Semi-flush air data sensor

[0002] The present invention relates to an air data sensor probe that will sense angle of attack or angle of sideslip as well as pivot and static pressure, and which is designed to substantially reduce drag, deicing/anti-icing power and weight over normal strut mounted probes, but yet give reliable results. The probe has an aerodynamically formed housing that extends like a small bulge outwardly from the side skin of an aircraft with angle sensing ports and a pitot port on a leading end, and static pressure sensing ports positioned in desired locations aft of the pitot port entry.

[0003] In the prior art, angle of attack has generally been measured either by vane sensors, cone sensors or multifunction probes with angle sensitive pressure ports. Vane sensors swivel about an axis to indicate changes in relative airflow direction, with suitable circuits for indicating the angle change. Multi-function probes have a barrel with top and bottom ports at the leading end of the barrel, and as the probe barrel axis changes angle, the ports sense differential pressure, to give an indication of angle of attack.

[0004] Static pressure has been sensed on probe assemblies as well, and flush mounted plates that have static pressure sensing ports in them are also utilized.

[0005] It is desirable to reduce drag and weight on high performance aircrafts, but reliable indications of angle of attack and static pressure are required for satisfactory high performance aircraft operation that is safe.

[0006] The present invention relates to a multi-function air data sensor that comprises an aerodynamically shaped body or housing protruding slightly from a mounting plate that is placed onto and is flush with the skin of an aircraft. The aerodynamic shape includes a rounded (part spherical) forward end, and smoothly contoured surfaces downstream from the forward end to result in low drag as air flows past the semi-flush body. The body is elongated in fore and aft direction generally aligned with the airflow. A cross section taken along a plane substantially perpendicular to the fore and aft axis and to the mounting area of the skin of the aircraft, has a shape similar to an end portion of an ellipse. The outer edge of the body decreases in lateral width gently, and the rear end is rounded back to the mounting surface.

[0007] The housing or body surface along the maximum outward dimension provides a location on which a static sensing port or ports can be placed.

[0008] The body extends from the mounting surface only a small amount and can remain in the boundary layer air along the aircraft surface. The body or housing is exposed to airflow and is positioned to provide a useable differential in pressure signals between the angle sensing ports.

[0009] In addition, the body of the semi-flush sensor has a port facing upstream, at its forward end, to provide a local total pressure or pitot pressure signal.

[0010] The mounting plate for the sensor can be flush with the aircraft skin, and can be curved to blend with curved aircraft surfaces. The “bubble” or housing forming the sensor body protrudes slightly into the airsteam, at a level and location to avoid adverse effects of aircraft components, and creates a small local disturbance in the airflow. The pressure ports can be located at various locations to measure the desired air data parameters. The housing forming the sensor body can be molded or formed integrally with the aircraft skin of a composite material or metal fuselage.

[0011] The protrusion from the aircraft skin is in the range of a few centimeters, and thus the sensor is lighter and has less drag than existing strut mounted air data sensing probes. The smaller size means that less power is required to deice or anti-ice. Very little ice accumulates near or on the aircraft fuselage skin, whereas strut mounted probes and vanes operate in a region spaced from the aircraft skin where moisture is concentrated due to the effects of flow past the fuselage of an aircraft. There are no moving parts in the present device, and the small size and aerodynamic shape means lower drag, lower weight, lower radar cross section, and less susceptibility to damage, such as bird strikes, refueling booms, and bumping by maintenance personnel. Many things that damage a strut mounted probe will merely flow over the aerodynamic shape of the present sensor. Since the sensor body does not protrude as far into the airstream from the fuselage or aircraft skin surface, there are fewer items that are likely to strike the protuberance or semi-flush sensor.

[0012] FIG. 1 is a elevational view of a semi-flush sensor made.according to the present invention;

[0013] FIG. 2 is a top plan view of the sensor of FIG. 1 on an enlarged scale;

[0014] FIG. 3 is a front elevational view of the sensor shown in FIG. 1;

[0015] FIG. 4 is a sectional view taken as in line 4—4 in FIG. 1; and

[0016] FIG. 5 is a front perspective view of the sensor.

[0017] Referring to FIG. 1, a semi-flush air data sensor indicated generally at 10 is mounted onto the skin 12 of an aircraft, utilizing a mounting plate 14 that is held in place with suitable countersunk fasteners 15, so that, as shown in FIG. 3, the plate is flush with the aircraft skin. A mounting with the plate inside the fuselage can be used, or the probe housing can be integrally formed or molded into a composite or metallic skin.

[0018] Sensor 10 has a bubble or blister type probe housing 20, that is aerodynamically smooth from a generally hemispherical or part spherical leading end shown at 22 which curves outwardly from the surface of the mounting plate 14 along a front edge 24 a desired distance, indicated generally by the double arrow 16 in FIG. 3. The front edge 24 of the leading end 22 joins a radius surface that is rounded to cause a minimum disruption of airflow, which is flowing in the direction indicated by the arrow 26 at 0° angle of attack. The semi-flush sensor or probe housing 20 smoothly transitions from the front end 22 outwardly to a generally longitudinally extending line 30 at the maximum lateral extension of the housing from the mounting surface. The line 30 may taper slightly inwardly toward the support surface 14 in rearward (downstream) direction. In cross section, as shown in FIG. 4, top and bottom walls 28 and 29 of the housing have outer surfaces 46A and 46B that converge from the peripheral edges of the housing at the support surface 14, laterally outwardly to a rounded part cylindrical outer end wall 48 on which line 30 lies. These top and bottom walls converge toward a central bisecting plane 31. Stated another way, the top and bottom walls diverge from the part cylindrical wall 48.

[0019] The central bisecting plane 31 passes through the central longitudinal axis of the probe housing 20 and is perpendicular to the surface of plate 14 and the aircraft skin surface.

[0020] The top and bottom edges 32 and 34 of the housing 20 along the outer surface of plate 14, and the peripheral edges of the housing at the leading and trailing ends 22 and 36, define a generally elliptical periphery in side view.

[0021] The top and bottom edges 32 and 34 join radiused surfaces that join the outer surfaces 46A and 46B of the top and bottom walls 28 and 29. In the side view of FIG. 1 the edges 34 and 32 curve upwardly and downwardly from the leading end 22 and then round back together, which is also rounded in side view, to form the small end of an elliptical shape. The FIG. 1 side view of the semi-flush probe housing 20 shows that the perimeter is a generally elliptical shape, but with different size leading and trailing ends, for smooth airflow characteristics. The top and bottom surfaces join surface 14 with radiused fillet surfaces and then join the outer surfaces of the walls 28 and 29, which converge toward and become tangent with the rounded, part cylindrical outer end wall portion 48.

[0022] The bottom or lower wall 29 tapers up to the rounded outer surface of the outer wall portion 48 and the upper wall 28 tapers downwardly to the surface of wall portion 48 of the housing, as shown in FIGS. 3 and 4. The upper wall 28 has an outer surface 46A and the lower wall 29 has an outer 46B that join the part cylindrical outer surface of portion 48. The maximum laterally outward dimension line 30 is a tangent line of a plane generally perpendicular to the bisecting plane 31 and engaging the outer surface of wall portion 48.

[0023] If desired, the plate 14 can curved to fit aircraft surfaces rather than being truly planar in order to permit mounting on various surfaces. The distance indicated by the double arrow 16 is such so that the housing 20 is preferably in the boundary layer of air that is on aircraft surfaces. The typical range of extension, but not as a limit, is between 0.5 and 2.5 centimeters. It is also recognized by the inventors that a variety of other flush shapes and configurations could be used to obtain flush air data angle of attack estimates. Keeping the protrusion of the housing, low but enough to obtain reliable pressure signals that indicate angle of attack is important.

[0024] The rounded front portion 22 has a pitot or impact pressure sensing port indicated generally at 50 for measuring P_t′m. The leading end 22 of the housing 20 also has angle of attack measuring ports including a top port 54 and a lower port . Port 54 will provide a pressure signal Pα, or P₁, and port 52 will provide a signal Pα₂or P₂.

[0025] A single static port or a tightly grouped pattern of static pressure sensing ports can be placed along the tangent line indicating the maximum outward dimension to achieve the desired aerodynamic performance. One such port is shown at 56 Additional static ports can be provided along this line and averaged, if desired, for obtaining the measured static pressure (P_s)

[0026] The various pressure signals are carried to an instrumentation package indicated generally at 60, as shown in FIGS. 2 and 4. Such instrument package can include various pressure sensors and conditioning circuitry, as well as a computer. The lines 52A and 54A shown in FIG. 4 provide pneumatic pressure signals to a differential pressure sensor 62 of known design. The line shown at 56A in FIG. 4 carries pressure signals from the static pressure sensing port 56 to an absolute pressure sensor 64, and the line 50A shown at FIG. 4 carries pressure signals from the pitot pressure port 50 to a pressure sensor 66. The pressure sensors provide electrical signals representing pressure at the connected ports to a central computer or processor 68 in the package 60. The computers or processors are programmed to utilize the pressure signals to provide the desired indications of angle of attack and static pressure.

[0027] The angle of attack measurement is presently carried out in the prior art multi-function probes by determining differences in pressures between top and bottom ports on a probe barrel that are positioned near the outer end of the probe. The pressure difference between the angle sensing ports is usually normalized by the local impact pressure (q_c1).

[0028] The semi-flush probe housing 20 of the present invention has been operated under wind tunnel test conditions. The semi-flush probe is first calibrated to zero angle of attack by adjusting the probe housing bisecting plane until the pressure difference between port 52 and port 54 is zero, meaning the sensors are indicating zero angle of attack. Then by changing the angle of attack of the bisecting plane the pressure signals (P₁−P₂)/q_c1are measured and are nearly linear between plus or minus 20° angle of attack of the semi-flush probe housing. At higher angles of attack the pressure signal has somewhat reduced sensitivity, but still provides a variable signal proportional to the angle of attack.

[0029] A useful range of measuring angle of attack is at least −40° to +40°. With the use of an equation with a normalizing factor as a denominator designated q_n2, where q_n2=(P_t′m−P₁)+(P₁−P₂)/2), an angle of attack signal can be determined for angles up to plus or minus 90°. This is accomplished by using (P₁−P₂)/q_n2for angles up to approximately plus or minus 40° and then using the negative inverse of the pressure difference, −q_n2/(P₁−P₂) for greater angles of attack. The use of the inverted ratio is described in U.S. Pat. No. 5,205,169, which is in corporated herein by reference.

[0030] The boundary layer has been found not to have a substantial effect on the angle of attack signal, It also has been found that measuring the static pressure along the maximum tangent line of the curved cross section probe provides adequate indications of static pressure.

[0031] The placement of the ports 52 and 54 can be essentially at the same angles as used on multi-function probes utilizing a cylindrical barrel. The location of such ports can be changed, as well, for reliable results.

[0032] The semi-flush probe housing 20 is formed so that the maximum extension from the surface of the air vehicle is kept small. The cross section taken along a plane perpendicular to the longitudinal center axis and perpendicular to the aircraft surface (FIG. 4) shows a rounded outer edge surface on wall portion 48 with a wall tapering up from the wall portion 48 relative to the central bisecting plane 31 another tapering down from wall portion 48 the top and bottom walls extend to the support plate 14 or aircraft surface in top and front views the leading edge is contoured or rounded in three dimensions (compound three dimensional curve), so that the form is a pact spherical surface 1 is about a quarter of a sphere. Although it is recognized other curved surfaces may also work, such as a parabola In side view (FIG. 1) the top and bottom edges at the aircraft skin are elliptical and taper to a narrow elliptical edge at the trailing end, which also is a compound curve surface rounded in three dimensions. The shape of the housing could be described as a half teardrop (cut through the axis of symmetry) that is mounted on a plate or formed integrally with a panel. A fillet round is placed where the half teardrop intersects the plate to gently transition between the housing surface and the mounting or panel surface.

[0033] Angle of sideslip (AOS) could be measured directly by mounting an additional unit on the bottom of the aircraft (instead of on the side). Alternatively, AOS could be derived by comparing differential static pressures or AOA angles between sensors on opposite sides of the aircraft.

[0034] The semi-flush system may also be integrated as a system and as a result P_t& ADS would be added to its outputs of AOA & P_sjthus producing a total air data system. Configurations using multiple semi-flush sensors would be able to provide P_t, P_s, AOA, and AOS Calibrations would be developed to relate the local values measured by the sensors to the desired free-stream values.

[0035] Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.