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. ............
