Aeronautics and astronautics – Landing gear – Wheel
Reexamination Certificate
2002-11-25
2004-04-20
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Landing gear
Wheel
Reexamination Certificate
active
06722610
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system, method, and computer program product for controlling maneuverable wheels on a vehicle, and, more particularly, to a method, system, and computer program product for a controlling a plurality of steerable wheels on a vehicle in order to individually steer each maneuverable wheel according to a steering radius and a crab angle.
BACKGROUND OF THE INVENTION
Vehicles require a high degree of ground maneuverability. Large vehicles tend to have limited maneuverability due to many factors. Many of the present steering system designs for such vehicles, however, do not always accommodate some of desired maneuvering situations. For example, aircraft typically taxi to a position at an airport where portable docking equipment is attached for loading and unloading. Some examples of portable docking equipment include passenger jetways, cargo conveyors, lifts, loaders, etc. To date, docking equipment must be portable due the inability of aircraft to precisely maneuver about fixed equipment or structures. The capabilities of docking equipment are limited due to size and weight constraints necessary to maintain portability. Thus, fixed docking equipment that accommodates aircraft has not been designed. If aircraft could precisely maneuver with respect to fixed structures then the potential for more complex docking equipment may be realized. Eliminating the size, weight, and portability requirements permits more complex systems, perhaps linking multiple airplanes, trucks, trains, and so forth. Such a system has the potential for high throughput and extensive automation, both factors in high efficiency. Therefore, for these and other reasons it would be advantageous to improve the ground maneuverability of many vehicles, including aircraft.
Ground maneuverability of many large vehicles is accomplished by a single wheel or set of wheels along the forward portion of the vehicle. Large transport vehicles, in particular, require a plurality of wheels, fore and aft, to effectively support a payload. These vehicles typically have very long wheelbases. Turning radius is increased with wheelbase on vehicles that steer by pairs of wheels, with pairs or multiple pairs of wheels tracking behind, cars and trucks for example. A large turning radius compromises maneuverability of such vehicles in close quarters, thus restricting their capacity to operate in confined spaces.
Large air transports, are also limited in maneuverability, however, this has more to do with typical wheel arrangements. Low wing transports that tend to align the landing gear along a spanwise axis arrange the tires in groups that are displaced fore and aft from the average spanwise axis of the landing gear. A typical grouping is two by two. These gears do not steer. Steering is provided by forward-mounted nosewheels. The ground maneuverability of aircraft with such landing gear is compromised by tire scrubbing on the non-maneuverable landing gears. The assembly of the wheels, tires, and interconnecting structure on landing gear is usually called a “bogey” or “truck”. The fore/aft displacement of the parallel wheels produces tire scrubbing. With such bogeys, there is no single intersection of the nosewheel and main gear axes.
A degree of scrubbing results from a fore/aft gear separation and is dependent primarily on the fore-aft dimension. An additional scrubbing factor is the track between the extreme left and right gears. A wide track gear will place the inboard gear close to the turn center point, exacerbating the scrubbing on the inboard gear. There are a few airplanes with six wheel bogies—three pairs of wheels. The large wheelbase of such a bogey reduces maneuverability to unacceptable levels if all wheels are fixed. The typical solution is to steer the rear pair of wheels on the bogey driven by the same steering input provided for the nose gear.
Nose wheel to main gear wheel base, that is the longitudinal distance between the nose gear axle and the main gear axles, also affects maneuverability, albeit to a smaller extent. When the airplane is steered by the nose gear alone, the main gear do not follow the same track as the nose gear. Instead, the main gear tends to track inside the path of the nose gear. This increases the effective width of the gear if the nose gear follows the taxiway centerline. To date, the common solution to this problem is to use only airports that have sufficiently large runways, taxiways, and aprons to allow for large steering maneuvers.
Some very large high-wing transports use main landing gears that are arrayed in a longitudinal direction along the fuselage sides at an average position that is behind the center of gravity. Steering is also provided by a forward-mounted nose wheel. Due to the longitudinal extent of the main gear, large turning diameters and increased tire scrubbing seriously reduce ground maneuverability. Some aircraft solve this problem by allowing the aft main gear struts to castor.
Other high-wing transports, such as the B-52 bomber, have main landing gear that is located well in front of the center of gravity and additional landing gear located well behind the center of gravity to make room for a disposable payload in a bomb bay. The B-52 has four main gear struts, two forward and two aft of the bomb bay. On each strut are two coaxial wheels. The angle of each pair can be controlled. For steering, only the forward pairs are controlled—the aft pair remains fixed. For crosswind landings and takeoffs the angle of all struts are moved in concert so that the axles are parallel. The principal shortcoming is that it is very narrow so that the airplane tends to tip over. The B-52 uses additional small, castering outrigger landing gears near the wing tips to prevent tip over. This limits the B-52 to very wide runways.
There are some ground transport vehicles with a plurality of wheels that can be steered. Most of these are steered only with the forward pair of wheels. This results in substantial tire scrubbing and limits the minimum turning radius. Some large trucks solve the maneuverability problem by introducing articulation between the tractor and the trailer, but articulation is not practical in many vehicles.
One successful attempt to improve steering on large ground transports has been effective on the Tunner 60K Loader, built by Systems & Electronics, Inc., of St. Louis, Mo. The 60K Loader is a 20-wheel cargo handling vehicle with ten pairs of wheels arrayed in two longitudinal columns and five rows. The forward two rows and aft two rows steer. The driver, via a mechanical linkage, provides steering command. If the design were applied to other vehicles, such as aircraft, the 60K loader design has limited maneuverability chiefly because the suspension geometry and proximity of the chassis limit the angle to which the wheels can be turned. The mechanical linkage additionally limits the maximum wheel turning angle. When steering the fore and aft gear the vehicle follows a common track, and the rear wheels do not track inside the front wheels. The 60K loader can pivot only about a point that is collinear with the fixed middle wheels. As such, a chief limitation of the 60K loader design is the inflexible steering geometry. Additionally, the 60K loader does not have any ability to steer to a crab angle. Therefore, when applied to other vehicles, the 60K loader design is limited by the heavy steering linkage, the inability to crab, and the inability to pivot about any point not on the axis of the fixed wheels.
Aircraft face an additional maneuverability problem with respect to crosswinds on takeoffs and landings. Almost all large air transports use one of two techniques for landing in a crosswind. In the first technique the airplane is flown wings-level with the airplane crabbed with respect to the ground track to account for the crosswind component. At the last moment before touchdown, the pilot uses the rudder to yaw the airplane and landing gear so that it is better aligned with the runway axis. This is a challenging maneuver
Hoisington Zachary C.
Rawdon Blaine K.
Alston & Bird LLP
Barefoot Galen L.
The Boeing Company
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