Aeronautics and astronautics – Landing gear – Tail supports
Reexamination Certificate
2000-03-07
2001-07-10
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Landing gear
Tail supports
Reexamination Certificate
active
06257521
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates generally to landing gear construction for small aircraft. More particularly, my invention relates to a tail wheel assembly for small aircraft that secures the tail wheel and eliminates jarring or jerking, and other unwanted vibration, thereby preventing tail wheel shimmying.
II. Description of the Prior Art
In general, the concept of stability relates to the characteristics of an aircraft in maintaining its course and direction. In flight, the term “stability” is often equated with the ability of the plane to fly itself. Stability can either be static or dynamic. Static stability involves only the return of the disturbed object to its original position. This was the goal of the early airplane designers; that the airplane would try to return to its original orientation (position) after a disturbance, such as a gust of wind. Dynamic stability is concerned with how much time it may take for the object to return to its original position. If the plane eventually returns to its original position, then the system is considered dynamically stable. If it does not, then it is considered dynamically unstable.
The concept of “control” is a science relating to the human experience in flying and handling a given aircraft. The concepts are related, because when “control” is optimized, a given airplane will be relatively easy for the pilot to fly, and highly stable in flight. The small airplanes used at local airports are very stable; they are good for both beginning pilots and the more experienced pilots. They are very easy to fly and very forgiving of pilot mistakes. Although usually discussed as flight characteristic, stability and control are equally important during takeoff and landing.
When the plane is in contact with the runway, sudden movements to the left or right of the landing surface are disfavored. Stability dictates that the plane move forwardly and decelerate smoothly during a landing without sudden “jerkiness.” Similarly, as a plane taking off leaves the runway and breaks contact with the ground, irregular movements caused by runway-contact can affect flight path stability. One significant cause of vibration and jerkiness during takeoffs and landings is the tail wheel assembly, that can vibrate deleteriously when I contact with the runway.
While on the ground, static stability is enhanced by the normal three-point wheels of the aircraft. Usually a single tail wheel assembly at the aircraft rear completes the “third point” necessary for establishing a stable, planar position. With older small planes having “fixed” tail skid assemblies, the tail skid may be permanently oriented in a position parallel with the longitudinal axis of the airframe. In some tail wheel mounting designs, upward or downward movements of the tail wheel are enabled. However, if the tail wheels are mounted too loosely, they will shimmy or vibrate during takeoffs and landings. On the other hand, if they are secured too rigidly, and cannot “give” in response to runway contact, proper handling can be negatively affected during landings. The time periods just before liftoff, and during landings, are often critical, and yet conventional tail wheel mounting assemblies allow the reartovibrate.
The latter problem can be particular vexatious when operating agri-chemical dispensing airplanes from dirt runways. When the plane takes off, it is full of fuel and agrichemical, at maximum weight. Jolts or jerking motions imparted by vibrating tail wheel assemblies during takeoffs can be disconcerting, to say the least. When the plane returns for a landing, it is much lighter, and flight characteristics are different than they were immediately after takeoff. During a landing, when the tail wheel makes first contact with the landing surface, a “smooth” and non-jerky transition is desirable. In the fraction of a second that the plane is neither fully airborne nor fully landed, the path of least resistance for wheel movement may not be straight down the runway. In other words, because of wind gusts and numerous other variables, a sleight movement in tail wheel orientation from “true straightness” can decrease stability.
In other words, during takeoffs and landings especially, conventional tail wheel assemblies vibrate, rattle, and shimmy. If the tail wheel assembly is modified to prevent vibration, it must nevertheless be able to “give” slightly when contacting the ground.
SUMMARY OF THE INVENTION
My new shimmy-preventing tail wheel assembly mounts between a conventional aircraft tail spring and an original tail wheel fork. A rigid hub assembly comprises a sleeve-like central hub, that is mated to a lower, cooperating spindle assembly. A rigid arm projecting from the hub is bolted to the tail spring. The spindle assembly comprises a rigid, lower flange adapted to mate with the aircraft tail wheel fork. The spindle assembly is rotatable relative to the hub assembly, so the tail wheel fork supported thereby can rotate around its axis.
The spindle assembly comprises a rigid sleeve coaxially extending from a lower mounting flange through and within the hub assembly. A pair of bearing assemblies are mounted on opposite ends of the hub assembly. A special bushing aids in axially pressuring and radially centering the bearings when they are compressed together. An internal, elongated bolt extending upwardly from the spindle assembly terminates in a threaded terminus engaged by a castellated nut that axially secures the bearings within suitable races fitted on opposite ends of the central hub.
The nut is tightened to approximately one hundred foot pounds of torque to preload the assembly. This “pre-load” prevents the tail wheel from swinging freely and shimmying or vibrating. Uncontrolled shimmying results in dangerous vibration that can cause damage if continued unabated. However, the dual bearings of the present construction combined with the weight of the aircraft on the ground, easily rotates the assembly about the longitudinal axis of the torqued bolt so that the aircraft can maneuver on the ground with ease. In fact, due to the bearings, the aircraft is able to move more “freely” than if it only had conventional metal bushings, as is commonly the situation. The “pre-loading” actually pits one bearing against the other in a highly unique manner not originally intended for the bearings.
This synergistic “pre-loading” of the axially spaced-apart bearings actually acts as a “brake” that makes it impossible for the tail wheel to shimmy and shake uncontrollably during the critical takeoff and landing rolls. The special bushing assures that the torque remains constant during normal operations.
Thus a basic object is to provide a shimmy-free tail wheel mounting assembly for small aircraft.
Another basic object is to provide an after-market system for mounting tail wheels that minimizes shimmying and vibration.
Another important object is to provide a tail wheel mounting system of the character described that is suitable for user-installation.
Conversely, an important object is to provide a system of the character described that can be installed with new aircraft.
Yet another object is to provide a bushing construction that both radially centers and axially stresses the bearings.
Another basic object is to provide a highly stable and impact-resistant tail wheel system for aircraft.
Another important object is to provide an aircraft tail wheel assembly of the character described that makes it easier to take off and land, especially on irregular dirt runways or grass landing strips.
A related object is to minimize jarring or jerking effects.
A still further object is to minimize noise, and maximize strength
These and other objects and advantages of the present invention, along with features of novelty appurtenant thereto, will appear or become apparent in the course of the following descriptive sections.
REFERENCES:
patent: 2105374 (1938-01-01), Saulnier
patent: 2329823 (1943-09-01), Camburn
patent: 2394825 (1946-02-01), Trader
patent: 2473645 (1949-06-
Best Christian M.
Carver Stephen D.
Jordan Charles T.
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