US2700305A - Precision balance - Google Patents

Description

Jan. 25, 1955 Filed Sept. 19, 1952 FIGJ.

J. M. KENDALL PRECISION BALANCE Y J; Maw/2F RAM +4 6 Sheets-Sheet 1 INVENTOR JAMES M. KENDALL ATTORNEYS Jan. 25, 1955 J. M. KENDALL 2,700,305

PRECISION BALANCE Filed Sept. 19, 1952 6 Sheets-Sheet 2 FIG.2.

I04 loe [I38 14- use I66 JAMES M. KENDALL INVENTOR ATTORNEYS 1955 J. M. KENDALL ,700,305

PRECISION BALANCE Filed Sept. 19, 1952 v s Sheets-Sheet 4 FIG.8.

INVENTOR JAMES M. KENDALL fflwm W. M. kind/14 ATTORNEYS Jan. 25, 1955 J. M. KENDALL PRECISION BALANCE 6 Sheets-Sheet 5 Filed Sept. 19, 1952 wZE mm m0 ZOrEFOm m0 ZOFOMEQ ATTORNEYS m mm W D N N 8 1 E M s Eoowojwmo E m N853 m O F J oziw w ozEfim MK 2 U: m woz 4 m EJ N9 when. e: MW m L FFQQQJ :6 RJ 102 368 8 2 91 2a U N 595m 053 F K i 3 w 2 OZ -t E w L 8 3 I m .0 n

the movable sting of the balance device;

United States Patent" PRECISION BALANCE James M. Kendall, Washington, D. C., assignor to the United States of America as represented by the Secretary of the Navy Application September 19, 1952, Serial No. 310,573

15 Claims. (Cl. 73-147) (Granted under Title 35, U. S. Code (1952), see. 266) tunnel whereby aerodynamic tests may be made to determine the effects of a fluid current thereon.

Furthermore, the invention relates to a new and improved balance wherein means are employed for movably supporting an object or model such, for example, as a model of a projectile or guided missile in a central longitudinal plane within a wind tunnel whereupon the model is maintained in the fluid current without permitting any deviation thereof with respect to the aforesaid plane, and in which means are provided for permitting free longitudinal movement of the model support or sting as the model secured thereto is moved by the fluid current with substantially no friction between the movable sting and the supporting structure therefor whereupon an accurate measurement of the drag force on the model may be obtained, and in which means responsive to the aforesaid movement measures and indicates the drag force and thus such measurements may be employed to determine the drag force on the model under conditions similar to those to which a projectile or guided missile is subyected in actual flight after being fired from a gun or started on its trajectory. Furthermore, the sting is operatively connected to a resilient element which resists the axial movement produced by the aforesaid drag force; however, upon movement of the model the resilient element is stretched a predetermined amount in response thereto and thus such movement of the resilient element is employed to measure the drag force on the model.

An object of the present invention is to provide a new and improved balance wherein means are provided for remotely indicating the drag force of an ob ect under test within a fluid current.

for movably supporting a test model in a fluid current in a longitudinal plane and for permitting free longitudinal sliding movement thereof in the aforesaid plane without permitting any movement thereof out of such a plane. Another object of the invention is the provision of a balance adapted for use in a wind tunnel for movably supporting a test model in a fluid current wherein means responsive to the movement of the sting and operated in response to the drag force on the model is employed to measure and indicate the drag force without being affected by the side forces.

Still another object of the invention is the provision of a balance wherein means are provided for eliminating friction between the movable stingand the supporting structure therefor. I

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 is a fragmentary sectional view of a wind tunnel provided with a balance device constructed in accordance with the present invention and illustrating a test body mounted thereon;

Fig. 2 is an enlarged fragmentary sectional view illustrating the manner in which the model is supported by 2,700,305 Patented Jan. 25, 1955 Fig. 3 is a plan view partially in elevation and partially in section of the rear assembly or control box of the Fig. 5 is a cross sectional view taken on the line 55 of Fig. 3;

Fig. 6 isa similar view to Fig. 5 taken on the line 6-6 of Fig. 3;

Figs. 7 and 8 are views taken on lines 7-7 and 88 of Fig. 3 respectively;

Fig. 9 is a view partially in elevation and partially in section of the sting arrangement;

Fig. 10 is an enlarged fragmentary longitudinal sectional view of the forward portion of the sting, rotatable tube and supporting structure therefor;

Fig. 11 is a sectional view taken on the line 1111 of Fig. 10;

Fig. 12 is a view similar to Fig. 10 illustrating the central portion of the sting, rotatable tube and supporting structure therefor;

Fig. 13 is a sectional view of the rotatable bearing and sliding sting illustrating the manner in which the oil film prevents metallic contact between the bearing and sting;

Fig. 14 is a schematic view of a reader suitable for use with the device of the present invention; and,

Fig. 15 is a diagrammatical view of a circuit arrangement suitable for-use with the present invention, the electronic equipment employed therewith being shown in block form.

Referring now to the drawings and more particularly to Fig. 1 thereof a fragmentary portion of a conventional wind tunnel is illustrated and generally indicated by the reference character 10. The tunnel comprises a tube or casing 11 having a test chamber 12 therein accessible by way of an opening 13 which is sealed by a door 14 when the tunnel is in operation, the door having the usual sight window 15 therein whereupon the model under test may be observed during a testing operation. An arcuate shaped member 16 is disposed within the chamber 12 and adjustably mounted on the casing 11 as by a suitable rack and pinion arrangement 17, the arcuate member being adapted to adjustably support the balance of the present invention generally indicated by the numeral 18 within the test chamber whereupon the model 19 mounted thereon may be arranged in the desired angle of attack during a testing operation. The member 16 is detachably secured to the balance 18 in any suitable manner such, [for example, as by a clamp 21 carried thereby and in clamping engagement with the balance as at 22.

As shown more clearly on Fig. l the balance comprises a substantially rectangular sealed casing 23 and an elongated windshield generally indicated by the reference character 25 consisting of a pair of tubular sections 26 and 27, section 26 being secured to the casing 23 as at 28, and sections 2627 being secured together as at 29.

Referring now to Figs. 3 and 4 it will be noted that a pair of U-shaped supports 31 are secured to wall 32 of the casing 23 as at 33 in spaced relation with respect to each other. Each support 31 is provided with a pair of bearings 34 for rotatably supporting a pair of shafts 35 and 36 respectively. Shaft 35 is provided with a pair of gears 37 and 38, gear 38 is secured to one end thereof and driven by a gear 39 secured to a stub shaft 41 rotatably supported in a bearing 42 secured to the wall 32 as at 43, rotary movement being transmitted to gear 39 by a gear 44 secured to the stub shaft 41 and driven by a gear 45 secured to the motor shaft 46 as the motor 47 is set in operation. Gear 37 is secured to the other end of shaft 35 and meshes with an enlarged gear 48 secured to a drive tube generally indicated by the humeral 49 as at 40, the purpose of which will be more clearly set forth as the description proceeds. A gear 51 is secured to one end of the shaft 36 in mesh with the gear 48 and thus upon rotation of gear 51 by gear 48 rotary movement is imparted to shaft 36. It will be understood from the foregoing gear arrangement rotary movement is imparted to both of the shafts 3536 as the motor is set in operation.

As most clearly shown on Fig. 3 a substantially U- shaped yoke generally indicated by the reference character 50 is slideably arranged on shafts 35-36 and comprises an elongated support 52 having formed thereon a pair of mutually spaced legs 53 and 54 and disposed at a right angle with respect thereto. Leg 53 has formed thereon a boss or nipple 55. in which is arranged a centrally disposed bore 56, Fig, 4. Secured to the-boss 55'as at 60 is" a pair' of oppositely disposed arms 57-58' extending laterally therefrom and having the end portion'thereof terminating in a pair of bearings 59' and 61 respectively, bearing59 being slideably arranged on shaft 35 and bear ing 6-1- being slideably arranged on shaft 36. The member 52 has formed thereon at the rear end portion thereof an arm 62" extending laterally therefrom and terminating in a bearing 63 slideably arranged on shaft 36.. By the aforesaid arrangement it will be apparent that the yoke 50 is supported on the rotatable shafts 3'5 36 for. longitudinal movement by the sliding bearings 59, 61 and 63.

Referring now to Fig. 9 it will be noted that the rotatable tube 49" comprises a pair 'of' tubular sections 64 and 65 coupled together at one end thereofby a rotatable bearing66, the other end" of tube 65 being connected to gear 48' by a'sieeve 67 and rotatably supported by a ball race 68 disposed within the enlarged portion 69 of the tubular section 26' of the windshield 25.. Tube 64 is probeing, clamped within the windshield. 25 by a shoulder 76 formed on tubular member 2l6and the end portion 77 of tubular member 27, a gasket 78 being disposed between portion 77 and the support 73. A pair of oppositely dis posed cylindrical members 79 are formed on the device 72 and having a plurality of openings or slots 81 arranged therein respectively. As more clearly shown on Fig. 12

. a plurality of pins 82 are secured to one end of each tubular, section 64 and 65' as at 83 and disposed in the aforesaid slot or opening respectively whereupon a driving connection is provided between members 64 and 65 and thus upon rotation of. gear 48 secured to the tubular member 65in the aforesaid manner rotative movement is imparted to the drive assembly 49. The bearing 71 is similar to the rotatable bearing 66 and is disposed at the leading or'forward end of tube 64 and comprises a spherical shaped portion 85 arranged within a bearing support 86, the support comprising a pair of supporting members 87 having the engaging surfaces 88 thereof concaved to receive the spherical portion 85. The bearing 86 is clamped within the leading end of the windshield section 27' by a shoulder 89 and a retaining nut 90 threaded into the end thereof into engagement with the bearing support 86. The rotatable bearing 84 is provided with a tubular sleeve 91 having a plurality of openings or slots 92 formed therein for receiving a plurality of pins 93-respectively, the pins being mounted on the tube 64 and secured thereto as at 94, Figs. 10 and 11.

By the aforesaid arrangement it will be understoodthat rotative movement is imparted to the drive assembly 49 by the gear 48 secured thereto when the motor 47 is set in operation and that the concaved bearing support. and the spherical bearing provide means for causing self alinement of the drive assembly. It will be further understood thatthe drive assembly 49 is protected frornthe forceof the: air stream within the tunnel by the windshield 25 which includes tubular sections 26-27.

A sting or model support generally indicated by the reference character 95 is disposed within the rotary drive assembly 49 for sliding movement and comprises an elongated shaft96 havinga pair of enlarged cylindrical portions 9-798-formed thereon and in spaced relation with respect to eachother, portion 97 being slideablyarranged within rotatable bearing '71 and portion 98 thereof. being islideably arranged within rotatable bearing 66. The aforesaid sting and bearing arrangement is more clearly shown on Figs. 9, 10 and 12. One end of the sting extends a predetermined amount beyond the forward or upstream end of the windshield 25 as at 99 and thus provides means whereby the model. 19-may be readily secured thereto and maintained in the fluid current during a testing operation. The other end of the sting is connected to the slideable yoke 50 by a flexible sleeve 10]., Fig. 4, composed of any material suitable for the purpose such, for example, as rubber or the like and arranged within the bore 6'f'ormed in the yoke and maintained therein by a nut 1'02 threaded onto the sting and into abutting engagement with the sleeve 101'. Thus by this arrangement means are provided for readily maintaining the yoke and sting in mutual alinement with respect to each other. The sting is provided with a centrally disposed bore 103 extending therethrough in communication with the interior of the casing 23 and with a chamber 104 formed in the model 19, chamber 104 being in communication with a chamber 105 formed at the base of the model. by way of a plurality of bores or ports 106. It will be noted that base chamber 105 is in communication with the wind tunnel by passageway 107 formed at the base of the model 19 and thus the pressure existing at the base of the model 19 enters the interior of casing 23 by way of passageway 107, chamber 105, ports 106', chamber 104 and thence through bore 103-arranged in sting. whereupon the base and casing pressures are equalized.

Furthermore, it will be understood that the flow resistance' due to the size of the sting, bore 103' and the duct system in the base of the'model is low enough such that the pressure equilibrium is established within the casing 23 withina very shorttime after any changeof pressure occurs at" the base of the model.-

A pair 'of 'nipples'2430 are secured to the front wall of the-'casingjz3. Nipple 24 is in communication with the interior" of" the casing and extends a substantial amount therebeyon'd and thus by'this arrangement a tube may be connected thereto and to a suitable pressure responsive device-such,,for example, as amanometer whereupon the casing pressure may be measured, if desired. Nipple 30' is" connected to one end of a flexible tube of negligible stiffness 70 within the casing 23, the other end of the flexibletube beingjconnecte'd to a tube 8'0arranged within the bore 103 of the sting 95 and spaced from. the walls defining, the bore, the tube StT-extendingthrough the sting; and having the other end thereofv disposed within a bore formed inthe nose of the model19. By this arrangement a tube or conduit may be connected to the nipple 30 and to a manometer or suitable pressure responsive device whereupon the nose pressure occurring at the nose of the model and caused by impingement of the fluid current therewith may be. measured, if desired, without in any way decreasing the accuracy of the force measurement simultaneously being made.

In regard to the aforesaid'self aligning bearing. struc ture which slideably supports the sting it will be understood that substantially all' the lift and side forces to which the. model is subjected/during.theutesting operation are taken up thereby. Furthermore,..the aforesaid 1 beari'ngs are of. the. self. aligning typeto prevent any binding action. of the sting should the sting flex in response to the aforesaid" side forces. However, should the sting flex 1n. response to such. forces it will be apparent that the selfv aligning bearings change their axes of. rotation in such a manner as to be parallelwithi the sting axes-at the bearing position thereof due to the spherical arrangement of the bearingsand the spherically curved sockets of supporting structure therefor. Thus by this. arrangement of outer. spherical surfaces of'the be'arings'compensationisp'rovided for. any orientation thereby preventing'any binding action between the aforesaid shaft and bearmgs.

Referring again to Fig. 3 it willbe noted that a precision spring108. isarranged within the? casing. 23, one.end.109 thereof beingzsecured to a fixed-support 1-11. by a clamp 1-12, the other" end. 113 thereof. being secured. to the leg. 54 of the. slideable'yoke 50' by a clamp 1 14; Thus upon movement of the yoke by the sting. in response to the. drag. force on the. model the. spring. is extended a predetermined. amount. It will be. understoodathat the precision. spring, resiststhe movement. of the. sting produced by the drag force on the model-,however, the amount. of; spring extension. caused by movement :of the yoke by the sting inresponse'to aforesaid drag forceon the. model carried thereby is employed to calculate. and determinev the aforesaid drag. force on. the model. The spring is the only component part of the balance structure that causes any restraint-on-the moving system thereof. when the :motor is-running. and thus-all the dragforce isutilized to. stretch: the-spring. Furthermore, on. account of the zero static friction feature-of the balance hysteresis effects are.substantially"eliminated with respect to the moving-system thereof- The amount of spring, extensionxis -measured. by any device suitable for the purpose such, for example, as a linear variable differential transformer generally indicated by the reference character 115 and mounted in a support 116 composed of Bakelite and secured to the wall 32 of the casing 23 in any suitable manner, preferably by screws or the like. The transformer comprises a suitable coil structure 117 having an armature 118 slideably arranged therein and having secured to one end thereof a shaft 119 composed of any suitable material such, for example, as wood, plastic or the like. As more clearly shown on Fig. 3 a driving connection is provided between the yoke 50 and the armature 118 by a connector 121 having one end secured to the shaft 119 as at 122, the other end thereof being secured to the yoke as at 123. By this arrangement and upon movement of the yoke in response to the drag force as heretofore set forth the yoke. and armature 118 are moved an equal amount and thus the precision spring 108 is extended an amount proportional to the drag force. The connector 121 is constructed in such a manner as to be readily flexible in a lateral direction, however, it is substantially rigid in a longitudinal direction and thus there is no lost motion between the yoke and armature when the armature is actuated in response to the movement of the yoke.

As shown on Figs. 3 and 4 a flanged member 125 is secured to the sting 95 as by screws 126 and disposed in a slot 127 formed in a member 128 and normally in engagement with the wall 129 defining one side of the slot 127. The disc is adapted to maintain the sting in its normal position and to limit the longitudinal movement thereof when the sting has been moved sufficiently to cause engagement of the flanged member with the'wall 131 defining the other side of the slot. Furthermore, to prevent rotative movement of the sting a substantially V-shaped member 132 is secured to the yoke 50 as at 133 and to the flanged member 125 as at 134.

As more clearly shown on Fig. 3 a pair of connector plugs 135-136 are secured to the front wall 137 of the casing 23 in spaced relation with respect to each other, connector plug 135 being electrically connected to the motor 47, and connector plug 136 being electrically connected to the linear variable differential transformer 115 and thus by the aforesaid arrangement means are provided for establishing an external electrical connection from a suitable source of electrical energy to the motor and for connecting the linear variable differential transformer 115 to suitable electronic equipment whereby the drag force on the model may be precisely determined.

In reference now to Fig. 13 which illustrates. asectional view through one of the rotatable bearings and the sting, it will be noted that the sting automatically arranges itself eccentrically within the bearings due to the viscosity of the film of oil which separates the moving surfaces of the bearings and sting from each other. .This behavior is in accordance with the well known theory of lubricated bearings. By this arrangement it will be obvious that the oil film provides a fluid support for the entire moving system of the balance which includes the sting and yoke arrangement. Furthermore, although the quantity of oil between the aforesaid elements is in the form of a relatively thin film such, for example, as

of the order of 0.001 of an inch, it will readily prevent .will be understood that when two sliding surfaces have a film of oil of a definite viscosity disposed between them, a resisting force is set up whose magnitude is proportional to the relative velocity of the two surfaces and whose direction is opposite to that of the relative velocity. In the case of a shaft rotating in a journal bearing, the resulting relative motion between the shaft and bearing produces a tangential force around the circumference of the shaft in the bearing. This tangential force is evidenced as frictional torque on the bearing. Let it be assumed, for example, that the shaft is stationary and the bearing is rotating, the frictional torque which has a tendency to cause the shaft to rotate will be resisted by the means 132, Fig. 3, used to prevent rotation of the shaft. Let

it be further assumed that while the shaft is prevented .side surface of the bearing. When this occurs the relative motion between the shaft and bearing is now helical .and thus the force resulting from the aforesaid helical motion constitutes two components: one component of force around the shaft, tangential, and the other component of force along the shaft, axial. The axial force has a very important characteristic for the reason that its magnitude is substantially proportional to the velocity of the axial sliding motion such that when the axial velocity is low the axial force is correspondingly low and thus the axial force approaches zero when the axial velocity approaches zero. Thus for zero axial velocity, zero axial force of resistance results whereupon the static friction is completely eliminated for the axial component of motion of the shaft or sting.

Fig. 14 illustrates a schematic view of a reader suitable for use with the balance of the present invention which makes use of a linear variable differential transformer and generally indicated by the reference character 138 and comprises a conventional micrometer 139 rigidly supported by a bracket 141 and having the usual shaft or spindle 142 rotatably supported therein for longitudinal movement.

A drum 143 is secured to the spindle 142 and rotatable therewith as the handle 144 carried thereby is actuated, the drum being provided with a suitable scale 145 in the form of a helix having the total length of approximately 62.8 inches whereupon a thousandth of an inch of sting deflection isrepresented by about A; inch of scale length. A gear 146 is secured to the drum and meshes with a gear 147 secured to a screw shaft 148 and thus upon rotation of the drum rotative movement is imparted to the shaft 148, the shaft being supported by suitable bearings 149. A carriage 151 is supported by the shaft 148 for sliding movement thereon as the shaft is rotated in the aforesaid manner. A support 152 is disposed above the drum 143, having one end secured to the carriage 151 as at 153, the other end thereof being slideably arranged on a member 154. Secured to the support 152 is a pointer or index finger 156 adapted to traverse the scale 145 as the drum is rotated in response to rotation of the micrometer spindle. Mounted on a flexible support 157 is a follower or step down device 158 having a ball 159 formed on one end thereof in abutting engagement with the micrometer spindle 142 as by spring 161. A linear variable differential transformer 162 is mounted in a support 163, the said transformer being identical in structure to the said transformer 115. The movable armature 169 within the transformer 162 is connected to the follower by means of a relatively stiff wire link 164 supported in a pair of guiding brackets 165 and having one end secured to a block 166 as at 167 and carried by the follower, the other end thereof being secured to a non-magnetic member 168 fixed to the armature 169 of the transformer in any suitable manner.

It will be understood, however, that the micrometer arrangement is adapted to move armature 169 of the transformer 162 through the 2.5 to 1 step down device 158 as the micrometer spindle 142 is rotated and moved longitudinally in response to the rotation thereof. Rotation of the spindle imparts rotary and longitudinal movement to the drum 143 which rotates screw shaft 148 through gears 146-147 whereupon carriage 151 operatively connected to shaft 148 is moved slideably along the shaft and thus the index finger carried by the support 152 and secured to the carriage is moved along the scale 145 on the drum as thecarriage is moved slideably and the drum is moved rotatably and longitudinally. Furthermore, one revolution of the micrometer spindle corresponds to 0.010.motion of the armature 169 of transformer 162 which is substantially the amount that the sting 95 is permitted to move in response to the drag force on the model by reason of the aforesaid stop 95 carried thereby and adapted to engage a shoulder on the casing 23 when the sting has reached the limits of its movement. The drum 143 carried by the micrometer spindle and having the aforesaid scale thereon is adapted to be rotated ten revolutions for the-full scale motion of 0.100 of the sting. Thus the scale is arranged on the drum in the form of a helix, the total length thereof being substantially 62.8 inches whereupon a thousandth of an inch of sting deflection is represented by about A of an inch of scale length. It will be understood that the smallest divisions on the scale correspond to one ten-thousandth of an inch as "a battery is indicated at B, the "battery being-com nected to the motor 47" by a pair-of conductors -171 472 whereupon electrical energy is supplied to themot'orwhen the switch SW' is actuated from. a normally opened pos'i' tion to a closed position whereupon thea'foresaid rotating bearing systemof the balance'is-s'et in operation with the elimination of all static friction in the moving system. It will 'be noted that the pair ofoutputcoils QP1 Olf2 of'transform'er 115 and" thepa'ir of output coils OP3 OP4 of. transformer 162 are connected in series and to the Y terminals of a cathode ray oscilloscope CRO by-conductors 17 174; By this arrangement the resulting voltagewhich is the vector sum of both pairs of output coils isLfe'd to the Y terminals of thea'foresaidoscilloscope over conductors *173-1-74i The X terminals of the oscilloscope are connected tothe; audio oscillator through the resistance-capacitor network to provide a 90 phase shift. The coils AC and AC of the transformers 115 and 162 are connected to the terminals of the audio oscillator respectively by conductors 175-176. By the aforesaid arrangement it will be understood that'when the electronic system is in operation an elliptical trace will appear on the screen of CR as long as no electrical balance' of the aforesaid transformers has been obtained. Furthermore, when the vector difference of the aforesaid outputs of the coils is zero the Y deflection is likewise zero and thus the ellipse collapses to a horizontal straight line which indicates that an electrical balance has been obtained, the response of the electrical balance system being substantially instantaneous. As heretofore set forth the precision spring 108 is extended an amount proportional to the drag force on the model and simultaneously therewith the armature 118 of the transformer 115 is moved an' amount corresponding to the extension of the spring. In order to obtain an electrical balance it'is necessary to rotate the mircometer spindle and reader drum until the armature 169 of transformer 162 is moved an amount corresponding to the movement of armature 118 of transformer 115, When this occurs the trans formers 115-462 are in a balanced condition and the zero voltage difference resulting therefrom causes the elliptical trace to collapse and form a horizontal trace line on the oscilloscope screen. After collapse of the aforesaid elliptical trace on the oscilloscope screen a scale reading of the micrometer is taken for determining the electrically balanced condition. By comparing the micrometer reading with a suitable calibrated curve it will be possible precisely to determine the drag force on the model arranged within the wind tunnel. Furthermore, it will be understood that the balance is calibrated by applying known forces to the sting, balancing the electrical system for each force, and reading the micrometer scale of the reader to the nearest one-hundred thousandth of an inch. The calibration curve, however, is sufficiently linear such that an equation of the type F=KR will represent the relationship between the force F and the reading RK depending on the size and strength of the precision spring employed.

From the foregoing, it will be apparent that the invention provides a new and improved balance device wherein a movable sting is employed for supporting a model within a wind tunnel in a fluid current and having rotatable-bearing means for supporting'the sting thereof for free longitudinal movement with effectively no friction between the aforesaid parts, and in which means responsive to the longitudinal movement of the sting, is adapted to measure the drag force on the model whereupon such measurement may be employed to determine the drag force under conditions similar to those to which a proiectile is subjected in actual flight.

Obviously man'y'modifications' and variations of the present invention are-possible in the light ofthe' above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by letters patent in the United States is:

1. A balance device comprising an elongated casing adapted to be mounted within a wind tunnel in a fluid current, a movable element mounted within said' casing and adapted to support'a test model on one end thereof in said fluid current and moved longitudinally in response to the drag force on said model caused by impingement of the fluid current therewith, rotatable lubricated bearingmeansfor supporting said movable element-for'said longitudinal movement thereby to eliminate static fricnon thercbet'we'en as" the" movable-element is actuated, means for imparting rotativemovement to said bearing means, means secured to said moving element and extended longitudinally thereby an amount proportional to said drag force, and means secured to and actuated by said movable element for measuring the longitudinal'e'xtension of said extendibjle' means whereby the drag force associated with the impingement of the fluid current on the model may be ascertained.

2. Aw'indtunn'el balance comprising acasing adapted to be mounted in a fluid current, supporting means 'sefcured tos'aidffc'a'sing', rotatable means disposed within and supported by said supporting mea n's, means arranged within the casing for imparting rotative movement to said rotatable means, means slidably arranged withinsaid rotatable" means and adaptedto support a test body there'- on Within said fluid current, said slideable means being movable in response to "the drag force on the body caused by impingement of the fluid current thereon, and-means including a resilient element secured to said slideable means and extended thereby an amount proportionalth said drag force, and measuring means securedt'o' and a'ctua'tedby said 'slideable means for measuring theextension of the resilient element whereby the dragforce associated with the impingement of the fluid current on said body may be ascertained.

3. A wind'tunnel balance comprising a casing adapted to be mounted in a fluid current, an elongatedtubular support secured to said casing, a tubular device disposed within and ro'tatablysupporte'd by said tubular support, means including a motor arranged'within said casing and operatively connected-to said tubular device for imparting rotative movement thereto, a shaft slide'ably" arranged within said tubular device and having the" free end thereof projecting beyond said tubular device and tubular member for supportir'i'g' a test model in: said fluid current, said shaft being moved longitudinally in response to the drag force on the model caused by ir'n pingement of the fluid current therewith, movable means arranged within said casing and operatively connected to said shaft for preventing rotation of said shaft, eX- tensible resilient means secured to said movable means and extended longitudinally thereby an amount proportional to said drag force, and means disposed within saidcasing ands'ecuredto and actuated by said movable means for measuring said longitudinal extension of the resilient means whereby the drag force associated with the-impingement of the fluid current on the model may be ascertained.

4. A- balance device comprising a casing adapted to bemounted' withina wind tunnel in a fluid current, an elongated tube secured to said casing, a pair of bearing supportssecured to said tube, a tubular shaft rotatably supported by said bearing, support means including a motor operatively connected to said tubular shaft for imparting. rotat-ive movement thereto, a sting. arranged within saidtubular shaft and adapted to support a test model thereon in-said fluid current, said sting 'being move'd longitudinally within said tubular shaft in response to the drag force on. said modelcaused by impingement of the fluid currenttherewith, a pair of shafts arranged within said casing, a y'oke arranged on said pair of shafts and carried by" said sting and moved slideably on said-shafts a's the'stin'g is actuated, a precision spring secured to saidyokeand extended: longitudinally thereby an amount proportional to said drag force, and linear measuring means secured to and actuated by said yoke'for measuring the longitudinal extension of said spring: whereby the dragforc'eon the model may be: ascertained;

5; A balance device comprising a easingadapted to heam'ounted within a wind tunnel in a fluid currenn'a rotatable shaft comprising a pair of tubular seetions a model support disposed within and extending through said tubular shaft and adapted to support a test model on the free end thereof, said model support being moved longitudinally by the drag force on the model in response to impingement of said fluid current therewith, a tubular windshield enclosing said' tubular shaft, a pair of bearing supports secured to said-windshield, a' pair of'self ali'gn' ing bearings connecting said pair of tubular sections and rotatably supported in said bearing sup orts-for slidela bly' supporting the-model support and for permitting freeax'ial movement thereof when the model current thereon, movable means secured tosaid model support and actuated thereby as the support is moved by said drag force, means-secured to said movable means and extended longitudinally thereby an amount propor tional to said drag force, and a linear measuring device secured to said movable means and moved thereby an amount proportional to said drag force for measuring the longitudinal extension of said extendible means whereby the drag force on' the model may be ascertained.

6. A balance device comprising a casing adapted to be mounted within a Wind tunnel in a fluid current, an elongated tube secured to said casing, a pair of bearing supports secured to said tube, a tubular shaft rotatably supported within said bearing support, a model support arranged within said tubular shaft and adapted to have a test model attached thereto, said model support being moved longitudinally within said tubular shaft in response to the drag force on the model caused by impingement of the fluid current therewith, a pair of shafts rotatably supported within the casing, a yoke slideably arranged on said pair of rotatable shafts and operatively connected to said model support and actuated thereby, means including a motor operatively connected to the tubular shaft and to said pair of shafts for imparting rotative movement thereto thereby to reduce the static friction between the slideable model support and the rotatable tubular shaft and the slideable yoke and the pair of rotatable shafts, flexible means disposed between the model support and yoke for maintaining the yoke and model support in mutual alinement with respect to each other, a precision spring secured to said yoke and extended longitudinally thereby by an amount proportional to said drag force, and linear measuring means secured to and actuated by said yoke for measuring the longitudinal extension of said spring whereby the drag force associated with the impingement of the fluid current on the model may be ascertained.

7. A balance device comprising a casing adapted to be mounted within a wind tunnel in a fluid current, an elongated tube secured to said casing, a pair of bearing supports secured to said tube, a tubular shaft rotatably supported Within said bearing supports, a model support arranged within said tubular shaft and adapted to have a test model attached thereto, said model support being moved longitudinally within said tubular shaft in response to the drag force on said model caused by impingement of the fluid'current therewith, "ayoke slideably supported within said casing and operatively connected to said model support and moved longitudinally thereby, a pair of shafts rotatably supported within the casing, bearing means secured to said yoke and'slidably mounted on said pair of rotatable shafts, a motor arranged within said casing, drive means on said. motor including means for imparting rotative movement to said pair of shafts and said tubular shaft thereby to reduce the sliding friction between said pair of shafts and said bearing means and said tubular shaft and said model support, flexible means disposed between the model support and yoke for maintaining said yoke and said model support in alinement, a precision spring arranged within said casing and having one end secured to said casing and the other end thereof secured to said yoke and extended longitudinally thereby by an amount proportional to said drag force, and linear measuring means secured to and actuated by said yoke for measuring the longitudinal extension of said spring whereby the drag force on the model may be ascertained.

8. A wind tunnel balance comprising a normally sealed casing adapted to be mounted in a fluid current, an elongated tubular support secured to said casing, a tubular device disposed within and rotatably supported by said support, means including a motor arranged within said casing and operatively connected to said tubular device for imparting rotative movement thereto, a shaft slidably arranged within said tubular device and adapted to support a test model on the free end thereof, said shaft being moved longitudinally in response to the drag force on the model caused by impingement of said fluid current therewith, movable means arranged within said casing and operatively connected to said shaft and moved slidably thereby as the shaft is actuated, resilient means secured to said movable means and extended longitudinally thereby an amount proportional to said drag force as the movable means is actuated, means disposed within said casing adjacent said resilient means and responsive 10 tothe-movement thereof for measuring said longitudinal extension of the resilient means whereby said drag force on the model may be ascertained, port means arranged within the base portion of said model for admitting the base pressure caused by impingement of said fluid current therewith into the interior of the model; duct means arranged within said shaft in communication with said port means and the casing for admitting said pressure into the interior of the casing whereby the casing pressure and base pressure are equalized, and means arranged on the casing in communication with the interior thereof whereby the casing pressure may be ascertained. 1 r 9, A balance device comprising a casing adapted to be mounted within a wind tunnel in a fluid current, a rotatable shaft comprising a pair of tubular sections, a model support disposed within and extending .through said tubular shaft and adapted to support a test model on the free end thereof, said model support being moved longitudinally in response to the drag force on said model, a tubular windshield enclosing said tubularshaft and a substantial portion of said model support, a pair of bearing supports secured to said Windshield and having a pair of concave surfaces formed thereon respectively, a pair of spherical members connecting said tubular section in engagement with said concave surfaces for supporting and permitting free axial movement thereof when the model support is flexed in response to side and or lift forces of the fluid current thereon, pressure admitting means for admitting the base pressure caused by impingement of the fluid current with the base portion of said model into the interior of said casing whereby the casing pressure and base pressure are equalized, a resilient element secured to said model support and extended longitudinally thereby an amount proportional to said drag force, and means including a linear measuring device secured to and actuated by said model support for measuring the longitudinal extension of said resilient element whereby the drag force on the model may be ascertained. 10. In an aerodynamic testing apparatus for use in a wind tunnel, an elongated casing comprising a movable member having a test model mounted on one end thereof in a fluid current, said movable member being moved longitudinally in response to the drag force on said model, a rotatable lubricated bearing member for supporting said movable system for said longitudinal movement, means for imparting rotative movement to said bearing system, means including a linear measuring device connected to said movable member and moved thereby an amount proportional to said drag force, means for connecting said measuring device to the movable member, measuring means movable byan amount proportional to the movement of the measuring device, means connected to including an actuating element connected to said measuring means for actuating said measuring means an amount proportional to the movement of said measuring device thereby to obtain a balance condition therebetween, and means including an indicator operated by said actuating element for ascertaining the drag force on said model when said balance condition has been obtained.

11. In an aerodynamic testing apparatus, for use in a wind tunnel, a casing supported by said tunnel, an elongated tube secured to said casing, a pair of bearing supports secured to said tube, a tubular shaft rotatably supported within said bearing supports, a model support arranged within said tubular shaft and adapted to have a test model attached thereto, said model support being movable longitudinally within said tubular shaft in response to the drag force on said model, a pair of shafts rotatably supported within the casing, a yoke slideably arranged on said pair of shafts and actuated by said model support, means including a motor geared to the tubular shaft and to said pair of shafts for imparting rotative movement thereby to reduce the friction between the slideable model support and the rotatable tubular shaft and the slideable yoke and the pair of rotatable shafts, flexible means disposed between the model support and yoke for maintaining the yoke and model support in mutual alinement, a precision spring secured to said yoke and extended longitudinally thereby an amount proportional to said drag force as the yoke is actuated by the model support, linear measuring device secured to and actuated by the yoke for measuring the longitudinal extensinner said spring, :inea'ns ao'tuatable'an amount proporfional to the degree of actuation of the measuring device f'dT b'fifi rlg 'a balanceeondition therebetween, elCfftii'e means" including an electrical cire'uit connected to said measuring means'and the measuring device for indicating Said balanced condition thereof, means including a movable element connected to said measuring means for ae tu'a'tin'g said measuring means; means including ashaft engagement with said movable element for actuatii'i'g' said movable element as'the shaft is rotated, and-means carried by Said shaft for ascertaining the-drag force on said" crlho'de'l when said balanced condition 'hasbeen obtame 1 2-. In an aerodynamictesting apparatus for use in a wind-tunnel, a movable device adapted to be mounted Withinsaid tunnel a'fl'uid current, a test model sup ported on one end of said movable device, said movable device being moved longitudinally in response to the dragforce 'on said model causedby impingement of the fluid current therewith, rotatable lubricated heating means for supporting-said movable system fors'aid-lon'gitudi'nal movementfthereby to reduce the static friction tne'rebetween as the movable device is aetuatedylnea'ns including a motor' geared to said bearing means torinrparting-nrotative movement thereto, means including a linear measuring device operatively' connected to said movable device for movement thereby an amount pro: portional to said drag'forceon the model,-meansincluding; a-s'econd' linear measuring device move'd an-amount proportional to said first name'd measuring device for obtaining a' balanced condition therebetween, means including an electrical circuit operatively connected to said measuringdevices for indicating said balanced condition ther-eo'f, means includin a lever connected to said second-named measuring device for actuating said meastiring device as saidlever is moved apredetermined amount, a shaft in engagement with said lever for moving the lever-saidpredetermined amount as the shaft is rotated and-means actuated by said shaftau'dincluding a drum carried thereby for ascertaining the drag force on said model when said balanced condition has been" obtained.

1-3. A balance-device comprising aig'casing-adapted-tohe mounted within a wind tunnelin a fluid current, an elongated tube secured to said casing, a'p'a'ir of bearing supports secured to'said tube, a tubular shaft rotatably supported within said bearing supports, amodel support arranged within said tubular shaft and having" atest model attached thereto, said model-support being moved lo'ngifudinally' Within said tubular shaft in response to the drag force on the model caused by" impingement of the timid current therewith, a pair ofsh'a'ft'srotat'ably supported within the casing,'- a yoke slideablyarrang'edon said air of rotatable shafts 'and op'erat'ively'eonneeted to said mo'de'l support and actuated thereby, means including a motor geared "to th'e tnbul'aesnattandto said: pair of is'haits 'for imparting rotativ movement thereto therebyto reduce the statie friction between the 'slideable modelsupport and the rotatable tubular'shafit, the s'lideable yoke-and the pair of rotatable shafts, and flexible meansdisposedbetween the model-support and yoke for maintaining the yoke-and model support inmutu'al alin'ement with respect to each other as th'e test-model is subjected to said fluid current 14.- A balance device comprising a casing-adapted to be mounted withina wind tunnel in a fluid current, an elongated tube secured tosaid casing, a" pair of bearing-supp'o'rtss'eoured to said tube, a tubular shaft rotatably' sup ported within said bearing supports, a model support arranged-within said tubular shaft and having a test model attached thereto, said model support being moved longitudinally within said tubulars'haft in response to the drag force-on said model caused by impingement of the fluid current therewith, a yoke sildeably supported within said casing and connected to said model support and moved longitudinally therehy, a pair of shafts rotatabl-y supported within the-casing, bearing-means secured to said yoke and slide'ahly mounted on said pair ofrotatable-shaft's, a motor arranged Within the easing, drive means driven by said motor" for imparting 'rota tiv'e movement to said pair of shafts and the tubular shaft thereby to reduc'e'the sliding frictionbet-ween saidpair of shafts and the bearing means and the tubular shaft and said model support, flexible means disposed between the model support and yoke-for maintaining said yoke and the model support in alinement, andrneans including a linear measuring device securedto and actuated by sai'd'yoke arr-amount proportional to sa'id drag force for measuring the longitudinal movement of said model support.

l5. A balance device adapted to be mounted in a Wind tunnel in a fluid current and comprising a movable element for supportinga test model insa'id fluid current and adapted to be moved longitudinally inresponseto the drag force on said model caused by impingement of said fluid current therewith,'means includinga'pair of linear measuring devices actuated an amount proportional to said drag force for measuring the 'dragfor ce on said model, means including a helical scal'e for indicating the drag force'on saidmodel when-said measuring devices are in abalance condition, and means connected to said measuring devices for indicating a balance condition therebetween.

References Cited the file of this patent UNITED STATES PATENTS 1,682,138 Merrill Aug. 28, .1928 2,072,912 Heydekampf Mar. 9, 1937 2,485,977 Mains Oct. '25, 1949 2,515,069 Zola -July 11, 1950

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