EVALUATION OF SERVICE LIFETIME OF AVIONIC
HYDROSTATIC DRIVES ON THE BACKGROUND OF
INFORMATION ACQUIRED FROM THE
HUMAN-INDEPENDENT FLIGHT CONTROL DEVICES
Ułanowicz L.
Air Force Institute of Technology, Warsaw
Abstract: The paper discloses the method for evaluation of service lifetime of on-board avionic
hydrostatic drives on the background of information acquired from human-independent flight control devices on the basis of description how the structural parameters of the system subject to alterations over the equipment lifetime. The description of structural parameters related to the hydrostatic drives takes advantage of these data from the human-independent flight control devices that have not been used so far and establishes correlation between these data and the measurement signals that are typical for the drives. Evaluation of the service lifetime employed by the presented method consists in comparison between the values for actual structural parameters and adequate threshold limits under provision that specific parameters affecting the process of predicted lifetime evaluation as well as describing the technical condition of the devices are mutually independent. Identification of structural parameters attributable to avionic hydrostatic drives was carried out on the basis of information that can be acquired from human-independent flight control devices. The theoretical backgrounds for the proposed method related to assessment of technical condition of an avionic hydrostatic drive and evaluation of its expected lifetime on the background of information acquired from the human-independent flight control devices are presented, as well as measurement data are listed whereas the data had been acquired from human-independent flight control devices and they refer to structural parameters of avionic hydrostatic drives for two types of aircrafts that are operated by Polish Air Forces.
1. Introduction
In this paper the author discloses the idea that was developed in the Air Force Institute of Technology and which refers to evaluation of service lifetime of on-board avionic hydrostatic drives on the basis of information acquired from human-independent flight control devices, such as SARPP-12, TESTER etc. The evaluation of the service lifetime of the on-board avionic hydrostatic drive has its roots in advantages of scheduled inspections of the system and measurements, how far the verifiable structural parameters of the drive or its subassemblies subject to gradual degradation. The method involves estimation of parameters and their comparison with the threshold limits (limited lifetime) to establish the relationships between the warning values of the monitored parameter and the
frequency of inspections, provided that the specific level of fault-tolerance is assured. The warning tolerances present a set of values specific for the monitored parameters that fall between the acceptable limits and inadmissible thresholds. Extending of the parameter value beyond the threshold is regarded a faulty condition of the hydrostatic drive.
Evaluation of the service lifetime of the hydrostatic drive is inseparably connected with the need to identify its technical condition. The hydrostatic drives of most aircrafts that are in service in the aviation of the Polish Army are hard to access and insusceptible to diagnostic operations, thus identification of their technical condition as well as location of the occurring faults is difficult and sophisticated. The technical condition of an avionic hydrostatic drive is understood as a sequence of momentary values of its technical parameters that reflect these properties (qualities) of the drive that are considered as essential. Is should be assumed that the condition of an avionic hydrostatic drive at the moment of ti determines a set of momentary values of those properties or qualities that
unambiguously specify the drive status.
The deterioration degree of an avionic hydrostatic drive can be evaluated on the basis of degradation of its structural parameters as well as quantitative and qualitative analysis of its volumetric efficiency.
Nowadays, assessment of the technical condition of the avionic hydrostatic drive is carried out by a single measurement signal of pressure that is indicated in the pilot’s cockpit. Thus, accuracy of information that is acquired by means of such a method is very insufficient. The undervalued indications of manometers in the pilot’s cockpit are frequently erroneously received as a signal of faulty condition of the hydraulic system. However, the aircraft must be taken out of service to enable the performance of time-consuming and expensive ground tests aimed to detect the reason for the inoperable condition of the avionic hydrostatic drive. Therefore, correct understanding and interpretation of measured parameters is the key factor for evaluation of actual technical condition of an avionic hydrostatic drive. It is why the technical staff frequently decides to replace individual subassemblies of the drive until the unit is considered operable, i.e. technical parameters of the drive match requirements of the Technical Specifications. Making amendments in the hydrostatic drive design to raise its diagnostic properties (i.e. improving its accessibility and diagnostic susceptibility) is an expensive and sophisticated task. Hence, only the methods that use those measurement signals that are typical for a drive can be considered as an alternative approach. Improvements in diagnostic susceptibility can be achieved by using new information that has never been used before. Taking advantage of such information for evaluation of expected lifetime of an avionic hydrostatic drive is the essence of the newly-developed method.
2.
Theoretical background for evaluation of service lifetime of
avionic hydrostatic drives on the basis of information from
human-independent flight control devices
Parameters of an avionic hydrostatic drive that are suitable to evaluate the expected lifetime of the unit can be subdivided into two groups of criteria: acceptable (warning) levels and threshold limits. Acceptable value of a certain technical parameter attributable to an avionic hydrostatic drive is defined as such a parameter value, measured at the moment t1, when the parameter does not reach its threshold limit until the moment t2 with
the probability p(t) pw, where pw is the presumed probability level of fault-free operation
of the unit over the period of time τ = t2 – t1. Thus, the probability of fault-free operation
of the unit during the presumed time interval can be expressed by the following equation: P(t) = P T > t = P W(T) < Wgr ,
where: W stands for a specific technical parameter whereas Wgr is the threshold limit of
that parameter.
The acceptable value of a technical parameter makes it possible to identify the units that tend to reach their threshold limits within a short period of time. The threshold limit of a technical parameter that describes the hydraulic module status is considered as such a value that any exceeding of it brings about to the fault probability Q(t) during a specific period of time and equals to the probability of the fact that the random function of a technical parameter W(t) > Wgr, i.e.
Q(t) = P T < t - P W(T) > Wgr .
In case if the threshold value is exceeded by the relevant parameter is serves as a proof that the avionic hydrostatic drive has already reached the end of its operational lifetime and cannot be used any longer.
Evaluation of the technical condition of any hydraulic system bases on comparison between actual (measured) values of specific parameters and their threshold limits provided that the values of defining parameters and the evaluation conditions are mutually independent.
Further deliberations included in the paper shall present theoretical background for preliminary evaluation of technical condition of the avionic hydrostatic drive incorporated into the military reactive aircraft Su-22. The physical parameters that characterize circulation of information between the components of the hydraulic system and between subassemblies of other system make up a set of structural parameters attributable to the systems and subassemblies in question. The process of information circulation between individual components of the hydraulic system implies that the technical condition of the system can be evaluated by the volumetric factor ih defined as a ratio of the hydraulic
delivery of the supplying system p and the total absorption of the hydraulic systems ch
e.g.: ch p ih
where: ch = chp + cho. The hydraulic delivery p is the volume of the pressure fluid that is
delivered to the pressurizing line over a time unit. The absorption of a hydraulic system is understood as the volume of pressure fluid that is delivered to the system from the supplying line over a time unit. For new hydraulic system the level of volumetric loss within the system is assumed to be no more than 10%, which can be expressed by the equation: p = 1,1 ch. Any variation in the absorption of the hydraulic system ch or the
delivery of the supplying hydraulic pump results in alteration of the volumetric factor of the system ih. The absorption of the hydraulic system ch depends on the intake zh of
individual hydraulic units of the system. On the other hand, the intake of a hydraulic unit zh depends on the flow intensity for internal leakages nw within the unit, thus can be
referred to its volumetric efficiency vzh. Hence, the volumetric factor of the system ih is
correlated with volumetric efficiency parameters vzh of individual units that make up the
entire system.
In a very practical way the volumetric factor of the system ih can be evaluated by
measurements of the time interval and shaft rotation of the pump driving motor that is necessary to achieve the required pressure in the hydraulic system. The pressure rise time for the hydraulic system tr during the system start-up depends on its volumetric efficiency,
the hydraulic pump delivery, hydraulic volume of the system (capacitance) and pressure differential within the system, i.e. on the volumetric factor of the system ih and pressure
differential, which can be expressed as:
tr = f(v,p, p) = f(ih, p)
where: v – volumetric efficiency of the system, p – delivery of the supplying pump, p - pressure in the hydraulic system.
The rise time in a hydraulic system can be determined from the equation for flow balance of fluid during the system start-up:
0
dt
dp
c
p
a
p p v p
where: p – delivery of the supplying pump, av – flow intensity factor for internal leakages
of the system components, pp – pressure differential in the hydraulic system, c - hydraulic volume of the system (capacitance), t – start-up time.
The above expression leads to the following inhomogeneous differential equation that describes pressure variation:
v p p p v
a
p
dt
dp
a
c
The solution of the equation can be fund as a sum of integrals, the general integral for the homogenous equation and the particular integral for the inhomogeneous one. After having determined the form of the general integral for the homogenous equation as well as the particular integral for the inhomogeneous one the following formula for pressure variations within the hydraulic system is obtained:
t
c
a
a
p
v v p p1
exp
.The above relationship makes it possible to calculate the pressure rise time for the hydraulic system: v p p p v r c p a a t
ln .By substitution of border limits of the parameters, i.e. delivery of the supplying pump p,
pressure differential in the hydraulic system pp and flow intensity factor for internal
leakages av, to the above equation the limit border for the pressure rise time for the system
is obtained. It is the time that is needed to increase the pressure up to the prescribed value. For any unit of a hydraulic system, the flow intensity factor for internal leakages av is
calculated by the following formula:
= av p,
whereas the overall leakage for the entire system:
n i i vi na
p
1
.The gathered expertise as well as the runtime tests allow to state that a hydrostatic drive performs the assigned functionalities if the ratio of the supplying pump delivery p and
absorption of the hydraulic system ch is not less than 0.95, which is noted down in the
following manner:
95
,
0
ch p
Shaft rotation of the pump driving motor for the moment when the system pressure reaches the required value is calculated from the balance equation for the flow intensity as below:
Therefore the border limit for such shaft rotation of the pump driving motor that guarantees achieving the prescribed pressure in the hydraulic system can be calculated from the following relation:
p p vp ch s p a n
0,95where: avp – flow intensity factor for internal leakages of the hydraulic pump, calculated
by means of the relation, p – unit delivery of the pump.
Pressure variation in the hydraulic system during the start-up period can be expressed by the following equation:
t tk v u p u s e c a p p p
,where: pu – effective pressure of a hydraulic pump during the start-up period, - damping
coefficient.
3. Description of the method
The human-independent flight control devices are designed to record selected parameters under both normal and emergency conditions of the flight and to secure storage of the recorded information in case of any aircraft breakdown. Every on-board aircraft log device records not only continuous parameters, but also one-shot (binary) signals, so called “one-shot commands”. Information on depressurization of the hydraulic system is just one of such signals. The one-shot commands are stored into the recording log when the pressure in the aircraft hydraulic system drops below the specified value. The described method uses information about the pressure drop below the limit that varies from one aircraft type to another, e.g. for the Su-22 it is the threshold of 14.7 MPa, for MiG-29 it is 9.810.44 MPa whereas 10.5 MPa is the limit for the TS-11 aircraft. During the aircraft engine start-up procedure the pressure in the hydraulic system increases until the rated value. The log device records the information on insufficient pressure in the hydraulic system until the monitored pressure reaches the aforementioned aircraft-specific limits. During the flight the pilot initiates movements of the aircraft actuators, i.e. undercarriage, aerodynamic brakes, etc. Such movements result in pressure drops in the hydraulic system. Further analysis of the flight-related parameters allows identification of the unit or the subsystem, which has caused dropping of the system pressure below the prescribed limits (as above).
For prophylactic purposes, identification of technical condition of the hydraulic system consists in measurements of the following parameters:
- time intervals and shaft rotation of the pump driving motor to identify the relevant values when pressure in the hydraulic system reaches the prescribed value, the measurements are carried out during starting up the aircraft engine,
- length of time intervals when pressure in the hydraulic system decreases due to movements of the aircraft actuators, i.e. flaps, undercarriage, aerodynamic brakes, flying controls, etc.
- length of time intervals when pressure in the hydraulic system decreases after killing the aircraft engine. The time is measured from the moment when the human-independent devices commence recording until the turbine rotation of the aircraft engine decreases to 20% of the initial speed.
On the basis of analytical calculations (as presented in par. 2 above) and measurement data collected during tests of hydraulic systems in Su-22 and TS-11 aircrafts over the period of five years the following parameters were determined:
- border limits (thresholds) for time intervals and shaft rotation of the pump driving motor that correspond to reaching a prescribed value of pressure in the hydraulic system,
- maximum duration of time intervals when pressure in the hydraulic system decreases below the prescribed values due to movements of the aircraft actuators,
- border limits for time intervals that expire after the aircraft engine is killed.
The first hydraulic system of the Su-22 aircraft is deemed to be in the sound operating condition if the pressure rise time in that system up to the value of 14.7 MPa is not longer than 25 s and the first hydraulic system reaches the pressure of 16.2 MPa at shaft rotation not more than 25%.
The second hydraulic system of the Su-22 aircraft is deemed to be in the sound operating condition if the pressure rise time in that system up to the value of 14.7 MPa is not longer than 20 s and the system reaches the pressure of 16.2 MPa at shaft rotation not more than 20%.
The first hydraulic system of the Su-22 aircraft is deemed to be in the sound operating condition if the time interval as measured by the human-independent flight control devices from the beginning of recording until the turbine slows down to 20% of the initial rotation after killing the aircraft engine is not shorter than 20 s.
The second hydraulic system of the Su-22 aircraft is deemed to be in the sound operating condition if the time interval as measured by the human-independent flight control devices from the beginning of recording until the turbine slows down to 20% of the initial rotation after killing the aircraft engine is not shorter than 25 s.
For hydraulic systems of the Su-22 aircrafts the pressure drop below 14.7 is permitted for the time not longer than 10 s.
Graphic interpretation for the values of time intervals and shaft rotation of the pump driving motor that correspond to reaching of the prescribed pressure in hydraulic systems of Su-22 aircrafts is shown on Fig. 1 and Fig. 2.
The hydraulic system of the TS-11 aircraft equipped with the flight recorders SARPP-12 or S2-3ai is deemed to be in the sound operating condition if the pressure rise time in the system up to the value of 10.5 MPa is not longer than 55 s and the hydraulic system reaches the pressure of 10.5 MPa at shaft rotation of the motor not more than 7,000 rpm. The maximum duration of pressure drop below 10.5 MPa that is permissible for the hydraulic system of the TS-11 aircraft is 5 seconds.
0 2 4 6 8 10 12 14 16 18 0 5 10 15 20 25 30
Pressure rise time in the hydraulic system [s]
Pr es su re in th e hy dr au lic s ys te m [M Pa ]
Fig. 1. Graphic interpretation of threshold limits for time intervals that expire until the hydraulic system pressure reaches the value of 16.0 MPa
a – permissible rise time for the pressure in the second hydraulic system; b – limit border for the pressure rise time in the second hydraulic system; c – permissible rise time for the pressure in the first hydraulic system; d – limit border for the pressure rise time in the first hydraulic system;
Operating condition area Non-operating condition area a b c d
0 5 10 15 20 0 5 10 15 20 25 30
Shaft rotation of the pump driving motor [%]
Pr es su re in th e hy dr au lic s ys te m [M Pa ]
Fig. 2. Graphic interpretation of limits (thresholds) for shaft rotation of the pump driving motor that correspond to the pressure in the aircraft hydraulic system of 16.0 MPa
a – limit value for shaft rotation of the pump driving motor that corresponds to the pressure in the second hydraulic system of 16.0 MPa, b – limit value for shaft rotation of the pump driving motor that corresponds to the pressure in the first hydraulic system of 16.0 MPa.
4. Assessment of the technical condition of the hydraulic system of the
Su-22 aircraft on the basis of information from human-independent
flight control devices.
In order to verify the above method of evaluation the hydraulic systems of five Su-22 aircrafts were examined during extensive ground tests. The aircrafts with the flying time parameters as shown in the Table 1 are in service in OKL JW 3388. For the purpose of verification the following information was read from the on-board recording logs:
- time intervals that expire until pressure in hydraulic systems of the aircrafts has reached the value of 16.0 MPa,
- shaft rotation of the pump driving motor that correspond to the pressure in the aircraft hydraulic system of 16.0 MPa,
- duration of pressure drops in the hydraulic systems during movements of aircraft actuators, i.e. flaps, undercarriage, aerodynamic brakes, flying controls, etc.
- length of time intervals when pressure in the hydraulic system decreases after killing the aircraft engine. The time was measured from the moment when the TESTER device commence recording of the system pressure decrease until the turbine rotation of the aircraft engine decreases to 20% of the initial speed.
Operating condition area Non-operating condition area a b
The rise time values and shaft rotation speed of the pump motor that was necessary to reach the required pressure in hydraulic systems of Su-22 aircrafts are shown in Table 1 and on Fig. 3, Fig. 4 and Fig. 5. Analysis of the data from Table 1 leads to the conclusion that the rise time of pressures as well as the motor shaft rotation that is necessary to reach the pressure of 16.0 MPa depends on the overall working time of the hydraulic system. The longer the hydraulic system is in service the higher rise time for the pressure it requires similarly to the shaft rotation that allows reaching 16.0 MPa of system pressure. It serves as a proof of natural wear and tear of hydraulic modules and subassemblies of these systems, in particular hydraulic pumps and solenoid valves.
Fig. 6 presents the characteristic curves of pressure for three hydraulic pumps NP-34M-1T from Su-22 aircrafts with numbers 8508, 7501 and 3306. As Fig. 6 shows, the delivery of the hydraulic pump from the Su-22 aircraft No 8508 is by about 3 dm3 lower than in case
Table 1. Rise time intervals that expire until pressure in the hydraulic
systems of Su-22 aircrafts reaches the value of 16.0 MPa along with
corresponding values of shaft rotation speed.
The Su-22 aircraft number
Working time of the
hydraulic systems Pressure rise timefor the hydraulic systems
Rotation of the pump motor that corresponds to the system pressure of 16.0 MPa
first second first second
- [h,min] [s] [s] [%] [%] 8508 700,10 16 12 18.4 16.6 750,25 16 12 18.8 16.8 814,45 18 13 18.7 16.9 852,02 17 12 19.3 16.8 904,06 18 13 19.8 16.8 952,26 18 14 19.9 17.2 1004,17 20 16 21.3 17.6 1052,12 22 16 21.5 17.5 1098,24 22 17 22.5 17.9 6307 632,23 15 13 17.6 16.9 660,14 15 13 17.8 17.0 700,28 16 13 17.7 17.0 751,43 16 14 17.9 17.1 806,52 17 13 18.1 17.2 851,37 16 15 18.1 17.6 901,31 19 15 19.4 17.6 954,52 19 15 19.7 17.5 1003,12 21 16 20.6 17.5 1055,43 21 16 20.8 17.5 8507 802,52 19 14 18.4 17.1 851,41 19 14 18.8 17.1 903,25 19 14 19.4 17.3 951,28 20 15 19.5 17.5 1001,43 20 15 19.4 17.5 7501 360,32 15 10 16.4 14.6 407,58 16 10 16.4 14.5 453,52 16 11 16.8 14.6 512,12 17 12 16.4 14.6 529,28 17 12 17.4 14.8 578,35 17 12 17.9 14.8 3306 96,53 16 9 16.4 14.5 142,25 17 9 16.8 14.2 201,16 17 10 16.9 14.2 262,24 16 10 16.9 14.8 337,07 17 11 16.8 15.5
Fig. 3. Pressure rise time for the first hydraulic system of five Su-22 aircrafts 0 2 4 6 8 10 12 14 16 18 0 200 400 600 800 1000 1200
Total working time of the hydraulic system [h]
Pr es su re r is e tim e fo r th e hy dr au lic s ys te m [ s] samolot 3306 samolot 7501 samolot 6307 samolot 8508 samolot 8507
Fig. 4. Pressure rise time for the second hydraulic system of five Su-22 aircrafts
0 5 10 15 20 25 0 200 400 600 800 1000 1200
T otal working time of the hydraulic system [h]
Pr es su re r is e tim e fo r th e hy dr au lic sy st em [ s] samolot 3306 samolot 7501 samolot 6307 samolot 8508 samolot 8507 aircraft 3306 aircraft 7501 aircraft 6307 aircraft 8508 aircraft 8507 aircraft 3306 aircraft 7501 aircraft 6307 aircraft 8508 aircraft 8507
Fig. 5. Shaft rotation of the pump driving motor that corresponds to the pressure of 16.0 MPa in the first stage of the hydraulic system for Su-22 aircrafts
33 34 35 36 37 38 39 40 0 5 10 15 20 25
Forcing pressure of hydraulic pumps [MPa]
D el iv er y of h yd ra ul ic p um ps [ l/m in ] samolot 8508 samolot 3306 samolot 7501
Fig. 6. Pressure-related characteristic curve for hydraulic pumps from the Su-22 aircrafts with numbers 8508, 7501 and 3306.
Fig. 7 presents the graph of flow intensity for internal leakages of hydraulic system components as a function of time. The graph shows that internal leakages of hydraulic system components have increased for all the aircrafts under test. In case of the hydraulic system of the Su-22 aircraft with the number of 8508 the internal leakages were higher by about 0.9 dm3/min that for pumps from the other aircrafts. The full report from
examination of hydraulic systems of the Su-22 aircrafts with the number of 8508, 7501 and 3306 are included in [1, 2, 3].
aircraft 8508 aircraft 3306 aircraft 7501 0 5 10 15 20 25 0 200 400 600 800 1000 1200
T otal working time of the hydraulic system [h]
M ot or s ha ft r ot at io n [% ] samolot 3306 samolot 7501 samolot 6307 samolot 8508 samolot 8507 aircraft 3306 aircraft 7501 aircraft 6307 aircraft 8508 aircraft 8507
0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 0 200 400 600 800 1000 1200
Total working time of the hydraulic system [h]
Fl ow in te ns ity f or in te rn al le ak ag es of h yd ra ul ic s ys te m c om po ne nt s [ l/m in ] samolot3306 samolot 7501 samolot 6307 samolot 8508 samolot 8507
Fig. 7. Characteristic curve of flow intensity for internal leakages in hydraulic systems of Su-22 aircrafts.
Analysis of measurement results from Table 1 as well as characteristic curves from Fig. 6 and Fig. 7 leads to the conclusion that information from human-independent flight control devices can be used for the fairly accurate evaluation of technical condition of the aircraft hydraulic systems.
Another type of aircraft where identification of technical condition of hydraulic systems was carried out by means of human-independent flight control devices is represented by TS-11 airplanes. For hydraulic systems of the TS-11 aircraft the rise time values and characteristics curves for pressure-related functions were determined on the basis of readouts for pressure variations stored on on-board log recorders of flight parameters SARPP-12 and S2-3ai. The measurements were taken in OKL 1 of the Aviation Training Centre in Dęblin. Results of investigations are included into Table 2 and Table 3. The ground tests that were carried out for hydraulic systems of TS-11 aircrafts confirmed usefulness of information obtained from human-independent flight control devices for evaluation of technical condition of hydraulic systems. Full measurement data related to tests of hydraulic systems of TS-11 aircrafts are included into [3].
aircraft 3306 aircraft 7501 aircraft 6307 aircraft 8508 aircraft 8507
Table 2. Rise time intervals that expire until pressure in the hydraulic systems of TS-11 aircrafts reaches the value of 10.5 MPa along with corresponding values of shaft rotation speed (data retrieved from the S2-3ai log recorder)
The TS-11 aircraft number Working time of the hydraulic system
Pressure rise time for the hydraulic
system
Rotation of the pump motor that correspond to the system
pressure of 10.5 MPa - [h,min] [s] [rpm] 1223 12,43 32 6500 54,32 32 6550 107,52 32 6600 164,37 33 6500 1224 5,31 30 6500 58,43 31 6600 102,11 31 6500 157,43 33 6600 198,37 34 6600 1608 6,14 35 6600 63,25 35 6600 112,43 36 6700 167,24 36 6700
Table 3. Rise time intervals that expire until pressure in the hydraulic systems of TS-11 aircrafts reaches the value of 10.5 MPa along with corresponding values of shaft rotation speed (data retrieved from the SARPP-12 log recorder)
The TS-11 aircraft number Working time of the hydraulic system
Pressure rise time for the hydraulic
system
Rotation of the pump motor that correspond to the system
pressure of 10.5 MPa - [h,min] [s] [rpm] 1008 12,14 41 6100 52,30 42 6100 104,27 41 6100 153,17 44 6300 207,43 44 6300 264,43 46 6400 318,14 45 6400 368,23 46 6400
5. Conclusions
In this paper the author outlined the method for identification of technical condition of avionic hydraulic systems on the basis of information that can be retrieved from human-independent flight control devices. The presented method can be used for those aircrafts where maintenance of the on-board hydraulic systems induces problems thus diagnostic susceptibility of such systems is very low. It is why identification of technical condition of the drives as well as detection and location of possible defects is difficult and sophisticated. The proposed method improves diagnostic susceptibility of the system with no need to adjust the design of hydraulic system and to adapt them to available diagnostic facilities. In that way diagnostic coverage of possible disturbances and malfunctions dramatically increases.
All the airplanes operated by aviation divisions of Polish Army are equipped with human-independent devices for monitoring of flight parameters. Analysis of such time intervals and shaft rotation of motors that drive hydraulic pumps that are necessary to achieve the prescribed pressure in the hydraulic system during the aircraft engine start-up as well as monitoring of pressure drops in hydraulic systems when movements of the aircraft actuators are performed, such as flaps, undercarriage, aerodynamic brakes, flying controls, etc. make it possible to evaluate actual technical condition of the system. The ground tests of hydraulic systems for the Su-22 and TS-11 aircrafts confirmed applicability of information that can be retrieved from human-independent flight control devices and opportunities to use such information for evaluation of current technical condition of the system as well as its expected lifetime.
All the relevant investigations, gathered numerical data and performed analysis serves as a background to state that information retrieved from human-independent flight control devices:
1) contain diagnostic symptoms for avionic hydraulic systems, 2) can be used for the derivative troubleshooting process,
3) can serve as a background for identification of technical condition of avionic hydraulic systems,
4) indirectly, are suitable for evaluation of expected lifetime of avionic hydraulic systems along with its modules and subassemblies just on board, with no need to dismantle the system from the aircraft.
References
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Technology, Warsaw, 2002. (in Polish language)
[2] Kolasa B., Ułanowicz L.: Examination of the pressure oil Petro-Oil H-515-Pl in order
to apply the product to hydraulic systems of military aircrafts. Ground tests. Laboratory tests. Internal development of Air Force Institute of Technology, Warsaw,
2002. (in Polish language)
[3] Ułanowicz L.: Report on the research work “Investigation of applicability of the
pressure oil Orlen Oil H-515to hydraulic systems of military aircrafts and ground technical facilities”. Internal development of Air Force Institute of Technology,
