Aeronautics and astronautics – Landing gear – Wheel
Reexamination Certificate
1998-11-06
2001-03-20
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Landing gear
Wheel
C188S380000, C301S036100
Reexamination Certificate
active
06202960
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to aircraft landing gear, and more particularly, to systems for inhibiting vibration of aircraft landing gear during braking.
BACKGROUND OF THE INVENTION
Certain friction characteristics in aircraft landing gear brakes can lead to fore-and-aft oscillations of the landing gear called “gear walk.” These friction characteristics are frequently associated with a particular type of brake lining. Historically, this brake lining friction characteristic has been called “negative damping,” since it effectively feeds energy into the landing gear system. Negative damping is mathematically defined as an increase in brake friction that is proportional to a decrease in brake lining rubbing speed. As the aircraft slows to a stop, the brakes become grabby and torque increases without having received an increase in brake pedal pressure. This change in torque can cause divergent oscillations of the landing gear in the fore-and-aft direction, such as those shown in FIG.
1
. The vibrations are initially small but become larger with each oscillation until some peak amplitude A is reached as shown in FIG.
1
.
Gear walk is generally an undesirable characteristic, due to the loads that can be imposed by the oscillations of the landing gear components. In addition, the resultant aircraft motion during braking may be disconcerting to passengers and crew.
Currently, it is known that a tuned mass absorber can be employed to address a forced steady state vibration problem where attenuation of vibration of some object is desired. The classic application is to apply a tuned mass absorber to a second order mass spring damper-type assembly that is being excited by an external sinusoidal force. A tuned mass absorber is attached to the assembly and is sized and tuned using a steady state analytical solution to the problem. This results in the peak amplitude assembly motions being greatly attenuated. The classic tuned mass absorber application can be demonstrated in the following simplified example. Referring to
FIG. 2
, an object O with mass M
1
is moved relative to ground through a spring S
1
having a spring constant K
1
. The object O is subjected to a force Fsin(&ohgr;t) which results in vibration of the object O. The force cannot simply be eliminated due to some unspecified reason. The goal is therefore to reduce the vibration of the object O by some other means.
One method of achieving this goal is to employ a tuned mass vibration absorber. This is represented in
FIG. 2
as an absorber mass M
2
attached to a spring S
2
having a spring constant K
2
. The spring S
2
is further attached to the object mass M
1
. The mass M
2
is allowed to move. If mass M
2
and spring S
2
are properly tuned, then the motion of the mass M
2
will exert a force on mass M
1
that is equal and opposite to the force already acting on the object O. The result is a cancellation of forces, with the object O remaining at rest while the absorber mass M
2
moves in a sacrificial manner. The design of a tuned mass absorber requires knowledge of the frequency &ohgr; of the object's motion, the magnitude of the sinusoidal force F acting on the object, and either the maximum allowable size of the absorber mass M
2
or its maximum allowable range of motion X
2
. The following equation describes the relationship between these variables.
F=−k
2
×X
2
=−&ohgr;
2
×M
2
×X
2
(1)
Using data from a recent case of gear walk as an example, calculation of the equivalent force F required to move the landing gear at the peak vibration amplitudes observed was as high as 2330 pounds. The landing gear motion occurred at a natural frequency of 9.7 Hz. With a space constraint of 3.1 inches of allowable peak to peak motion, then equation (1) indicates that a mass M
2
of about 150 lbm is required to produce a counterbalancing motion for amplitude A.
It is clear that using the classical design methodology, a rather heavy tuned mass absorber is required to reduce the undesired landing gear motion. This is an impractical solution for aircraft due to the weight penalty, and the fact that landing gear retraction actuators would not be sized for this additional load. Thus, a need exists for eliminating gear walk in a manner that does not add large amounts of weight to the aircraft and that does not require large amounts of space. The present invention is directed to fulfilling this need.
SUMMARY OF THE INVENTION
In accordance with aspects of the present invention, an improvement to an aircraft landing gear system is provided. The landing gear system includes a braking assembly, an elongated strut, and a wheel and tire assembly attached to a strut distal end. During use, the landing gear system exhibits fore-and-aft gear walk motion about an axis of rotation located above the wheel in a lateral plane. The gear walk motion is divergent and is caused by self-excited brake forces. The divergent motion includes a peak amplitude motion and a pre-peak amplitude motion. The improvement includes a tuned mass absorber attached to the strut near its distal end. The tuned mass absorber is oriented to cause its mass to move in a fore-and-aft direction at a frequency and amplitude that counterbalances the gear walk pre-peak amplitude motion by using a mass of an amount less than the mass required to counterbalance the gear walk peak amplitude motion. The tuned mass absorber thereby eliminates the gear walk motion in its formation.
In accordance with other aspects of this invention, a method of eliminating aircraft landing gear fore-and-aft vibration is provided. The vibration includes a peak amplitude motion and a pre-peak amplitude motion. The method includes using a tuned mass absorber attached to the landing gear. The tuned mass absorber includes a mass of an amount addressed to the pre-peak amplitude motion.
In accordance with other aspects of this invention, the tuned mass absorber includes a housing canister having first and second interior regions and a middle interior region, a metal coil spring housed in the first interior region, and a mass housed in the middle interior region and engaged with the spring. In an alternative embodiment, the tuned mass absorber includes a housing canister, an elastomeric material, and a mass.
REFERENCES:
patent: 2736393 (1956-02-01), O'Connor
patent: 2838137 (1958-06-01), Wallerstein
patent: 3133717 (1964-05-01), Hartel
patent: 4326755 (1982-04-01), Fretz, III
patent: 4475634 (1984-10-01), Flaim et al.
patent: 4619349 (1986-10-01), Braun
patent: 4697781 (1987-10-01), Hamano et al.
patent: 4991698 (1991-02-01), Hanson
patent: 5099961 (1992-03-01), Dreilich et al.
patent: 5255761 (1993-10-01), Zaremsky
patent: 5310025 (1994-05-01), Anderson
patent: 5564537 (1996-10-01), Shoureshi
patent: 5573088 (1996-11-01), Daniels
patent: 5590743 (1997-01-01), Houmard et al.
patent: 5746394 (1998-05-01), Gunnoe et al.
patent: 5806794 (1998-09-01), Hrusch et al.
patent: 5816373 (1998-10-01), Osterberg et al.
patent: 5945598 (1999-08-01), Enright
Batts Nathan D.
DeVlieg Garrett H.
Travis Matt H.
Christensen O'Connor Johnson & Kindness PLLC
Jordan Charles T.
Palo Francis T.
The Boeing Company
LandOfFree
Aircraft landing gear absorber does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aircraft landing gear absorber, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aircraft landing gear absorber will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2448533