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Home , Airspeed, Airspeed indicator, Indicated airspeed, Pitot tube, True airspeed

Sept. 12, 1950 W. ANGST 2,522,337 MACH METER Filed Dec. 9, 1944 2 Sheets-Sheet.

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"/m2.ATTORNEY. . . . Patented Sept. 12, 1950 2,522,337

UNITED STATES ; : PATENT OFFICE 2,522,337 MACH METER Walter Angst, Manhasset, N. Y., assignor to Square D Company, Detroit, Mich., a corpora tion of Michigan Application December 9, 1944, Serial No. 567,431 3 Claims. (Cl. 73-182). is 2 This invention relates to a Mach meter for air plurality of posts 8. Upon one of the posts 8 are craft for indicating the ratio of the true mounted a pair of serially connected aneroid cap of the craft to the of sound in the medium sules 9 and upon another of the posts 8 is in which the is traveling and the object mounted a diaphragm capsuler it. The aneroid of the invention is the provision of an instrument s: capsules 9 are sealed and the interior of the cas-l of this type for indicating the of an . ing is placed in communication with the static aircraft in fight. opening of a Pitot static tube through an opening The maximum safe Mach number of any air in the casing, not shown. The interior of the dia craft is the value of the ratio of to phragm capsule is connected through the tub the at which the laminar flow of ing 2 to the Pitot or opening of the Pitot air over the wings fails and shock Waves are en static tube through the opening 3 in the back countered. This indicates an undesirable and wall of the casing...... dangerous condition because of control difficul A lug 4 is connected to the diaphragm capsule ties and structural stresses. The instrument, ac- . lf and has pivoted therein a link 5 to which is '' cording to the present invention, permits the de adjustably attached a link 6. Upon the link 6 . termination of this maximum safe Mach number is adjustably mounted a plate f7 carrying a lever for any given aircraft, which number when ap arm 8. An extension on the link 6 terminates in an abutment 9 against which bears a spring plied correctly to a conventional airspeed indi 2 of U-shape. One of the supporting posts 8 has catorspeed. shows the maximum safe indicated air 20 a platelike transverse extension 22 at the edge of The Conventional measures.’ which are disposed a plurality of adjustable studs. the difference between the Pitot and static pres 23 forming stops for the elongated leg of the U Sures of a Pitot static tube and is conventionally. ' shaped spring 2 and serving to calibrate the referred to as the . To inter movement of the diaphragm capsule fl. Upon pret this measurement in terms of true airspeed, the rear surface of the plate 7 are a pair of sup it is necessary to compensate for variation in air ports 24 and 25. Within the supports 24 and 25 temperature and altitude pressure. The speed of is mounted a shaft 26 for rotative and limited . sound varies with air temperature, but is inde longitudinal movement. A light spring 27 biases: pendent of altitude pressure. Since true airspeed the shaft 26 for rotation in a counterclockwise di and the speed of Sound are equally affected by air rection as viewed in Figure 4 and also for move temperature no compensation for temperature is 30 ment downwardly as viewed in Figure 2. A lever necessary in the determination of the Mach num arm 30 is rigidly mounted on the shaft 26 and is ber or ratio of the true airspeed to the speed of rotatable thereWith. '' Sound. The uppermost portion of the aneroid capsules Other objects and features of the invention will 35 9 is provided with a hub 28 connected by a short be readily apparent to those skilled in the art link 29 to an arm 3 on a shaft 32 pivoted in the from the specification and appended drawing il support 25. Also mounted on the shaft 32 is an: . lustrating certain preferred embodiments in arm 33 engaging the lower end of the shaft 26 as Which: viewed in Figure 2. Rigidly mounted on the shaft ; Figure 1 is a representation of a dial face and 40 26 is a lever arm 34 engaging with the lever arm. indicator of the Mach meter according to the 8 to be moved thereby to effect rotation of the present invention. shaft 26. A bimetallic fork 35 is provided about Figure 2 is a longitudinal sectional view through the aneroid capsules 9 between the ends of which the instrument of Figure 1. : ...... and the hub 28 are disposed the force applying Figure 3 is a transverse sectional view on the pins 36 to provide temperature compensation for lineFigure II-III 4 is ofalongitudinal Figure 2. sectional view through theForwardly movement of of the the plate aneroid 7 is capsules. disposed a gener."...... the instrument at right angles to the section of ally diagonally shaped plate 37 upon posts 38. In Figure 2. . . . . the plate 7 and the support 24 is pivotally mounted The instrument comprises an outer casing f 50 a shaft 39 upon which is secured a gear sector 4, which is sealed airtight through the gasket re the shaft 39 being biased for rotation in a clock tainer ring 2, rubber gasket 3, glass 4 and bezel wise direction as viewed in Figure 3 by the coil ring 5. Within the casing is disposed a support. Spring 42. A lever arm 4) is mounted on the shaft ing framework constituted by plates 6 and 7 39 and positioned to engage the lever arm 30 for Spaced apart in a rigid cage arrangement by a 55 movement thereby. In the plates 7 and 37 is piv., 2,522,887 3 4 otally mounted a shaft 43 carrying a pinion 4 While a certain preferred embodiment of the meshing with the gear sector 4. Upon the plate invention has been specifically disclosed, it is 3 is mounted a stationary dial 5 bearing indicia, understood that the invention is not limited of Mach number as indicated in Figure 1. The thereto, as many variations Will be readily ap forward end of the shaft 43 extends through the parent to those skilled in the art and the inven plate 37 and dial 45 and carries a pointer 46 ro tion is to be given its broadest possible interpre tatable with respect to the indicia, upon the dial tation. Within the terms of the following claims. 45 to indicate the Mach number of the aircraft. What is clained is: The operation of the instrument will now be de 1. In a Mach meter for aircraft, a dial bear Scribed: 10 ing indicia of Mach number, an indicator now As the speed of the aircraft is increased, the able relatively to Said dial to indicate a Mach pressure difference between the Pitot and the number reading thereon, means responsive to the Static of the Pitot static tube increases Pitot pressure of an aircraft in fight for effect to effect an expansion of the diaphragm capsule ing novernent of Said indicator, and means re f. This movement of the diaphragm capsule 5 Sponsive to the altitude pressure of the aircraft moves the lever arm 8 downwardly as viewed in for varying the response of the indicator to a Figure 4 and permits movement of the lever arm given change in the Pitot pressure, said last nen 34 to effect a rotation of the shaft 26 in a cour. tioned means increasing the indicator Irovement terclockwise direction under the bias of spring 2. as the altitude pressure decreases. Rotation of the shaft 26, effects rotation of the 20 2. A Mach meter for aircraft comprising a dial lever arm 3 in the same direction and this will bearing Machnurnber indicia, an indicator now effect movement of the lever arm 4 upwardly as able relatively to said dial to indicate a Mach viewed in Figure 4 to rotate the shaft 39. Rota number reading thereon, a diaphragm - capsule tion of the shaft 39 is accompanied by rotation of for effecting movement of Said indicator, and the gear sector 4 which in turn rotates pinion 44 25 an aneroid capsule for varying the response of on shaft 43 to rotate pointer 46 with respect to Said indicator to a given movement of Said dia the dial 45 and the Aach number indicia, thereon. phragm capsule, said aneroid capsule increasing Upon a change in the altitude pressure, the the indicator movement as the altitude pressure pressure within the casing connected to the static decreases. opening of the Pitot static tube will be changed 30 3. A. Mach meter for aircraft comprising a dial and Will be accompanied by movement of the bearing Mach number indicia, an indicator move aneroid capsule 9. Upon a decrease in altitude able, relatively to Said dial to indicate a Mach preSSure the aneroid capsules will expand to ro number reading thereof, a diaphragm capsule tate the shaft 32, in a counterclockwise direction adapted to be connected to the pressure line of as viewed in Figure 2, by movement of the lever. 35 a , means for effecting movement of arm 3 through the link 29. As the shaft 32 ro said indicator in response to change in the Fitot tates, the lever arm 33 Will move - thereWith to tube pressure, an aneroid capsule responsive to move the shaft 26 bodily upwardly as viewed in the altitude pressure of the aircraft, and means Figure 2. The lever, arm. 39 Will move upwardly for varying the response of said indicator to with the shaft 26 and Will decrease the distance 4. movement of Said aneroid capsule as the altitude between its point of engagement with the lever pressure changes, said aneroid capsule movement arm 4) and the axis of the shaft 39 and hence increasing the indicator response as the altitude will increase: the angle of rotation of the shaft preSSLIre decreases. 39 Occasioned by a given angular rotation of the WALTER ANGST. shaft. 26. Therefore, by the longitudinal move.-- 45 ment of the shaft 26 in response to expansion REFERENCES CITED and contraction of the diaphragm capsules 9, the - rotation of the pointer 46 effected by expansion The following references are of record in the: and contraction of the diaphragm capsule will file of this patent: be modified. Thus, a decrease in altitude pres 50 UNITED STATES PATENTS sure will result in greater rotation of the pointer Number Nare Date. 46 for a given movement of the diaphragm cap 1,489,463 Sherrin ------Apr. 8, 1924 Sue , while With increased altitude pressure 2,177,244 Cianberlini ------Oct. 24, 1939 the movement of the pointer for a given dia 2,302.713 Paulin ------Nov. 24, 1942 phragm capsule movement will be decreased. 5 5 The instrument according to the present in 2,379,328 Weingart ------June 26, 1945 vention will continuously indicate the Mach num 2,385,845 Schairer ------Oct. 2, 1945 ber of an aircraft in flight or the ratio of the FOREIGN PATENTS true airspeed of the aircraft to the speed of Niner Country Date Sond in the local medium in which the aircraft, 60 is traveling. When used to determine the max 217,358 Great Britain ----- June 9, 1924 imum safe Mach number of an aircraft, the air 532,638 France ------Nov. 18, 1921 craft is speeded up until discontinuity of laminar 823,949 France ------Oct. 25, 1927 foW of air and the occurrence of Shock waves OTHER REFERENCES is initiated at which time the reading. Of the instrument will indicate the maximum safe Mach National Advisory Committee for Aeronautics number for the aircraft. The known maximum Wartime Report L-423 entitled “NACA Mach safe Mach number may be utilized with the pres Number indicator for Use in High-speed Tun ent instrument or with other instruments to in nels' by Norman F. Smith, originally issued July dicate the maximum safe airspeed. 70 1943 as Advance Confidential Report 3G31.