shown in fig1 is a window 10 including a window case or frame 12 in which an upper sash 14 and lower sash 16 are slidably mounted for vertical movement in a plane generally defined by the window case 12 . the window case 12 is defined by vertical members or jambs 18 and 19 and by horizontal members 20 and 21 . as shown in fig2 a , at least the lower sash 16 is mounted in the window case 12 so that it may be pivoted out of the plane of the window , such as for cleaning the glass or other such glazing panel 22 mounted within sash 16 . more preferably , as shown in fig2 b , both upper and lower sash 14 and 16 are mounted in window case 12 so that they can be pivoted out of the vertical plane generally defined by window case 12 , such as to allow for cleaning of the outer sides of glazing panels 22 and 23 mounted in sash 14 and 16 , respectively . upper sash 14 is generally defined by vertical members or stiles 24 and 25 , and by upper and lower horizontal rail members 26 and 27 , respectively . stiles 24 and 25 and horizontal rail members 26 and 27 together frame glazing panel 23 . likewise , glazing panel 22 of lower sash 16 is framed by stiles 28 and 29 , and horizontal rail members 30 and 31 . upper horizontal member 30 of lower sash 16 is provided with a latch 32 configured to engage a catch 33 mounted on lower horizontal member 27 of upper sash 14 to lock upper and lower sash 14 and 16 in a closed position as shown in fig1 . the members comprising the sash can be made of various suitable materials , including wood . secured to each of the jambs 18 and 19 are jamb liners 34 and 35 , which are shown in fig3 and 7 , respectively . each of the jamb liners is an elongated extruded member which extends along the height of the jambs between the horizontal members 20 and 21 , the jamb liners being mounted on the side of jambs 18 and 19 which face toward each other and toward the sash 14 and 16 . jamb liners 34 and 35 are mirror images of one another . accordingly , jamb liner 34 , shown in fig3 will be described in detail , it being understood that the description of jamb liner 34 applies equally to jamb liner 35 . jamb liner 34 includes jamb - engaging rear walls 36 and 37 which are laterally spaced apart , a central , sash - engaging front wall 38 , and transverse walls 40 and 41 which connect rear wall 36 and rear wall 37 to front wall 38 . rear walls 36 and 37 are generally aligned in the same plane , and transverse walls 40 and 41 space front wall 38 from rear walls 36 and 37 in a plane which is generally parallel to that of the rear walls . also projecting into the window space from rear wall 36 is a transverse wall 42 which is connected to an outside front wall 43 which is aligned in the same plane as front wall 38 . an outside end wall 44 extends rearwardly from outside front wall 43 toward jamb 19 . extending outwardly at a right angle from end wall 44 is a rear wall flange 45 which is aligned in the plane defined by rear walls 36 and 37 . extending forwardly from outside front wall 43 into the window opening is an outside abutment wall 46 . front wall extension 47 , rear wall 36 , transverse walls 40 and 42 , and outside front wall 43 together define a vertical guideway 48 having a vertically elongate slot 49 defined by spaced apart front wall 43 and front wall extension 47 . extending forwardly from rear wall 37 toward the window opening is a transverse end wall 50 , and extending outwardly from the forward end of end wall 50 is an inside front wall 51 which extends in the plane defined by front walls 38 and 43 . extending inwardly from and in the same plane as that of front wall 38 is front wall extension 52 . together , rear wall 37 , transverse wall 41 , end wall 50 , inside front wall 51 , and front wall extension 52 define a vertical guideway 53 having a vertically elongate slot 54 defined by the spacing between inside front wall 51 and front wall extension 52 . vertical guideways 48 and 53 , which are substantially identical , each include a friction shoe engagement wall 55 and 56 , respectively , which project outwardly from side wall 40 and inside end wall 50 , respectively , and extend in a plane substantially parallel to and intermediate between the planes defined by rear walls 36 and 37 , and front walls 38 , 43 and inside front 51 . the jamb liners 34 and 35 can be made of any of a variety of materials , but are preferably made of extruded plastic , such as polyvinyl chloride . a cushion or compressible pad 57 is disposed between jamb 19 and jamb liner 34 ( and between jamb 18 and jamb liner 35 ). cushion pad 57 is preferably a relatively thin , resiliently compressible material , such as a foamed plastic material exhibiting elastomeric properties , such as a foamed polyurethane material . cushion pad 57 resiliently urges jamb liners 34 and 35 against the sides of sash 14 and 16 to ensure contact therebetween and compensate for minor dimensional variations along the length of either the stiles or the jambs . cushion pad 57 can be secured to jambs 18 and 19 using any of various suitable fastening means , such as adhesives , screws , nails , staples , and the like , but more conventionally is secured to the jamb liners 34 and 35 using any of such fasteners . securement of the jamb liners to the jambs is aided by inner and outer jamb trim pieces 58 and 59 which engage inside and outside end walls 50 and 44 , respectively . rear wall flange 45 and the outer edge of cushion pad 57 are preferably wedged within a recessed area defined by a cutout section in outer jamb trim piece 59 . as illustrated in fig2 a , 2b , 3 , and 7 , the side edges 60 of stiles 24 , 25 , 28 , and 29 of sash 14 and 16 have flat or planar surfaces which are smooth and free of recesses , grooves or protuberances . the flat sides of the stiles minimize interengagement between the sash and the jamb liner , allowing the sash to be easily pivoted out of the plane of the window . thus , the flat sides of the sash facilitate tilting and removal of the windows for cleaning of the outer surfaces of the glazing panels 22 and 23 , or other parts of the window assembly which are not normally accessible from the inside . because the sash 14 and 16 do not include the customary plows or vertical grooves along their sides which are engaged by ridges protruding from the jamb liner , improved , alternative weathersealing means are provided . specifically , the jamb liners 34 and 35 are provided with a weatherstrip 61 , as shown in fig3 , and 7 . weatherstrip 61 includes a t - shaped base portion 62 and a pile portion 63 which achieves weathersealing engagement between the sash 14 and 16 and the jamb liners 34 and 35 . jamb liners 34 and 35 are preferably provided with t - shaped recesses which are configured to receive the t - shaped base portion of weatherstrip 61 . in particular , weatherstrip 61 is secured to jamb liners 34 and 35 by sliding the t - shaped base portion of the weatherstrip into the t - shaped recess or groove provided in the jamb liners with the pile portion 63 projecting outwardly to engage the sash , so that the weatherstrip is physically held by the jamb liners . however , any of various suitable alternative weatherstripping can also be utilized with corresponding means for attaching the weatherstrips to the jamb liners . in fig5 and 6 there is shown a shoe 64 which is configured to be freely but closely received within vertical guide 53 . the lower portion of shoe 64 has a generally rectangular horizontal cross section , complementary to that of guideway 53 into which it fits . the clearance or gap between the inner walls of the guide 53 and the outside surfaces of shoe 64 are , on average , large enough to allow the shoe to freely slide vertically within the guide 53 , but sufficiently small to prevent the orientation of the shoe 64 with respect to the guide 53 from varying to any significant extent . as shown in fig5 and 6 , shoe 64 has an l - shape and includes a vertically elongate portion 65 having a vertically angled inner face 65a , together with a pair of laterally aligned , parallel , and mutually spaced engagement walls 66 and 67 which project outwardly from a generally arcuate recess 65b disposed below the vertically angled surface 65a of shoe 64 . the spacing between walls 66 and 67 of shoe 64 is sufficient to allow the interior jamb liner wall 56 to be slidably disposed therebetween . shoe 64 can be made of any of a variety of suitable materials , particularly plastic , nylon being preferred . spring 68 is connected at its lower end to shoe 64 ( fig5 and 6 ), and at its upper end to the jamb liner 34 . sash 16 includes a pivot pin 69 of generally triangular or wedge - shaped cross section which projects from a lower portion of each stile through slot 49 and into a respective one of the guides 48 and 53 , where it engages and is supported by the shoe 64 disposed within the guides , as described further below . as shown in fig5 and 6 , shoe 64 includes a braking element 70 which is pivotally connected to the walls 66 and 67 at a point near the arcuate recess 65b . braking element 70 includes first and second prongs 71 which engage end wall 50 of jamb liners 34 and 35 when sash 16 is pivoted out of the plane of the window and into that shown in fig6 . pin 69 has a wedge - shaped cross section with a side disposed adjacent the top of braking element to act as a camming surface which comes into flush engagement with the upper side of braking element 70 when sash 16 is pivoted out of the plane of the window , causing braking element 70 to pivot from the position shown in fig5 wherein the prongs 71 are spaced away from wall 50 , toward the position shown in fig6 wherein the prongs engage and slightly embed themselves into wall 50 of jamb liners 34 and 35 . this engagement securely holds shoes 64 in place as sash 16 is pivoted out of the plane of the window , thus preventing the lower end of the sash from being moved vertically by spring 68 as the window is pivoted and its weight is increasingly removed from the shoe 64 . braking element 70 is preferably made of a hard , durable material , such as steel or other metal or alloy . because the sides of sash 14 and 16 are flat , i . e ., do not include a plow which is engaged by a ridge projecting from the jamb or jamb liner , sash 14 and 16 are provided with guide - engagement members 74 ( fig7 ) which project laterally from an upper portion of each of the stiles into a respective one of the guides 48 and 54 through the vertically elongate slots 49 and 54 , respectively . as shown in fig7 guide - engagement members 74 engage the edges of wall 51 and wall extension 52 defining slot 54 , and wall 43 and extension 47 defining slot 49 , thereby preventing tilting of sash 14 and 16 away from the plane of the window as sash 14 or 16 are raised or lowered within the plane of the window . the close engagement between guide - engagement members 74 and the portions of jamb liners 34 and 35 defining slots 49 and 54 ensure smooth tracking of the sash as they are being raised or lowered . in order to allow the sash 14 and 16 to be pivoted out of the plane of the window , guide - engagement members 74 are retractably mounted into the sash , as indicated in phantom outline in fig7 by reference numeral 75 . sash 14 is pivoted out of the plane of the window by shifting slide lever 76 in the direction indicated by arrow 77 and rotating the upper end of the sash in the direction generally indicated by arrow 78 . likewise , sash 16 is pivoted out of the plane of the window by shifting slide lever 79 in the direction indicated by arrow 80 and rotating the upper end of sash 16 in the direction generally indicated by arrow 81 . pivot pin 69 is not fixed to shoe 64 , but instead merely rests upon the latter . when the sash is disposed generally in the plane of the window , as shown in fig5 the pointed edge of wedge - shaped pin 69 is disposed at the bottom of a v - shaped notch area generally defined by the angled upright wall of recess 65b and the top of braking element 70 , in which position it is held by the weight of the window . when the sash is rotated out of the plane of the window , the side of pin 69 closest to brake element 70 is rotated into flush contact with the latter to pivot it toward the position shown in fig6 . as that occurs , pin 69 continues to rotate and this brings a second angular edge thereof into contact with the top of brake element 70 at a point spaced from that shown in fig5 as shown in fig6 located on the opposite side of the pivot which secures braking element 70 to walls 66 and 67 . this applies a greater force to braking element 70 , assuming that its prongs 71 will forcefully contact , and preferably embed into , the wall 50 . when that occurs , the shoe 64 is locked in place within the jamb liner and one side of the sash can be raised upwardly to lift the pin 69 on that side of the sash away from its associated shoe 64 and out of the guide 53 defined by jamb liner 34 or 35 , freeing that side of the window from the jamb liner . of course , the shoe on the opposite side of the sash has also been locked in place by the same chain of events , and after the first side of the tilted window has been lifted in the manner just stated the other pin 69 can be easily withdrawn from the other shoe and jamb liner by moving the window laterally away from the jamb liner on that side . referring to fig3 and 7 , a spring cover 83 is preferably installed within an upper portion of guideways 53 associated with the inner ( lower ) sash 16 . more specifically , the vertical edges of spring cover 83 are positioned within slots defined in jamb liner rear wall 37 and front wall extension 52 to define an enclosed area within the guideway wherein the spring 68 is disposed and concealed from view . the spring cover 83 generally extends from the top end of guideway 53 to a height which is at or just below the upper edge of sash 16 when sash 16 is lowered to the position shown in fig1 . thus , spring 68 is completely concealed irrespective of the position of sash 16 . spring cover 83 is preferably made of any suitable flexible material which will allow the spring cover to be snapped into position as shown in fig3 or slid downwardly into the jamb liner from the top prior to installation . suitable materials include flexible polyvinyl chloride , such as those having a durometer of about 70 . having described the preferred embodiment of the invention , it will be recognized that modifications and other embodiments may be possible without departing from the principles of the invention . such modifications and embodiments are to be considered as included in the appended claims , unless these claims , by their language , expressly state otherwise .