Patent GB-507990-A (GB)
Title: Improvements relating to rate of climb indicators for aircraft and like rate of change of fluid pressure responsive instruments
IPC: G01P3/62
Filed: 1937-09-17
Abstract: 507,990. Pressure gauges. BENDIX AVIATION CORPORATION. Sept. 17, 1937, No. 25327. Convention date, Sept. 17, 1936. [Class 106 (ii)] A rate of climb indicator for aircraft comprises a pressure iespoiisive element operating through mechanism to indicate a pressure differential on opposite sides of the element due to rate of change of altitude as a result of the retarded rate at which the pressures on opposite sides of the element tend to equalize through restricted flow communication between the fluids on opposite sides of the element, characterized in that the restricted communication is constituted by a diffuser of a porous nature so chosen that the rate of pressure equalization is independent of the altitude. Two intercommunicating aneroid capsules 6 communicate by a pipe 9 with a vessel 10 and are connected by a link 7 and quadrant and pinion 4, 3 to a needle 1. The walls 11 of the chamber 10 are made of porous material. If the pressure on the outside of the chamber formed by vessels 10, 6 decreases due to ascent into higher altitudes, the vessels 6 expand and move the pointer to the left. If the instrument descends the pointer moves to the right. In another form of diffuser the walls are made of concentric tubes, each two adjacent walls at one end being connected together and the two adjacent pairs are connected together at the other end. Another form comprises capsule-like members made of porous material in communication at the central portions to form a closed chamber. Fig. 4 shows a form in which the diffuser is formed by a number of thin washers 22 preferably of metal clamped tightly between upper and lower clamping members 23, 24 by a bolt 25 and nuts 26. The member 23 has an extension 27 provided with parallel grooves 28 to permit passage of air from the stack of washers to the chamber 29 and thence through tube 30 to the pressure responsive element. The surfaces of the washers are etched or corrugated to give the desired porosity, and they may be of such material as to provide a bimetallic temperature control as described in Specification 508,059. The bolt 25 may be of copper and thus cause pressure to decrease as temperature increases. In a modification of this form a spacing member of selected material is used which coacts with the bolt to give the necessary compensation. Fig. 7 shows a rate of climb indicator. A case 37 is closed at one end by a plate 38 and at the other by a glass 39. A standard 41 secured to the base supports a post 42 to which the capsules 44 are connected by a resilient arm 43, a screw 58 affording zero adjustment. The capsules are connected to a pivoted lever 52 by a bimetallic strip 50 the lever operating a pointer 56 by means of a chain 54. The capsules are connected by a pipe 62 to a closed vessel 60 the walls of which are of porous material. The casing is vented to outside atmosphere through a suitable dehumidifying medium 64 such as silica gell and holes 68. The Specification as open to inspection under Sect. 91 comprises also a form in which a pointer shaft is journalled in a stationary block to which one end of a spiral metal strip is connected. The other end engages the pointer. The strip is faced with porous material or is of such a cross-section that a space is left between the strip and the porous facing to form a chamber. This strip behaves after the manner of a Bourdon tube, straightening out when the pressure in the porous material is greater than outside. This subjectmatter does not appear in the Specification as accepted. Reference has been directed by the Comptroller to Specification 141,244, [Class 106 (ii)]