Technology associated with Air Data Testers
D.Marchiori (DMA) have been associated with the design, development and manufacture of aircraft test instrumentation for over 70 years, from the early use of aircraft instruments mounted into a portable carrying case to enable confidence checks to be performed.
Today the DMA products are sophisticated instruments encompassing a wide range of engineering disciplines from sensor technology and digital compensation techniques to pneumatic control systems, compressor and vacuum pump design, computer interfacing for ATE systems and rugged packaging design.
For those having an interest in the technology associated with the Design and Development of air data test sets in use as Aircraft Ground Support Equipment, the following information will be of interest.
For any further detailed enquires please contact DMA and we will be happy to provide additional specific answers to your questions.
Air Data Test Sets
The Technology of Air Data Test Sets
The continuous improvement of aircraft installed Air Data Instruments instigated by the increase of world wide air traffic is also demanding air data test systems (ADTS) with increasing accuracy and operating functions.
To satisfy these present flightline air data instruments requirements all ADTS must provide the following features:
– Absolute accuracy of testing
– Availability of all necessary functions.
– Ease of use for the Operator
– Reducing testing time
Manufacturers of air data test systems must respond to these requirements. I would like to describe here how the D. Marchiori MPS2X, MPS3X and MPS4X ADTS series cover all of these aspects.
ABSOLUTE ACCURACY OF TESTING
To satisfy this requirement one of the most important and critical tasks is to select appropriate pressure sensors / transducers.
This is the fundamental need of the pressure measurement and must be accurate to satisfy the requirements of the RVSM, (reduced vertical separation minima) international regulations. This demands a stability suitable to ensure the declared measurement accuracy for a period of one year (or more) without any additional calibration, and independent of ambient conditions over the full specified range.
Our experience has shown that there are two ways to obtain this necessary precision:
The use of Vibrating Cylinder resonant transducers that are intrinsically accurate (probably the most accurate available at present), but gas density dependent.
The use of high quality silicon diaphragm piezo-resistive transducers with corrections for ambient conditions (mostly temperature) by individual characterization techniques to obtain the required accuracy.
Other solutions, such as other types of resonant transducers or quartz transducers can be used but in fact the characterization installed internally by the manufacturer of the transducer, may be the main problem.
We will now describe the specific method used by D.Marchiori in the 2 cases described above:
With the vibrating cylinder, to be independent from the gas density function of temperature and the humidity of air, the air is dehydrated before entering the transducer, and the temperature is constantly measured with a high resolution, multiple times per second, to correct any false readings and to additionally compensate for variations over time.
In this way the density is fully corrected, whereas on the contrary, the method of reading humidity to compensate this effect is considered by us as too imprecise to obtain sufficient accuracy during the pressure variations.
With the piezo-resistive transducers, if a high quality transducer is used, the main problem is then the individual characterization. D.Marchiori have developed a mathematical model to calculate the correction functions after tests in environmental chambers with algorithms designed to define the best possible data to achieve the necessary accuracy.
This modelling must be so written to achieve the minimum possible number of bits in accordance with the second law of thermodynamics, avoiding the situation where the functions calculated to improve the pressure readings actually create indeterminate results instead of more accuracy.
After exhaustive testing of many different transducers, mainly to have the highest quality level of long term stability, and discarding the analog techniques of compensation for temperature and linearity errors, D.Marchiori have achieved a linearity error less than 30 ppm fs, and similar long term stability.
Hysteresis (mechanical and thermal) is negligible, so the RVSM requirements are fully satisfied by all the ADTS instruments produced by D.Marchiori.
To achieve the full potential of the transducers there are another considerations.
The readings are corrected for temperature over a wide range as needed by the ambient operating range. But it is not possible to correct exactly for the gradient of temperature, in time and space, due to the fact that the power absorbed by the ADTS is transformed into heat generation. The best way to avoid the indeterminate variations caused by the dT/dt, dT/dx, dT/dy, dT/dz derivatives, is to reduce the power absorption. So the instrument design is concentrated on minimal heat being generated, and, consequently, it is possible to have additional features incorporated such as internal batteries without incurring large weight and dimension penalties.
CONTROL ACCURACY
All the D. Marchiori air data testers have a digital control based system.
Compared to the previous solutions, i.e. digital readout and analog control, the digital control provides best adaptability to the volume under control. That means: in presence of a leak on the system under test, the digital control will stabilize the reading depending on the leak itself (large leak, bad stabilization), avoiding the well-known problems of analog control which stabilizes the readings correctly by compensating for very large leaks; this will mislead the operator by giving the impression that the test is carried out correctly, while it is universally known that the presence of a large leak severely compromises the accuracy of the testing.
In addition, the digital control gives the capability of compensating the proportional control valves, which can show over time and usage, some shift, automatically without any mechanical adjustment.
Lastly, but by no means least, the digital control provides the capability of adding to the ADTS extra capabilities and more functions, by the simple expedient of loading new software into the instrument, for example during the annual calibration exercise.
All of the features mentioned permit the performance of the aircraft checking with very high accuracy, confidence and repeatability.
OPERATIONAL FLEXIBILITY AND EFFECTIVENESS
All ADTS series MPSXY can be easily controlled to perform all the functions
required to accomplish a calibration or a leak check of the Pitot/Static systems.
Due to the high readings rate (from 20 to 100 times per second depending on the different models) all the test functions to simulate the aircraft flying characteristics, are entered via the colour-arranged keypad on the ADTS, or on the Hand Held Remote Control Unit (HHRCU) in a simple and intuitive way. The test is simple and straightforward even for the first time user, since the air data required to accomplish all the functions are clearly shown either in English or Metric values.
The keyboards are colour-coded and arranged to allow easy and logical operation.
All indications and controls are located exactly where the operator expects them to be.
Commanded values can be entered either by digitizing directly the values or by increasing or decreasing the values of a fixed step using UP and DOWN arrows.
In addition the MPSXY ADTS also provide the additional, following features:
MACH Mode where the operator directly enters the target Mach Number.
EPR Mode to carry out engine EPR system tests.
TAS generation.
Up to 30 programmable different test profiles, each one with 26 different test points, can be stored and executed to provide automatic testing capability for a considerable time saving. This allows the full automatic testing of FAR 43 Appendix E ; it is possible to program the stabilization time, the reading time for the leak test as well as the waiting time before recording the readings.
Automatic or Semiautomatic Leak Test.
Centre-line Correction, to compensate for height difference between the ADTS and the UUT (or cockpit or flight deck height above ground).
Encoding Altimeter or Encoder Test with automatic check of all tests points sequence.
Automatic Test of Radio Altimeter for the complete EGPWS test
Self-contained Battery pack to allow up to 4 hours of full operation without external power.
ARINC 429 bus.
Full ADTS Control via an external PC.
ULTRA LOW SPEED Function to generate very low airspeed (5 to 200 kts) values.
Full Automatic Calibration by using a D.Marchiori PAMBX and a specific SW.
Rugged LCD with back lit display HHRCU, for one-person only operation.
Programmable safety limits to ensure safe aircraft testing.
Different type of remote control units, also with touch-screen colour display and USB flash disk to store the test results and examine directly with the remote unit or by an external PC.
With the MPSRE terminal it is also possible to store more and more test profiles with a large number of features like quantity of different instruments under test, tolerances for every profile step, leak test with programmable stabilization time, reading time, tolerances etc.
For special needs there is an ATEX remote control unit with touch screen colour display.
EASE OF OPERATION
The design of MPSXY has been particularly developed to ensure an easy and intuitive operation.
Training required for the operation of MPSXY is very limited; all the HW and SW protections will allow the first time user to operate safely and with confidence.
TESTING TIME
Length of time for testing is mainly determined by the airplane limitations, mainly the Altitude Rate of Change, which cannot be exceeded.
The ADTS can save time by stabilizing test altitudes and airspeed values in a very short time.
One very interesting feature is the Multiple Isolator, integrated in the ADTS box to enable up to four separate pitot/static outputs to be connected to the aircraft simultaneously. This provides the capability to switch between the aircraft pitot/static systems directly controlled by the Hand Held Remote Control Unit.
This feature makes leak checks very simple, detecting the exact location of system leaks for immediate rectification without wasting time to vent to ambient, disconnect and reconnect hoses to aircraft.
Otherwise the use of a dedicated external box to accomplish such function compromises the one-man operation capability and makes the hoses connections more difficult.
Additionally; the leaks can be controlled in separate modes:
classic mode, but with multiple isolator to find the particular line that is leaking.
static measure mode and pitot control mode or vice versa allows the leak check for the two lines simultaneously thus reducing further measurement time.
These described modes of leak testing have another advantage in addition to saving time, it is the test reliability, not comparable with multiple lines in parallel used in standard two connections (static and pitot) leak test, and without the mix measure/Ps – control/Pt and vice versa mode.
OTHER ADTS PRODUCTS
The improvements in aircraft instrumentation have resulted in the determination of the angle of attack readings through a special pitot tube with 3 or 4 different pressure measurement ports for data acquisition.
These are Ps, Pt, AoA and also 2nd AoA. To test these new types of pneumatic readings the ADTS needs 3 or 4 different pressures generated simultaneously, or it is necessary to use 2 different ADTS with the resultant extra cost and more complication.
D.Marchiori produces 3 types of ADTS, two different instruments with 3 independent pressure generators and one instrument with 4 pressures generators. All these instruments have all the capabilities previously described, such as battery, multiple isolator option, complete leak test, various different HHRCU, Bluetooth useful to control the ADTS from a PC or notebook, etc.
Another recently introduced product is the smallest ADTS available today: housed in a very small box (30 x 25 x 12 cm) and with a total weight of 4 (four) Kg there is a fully automatic ADTS , RVSM capable with colour touch screen display, and a host of features such as user programmed test profiles, UUT readings, automatic LEAK, different measure units, ultra low speed readings etc.
Pitot-Static Testing
Pitot-static Testing and the Role of the Probe Adaptors
As a designer and manufacturer of precision, high accuracy pitot-static test instrumentation, DMA – Aero are acutely aware of the significant role that the junction between the test equipment and the aircraft plays in ensuring a viable test system. The aircraft mounted pitot static probes for the sensing of the aerodynamic values of altitude, airspeed, rate of climb and other related parameters are the commonly used connection points for the ground support test instrumentation.
The design and construction of the pitot static test adaptors that can be installed onto the probes to enable the air data parameters generated by the air Data test Set (ADTS) to be faithfully transmitted to the flight-deck instruments calls for a full understanding of all the requirements to be considered.
Airframe mounted probes are basically designed to provide the best possible results for sensing the air data parameters. The pitot static probe adaptors that will be used to fit onto the probes must accept that the probe design is first and foremost for the aircraft and the adaptor must somehow contend with the vagaries that exist.
It is imperative that the pitot static tube adapters do not in any way damage the pitot-static system. The whole air data test system needs to be able to simulate the appropriate values of pressures and vacuums corresponding to the desired altitudes and airspeeds etc. The mounting of the pitot and static adaptors, and the relevant hoses forming the whole of the assembly onto the probes must not result in any damage to the aerodynamic contour or surface finish nor impose any undue stress loading that could potentially result in misalignment of the probe.
Additionally there needs to be certainty that the particular adaptor sealing method employed does not in any way result in material from the sealing media becoming loose and entering the probe causing blockages.
Since the tests called for on modern aircraft specify air data values to be of extremely high accuracy, for example to meet the requirements -”Reduced Vertical Separation Minima, (RVSM), there must be absolutely minimal leaks in the overall system. This includes all pitot static test connections and pneumatic fittings employed at the adaptor, the hoses to the air data test set (ADTS) and the ADTS panel mounted connectors. A leaking system would result in the observed value on the ADTS not being the received value at the aircraft, thereby negating all the precision so carefully engineered into the ADTS.
The types of probe or sensing point on the aircraft fuselage presents the pitot and static test adaptor designer with a challenge to enable the best result to be achieved to ensure a practical solution. Single pitot probes / tubes allow fairly straightforward sleeve style pitot test adaptor solutions to be used with minimal concerns regarding datum points for the fitting depth. However if the probe is a combined pitot and static variety then the pitot static test fittings must ensure that the static hole in the probe is exactly in line with the adaptor matching connection. Some form of mounting reference needs to be provided to ensure correct placement of the pitot static connectors.
Multi port pitot and static adaptor
This reference feature becomes particularly important if the probe is even more complex as in the instance where the probe also serves as an Angle of Attack (AoA) sensor. Where the traditional vane form of AoA measurement has been replaced by pneumatic sensing incorporated into the pitot static probe then there are multiple static ports in the probe to which the adaptor must interface.
Angle of Attack adaptor
Static measurement ports on the aircraft fuselage present another challenge for the connection point for the ADTS. Now the adaptor must be so designed that it surrounds the sensing hole in the flat plate of the sensing port. The method employed needs to be both practical and again cause no damage to the static plate, remembering not all aircraft provide mounting features.
The adaptor must include some sensible feature to achieve the desired result. Various methods are used, some more attractive than others. DMA-Aero utilise rubber suction cups to clamp the adaptor onto the plate surface, providing a vacuum source from the MPS range of air data test sets to ensure a firm fixing of the adaptor. Some systems employ the actual sensing hole as the fixing point but this risks damaging the contour of the static point.
Static adaptor for aircraft skin mounting
For commercial aircraft there are generally multiple probes fitted to allow independent systems for the Captain and the 1st Officer and also generally a Standby channel. In these situations the pitot static test kit manufacturer supplies complete kits that provide all the relevant air data test adaptor kit and the hoses and interconnecting pneumatic fittings for the whole aircraft since the testing of the various parameters is often carried out simultaneously, the ADTS supplying the necessary altitudes, airspeeds etc to all the systems.
The air data accessories kit must also include a static blanking adaptor and a pitot tube dummy adaptor blanking feature to allow the whole air data test adaptor kit to be itself leak tested before installation onto the aircraft.
Multi-port pitot-static adaptor kit
When such multi probe systems are being catered for then the overall air data accessories kit will be housed in suitable cases / boxes giving the Operator all the equipment needed. These Kits will have been so designed to match the needs of individual aircraft, not only to provide the correct adaptors but also to ensure the appropriate lengths of the hoses do stretch to the remotest aircraft measurement point, often resulting in very long hoses. The hoses selected will have been verified as being suitable for the flight-line environment being rugged and not adversely affected by exposure to fluids such as Skydrol hydraulic leakage that can be a problem in the flight-line working environment.
The complexity of these numerous hoses is alleviated by colour coding the different lines and by utilising self coloured material that is also transparent so that it additionally proves beneficial in that any contamination of the internal pitot-static lines can readily be seen. Using lightweight hose material helps enormously in the overall handling of the complete kit assembly and additionally reduces loading on the installed adaptors.
Since the Adaptors will most likely be in service for many years it is important that the sealing features of the design are capable of being replaced by the operator. Consequently the use, in the design, of readily available commercial “O” ring seals are adopted by DMA as a sure way of allowing ongoing straightforward replacement. The seals become damaged when not installed in a correct manner, and on occasions when the probe heaters are inadvertently turned on by error and the seals damaged as a result.
A very wide range of different Adaptors need to be available for the vast range of aircraft and DMA are constantly introducing new designs to meet new aircraft needs.
The Technology of Air Data Test Sets
The continuous improvement of aircraft installed Air Data Instruments instigated by the increase of world wide air traffic is also demanding air data test systems (ADTS) with increasing accuracy and operating functions.
To satisfy these present flightline air data instruments requirements all ADTS must provide the following features:
– Absolute accuracy of testing
– Availability of all necessary functions.
– Ease of use for the Operator
– Reducing testing time
Manufacturers of air data test systems must respond to these requirements. I would like to describe here how the D. Marchiori MPS2X, MPS3X and MPS4X ADTS series cover all of these aspects.
ABSOLUTE ACCURACY OF TESTING
To satisfy this requirement one of the most important and critical tasks is to select appropriate pressure sensors / transducers.
This is the fundamental need of the pressure measurement and must be accurate to satisfy the requirements of the RVSM, (reduced vertical separation minima) international regulations. This demands a stability suitable to ensure the declared measurement accuracy for a period of one year (or more) without any additional calibration, and independent of ambient conditions over the full specified range.
Our experience has shown that there are two ways to obtain this necessary precision:
The use of Vibrating Cylinder resonant transducers that are intrinsically accurate (probably the most accurate available at present), but gas density dependent.
The use of high quality silicon diaphragm piezo-resistive transducers with corrections for ambient conditions (mostly temperature) by individual characterization techniques to obtain the required accuracy.
Other solutions, such as other types of resonant transducers or quartz transducers can be used but in fact the characterization installed internally by the manufacturer of the transducer, may be the main problem.
We will now describe the specific method used by D.Marchiori in the 2 cases described above:
With the vibrating cylinder, to be independent from the gas density function of temperature and the humidity of air, the air is dehydrated before entering the transducer, and the temperature is constantly measured with a high resolution, multiple times per second, to correct any false readings and to additionally compensate for variations over time.
In this way the density is fully corrected, whereas on the contrary, the method of reading humidity to compensate this effect is considered by us as too imprecise to obtain sufficient accuracy during the pressure variations.
With the piezo-resistive transducers, if a high quality transducer is used, the main problem is then the individual characterization. D.Marchiori have developed a mathematical model to calculate the correction functions after tests in environmental chambers with algorithms designed to define the best possible data to achieve the necessary accuracy.
This modelling must be so written to achieve the minimum possible number of bits in accordance with the second law of thermodynamics, avoiding the situation where the functions calculated to improve the pressure readings actually create indeterminate results instead of more accuracy.
After exhaustive testing of many different transducers, mainly to have the highest quality level of long term stability, and discarding the analog techniques of compensation for temperature and linearity errors, D.Marchiori have achieved a linearity error less than 30 ppm fs, and similar long term stability.
Hysteresis (mechanical and thermal) is negligible, so the RVSM requirements are fully satisfied by all the ADTS instruments produced by D.Marchiori.
To achieve the full potential of the transducers there are another considerations.
The readings are corrected for temperature over a wide range as needed by the ambient operating range. But it is not possible to correct exactly for the gradient of temperature, in time and space, due to the fact that the power absorbed by the ADTS is transformed into heat generation. The best way to avoid the indeterminate variations caused by the dT/dt, dT/dx, dT/dy, dT/dz derivatives, is to reduce the power absorption. So the instrument design is concentrated on minimal heat being generated, and, consequently, it is possible to have additional features incorporated such as internal batteries without incurring large weight and dimension penalties.
CONTROL ACCURACY
All the D. Marchiori air data testers have a digital control based system.
Compared to the previous solutions, i.e. digital readout and analog control, the digital control provides best adaptability to the volume under control. That means: in presence of a leak on the system under test, the digital control will stabilize the reading depending on the leak itself (large leak, bad stabilization), avoiding the well-known problems of analog control which stabilizes the readings correctly by compensating for very large leaks; this will mislead the operator by giving the impression that the test is carried out correctly, while it is universally known that the presence of a large leak severely compromises the accuracy of the testing.
In addition, the digital control gives the capability of compensating the proportional control valves, which can show over time and usage, some shift, automatically without any mechanical adjustment.
Lastly, but by no means least, the digital control provides the capability of adding to the ADTS extra capabilities and more functions, by the simple expedient of loading new software into the instrument, for example during the annual calibration exercise.
All of the features mentioned permit the performance of the aircraft checking with very high accuracy, confidence and repeatability.
OPERATIONAL FLEXIBILITY AND EFFECTIVENESS
All ADTS series MPSXY can be easily controlled to perform all the functions
required to accomplish a calibration or a leak check of the Pitot/Static systems.
Due to the high readings rate (from 20 to 100 times per second depending on the different models) all the test functions to simulate the aircraft flying characteristics, are entered via the colour-arranged keypad on the ADTS, or on the Hand Held Remote Control Unit (HHRCU) in a simple and intuitive way. The test is simple and straightforward even for the first time user, since the air data required to accomplish all the functions are clearly shown either in English or Metric values.
The keyboards are colour-coded and arranged to allow easy and logical operation.
All indications and controls are located exactly where the operator expects them to be.
Commanded values can be entered either by digitizing directly the values or by increasing or decreasing the values of a fixed step using UP and DOWN arrows.
In addition the MPSXY ADTS also provide the additional, following features:
MACH Mode where the operator directly enters the target Mach Number.
EPR Mode to carry out engine EPR system tests.
TAS generation.
Up to 30 programmable different test profiles, each one with 26 different test points, can be stored and executed to provide automatic testing capability for a considerable time saving. This allows the full automatic testing of FAR 43 Appendix E ; it is possible to program the stabilization time, the reading time for the leak test as well as the waiting time before recording the readings.
Automatic or Semiautomatic Leak Test.
Centre-line Correction, to compensate for height difference between the ADTS and the UUT (or cockpit or flight deck height above ground).
Encoding Altimeter or Encoder Test with automatic check of all tests points sequence.
Automatic Test of Radio Altimeter for the complete EGPWS test
Self-contained Battery pack to allow up to 4 hours of full operation without external power.
ARINC 429 bus.
Full ADTS Control via an external PC.
ULTRA LOW SPEED Function to generate very low airspeed (5 to 200 kts) values.
Full Automatic Calibration by using a D.Marchiori PAMBX and a specific SW.
Rugged LCD with back lit display HHRCU, for one-person only operation.
Programmable safety limits to ensure safe aircraft testing.
Different type of remote control units, also with touch-screen colour display and USB flash disk to store the test results and examine directly with the remote unit or by an external PC.
With the MPSRE terminal it is also possible to store more and more test profiles with a large number of features like quantity of different instruments under test, tolerances for every profile step, leak test with programmable stabilization time, reading time, tolerances etc.
For special needs there is an ATEX remote control unit with touch screen colour display.
EASE OF OPERATION
The design of MPSXY has been particularly developed to ensure an easy and intuitive operation.
Training required for the operation of MPSXY is very limited; all the HW and SW protections will allow the first time user to operate safely and with confidence.
TESTING TIME
Length of time for testing is mainly determined by the airplane limitations, mainly the Altitude Rate of Change, which cannot be exceeded.
The ADTS can save time by stabilizing test altitudes and airspeed values in a very short time.
One very interesting feature is the Multiple Isolator, integrated in the ADTS box to enable up to four separate pitot/static outputs to be connected to the aircraft simultaneously. This provides the capability to switch between the aircraft pitot/static systems directly controlled by the Hand Held Remote Control Unit.
This feature makes leak checks very simple, detecting the exact location of system leaks for immediate rectification without wasting time to vent to ambient, disconnect and reconnect hoses to aircraft.
Otherwise the use of a dedicated external box to accomplish such function compromises the one-man operation capability and makes the hoses connections more difficult.
Additionally; the leaks can be controlled in separate modes:
classic mode, but with multiple isolator to find the particular line that is leaking.
static measure mode and pitot control mode or vice versa allows the leak check for the two lines simultaneously thus reducing further measurement time.
These described modes of leak testing have another advantage in addition to saving time, it is the test reliability, not comparable with multiple lines in parallel used in standard two connections (static and pitot) leak test, and without the mix measure/Ps – control/Pt and vice versa mode.
OTHER ADTS PRODUCTS
The improvements in aircraft instrumentation have resulted in the determination of the angle of attack readings through a special pitot tube with 3 or 4 different pressure measurement ports for data acquisition.
These are Ps, Pt, AoA and also 2nd AoA. To test these new types of pneumatic readings the ADTS needs 3 or 4 different pressures generated simultaneously, or it is necessary to use 2 different ADTS with the resultant extra cost and more complication.
D.Marchiori produces 3 types of ADTS, two different instruments with 3 independent pressure generators and one instrument with 4 pressures generators. All these instruments have all the capabilities previously described, such as battery, multiple isolator option, complete leak test, various different HHRCU, Bluetooth useful to control the ADTS from a PC or notebook, etc.
Another recently introduced product is the smallest ADTS available today: housed in a very small box (30 x 25 x 12 cm) and with a total weight of 4 (four) Kg there is a fully automatic ADTS , RVSM capable with colour touch screen display, and a host of features such as user programmed test profiles, UUT readings, automatic LEAK, different measure units, ultra low speed readings etc.
Pitot-static Testing and the Role of the Probe Adaptors
As a designer and manufacturer of precision, high accuracy pitot-static test instrumentation, DMA – Aero are acutely aware of the significant role that the junction between the test equipment and the aircraft plays in ensuring a viable test system. The aircraft mounted pitot static probes for the sensing of the aerodynamic values of altitude, airspeed, rate of climb and other related parameters are the commonly used connection points for the ground support test instrumentation.
The design and construction of the pitot static test adaptors that can be installed onto the probes to enable the air data parameters generated by the air Data test Set (ADTS) to be faithfully transmitted to the flight-deck instruments calls for a full understanding of all the requirements to be considered.
Airframe mounted probes are basically designed to provide the best possible results for sensing the air data parameters. The pitot static probe adaptors that will be used to fit onto the probes must accept that the probe design is first and foremost for the aircraft and the adaptor must somehow contend with the vagaries that exist.
It is imperative that the pitot static tube adapters do not in any way damage the pitot-static system. The whole air data test system needs to be able to simulate the appropriate values of pressures and vacuums corresponding to the desired altitudes and airspeeds etc. The mounting of the pitot and static adaptors, and the relevant hoses forming the whole of the assembly onto the probes must not result in any damage to the aerodynamic contour or surface finish nor impose any undue stress loading that could potentially result in misalignment of the probe.
Additionally there needs to be certainty that the particular adaptor sealing method employed does not in any way result in material from the sealing media becoming loose and entering the probe causing blockages.
Since the tests called for on modern aircraft specify air data values to be of extremely high accuracy, for example to meet the requirements -”Reduced Vertical Separation Minima, (RVSM), there must be absolutely minimal leaks in the overall system. This includes all pitot static test connections and pneumatic fittings employed at the adaptor, the hoses to the air data test set (ADTS) and the ADTS panel mounted connectors. A leaking system would result in the observed value on the ADTS not being the received value at the aircraft, thereby negating all the precision so carefully engineered into the ADTS.
The types of probe or sensing point on the aircraft fuselage presents the pitot and static test adaptor designer with a challenge to enable the best result to be achieved to ensure a practical solution. Single pitot probes / tubes allow fairly straightforward sleeve style pitot test adaptor solutions to be used with minimal concerns regarding datum points for the fitting depth. However if the probe is a combined pitot and static variety then the pitot static test fittings must ensure that the static hole in the probe is exactly in line with the adaptor matching connection. Some form of mounting reference needs to be provided to ensure correct placement of the pitot static connectors.
Multi port pitot and static adaptor
This reference feature becomes particularly important if the probe is even more complex as in the instance where the probe also serves as an Angle of Attack (AoA) sensor. Where the traditional vane form of AoA measurement has been replaced by pneumatic sensing incorporated into the pitot static probe then there are multiple static ports in the probe to which the adaptor must interface.
Angle of Attack adaptor
Static measurement ports on the aircraft fuselage present another challenge for the connection point for the ADTS. Now the adaptor must be so designed that it surrounds the sensing hole in the flat plate of the sensing port. The method employed needs to be both practical and again cause no damage to the static plate, remembering not all aircraft provide mounting features.
The adaptor must include some sensible feature to achieve the desired result. Various methods are used, some more attractive than others. DMA-Aero utilise rubber suction cups to clamp the adaptor onto the plate surface, providing a vacuum source from the MPS range of air data test sets to ensure a firm fixing of the adaptor. Some systems employ the actual sensing hole as the fixing point but this risks damaging the contour of the static point.
Static adaptor for aircraft skin mounting
For commercial aircraft there are generally multiple probes fitted to allow independent systems for the Captain and the 1st Officer and also generally a Standby channel. In these situations the pitot static test kit manufacturer supplies complete kits that provide all the relevant air data test adaptor kit and the hoses and interconnecting pneumatic fittings for the whole aircraft since the testing of the various parameters is often carried out simultaneously, the ADTS supplying the necessary altitudes, airspeeds etc to all the systems.
The air data accessories kit must also include a static blanking adaptor and a pitot tube dummy adaptor blanking feature to allow the whole air data test adaptor kit to be itself leak tested before installation onto the aircraft.
Multi-port pitot-static adaptor kit
When such multi probe systems are being catered for then the overall air data accessories kit will be housed in suitable cases / boxes giving the Operator all the equipment needed. These Kits will have been so designed to match the needs of individual aircraft, not only to provide the correct adaptors but also to ensure the appropriate lengths of the hoses do stretch to the remotest aircraft measurement point, often resulting in very long hoses. The hoses selected will have been verified as being suitable for the flight-line environment being rugged and not adversely affected by exposure to fluids such as Skydrol hydraulic leakage that can be a problem in the flight-line working environment.
The complexity of these numerous hoses is alleviated by colour coding the different lines and by utilising self coloured material that is also transparent so that it additionally proves beneficial in that any contamination of the internal pitot-static lines can readily be seen. Using lightweight hose material helps enormously in the overall handling of the complete kit assembly and additionally reduces loading on the installed adaptors.
Since the Adaptors will most likely be in service for many years it is important that the sealing features of the design are capable of being replaced by the operator. Consequently the use, in the design, of readily available commercial “O” ring seals are adopted by DMA as a sure way of allowing ongoing straightforward replacement. The seals become damaged when not installed in a correct manner, and on occasions when the probe heaters are inadvertently turned on by error and the seals damaged as a result.
A very wide range of different Adaptors need to be available for the vast range of aircraft and DMA are constantly introducing new designs to meet new aircraft needs.
