CA2023934A1

CA2023934A1 - High aspect ratio tennis racket head and method of stringing

Info

Publication number: CA2023934A1
Application number: CA002023934A
Authority: CA
Inventors: Richard Janes
Original assignee: Spalding and Evenflo Companies Inc
Current assignee: Spalding and Evenflo Companies Inc
Priority date: 1989-10-30
Filing date: 1990-08-24
Publication date: 1991-05-01
Also published as: DE4028401A1; FR2654352A1; DE9017690U1; GB9019585D0; SE9003442L; AU6487190A; IT9048388A0; SE9003442D0; ES2026056A6; IT9048388A1; IT1246320B; JPH03170174A; GB2237513A

Abstract

ABSTRACT OF THE DISCLOSURE
An improved tennis racket with a frame fabricated of graphite fibers in an epoxy resin matrix formed in a tubular configuration, the frame including a handle at one end; a head at the other end; beams therebetween coupling the head and handle; and a yoke cohered to the lower ends of the head to thereby generally form an ellipse, the head having a major axis coextensive with the axis of the frame and being of a first dimension when measured at the widest point of the interior edge and having a minor axis transverse with respect thereto measured at the widest point of the interior edge of the frame, the minor axis to major axis aspect ratio being about 0.9:1, the beams being formed linearly and diverging from the central axis equally and oppositely at about 30 degrees for supporting the head, at their upper ends, at regions widely spaced from the axis, the area within the head being between about 95 and 105 square inches. Also disclosed is a frame for such tennis racket. Also disclosed is a method of stringing such frame with the horizontal strings at a higher pull tension than the vertical strings.

Description

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, HIGH ASPECT RATIO TENNIS RACRET HEAD AND METHOD OF STRINGING
BACl!tGROUND OF T~E INVENTION
Field of the Invention I This invention relate~ ~o a high aspect ratio ., .~i tennis racket head and method of ~tringing and, more particularly, to a tenni~ racket having an elliptical head ~:
- with about an 0.9 to 1 aspect ratio with linear be2m portions coupling the head and handle and to a method of stringing such racket to insure proper ten~ioning without deformation of the racket frame.
Backqround of the Prior Art -: In tennis, players u~e rackets to ~trike a resilient ball acros~ a net. The racket is constructed of a frame having a handle end gripped by the player, and having a looped head portion with crossed strings, and having an intermediate portion or beam~ coupling the handle and head. -Rackets are normally symmetric about a central axis along the length of the handle and through the head. Most rackets have head~ which are oval or elliptical in shape with itB longer dimension in the direction of the axis and with it~ smaller dimension tran~verse thereto. The strings are strung through the head at a predetermined tension ad~usted to the style of play of the u~er.. Generally, the string~
define a sweet spot located at or sligh~ly below the ... . .
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l geometric center of the head. The 6weet spot i8 that point i where, when ~triking a ball, minimum vibrations are imparted to the player and near maxlmum power i8 generated for propelling the ball away from the strings. A particular distance from the sweet spot in all directions i8 the power zone where ignificant power is 8till imparted to a ~truck ball even though not at the sweet ~pot it~elf. Ihe power zone may al~o be defined as any point on the ~trings with a 0.35 or greater coefficient of restitution.
Head~ are elliptically designed with their ~ transver~e dimen~ion, mea~ured at their widest point, being - about 75 percent of their longitudinal or axial dimension, measured at their widest point. This i8 a 0.75 to 1.0 (0.75:1) aspect ratio. By having hi~her aspect ratio~
approaching 1:1 or even higher, there will be a movement of ` the sweet ~pot higher on the racket head away from the i handle. Due to the shorter overall head length, the sweet i~ ~pot i8 moved a greater distance from the handle. Thi~
incresses the mechanical advantage of the racket ~ince the ~weet spot is further from the handle and area of holding by the player.
;~ Increa~e~ of the aspect ratio ha~e the positive effect of abating twistinq of the racket about its axis in the hand of the player when a ball i~ ~truck laterally off~et ?

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, from th~ sweet spot and axis. However, most beam portions coupling the head and handle are curved in a rever~e direction, concave, with respect to the curvature of the head, convex. Such a curved beam configuration generates conta~t points on the head undesirably close to the axis,weakening head support and reducing racket ~tability while increasing the tendency of racket twisting during off-axis hits. In sddition, any curvature of the beams structurally weakens them from a mechanical ~tandpoint when compared to 6traight beams. Curved beams, whether concave or convex, deform more than straight beams. Further straight -~
beams couple with and ~upport the head at widely spaced tangent point~ for greater head stability.
`A collateral problem encountered with attempt~ to increase the aspect ratio of tennis racket heads i8 in the stringing. Tennis racket~ are normally held in a vice and ~trung by a machine preset to apply a particular nominal tension to the strings while interweaving them through hole6 ; in the frame. The ma~or or vertical string~, parallel with the axis, are normally strung from a first common string.
The minor or horizontal or cross string~, transverse to the axis, are then ~trung from a ~econd common string at the same !`~ tension. Becau~e of their ~hape approaching a circle, high ~ a3pect ratio rackets do not provide adequate frame strength .. :

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' and/or predetermined string ten~ion when strung in the conventional manner. AB a re~ult, it i8 not unconm~Smon to ~ee high aspect ratio heads which are deformsed and/or play with -~
string tensions at variance from their intended tensions due to unpredictable tensions and/or deformations of the frame during stringing. ~he present invention provide~ a more even response on the ball by the string~ ~n both axes.
The patent literature discloses various approache~
to high aspect ratio tenni~ racket frames. Note, for exam~sple, U.S. Patent No. 4,732,384 to SeymSour wherein a 1:1 a~pect ratio is utilized thus resulting in a totally circular frame. Such tennis racket feature~ a high 6weet spot with respect to the handle but, unfortunately ~uffers from the , defect of difficulty to string accurately. Further, the beam portions of the frame coupling the head and handle are in a `~reverse curve thereby weakening the frame at this area. The weakening is sufficient that it could deform during hitting to create errant ~hots. Further, such reverse curve makes ":
the beam contact with the ad~acent portions of the head excessively close to the axis thereby increa~ing the tendency of the racket to twist about it~ axis or the player's hand when striking the ball on the strings laterally off~et fro~
the sweet ~pot and axis. Lastly, such reverse curve makes contact lower on the head further weakening the coupling.

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United Kingdom Patent No. 427,206 to Naah disclose~
another circular racket having a 1:1 aspect ratio. It~ bea~ -~-portions of the frame coupling the head and handle are e~sentially linear. Such tennis racket wa~ designed in 1933 or earlier and was obviously constructed of wood and not of the more advanced material~ in a cylindrical configuration a~
utilized today.
7 Another patent, U.S. Patent No. 3,801,099 to Lair, illustrates an aspect ratio in a tenni~ racket head in exces~
of 1:1. In other words, its head width is greater than its length measured along the axi~. Such a design increa~es the mechanical advantage of the racket by raising the ~weet spot i with respect to the handle. Such racket, however, even further increa~es the problem of Rtringing and frame ~tability and, from a playing standpoint, i~ generally ' con~idered unwieldy.
A last patent of note is ~.S. Patent Number ;i 3,999,75 to Head. One of the ma~or disadvantages of the over~ized racket~ a8 disclosed in this patent is the fact that in order to realize control, the strings must be strung ,. ~
at extremely high tensions. This adds vibrations and i detracts from gripping of the ball by the string~ during hitting. This high string tension al~o adds to the danger of racket breakage due to the increased amount of force being f ~ :

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applied to the racket during ~tringin~. The pre~ent invention create~ a unique combination of characteristics not all present in the current over-sized racket. Th~ present racket has equal or greater stability due to the width of the head and throat which $8 the distance of the beam from the twist axis which i8 an imaginary line extending longitudinally along the center of the racket and handle.
Additionally, the present racket differs from the typical oversize racket in that the head is very ~hort instead of very long to thereby combine the stability advantage of wide head~ with the mechanical advantage of a short head. This i~
because the average player ~lway~ tries to hit the ball in the center of the head. Therefore, the center of the head of the present invention is a significant distance greater from ~: .
the player~ hand than in the prior art. Another distinct advantage i~ that due to the shorter string lengths, the present rackets are strung at`~ relatively lower string tension providing final tensions which are even in the cross and main strings.
The final prior art are those small headed rackets which have been commercially sold for several years. Such rackets have aspect ratios approaching 0.89sl but the area of the strings in the head is less than 70 square inche~. Such rackets used curved beams and have short ~trings. They do ~.~

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not have the stability of racket~ with wider heads and their ` target area are unacceptably ~mall. Simply ~tated, they were not very playable.
A~ illustrated by these patent~ and a great number - of other patents as well as commercial rackets, effort~ ara continuously being made in an attempt improve tennis rackets.
Such effort~ are made to render tenni~ racket~ of ever increasing capabilities during play. None of these previou~
efforts, however, provide~ the benefits attendant with the present invention. Additionally, the prior patents and commercial device~ do not suggest the present inventive combination of method steps and component elements arranged ~`
and configured as disclosed and claimed herein. The present ~-f~`i invention achieves its intended purposes, ob~ects and - ;
advantages through a new, useful and unobvious combination of method step~ and component elements, with the use of a ~` minimum number of functioning parts, at a reasonable cost to manufacture and by employing only readily available ; materials.
~` Therefore, it i8 an ob~ect of thi~ invention to provide an improved tennis racket with a frame fabricated of ,,.~ , graphite fibers in an epoxy resin matrix f~rmed in a tubular conf~guration, the frame includ~ng a handle at one end; a .. .
~`~ head at `the other end; beams therebetween coupling the head .~ ' -. '~ "'.
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and handle; and a yoke cohered to the lower ends of the head to thereby ganerally form an ellipse, the head having a ma~or axis coextensive with the axis of the frame and bein~ of a first dimension when mea~ured at the wides~ point of the interior edge of the frame and having a minor axis transverse with respect thereto when measured at the widest point of the interior edge of the frame, the minor axis to ma~Zor axis aspect ratio being about 0.9:1, the beams being formed linearly and diverging from the central axi~ equally and oppositely at about 30 degree~ for supporting the head, at their upper ends, at region~ widely spaced from the axis, the area within the head being between about 95 and 105 square ~nches and to provide a frame for such tennis racket and to provide a method of ~tringing such frame with the horizontal strings at a higher pull tension than the vertical stringZ~.
It is a further ob~ect of this invention to increase the aapect ratio of tennis rackets and thereby create a higher sweet ~pot and power zona with respect to the handle It is a further ob~ect of this invention to increase the mechanical advantage and stability of tennis rackets.
It iB a further ob~ect of this invention to coupl~
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;~ the head and handle of high aspect ratio tennis racket~ by .;~

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essentially linear beam portions coupling with the head tangentially at widely spaced points high on the head.
La~tly, it i8 an ob~ect of thi~ invention to string high a~pect ratio tennis rackets at different pull tensions - horizontally and vertically in order to attain resultant similarity of final tensions ~n the cross and main string~ ~ -.., ; and without deormation of the frame.
The foregoing has outlined some of the more !
'` pertinent ob~ects of the invention. ~he~e ob~ects ~hould be con~trued to be merely illu6trative of ~ome of the more , prominent feature~ and applicat~ons of the intended invention. Many other beneficial results can be attained by applying the di~clo~ed invention in a different manner or by ; modifying the invention within the ~cope of the disclosure.
,:, Accordingly, other ob~ects and a fuller under3tanding of the invention may be had by referring to the ~ummary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in con~unction with the accompanying drawings.
S~RY OF THE INVENTION
The invention is defined by the attached claims with the specific embodiments shown in the attached drawings.
For the purpo8e of summarizing the invention, the invention , .

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~ ~J ~ 3 ~ ~ 4 may be incorporated into an impro~ed tenni~ racket comprising ! a tubular fram~ configured into a handle, a head, intermediate beam~ therebetween and a yoke cohered to the lower portion of the head to thereby generally form an ellip~e, the head having a ma~or axis coextensive with the axis of the racket of a first ~imen~ion and having a minor axis trans~erse with re~pect thereto, the minor axis to ma~or axis aspect ratio being about 0.9:1, the beam~ of the frame being linear and diverging from the central axis equally and oppositely for supporting the head at location~ widely spaced from the axi~, the racket also including string~ ~trung hor~zontally and vertically through the head to constitute the striking surface of the racket.
' The beam~ extend at angles of about 30 degree~ from `~ the axis. The frame is fabricated of graphite fibers in an ~--epoxy resin. The strings form an area of between about 95 y and 105 sguare inches. The head is formed as an ellipse with its two focal point lying on the axis of the frame and racket. The racket further includes a grommet strip extending around the external periphery of ths head through which the strings pass in a serpentine path to con~titute the striking surface of the racket. The racket further include~
a bumper guard on the upper external periphery of the head.

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The invention may also be incorporated into an . improved frame fabricated of graphite fibers in an epoxy resin matrix formed in a tubular configuration, the frams including a handle at one end; a head at the other end; beams therebetween coupling the head and handle; and a yoke cohered

3 to the lower end~ of the head to thereby form an ellipse with the two focal point~ of the ellip~e lying on the longitudinal axis of the frame, the head havin~ a ma~or axi~ coexten3ive with the axis of the frame and being of a first dimen~ion when measured at the widest point of the interior edge of the : frame and having a minor axis transverse with respect thereto when measured at the widest point of the interior edge of the frame, the minor axis to major axis aspect ratio being about O.9sl, the beams being formed linearly and diverging from the central axi~ equally and oppositely at about 30 degree3 for .~ supporting the frame, at their upper ends, at regions widely paced from the axis, the area within the head being about 95 ;~
and 105 square inches. ;~:
Lastly, the invention may be incorporated into an ` improvad method of ~tringing a racket having a high a~pect ratio, the method including the ~teps of stringing a first common ~tring in a serpentine path through vertically ~:
di~placed holes in the frama at a first pull tension; and, ;-.
thereafter strLnging a ~econd common ~tring in a ~erpent~ne . ~, ~ .

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path through the horizontally displaced holes in th~ frame and interleafed through the ~trings of the first common , ~tring at a pull tension greater than the first tension to - thereby constitute primary and secondary string in a grid j pattern at an essentially common final tension without ,~ distorting the frame. The tension of the Recond ~tring is , i`1 `7-i about 10 lbs. greater than the firs~ tension. The first string is strung vertically and the second string i8 strung ~; horizontally. The vertical strings are longer than the horizontal 6trings.
The foregoing has outlined rather broadly the more ~ pertinent and important feature~ of the present invention in ', order that the detailed description of the invention that b ~
~`i follows may be better understood 80 that the present contribution to the art can be more fully appreciated.
Additional features of the invention will be described ~` hereinafter which form the sub~ect of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the disclosed specific ambodiment may be readily utilized as a basis for modifying or designing other structures for carrying out the same purpose~ of the ;
present invention. It should also be realized by thosQ
skilled in the art that ~uch equivalent conRtructions do not . . .
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depart from the ~pirit and scope of the invent~on as ~et forth in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the nature and ob~ects of the inventlon, reference should be had to the following detailed de~cription taken in con~unction with the -accompanying drawing~ in whichs Figure 1 is a perspective illustration of a tennis racket con~tructed in accordance with the principles of the present invention.
Figure 2 i~ a plan ~iew of the frame of the tennis racket ~hown in Figure 1.
~ Similar reference characters refer to similar part~ -~
;` throughout the several figures.
DETAI~ED DESCRIPTION OF THE INVENTION
With particular reference to the Figures, there i8 ~hown in Figures 1, a perspective illustration of a tennis racket lO constructed in accordance with the principles of the present invention. The frame 12, by 1tself, is shown in Figure 2, a plsn view.
The ma~or component of the tenni~ racket iB the frsme 12. Th~ frsme is constructed of conventional materiRls prefersbly graphite fiber impregnated with an epoxy resin a~
i~ commonly used in tenni~ rac}cets today. Other acceptable :-.

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materials include epoxy re~in with ceramic fiber, kevlar fiber or fiberglass fiber as well a~ aluminum. It is of a hollow tubular construction shaped in an oval configuration at the head or head end 14 and with the tube in parallel, ~ide-by-side relationship at the handle end or handle 16.
Therebetween, the frame ha~ an intermediate portion or beams lB coupling the head and the handle. A yoke 20 clo~e~ the oval at itCi lower end. The yoke i~ initially formed separately but coupled to the remainder of the frame during the fabrication process to thereby become an essentially integral component of the frame and racket. The beams and ~ -yoke form an open throat. The ~oining of the yoke with the head and the beam~ with the head i~ by cohe~ion, an intermingling of common components including fiber~ of the cohered material~. Adhered material~ such as wood components ~oined by glue are simply inadequate for the reguirements of the pre~ent lnvention. ?
The other principle component of the racket i~ the strings 24 and 26 which are ei6entially interwoven through holes in the frame along parallel lines. Main or vertical i stringi 24 extend parallel with the central axi~ 30 of the frame and racket. Minor or cross horizontal ~tring~ are strung in the head perpendicular to the central axis in an axis 32 and are interwoven through the vertical strings.

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Togather the stringR lie in a plane and constitute the striking surface for hitting the ball during play. The string~ extend through small hole~ or apertures 36 and 38 around the entire periphery of the head including the yoke which can be considered as an integral extension of the lower portion of the head. The main string~ are formed from a common first string extending through vertically aligned holes 36 while the minor strings are formed from a common ~econd string extending through horizontally aligned holes -~8.
` Another principle component of the racket i~ the handle 16. The handle is fa~ricated of a pallet or underlisting on the frame which i~ then covered by ~pirally wrapping leather or synthetic grip thereover. Neight~, as of lead, may be added to the handle portion of the frame beneath ~; the pallet for balancing purposes.
The head end of the frame may be provided with a grommet ~trip 42 and/or bumper strip 44. The ~rommet ~trip 42 is a moldable, hsrd, ~ynthetic material ~uch as nylon on ` the radial exterior of the head with barrel~ extending through the head hole~ through wh~ch the strings pass. The bumper ~trip 44 is also of a similar material and extend~
radlally exterior of the head at its upper extent. It extend~ axially a greater di~tance than the grommet strip to ,;

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pre,clude scraping the frame. Such components are conventional in the tennia art.
A~ can be seen in the Figures, the inner periphery of the head is of an elliptical shape. The two focal points 48 and 50 of the ellip3e are located on the main axis 30 of the frame within the head. The ma~or dimen~ion of the racket along the axi~ 30 i~ greater than the minor dim~,en~ion axis 32 which i~c~ perpendicular with respect to the ma~or dimen~Zion and axi~. Note the X and Y arrows of Figures 2. When measured at their w~dest points, the ratio of the minor axis to the ma~or axis is 0.9:1 plus or minu~ 5 percent. Thia~
relationship constitutea~ the aspect ratio of the head and racket. An aspect ratio iB defined as the ratio of one dimension to another. In the instant application the aspect ratio of the head aa referred to herein is the ratio of the width of the head measured at its wide~t point to the length of the head measured at its widest po$nt. In one preferred embodiment, the minor axis i~ 10.44 inches and the ma~or axi~
~'8 11.60 inches measured at the interior edges of the frame.
The overall length of the racket i~ 27 inche~. This represents a O.9sl aspect ratio with a 95 ~quare inch face ~;
within the head. In another preferred embodiment, the minor axi~ iB 10.98 inche~ and the ma~or axis i~ 12.20 inche~
meaRured at the interior edge~ of thZ'- fram~,e. Z~''he ov,erall ~ ' ~, ' ., ' .
~ length of the racket iB 27 inches. This repxesents a O.9sl ; aspect ratio with 105.1 ~suare inch face within the head. A
tring area of betw~en about 90 quare inche~ plu8 or minu~ 5 i percent i~ preferred, i.e., 95 to 105 ~quare inches.
The ma~ority of tenni~ racket~ in use today have an , aspect ratio of about 0.75sl. By keeping the overall length of the tennis racket of the present invention e~3entially the same a~ that of the conventional racket, the ~weet spot of the racket, a~ well a~ the peripherally ad~acent power zone .
arGund the sweet spot, is located upwardly with re~pect to the handle.
~ he ~weet ~pot 54 i6 that particular point on th~
strings of a racket where, when ~triking the ball, the vibration imparted to the racket and hand of the player are at a minimum. The sweet spot i~ at or slightly below the geometric center of the head. At the ~weet ~pot the power transferred by the string~ to struck ball approach the greatest. This iB the preferred place for the player to ~trike the ball with the racket. Peripherally therearound i8 the power zone where vibration~ are al~o minimal and power approaches the power of the ~weet ~pot. The more remote from : .
the sweet spot, the more vibration~ ar~ generated and the less power i~ tran~ferred from the ~trings to the ball.

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If one would con~ider the sweet spot as the striking surface of a hammer, it can be readily under~tood that the present racket, in effec~, increase5 the length between the handle and the striking surface. This increa~e~
the mechanical advantage of the racket of the present invention over prior art rackets gi~en the same head size.
And, since the power zone is also rendered higher on the axi~, the racket provides a greater mechanical advantage for ~tronger shot making by the player.
Another feature of the present invention is in the intermediate portion or beam~ of the frame coupling the head and the handle. The beam~ are linear in oonstruction over the ma~ority of their lengths and are each angled at about 30 degrees from the central axi~. All known racket~ of modern tubular design, 6uch as those fabricated of graphite as in .~
the preferred embodiment, have beams coupling the head to the handle which are curved concave, oppo~itely from the convex ,. . .
` beam curvature. The present invention, however, ha~ straight ; or linear segment~ of frame along their entire extent of the beam~ 18 except at the point~ of merging the handle.
The straight line design of thi~ portion of the frame adds ~tability to the frame and racket when a ball iB
~truck on the string3 offset from the axi~. The further the ;~
ball strike~ the string~ from the axi~ the greater will be , , the force tending to twi~t the frame about its axis and the racket ~n the hand of the player. Such force~ tending to twist the racket create an adverse torque force, unintentionally twisting the plane of the string3. This tend~ to propel the ball from the ~trings in uther than its intended line of motion resulting in bad shots. By strengthening the intermediate portion of the frame, such torquing is abated and truer shots will be hit. This benefit comes from the qtrength of the ~traight line design of the beam~ a~ opposed to the prior art curved design.
The straight line design of the beam~ 18, at the angle~ utilized in the present invention, adds a further benefit. Specifically, the beam portions of the frame make contact tangentially with the head for coupling at a distance further removed from the axis than in prior art designs.
This design feature adds further stability against torquing forces since the stabilizing forces of the frame coupling the head are further separated. This is akin to attempting to ~ ~-~top rotation of a body by holding it at two point~ close to the point of rotation. By holding the rotating body further from the axis of rotation, the rotation inhibiting moment ,........ -forces are increa~ed tending to more efficiently abate ~ ~-rotation. The beam to head contact i~ also higher on the - 19 - . ' .'` ' ~ ;;' ~a~3~)~4 head further increasing stability and the strength of the coupling.
The last significant feature of the present invention is in the ~tringing of the racket. In the conventional racket, which i8 more elongated along the axis - 30 as compared to the present racket, the main or vertical strings 24 ara strung first and unre~tricted. The cross or horizontal strings 26, however, being 6trung second are restricted by the friction of the main strings.
Consequently, when the racket is fully strung, the vertical i strings are usually about 10 lbs~ greater in tension than the horizontal strings. The rea~on for this is the friction of the vertical ~tring~ inhibits the horizontal strings to i decrease their tension and also act to deform the vertical strings to increase their tension. Secondly, the vertical strings are displaced slightly by the interweaving horizontal stringq 80 the vertical strings will pick up a slight amount ;~ .
of additional ~ension. The displacement of the strings is ~;
perpendicular to the plane of the strings. For example, when a racket i8 completely strung, with the stringing machine set at about 60 lbs. nominally it will have a finished string tension of strings about 50 lb~. in the vertical strings.
The horizontal string~ will have a tension of about 40 lbs.

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Conventional racket~ have greater frame strength at their upper and lower ends where they are formed with smaller radii of curvature than the side~ at 3 o~clock and 9 o'clock.
The string tensions are matched to accommodate thi~ feature of ~tructural difference with greater ~tring tension vertically than horizontally. It can thu~ be ~een that variations from the standard in either frame design 6hould be compensated for by a correlated variation in ~tring tension.
Such was not understood by ~he prior art designers of tennis racket frames.
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This example i~ exaggerated when one deviates from the standard type elliptical head in favor of the present 0.9:1 aspect ratio or greater. Elliptical rackets of the past were designed to overcome the inherent problems of :' :
variation of string rate because they were designed to have an aspect ratio of 0.75:1. When aspect ratio is increased to about 0.9 or greater, the vertical 6tring~ and the cross string~ mu~t be very close to equal in final ~tring ten~ionR.
The reason for this i8 because the arcs at 3 and 9 o'clock on ths frame are almost identical to the arc~ at 12 and 6 o'clock. Therefore, the load bearing capability of all strings have to be equal. In order to make the load bearing capabilities equal, one must string the vertical ~tring3 at lO lb~. lower in pull tension than the horizontal ~trin~s.

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Then the final finished string tension will be es~entially equal in all directions. Such ~tring tensioning provide~ the benefit of equal forceis being applied to the ball. Because ;i of strings of equal length, the main ~trings are reduced in length which result~ in reduced trampolining during a shot, a further benefit. Trampolining i~ too much elastic reaction during a i6hot due to long 6trings. The present invention pro~ides isuperior reisulti~ with less trampolining Strings of equal length and tension horizontally and vertically abate trampolining due to the two above described factors. Such equal stringis provide greater control of the depth of the shot when compared wi~h larger area racket heads or high aspect ratio heads ~trung conventionally.
~; The pre~ent disclosure includes that contsined in i the appended claimis as well as that of the foregoing "
description. Although this invention has been deqcribed in its preferred forms with a certain degree of particularity, ~i it i8 understood that the present disclosure of the preferred form has been made only by way of example and numerous ., -changes in the details of construction and combination and - arrangement of part~ may be resorted to without departing from the spirit and ~cope of the invention.

Now that the invention has been described, "
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Claims

WHAT IS CLAIMED IS:

1. A tennis racket comprising a tubular frame configured into a handle, a head, intermediate beams therebetween and a yoke cohered to the lower portion of the head to thereby generally form an ellipse, the head having a major axis coextensive with the axis of the racket of a first dimension and having a minor axis transverse with respect thereto, the minor axis to major axis aspect ratio being about 0.9:1, the beams of the frame being linear and diverging from the central axis equally and oppositely for supporting the head at locations widely spaced from the axis, the racket also including strings strung horizontally and vertically through the head to constitute the striking surface of the racket.

2. The racket as set forth in claim 1 wherein the beams extend at angles of about 30 degrees from the axis.

3. The racket as set forth in claim 1 wherein the frame is fabricated of graphite fibers in an epoxy resin.

4. The racket as set forth in claim 1 wherein the strings form an area of between about 95 and 105 square inches.

5. The racket as set forth in claim 1 wherein the head is formed as an ellipse with its two focal points lying on the axis of the frame and racket.

6. The racket as set forth in claim 1 and further including a grommet strip extending around the external periphery of the head through which the strings pass in a serpentine path to constitute the striking surface of the racket.

7. The racket set forth in claim 6 and further including a bumper guard on the upper external periphery of the head.

8. For use in a tennis racket, an improved frame fabricated of graphite fibers in an epoxy resin matrix formed in a tubular configuration, the frame including: a handle at one end; a head at the other end; beams therebetween coupling the head and handle; and a yoke cohered to the lower ends of the head to thereby form an ellipse with the two focal points of the ellipse lying on the longitudinal axis of the frame, the head having a major axis coextensive with the axis of the frame and being of a first dimension when measured at the widest point of the interior edge and having a minor axis transverse with respect thereto measured at the widest point of the interior edge of the frame, the minor axis to major axis aspect ratio being about 0.9:1, the beams being formed linearly and diverging from the central axis equally and oppositely at about 30 degrees for supporting the frame, at their upper ends, at regions widely spaced from the axis, the area within the head being between about 95 and 105 square inches.

9. A method of stringing a racket having a high aspect ratio, the method including the steps of:
stringing a first common string in a serpentine path through vertically displaced holes in the frame at a first pull tension; and thereafter, stringing a second common string in a serpentine path through the horizontally displaced holes in the frame and interleafed through the strings of the first common string at a tension pull greater than the first tension to thereby constitute primary and secondary string in a grid pattern at an essentially common final tension without distorting the frame.

10. The method as set forth in claim 9 wherein the tension of the second string is about 10 lbs. greater than the first tension.

11. The method as set forth in claim 9 wherein the first string is strung vertically and the second string strung horizontally.

12. The method as set forth in claim 11 wherein the vertical strings are longer than the horizontal strings.