SG182019A1 - Apparatus and method for measuring static pressure in an aircraft - Google Patents

Abstract

System and method for measuring static pressure of an aircraft are disclosed. Thesystem comprises: a plurality of static ports mounted on the fuselage of the aircraft, wherein outputs of each of the static ports are connected to a pressure stabilizer, and the pressure stabilizer is operable to provide average pressure from the plurality of the static ports to a static pressure sensor located on a flight control computer(FCC) board of the aircraft.Figure 7b

Description

I

Apparatus And Method For Measuring Static Pressure in An Aircraft

FIELD OF INVENTION i

The invention relates broadly to an apparatus and method for measuring static pressure in an aircraft. In particular, the invention relates to an apparatus and method for measuring static pressure in an aircraft utilising vertical take-off and landing (VTOL) as well as fixed-wing aircraft.

BACKGROUND

Accurate stafic pressure measurements are important for maneuvering an aircraft.

Figure 1 is a schematic block diagram of a conventional pitot-static system 100 of an aircraft. The pitot-static system 100 generally consists of a pitot tube 101, a static port 109, and pitot-static instruments 103, 105, 107.

An altimeter 107 measures the height of the aircraft with respect to a fixed reference level. A vertical speed indicator 105 measures the rate of accent or descent of the aircraft.

The altimeter 107 and the vertical speed indicator 105 are operated by the aircraft's static pressure system comprising a static port 109 and an alternate static source 111. The static port 109 is an opening cn the exterior of the aircraft for sensing the static pressure i.e. the atmospheric pressure at an altitude at which the aircraft is flying. The static port 109 is often a flush-mounted hole on the fuselage of an aircraft and located such that it can sense the local static pressure in a relatively undisturbed area.

An airspeed indicator 103 measures the dynamic pressure of the air through which the aircraft is flying. The airspeed indicator 103 is operated by the aircraft's static and pitot pressure system. The pitot pressure system consists of a pitot tube 101 for measuring the dynamic pressure.

Figures 2a, 2b, 2c are sketches of conventional devices used in the pitot-static system 100. Figure 2a is a simple pitot tube 201 with an opening 203 for admitting

, air for dynarnic pressure measurement. Figure 2b. is a static source 205 comprising an opening 207 for allowing static air flow. Figure 2c is a pitot-static tube comprising an opening 211 for aliowing dynamic air flow and another opening 213 for aliowing static air flow.

Figure 3 is a perspective view of a conventional fixed wing unmanned aerial vehicle (UAV) 300 and Figure 4 is a perspective view of a flight control computer (FCC) board 407 used in the UAV of Figure 3. Figure 3 shows a pitot tube 305 attached to a leading edge of a wing 303 and connected to the dynamic pressure sensor 401 (Figure 4) of the FCC board 407. The FCC board 407 is embedded to the middie segment of the fuselage 301. Since the fuselage 301 is not a pressurized cabin, a static pressure sensor 403 located on the FCC board 407 is able to sense ihe atmospheric pressure.

Figure 5 is a perspective view of a conventional FanTail VTOL UAV 500. The FCO board 407 is integrated into the middle segment of the upper fuselage 501 sitting on a circular shroud 503. Unlike the conventional fixed-wing UAV 300, static pressure measurements are influenced by propeller down-wash 510. The propeller gown- wash 510 is unsteady even at a constant throttle getting. As a result, static pressure measurements fluctuate even at a fixed flying altitude or with engine operating at a constant RPM. This causes the aerial vehicle 500 to resonate at its operating height.

This phenomenon is encountered even when the aerial vehicle 500 is hovering in a gusty environment or moving at a constant height. This phenomenon also ocsurs when there is a change in angle of attack {A0A) or heading direction,

During flight, the air pressure is slightly different at different positions around the exterior of an aircraft. There is no position on the exterior of an aircraft at which the air pressure, for all angies of attack, is identical to the atmospheric pressure at the altitude at which the aircraft is flying. The difference in pressure causes an error in the altitude indicated on the alfimeter 107, and the airspeed indicated on the airspeed indicator 102. This error is known as position error. Position errors in a pitot-static system can be exiremely dangerous {o the flight of the aircraft.

As explained above, position errors can be caused when the static pressure of an aircraft is different from the free-stream pressure remote to the aircraft. Therefore, it is critical to position the static port in a position where the local air pressure in flight is always equal to the pressure remote from the aircraft

Position errors can be of two types namely “fixed errors” and “variable errors". Fixed errors are errors that are specific to a particular make of an aircraft. Variable errors are caused by exiernal factors, such as deformed panels that may obstruct the flow of air, or situations which may overstress an aircraft.

Position errors may be positive or negative, depending on factors, such as airspeed, angle of attack, aircraft weight, acceleration, aircraft configuration, and in the case of helicopters, rofor downwash. :

There is thus a need to provide an apparatus and method for measuring static pressure in an aircraft that seek to address one or more of the above disadvantages.

SUMMARY

According a first aspect of the present invention, there is provided a system for measuring static pressure of an aircraft comprising: a plurality of static ports mounted on the fuselage of the aircraft, wherein outputs of each of the static ports are connected to a pressure stabilizer, ang the pressure stabilizer is operable to provide average pressure from the plurality of the static ports to a stafic pressure sensor located on a flight control computer (FCC) board of the aircraft.

The static port may comprise a static port valve comprise a receptacle operable to be inserted into a through-hoie of payload adaptor: and a valve cap co-operabie with the receptacie, wherein the valve cap is operable fo regulate static pressure entering into the stabilizer.

The receptacle may comprise a cylindrical head and a base, the base comprising a through-hole along ifs length, wherein the base is operable to be inserted into a + through-hoie of the payload adaptor.

The receptacle may have a through-hole and comprises an annular head with sharp edges, and a truncated conical base connected by recessed portions, wherein the annular head is operable to receive the valve cap.

The conical base may have a 80° undercut for gripping a flexible tube, wherein the flexible tube connects the output of the static port valve to the input of the stabilizer.

The valve cap may comprise a substantially flat head with substantially sharp edges and a cylindrical shaft, wherein the receptacle is operable to receive the shaft of the vaive cap.

The inner surface of the valve cap head and the shaft may have a plurality of channels that lack material, wherein said channels are operable to control the static pressure input. The channels may be spaced at 120°,

The pressure stabilizer may comprise a pressure reservoir for receiving static pressure from the plurality of static port vaive; and an accurnulator valve positioned at the base pressure reservoir for directing the average static pressure output to the static pressure sensor located on the FCC.

The pressure reservoir may have a cylindrical wall, a base and an annular cap, the inner surface of the cylindrical wall and the outer surface of the cap having screw- threads whereby an enclosed space is formed when the cap is fitted onto the pressure reservoir

The pressure reservolr may comprise a plurality of inlet ports communicating with a corresponding static port valve, wherein the inlet ports are mounted radially and at equal distance on the outer surface of the wall.

The inlet port may comprise a base and an arm, the arm comprising a truncated conical head connected by a recessed portion, wherein the head has a 80° undercut for receiving and gripping a flexible tube connecting a respective static port vaive,

The base of the inlet port head may comprise internal screw-thread for receiving corresponding screw-thread on the recessed portion of the arm.

The base of the pressure reservoir may have a through-hole for receiving the 5 accumulator valve. The accumulator valve may have a through-hole along its length, the accumulator valve comprising an annular head; and a hollow shaft, wherein adjacent to the head the shaft has a threaded portion, a recessed portion, and a truncated conical base for inserting a flexible tube, the flexible tube terminating above the static pressure sensor on the FCC board.

The system may further comprise an adaptor bar for positioning the pressure stabilizer to the FCC; and a fastener for locking the assembly of pressure reservoir, the accumulator valve and the adaptor bar.

The adaptor bar may comprise a through-hole on either side for mounting the pressure stabilizer to the FCC board; a through-hoie at the center for receiving the pressure reservoir and the accumulator valve.

The adapter bar may have a recessed portion for co-operating with an oval shaped emboss on the outer surface of the base of the pressure reservoir.

The aircraft may be an unmanned aerial vehicle (UAV). The aircraft may be capable of vertical take-off and landing (VTOL). The aircraft may be a FanTail VTOL UAV.

The payioad adaptor may be integral to the fuselage.

According to a second aspect of the present invention, there is provided a methed for measuring stafic pressure of an aircraft comprising: mounting a plurality of static ports on the fuselage of the aircraft, connecting the outputs of each of the siatic ports to a pressure stabilizer, providing average pressure from the plurality of the static ports to a static pressure sensor located on a flight control center (FCC) board of the aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be better-understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

Figure 1 is a schematic block diagram of a conventionai pitot-static system of an aircraft;

Figure 2a is a sketch of a conventional pitot tube;

Figure 2b is a sketch of a conventional static source:

Figure 2c is a sketch of a conventional pitof-static tube:

Figure 3 is a perspective view of a conventional fixed wing UAV,

Figure 4 is a perspective view of a flight control computer (FCC) board used in Figure 3;

Figure 5 is a perspective view of a conventional FanTail VTOL UAV, rigure 6 is a perspective view of the FanTail VTOL UAV of Figure 5 with 2 static pressure stabilizer assernbly In accordance with an embodiment of the present invention;

Figure 7a is a perspective view of the static pressure stabiiizer assembly of

Figure 6 integrated into the FCC module: ‘Figure 7b is a perspective view of a complete static pressure stabilizer system of Figure 6;

Figure 8 is a top view of the static pressure stabilizer assembly of Figure 6;

Figure 8a is an exploded perspective view of a static port vaive in accordance with an embodiment of the present invention:

Figure 9b is a perspective view of the components of the static port vaive of

Figure 8g;

Figure 9c is another perspective view of an assembled static port vaive of

Figure Ba,

Figure 10a is a perspective view of a pressure reservoir assembly in accordance with an embodiment of the present invention;

Figure 10b is an exploded perspective view of Figure 10a;

Figure 11 is an exploded perspective view of a pressure reservoir and an -adaptor bar used Figures 10a and 10b.

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Figure 12a is a perspective view of the pressure reservoir of Figure 11 with an accumulator valve;

Figure 12b is a sectional view of the pressure reservoir of Figure 12a; :

Figure 13 is a front view of Figure 7 to iliustrate the flow of free-stream when an aircraft moves vertically,

Figure 14 is another front view of Figure 7 io illustrate the flow of free-stream when an aircraft moves horizontally,

Figure 15 is a partial cross-sectional view of the static port valve mounted on the payload adaptor;

Figure 16 is a cross-sectional view of the static port vaive subjected to frontal free stream,

Figure 17a shows actual plots obtained using the aircraft of Figure 5 the without a static pressure stabilizer; and

Figure 17b shows actual plots obtained using the aircraft of Figure 5 with the static pressure stabilizer according fo an embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention provide a piurality of static port valves positionad on the fuselage of an aircraft so that an average pressure is measured for improving the accuracy during specific flight maneuvers. The static port valves advantageously assist in collecting localized static pressure at respective positions on the fuselage while minimizing errors. The output of the static port valves are connected to a static pressure stabilizer, which accumulates all the iocal static pressure. Any differential pressure reading will be balanced within an enclosed space of the static stabilizer to channel the average pressure to a stafic pressure sensor located on the FCC board through a flexible tube

Embodiments of the present invention provide a system for measuring static pressure in an aircraft independent of airspeed, aircraft weight, acceleration, angle of attack (AoA), rotor downwash or heading direction.

Embodiments of the present invention minimize position errors by eliminating fixed errors ie. calibrating each individual mode! noting that all identical models of an aircraft will have the same calibration factor.

Embodiments of the present invention provide a system for measuring stafic pressure that can minimize position errors by eliminating variable errors to a tolerable value by introducing static port vaives and a pressure stabilizer to the existing static pressure sensor.

Embodiments of the present invention provide a system for measuring static pressure that can be deployed in both fixed-wing aircrafts and helicopters.

Embodiments of the present invention provide a system for measuring static pressure that has the fiexibility to be adapted to a fuselage of any profile. 135

Embodiments of the present invention provide a system for measuring static pressure that can be integrated into any preferred location on the aircraft.

Embodiments of the present invention provide a system for measuring static pressure that is adaptable to any static pressure sensor

Figure 6 is a perspective view of the FanTail VTOL UAV of Figure 5 including a static pressure stabilizer system 700 (refer Figure 7b) in accordance with an embodiment of the present invention.

The static pressure stabilizer system 700 is integra! with the circular shroud 503 and is mounted co-axially to the middie section of the upper fuselage 501. The static pressure stabilizer system 700 is integrated to the payioad adaptor 605. The payioad adaptor 605 has a plurality of through-holes for receiving a respective static port valve 601 or pitot 603.

Figure 7a is a perspective view of the static pressure stabilizer system of Figure 7b integrated into the FCC module 600 located at the middie section of the upper fuselage 501 showing static port valves 601, and a pressure reservoir 701. The static port valves 801 are connecied to the pressure reservoir by flexibie tubes 703.

The pressure reservoir 701 is cylindrical in shape and consists of four inlet ports 705 that are mounted radially and at equal distance on the surface of the cylindrical wall 707. Each inlet port 705 is adapted to receive one end of a respective flexible tube 703. The other end of each flexible tube 703 is connected to a respective static port vaive 801 so that the static port vaive 801 and the pressure reservoir 701 are in fluid communication. The pressure reservoir 701 in the embodiment has four static port valves 601. An adaptor bar 750, partly seen below the pressure reservoir 701, and pillars 7680 are used to mount the pressure reservoir 701 to the FCC board 407.

Figure 7b is a perspective view of a complete static pressure stabilizing system 700 comprising four sets of static port valves 601, flexible silicon tubes 703 connected to a pressure reservoir 701 that is rigidly mounted onto an adaptor bar 750,

Figure 8 is a top view of the stafic pressure stabilizer assembly 800 of Figure 7 clearly showing four flexible tubes 703 at an angle of 80° and connecting a respective inlet port 701 and static port valve 601. Also seen are the dynamic pressure sensor 401 and stafic pressure sensor 403 on the FCC board 407. One end of a flexible tube B01 connects an inner end of the pitot 803 (not shown) while ihe other end terminates above the dynamic pressure sensor 403. Similarly, one end of a flexible tube 730 connects the output of the pressure reservoir 701 (not shown) while the other end terminates above the static pressure sensor 401.

The pressure reservoir 701 normalizes the static pressure from the static port valves

B01 by obtaining an average of pressure received from the static port valves 601.

The pressure reservoir 701 also acts as a buffering reservoir to prevent sudden changes in pressure caused by abrupt movements of an aircraft,

The flexible tubes 703 enable adaption of the static pressure stabilizer system 700 to any fuselage. The pressure reservoir 701 need not be positioned at the center of the payload adaptor 605. Rather, the pressure reservoir 701 can be located away from

10 oo the center of the payload adaptor 805 or anywhere in the fuselage 503 and the length of the flexible tubes 703, 730, 801 can be appropriately altered.

The pressure reservoir 701 may not be limited to only four static port valves 601.

Accuracy of static pressure readings can be increased by creasing the number of static port valves 801. Accordingly, suitable holes are drilled at desired positions on the payload adaptor 805 to allow adaption of the static port valves 601.

The static port valve 801 is generally made of a material that is fight-weighted and having chemical resistance e,g, deirin or aluminium. The fiexible tubes, 703, 730, -801 may be made of soft silicon. The pressure reservoir 701 is made of delrin. : Figure 8a is an exploded perspective view of a static port vaive 601 in accordance with an embodiment of the present invention. The static port valve 601 can help in eliminating errors that are induced by movements of an aircraft and rotor downwash.

The static port valve 601 consists of a valve cap 901 and a receptacie 909. The cap 901 is in form of a rivet comprising a buttor-shaped head 802 and a cylindrical shaft 804. The inner surfaces of the cap head 902 and the shaft 904 have three channels

B03 at an angie of 120° These channeis 903 act as pressure inlet ports. The receptacie 80% has an annular nead 911 and a truncated conical base 907 The head 911 and base 807 are connected by two recessed portions 806, 808. The conical base 907 helps in sasy insertion of the fiexibie tubes 702. Furthermore the base 807 has a 80° undercut for gripping the flexible tubes 703. The head 911 of the receptacle 909 has sharp inner and outer edges. Similarly, the head 902 of the cap 801 has sharp edges.

Figure 9b is a perspective view of the components of the static port vaive 901 revealing the inner areas of the cap 901 and the receptacle 909, A through-hole 913 is seen af the center of the receptacie 909. This through-hole 913 has receives the shaft 904 of the cap 901. The receptacle 909 and the cap 901 are so designed that upon assembly a fiat surface of the head 902 of cap 901 is fiush with an outer surface of the head 911.

; Figure 9c is another perspective view the receptacle 909 with the cap 901 inserted into the head 811 clearly showing the conical base 807. the actuator 804 and the head 911.

Figure 10a is a perspective view of a pressure reservoir assembly 1000 in accordance with an embodiment of the present invention. The pressure reservoir assembly 1000 consists of an accumulator valve 1001, a fastener 1003, an adaptor bar 750 and a pressure reservoir 701.

The accumulator vaive 1001 neips in delivering normalized static pressure from each of the static port valves 601 to the static pressure sensor 403. The pressure reservoir 701 and the adaptor bar 750 are fastened with the fastener 1003 e.g. a nut.

The adaptor bar 750 is used for positioning the pressure reservoir 701 to the pressure sensor system on the FCC board 407, The elongate adaptor bar 750 has a pair of through-holes 1015, 1017 on either side for mounting the pressure stabilizer 1000 on the FCC board 407. The adaptor bar 750 has another through-hole 1013 (refer figure 10b) at the center for receiving the accumulator vaive 1004.

When assembled, the pressure reservoir 701 forms an enclosed space with a controlled environment. The pressure reservoir 701 has a cylindrical wall 707, a flat base 1008 and an annular cap 1007. The base 1008 has a through-hole 1018 (refer

Figure 10b) for receiving the accumulator valve 1001. The outer surface of the cap 1007 is fiat while the inner surface has an annular ring 1010. The annular ring 1610 has screw thread on its outer surface for mating with a corresponding screw thread found on the inner surface 1103 of the base 1008.

The pressure reservoir 701 consists of four inlet ports 705 that are mounted radially and at equal distance on the outer surface of the cylindrical wall 707. The inlet port 705 has a rectanguiar base 1011 and a truncated conical head 1009. The base 101 and the head 1009 are connected by a recessed portion 1012. The conical head

1000 aids in easy insertion of the respective flexible tube 703. Furthermore, the ‘head 1009 has a 80° undercut 1014 for gripping the fiexibie tube 703. igure 10b is an exploded perspective view of the pressure stabilizer 1000 of Figure 10a showing the cap 1007 and the accumulator vaive 100+. The outer surface of the base 1008 of the pressure reservoir 7071 has an oval-shaped embess 1020, around the through-hole 1018, for co-operating with a corresponding oval-shaped recessed portion 1101 (refer Figure 11) surrounding the through-hote 1013 of the adaptor bar 750. The thickness of the adaptor bar 750 is the same or more than the height of the recessed portion 1101.

Figure 11 is an exploded perspective view of the pressure reservoir 7071 and adaptor bar 750 of Figures 10a and 10b. The pressure reservoir 701 is shown without the cap 1007 revealing screw threads on the inner surface 1103 of the pressure reservoir 701 for receiving the cap 1007. Through-holes 1105 connect the pressure reservoir 701 and the static ports 801. Through-iole 1019 is for receiving the accumuiator vaive 1001. An oval-shaped recess 1101 surrounding the through-hole -1013 aids in receiving and holding the oval-shaped emboss 1020.

The emboss 1020 protruding from the base 1008 of the pressure reservoir 701. in conjunction with the adaptor bar 750, helps in aligning and locking the pressure reservoir 701 to the pressure sensor system of the FCC board 407.

Altematively, the stabilizer 600 can be directly mounted to the pressure sensor system of the FCC board 407, without the adaptor bar 750. in case of direct mounting, an undercut of appropriate size can be made fo mate with another part of the FCC board 407.

Figure 12a is a perspective view of the pressure reservoir 701 of Figure 11 with the accumulator valve 1001 installed into the through-nole 1018.

Figure 12b is a sectional view of the pressure reservoir 701 of Figure 12a, in a direction 1200 with the accumulator valve 1001 and the cap 1007 installed into their respective positions. in the embodiment, the base 1011 of the inlet port 705 and the head 1008 are shown as discrete parts. The base 1011 has internal screw-threads 1212 at its center. A recessed portion 1012 adjacent to the head 1009 also has screw-thread on its outer surface io enable installation of the head 1009 io its respective base 1011.

Each of the inlet port 705 has through-holes 1201 for connecting the pressure reservoir 701 with respective static port valve 801.

The accumulator valve 1001 is in the form of a holiow-bott having a through-hole 1203. The accumulator valve 1001 consists of a head 1213 and a hollow shat.

Adjacent to the head 1213, the shaft has a threaded portion 1030, a recessed portion 1207 and a truncated conical base 1209. The base 1208 aids in easy insertion of the flexible tube 730 that terminates above the static pressure sensor 403. in order to assemble the static pressure stabilizer 700. the static port valves 801 are inserted into respective through-holes on the payload adaptor 805. One end of a flexible tube B01 is inserted and positioned to the output of the pitot 603.

Meanwhile, the accumulator vaive 1001 is inserted and positioned into the through- hole 1019 of the pressure reservoir 701 and the cap 1007 is fitted onto the prassure reservoir 701 fo form an enclosed space. The conical head 1008 is inseried and positioned into the respective base 1011 of the inlet port 705. The adaptor bar 750 is fitted to the pressure reservoir 701 such that the embossing 1020 of the base 1008 mates with the recessed portion 1101 on the adaptor bar 750. A fastener 1003 jocks the adaptor bar 750 and the pressure reservoir 707

One end of each of the flexible tubes 703 is inserted and positioned on the respective head 1008. Similarly, one end of the flexible tubes 730 is inserted and positioned on the accumulator vaive 1001.

The assembly of the pressure reservoir 701 and the adaptor bar 750 with the fiexibie tubes 703, 730 is positioned and fastened to the FCC board 407.

The other end of each flexible tube 703 is inseried and positioned fo the respective neads 207 of the static port valve 601.

The other end of the flexible tube 730 is bent and positioned above the static pressure senor 403 of the FCC board 407. Likewise, the other end of ihe flexbie tube B01 is bent and positioned above the dynamic pressure senor 403 of the FCC board 407.

Figure 13 is a front view of Figure 7 fo illustrate the flow of free-stream when an aircraft moves vertically i.e. in a direction 1301. As the aircraft moves in the direction 13 of 1301, an induced free-stream 1303 flows around the skirting of the static port vaive 801 instead of ingesting into the static port valve 801. If the aircraft moves downwards, the induced free-stream 1303 fiows in the opposite direction. This helps in achieving accurate static pressure measurements during upward and downward movement of the aircraft.

Figure 14 is a front view of Figure 7 to illustrate the flow of free-stream when an aircraft moves horizontally Le. in a direction 1401. As the aircraft moves in the direction of 1401, an induced free-stream 1403 flows around the skirting of the static port vaives 801 instead of ingesting into the static port valve 801. This helps In achieving accurate static pressure measurements during horizontal movement of the aircraft,

Figure 15 is a partial cross-sectional view of the static port valve 601 mounted on the pay-ioad adaptor 605 to illustrate the flow of free-stream 1503 in a direction 1501. As the free-stream 1503 flows past the head 911 of the static port valve 601, most of it flows around the skirting of the static port valves 601. A portion of the free-stream 1503 e.g. at an entry position 1505, may flow over the fiat surface of the actuator 901 of the static port vaive 601. Under normal circumstances, the pressure above entry position 1505 of static port valve 601 will reduce, causing a vacuum effect over the cap opening, thus introducing error into the system. tn order to prevent this phenomenon, the inner and outer edges of the receptacle head 911 and the cap 801 have sharp edges to retard flow of free-stream over the static port valve opening.

The sharp edges induce a separating flow of free-stream at the entry position 1505.

This helps in minimizing the errors induced by the fast moving free stream over the entry position of the static port valves. :

When the static port 801 is subjected to rotor downwash, a simiiar phenomenon as explained in Figure 15 will be encountered. The sharp edges of the head 911 and anchor 801 can assist in inducing a separating flow of free-stream at the entry position 1505 of the static port valve 801 whereby accurate static pressure measurements are possible during rotor downwash.

Figure 16 is a cross-sectional view of the static port valve of Figure 15 to Hiustrate the effect of frontal pressure on the static port valve 801. Often, a static port valve 601 may be subjected to direct frontal free-stream 1601 whereby the valve cap 901 may compietely block the through-hole 913 causing positional error. To minimize such errors, the inner surfaces of the cap head 802 and the shaft 904 have three channels 903 that are at an angle of 120°. Since the free-stream 1603 bends twice at 80° before reaching the flexible tube 703, the pressure build-up because of orientation of the free-stream can be reduced thereby increasing the accuracy of static pressure measurements. This deficiency is further compensated by pressure obtained at the remaining static port vaives which is not subjected to the frontal pressure buiidup.

Figure 17a shows the actual plots obtained without the static pressure stabilizer 700.

The data was coliected at 0.6m altitude as indicated by the chart 1701. Depending on the rotation speed (RPM) of the rotor of the engine (as per chart 1703), the propelier downwash or suction aiso varies (as per chart 1705). As seen in the plot, an errar in the heignt (between 15m to 22.5m) was recorded. This demonstrates the negative impact of propeller downwash 510 on a conventional static pressure sensor

Figure 17b shows the actual plots obtained with the static pressure stabilizer 700 of the present invention. The data was again conducted at 0.6m aliftude as indicated by the chart 1707. For various rotation speeds (RPM) of the rotor (as per chart 1708), the rotor downwash or suction was measured (as per chart 1711). it can be clearly seen that the error in static pressure is reduced sharply within a resolution of +-im. This can be a breakthrough in measuring static pressure under adverse conditions. Accurate measurement of data can assist in deciding the appropriate location of the static ports on the fuselage.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made fo the present invention as shown in the specific embodiments without departing from the scope of the invention as broadly described. The present embodiments are, therefore, to be considerad in all respects to be iustrative and not restrictive.

For instance, the static pressure stabilizer 700 can comprise components that are integrally made. The pressure reservoir 701 comprising, the base 1008, the wall 70, the cap 1007 and the inlet ports can be integrally made. The payicad adaptor 605 can be tailored 10 match the shape of the fuselage.

The number of the static port valves 801 can be altered with appropriate provisions made on the payload adaptor 805 for insertion of the static port valve 801.

The number of the channels 803 can be more than three.

Claims (1)

17 oo CLAIMS

1. A system for measuring static pressure of an aircraft comprising: - a plurality of static ports mounted on the fuselage of the aircraft, wherein outputs of each of the static ports are connected to a pressure stabilizer, and the pressure stabilizer is operable to provide average pressures from the plurality of the stafic ports to a staiic pressure sensor located on a fight control computer (FCC) board of the aircraft.

2. The system according to claim 1, wherein each of the static port comprises a static port vaive comprising: a receptacie operable {0 be inserted into a through-hoie of payload adaptor; and a valve cap co-operable with the receptacle, wherein the valve cap is operable to regulate stafic pressure entering info the stabilizer.

3. The system of claim 2, wherein the receptacle comprises a cylindrical head and a base, the base comprising a through-hole along its length, wherein the base is operabie to be inserted into a through-hole of the payload adaptor, 4, The system according to claim 2 or 3, wherein the receptacle has a through- hole and comprises an annular head with sharp edges, and a truncated conical base connected by recessed portions, wherein the annular head is operable to receive the valve cap.

B. The system according to claims 2, 3 or 4, wherein the conical base has a 90° undercut for gripping a flexible tube, wherein the flexible tube connects the output of the static port valve to the input of the stabiiizer.

8. The system according to any one of claims 2 to 5, wherein the valve cap comprises a substantially fiat head with substantially sharp edges and a cyiindrical shaft, wherein the receptacie is operable to receive the shaft of the valve cap.

7. The system according to any one of claims 2 to 6, wherein the inner surface of the vaive cap head and the shaft have a plurality of channels that lack material, wherein said channels are operable to control the static pressure input. 8 The system according to claim 7, wherein the channels are spaced at 120°,

9. The system according fo any one of claims 2 to 8 wherein the pressure stabilizer comprises: a pressure reservoir for receiving static pressure from the plurality of static port vaive; and an accumulator valve positioned at the base pressure reservoir for directing the average static pressure output to the static pressures sensor located on the FCC.

10. The system according to claim 8, wherain the pressure ressrvoir has a cylindrical wall, a base and an annular cap, the inner surface of the cyviindrical wall and the outer surface of the cap having screw-threads whereby a enciosed space is formed when the cap is fitted onto the pressure reservoir,

11. The system according to claim 10, wherein the pressure reservoir comprises a plurality of niet ports communicating with a corresponding static port valve, wherein the inlet ports are mounted radially and at equal distance on the outer surface of the wall.

12. The system according to claim 11, wherein the inlet port comprises a base and an arm, the arm comprising a truncated conical head connected by a recessed poriion, wherein the head nas a 80° undercut for receiving and gripping a flexible tube connecting a respective static port valve,

13. The system according fo claim 12, wherein the base of the inlet port head comprises internal screw-thread for receiving corresponding screw-thread on the recessed portion of the arm.

14. The system according to any one of claims 9 to 13, wherein the base of the pressure reservoir has a through-hole for receiving the accumulator vaive. 15 The sysiem according to ciaim any one of claims S to 14, wherein the accumulator vaive has a through-hole along its length, the accumulator valve comprising: an annular head; and a hollow shaft, wherein adjacent to the head the shaft has a threaded portion, a recessed portion, and a truncated conical base for inserting a flexible tube, the flexible tube terminating above the static pressure sensor on the FCC board.

16. The system according to claim any one of claims © to 15, further comprising: an adaptor bar for positioning the pressure stabilizer to the FCC: and a fastener for locking the assembly of pressure reservoir, the accumuiator valve and the adaptor bar.

17. The system according to claim 18, wherein the adaptor bar comprises: a through-hole on either side for mounting the pressure stabilizer to the FCC board, a through-hole at the cenier for receiving the pressure reservoir and the accumulator valve. 18 The system according to claim 16 or 17, wherein the adapier bar has a recessed portion for co-operating with an oval shaped emboss on the outer surface of the base of the pressure reservoir.

18. The system according to any one of the preceding claims, wherein the aircraft is an unmanned aerial vehicie (UAV).

20. The system according fo any one of the preceding claims, wherein the aircraft is capable of vertical take-off and ianding (VTOL).

21. The system according fc any one of the preceding claims, wherein the aircraft is a FanTail VTOL UAV.

22. The system according fo any one of the preceding claims, whersin the pavyioad adaptor is integral to the fuselage.

23. A method for measuring static pressure of an aircraft comprising: mounting a plurality of static ports on the fuseiage of the aircraft, connecting the outputs of each of the static ports to a pressure stabilizer, providing average pressure from the plurality of the static poris fo a static pressure sensor located on a flight control computer (FCC) board of the aircraft,