Abstract: A self-contained, hand-held device for testing an aircraft helmet communication system including a microphone and earphones in which a selection switch on the housing of the device is movable from an off position to a talk-through position at which the microphone is connected to both the earphones and a volume indicator on the housing and to a self-test position in which actuation of a pushbutton switch on the housing applies the output of an oscillator both to the volume indicator and a circuit having a voltage divider made up of a potentiometer and a fixed resistance to provide a self-test signal which energizes an illuminable element on the housing if the device is functioning properly and to an earphone impedance test position at which the output of the oscillator is applied to a circuit having a voltage divider made up of the potentiometer and the earphones to produce an earphone impedance-test signal which energizes the illuminable element if the earphone impedance is of the correct value.

Abstract: Helical screw rotors for a screw rotor machine wherein, for both the male and female rotor, the rotor profile includes involute curves for the male and female rotor lobe tip portion and rotor root portion, thereby generating mating involute curved surfaces of the corresponding groove, root and tip portion for the female rotor, resulting in low leakage path between the high and low pressure volumes when the rotors are in mesh, and causing ramps on the lobe tips of both the male and female rotors to form high points thereof which act as sealing strips during intermesh rotation of the rotors and in conjunction with the screw rotor machine casing.

Abstract: Helical screw rotors for a screw rotor machine wherein, for both the male and female rotor, the rotor profile includes involute curves for the male and female rotor lobe tip portion and rotor root portion, thereby generating mating involute curved surfaces of the corresponding groove, root and tip portion for the female rotor, resulting in low leakage path between the high and low pressure volumes when the rotors are in mesh, and causing ramps on the lobe tips of both the male and female rotors to form high points thereof which act as sealing strips during intermesh rotation of the rotors and in conjunction with the screw rotor machine casing.

Abstract: Helical screw rotors for a screw rotor machine having improved profiles on both male and female rotors, wherein the female rotor leading and trailing flanks comprise first and second circular arcs with the first circular arc subscribed by a first radius whose center lies inside the pitch circle and a second circular arc subscribed by a second radius whose center also lies inside the pitch circle. The leading and trailing flank portions of the male rotor are travel generated by first and second radii on the female rotor resulting in effective driving and driven lobe surfaces on the leading and trailing lobe surfaces. This also results in minimized blowholes and effective sealing surfaces on the intake and discharge sides of the screw rotor machine. The female rotor lobes have a main peripheral surface defined by a true circular arc swung from the axis of the female rotor.

Abstract: A throat microphone has an outer resonant diaphragm which is adapted to be secured against the throat of a wearer and which cooperates with a housing to form an outer chamber. An electret microphone element disposed inside the outer chamber includes an electret diaphragm acoustically coupled to the outer diaphragm and an electret housing forming an inner chamber with the electret diaphragm. The electret diaphragm is perforated to provide pressure relief between the two chambers to give the electret microphone element a rising response characteristic, which is enhanced by a differentiating network in the input circuit of a local preamplifier. The outer diaphragm is so formed as to have a principal resonance at about 3 kilohertz to provide a further emphasis to voice frequencies at or near that resonance.

Abstract: Helical screw rotors for a screw rotor machine having improved asymmetric screw profiles on both male and female rotors, wherein the male rotor lobe leading flank comprises solely first and second circular arcs with the first circular arc subscribed by a first radius which lies on a radial line through the male rotor center at an offset angle to the male rotor lobe center line in the direction of the trailing flank of the rotor lobe to create a male rotor tip point inherently including a male rotor lobe sealing strip.

Abstract: A local external communication system for use by a person wearing a mask covering the nose and mouth and in sealing engagement with the face in which an assembly secured to the outer surface of the mask without in any way affecting the integrity of the mask seal generates an output signal in response to the wearer's voice. The output signal is fed to a speaker carried on the wearer's body to produce an output which is audible to other persons in the vicinity of the wearer.

Abstract: An improved screw compressor for the compression and axial displacement of a gas is set forth. The compressor is of the type having a housing formed with an axially extending passage. The axially extending passage has at one axial end thereof a gas inlet and at the other axial end thereof a gas outlet. A one piece male rotor is positioned in the passage and extends axially therein. The male rotor is formed with a plurality of helical ribs having generally convex flanks and root regions which are at least partially formed as involutes in cross section. Each rib of the male rotor has a profile consisting of a leading flank formed at least partially as an involute generated from a first base circle and a trailing flank at least partially formed as an involute generated from a second base circle. The second base circle has a diameter greater than the first base circle.

Abstract: Screw rotors for a screw compressor or expander incorporating improved screw profiles on both male and female rotors wherein certain mating portions of the two rotor screws have involute profiles to provide conjugate action of these screw portions with minimum sliding motion of such mating portions and with the remaining non-involute screw portions having generally circular arc profiles so that gear cutting and measuring techniques can be used in the production of such screw rotors.

Abstract: Screw rotors for a screw compressor or expander incorporating improved screw profiles on both male and female rotors wherein certain mating portions of the two rotor screws have involute profiles to provide conjugate action of these screw portions with minimum sliding motion of such mating portions and with the remaining non-involute screw portions having generally circular arc profiles so that gear cutting and measuring techniques can be used in the production of such screw rotors.