Abstract: The invention provides a system for selective reduction of infrared signature of a vehicle subjected to aerodynamic heating. Liquid coolant under pressure vaporizes in porous sections of the skin of the vehicle to transpiration-cool the skin. Adjacent downstream solid skin sections are film-cooled by the vapor introduced in the boundary layer. Coolant flow control is achieved by pressurizing the liquid coolant, by modulating flow control valves, and, optionally, by configuring the porous section to operate as a cavitating venturi, or combinations of these methods.

Abstract: Apparatus and methods for thin film formation from which structures may be constructed for use in space. An elastic expandable torus is rolled upon itself about its circular axis as a bubble is formed so that the bubble attachment line may be repositioned to maintain an optimal ratio of attachment diameter to bubble diameter and to maintain an appropriate bubble contact angle and to provide a pre-wetted surface for the bubble at the bubble attachment line. Also included is a frame composed of memory metal which is compacted for immersion in thin film forming fluid and heated to its transition temperature for self erecting to a predetermined thin film shape whereby the need for pressurized gas for formation of the thin film is eliminated.

Abstract: A microwave-powered aircraft has lifting surfaces for exerting lifting forces on the aircraft in response to the propulsion of the aircraft and a rectenna array for receiving and rectifying microwave energy transmitted to the aircraft from a location remote from the aircraft. An electric motor for driving a propeller is energized by microwave energy received by the rectenna array, which is provided in a body at the underside of the aircraft. The body has its major dimensions extending horizontally and is relatively shallow with a periphery which is vertically curved so as to reduce turbulence in the airstream over the body during flight. The body is separate from the lifting surfaces and shaped to at least substantially avoid the generation of lifting forces by the body.

Abstract: A crash survivable enclosure for flight data recorders used in aircraft and other vehicles operating over land and water includes a strong, light-weight metal shell for enclosing and protecting an information storage device having power, signal, and address lines connected thereto. The memory device is supported inside the shell in a wax filler of the type having a high melting temperature and a high heat of fusion to act as a heat sink for absorbing a large quantity of heat to minimize possible damage to the memory device because of excessive heat, flames and/or high temperature. A strong lightweight metal shell is provided to enclose and protect the inner shell and contents against substantial, external mechanical forces commonly occurring in a crash and flames, heat and fire resulting therefrom.

Abstract: A decoy aircraft construction of compact format during transport and able to form a decoy model of an aircraft on disposition on an airfield has the form of a rectilinear box blank having six primary panels joined at edges so as to form a box on bringing together free edges thereof. The panels have hinged to each of one or more thereof a single secondary panel or a secondary panel complex formed in turn of a plurality of panels hinged together. No secondary panel or secondary panel complex of the construction when folded at its hinges has overall dimensions greater than those of the primary panels. The location and shape of the secondary panel(s) and secondary panel complex(es) are such that on dismantling to a flat format, the primary panels of the box with the secondary panel(s) and secondary panel complex(es) housed therein, the secondary panel(s) and secondary panel complex(es) augment the flat format by unfolding to impart to it a three dimensional shape simulating that of an aircraft construction.

Abstract: A flight motion simulator includes a unit under test supported on a stationary frame for angular and translational movement along pitch, roll, and yaw axes. A rotor element is secured to the unit under test and has a spherical configuration. Magnetic bearings supported by the stationary frame support the rotor element in three degrees of freedom of movement. A drag-cup induction motor is mounted on the frame and connected to the unit under test to generate three degrees of freedom of movement by generating a rotating magnetic flux in a stator assembly to induce a corresponding flow of currents in the rotor element to produce torque and motion in the unit under test in the same direction as the flux movement in the stator assembly.

Abstract: A cylindrical roll drum housing (12) is mounted to the roof (18) of an aircraft fuselage. Enclosed in the housing (12) is a sensor (22) that pivots about an azimuthal axis (82). The sensor (22) normally looks outwardly through sliding window (20) that moves back and forth in correspondence with sensor pivoting. Pressurized air is blown directly across the window's opening (40), and is also blown directly into the housing (12). The window (20) has an inwardly directed airflow-deflecting edge which, in combination with the air blowing, is used to control boundary layer vortices across the window's opening so that they do not interfere with sensor properties.

Abstract: An imaging device that automatically rotates upon descent through an atmosphere provides an onboard image detector a sweeping panoramic scan as it descends. No moving parts or propulsion system are required. The location, angle and pitch of the winged structure, together with its inertia properties, passively induces rotation. The angled location of the image detector takes advantage of the resulting rotation. Data generated by the image detector may be transmitted to a remote receiver or, alternatively, stored for subsequent recovery.

Abstract: An explosives detection system for an aircraft to deter terrorist activity in which a plurality of explosives detectors are located about the interior passenger compartment of the aircraft in order to detect the presence of explosives. The explosives detectors generate an electronic signal upon sensing explosives and are periodically sampled so that an appropriate alarm signal may be generated upon the detection of explosives. The alarm signal causes a pair of cameras to be directed towards the vicinity in which explosives were detected and may also automatically shut down the aircraft.

Abstract: Apparatus for reducing drag and improving optical observation through an open aircraft port includes a ramp mounted on the port downstream edge, orifices or slots in the ramp surface interconnected by a manifold, and an associated air pump for withdrawing air from the free shear layer through the ramp to provide reattachment of the free shear layer at a preselected location on the ramp. The apparatus also can include conduits for supplying the extracted air to apertures located in a lip on the port upstream edge for injecting air along the free shear layer to control detachment.

Abstract: An integrated primary flight display apparatus for an aircraft provides coordinated information with minimum eye scan distances. Various cathode ray tube generated presentations are centered toward a common electronic attitude director indicator having indicia thereadjacent and pointers centrally directed. A moving altitude scale is utilized with a fixed vertical speed scale employed to select the correct vertical speed for leveling off at a given altitude. An arcuate shaped heading indication is expanded in angular extent to achieve enhanced sensitivity.

Abstract: A landing gear load sensor (24) for an aircraft (10) having a skid type landing gear (14) is provided. The sensor (24) includes a shear beam (30) having a loadbearing area (40). Structure (32, 34) is provided for mounting the shear beam (30) to the aircraft (10), such that the loadbearing area (40) is disposed adjacent the landing gear (14). Structure (50) is disposed on the shear beam (30) between the mounting structure (32, 34) and the loadbearing area (40) for sensing shear load on the shear beam (30).

Abstract: An active, automatic-firing, impact responsive cable-cutting apparatus for use on conventional aircraft such as helicopters for virtually instantaneously forcibly severing obstructive cables. A lightweight, non-corrosive frame comprising a mounting base portion and an integral, outwardly extending, angular deflection arm is adapted to be selectively mounted on an aircraft or on an extension pole which extends downwardly toward the ground or forward of the nose of the aircraft. Mechanical firing components of the assembly are housed within a cylindrical sleeve adapted to be accessed for maintenance through a removable butt. Sharpened, serrated guide blades extending along outwardly angled forward edges of the frame are adapted to strain the outer periphery of a cable as it is forcibly deflected and guided into a central mouth. A removable cutting block is provided at the interior of the apparatus adjacent the cutting assembly mouth in operative association with a rigid, angular, cutter knife.

Abstract: Vacuum systems for use aboard aircraft and other vehicles, wherein, by simplified design, the systems of this new invention are virtually foolproof. This new invention utilizes the age old venturi due to its simplicity and lack of moving parts, but due to innovation, the limitations of the venturi have been overcome. This new invention installs the venturi within the exhaust tailpipe of engines and puts the extreme high velocity of exhaust gas movement to good use. These systems are compatible with just about any engine, and obviously venturi ice problems are eliminated. These systems may be used to provide redundant power for gyro systems and windshield wiper systems. By the addition of a suction relief valve and connective tubing the system will provide regulated suction pressure for the operation of a Gyro Horizon and or a Directional Gyro. By further addition of a restrictor needle valve and additional connective tubing, one can power either a Turn and Bank indicator or A Turn Co-ordinator.

Abstract: An in flight damage assessment and surveillance system for aircraft using imaging apparatus for capturing optical images of predetermined portions of the aircraft disposed along the exterior of said aircraft in a manner such that the flight characteristics of the aircraft remain substantially unaltered. The images captured are recorded on a storage media mounted within the aircraft and having an enclosure which provides for the survival of the storage media even when subjected to the harsh environment of an aircraft crash. A display for displaying the captured optical images to aircraft crew members is also positioned within the aircraft along with apparatus for interfacing the imaging apparatus to recording apparatus and the display. The system can also include second imaging apparatus for capturing optical images of selected portions of the interior of the aircraft as well as a telemetry device for transmitting images to or from ground based stations.

Abstract: A passive load mitigation system for supporting transducers on a body moving through a fluid stream is described. According to the invention, a streamlined aerodynamic surface for supporting the transducers is attached to the body via a pivot axis. The axis supports the surface in a torsionally unrestrained manner in at least one rotational degree of freedom about the pivot axis. Therefore, as the body moves through the fluid stream, the surface remains substantially parallel to the plane of the stream. Aerodynamic stability is ensured by forming the surface with substantially trapezoidal or parallelogram shaped sidewalls and by mounting the surface on the pivot axis such that the surface's aerodynamic center is located downstream of the pivot axis. Flutter is prevented or substantially reduced by increasing the surface's bending stiffness or by incorporating ballast weights on a tip pod attached to a portion of the surface.

Abstract: Apparatus and method for background matching of an aircraft or spacecraft which includes the direct electrical heating of the aircraft skin to minimize a negative infrared contrast signature detected from above platform infrared detectors. An infrared detector on the bottom of the aircraft detects the background radiance which is compared with the aircraft radiance determined from the power flight conditions or from direct sensors. An on board computer compares the background and aircraft radiance to determine the amount of heat required to match the background. The computer controls a power source that heats an electrical resistor within the aircraft skin to increase the skin temperature. Selective heating of portions of the aircraft skin may be provided by a plurality of resistors strategically placed on the aircraft fuselage.

Abstract: In the event of an earthquake or fire, important objects like a recording medium used in a location where important information to the outside are relayed or in a location where natural phenomena are observed, are carried away, hanging from an airborne balloon that is inflated and released in response to the mechanical shock of an earthquake or the heat of a fire.

Abstract: An apparatus for training aircraft pilots wherein the apparatus includes a boom defined by a central bracket, a large rigid arm and a small rigid arm collectively supported on a vertical mast for pivotal movement about horizontal and vertical axes. The large and small arms extending outwardly from the mast along a common longitudinal axis, the outward end of the small arm being provided with an adjustable balance weight and the outward end of the big arm being provided with a sling for suspending an aircraft at its center of gravity.

Abstract: A preheat apparatus for a helicopter wherein certain critical helicopter components are preheated preparatory to takeoff of the aircraft. The critical components include the main rotor gear case, the intermediate gear case, the tail rotor gear case, the oil tank and cooling assembly and the engine gear cases. In certain aircraft, these also include the fuel control unit and the drive reduction gear case. Heat pads are installed with respect to the critical components in strategic locations and are sized and shaped to fit the component. The heat pads are connected by wiring harness that is connected to an external source of electrical power.

Abstract: A safety apparatus for a hang glider that indicates any failure of a pilot to properly hook in a flight harness. The apparatus includes a circuit having a power source, such as a dry cell battery, connected to an alarm through a harness hook in sensor. When the pilot fails to properly hook in the harness, an alarm sounds. The circuit also includes an on/off switch that activates the circuit only in direct response to erection of the hang glider. Thus, the circuit is deactivated when the hang glider is disassembled for transport to or from a launch site and during storage. Consequently, annoying alarm soundings are avoided and battery life is increased. In addition, the circuit includes a deactivation switch that prevents the alarm from sounding when the hang glider is resting on the ground. Finally, a test switch is provided to allow manual testing to confirm proper activation and operation of the circuit.

Abstract: At least one hook or clip is mounted to the inside surface of the engine compartment hatch door so as to removably receive the engine oil dipstick so that the dipstick protrudes beyond an edge of the hatch door and prevents its full closure.

Abstract: The collision of birds with aircraft is prevented by means of at least one light source installed on an aircraft which produces light flashes. The frequency of the light flashes produced thereby is varied during at least one cycle time period. The frequency of light flashes is advantageously continuously increased one or more times in a range of from approximately 0.1 Hz to 3.0 Hz, and the maximum frequency may then be maintained. Two such light sources are preferably visible to the birds.

Abstract: An aircraft instrumentation system includes a plurality of air-driven instruments and a primary air pump for operatively driving the instruments. An air pressure regulator, coupled to the primary pump, selectively exhausts compressed air discharged by the primary pump so as to maintain a constant desired pressure at the instruments, and a backup pump is provided for operating the instruments in the event the primary pump fails. To avoid excessive cooling of the backup pump when the backup pump is not being operated and the aircraft is at altitude, a shroud is mounted so as to form an air space around the backup pump. Warm air, heated through compression by the primary pump and exhausted through the pressure regulator, is collected by a housing surrounding the pressure regulator and is conveyed, through a conduit, to the air space to warm the backup pump when the primary pump is operating.

Abstract: An apparatus for ejecting an aircrewmans helmet-mounted electro-optical equipment from an aircraft cockpit comprising an arm having a first end pivotally mounted at a position behind an aircrewmans ejection seat, a second end of the arm having on it a line reel-in apparatus and a flexible line depending therefrom, the flexible line attachable to helmet mounted electro-optical equipment, a guide and damper connecting the arm to the ejection seat, upon operation of the ejection seat the electro-optical equipment being detached from the helmet, the ejection seat rising in the cockpit and causing rotation of the arm about the pivot point, the line reel-in apparatus locking to prevent the line extending and the electro-optical equipemnt being ejected from the cockpit into the airstream by rotation of the arm prior to the ejection seat leaving the cockpit.

Abstract: Vacuum systems deriving their trustworthiness by means of simplified apparatus, wherein, the vacuum source will be derived from simple venturis common to the state of the art, whereby, ice prevention will be achieved by use of bleed air from the turbine section of the jet engine used to power the aircraft. Venturi ice prevention will be selectable by the pilot and will fail safe to the on position should the aircraft encounter a complete electrical failure. The remaining units comprising of the vacuum system and connective tubing will all be common to the state of the art. One of the vacuum systems will supply regulated vacuum pressure to the earth reference gyros by means of a venturi being located within the inlet mouth of a jet engine, said pressure then routed to a pressure regulator and then routed to the gyros, therefore, regulated pressure will be available immediately following engine start and will remain available in flight even should its respective engine fail.

Abstract: A method and apparatus for providing an aero-optical interface by stabilizing a shear layer in a fluid flowing over an aperture. The apparatus extracts fluid from a remote part of the flowing fluid and conveys it to the underside of the shear layer where it feeds the shear layer and prevents the shear layer from deflecting into the cavity underlying the aperture. A preferred embodiment also includes a ramp downstream of the aperture. Stability of the shear layer is optimized by placing the aperture where the pressure distribution absent the aperture would have been constant. The resulting thin, self-similar shear layer is an optimized viscid flowfield interface for uniform transmission of optical radiation.

Abstract: A mounting and mounting method for a sensor positioned within a tubular axle of an aircraft undercarriage which will provide an output voltage proportional to the angular deflection of an axle for computation of aircraft gross weight. The sensor is not affected by cross-sectional distortions of the tubular axle under loading, undersirable shear frictional effects at the interface between the sensor mounting and the tubular axle and differential angular deflections of the axle.The cylindrical mounting member for the sensor has a pair of O-rings adjacent opposite ends thereof which are positioned to space the periphery of the mounting member from the bore of the tubular axle and which are under radial compression and act to provide uniform radial compressive forces applied about the full circumferential periphery of the cylindrical mounting member and absorb distortions of the axle by elastic deformation thereof.

Abstract: A turn-and-bank indicator can integrate with regard to time the displacement of a pointer of the turn-and-bank indicator, the pointer indicating the turning rate of the airplane. It includes a non-contact converter which outputs an electrical signal in proportion to the deflection of the pointer; an amplifier which amplifies the output of the non-contact converter; an integrator which integrates the output of the amplifier with respect to time; and a digital display unit which displays the output from the integrator at a close position with the pointer.

Abstract: A pump system for use with an air operated instrument system of an aircraft. A primary pump is connected to an air operated instrument and a backup pump is provided in the event of failure of the primary pump. Heated air from the discharge port of the primary pump is used to heat the backup pump during operation of the primary pump.

Abstract: A direct air cooling system 12 for electronics carried by aircraft. The cooling system provides a submerged air scoop 16 which directs outside air to several electronic modules 14. The air flows through passages 76 in the modules 14 which are adjacent to circuit boards 74, 78 bearing discrete electronic components 88. A foil layer 86 and aluminum fin stock help transfer heat from the electronic components to the directed air. Heated air is then exhausted through exhaust port 24 or 28.

Abstract: An aircraft control position indicator is provided that displays the degree of deflection of the primary flight control surfaces and the manner in which the aircraft will respond. The display includes a vertical elevator dot/bar graph meter display for indicating whether the aircraft will pitch up or down, a horizontal aileron dot/bar graph meter display for indicating whether the aircraft will roll to the left or the right, and a horizontal rudder dot/bar graph meter display for indicating whether the aircraft will turn left or right. The vertical and horizontal display or displays intersect to form an up-down-left-right type display. Internal electronic display driver means receive signals from transducers measuring the control surface deflections and determine the position of the meter indicators one each dot/bar graph meter display.

Abstract: Apparatus for detaching helmet-mounted equipment (6) from the helmet (4) of a vehicle-mounted user (1) includes a quick-release fastening (8) securing the equipment to the helmet. A removal cord (11) passes from the equipment by way of a guide (10) and is attached to the vehicle (12). The action of the apparatus is to remove the equipment from the helmet to a position of safety when the user has to leave the vehicle in an emergency.

Abstract: An advanced fuel receptacle lighting system for aerial refueling of receiver aircraft during night time operations. The receptacle lighting system mounted on a tanker aircraft for enhancing a boom operator's visual view of a fuel receptacle area on the receiver aircraft without blinding or distracting the receiver pilot.

Abstract: A removeable spoiler is described for reducing the wing lift of parked aircraft. It includes a spoiler member in the form of a strip temporarily mountable to stand upright and project into the airstream on the top of the wing. It extends parallel to the wing axis and is supported by a clamp contacting the outer surface of the wing for securing the spoiler to the wing.

Abstract: An IR filter assembly for use with a lighted instrument panel mounted to a control panel includes a support frame surrounding the lighted instrument panel but through which the lighted instrument panel is visible, and IR filter panel mounting bracket to which a IR filter panel is mounted and a stowing bracket. The filter bracket is mounted to the support frame and is displaceable along the support frame and into the stowing bracket for stowing the IR filter panel when not in use. For operation, the IR filter panel is withdrawn from the stowing bracket and locked to the support frame such that the IR filter panel covers the lighted instrument panel.

Abstract: A helicopter protector designed to protect the exterior of a helicopter from exposure to the elements and at the same time allow servicing of the helicopter. The protector utilizes the main rotor blade of the helicopter as a ridge-pole running forward and aft along an offset center line of the helicopter body; and includes main rotor support holders, main rotor tie-down means, a sheet of protective covering material and a plurality of tension binding straps.

Abstract: A camouflage and deceptive perception distorted vehicle such as an aircraft or surface vessel or the like for combat use at least a substantial portion of which will remain undetected until the vehicle subtends an arc of substantially five minutes when used against at least one predetermined light background reflectivity in which one of the surfaces of the vehicle includes a substantial area with a predetermined reflectance matching the predetermined light background reflectance. The area includes at least three defined portions at least two of which have different reflectances so that when the reflectance of one defined portion is added to the total reflectances of the others of the three defined portions, and the result averaged, they will have a reflectance substantially that of the predetermined light background.

Abstract: Pressure tapping for rigid sails, the tappings (10, 11, 12, 15, 16) being located to either provide a stall warning or to enable tuning of the sailset to the desired operating angles. A particular flow-state sensitive stall warning device is also described.

Abstract: A protective device for outer airplane surfaces is provided which includes a laminate to envelop, for example a portion of an airplane wing having a water-impervious dense outer layer and a less dense inner layer to provide impact resistance to prevent damage to the airplane wing and which is easily removed prior to flying.

Abstract: A towed body deployment/retrieval system which includes first and second hollow arms for passage of a cable from a winch to the towed body. The adjacent ends of the arms include forked fittings which are in cooperative engagement with a slip boundary sheave having, in a peripheral channel thereof, an endless belt slidable in the channel and having a groove which receives the cable. The arms are movable relative to the slip boundary sheave over a limited distance during normal usage. The slip boundary sheave rotates about an effective center located outside of its contour and accordingly is much smaller and can fit into a smaller space than an equivalent circular sheave which would normally be required for the same diameter towing cable.

Abstract: Apparatus is disclosed for protecting the exterior of an aircraft which comprises a plurality of elastomeric foam members; each substantially in the form of a sheet for covering a respective portion of the exterior of the aircraft. The invention additionally comprises straps for removably attaching the foam members to their respective portions of the exterior of the aircraft and air spaces for preventing moisture from building up between the foam members and their respective portions of the exterior surface of the aircraft.

Abstract: A self-contained, standby flight instrument includes sensors, processing circuitry, rechargeable power supply, voltage regulation circuitry, and display hardware arranged to provide a continuous display of aircraft airspeed, altitude, roll, pitch and heading regardless of any partial or complete failure in the primary instrumentation, an interrelated subsystem, or the electric power supply.

Abstract: An object intended for concealment or a facsimile thereof is used to generate the pattern by creating shadows on a flat surface at several elevation angles, with the resulting set of shapes then rotated in azimuth, in order to produce an abundance of quasi-object shapes within the pattern. The shapes are created in such a way as to be viewing-angle independent, thus producing a background upon which the object is difficult to see from any viewing angle. Selected azimuth and/or elevation angles can also be employed, resulting in patterns that are viewing-angle dependent.

Abstract: A fail-safe, automatic interlock connector arrangement automatically electrically interconnects an electrical component on a wing to another electrical component on a fuselage of a radio-controlled model airplane at the same time that the wing is connected to the fuselage.

Abstract: An improved fire-safe waste disposal system uniquely suitable for use in the aft bulk cargo hold (22) of a large capacity passenger aircraft which is compatible with, and can be readily interfaced with, FAA approved waste disposal chutes (39) extending through the passenger deck (25) from the aft galley into the bulk cargo hold (22) and comprising a standardized aircraft cargo container base (40), a floor (45) mounted on the base (40) and parallel therewith, a first pair of vertically extending walls (46, 49) secured to the floor (45) with one of the walls (49) being normal to the floor (45), the other of the walls (46) defining an included obtuse angle with the floor (45) and with the wall (49) having a greater height than the wall (46), and with a second pair of walls (50) rigidly secured to the first pair of walls (46, 49) and to the floor (45) in airtight fire-safe relation, a top (44) secured to the walls (46, 49, 50) in airtight fire-safe relation with the top (44) being normal to the wall (46) and defi

Abstract: An adjustable mounting tray for installation of an aircraft gyroscopic and/or inertial reference apparatus, comprises, a baseplate member mounted so that it is substantially level in roll and pitch on the equipment shelf or rack of a levelled aircraft. A top plate or tray member is pivotally mounted on the baseplate for azimuthal adjustment thereon. The aircraft is pitched up or down and the top plate rotated in azimuth to remove any roll/yaw cross-axis coupling thereby assuring precision longitudinal axis alignment.

Abstract: An instrument and method for continuously measuring by differential air pressure the surplus of kinetic energy of an aircraft mass and the resulting potential of wing lift (POWL) above an empirical datum which coincides with the incremental onset of mushing sink, and for coincidentally and continuously displaying the margin of measured airspeed above the calibrated datum within the airspeed range of transitional flight. The instrument includes a sensing probe having a pair of fixed plane surfaces normal to a common vertical plane and adjustably mounted in a region of induced, stable, incident airflow under the wing or other part of an aircraft to sense differential impact pressure on the fixed plane surfaces, and an instrument to measure and display the sensed differential pressure.

Abstract: A non-intrusive duct system is disposed in a component of an air vehicle. The component has an external surface in a free stream flow. The duct system is disposed substantially flush with such external surface and is disposed with respect to the free stream flow to receive such flow. The duct system receives a portion of the free stream flow and conveys such portion through the duct system such that the portion bears a known relationship to the free stream flow. A flow data sensor for sensing a parameter of the portion of free stream flow is suitably disposed with respect to the duct system to be affected by the portion of flow therethrough and to sense such parameter. The duct system has a flow control apparatus disposed in the duct system to control the portion of flow such that the portion of flow is compatible with the sensing capabilities of the flow data sensor throughout the range of rates of free stream flow over which sensing of a parameter thereof is desired.

Abstract: A system for lowering the level of turbulence in an opening through a wall ver which air is flowing at a subsonic velocity wherein an arcuate flange is secured to the downstream edge of the opening and extends into the opening a distance of 0.11 to 0.22 times the length of opening in the direction air flow, the flange being tangent to the wall at the part of attachment of the branch.