Specification
(a) Title:
METHOD AND APPARATUS FOR COMPREHENSIVE ON-GROUND EVALUATION OF AIR DATA COMPUTER FOR AIRCRAFT APPLICATIONS BY FLIGHT PROFILE RE-CREATION METHODOLOGY.
(b) Field of Invention:
This invention relates to the testing methodology of Aerospace equipments.
(c) Use of Invention:
A comprehensive methodology to verify and validate the functionality of air data computer for aircraft applications with the intention of reducing the quantum of flight testing efforts.
(d) Object of Invention:
The principal object of the invention is to define a comprehensive methodology to verify and validate the functionality of air data computer for aircraft applications with the intention of reducing the quantum of flight testing efforts. Another object of this invention is to validate the newly developed air data computer and define its production baseline without carrying out the real flight trials.
(e) General statement of invention:
The invention provides a method and apparatus for comprehensive on-ground evaluation of air data computer for aircraft applications by flight profile re-creation methodology.
(j) Detailed Description of Invention:
Background:
Air data computer (ADC) used in aircraft provides basic air data parameters like pressure altitude, calibrated airspeed, true air speed, Mach no, vertical velocity, total air temperature, static air temperature etc. The testing of the same is found to be tedious process as it involves various stages of testing like pre-installation checks, aircraft level testing, and flight test evaluation. The flight testing takes considerable time & cost to validate the system performance for entire flight envelope of the aircraft. In order to reduce the flight testing efforts, an alternate testing methodology is proposed as follows.

Methodology & Apparatus:
A hardware-in-loop testing methodology has been established by stimulating the ADC, in the laboratory, with the profile of flight data. The performance of the ADC is assessed by interfacing it with other aircraft systems (like Mission Computer, navigation systems, and displays) along with the recording of input/output parameters simultaneously for validation. The flight data of various sorties with different dynamic manoeuvring cases have been considered. The basic air data parameters (like pitot-static pressures, total air temperature etc.) are recreated using the inverse air data algorithm and necessary test equipments (like air data test set and temperature chamber). The approach of hardware-in-loop cum flight profile recreation testing methodology has reduced the efforts of real flight testing, in terms of time and cost. This has aided the early identification of problems pertaining to the functional algorithm, implementation, and hardware design; and to improve the overall system performance. Based on the results of this testing methodology, the software and hardware logics of the prototype air data computer have been corrected, re-validated, and the baseline for the production unit has been defined. This approach has supported the certification process of indigenously developed air data computer for aircraft applications.
The test set-up is shown in Fig 1.0. In this set-up, ADTS is used to generate the pressures (Ps & Pt) corresponding to the flight recorded altitude and speed. The ADTS is commanded by a Computer via GPIB (IEEE 488) interface. Suitable GUI based application software was developed to interface the PC with ADTS, and command the ADTS with the flight recorded parameters to generate Ps (static) & Pt (total) pressures. The pneumatic ports of the ADTS are interfaced with ADC-1 and ADC-2 by suitable pneumatic routing. The digital outputs of the ADCs (ARINC-429 interface) are recorded in a PC hosting an ARINC-429 add-on card and the compatible data acquisition software. The outputs of the ADCs are interfaced with displays to have a real time indication of the parameters such as altitude, airspeed, Mach No, and Vertical Speed. One cockpit set of displays for indicating the parameters from ADC-1 and another cockpit set of displays to indicate the parameters from ADC-2 are configured. This kind of real time display is found to be quite helpful for the effective assessment by engineers/pilots and to detect the problems qualitatively, if any. The pneumatic routing shown in Fig: 1.0 has undergone leak check to ensure that pressure leak is minimal for the satisfactory performance of the integrated system. During the leak test, the ADTS was manually set for Ps & Pt (as per the test cases). The leak test results are tabulated in Table 1.0.

Both the ADCs are powered by a 28VDC power supply, and the ADCs are electrically interfaced with an ARINC-429 add-on card of the data acquisition computer. Different channels are used on ARINC-429 add-on card to receive the data from two different ADCs. The ARINC-429 output signals of the ADCs are interfaced with respective set of displays. A Break IN/OUT Box is used in between of the electrical routing for need basis debugging/analysis. The data acquisition computer is equipped with an ARINC-429 add-on card and the acquisition system is deployed under suitable operating system. A data acquisition software and associated hardware environment is used which enables for label based parameter monitoring and recording along with time tagging.
The ADTS shown in the Fig: 1.0 plays a major role in the proposed methodology. The ADTS generates static and total pressures based on the parameter that is set manually or automatically. The ADTS has the required performance figures to evaluate the air data system of modern flight vehicles. For the manual setting of the ADTS, key panel on the unit is used. The above

discussed leak test has been done by setting the parameters using the key panel. However, rest of the testing is carried out automatically by driving the ADTS from a computer with GUI to control the ADTS in real time. The control computer is equipped with GPIB (IEEE 488) add-on card hardware and with application software which is developed for the present work. This control module has the features as follows,
a) Graphical User Interface (GUI)
b) Reading flight data files for altitude, speed, mach no, and vertical speed;
c) Apply inverse pressure error correction to estimate the uncorrected parameters;
d) Apply inverse air data algorithm to derive Ps and Pt from altitude and speed;
e) Initialise the GPIB add-on card;
f) Command the ADTS for the uncorrected Ps and Pt (derived flight data) via GPIB port, and run the program in a loop for complete flight data.
The flight data, considered for the present work, covers the flight profile corresponding to aircraft taxing at low speed and high speed, take-off, climbing, straight and level flying, accelerating and decelerating, banking and turning, flying at maximum altitude and (or) maximum speed of the flight envelope, descending, approach, landing, and manoeuvring cases like vertical loop, pitch up an diving, roll, side slip, and stalling of a fixed wing aircraft. The flight data by the onboard flight test instrumentation is the data source for the present work (in addition to flight dynamic simulation data). The data was recorded at the sampling rate of 64 Hz. The flight recorded altitude & speed parameters are processed by applying inverse of the pressure error correction (i.e., inverse of the static source error correction-SSEC) in order to determine the uncorrected altitude and speed. The inverse air data algorithm is applied to the uncorrected altitude & speed to determine the uncorrected static pressure, total pressure, and dynamic pressure. The uncorrected static pressure (Ps) and the -uncorrected dynamic pressure (Qc) are- used to drive the ADTS. The ADTS is commanded automatically from the control computer in order to generate the pneumatic field corresponding to the uncorrected pressures. These pressures are used to stimulate the respective ports (Ps & Pt) of both ADCs simultaneously. The ADCs are stimulated with the uncorrected static and total pressures (Ps and Pt respectively) being obtained by processing the flight data. The tolerance band for the expected value of the parameters (altitude and calibrated air speed.) is given in Table 2.0. The time delays at various stages are accounted in the analysis. These include:
a) Real time performance of the ADTS
b) Time synchronization between stimulation data and recorded data
c) Pneumatic lag

Table 2.0: Tolerance band for the parameters
The overall sluggishness of the test set-up (comprising sluggishness of ADTS, sluggishness of ADC, and pneumatic lag) is quantified and reported in Table 4.0. This is done by commanding the ADTS from the control computer by using data files that correspond to different rate of change of altitude / speed. These data files can be obtained as sub-set of flight data files or can be generated by simulation. While stimulation and recording of the parameters, the following points are taken care of:-
i) The system time of the stimulation computer (or control computer) and the
recorder PC are ensured such that they are matching for 1 sec resolution; ii) All the subsystems involved in the test set-up are initialised prior to the
commencement of stimulation and recording; iii) The sluggishness of the ADTS and ADCs are quantified, and reported in
Table 3.0. iv) The pneumatic lag is considered; v) The fine tuning to correct the recording time mismatch is done during the
post-experiment analysis by,
a) Synchronizing the time at which default CAS corresponding to the expected value, and the output from ADCs commence varying;
b) Synchronizing the time for peaks/valleys for suitable legs.
The time delay in stimulating ADC-1 and ADC-2 due to the parallel pneumatic routings was quantified. This was verified by connecting two ADC of same types in parallel and providing a segment of the flight data through the control PC. The recorded data was analysed and both the ADCs gave similar performance by time delay of 500 msec (maximum). The approach of synchronizing the peaks/valleys eliminates the uncertainties in the lag characterisation.

# The overall system sluggishness includes the sluggishness of ADTS and the sluggishnes ADC, the pneumatic lag, and the offset of parallel routing (if any). The pneumatic lag is dependent on the length of pneumatic routing from ADTS to ADC and diameter of the tube. Ir present test set-up the pneumatic routing details are as follows,
a) Length of plumbing between ADTS and ADC-1 Ps line : 3.04 m
b) Length of plumbing between ADTS and ADC-1 Pt line :2.99 m
c) Length of plumbing between ADTS and ADC-2 Ps line : 2.94 m
d) Length of plumbing between ADTS and ADC-2 Pt line : 2.99 m
e) External Diameter of the connectors: 4/16 inches for Pt line and 6/16 inches for Ps line The above plumbing parameters to be viewed along with the following points,
i. The length of 3 m corresponds to acoustic lag of about 9.1 msec at 0 degC.
ii. The plumbing length within 200 ft and tube internal diameter less than
corresponds to a typical pneumatic lag of 400 msec as per the open literature, iii. *The additional lag of 500 msec in the case of TADCI is due to offset of the pai pneumatic routing'. Note: In the post test analysis, time offsets are adjusted by synchronizing the peaks/va (segment dependent) of the expected and response from the ADCs, based on the ai assessments.
Table 4.0: Quantification of the sluggishness of the test set-up.

The test set-up for the temperature checks is provided in Fig 2.0.
Parameters applicable:
a) Pressure altitude
b) Baro corrected altitude
c) Calibrated air speed (CAS)
d) Mach no
e) Vertical speed(altitude rate)
f) True air speed
g) Total air temperature
h) Static air temperature
i) Air density ratio
Results and Discussions:
For evaluating the ADC performance, different flight profiles have been recreated. The pressure altitude, calibrated air speed, Mach No, and vertical speed comparisons have been made between actual and the expected figures.
Table 5.0.provides the summary of the altitude testing observations.

Fig 3.0 provides a typical altitude profile used for envelope testing.
Fig 4.0 provides altitude error of ADC1 and ADC2 observed based on the testing under this methodology. .

Table 6.0 provides the summary of CAS testing. The performance of Mach No computation is verified along with altitude and speed checks.
Fig 5.0 provides a typical CAS profile used for testing. Fig 6.0 provides a typical profile for vertical speed checks.

Summary:
The comprehensive evaluation of the ADC by flight profile recreation methodology has been performed. This establishes an innovative methodology for performance verification of the ADC prior to real flight testing, and it helps to reduce the flight testing effort considerably. The test methodology stimulated the ADC with real variations of Ps and Pt pressures and temperature as experienced in the flight.

CLAIM:
We claim that
1. The proposed method and apparatus establish a comprehensive on-ground evaluation methodology to verily and validate the functionalities of air data computer prior to the real flight (or field) testing.
2. The proposed method and apparatus reduce the flight testing efforts of air data system.
3. The proposed method and apparatus work on flight profile re-creation approach along with real time simulation and stimulation.
4. The proposed method and apparatus stimulates air data system with the static pressure, total (or pitot) pressure and outside side air temperature as experienced during the intended application.
5. The proposed method and apparatus result a hardware-in-loop test facility for air data system.
6. The overall sluggishness of the hardware-in-loop system is accounted in the proposed methodology. The pneumatic lag, real time performance of the system which generates the pressures corresponding to the flight profile, time synchronisation of the control and recording systems are considered.
7. The apparatus accounts for the pressure error correction factors of the aircraft air data probes and associated air data algorithm.
8. The apparatus uses standard inverse air data algorithm to generate pitot static pressures and outside air temperature corresponding to the flight profile.
9. The different cases of flight manoeuvring cases are considered in the proposed testing methodology to validate the air data computer.
10. The methodology is established for aerospace applications, but can be extended for other domains.