INFLUENCE OF MASS CHANGES OF FLYING OBJECTS ON THEIR DYNAMIC FEATURES

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1 Journal o KONES Powertrain and Transport, Vol. 17, No INFLUENCE OF MASS CHANGES OF FLYING OBJECTS ON THEIR DYNAMIC FEATURES Witold Wi niowski Institute o Aviation Krakowska Av. 110/114, Warszawa, Poland tel.: , ax: witold.wisniowski@ilot.edu.pl Abstract The aim o this work is the experimental study o the weight loss impact on the properties o lying objects. Work is based on the results o resonance tests o the helicopter, gliders and military aircrat. In the presented lying objects group the possible occurrence o weight losses during the light are up to 50%. The paper posed the ollowing questions: How big can be, in practice, the weight loss during the light? To which resonance the mass loss has the greatest impact? How and by what rules the map o resonances changes? Does in the process o weight loss there are other, worth-knowing events? Gliders, s and a helicopter were investigated in the Resonance Test Laboratory o Institute o Aviation. The author has organized and or over 20 years led the Resonance Test Laboratory at the Institute o Aviation, in which he made or directed the investigations o dozens o aircrat, gliders, helicopters and their elements and components. Eect o weight loss on the lying objects properties is one o several unusual research topics phenomena, which the author observed during a standard resonance tests. The resonance o the mode shape o Jantar 15 glider, comparison o the relative increase in the requencies o the resonances with mode shape or SZD-50 Jantar 15-2 and IS-2 Revelation gliders, results o investigations o the underwing stores loss o mass impact on the Pattern aircrat resonances requencies, the resonance requency o the I-22 Iryda aircrat are presented in the paper. The resonance o the mode shape o Jantar 15 glider, comparison o the relative increase in the requencies o the resonances with mode shape or SZD-50 Jantar 15-2 and IS-2 Revelation gliders, results o investigations o the underwing stores loss o mass impact on the Pattern aircrat resonances requencies, the resonance requency o the I-22 Iryda aircrat are presented in the paper. Keywords: transport, air transport, dynamics eatures, resonance researches, mass loss 1. Scope o the work The aim o the study is to examine the impact o weight loss on the behaviour o lying objects. The paper posed the ollowing questions: How big can be, in practice, the weight loss during the light? To which resonance the mass loss has the greatest impact? How and by what rules the map o resonances changes? Does in the process o weight loss there are other, worth-knowing events? Dynamic properties o aircrat structures are examined, modelled and analyzed in order to anticipate and avoid behaviour that could endanger the lives and saety o people and equipment. The model o lying object dynamics is represented by a system o equations: where i = 1. mq i i cq i i kq i i i q ˆ i bq i i iqi i, The experimental way to obtain the m i, c i, k i coeicients are the resonant tests. Implementation o resonance tests proceeded in accordance with developed procedures.

2 W. Wi niowski These procedures and adapted laboratory equipment are the tools needed to assess knowledge and understanding o the object properties. The author has organized and or over 20 years led the Resonance Test Laboratory at the Institute o Aviation, in which he made or directed the investigations o dozens o aircrat, gliders, helicopters and their elements and components. 2. Test procedures In order to imitate the ree light conditions the object was suspended by elastic cords so that own requency o its movement on the suspension was signiicantly lower than the resonant vibration requencies o its structure. In the case o studies o on the ground resonances the tested object stand on its own undercarriage. The electro-dynamic actuators were used to induce vibrations, the piezoelectric vibration sensor transducers were used or the vibrations measurements. The size and phase o constraint orces and their points o application were selected individually or each resonance, so as to obtain the best isolation o it [4]. The irst stage o the investigations consisted o recording o the requency-amplitude characteristics. The second stage o the study was the identiication o individual requencies and mode shapes or each o the resonances, which was implemented by choosing the size and the proportion o mutual phase shits between the constraint orces. Used in the selection criteria were based on minimizing the vibrations phase dierence measured at several points o the structure. The inal stage o the investigations was to register the requency and mode shapes o the tested generalized masses resonance and the resonance damping coeicients [4]. As a result o resonance test, the several resonances register (the resonance map) was obtained, essential rom the lying object saety and comort standpoint. Tab. 1. Possible in-light loss o weight or the selected gliders, helicopters and s Item Flying object Airbus 380 SZD-52-2 Jantar 15 Glider IS-1 Revelation Helicopter PZL Sokó H-18 Dromader Glider Wrona 2 Skytruck Cessna 378 I-22 Iryda Own mass [kg] Fuel mass [kg] Cargo mass [kg] Take-o mass m TO [kg] Possible in-light weight loss m m m _ _ _ _ TO 592

3 Eect o Flying Objects Mass Change on Their Structures Dynamic Characteristics 3. The in-light object loss o mass During the light, rom the take-o to landing the mass o lying objects changes due to uel consumption, dropped armament, ballast water discharge, paratroopers, plant protection products, ire extinguishing, etc. As an example, in the Tab. 1 are presented the mass data, including variable cargo load mass o selected lying objects. In the presented cases, the mass o spent uel and dropped loads are within the range rom 0.19 to 0.59 o the take-o weight. Gliders, s and a helicopter (with the exception o item no. 1 and no. 3) the data o which are presented in the table were investigated in the Resonance Test Laboratory o the Institute o Aviation. The tested gliders water ballast is located in the near uselage wing tanks. In the helicopters and agricultural s the uel and dropped agricultural load is distributed within the uselage. The combat aircrat uel and weaponry is located both in the uselage and on the under wing pylons/pods. Fig. 1. The resonance o the mode shape 4-nodal vertical wings bending o Jantar 15 glider 4. The resonances map Results o the resonance tests orm a map which illustrates the dynamic properties o the structure. This map is a list o resonance requencies (generalized masses and damping coeicients) and the igures and tables o vibration modes coordinates. Fig. 1 shows an example o one o the elements o the map: the results o resonance test with the mode shape 4-nodal vertical wing bending o Jantar 15 glider. From the impact perspective o the weight loss during light, resonances o the ollowing groups were selected or the analysis: a. a group o six resonances o an object standing on ground on its own undercarriage, b. a group o resonances with the mode shapes vertical wing bending and twisting, c. s with underwing tanks and munitions undamental resonances group. Selected three groups o resonances include and represent typical cases where the inluence o weight loss occurred to the greatest extent. 593

4 W. Wi niowski 5. A group o six resonances o an object standing on ground on its own undercarriage The study o resonances o lying object standing on its own undercarriage, rom the cognitive and utilitarian point o view concerns mostly helicopters. Tab. 2 presents the results o the 6 main resonances o helicopter standing on its own undercarriage. Item Tab. 2. The results o the 6 main resonances o helicopter standing on its own undercarriage Resonance mode shape 1 [ Hz ] m=3190 kg 2[ Hz ] m = 5410 kg 1. Roll Pitch Yaw Vertical oscillations Longitudal oscillations Lateral oscillations Changes o the helicopter mass minimally aected the value o the requencies o these resonances, which mode shapes are related to the rotations: rolling, pitching and yawing. Changing o the helicopter mass clearly aected the values o the resonances, which mode shapes are related to the oscillations along the x-, y-, z-axis. 6. Group o resonances with mode shapes o vertical bending and twisting o glider wings Changes in properties o resonances with mode shapes 2-, 3-, 4-, 5-, 6- and 7-nodal vertical wing bending and wings twisting arise rom placement o water ballast tanks in near-uselage part o the gliders wings. The nature o the resonances changes is presented on examples o Polish glider SZD-52-2 Jantar - 15 [6] and South Arican glider IS-1 Revelation [7] investigations. Tab. 3 presents the results o the resonance tests with mode shapes vertical wings bending and the twisting o the wings o SZD-50 Jantar 15-2 glider with empty and ull ballast tank.1 [H2] - resonance requency o the glider without ballast; 2 [H2] - resonance requency o the glider with 140 kg ballast. Tab. 4 presents the results o the resonance tests with mode shapes vertical wings bending o IS-1 Revelation glider with empty and ull ballast tank, 1 [H2] - resonance requency o the glider without ballast; 2 [H2] - resonance requency o the glider with ballast. 7. Group o resonances o aircrat with underwing tanks and munitions A major inluence on changes in the wings resonance is the hanging on their ends and on the underwing pylons/pods the uel tanks and munitions. The problem is illustrated in the examples made by the author - a study o two s: pattern aircrat, and the I-22 Iryda aircrat. The pattern aircrat was tested in three versions: with no underwing stores, in the version with ull tanks at the wings ends and in the version with ull tanks at the ends o the wings and underwing pods. Fig. 3 presents results o investigations o the underwing stores loss o mass impact on the Pattern aircrat resonances requencies. Most susceptible to weight loss are resonances with mode shapes twisting o the wings

5 Eect o Flying Objects Mass Change on Their Structures Dynamic Characteristics Emptying the tanks at the ends o the wings increases the requency o these resonances about 2.6 times. Fig. 4 presents the results o studies o the underwing stores impact on resonances or I-22 Iryda aircrat. The plane has been studied in an empty version and in a version with underwing stores. Ratio o resonance requency 1 / 2 o a wing with twisting mode shape or empty version and the version with loaded underwing stores is equal to 3.3 times. Tab. 3. The results o the resonance tests with mode shapes vertical wings bending and the twisting o the wings o SZD-50 Jantar 15-2 glider with empty and ull ballast tank.1 [H2] - resonance requency o the glider without ballast; 2 [H2] - resonance requency o the glider with 140 kg ballast Item Resonance mode shape 1 [H2] empty 2 [H2] ull node wing bending node wing bending node wing bending node wing bending 2-node uselage bending node wing bending node wing bending node wing bending node wing bending node wing bending Tab. 4. The results o the resonance tests with mode shapes vertical wings bending o IS-1 Revelation glider with empty and ull ballast tank, 1 [H2] - resonance requency o the glider without ballast; 2 [H2] - resonance requency o the glider with ballast Item Resonance mode shape 1 [H2] empty 2 [H2] ull 1 2-node wing bending node wing bending node wing bending node wing bending node wing bending node wing bending The resonances map decomposition The lying object mass loss increases its resonance requency. Gradients o the individual resonances increases may be dierent

6 W. Wi niowski For this reason, in some cases, two dierent resonance requencies can approach to each other and become equal. Phases o the requencies approach are shown in Fig. 5, where requency-amplitude characteristics are drawn. Diminishment o uel and cargo mass decomposes lying object resonances map. Decomposition involves changes in resonances requencies arrangement and changes in their mode shapes. Fig. 2 presents comparison o the relative increase in the requencies o the resonances with mode shape vertical bending wings without and with water ballast or SZD-50 Jantar 15-2 and IS-2 Revelation gliders. Fig. 2. Comparison o the relative increase in the requencies o the resonances with mode shape vertical wings bending without and with water ballast or SZD-50 Jantar 15-2 and IS-2 Revelation gliders Fig. 3. Results o investigations o the underwing stores loss o mass impact on the Pattern aircrat resonances requencies 596

7 Eect o Flying Objects Mass Change on Their Structures Dynamic Characteristics 9. Summary and conclusions The aim o this work is the experimental study o the weight loss impact on the properties o lying objects. Work is based on the results o resonance tests o the helicopter, gliders and military aircrat. Fig. 4. The results o the underwing stores impact on the resonance requency o the I-22 Iryda aircrat Fig. 5. Frequency-amplitude characteristics, phases o the two resonance requencies approach 597

8 W. Wi niowski In the presented lying objects group the possible occurrence o weight losses during the light are up to 50%. The biggest impact o weight loss was ound in the resonance requencies with mode shapes wings twisting or the combat aircrat with underwing uel tanks and munitions. The weight loss also had signiicant impact on the resonance requencies with mode shapes vertical bending o the wings or gliders with water ballast tanks and s with wing uel tanks and the underwing stores and on the resonance requencies with mode shapes rocking along the x-, y-axis, with helicopters and s with cargo in the uselage, standing on their own undercarriage. The gradients o the requency resonances increases are dierent, depending on whether the weight losses are close to the crests, or close to the nodes o vibrations. One should pay particular attention to the phenomenon o individual dierences o resonances requency, the decanting and the resulting changes in the resonance mode shapes. Resonances approaching and blending in decomposes lying object resonances map. Eect o weight loss on the lying objects properties is one o several unusual research topics phenomena, which the author observed during standard resonance tests [10]. The list o these investigations include, inter alia: - phenomenon o near or equal requencies resonances, - eect o backlash on the properties o resonances, including the development o resonance method or assessing the backlash, - generalized backlash deinition, - development o method or strain gauges resonance scaling, - development o the resonance test method or resistance to vibration o thin-walled structures, - developing principles o resonances classiication based on the idea o groups related to vibration mode shapes. Reerences [1] Lenort, F., Niepokólczycki, A., Application o the correlation unction or determination o damping during in light lutter tests. Transactions o the Institute o Aviation, No. 183, Warsaw 2005 [2] Chajec, W., Flutter calculation based on 9GVT results and theoretical mass model, Research Jornual o Vilnius Gediminos Technical University, Vol. 13, No. 4, [3] Goraj, Z., Zakrzewski, P., Aircrat uel systems and their inluence on stability margin, Transactions o the Institute o Aviation, Nr 183, Warsaw [4] Wi niowski, W., Identyikacja w asno ci dynamicznych uk adów mechanicznych metod bada rezonansowych, rozprawa doktorska Politechnika Warszawska,Warszawa [5] Wi niowski, W., Próby rezonansowe mig owca W-3, Sprawozdanie Instytutu Lotnictwa 18/RW-WZ/83. [6] Lorenc, Z., Próby rezonansowe szybowca SZD-52-2 Jantar 15, Sprawozdanie Instytutu Lotnictwa 34/RW-WZ/83. [7] Próby rezonansowe szybowca IS-1 Revelation, Soaring Magazine, [8] Wi niowski, W., Sposoby przedstawienia wyników prób rezonansowych samolotów, Prace Naukowe Instytutu Metrologii Elektrycznej Politechniki Wroc awskiej Nr 11, Wroc aw [9] Wi niowski, W., Porównanie wyników prób rezonansowych prototypów wyrobu 300, Sprawozdanie Instytutu Lotnictwa 24/BW-WZ/90. [10] Wi niowski, W., Untypical causes and incorrect results o vibration tests, Journal o KONES European Science Society o Powertrain and Transport Publication. Warsaw