GB2418739A

GB2418739A - Pressure testing apparatus

Info

Publication number: GB2418739A
Application number: GB0426750A
Authority: GB
Inventors: John Talbot
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-09-21
Filing date: 2004-12-07
Publication date: 2006-04-05
Also published as: GB0420913D0; GB0426750D0

Abstract

The present invention relates to a pitot-static system on an aircraft, which is used as the basis for measuring airspeed and altitude. The present invention provides an apparatus for unblocking the lines 6,12 comprising a means 22,24 to introduce a pressurised fluid flow into the line and a means for determining, from the resultant pressure, whether or not a blockage is present. Furthermore, there is also provided a means for introducing a pressurised fluid flow into the line thereby ejecting the blockage.

Description

24 1 8739 Pressure Testing Apparatus The present invention relates to the

system by which the air pressure on an aircraft alters with speed and altitude.

All aircraft ranging from small Cessnas to airliners and military aircraft have a pilot-static system as the basis for measuring airspeed and altitude information. This is important information when flying visually (VFR) for safe take off and landing, and even more critical when flying in non-visual instrument conditions (IFR).

There have been numerous cases of fatal crashes and near misses due to failure of the pitot static system. The system basically comprises two sets of simple pipework leading from the outside of the aircraft to the aircraft's instruments, or sensors acting within a computerised flight system. The first set of pipework is that for the pilot system, which is comprises a pilot head orientated such that it is exposed to the full force of the airflow attacking the aircraft from ahead. The air pressure being rammed into this tube is measured. The second set of pipework comprises a static head orientated such that the air pressure outside the aircraft is measured, excluding the increased force due to the speed of the arcrafl. This is called the static system.

The readings from the pitot and static system are compared to provide the air speed. The static system also enables measurement of the vertical speed and the altitude. However, should either system fail then the reading on the pilot's instrument panel will be incorrect, with potentially disastrous consequences. The effect of a blocked pilot tube is that the airspeed indicator acts like an altimeter, creating the illusion that the aircraft has a greater speed on ascent than it actually has, causing the autopilot/pilot to wrongly slow the plane resulting in a potential stall or spin. If the aircraft is descending, then an illusion of less speed is created, causing the autopilot/pilot to wrongly speed the plane up resulting in excessive landing speed.

Alternatively, if the static system is blocked, this provides a constant altimeter and vertical speed reading whether the aircraft is ascending or descending, causing the potential of the aircraft flying into terrain etc. On ascent, the air speed indicator reads low, and the pilot may therefore try to speed the plane up, resulting in a danger of the pilot aborting take off or exceeding the aircraft's structural limits. On descent, the air speed indicator reads high, and therefore the autopilot/pilot wrongly tries to slow the plane potentially resulting in a stall or spin.

A blockage in either system is most dangerous in an IFR situation with an autopilot or computer flight system, which attempts to maintain the speed set by the pilot, and therefore accelerates or decelerates to apparently correct the error. This can creep up on the aircraft leading suddenly to critical incidents. Even in VFR it is still dangerous, as the pilot may not recognise the failure of equipment and try and land at excessive speed, or may stall or spin. Experienced and vigilant pilots without an autopilot system are more likely to recognise the problems, however those of more complex aircraft with autopilots and computer flight systems are prone to confusion and cognitive overload when the situation becomes critical and complacency in the build up to the critical incident.

For example, investigators of a Peruvian plane crash found that duct tape covering crucial sensors resulted in the pilot believing his flight computer system had failed, such that air speed and altitude could not be determined. Cockpit voice recorders highlighted prolonged confusion and consternation in the Air Peru disaster and a relaxed interest in the "superior" climb performance of the aircraft in the Bergen Air disaster as its airspeed fatally decayed.

There are currently no fail safe tests or ongoing monitoring of the pilot or static systems, or even pre-ilight tests for failure of this vital and technologically simple but vulnerable piece of equipment. The only preflight check is the inspection of the heads for obvious blockages, and this is prone to human error. This also is of no use if the fault occurs in flight, by a blockage caused by, for example, insects or the icing of the pipes. A heater is often provided to melt the ice forming, but this has little effect if the blockage is not caused by icing. Further blockages could be caused by failure of the heater allowing icing, the heater may not be switched on, the pilot cover is left on, water as condensation is blocking the tubes, or the static vents are taped.

The present invention aims to address the issues associated with the function of the pitot- static system actively, and may be set up to monitor it and to clear any blocked heads from any cause even if the head heaters have failed.

s According to a first aspect of the present invention, there is provided an apparatus for testing for blockages in a line, wherein said line defines a fluid now channel, the apparatus comprising means to introduce a pressurised fluid flow into said line and a means for determining from the resultant pressure within the line whether or not a blockage is present.

The apparatus preferably includes means to introduce an increased pressurised fluid flow into said line for ejecting blockages from said line.

According to a second aspect of the present invention, there is provided an apparatus for ejecting a blockage from within a line, wherein said line defines a fluid flow channel, the apparatus comprising means for introducing a pressurized fluid flow into said line thereby ejecting said blockage from said line.

The apparatus preferably comprises two lines. The lines preferably correspond to the pitot and static pressure lines of a vehicle. The vehicle is most commonly an aircraft, in which the pressure resulting in pitot and static lines are measured such that the aeroplane speed and altitude are determined.

Beneficially, there are means to block the pressurised fluid now provided in either or both 2s of the static or pitot lines, preferably located adjacent the vehicle's instruments. The means to block the pressurised fluid are preferably valves, and may be selectively controllable by computerized means. Alternatively, the valves may be actuated automatically by a computerized means in response to a predetermined threshold pressure. The valves may also be manually aetuable. The valves provide the benefit that they may be selectively opened and closed such that a pressurised fluid may flow through the lines without damaging the vehicle instruments.

The means for determining a blockage from the resultant pressure preferably comprises a pressure sensor. Alternatively, the air speed indicator, altimeter and vertical speed' indicator may be arranged to determine the pressure.

The means to provide a pressurized fluid flow through either pilot line or static line may be independcrtly selected. The fluid flow is preferably a pressurised gas. The means to provide a pressuriscd fluid flow is preferably a pneumatic pressurised gas system.

Alternatively, the means to provide a pressurized fluid flow may be a manual arrangement.

lo The pressure of the gas supply is preferably controllable. Beneficially, an initial burst of low pressure gas is applied to the pilot and/or static lines by the pressurised gas system. If a blockage is detected by the pressure sensors, a burst of higher pressure gas is preferably forced through the required line such that the blockage is ejected. The most likely place for the occurrence of blockages would be in the external orifices of a system, although this is not strictly always the case.

There is preferably provided a further back up valve, positioned within a line between the valve and the vehicle instruments. Pressure detennining means are preferably provided between the valve and the back up valves. 2'

It is also possible that insects may block one or more lines. These may generally be ejected from the system as previously described. However, it is possible that insects may travel up the line between the vehicle instruments and the means to block pressurised fluid flow.

Therefore, there is preferably provided a filter means, said filter means arranged and configured with suitable size apertures to prevent the passing there through of insects. The filter is preferably located between the pressure sensor and the valve.

There may be further provided a vent for release of blockages. The vent is preferably located in the line between the external orifice of said line and said pressure determining means. The bore of the vent aperture is preferably greater than the bore of the external orifice of the line. The vent enables large insects or insect infestation to be ejected easily and quickly.

Beneficially, there is further provided a means to block said line such that said line may be tested for leaks.

According to a further aspect of the present invention, there is provided a method of testing for blockages in a line wherein said line defines a fluid flow channel, comprising the steps of introducing a pressurised fluid Cow into said line and determining from the resultant pressure within the line whether or not a blockage is present.

According to a further aspect of the present invention, there is provided a method of lo ejecting a blockage from a line wherein said line defines a fluid flow channel, comprising the introduction of a pressurised Buid flow into said line thereby ejecting said blockage from said line.

It will be appreciated that the term "valve" may incorporate any type of gate wherein a fluid flow may be opened or closed to a predetermined degree.

The present invention is now described by way of example only with reference to the accompanying drawings, in which: Figure l is a schematic representation of a standard prior art arrangement of a pilot-static system.

Figure 2 is a schematic diagram of a preferred exemplary embodiment of the present invention.

Figure 3 is a schematic diagram of a failsafe mechanism against failure of the instrument protection valves.

Figure 4 is a schematic diagram of an exemplary embodiment of the present invention for a small aircraft.

Figure 5 is a schematic diagram of an additional testing mechanism for leakage from a line.

The present invention provides an improvement in respect of a standard pilot-static system described in the art. Referring to Figure l, this usually comprises a pitot head 2 which may be optionally heated by any suitable means 4, and a tube 6 running to the air speed indicator (ASI) 8 in the pilot's instrument panel. The pitot head is orientated directly into the full force of the air flow attacking the aircraft from ahead, indicated by the arrows. A static vent 10, again optionally heated 4, measures the outside pressure away from the pressure of forward motion, and is connected to or integral with a further tube 12 which is then connected to the pilot's instrument panel. There may be further features such as an alternate static source l 4, and/or auxiliary pitot and static lines, however, like the heaters, lo are optional and are not an absolute requirement to the basic functioning of a pilot/static system. The ASI is commonly linked to the altimeter 16 and the vertical speed indicator 18 via the static system. The ambient air pressure is received through the static vent 10, and is linked to the ASI 8, altimeter 16 and vertical speed indicator 18. The air speed is calculated by subtracting the static line measurement from the pitot measurement.

Figure 2 shows a preferred exemplary embodiment of the present invention, with the addition of the safety feature of the apparatus to check that the pitot 6 and static lines 12 arc clear, and i f they are not, to force gas through them to unblock the disruption. A compressed gas source 22 has lines 24 linked to the pitot 6 and static 12 lines as close to the instruments as practicable, at least well away from the pitot static external orifices. The compressed gas may be air, or alternatively, in vehicles other than aircraft the embodiment may be a liquid such as water. Valves 26 may be provided at the intersection between the compressed gas lines 24 and the pitot 6 and static 12 lines, or alternatively are positioned at any point within the gas lines 24 as shown in Figure 2. The valves 26 may be controllable by hand, or alternatively may be computer controlled, for example via the pilot's control panel. This enables each of the pitot 6 and static 12 lines to be selected for testing and/or clearing independently. It is envisaged that one valve could be placed in the gas line 24 before it separates into independent lines, however, although simplifying the arrangement, the flexibility of being able to independently select the desired line is compromised.

Valves 28 are provided in the pitot 6 and static lines 12 to block a pressurised fluid flow.

In use, the static line 12 and pitot line 6 are tested for blockages or malfunction by applying a known low pressure gas through the lines, from the source 22. It will be appreciated that the gas source 22 may also be powered by such means as a simple hand powered pump or a complex aircraft's existing pneumatic system. If one or more of the flight instruments is s designed and specified to be a blockage determining means, the valves 28 are retained in the open position such that the output devices 8 and/or 16 and/or 18 receive the known value of pressure increase, and provided there is no blockage in the system, then there would be little or no increased pressure reading on the output devices 8, 16 and 18.

Alternatively, the valves 28 may be configured such that they are open until receiving a lo threshold force associated with a high pressure gas injection, at which time they automatically close. However, in a preferred embodiment, if there is a blockage within the tube, then the pressure would exceed that expected, and once detected, the valves 28 would be closed to protect the night instruments, and a high pressure gas injected into the lines to blast out any obstruction through the pilot head 2 and the static vent 10 and/or any other vent. The compressed gas can therefore be applied in a low-pressure test setting and a high pressure blockage removal setting. Even more preferably, the pressure is read on a further pressure sensor 25 provided in the lines between the compressed gas source 22 and the valves 28. The sensors are linked to the in flight computer. This removes the requirement that the instruments are susceptible to receiving the low test pressure. This would enable the valves 28 to be closed in both the low pressure testing configuration and the high pressure blockage removal configuration, thereby further protecting the instruments. In the case of a check, the pressure in the system, read on pressure sensor 25, rapidly decays to zero i f there is no blockage present. However, i f the pressure on the sensor 25 remains higher than expected, then there is a blockage and the lines should be cleared. 2s

Both the flow of compressed gas in the low pressure test and high pressure blockage removal is applied by a pulse or more than one pulse.

Such that the output devices such as the AST are not damaged by actuation of the high pressure gas, instrument protection valves 28 are automatically shut in the line to be cleared. This automatically protects the instrumentation when the lines are cleared without the requirement that a setting is adjusted.

ln case of the valves 28 failing in a shut position, and provided the instruments are not themselves being used as the blockage determining means (rather the pressure sensors 25 performing the function), then a line 30 which bypasses the blocked valve 28 and which is not exposed to the pressurised fluid flow can provide a failsafe for the blocked valves 28.

s This line could be an existing or further additional line. This extra line would not, however, be a failsafe system for a blocked pilot/static line as would possibly fail in the same way as the first line through icing, for example.

As a failsafe mechanism, and referring additionally to Figure 3 of the drawings, for the lo instrument protection, should valves 28 fail in the open position, a further failsafe valve 32 is provided between the main instrument protection valve 28 and the instruments, in either or both of the pilot and static lines. This is not a failsafe for the pitot static system, rather a failsafe for valve failure. Positioned between the valves 28 and failsafe valves 32 is a pressure sensor 34, which operates to detect an increased pressure should the valve 28 have failed. If an increased pressure is recorded, then the valve 32 is automatically closed, thereby protecting the instruments. The valves 32 may also be arranged to close when the valves 28 are closed in preparation for an increased pressure gas to be injected to clear the system. if an increased pressure is recorded on the pressure sensor 34, then there is indicated a fault associated with the valve 28. A signal may then be sent to the aeroplane instrument panel to warn the pilot of the malfunction and a high pressure gas which could escape through failed valve 28 would be stopped from reaching the flight instruments by valve 32.

Figure 4 shows an exemplary embodiment of the present invention suitable for use in a small aircraft. The general operation is the same as that described above, however the system utilises a manual clearing arrangement, with a blood pressure type inflator 36 for the low pressure testing, and a pump means such as a high pressure manual pump 38 such as a bicycle pump which is capable of pulsing compressed air. The blockage determining means is, for example, a simple pressure gauge 40. A blockage would display a higher than expected pressure remaining steadily or being slow to decay. An unblocked system would display no or transient pressure rise rapidly decaying. A failsafe linkage (not shown) between the instrument protection valves 28 and the inlet valves 26 for the high pressure gas provides protection for the instruments by automatically closing the valves 28 when the high pressure gas is supplied to clear the lines.

It is a further feature of the present invention that insects or insect infestation may be removed from the system. In a further embodiment, there is provided a large bore vent located within a line near to the pilot or static orifice. In one embodiment, the line is routed to have a sharp angle, such as 90 , near to the orifiec. The vent may be located at the change in direction of the line. This vent would enable the expulsion of multiple or large insects. The vent may be manually or electronically opened when the system is 0 unblocked. The vent may, however, be positioned anywhere within the line between the valve 28 and the orifice 2,10. It is envisaged that the compressed gas inlet to the line is as close to the valves 28 as possible to ensure the maximum volume of line is cleared.

In order to prevent insects from passing through the valve 28 and entering the line between Is the valve 28 and instruments wherein no pressurised fluid how enters, there is provided a reticulated mesh filter of sufficiently small apertures to prevent the passing there through of insects, positioned adjacent the valve 28 in the line on the side susceptible to the increased pressure fluid flow.

A further additional feature of the present invention described with reference to Figure 5, is the provision of an internal leak detection means. This is enabled by the provision of a further valve 42 adjacent the orifice of a line. When a low pressure test is applied the valve is closed, and the pressure drop is recorded. If an immediate significant pressure drop is recorded, reducing substantially to zero, then the system may have a leak and should be checked. Once this test has been carried out, the valve (manually or automatically) is opened.

If the portion of line between the instrument protection valve 28 and instruments is to be tested, then the valve may be left open and the system tested at low pressure, providing the instruments arc enabled to withstand low pressures. Alternatively, an instrument safe low pressure test source (compressed gas) 44 is arranged to inject a gas into that segment ofthe system. A further pressure gauge 46 is enabled to indicate any associated pressure drop.

lt is envisaged that the system may be incorporated into the pneumatic system if already in use within an aeroplane to obviate the need for a further compressed gas source for the pilot/static system.

s The arrangement described above provides a distinct safety benefit, and removes the potential for blockages of any type to go unnoticed, if effected as part of the pre-flight checks. Regular in-flight checks can also be performed at pilot discretions or via flight computer checking systems. It also provides the advantage that if the pilot has reason to believe there may be an error with any readings within the output devices, then he can lo effect the clearing of the pilot static lines whilst in flight, ensuring that the system can continue to function correctly. This may be particularly relevant if, for example, the pilot head heater ceases to function and ice begins to form, if water as condensation forms, a pitot cover is left on or other obstruction occurs, then such problems can be resolved by blasting them away with the high pressure system.

It will be appreciated that the high pressure gas may be replaced by any suitable fluid for example. It will also be appreciated that this arrangement may be used for underwater vessels such as submarines or surface vessels using a pitot static system. It should also be appreciated that the present invention may be controlled manually or by computer systems.

Any variations or iterations of checking or warning routines could be integrated into the pneumatic and/or onboard computer systems of the aircraft. It is further understood that references to valves are exemplary only, and any suitable mechanism could be applied.

Flight instruments are also referred to in order in incorporate the arrangements wherein sensors are linked to the flight computer rather than being traditional mechanical instruments.

It is also envisaged, in the testing phase, that as an alternative to a compressed gas being applied to the lines and the resultant pressure being read on the pressure sensor 25, a negative pressure may be effected.

Embodiments of the present invention have been described by way of example only and it will be appreciated by a person skilled in the art that variations and modifications can be made in respect of the described embodiments without departing from the scope of the invention as defined in the appended claims.

Claims

Claims I. An apparatus for testing blockages in a line, wherein said line

defines a fluid flow s channel, the apparatus comprising means to introduce a pressurized fluid flow into a said line and a means for determining from the resultant pressure within the line whether or not a blockage is present.
2. An apparatus according to the Claim I for ejecting blockages from said line lo through the introduction of an increased pressure fluid flow.
3. An apparatus for ejecting a blockage from within a line, wherein said line defines a fluid flow channel, the apparatus comprising means for introducing a pressurised fluid flow into said line thereby ejecting said blockage from said line.
4. Apparatus according to any of Claims 1 to 3 comprising two lines corresponding to the pilot and static pressure lines of a vehicle.
5. Apparatus according to any preceding claim, further comprising means to block the pressurised fluid flow in either or both of the static or pilot lines, wherein said blocking means is located adjacent the vehicle instruments.
6. Apparatus according to Claim 5 wherein said means to block the pressurised fluid comprise at least one valve.
7. Apparatus according to Claim 6 wherein said valve is actuated automatically by a computerized means in response to a predetermined threshold pressure.
8. Apparatus according to Claim 6 wherein said valve is manually actuable.
9. Apparatus according to claim 1 wherein said means for determining a blockage from the resultant pressure is a pressure sensor.
10. Apparatus according to Claim 1 wherein said means for determining a blockage s from the resultant pressure comprises an air speed indicator, and/or an altimeter and/or a vertical speed indicator.
11. Apparatus according to Claim 1 wherein the means to provide a prcssuriscd fluid flow through either pilot line or static line may be independently selected.
12. Apparatus according to Claim 1 or 1 1 wherein said means to provide a pressurised fluid flow is a pneumatic pressurised gas system.
13. Apparatus according to Claim 1 or I 1 wherein said means to provide a pressuriscd fluid flow may be a manual arrangement.
14. Apparatus according to Claim 1 further comprising at least one backup pressurised fluid flow blocking means.
15. Apparatus according to Claim 14 further comprising pressure determining means located between the valve and said back up blocking means.
16. Apparatus according to any of claims 5-15 further comprising a filter means located in said line between said pressure determining means and said valve. 2s
17. Apparatus according to any preceding claim further comprising a valve located between the external orifice of said line and said pressure determining means.
18. Apparatus according to any preceding claim further comprising a means to block said line such that said line is able to be tested for leaks.
19. A method of testing blockages in a line wherein said line defiers a fluid flow channel, comprising the steps of introducing a pressurised fluid flow into said line and determining from the resultant pressure within the hne whether or not a blockage is present. s
20. A method of ejecting a blockage from a line wherein said line defines a Quid flow channel, comprising introduction of a pressurised fluid flow into said line thereby ejecting said blockage from said line.