Working out of the search algorithm of failures of Air Conditioning System of TU-154
Ministry of education and science of Ukraine
National Aviation University
Course work
on the discipline
Diagnostics of aircraft state
‘Working out of the search algorithm of
failures of Air Conditioning System of TU-154’
the work is performed by
the student of 505 FLA
D. Zhuravel
the work is checked by:
Y. A. Sapeljuk
Kyiv 2009
Content
1. Work’s goal
2. Description of ACS of Tu-154
3. Principal scheme of ACS of Tu-154
4. Theoretical base of algorithm
developing process
5. Description of obtained algorithm
Description and operating principles of Air-Conditioning System
of Tu-154
The
air conditioning system (ACS) provides pressurization, ventilation,
heating of the pressure cabin. Air is taken from the 9th compressor
stage of three engines in amount of 5000-5500 kg/h, temperature is
between 240 - 350 °C and differential pressure is 7,5 - 9kg/sm2.
The
ACS supply conditioned air to the control cabin, passenger cabin,
electronic equipment compartment, forward cargo compartment, air
conditioning distribution bay and aft cargo compartment, and provides
constant pressure and temperature in pressure cabin. It is maintained
by air flow regulation. Air supply to the air conditioning system is
furnished by the pneumatic system from either engine bleed air or the
auxiliary power unit (APU) in flight; from engine bleed air, APU
bleed air, ground pneumatic supply cart, or from a ground conditioned
air supply cart during ground operation. All cold air required for
air conditioning is provided by air conditioning packs. Passing bleed
air through a primary heat exchanger, an air cycle machine, and a
secondary heat exchanger cools the air sufficiently to handle any
cooling situation required. A ram air system provides coolant air for
the heat exchangers.
In
each of three pipelines there is regulated check valve to prevent air
masses flow in returned direction. Pipelines attachment is realized
with the help of compensators.
Further
three pipelines are connected into single one mainline, which leads
to the first cooling stage - preliminary air-to-air heat exchanger.
Temperature of hot air after AAHE is ranged between 100 - 200°C.
AAHE is the first stage of cabin air cooling maintained by atmosphere
ram-air flow. AAHE is one-flow.
In case
of overcooling there is by-pass line to bleed off air besides AAHE.
Before air enters pressure cabin the main line is divided on two
parallel pipelines: right and left.
They lead
to two main cooling stages, where AAHEs and air cycle machines
installed. Here, after AAHE air temperature should be not more than
60°C, behind ACM - 10 - 20°C. In case of overcooling there
are two by-pass lines besides AAHE and ACM. By-pass of air is carried
by air distributers mounted on AAHE. Regulation of distributers is
automatic or manual.
ACM has
two functions: to cool air flowing from AAHE being secondary stage of
air cooling; to suck scavenged air through AAHE during ACS operation
being on the ground. There is also oil system of ACM. It`s function
is to lubricate ACM bearings.
Then
air comes to distributive main line where air mixtures and air
distributers are located.
Air
mixture is used to mix cold and hot air. Air distributors of hot and
cold air are used to regulate definite temperature of air in pressure
cabin. Noise suppression device.
Theoretical
basis of working out of algorithm
For
algorithm working out let’s use the method that is based on the
theory of information. In it the leading function is information
quantity, which can be got during control of diagnostic parameter or
making another check. By the results of the check we define diagnose
of the system. Practically, the process of the algorithm working out
begins from the construction of the table of functional failures and
calculation of information quantity, got during every check, and then
the algorithm of failures searching is formed. During this there are
considered certain functional system of the aircraft, structure of
its aggregates and principle of their work, and also parameters,
which characterize system workability and signs of failures and
defects appearance. Aggregates, which are included to the system, in
the process of operation fail. Failures happen for different reasons,
among which the most wide-spread are wear and failure of the
aggregate’s elements, shrink of the springs, loose of
pressurization, jamming of slide valves, filter clogging etc. Certain
type of the aggregate failure is considered as its diagnose Di, which
is followed by certain signs (parameters) Xi, which become evident in
operation and are fixed during use of the system by the assignment or
during making of maintenance. Functions of the failures are made for
hydraulic system of retraction-extension of landing gear of the
aircraft, table 1.
Functions
of the system failures.
Table 1
|
Component
name
|
Diagnosis
(Di)
|
Malfunction
features
(Xj)
|
Number
of diagnosis appearance
(n)
|
Probability
of diagnosis appearance
(Qi)
|
|
|
X1
|
X2
|
X3
|
X4
|
X5
|
|
|
|
AAHE
|
D1
|
+
|
+
|
|
|
|
4
|
0.25
|
|
D2
|
+
|
|
|
|
|
5
|
0.31
|
|
ACM
|
D3
|
|
|
+
|
|
|
3
|
0.
19
|
|
NSD
|
D4
|
|
|
+
|
|
|
1
|
0.06
|
|
Pipelines
|
D5
|
|
+
|
|
|
+
|
2
|
0.13
|
|
Check
valve
|
D6
|
|
|
|
+
|
|
1
|
0.06
|
|
*
|
2
|
2
|
2
|
1
|
1
|
|
|
|
**
|
D1
D2
D12
|
D1
D5
D
15
|
D3
D4
D36
|
D6
|
D5
|
|
|
Abbreviations
and reference designation:
Diagnoses:
D1
- incorrect tubes` installation
D2
- non-pressurized internal cavity
D3
- weakened fitting
D4
- damage of a housing
D5
- non-pressurized part of line
D6
- wrong installation
* -
number of diagnoses that are controlled by this sign
**
- diagnoses, which are controlled
Signs
of failures:
X1
- raised temperature in pipeline
X2
- unsatisfactory pressurization of right mainline
X3
- unusual noise in the cabin
X4
- no air supply to ACS
X5
- fumes in passenger cabin
Evaluation
of probability of diagnoses appearance is calculated by the formula:
,
,
(1)
where
ni - number of cases of appearance of і
diagnose; N - number of all diagnoses of system aggregates.
In
the table 1 there are written aggregates’ names, their possible
diagnoses, and their signs. If some sign from the totality Xj
corresponds to diagnose Di on the crossing of their columns we put
the sign (+), that shows stochastic relation between them. Presence
of relations between diagnoses and signs is defined by the making of
engineering analysis of work of the system and its aggregates with
taking into account possibilities of system control, which is used on
the given type of aircraft. Diagnoses are chosen by statistic data
that are collected on operational enterprises in the process of
operation of aviation technique.
For
functional systems of the aircraft it is typical the appearance
simultaneously several signs during failures appearance, that is
underlined presence of several signs (+) in the columns of the table
1.
Data
analysis attests that some signs may be shown in appearance of
different failures and defects of aggregates, that’s why in
penultimate line there are written number of diagnoses, which are
controlled by each sign. If some sign is shown in appearance of
several diagnoses, then its appearance may be caused by appearance of
either one diagnose or another one, and also when diagnoses appear
together. That’s why in the last line of the table there are
written possible combinations of the diagnoses. In spite of that
during analysis of functional systems of the aircraft it is
considered that simultaneous appearance of several types of the
failures of aggregates, but from theoretical point of view accounting
uncertainty of information about the state of aggregates, in the case
of appearance of such situation it is necessary to take into account
this possibility. For usage of mathematical apparatus of theory of
information it is necessary to define values of probabilities qi of
appearance of this or that diagnose. For their calculation in
penultimate column of the table there are written number of cases of
appearance of each diagnose by statistical data, which are collected
for some period of AT operation. It is evident that it is not
possible to calculate probability of diagnose appearance, but it is
possible to get their evaluation. Control of one or several
parameters (signs) of the system, which is called check, gives
information j about presence of aggregate diagnose. Quantity of
information, accounting that we consider dichotomy, is evaluated as
difference between level of system state uncertainty before H (S) and
after check H (S/nj):
J=
H (S) - H (S/nj). (2)
Level
of uncertainty of system states before the check in condition that
system can be unworkable as a result of appearance of only one any
diagnose from their general quantity with probability qk is
calculated by the formula:
(3)
Level
of uncertainty of system states after the check:
(4)
Where
-
total probability of appearance of m diagnoses, which are enveloped
by the check ni; qn - probability of appearance of diagnose from
totality m, enveloped by the check ni.
Then
(5)
Setting
of the diagnose in the system should be begun from the check ni,
which carries the greatest quantity of information. As a result of
making of the check table 1 is transformed. We will two tables as a
result of this. If in the first check it is fixed that sign was
confirmed (such situation is signed as R = 1), diagnoses should be
looking for in that totality, with which this sign has stochastic
relation. Second step for refinement of diagnose is made with the
help of transformed table, which includes m diagnoses. As in the
previous case setting of diagnose will be made with taking into
account quantity of information, got during second check. Quantity of
information in this case is calculated by the formula:
(6)
If
R = 0, that means sign is not confirmed, then search of diagnose is
made by another transformed table, which includes diagnoses from the
number m+1…N. in such case quantity of information is
calculated by formula:
(7)
For
usage of expressions (1) - (7) it is made table of
calculated-informational data (table 2).
Table
of calculated-informational data.
Table 2
|
№
|
Parameters
and features
|
System
components diagnoses
|
Sq
|
I
|
|
|
D1
|
D2
|
D3
|
D4
|
D5
|
D6
|
|
|
|
1
|
X1
|
0.25
|
0
|
0
|
0
|
0
|
0
|
0,25
|
0.81
|
|
2
|
X1
|
0
|
0.31
|
0
|
0
|
0
|
0
|
0,31
|
0.88
|
|
3
|
X1
|
0.25
|
0.31
|
0
|
0
|
0
|
0
|
0.56
|
0.98
|
|
4
|
X2
|
0.25
|
0
|
0
|
0
|
0
|
0
|
0.25
|
0.81
|
|
5
|
X2
|
0
|
0
|
0
|
0
|
0.13
|
0
|
0.13
|
0.55
|
|
6
|
X2
|
0.25
|
0
|
0
|
0
|
0.13
|
0
|
0.38
|
0.95
|
|
7
|
X3
|
0
|
0
|
0.
19
|
0
|
0
|
0
|
0.
19
|
0.69
|
|
8
|
X3
|
0
|
0
|
0
|
0.06
|
0
|
0
|
0.06
|
0.32
|
|
9
|
X3
|
0
|
0
|
0.
19
|
0.06
|
0
|
0
|
0.25
|
0.81
|
|
10
|
X4
|
0
|
0
|
0
|
0
|
0
|
0.06
|
0.06
|
0.32
|
|
11
|
X5
|
0
|
0
|
0
|
0
|
0.13
|
0
|
0.13
|
0.55
|
Algorithm
for checking of aggregate state. Table
3
|
№
row
|
|
Sq
|
I
|
|
D1
|
D2
|
D3
|
D4
|
D5
|
D6
|
|
|
|
1
|
0.25
|
0
|
0
|
0
|
0
|
0
|
0,25
|
0.81
|
|
2
|
0
|
0.31
|
0
|
0
|
0
|
0
|
0,31
|
0.88
|
|
3
|
0.25
|
0.31
|
0
|
0
|
0
|
0
|
0.56
|
0.98
|
|
4
|
0.25
|
0
|
0
|
0
|
0
|
0
|
0.25
|
0.81
|
|
5
|
0
|
0
|
0
|
0
|
0.13
|
0
|
0.13
|
0.55
|
|
6
|
0.25
|
0
|
0
|
0
|
0.13
|
0
|
0.38
|
0.95
|
|
7
|
0
|
0
|
0.
19
|
0
|
0
|
0
|
0.
19
|
0.69
|
|
8
|
0
|
0
|
0
|
0.06
|
0
|
0
|
0.06
|
0.32
|
|
9
|
0
|
0
|
0.
19
|
0.06
|
0
|
0
|
0.25
|
0.81
|
|
10
|
0
|
0
|
0
|
0
|
0
|
0.06
|
0.06
|
0.32
|
|
11
|
0
|
0
|
0
|
0
|
0.13
|
0
|
0.13
|
0.55
|
|
#
|
D1
|
D2
|
Sq
|
I
|
|
1
|
0.44
|
|
0.44
|
0.98
|
|
2
|
|
0.55
|
0.55
|
0.99
|
|
4
|
0.44
|
|
0.44
|
0.98
|
|
5
|
|
|
1.00
|
0
|
|
6
|
0.44
|
|
0.44
|
0.98
|
|
7
|
|
|
1.00
|
0
|
|
8
|
|
|
1.00
|
0
|
|
9
|
|
|
1.00
|
0
|
|
10
|
|
|
1.00
|
0
|
|
11
|
|
|
1.00
|
0
|
|
#
|
D3
|
D4
|
D5
|
D6
|
Sq
|
I
|
|
1
|
|
|
|
|
1.00
|
0
|
|
2
|
|
|
|
|
1.00
|
0
|
|
4
|
|
|
|
|
1.00
|
0
|
|
5
|
|
|
0.29
|
|
0.29
|
0.86
|
|
6
|
|
|
0.29
|
|
0.29
|
0.86
|
|
7
|
0.43
|
|
|
|
0.43
|
0.98
|
|
8
|
|
0.13
|
|
|
0.13
|
0.56
|
|
9
|
0.43
|
0.13
|
|
|
0.56
|
0.99
|
|
10
|
|
|
|
0.13
|
0.13
|
0.56
|
|
11
|
|
|
0.29
|
|
0.29
|
0.86
|
|
#
|
D5
|
D6
|
Sq
|
I
|
|
1
|
|
|
1.00
|
0
|
|
2
|
|
|
1.00
|
0
|
|
4
|
|
|
1.00
|
0
|
|
5
|
0.65
|
|
0.65
|
0.93
|
|
6
|
0.65
|
|
0.65
|
0.93
|
|
7
|
|
|
1.00
|
0
|
|
8
|
|
|
1.00
|
0
|
|
10
|
|
0.29
|
0.29
|
0.86
|
|
11
|
0.65
|
|
0.65
|
0.93
|
|
#
|
D3
|
D4
|
Sq
|
I
|
|
1
|
|
|
1.00
|
0
|
|
2
|
|
|
1.00
|
0
|
|
4
|
|
|
1.00
|
0
|
|
5
|
|
|
1.00
|
0
|
|
6
|
|
|
1.00
|
0
|
|
7
|
0.76
|
|
0.76
|
0.79
|
|
8
|
|
0.23
|
0.23
|
0.76
|
|
10
|
|
|
1.00
|
0
|
|
11
|
|
|
1.00
|
0
|
Description
of obtained algorithm
So,
using this algorithm of malfunctions discovering we can compose an
order of system checking, namely, steps of inspection (diagnostics).
These steps are:
1.
Check internal cavity of air-to-air heat exchanger
2.
Check correctness of tubes installation
3.
Check fittings of air-cycle machine
4.
Inspect noise suppression device housing for cracks
5.
Inspect places of pipeline and other aggregates mounting
6.
Check correctness of installation
List
of abbreviations:
1.
ACS - air conditioning system
2.
AAHE - air-to-air heat exchanger
3.
ACM - air-cycle machine
4.
NSD - noise suppression device.