aforementioned of an approximate thickness of 0 006 inches much like a slat of a mini blind the radius of the curvature of approximately five eights of an inch is found to be very satisfactory other thickness and radius of curvature may be chosen depending on the type of material and thickness with which the stays are constructed referring now specifically to fig6 a cutaway view taken along line 6 6 of fig1 is shown the flexible tape 36 extends from the reel 34 of the stored energy device around a direction turning guide roller 58 constructed of lubricious material the roller 58 is rotatably connected through axle 60 to mounting bracket 62 attached to structure 14 the tape 36 extends along the inside of track 26 to the distal end 64 of the track positioned within the track adjacent to the distal end 64 is a pulley 66 rotatably mounted to the side walls of the track the tape 36 extends around the pulley and extends back up the inside of the track where it is attached to bracket 52 attached to stiffner 38 in a manner hereinbefore described although the spring device 30 is shown and described as attached to structure for ease of explanation it should be understood that the spring device 30 would work equally as well if positioned at the lower.