1.

INTRODUCTION

In all technical devices (mechanical, hydraulic, pneuma-

tic and so on) operating in the changing conditions of lo-
ading, especially cyclically ones, it is the probability to
VIBRATION OF TURBINE ENGINES
occur the resonance phenomenon. Sometimes this phe-
AS THE CRITERION OF PRODUCTION nomenon is used, for example, to improve the filling up the
cylinders of piston engine, by suitable tuning of the fre-
QUALITY OF ROTOR ASSEMBLIES
quency of vibration of air column in the inlet pipe according
AND THEIR CURRENT TECHNICAL STATE to the rotational speed of engine. In other way, this phe-
nomenon can be used to estimate the crack magnitude of
compressor or turbine blades of the jet engine during ope-
ration. The determining of the natural frequency range
(scatter of this frequency) of engine units can be the measure
of the production quality of the given manufacturer.
Stefan SZCZECIŃSKI Frequencies and amplitudes of vibration of the running
Włodzimierz BALICKI aircraft turbine engine depend on the rotational speed of
Institute of Aviation rotors and flight conditions. In the dynamic (transitory)
states of operation so typical in the case of combat heli-
copters and airplanes, it is difficult to determine the
operation ranges in which the resonance can occur par-
ticularly.
A lot of polytechnic textbooks relating to aircraft power-
The article deals with the problem of vibration of the plants advise to avoid the even numbers of blades in the
aircraft turbine engines with special attention devoted to the blade ring of rotating machines (rotors and guide rings of
unbalance stages of rotors. This problem is rarely mentio- compressors and turbines) and it would be the best if they
ned in the specialist engine reference books. It was shown have the prime numbers of blades. It is also thought that it is
that the amount of information contained in the data got unacceptably to apply the equal numbers of blades in the
from the permanently made measurements of amplitudes several stages of rotor assembly. Indeed, in the first
and frequencies of the transverse vibration of engines, par- „Dervent” and „Nene” jet engines (and their tracings) pro-
ticularly in case of the multi-rotors, can not be overes- duced in series by the Rolls-Royce the number of rotor
timated. The relationships of these parameters to: the con- blades of compressor was equal to 29 when the number of
structional form of rotors, the quality of their realization and guide veins of diffuser was 18. Such solution effectively
assembling, the effect on the clearance changes in supports protected compressors of these engines against the appea-
and the possibilities to detect emergency states of engines rance of dangerous resonance of vibration. However, nowa-
have been presented. days the two-spool jet engines are in operation (such as the
D -30KU powered the Ił-62M and Tu-154M airplanes), in
which the four-degree turbine driving the ventilator
assembly has the identical rotor carrying disk with equal
numbers of rotor blades and guide veins in all stages.
Undoubtedly, this is the result of tendency to reduce the pro-
duction costs of engines (to obtain the unification of
assemblies). Also in the most modern engines such as the
General Electric CF-6 families, the even number of ven-
tilator blades have been applied. In this case, the con-
structors made possible to replace the broken-down blade
(ventilator blades are particularly subjected to damage by the
bird strikes or other „alien bodies” suction through engine,
for example, the crumbs of concrete from landing strip)
together with the second one, fixed on the opposite side of
carrying disk, by the set of reserve blades. It is done without
necessity to demount the engine and check the rotor balan-
cing. These examples illustrate the fact that rotor blades and
guide vanes are the source of disturbance of stream flowing
through the „gas track” of engine and can force the dan-
gerous vibration, particularly when the forcing frequencies
(most often dependent from a rotational speed of rotors) are
close to the natural frequency of any engine units (usually
blades).
In engines of the combat airplanes these forced input
functions come from the changes of flight condition (density
and temperature of air and combustion gases are changed

VIBRATION OF TURBINE ENGINES AS THE CRITERION ... 9

considerably due to the considerably changes of the height individual stages and shaft sections are made, and next after
and speed of flight), the changeable modes of engine their assembling, the static and dynamic balancing of com-
operation, and the action of mechanization assemblies (such plete rotors are conducted. During engine operation on the
as: air bleeding valves, adjustable guide rings of compres- nominal range, the real unbalance degree of rotors strongly
sors, and mechanism to control cones and claps of the air depends from their transverse stiffness. For these reasons,
inlets and the cross-section of escape nozzles) in the fluid- the drum-disk constructions, with the possibly small span of
flow channel. Particularly dangerous are the cases when supports, are most profitable. The majority of aircraft turbine
inlet channels of compressors are not axially-symmetrical engines have the separate rotors of compressors and turbines
placed. The source of similar problems can be the non- with own bearings, but often with the common central bea-
uniform temperature field of gases before the turbine or into ring. Such solution makes possible to relief the internal
the engine afterburner. bearing from reactionary unbalancing forces of every sepa-
The above mentioned factors create the necessity to carry rate rotor through the suitable „adjustment” of the mutual
out experimental researches to obtain the information about angular position of compressor and turbine rotors.
the real values of vibration amplitudes which can appear The forces due to the unbalancing depend only from the
during the flight. Such study can be performed with the labo- square of a rotor rotational speed, of course at assumption
ratory precision in the stationary, so called, „height” test bed. that the mass centre of rotor does not change its position in
The engine subjected to such tests should be placed in the relation to its rotation axis. The change of a mass centre
complete airframe and controlled exactly in the same way as position during the engine operation can be caused by
in the specific flight task, e.g. the combat mission. following factors: the small transverse stiffness of rotor (and
It seems that both the specialist textbooks and polytechnic its deformation), the decrease of mass (e.g. to tear the part of
studies devote too little attention to effects of the unbalance rotor blade off), and the clearance increase in the rotor sup-
degree of the aircraft turbine engine rotor assemblies on their porting bearing.
loading and dynamic deformation. These unbalance also The loadings due to the unbalancing of rotors occur as
cause the loading of bearings, engine frames and the fixing a result of the action of mass forces during the rotor rotation;
engine units to the airframe. As well, it has not been any in case of the gas-dynamic forces depend not only on the
attempt to estimate the influence of these loading on the con- mode of engine operation (so indirectly from a rotational
struction durability and the flight safety. The determination speed) but also from the altitude and speed of flight (exactly
of effects of the rotor unbalancing degree on the amplitude of from the air density in an engine inlet).
transverse loading of airframe assemblies is relatively simple, The continuous measurement and recording of ampli-
but it is difficult to estimate the changes in airframe durability tudes and frequencies of the engine frame vibration in the
due to this unbalance. All of this put the stress on the research chosen plane (e.g. perpendicular) makes possible to create
workers to intensify the cognitive works in this field. the special diagnostic parameter which can be called the
The basic problem to determine the value of rotor unba- „coefficient of flight safety”.
lance degree is to supply the necessary power to reach the
suitable rotational speed of the entire rotor during measu- 2. BALANCING OF ROTORS
rements. In the manufacturing process, measurements of the
rotor unbalancing are practically made at the rotational It was known from a long time, that in some constructional
speed typically from 10% to 20 % of its nominal value. cases (e.g. bicycle wheels) the static balancing is quite suf-
Hence, if we assume that measuring error obtained in these ficient because of their small circumferential speeds and flat
conditions is only ± 1%, then in a operation range the inac- structure. The units rotated at greater speeds and having the
curacy of a loading estimation due to the rotor unbalancing considerable „along axis” sizes have also in addition requi-
grows up to over ±25% – 100 % (because centrifugal force red the dynamic balancing (e.g. wheels of personal cars).
is proportional to the square of rotational speed). It is pos- The principles of the static and dynamic balancing of rotated
sible to increase the measurement accuracy of a rotor unba- blocks were explained in Fig.1. For simplicity, unbalanced
lance degree by location of this tested rotor in the vacuum masses were imported to the common plane. Hence, it cle-
chamber (or helium filled chamber) and increase its rota- arly follows that the static balancing can be recognised to be
tional speed to the operation value. sufficient only for the flat axial symmetrical disks (such as
Starting from time of the origin of turbine engines, the e.g. rotor disks of low pressure turbines).
compressor and turbine rotors are statically and dynamically The multistage assemblies of these turbines and multi-
balanced. The case of the turbine of the Armstrong-Siddley stage compressor rotors are the axially extended rotated
Viper ASV - 8 engines was perhaps only one exception, blocks having a lot of the mutually connected disks, drums
which the balancing relied on the shortening tongues (lea- and shafts with the palisades of rotor blades severally placed
ding edges) of rotor blades and according to this the requi- on the external rings of disks.
rement of a static balancing was only fulfilled. This solution The process of balancing, both static and dynamic, de-
comes maybe from the following reasons: disk of this turbi- pends on the removal of the mass from the „heavier” places
ne was exceptionally flat, the number of blades was relati- (by milling, polishing or scraping) or the addition of the
vely large (about 100), and the balancing machines being at mass (e.g. in form of suitable screws) in the „lighter” places
that time in disposal of producer were busy to perform the of rotors (as was explained in Fig. 2).
measurements of rotors of radial compressors used for the
supercharging of piston engines.
In the extended (along axis) axial rotors of multistage
compressors and turbines the preliminary static balancing of

10 TRANSACTIONS OF THE INSTITUTE OF AVIATION NO. 183

 thrust jet engines. The location one of supports „inside” the
ventilator rotor, almost in plane of its centre of mass allows
to apply only the static balancing and causes that the critical
rotational speed of this rotor theoretically aims to infinity.
In each turbojet engine the compressor rotor is mechani-
cally coupled with turbine rotor (according to the principle
of operation). In coupling of these assemblies two methods
are applied. The first one depends on the factory adjustment
of their common position, e.g. by the special asymmetrical
splined coupling. Using this method the Rolls-Royce Dervent
and Nene family engine rotors (and their developmental ver-
sions) were coupled. In the second method, called as Ameri-
can one, compressor and turbine rotors are coupled in such
a way, that vectors of residual unbalancing of compressor
and turbine rotors have the opposite directions. This was
Fig. 1. Balancing principles of axially-symmetrical blocks a) sta-
graphically shown in Fig. 4.
tic balancing; b) dynamic balancing

Fig. 3. Basic schematic diagram of rotor bearings: a) two-point

support; b) three-point support; c) bearings of two-spool struc-
ture; d) bearings of three-spool structure
Thanks to such method of the rotor assembly the unba-
Fig. 2. Methods of rotor balancing: a) removal of mass; b) addi- lancing vector of an entire assembly is the smallest (smaller
tion of mass: 1 – shortening of blade top; 2 –removal of material than each unbalancing vectors of component rotors). Howe-
from the side surface of disk; 3 – balancing screw; 4 – balancing ver in this case, it is necessary to ensure the possibility to
mass couple the turbine rotors with compressor rotor in the va-
The process to join the compressors to turbines in the rious mutual angular settings. It should also be possible to
entire rotor assemblies requires the thorough analysis. The perform this operation in the engine repairing shops. This
best precision is obtained for the integral constructions with method of rotors coupling also allows to compensate the ac-
bearings placed in two frame supports. The schematic dia- tion of unbalancing forces on extreme supports by using the
gram of such supported assembly was shown in Fig. 3. additional balancing mass.
The stiff structure guarantees the balancing stability du- The essential restriction in the rotor balancing process
ring the operation and it can only be disturbed by the erosive (especially compressors) is the value of necessary power to
losses (chipping) of rotor blades. On the same figure was keep their rotation with the sufficient speed to precise mea-
also shown the „classic” position of supports of the single- sure the unbalancing forces in the planes of rotor supports.
stage ventilators rotors applied in the constructions of huge The values of power taken by compressors of present-day jet

VIBRATION OF TURBINE ENGINES AS THE CRITERION ... 11

engines reach the hundreds of kilowatts (on maximum po-
wer ranges even many megawatts). Although the necessary
external powers to keep turning rotors of compressors, ven-
tilators and turbines during the testing are smaller than in
case of the operating engine but these necessary external
power is the serious restriction for the present-day balancing
machines. From this reasons the border possibilities of the
applied balancing machines practically allow to make the
measurements on rotational speeds reaching only just a do-
zen percentage of the nominal rotational speed of rotors. It is
possible to get the somewhat higher rotational speeds pla-
cing the tested rotors in vacuum chambers or in chambers
filled with helium (density of helium is about seven times
less than density of air).

Fig. 5. General schematic diagram of engine and temporary an-

gular position of vectors of unbalancing forces: a) engine; b) ro-
tor of low pressure ( WNC); c) rotor of gas producer (WWC);
d) resultant force of both rotors: 1 - vibration pick-ups; 2 - plane
of supports; 3 - supports
In the two-spool engine (with rotors coupled only gas-
dynamically) the function graph of total vertical component
Fig. 4. Effect of assembly method of rotor assemblies on their of forces, coming from both rotor unbalancing, imposed on
balancing: a) factory adjustment of mutual angular position of the frame of engine is cyclically changing and depends from
rotors; b) optimum position set in repair shop the temporary slip of rotors. Figure 6 shows: the temporary
values of vertical component of inertia forces, coming from
The measurement of the unbalance degree value of rotors
the unbalancing, as a function of the angular position (sepa-
in the factory or repair shop is the important criterion to
rately for both rotors) and the resultant force as a function of
estimate the quality of assembly, repairs and manufacturing.
the angular position of gas producer rotor.
Observation of changes of the unbalance degree value du-
The above introduced considerations allow to calculate
ring rotor operation makes possible to estimate the current
the value of forces coming from the unbalancing. The expe-
technical state of engine and to predict the safe usage period.
rimental verification of these calculations is made through
The reducing of the unbalanced degree of turbine engine ro-
processing of electronically recorded displacements, accele-
tors has the significant influences on its structure durability.
rations or (usually) the speeds of displacement as a function
of their occurrence frequency.
2. ENGINE TRANSVERSE VIBRATION

The main source of the transverse vibration of a turbine

engine are inertia forces acting on rotors when, due to the
unbalancing, the mass centres of rotors do not coincide with
their rotation axes.
The general schematic diagram of engine, together with
the location of sensors and the measurement of vibration
directions, was shown in Fig. 5. It was also presented the
drafts of movements of vectors of unbalancing forces (F) as
a function of the temporary angular position of rotors of two-
spool jet engine and the resultant forces of both rotors. The
rotational speeds of both rotors are different so the values of
unbalanced forces are different too. In operation conditions,
in case of rotors balanced with the similar accuracy - the un-
balancing forces of the high pressure rotor (gas producer) are Fig. 6. Changes of vertical components of unbalanced forces Fy
several times greater than the low pressure rotor. vs. angular position of rotors: NC – low pressure; WC – high
pressure; NC+WC – resultant forces of both rotors

12 TRANSACTIONS OF THE INSTITUTE OF AVIATION NO. 183

 Figure 7 shows the characteristic dependences of vibra- trifugal force. The bearing races can also to be reeled in ran-
tion amplitudes (as a function of frequency) due to the unba- ge of the flexibility of supports in which are placed. Fig. 8
lancing forces of the bypass two-spool jet engine during shows how the mentioned factors have an influence on the
operation on the maximum power. The frequency of occur- radial displacement of mass centre of rotor in relation to its
rence of the largest amplitudes (peaks) allows to identify, by rotation axis.
comparison of rotational speeds of individual constructional
units, which rotor or unit creates these peaks (e.g. the rotor
of oil froth breaker or the rolling bearing cage). The predo-
minant amplitudes are generated by rotors which unbalan-
cing is changed during operation. Monitoring of these chan-
ges allows, in time, to notice the damages which can cause
the break-down of engine e.g. the excessive wear of bearing,
or chipping of part of rotor blade. Particularly essential, it is
suitably early to detect the appearance of the vibration am-
plitude having the frequency twice larger than the basic fre-
quency resulting from the rotational speed of rotor (f =
= n/60 [1/s]). This symptom points that the circumferential
clearance of a bearing race already reached the value causing
the loss of contact point (separation of the rolling elements
from a bearing race). As a result, the striking elimination of
clearance occurs - twice during one turn. This threatens that
the bearing wear and the liquidation of tip clearance of rotor
blades (friction between blades and a frame occurs) will be
accelerated and the break-down of engine will come shortly.

Fig. 8. Movement of mass centre of rotor due to the action of un-

balancing forces taking into consideration: a) eccentric of mass
centre; b) deformability of rotor; c) radial clearance in one bea-
ring; d) deformability of one support
In all of these cases it was assumed, that one of rotor
Fig. 7. Amplitude (A) of engine vibration vs. imposed frequency supports is undistortable and the bearing placed in it has no
(f): WC – from rotor of high pressure; NC – from rotor of low
radial clearance. The radial movement of the mass centre of
pressure
In order to practically use the above mentioned consid- rotor (m) initially has the value of the eccentric (e) to which
erations to diagnose the specific engine and the entire popu- in turn are added: the rotor deflection (y), the displacement
lation of engines, it is necessary to find the effect of the ope- (δł) coming from the bearing clearance, and the displace-
ration conditions, constructional and assembly features on ment (δp) due to a susceptibility of support.
the formation of vibration. The above mentioned description of main factors influ-
The position of mass centre of rotor placed in the frame encing on the radial movement of a mass centre of rotor in
bearing has been effected by their radial clearances. In the relation to its geometrical axis explains, that the construc-
state of rest of rotor and its small rotational speed they are tional (rotor stiffness and stiffness of bearing frame sup-
eliminated in the direction of the action of gravitational ports) and assembly (bearing clearance) features have the si-
forces. When the rotational speed increases, the transverse milar (comparable) influence on the position of mass centre
displacement of mass centre of rotor increases as well to in operation conditions of engine as the residual unbalancing
reach the value of its deflection. After crossing the rotational of rotor obtained during its manufacturing and assembly
speed, at which the centrifugal force acting radially on the process. Besides the above enumerated factors, the position
moved mass will cross the gravitation force it will happen of mass centre of rotor has also been changed by the thermal
the circumferential „reeling” of rotor on external bearing deformations of rotor component units, frame supports and
races to eliminate the radial clearance of bearings accordin- bearings (not always the axially-symmetrical ones). These
gly to the temporary direction of the resultant vector of cen- thermal deformations strongly depend from the current
loading of engine (thrust or power), the height and speed of
VIBRATION OF TURBINE ENGINES AS THE CRITERION ... 13
flight, and even the climatical zone where the airplane or universally applied. Accordingly to their light constructions
helicopter are used. all supports of aircraft engines are flexible in the notable
During the engine operation occurs: the bearings wear degree, but in this case the flexibility was intentionally intro-
(abrasion of races and rolling units), the increase of bearing duced. In Fig. 9 was presented the typical constructional
fitting in frame supports and the erosive decreasing of a ma- methods to get the required flexibility of supports of aircraft
terial in rotor blades. All of these have the influence on the engines. The first of them (Fig. 9a) – the oldest one, was
change of position of rotor mass centre and its unbalancing applied in the Rolls-Royce Dervent and Nene family engi-
degree. For each specific engine the changes of the unbalan- nes, the second (Fig. 9b) was also worked out at this firm
cing of rotors depend on the kind of mode of its operation. and was applied among others in the Spey engines. The spe-
Nowadays almost universally, it is used the method in which cial attention deserves the solutions shown in Fig. 9c and 9d.
the safe usage period of engine is estimated according to its In these solutions the vibration was damped by the insertion
current technical state. In this method it is necessary to com- of oil into the closed spaces between the external race of be-
pare the initial values of engine (new or repaired) diagnostic aring and its support in a frame. This oil, under the action of
parameters with the current ones. This should also be related changing loading forces of the bearing, squeezes through the
to the vibration profile determined on the engine built-up in crevices in the flexible insertions.
the airframe. The introduction into the structure of aircraft turbine en-
gines the flexible bearing supports for ventilators, compres-
sors and turbines rotors has considerably changed the dyna-
mic characteristic of rotor assemblies and the engine vibration
spectrum transferred on the airframe. The favourable effect,
which comes from these, is the quite good reduction of
vibration amplitudes transferred on the structure of airframe
or even their total removing. This mainly relates to the vibra-
tions created by the residual production unbalancing of ro-
tor. This unbalancing increases in time during the long-la-
sting operation as a result of the formation of erosive losses
of rotor blades and also due to the dusts settled down on
them. The flexibility of rotor supports significantly reduces
the ranges of critical speeds of rotors but it seldom, if ever,
is the desirable feature of engine. The rotors of aircraft
engines are usually the subcritical ones. It is thought that
operation range of their rotational speeds should be remote
from the critical range at least of 20 to 25%. These values
come, first of all, from the experience obtained on the
following base : the determination of causes of the break-
down of engines, the analysis of parameter changes recorded
during the operation conducted according to the technical
state of engines and the manufacturing tests conducted at the
extreme loading of engines.
3. CHANGES OF AMPLITUDES AND
FREQUENCIES OF VIBRATION
DURING OPERATION OF ENGINES
In aviation, the use of turbine engines is unusually diver-
sified because their changing loading coming from: the air-
frame demands on power or thrust, the operation conditions
dependent from the climatical zone, a time of the year, the
dustiness degree of air and other factors relative to the kind
of mission realized by airplane or helicopter. These mentio-
ned factors, first of all, have the influence on the progressive
erosive and corrosive wearing of parts located in the fluid-
flow channels of engines and the bearings which support the
rotors. It comes from the experience that the largest loadings
of engine occur in case of the fighter airplane during the air
Fig. 9. Principles of construction of flexible supports of rotors:
a) with flexible rib; b) with susceptible pegs; c) with wavy flexible fight. In this case the transverse overloads of rotors reached
insertion d) with packet of tin insertions 1 - shaft; 2 - bearing disc even 8 to 10g. The repeated overloads can cause the stiffness
of rotor; 3 - bearing; 6 - flexible rib; 7 - flexible plugs; 8 - wavy changes of rotors due to permanent deformations of the
flexible insertion; 9 - packet of tin insertion screw joints of drums and shafts collars and the changes of
bearing clamps placed in supports. As a result, the deflection
In order to soften the vibration transferred from rotors of rotor and the bearing clearances increase so in effect the
through bearings on: the supports, the different units of en- progressive growth of the rotor unbalancing degree has been
gine and its suspension in airframe - the flexible supports are noted.

14 TRANSACTIONS OF THE INSTITUTE OF AVIATION NO. 183

 The accelerated wear of rotor bearings happens particu-
larly in case of engines of helicopters often started from the
accidental landing strips. In this case the stirred up dust is
sucked by the running engines (here, it should be noted that
the turbine engine demands about four times greater of air
than the piston engine having approximate the same power).
Similarly, the large amount of dusts is sucked by the power-
ful bypass jet engines installed on the present-day transcon-
tinental passenger airplanes. First of all, it is due to the huge
intensity of air flow which reaches from 600 to 800kg/s du-
ring take-off and landing when, so called, the thrust reverse
is switch on to slow down. From these reasons the rotor bea-
rings of aircraft turbine engines are subjected to the special
supervision to escape from the break-down in flight. It is
widespread method to control the wear state by the observa-
tion of amount of sediment („file dust”) on magnetical corks
placed in channels draining oil from every bearing. The Fig. 11. Observed amplitudes of vibration(A) vs. operation time of
different method applied in the bearing diagnostics used the engine: 1 – „soft” condition of engine operation; 2 – „hard” con-
addition of the various chemical element into the material of dition of engine operation; 3, 3’ – ranges of safe operation
rolling elements (rollers and balls) to permit the identi-
fication of wear products coming from the specific bearing In order to easily interpret of such records the hypothetic
(during testing of the oil samples). extreme curves were marked: for the „soft” condition of en-
In one of the leading American manufacturer the gine operation (e.g. in case of a transcontinental passenger
„shrewd” method, to diagnose the particularly heavy loaded airplane) and for the „hard” condition of engine operation
and hard to reach rotor bearing, has been worked out. In this (e.g. in case of operation in a military aviation training
method, on the internal bearing race, the flat surface of about school). The shown differences indicate the necessity to
2mm width was made. This flat surface makes up the conduct individual observations of the technical state of
transverse „groove” for the rolling over rollers (draft of this every engine in order to lengthen its operation time to the
solution was shown in Fig. 10). When the every roller goes borders of its durability keeping in the same time the
over this groove the acoustic signal (and not only) is gene- required margin of safe flying.
rated. The decrease of these signal frequency in relation to In companies using in similar way the considerable
the early registered signals of rotors of new engines, of number of airplanes of one type (in the similar climatical
course for the same of rotational speed, indicates the growth conditions) – as it occurs for example in case of the big
of slip of the rollers in bearing races (here in the internal airlines – it is possible to conduct the continuous observation
race) due to the increase of the bearing clearance. The of the current technical state of the entire population of engi-
further development of phenomenon leads to state shown in nes. Figure 12 is a sketch of the relationships of dynamic
Fig. 8c. features area of engines as a function of the operation time.
The quantitative character of the distribution of its features
in population was marked. On both figure (11 and 12) the
admitted by manufacturer level of vibration amplitudes and
resulting from this the limitation of the safe operation time
were marked. Conducted in this way, the continuous mon-
itoring of dynamic features of the entire population of engi-
nes can make up the basis to predict the overhauls, replace
the modules and pass the engines to be repaired. All of these
make possible to achieve the operational availability of the
possessed group of airplanes.
Recording and the continuous observation of the amplitu-
des and frequencies of engine vibration give the possibility
to detect in time, for example, the growing wear of bearing,
the break of part of rotor blade and due to this it will be
Fig. 10. Inner race of roller bearing prepared for diagnosis:
1 – inner bearing race; 2 – bearing roller; 3 – groove on bearing possible to prevent the serious break-down of engine.
race 5.SUMMARY
The described cases belong to the group which has the It is quite obvious that the values of amplitudes and fre-
„soft” influence on the wearing process of engines. The con- quencies of engines transverse vibrations are the most im-
tinuous observation of enlarging amplitudes of vibration portant (and the most sensitive) diagnostic parameters,
connected with rotational speeds of rotors and the appea- which the changes (the growth of amplitudes and the appea-
rance of vibration amplitudes with diversified frequencies rance of new frequencies) indicate the threat of engine bre-
indicates the wear degree of the engine. Fig.11 shows the ak-down. However, they are not only ones, which warn the
growing amplitudes of vibration (mainly identified as „ro- user about the progressive wear (damage) of rotor
tor”) recorded in function of the engine operation time. assemblies, their bearings and supports in the engine frame.
VIBRATION OF TURBINE ENGINES AS THE CRITERION ... 15
 [8] Łagosz M., Nowotarski I., Szczeciński S.: Wpływ
cech konstrukcyjnych silników odrzutowych na kry-
tyczne prędkości obrotowe. Prace Instytutu Lotnictwa
1994, nr 137.
[9] Ponomariov S. i in.: Osnovy sovriemiennych mieto-
dov rasciota na procnost’ v masinostrojenii. Wyd.
„Oborongiz”, Moskwa 1952 r.
[10] Stodola A.: Dampf und Gasturbinen. Berlin 1924 r.
[11] Szczeciński S.: Lotnicze silniki tłokowe. Wyd. MON,
Warszawa 1969 r.
[12] Szczeciński S.: Studium o luzach wierzchołkowych
zespołów wirnikowych lotniczych silników jako para-
metrze konstrukcyjnym i eksploatacyjnym – rozprawa
habilitacyjna. Dodatek do Biuletynu WAT nr 4/1973 r.
[13] Szczeciński S.: Lotnicze silniki turbinowe Wyd.
MON, Warszawa 1964 r.
Fig. 12. Maximum amplitudes of vibration of engine population [14] Timoszenko S.:Tieorija kolebanij v inżeniernom
vs. operation time of engine: 1, 1’ – quantitative distribution of dielie.Wyd. GTTI, Moskwa 1932 r.
engines (having dynamic features in range DA1 i DA2) in popu-
lation after operation time: t1 and t2; 3, 3’ – boundary of safe
operation
The diagnostic methods are subjected to the continuous
development which tempo, first of all, depends on: S. Szczeciński, W. Balicki
– the growing knowledge of scientific workers widened by DRGANIA SILNIKÓW TURBINOWYCH
the PhD and professor theses and the promotion of this JAKO KRYTERIUM JAKOŚCI WYTWARZANIA
knowledge to the next generation of engineers; ZESPOŁÓW WIRNIKOWYCH I ICH BIEŻĄCEGO
– the technical progress in the automatic recording, data STANU TECHNICZNEGO
acquisition and processing systems using the micro- W artykule poruszono problem drgań lotniczych silników
processor technique, turbinowych ze szczególnym uwzględnieniem stopnia nie-
– the growth of the ability for the close cooperation among wyważenia wirników. Zagadnienie to bywa jedynie śladowo
expert teams presented the different disciplines such as: poruszane w silnikowej literaturze specjalistycznej. Tym-
physics, chemistry, mechanic, electronic engineering, czasem ilość informacji zawarta w danych uzyskanych
control system engineering and so on; it is also necessa- z permanentnie dokonywanych pomiarów amplitud i często-
ry to set the close co-operation among the research te- tliwości drgań poprzecznych silników, zwłaszcza wielowir-
ams, manufacturers and users of engines, nikowych, jest nie do przecenienia. Przedstawiono związki
– the popularization of individual and team achievements tych parametrów z formą konstrukcyjną wirników, jakością
in the wide accessible scientific literature, popular scien- ich wykonania i montażu, wpływem zmian luzów w pod-
ce periodicals and the widely available internet pages. porach i możliwościami wykrywania stanów zagrożenia
bezpiecznego użytkowania silników.
REFERENCES

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яний угрозы безопасной эксплуатации двигателей.

16 TRANSACTIONS OF THE INSTITUTE OF AVIATION NO. 183