fig1 illustrates the basic elemental arrangement of an ink jet printer of the type requiring air turbulence control of inflight ink droplets , such elemental arrangement being described in detail relative to a 300 kilocycle range ink jet printer in u . s . ser . no . 577 , 667 filed may 15 , 1975 and assigned to the assignee of the present application . in ink printers of the referenced type ink droplets 19 are directed from an ink droplet generator 18 onto a moving print document 15 . the droplet generator ejects a perturbed ink stream 11 which separates into a plurality of droplets 19 while passing through a charging electrode 17 . the charging electrode 17 may fully or partially surround the jet droplet stream at the point of its separation into individual droplets for applying an electrical charge to the droplets as a function of the voltage present upon the charging electrode as droplet separation occurs . a pair of deflecting electrodes designated 21 in the drawings are positioned downstream from the charging electrode 17 for deflecting the charged droplets out of their straight line path of movement into a proper printing path determined by electrical information transmitted to the charging electrode 17 . the extent of droplet deflection is determined by the magnitude of the charge on the droplets and the voltage that is maintained on the deflecting electrodes 21 . fig2 illustrates one embodiment of the present invention wherein air turbulence control apparatus is provided for use with a 300 kilocycle range droplet generator that produces a droplet flight rate of approximately 2000 inches per second . in this embodiment the deflecting electrodes 21 are comprised of a pair of flat parallel plates set in an opposed relationship about the droplet pathway , the plates being supported within a passageway 13 in any convenient manner such that the droplet flight path is unobstructed . the passageway 13 is formed from an electrical insulating material to prevent electrical interference with the deflecting electrodes 21 . droplets not to be printed are not affected by the charging electrode 17 and accordingly experience no deflection from the deflecting electrodes 21 . they therefore follow a straight line path into a droplet catcher 23 . the ink from the droplet catcher 23 is recirculated back to the ink droplet generator for further use as illustrated in fig1 . the walls of the passageway 13 are shaped to maintain a laminar flow of air passing therethrough . the air flow originates closely downstream of the charging electrode 17 , as indicated in fig2 by the numeral 37 , and passes over the deflecting electrodes 21 moving down the passageway in a relatively straight - line direction substantially orthogonal to the print medium 15 . the laminar flow of air is used to reduce the relative velocity of the droplets with respect to the surrounding air in order to eliminate air retardation effects and droplet wake effects . the rate of air flow within the passageway , corresponding to the above - mentioned droplet flight rate characteristic of 2000 inches per second , is designed to provide an approximate mean air velocity of 930 inches per second and a range of from 800 - 1100 inches per second . the range of permissible mean air velocities of the laminar air flow for a given droplet will vary with the size and speed of the droplet in flight as is known by those skilled in the art of droplet aerodynamics . it is to be noted in this connection that the ink droplet generator described in the above referenced u . s . patent application produces droplets having a mass of 0 . 50 × 10 - 6 grams and a diameter of 3 . 7 × 10 - 3 inches . the laminar flow of air within the passageway must be predicted exactly in an orderly and repeatable fashion in order to control the printing of droplets in a predictable manner . thus , the inside walls of the passageway are shaped such that the product of the air velocity traveling down the passageway times the minimum lateral dimension of the passageway times the air density , divided by the air viscosity yields a constant , r , less than 2300 . r , therefore , may be expressed according to the formula : regardless of the shape or smoothness of the inner surfaces of the passageway , if r is maintained less than 2300 the flow of air through the passage will be laminar . however , design values of r up to 5000 - 6000 can be obtained and still maintain smooth laminar flow if reasonable care is taken to provide rounded corners and tapering cross sections of the passageway rather than abruptly changing cross sections in the direction of air flow . straightening fins or other means may also be provided within the passageway to smooth the incoming air flow . the passageway 13 is preferably provided with a rectangular cross section smoothly tapering in the direction of air flow and reaching a minimum lateral dimension of 0 . 200 inches and a minimum height of 0 . 050 inches . such a height provides an appropriate value of r to permit a laminar flow of air through the passageway at the aforesaid rate of 930 inches per second . the passageway 13 of the embodiment of fig2 has integrally formed thereto an expansion section 25 to extend the passageway to the print medium 15 . the expansion section 25 serves to decrease the velocity of the air as the air column approaches the medium by providing a progressively greater cross sectional area of air flow passageway in the direction of air flow . the expansion section 25 is preferably rectangular in cross section having its width maintained constant while the height of the section is progressively increased in a cosine hyperbolic fashion . the height of the ceiling of the section 25 may be progressively increased in a fashion other than cosine hyperbolic , for example , parabolic , straight line , etc ., to provide a progressively greater cross sectional area in the direction of air flow for slowing the same . the length of the expansion section taken along the path of air flow is approximately 0 . 3 inches . as the air flow slows within the expansion section 25 , the tendency for the flow is to lose its laminarity . therefore , to maintain a laminar flow of air as the column slows , small air suction holes or apertures 27 are positioned in the ceiling of the expansion section for withdrawing a sufficient quantity of air to maintain air laminarity . the holes approximate 1 / 16 inches in diameter and are equally dispersed in the ceiling of the expansion section in a matrix fashion with 1 / 4 inches set between the holes to provide an effective withdrawal of air to maintain air laminarity within the expansion section . the holes are circular in shape but may take other forms , for example , narrow , suction slits oriented at right angles to the flow of air along the ceiling of the expansion section . the apertures 27 must be sized to promote adequate air suction therethrough to maintain air laminarity and are positioned where the air column begins to lose its velocity and continue in arrangement to the document . a second group of holes or apertures 29 are located on both side walls of the expansion chamber 25 and serve as ducts to extract air from the passageway before the flow reaches the document to prevent air buildup and wave interference patterns along the document interface . the holes 29 are circular in shape with an approximate diameter of 1 / 16 inches and are arrayed in a matrix configuration with 1 / 4 inches set between the holes . the matrix array of holes 29 on each side wall are positioned in mirror - like respect to the relative droplet flight pathway . the holes 29 may be replaced by a single vertical slit spaced closely to the document 15 on both side walls of the chamber 25 . such air extraction through the holes 29 eliminates air buildup at the document interface making the air flow through the passageway smooth . the quantity of air suction through the apertures 27 and 29 is set at approximately 12 . 9 cubic inches per second . the air suction holes 27 in the expansion section 25 do not extract a large fraction of the air flow but only serve to maintain the laminarity of the flow within the expansion section 25 . the holes 29 on the other hand extract a larger quantity of air to provide smooth flow of air through the passageway and out of the holes 29 . the amount of air flow , if any , that continues to the document must be of such a degree as to have negligible effects in the form of air wave disturbance at the print interface . as the droplet approaches the document the relative velocity of the droplet with respect to the air flow begins to increase , although the effect of such air retardation is rendered negligible by the short remaining flight path to the document . a second embodiment of the present invention is illustrated in fig3 , 5 and 6 , wherein elements corresponding to those of fig2 are identified by the same reference numerals and no detailed description thereon will be repeated . in this second embodiment the small air suction holes 27 and 29 of fig2 have been replaced by a single air withdrawal aperture 35 located in an insulating wedge 36 forming the ceiling of the passageway 13 adjacent the document 15 . the passageway 13 of this embodiment is h - shaped in the area adjacent the charging electrode 17 and rectangularly shaped in the area adjacent the document 15 , the length of the passageway 13 being 2 . 57 inches . the h - shaped section of the passageway adjacent the charging electrode 17 is provided with an area of 0 . 035 square inches having a width of 0 . 220 inches and a mean height of 0 . 050 inches , and the rectangularly shaped section adjacent the document interface is provided with an area of 0 . 030 square inches having a width of 0 . 120 inches and a mean height of 0 . 250 inches . the air withdrawal aperture 35 is preferably semi - circular in configuration having a width of 0 . 060 inches , a circumference of 0 . 472 inches , and an area of 0 . 0283 square inches . the single aperture 35 permits withdrawal of the air flow necessary to eliminate air disturbance as the droplet travels from the generator to the document interface . the quantity of air withdrawn through the aperture 35 is approximately 27 . 2 cubic inches per second . as shown in fig3 - 6 , the second embodiment of the invention also provides a gap 39 that separates the insulating wedge 36 and the upper deflecting electrode 21 , such gap serving to provide extra electrical insulation to prevent high voltage breakdown between the upper deflecting electrode 21 and the wedge 36 . it is to be understood , however , that no suction is provided through the gap 39 , and that such gap is not considered to form a part of the inventive air turbulence control apparatus . in both the fig2 and fig3 and 4 embodiments of the invention , a minimal suction is maintained in the droplet catcher 23 , to prevent ink from being drawn upward away from the catcher and into the suction holes 27 - 29 or 35 . in both embodiments , also , the laminar flow of air within the passageway 13 is effected by applying a vacuum source to the extraction apertures , as for example to the apertures 27 and 29 of the fig2 embodiment and to the aperture 35 of the fig3 - 6 embodiment . it should be understood , of course , that the foregoing disclosure relates to preferred embodiments of the invention and that other modifications or alterations may be made therein without departing from the spirit or scope of the invention as set forth in the appended claims .