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 failuresof Air Conditioning System of TU-154 '
the work isperformed by
the student of505 FLA
D. Zhuravel
the work ischecked 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-ConditioningSystem of Tu-154
The air conditioning system (ACS) provid
es pressurization,ventilation, heating of the pressure cabin. Air is taken from the 9thcompressor stage of three engines in amount of 5000-5500 kg/h, temperature isbetween 240 - 350 В° C and differential pressure is 7,5 - 9kg/sm2.
The ACS supply conditioned air to the control cabin, passengercabin, electronic equipment compartment, forward cargo compartment, airconditioning distribution bay and aft cargo compartment, and provides constantpressure and temperature in pressure cabin. It is maintained by air flowregulation. Air supply to the air conditioning system is furnished by thepneumatic 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 coldair required for air conditioning is provided by air conditioning packs. Passingbleed air through a primary heat exchanger, an air cycle machine, and asecondary heat exchanger cools the air sufficiently to handle any coolingsituation required. A ram air system provides coolant air for the heatexchangers.
In each of three pipelines there is regulated check valve to preventair masses flow in returned direction. Pipelines attachment is realized withthe 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 В° C. AAHE is thefirst stage of cabin air cooling maintained by atmosphere ram-air flow. AAHE isone-flow.
In case of overcooling there is by-pass line to bleed off airbesides AAHE. Before air enters pressure cabin the main line is divided on twoparallel pipelines: right and left.
They lead to two main cooling stages, where AAHEs and air cyclemachines installed. Here, after AAHE air temperature should be not more than60 В° C, behind ACM - 10 - 20 В° C. In case of overcooling there are two by-passlines besides AAHE and ACM. By-pass of air is carried by air distributersmounted on AAHE. Regulation of distributers is automatic or manual.
ACM has two functions: to cool air flowing from AAHE being secondarystage of air cooling; to suck scavenged air through AAHE during ACS operationbeing on the ground. There is also oil system of ACM. It `s function is tolubricate ACM bearings.
Then air comes to distributive main line where air mixtures and airdistributers are located.
Air mixture is used to mix cold and hot air. Air distributors of hotand 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 thetheory 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, theprocess of the algorithm working out begins from the construction of the tableof functional failures and calculation of information quantity, got duringevery check, and then the algorithm of failures searching is formed. Duringthis there are considered certain functional system of the aircraft, structureof its aggregates and principle of their work, and also parameters, whichcharacterize system workability and signs of failures and defects appearance. Aggregates,which are included to the system, in the process of operation fail. Failureshappen for different reasons, among which the most wide-spread are wear andfailure of the aggregate's elements, shrink of the springs, loose ofpressurization, jamming of slide valves, filter clogging etc. Certain type ofthe aggregate failure is considered as its diagnose Di, which is followed bycertain signs (parameters) Xi, which become evident in operation and are fixedduring use of the system by the assignment or during making of maintenance. Functionsof the failures are made for hydraulic system of retraction-extension oflanding 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...
