US2332565A - Altimeter or the like - Google Patents

Description

Oct. 26 1943. M. N. FAlRB ANK ALTIMETER OR THE LIKE Filed Sept. 13, 1940 2 Sheets-Sheetyl Oct. 26, 1943. M. N. FAIRBANK 2,332,565

' ALTIMETER OR THE LIKE Filed Sept. 15, 1940 2 Sheets-Sheet 2 Patented Oct. 26, 1943 UNITED STATES: PATENT OFFICE ALTIMETEB OR THE LIKE Murry N. Fairbank, Weston, Mass.

Application September 13, 1940, Serial No. 356,619

Claim.

This invention relates to a new and improved altimeter, and more particularly to a device of the character described which is adapted to be used on airplanes.

An object of the invention is to provide a device of the character described which may be readily and cheaply manufactured, and which is durable and accurate in operation Other objects of the invention are to provide, I

in a device of the character described, readily assembled and easily operated means for effecting an air-tight seal between the portions of the casings of the device; to provide a device of the character described in which operative elements may be readily mounted within the casing; to provide, in a device of the character described, novel easily assembled means for providing accurate gauge readings throughout the entire gauge scale; to provide manually adjustable means for compensating for alterations in barometric pressure at the point of take-off; and to provide novel operative means, including novel pressure sensitive means, for effecting alterations in the gauge readings.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements and arrangement of parts which will be exemplifled in the article hereinafter set forth and the scope of the application of which. will be indicated in the claims For a fuller understanding of the nature and objects of the invention, reference should be had to the accompanying drawings, in which:

Figure l is a front view in elevation, with certain elements shown in dotted lines, of a device embodying the invention;

Fig 2 is a side view in section, and drawn to an enlarged scale, of the device shown in Fig 1 along the line 2-2;

Fig. 3 is a view in section of a portion of the device shown in Fig. 2 and taken along the line .3-3;

Fig. 4 is a view in horizontal section of the device shown in Fig. l somewhat enlarged and taken along theline l-; and

Fig. 5 is an enlarged fragmentary view of a portion of the device shown in Figs 2 and 4.

In the form of the invention shown in the portion ll of the casing. The forward part of the casing is preferably provided with rearwardly extending supporting elements, hereinafter described, upon which the operative elements of the device are mounted. These elements and the forward part of the casing are preferably so designed that the operative elements of the device may be easily assembled. When assembled, they are enclosed within the relatively light rear portion M of the casing, which is adapted to seat against a rearwardly extending shoulder of the portion i2 of the casing, as'at it. I

An air-tight seal is efiected at the joint between the two portions of the casing by the provision of a supplemental ring member 08 positioned within the portion l4 and adapted-to bear against the resilient gasket 20, which may be preferably of rubber. After the section it of the casing has been slid into place, the ring member 68 is drawn forwardly against the gasket 20 by means of the screw elements 22 which extend through the dial face 26, as shown for example in Fig. 1. These screws are threaded into the ring element 88, as shown in Figs. 2 and 4, and, as they are tightened, the ring element i8 is drawn towards the front portion M of the casing, thus forcing the resilient member 20 against the rear portion of the casing, and causing the seal between the two portions of the casing to become air-tight Such a seal is preferred, for while it is intended that the device-shall respond to alterations in barometric pressure occasioned by alterations in altitude of the airplane equipped with the device, it is desirable that the device be shielded from alterations in the pressure of the atmosphere within the plane itself, as atmospheric pressure within the plane may fluctuate independently of external atmospheric pressure Accordingly means are provided, for example the pipe 38 leading directly from within the casing of the device to a static tube outside the airplane in which the device is mounted With such an arrangement the device will respond only to alterations in external atmospheric pressure .Means are provided, for example the drilled lugs 24, preferably associated with the front portion l2 of the casing, for affixing the device to a suitable instrument panel, not-shown.

Within the casing and at the forward part thereof there is provided a dial face 26 hearing suitable evenly-spaced indicia 28 indicative of the altitude reached by the plane equipped with the device. The dial 26 may be mounted upon screws 82. A glass cover-plate 84 is provided which is held in place by a snap ring 88 which forces the glass plate asainst the gasket 40.

A small window 42, shown clearly in Fig. l, is

provided in the gauge face 28, and, in registrywith this window, there is provided a walking beam 44 bearing on its forward face a strip bearing a series of indicia 48, shown for example in Fig. 1. The device is so adjusted that with each complete rotation of the needle or indicating element 88 a new numeraLof the series of indicia 48 is brought into position behind the window 42 in the dial face. This is accomplished by the downward movement of the front of the walking beam 44, as shown in Fig. 2, which in turn is caused by an expansion of the bellows 41 inresponse to a lowering of the outer atmospheric pressure, as will be hereinafter described.

The bellows 41, the walking beam 44, and the other operative elements of the device, are in large part mounted upon the rigid frame elements which are integral with or securely affixed to the heavier forward part of the casing. These elements, in the form of the invention shown, comprise a rearwardly extending cylindrical element 48 and a vertical element It which, as-shown in Fig. 4, is preferably so shaped as to position most of the operativ elements of the device to one side of the element 48, which is not centrally disposed in the device.

Pivotaliy connected as at I! to the upper portion of the element 88 there is a substantially horizontal arm 84, to the rear end of which the walking beam 44 is pivotally connected. as at 86. At the lower end of the element 88 there is pivotally connected, as at 88, a substantially horizontal forwardly extending arm 80, which is connected to the arm 84 by means of the element 82, which is countersunk in the arm 88 and in the adjustable screw 84. The spring 88, which-is amxed to the element 54, as at 88, and to the element 80, as at ill, serves to hold these two elements firmly against the vertical element 82, so that as the element 8!! is pivoted about the pivot I8, its motion is translated to the element 84, which pivots about the pivot 82.

It will be understood that the relative positions of the arms 84 and Il may be altered within reasonable limits by adjusting the screw 84. This alteration is ordinarily only necessary when the device is first assembled to so adjust the element 84 with respect to the element 88 that the device may function in the manner hereinafter to be explained to giv an accurate reading.

The forward portion of the arm 80 is held downwardly against the ball-bearings 12, or any other suitable element, by the spring 14, whichmay be affixed to the portion 21 of the frame means. The ball-bearings 12 rest upon the tapered end 18 of a manually adjustable threaded element I8. As this element is moved to the right. as shown in Fig. 2, the: ball-bearings 12 are raised in the channel in the frame in which they are positioned and they elevate the forward portion of the arm 80. This, in turn, causes the a transverse frame element 21 by means of the eating needle 30. Thus, by adjusting the element I8 and henceraising or lowering the forward portion of the arm 80 against the action of the spring 14, the indicator 80 can be set at zero reading on the dial, irrespective of changes in atmospheric pressure at th point of take-off.

At the rearof the device and mounted upon the horizontally extendingframe element 48 is the evacuated bellows 41 and its associated elements. In the form of the invention shown in the drawings the base of the bellows rests upon a lateral extension 82 of the fram element 48, to which the bellows is rigidly mounted, as at 84. The upper portion of the bellows supports a vertically extending arm 86 terminating in the pivoted connection Iii with the rear end of the walking beam 44, as previously described. Within the bellows there is provided a helical spring 88 under compression, the spring acting constantly to force the bellow outward against atmospheric pressure which tends to compress the evacuated bellows. A preferred arrangement is one in which the bellows structure itself has been so treated as forward portion of the arm 54 to rise and the to relieve initial strain in the metal thereof. Under these circumstances, the tendency of the bellows to expand with a reduction of pressure within the casing is due almost solely to the spring 88 which, as has been pointed out. is under compression at atmospheric pressures, and tends to elongate as the pressure is reduced. With such an arrangement a much more accurate reading can be secured, as the device can be adjusted substantially to respond to the reaction of the spring alone and thus the well known lag in the response of bellows members such as that shown at 41 is reduced.

A preferred means for mounting thespring element is shown clearly in Figs. 2 and 3. The ends of the helical spring element are bent inwardly as shown in Fig. 3 to provide upper and lower arms 80. These arms are countersunk as at 82 along the axis of the helix formed by the spring, and pin means 94 are provided in the upper and lower portions of the frame holding 7 the bellows element. These pins sit in the countersunk portions 82 and thus hold the spring firmly and centrally in the bellows. The entire spring action is thus along the axis of the helix formed by the spring and,.with the structure as shown and described, there is no tendency for a portion, however small, of the spring to come into contact with any other portion thereof during the operation of the device. 86 illustrates the tube through which the bellows member is evacuated.

It will be apparent that with a device such as has been described a drop in atmospheric pressure within the casing ID will cause an expansion of the bellows element 41 by means of the out ward thrust of the spring element 88. This will raise the arm 86 and the pivot 80. thus elevating the rear portion of the walking beam 44, which pivots about the point 56 so that the forward portion of the beam will be forced downwardly.

Means are provided to convert this downward movement of the forward portion oi the walking beam into a rotation of the needle 30, so that changes in altitude may be read directly from the position of the needle with respect to the dial face 26. The needle is mounted upon the end of a spindle shown generally as at I00. A detailed drawing of the spindle and its associated elements is shown in Fig. 5. The forward portion of the spindle comprises a member I02 mounted in a bearing I04 of the frame 21. The

2,832,505 needle 30 as shown is mounted upon the outward end 'of the member I02. The rear portion of the spindle shown as at I06 is mounted in an arm I08, which in turn is rigidly afllxed to the frame 21 by the posts I I (Fig. 4) in which it is mounted and which are riveted into the frame.

The main body of the spindle I00 comprises two portions,a tapered portion H2 at the forward end of the spindle, and a generally cylindrical portion H4 at the rearward end of the spindle. About the tapered portion H2 there is coiled a wire H6 which is aflixed to the tapered portion of the spindle and which provides an inclined groove between adjacent portions of the wire. As shown in Fig. 5, this groove is adapted to receive a thin, pliable wire II 8 which may be amxed to the upper portion of the walking beam element 44 as at I20 (Fig. 2). This Wire IIB may preferably be formed of a plurality, for example three, strands of tungsten wire of small diameter, for example the individual strand may have a diameter of approximately .001 of an inch, and the three strands may be woven to form a cable. This wire is preferably afilxed to the large end of the tapered portion H2 of the spindle I00 in the last groove formed by the coiled wire IIB, as for example at I22, so that rotation of the spindle causes the wire H8 to wind in the groove, each full rotation of the spindle winding the wire IIB once around the spindle and progressively in a group of shorter length. It will be apparent that the first rotation of the spindle will cause a greaterlength of the wire H8 to be wound thereon than the second rotation. As shown in Fig. 5, the device is adapted for four successive rotations of the spindle, each drawing a smaller amount of the wire H8 on to the tapered portion I I2. Each rotation of the spindle causes one complete rotation of the needle 30 and corresponds to such downward movement of the walking beam 44 as causes the next successive numeral in the.list of indicia 46 on the front thereof to come into position behind the window 42 in the dial face 26. At the end of one complete revolution of the spindle, for example, the walking beam 44 will have been lowered to such an extent that the numeral 4 appears in the window 42 and, at the end of four complete revolutions of the spindle, the numeral I6 will appear in the window 42. This will be apparent from an inspection of Fig. 1. The de-. vice is thus adapted to record changes in elevation from zero to 16,000 feet.

The tapering of the spindle, as shown clearly in Fig. 5, resulting in a less downward movement of the walking beam 44 with each complete revolution of the spindle, is to compensate for the fact that at higher altitudes the bellows 41 and its associated elements expand somewhat less with an increase in altitude of, for example, 1,000 feet than at lower altitudes and, since the dial is fixed, means are provided to compensate for the decreasing expansion of the bellows element with changes in barometric pressure at high altitudes.

While the wire H8 may be affixed as at I22 to the spindle, in the preferred form of the invention an extension of the wire is coiled around the cylindrical portion of the spindle H4, as for example at I 24, and the end of the wire may be afilxed,'as at I26, to a spring element I28 affixed to the walking beam 44, as at I30. The spring I28 holds the wire II8 under tension and, as the walking beam is lowered, its pulls down upon the lower end of the wire I I8, thus unwinding the coils I24 from the cylindrical portion H4 oi the spindle, andthus in turn causing the spindle to rotate and to wind thereupon the wire H8 in the manner previously described. It will, of course, be apparent that there should be suiilcient take-up wound upon the cylindrical portion H4 of the spindle so that four complete turns of the spindle may be made.

It will be apparent that other means for causing a rotation of the needle element 30 may be substituted for wire and spindle means shown and described. For example, a fine cable might be substituted for the wire H8 with the addition of a hair spring tending to rotate the spindle instead of the spring I28. Other modifications in the structure will be obvious to those skilled in the art.

The operation of the device will be apparent from the description. The device is first set at any desired position, as for example at zero reading, by rotation of the element 18, which in turn causes an adjustment of the walking beam and of the needle element 30 through the pivoting of the arms 60 and 54 about the pivots 58 and 52 in the manner previously described. After this initial adjustment, the device is ready for operation. Changes in altitude result in changes in expansion or contraction of the spring 08 within the evacuated bellows 41, as previously described, and these changes are translated to the walking beam 44 through the pivot 80. As the front part of the walking beam 44 is lowered or raised it causes a rotation of the spindie I00 with a corresponding rotation in the needle 30. The spindle I00 is constructed to compensate for changes in the degree of expansion and contraction of the bellows element 41 with changes in altitude.

The element I32 shown in Figs. 2 and 4 is a counterbalancing weight aflixed to the walking beam 44 to aid in balancing the elements of the device.

Means are also preferably provided for adjusting the position of the pivot and the upper end of the bellows element 41 with respect to the walking beam 44. An adjustment of the position of this pivot is desirable in connection with the initial adjustment of the various parts of the device. As shown in the drawings, this is accomplished by providing a slidable plate I40 in which the pivot is mounted, the plate I40 being held in position between extending flanges I42 from the walking beam 44 by means of a screw I44 threaded in the plate I40 and extending through the slot I46 in the element 44. It will be apparent that the position of the plate I40 may be controlled within the limits of motion of the screw I 44 within the slot I46.

Since certain changes may be made in the above article and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter. contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described my invention, what I claim as new and desire to secure by Letters Patent 1. In an altimeter, in combination with presmove through a greater distance at low pressures than at high pressures in response to the same extent of motion of said movable scale, said means comprising a tapered spindle upon which said pointer is mounted and acable mounted for motion with said movable scale and adapted to cause rotation of said spindle, there being an aperture in said fixed scale, said movable scale bearing a series of indicia thereon and being so positioned with respect to said aperture that successive ones of said indicia are brought into view therethrough with each complete rotation of said pointer.

2. In a device of the character described, in combination, means providing a two-part casing, means for rendering substantially air-tight the joint between said casing parts after said parts have been assembled, frame means mounted within and extending from one of said casing parts, pressure sensitive means carried by said frame, a scale-carrying beam pivotally connected to said frame and movable in response to motion of said pressure sensitive means, cable means afflxed to and movable with said beam, a tapered spindle mounted in said frame and engaged by said cable, a second fixed positioned scale having an apcr-. ture therein, and a pointer mounted to rotate with rotation of said spindle and positioned for rotation adjacent the face of saidfixed scale, said first-mentioned scale bearing a, eries 1 1ndicia so position thereon that a succeeding one of said series is brought into view through the aperture in said fixedly positioned scale with each complete rotation of said pointer.

3. In an altimeter, in combination, pressure sensitive means comprising an evacuated bellows having mounted therein, under compression, a helical spring, the mounting means for said spring being positioned along the axis of the helix formed by said spring, a dial having an aperture therein, a scale thereon, a movable pointer associated therewith, and means for mechanically connecting said pointer to said bellows whereby motion of said pointer is responsive to expansion and contraction of said bellows. said connecting means comprising a tapered spindle, cable means windable thereon and a pivotally mounted arm aillxed to said cable means, said arm carrying, on the endtthereoi' adjacent said first-mentioned scale, a second scale, said second scale bearing a series of indicia so positioned thereon that a succeeding one of said series is brought into view through the aperture in the dial with each complete rotation of said pointer.

4. Pressure sensitive means for use in an altimeter or the like, comprising an evacuated metallic bellows and a helical spring mounted within said bellows under constant compression, the active length of said spring remaining constant under all conditions of operation of said pressure sensitive means, the means for mounting said spring within said bellows being positioned along the axis of the helix formed by said spring and comprising a pair of inwardly projecting pointed elements, each end of said spring being turned inward and being to engage one of said pointed elements.

5. Pressure sensitive means for use in an altimeter or the like, comprising an evacuated metallic bellows and a helical spring mounted with in said bellows under constant-compression, the active length of said spring remaining constant under all conditions or operation of said pressure sensitive means, the means for mounting said spring within said bellows being positioned along the axis of the helix formed by said spring and comprising a plurality of recess-providing ele ments and a plurality .0! pointed elements, one pointed element seated in each said recess, each end of said spring being turned inward and comprising one element of said mounting means.

MURRY N. FAIRBANK.

provided with a recess adapted CERTIF ICAIE OF C ORREC TI ON Patent No. 2,552,565. October 26, 19145.

HURRY N. FAIRBANK- 'It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 14., first column, line 55,claim 2, for "fixed" read "fixedlyline same claim, for "position" read --pos itioned--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 18th day of January, A. D. 191-411..

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

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