System and method for landing a tailless aircraft in a crosswind

The method of landing a flying wing type aircraft in a crosswind includes the steps of disengaging the nose landing wheel upon impact with the runway so that it is free to castor; and thereafter, engaging the nose wheel after a specific time period after the nose wheel impacts the runway such that the nose wheel is steerable. The system for landing a flying wing type aircraft in a crosswind on a runway includes a steering system for steering the nose wheel, the steering system having a first condition wherein it controls the angular position of nose wheel and a second condition wherein the wheel is free to castor. A control system moves the steering system from the first condition to the second condition upon the wheel contacting the runway and moves the steering system back to the first condition after a specified time after the wheel contacts the runway.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of aircraft and, in particular, to a system and method for landing an unmanned tailless or flying wing type aircraft in a crosswind.

2. Description of Related Art

Flying wing or tailless aircraft have a particularly unique problem. They have no vertical surfaces to provide a lateral force to control the effect of a crosswind during landings where the aircraft's flight path is at an angle to the longitudinal axis thereof. While the tailless aircraft can land flat, its wheels will strike the runway with a larger lateral offset than a conventional aircraft with vertical surfaces. The nose wheel is in front of the center of gravity (CG) and the side force generated by the wheel is very unstable. The offset in the angle means that when the aircraft touches down there will be a sudden lateral jerk in the direction the wheels are pointing. The resulting acceleration will cause one wing tip to dip or in a worst case, it can result in a ground loop.

U.S. Pat. No. 5,523,921 Aircraft Steering System And Method For Large Aircraft Having Main Landing Gear Steering During Low Taxi Speed While Nose Gear is Castored by H. C. Ralph discloses the concept of allowing the nose wheel to castor so that differential braking of the main landing gear can be used to turn the aircraft. The nose wheel landing gear includes a system to allow for turning with the nose wheel, but allows it to castor on command. The nose wheel steering system is described in Great Britain Patent No.: 879,279 Improvements Relating To Steering Mechanism For An Aircraft Ground Wheel Mounting by H. Cyril, et al. and is herein incorporated by reference.

Thus, it is a primary object of the invention to provide process to allow a tailless aircraft to land in a crosswind.

It is a further object of the invention to provide a process to allow a flying wing type aircraft to land in a crosswind by reducing the adverse effect at the moment of touchdown due to crabbing of the aircraft in a crosswind.

SUMMARY OF THE INVENTION

The invention is a method and system for landing a flying wing or tailless type aircraft on a runway in a crosswind. The aircraft includes a nose landing gear equipped with a steering system to steer the nose wheel that includes a control system to engage and disengage the nose landing gear wheel, and a main landing gear. The method includes the steps of:

1. Disengaging the nose landing wheel steering system upon impact with the runway so that it is free to castor; and

2. Engaging the nose wheel steering system after a specific time period after the nose wheel impacts the runway such that the nose wheel is steerable.

Preferably, the step of disengaging the nose landing wheel steering system upon impact with the runway so that it is free to castor includes the step of actuating a switch upon maximum contraction of the nose landing gear upon impact with the runway. Preferably, the step of actuating a switch upon maximum contraction of the nose landing gear upon impact with the runway includes the step of initiating a timing device to automatically reengage the nose landing gear steering system after the specific time period has passed. Furthermore, the step of engaging the nose wheel steering system after a specific time period after the nose wheel impacts the runway such that the nose wheel is steerable includes the step of deactivating a switch upon the nose landing gear returning from its maximum deflection upon impact with the runway.

The system includes a steering system for steering the nose wheel, the steering system having a first condition wherein it controls the angular position of the nose wheel and a second condition wherein the wheel is free to castor. The system also includes a control system for moving the steering system from the first condition to the second condition upon the wheel contacting the runway and to move the steering system back to the first condition after a specified time after the wheel contacts the runway.

The system further includes a position sensor mounted on the nose landing gear adapted to sense the initial compression of the nose landing gear upon touchdown on the runway and send an actuation signal to the steering system to cause the steering system to move to the second condition. Additionally, a timing device is incorporated to cause a second signal to be sent to the steering system to cause the steering system to return to the first condition after a specific period of time.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings in which the presently preferred embodiments of the invention are illustrated by way of examples. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1and, the tailless or flying wing aircraft, generally indicated by numeral10, includes a center fuselage section12having a longitudinal axis13, wing14, and a nose16with an extended nose landing gear18having a shock strut19with wheel20, and an extended main landing gears22A and22B with shock struts23A and23B with wheels24A and24B. The CG of the aircraft, indicated by numeral24, lies between the nose16and main landing gear22. The aircraft10is shown at a point just prior to landing on the runway30at an angle of attack, indicated by numeral32.

FIG. 4is a cross-sectional view of the nose landing gear, which is a modified version of the landing gear disclosed Great Britain Patent No.: 879,279 Improvements Relating To Steering Mechanism For An Aircraft Ground Wheel Mounting by H. Cyril, et al. aircraft such that one wing will dip and may strike the ground. It may even cause a ground loop.

Now referring toFIG. 3, with the nose wheel20free to castor, the above-described problem is eliminated. Now when the aircraft10touches down on the runway30, the nose wheel20castors eliminating any gripping action that the nose wheel would otherwise produce. The main landing wheels24A and24B being behind the CG will automatically straighten the aircraft10out so faces the direction it is traveling which is directly down the runway30.

To accomplish this action, a nose wheel assembly such as disclosed in described in Great Britain Patent No.: 879,279 Improvements Relating To Steering Mechanism For An Aircraft Ground Wheel Mounting by H. Cyril, et al. is used as modified as follows. Because the Cyril, et al. invention is fully described in the published patent only a general outline of that invention is provided herein and inFIG. 4. The landing gear18includes a housing44having a closed off first end46and open second end48. Rotatably mounted within the housing44is a hollow steering member50having a reduced portion52extending through a hole54in the first end46of the housing44and a second end terminating in a crank portion56. A lever58is connected by a first end60to the end of the crank portion56and by a second end62to the wheel20providing support therefore.

A shock strut19connects by a first end64to the lever58between the first end60and second end62, and extends into the steering member50and is connected by its second end66thereto. Thus loads induced by the wheel20in contact with the runway30will cause the lever58to pivot about its first end60causing the shock strut19to compress and absorb loads. The reduced end52of the steering member50connects to a hydraulically actuated rack and pinion system70having a hydraulic control circuit71. The system70is used to rotate the steering member50and thus the wheel19. This rack and pinion system70can be switched to a condition wherein the steering member70is free to rotate upon demand. As previously stated the details of the system are fully discussed in the Cyril, et al. patent. The Cyril, et al. system is modified by the incorporation of a position sensor72mounted between the lever58and crank portion56that is designed to send a signal to a timing device74which in turn couples to the hydraulic control circuit76.

Still referring toFIGS. 3-4and additionally toFIG. 5, when the aircraft10lands on the runway30, the initial contact of the wheel20with the runway will cause the lever58to rotate about its first end60to a maximum deflected position indicated by numeral58A. This immediately causes the sensor72to move from a normally open position to a closed position and causing the timing device74to send a signal to the hydraulic control circuit76that allows the steering member50to freely rotate allowing the wheel20to castor. After some time delay, the timing device74then sends a second signal to the hydraulic control circuit76reinstating steering control. The time delay typically ranges from 1 to 3 seconds. Thereafter, the lever58, now under normal aircraft loads, returns to a semi-compressed state indicated by numeral58B at which points the sensor72returns to its normally open position.

In Applicants co-pending patent application Serial No.: 11/165,018 Process For landing A Tailless Aircraft, Filed June 2005, herein incorporated by reference, system is disclosed that makes use of a shock strut having rebound rate much slower than the compression rate. Thus, the shock strut were incorporated, there would be no need for a timing device. The sensor72can then be a switch that would sense the initial movement of the lever58and send a second signal when the shock strut returned to its normal partially compressed state wherein only the weight of the aircraft is absorbed.

The shock struts19of the nose landing gear18and the shock struts23of the main landing gears22are the key to the invention. The nose landing gear strut19is designed to have a shock return time greater than the shock struts23.

Thus it can be seen that the use of the Cyril, et al. landing gear with the incorporation of a sensor72, can eliminate the adverse effects caused by a non-castoring nose wheel when landing a flying wing or tailless type aircraft in a crosswind.

While the invention has been described with reference to particular embodiments, it should be understood that the embodiments are merely illustrative, as there are numerous variations and modifications, which may be made by those skilled in the art. Thus, the invention is to be construed as being limited only by the spirit and scope of the appended claims.

INDUSTRIAL APPLICABILITY

The invention has applicability to the aircraft manufacturing industry.