connector locations.
The cross-member mount may have a cross-member track configured to retain the cross-member in contact with the cross-member mount, but allow the cross-member to slide between the first mounting position and the second mounting position when the cross-member is not fixed to the cross-member mount.
The cross-member mount may have a rail and the cross-member may have a collar slidably mounted on the rail.
The cross-member mount may have a screw and the cross-member may have a threaded collar mounted on the screw, such that the screw is rotatable to displace the threaded collar in the longitudinal direction. A motor may be provided to rotate the screw.
The cross-member may have a first mounting position configured to attach the cross-member to the cross-member mount in the first configuration, and a second mounting position spaced longitudinally from the first mounting position and configured to attach the cross-member to the cross-member mount in the second configuration.
The cross-member may be reversible relative to the cross-member mount between a first orientation in which the cross-member is in the first configuration, and a second orientation in which the cross-member is in the second configuration.
Exemplary embodiments will now be described, strictly by way of example, with reference to the accompanying drawings, in which:
Embodiments described herein provide an aircraft having its landing configured to operate in a hybrid of conventional and tricycle landing gear configurations. Embodiments also may provide main landing gear that are movable relative to the longitudinal axis of the aircraft between a first (hybrid) landing gear configuration and a second (tricycle) landing gear configuration. Such embodiments may be provided as an aircraft assembly, as a complete aircraft, as a retrofit assembly, or in any other suitable form.
A first exemplary embodiment is illustrated in
As best shown in
The illustrated cross-member 116 is a beam axle that is configured to flex to allow the wheels 114′ to move to some degree to provide a rudimentary suspension. The cross-member 116 alternatively may include articulated suspension members, such as a separate spring-biased trailing arm supporting each wheel 114′, telescoping shock absorbers, and so on. The cross-member 116 also may be replaced by any other suitable separate suspension member or linkage for each wheel 114′.
The aircraft 100 also includes a tail support 118 located at or near the tail 106, and a nose wheel 120 located at or near the nose 108. The tail support 118 is located aft of the main wheel assembly 114 with respect to the longitudinal direction L. The tail support 118 may include one or more wheels, skids or the like (a wheel is shown in
As shown in
When the main wheel assembly 114 is in the first configuration, the aircraft 100 is in a hybrid conventional/tricycle landing gear configuration (hereinafter a “hybrid” configuration). In the hybrid configuration, the aircraft 100 may be operated as a tricycle gear configuration, in which it is supported during takeoff and landing by the nose wheel 120 in the front and the main wheel assembly 114 in the rear. To this end, the positions of the main wheel assembly 114 and the center of gravity 122 are selected such that the center of gravity 122 is between the main wheel assembly 114 and the nose wheel 120 when the aircraft 100 is on the ground with the nose wheel 120 in contact with the ground. More specifically, the nose wheel 120 defines a front point of contact 124 with the ground G, and the main wheel assembly 114 defines a rear point of contact 126 with the ground G, and the center or gravity 122 is located between the front point of contact 124 and the rear point of contact 126 with respect to a horizontal direction H extending from the front point of contact 124 to the rear point of contact 126 (e.g., in front of the rear point of contact 126 by a distance A as shown in
For purposes of this explanation, the “point of contact” refers to the effective point of contact at the lateral center of the aircraft 100 (e.g., for the main wheel assembly 114 the “point of contact” is a location where a straight line connecting the points of contact for each individual wheel 114′ intersects the centerline of the aircraft 100). In most cases, the aircraft main landing gear will be symmetrical, and thus the point of contact will be understood to simply be the location at which the wheels 114′ of the main wheel assembly 114 contact the ground G.
It will also be appreciated that the points of contact 124, 126 and center of gravity 122 of the aircraft 100 can move depending on the underlying terrain (uneven ground, local bumps and holes, etc.) and the aircraft load (e.g., fuel, passengers, equipment, luggage, and the like). Thus, except as otherwise indicated, references to the points of contact are to the points of contact on level ground, and references to the center of gravity are to the aircraft's aft center of gravity (i.e., the rearmost limit of the center of gravity during flight, as specified by the aircraft manufacturer) while the aircraft 100 is parked on level ground.
In the first (hybrid) configuration, the main wheel assembly 114 optionally may be positioned relative to the center of gravity 122 such that the aircraft 100 can statically rest on the ground G on either the tail support 118, or on the nose wheel 120. For example, when the aircraft 100 is tilted rearward with the tail support on the ground G (as shown by the broken line) the center of gravity 122 may be positioned between a front point of contact 128 between the main wheel assembly 114 and the ground G, and a rear point of contact 130 between the tail support 118 and the ground G. Thus, the aircraft 100 is stable on the ground in either of two positions: nose down or tail down.
More preferably, however, the main wheel assembly 114 is positioned in the hybrid configuration such that the aircraft 100 will statically rest only on the nose wheel 120 (in combination with the main wheel assembly 114). In this embodiment, an external force may be applied to move the nose 108 up and the tail 106 down to place the tail support 118 on the ground, but the aircraft 100 will return to the nose-down position upon removing the external force. For example, in some embodiments, an operator could apply throttle and up elevator to cause the propeller 110 to generate propeller wash over the elevators, to force the tail 106 down into support on the tail support 118. This provides greater flexibility in how the aircraft is operated. For example, an operator can taxi the aircraft with the elevator in a neutral position and the nose 108 down for visibility, then apply thrust and up elevator at the beginning of takeoff to position the aircraft in a tail-down attitude for takeoff.
In the hybrid configuration shown in
For example, when approaching a paved runway, the pilot can land the aircraft 100 in the tricycle configuration by applying down elevator to push the nose 108 towards to the ground. When doing so, the placement of the main wheel assembly 114 close behind the center of gravity 122 allows the brakes to generate greater braking force than a conventional tricycle configuration (discussed below), due to the greater distribution of aircraft weight on the main wheel assembly 114. In this mode, the support provided by the nose wheel 120 makes the aircraft 100 less susceptible to nose-overs and ground loops.
In contrast, when approaching a field or other rough terrain, the pilot can land the aircraft 100 in the conventional “tail dragger” configuration with the tail support 118 on the ground, by applying up elevator to push the tail 106 towards the ground. In this mode, the nose wheel 120 is not used as a primary support during the initial landing, but the pilot may transition to the tricycle landing gear configuration (i.e., put the nose wheel 120 down by switching to down elevator) later in the landing process when there is less chance of the nose wheel 120 digging into the ground. During operation as a conventional landing gear aircraft, the nose wheel 120 is available to support the nose 108 of the aircraft 100 if the main wheel assembly 114 digs into the ground, to thereby reduce the likelihood of a nose-over. The nose wheel 120 can also contact the ground to help prevent a ground loop.
During takeoff, the aircraft 100 can be operated as a tricycle gear aircraft, with the nose down during initial taxiing and acceleration to the liftoff roll. In this configuration, the main wheel assembly 114 also optionally may be positioned to allow takeoff in the conventional configuration. For example, the aircraft 100 can start taxiing in the conventional configuration or transition from a tricycle configuration to the conventional configuration when the aircraft 100 gains enough speed to use the elevator to push the tail down.
Thus, an aircraft according to the embodiment of
Referring to
In the second configuration, the main wheel assembly 114 and center of gravity 122 preferably are not configured to statically support the aircraft when the aircraft 100 is tilted back to rest on the tail support 118.
The option to move the main wheel assembly 114 between the hybrid and tricycle configurations enhances the flexibility of the aircraft 100, and offers manufacturers and consumers the ability to tailor a single aircraft for significantly different uses. For example, a pilot who primarily operates on paved landing strips may opt for the tricycle configuration during normal use to maximize ground stability and provide somewhat simpler landing procedures. But the same pilot might enjoy the option of transitioning the aircraft 100 to the hybrid mode to occasionally operate the aircraft 100 in fields. The option of being able to select one configuration or the other is also a benefit to manufacturers to reduce manufacturing costs and reach a larger range of potential customers. This option is also a benefit to aircraft owners, even if they never make a transition from one mode to another, to maximize the resale market of the aircraft. Other benefits also may be available.
The exact position of the center of gravity and contact points with the ground for both the first (hybrid) configuration and the second (tricycle) configuration will vary depending on the size, shape, and weight distribution of the particular aircraft. However, desirable positions for the main wheel assembly 114 in the first configuration and the second configuration can be determined using conventional methods. In one example, particularly a small single-engine aircraft such as a variant of the “Piper Cub” aircraft, the main wheel assembly 114 may be positioned in the second configuration such that the wheel axles are about 12 inches behind the center of gravity 122 (Dimension B in
In this example, the main wheel assembly 114 is moved from one configuration to the other by sliding them along an axis that is parallel with the ground G when the aircraft 100 is supported on the nose wheel 120. This is not strictly required, and in other cases, the main wheel assembly 114 may be repositioned between the configurations by moving them along different directions (e.g., see
Each mounting position 140, 142 may include any suitable arrangement of connector locations to attach the cross-member 116 to the cross-member mount 136. For example, each mounting position 140, 142 may include a pair of holes 144 that are shaped and sized to receive corresponding threaded fasteners 146 (e.g., bolts and nuts). For convenience, the connector locations at the first mounting position 140 may be identical to the connector locations at the second mounting position 142 (i.e., have the same physical layout), but spaced apart in the longitudinal direction. Thus, a single set of fasteners may be used to mount the cross-member 116 in either position, without changing the layout of the connectors. However, this is not necessary in all embodiments, and it will be appreciated that the connector locations may vary depending on the layout of the remaining parts of the aircraft. For example, the fuselage or frame may narrow in the longitudinal direction L, leading to connector locations that are more closely spaced at whichever mounting position 140, 142 is located in the narrower region. The cross-member 116 also preferably includes its own connector locations to properly match the connector locations on the cross-member mount 136.
In the shown example, the cross-member mount 136 comprises two laterally-spaced mounting rails 148, which are connected to each other by lateral frame members 150 to form an assembly. The assembly is then rigidly attached to the aircraft frame 138, such that it is internal or external to the fuselage fairing. In the shown example, the assembly is internal to the fairing, such that the cross-member 116 moves along slots along either side of the fairing, which provides relatively low drag. Any suitable connections may be used for these attachments, such as nuts and bolts, welding, and so on. In the case of a retrofit of an existing aircraft, the cross-member mount 136 may be provided as a separate part that is attached to the frame 138. In the case of new construction (or a more substantial rebuild), the cross-member mount 136 may be integrally formed with the rest of the frame 138 (e.g., the rails 148 are formed as structural members of the frame 138).
The illustrated mounting rails 148 are formed as metal plates that extend in the longitudinal direction L and include the required holes 144 for connecting the crossmember 116 at the desired mounting positions 140, 142. Additional sets of holes 144 may be provided to connect the cross-member 116 at other positions that are between, forward, or aft of the first and second mounting positions 140, 142. Such additional positions may be useful, for example, to accommodate different weight distributions among different aircraft (particularly if the cross-member mount 136 is a retrofit part that may be used in multiple different aircraft), to accommodate different aircraft loadings that might arise from changes in loadout (e.g., adding auxiliary fuel tanks or other equipment), or according to prevailing use conditions (e.g., further forward for more extreme off-runway use, or further backwards for on-runway use with higher luggage weights). In some cases, an additional mounting position may be provided to position the main wheel assembly 114 at a typical position for a conventional landing gear, which would be well in front of the hybrid position, such as shown by the broken line depiction 154 of the main wheel assembly in
The cross-member mount 136 also may have additional features to add operating convenience, safety or the like. For example, the cross-member mount 136 may include a cross-member track that holds the cross-member 116 adjacent the cross-member mount 136 as the cross-member 116 is moved between the mounting positions 140, 142. In the shown example, the cross-member track comprises a pair of lower rails 152 that extend parallel to and below the mounting rails 148. The lower rails 152 are connected at their ends to the mounting rails 148 to capture the cross-member 116 in place. Thus, the cross-member 116 is slidably mounted to the cross-member mount 136 by the lower rails 152, which allow the cross-member 116 to slide between the mounting positions 140, 142 when the fasteners are removed, but prevent it from falling away from the cross-member mount 136.
Embodiments according to
The cross-member 116 may be configured to rotate relative to the cross-member mount 136 using any suitable collection of mechanisms or connectors. In one example, the cross-member 116 may be attached to the cross-member mount 136 by two bolts that are equally spaced from the lateral centerline of the aircraft 100, and so the configuration can be changed simply by removing the two bolts, reversing the cross-member 116, and reattaching the bolts. The cross-member 116 also may be attached to the cross-member mount 136 by a swivel that holds the two parts together as the cross-member 116 is being rotated. Such reconfiguration also may require reversing the brakes, or making other changes to address features that might not operate properly or as well when operated in reverse (e.g., reversing fairings on the wheels). Other alternatives and variations will be apparent to persons of ordinary skill in the art in view of the present disclosure.
Another exemplary embodiment is illustrated in
In an alternative embodiment, the pivot connector 1104 may comprise a connecting rod that rigidly joins the two wheel assembly 114. For example, each wheel 114′ may be rigidly connected by a splayed leg to one end of a horizontal shaft that acts as a cross-member, similar to what is shown in
Another exemplary embodiment is illustrated in
As another example (shown in
It will be appreciated that in each of the foregoing embodiments, one or both of the cross-member 116 and the cross-member mount 136 is configured to selectively and alternately fix the cross-member 116 to the fuselage in a first configuration with the main wheel assembly 114 in a first longitudinal position, and in a second configuration with the main wheel assembly 114 in the second longitudinal position. It is also envisioned that both the cross-member 116 and the cross-member mount 136 may be configured to allow such reconfiguration (e.g., a combination of the embodiments to allow multiple repositioning options).
Other alternatives and variations will be apparent to persons of ordinary skill in the art in view of the present disclosure. For example, in some embodiments the main wheel assembly 114 may be movable between the hybrid and tricycle positions (or to other positions) by separately moving each main wheel 114′. An example of this is shown in
It will also be appreciated that the landing gear need not be directly attached to the fuselage of the aircraft. For example, the main landing gear may be indirectly attached to the fuselage by being mounted on the wings, as is often the case with low- and mid-wing aircraft (i.e., aircraft in which the wing is located at the vertical midline of the fuselage or below). It will be understood that all references herein to connecting the landing gear assemblies to the fuselage include direct or indirect attachment.
It will be appreciated from the foregoing disclosure that embodiments of the invention may provide various benefits and advantages over conventional aircraft and landing gear. In addition to the benefits provided by the hybrid configuration (such as discussed above), adding a movable landing gear assembly provides even greater flexibility to the operator. For example, the operator may selectively change the landing gear configuration depending on the expected use conditions of the aircraft, such as: selecting the hybrid landing gear configuration for off-runway use; selecting the tricycle landing gear configuration for on-runway use; selecting the tricycle landing gear configuration when heavy crosswinds are expected or to obtain negative wing angle of attack to improve stability in windy weather; or selecting the hybrid landing gear configuration for short takeoff and landing operations. Embodiments may also may provide additional stability and safety when operating in either configuration, by including a nose gear when operating in the hybrid landing gear configuration with the tail down (thus helping prevent nose over), and including a tail gear when operating in the tricycle landing gear configuration (thus helping prevent damage from ground strikes). The foregoing benefits and advantages are provided as examples only, and it will be understood that embodiments may or may not accomplish or provide any particular one or the enumerated benefits.
The present disclosure describes a number of inventive features and/or combinations of features that may be used alone or in combination with each other or in combination with other technologies. The embodiments described herein are all exemplary, and are not intended to limit the scope of the claims. It will also be appreciated that the inventions described herein can be modified and adapted in various ways, and all such modifications and adaptations are intended to be included in the scope of this disclosure and the appended claims.
