Abstract
The new Finite Elements Model (FEM) allows the visualization of the results and the study of the behavior of the structure at the local level (frames; lises; spars; frame-body, shell-body and longeron-body interaction) in the case of global dynamical phenomena. After creating FEM of the aircraft IAR-99 HAWK in the empty equipped configuration using special elements, the team decided to extend the study of flutter to aircraft in different external stores configurations. The results of the theoretical free-free vibrations obtained for the IAR-99 HAWK in different external stores configurations are presented and compared to those obtained from ground tests, thus confirming the accuracy of the new Finite Element Model (FEM). The aerodynamic idealization of the IAR-99 HAWK in external stores configurations aircraft was made using the Doublet Lattice Method (DLM) for subsonic flow, also considering the load-bearing wing/fuselage/pylon/store interference and aims to determine the generalized aerodynamic forces. The flutter calculation for the IAR-99 HAWK in external stores configurations aircraft, was made using the p-K methodology presented in the MSC. Nastran program, using the vibration modes obtained on the basis of the new finite element model and the matrix of generalized aerodynamic forces in subsonic flow. The V-g curves drawn lead us to flutter speeds outside the safety margin related to the maneuvering diagram, according to the regulations in force, both in the case of the plane in smooth configuration and the plane in the selected external storers variants.
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Published in
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Science, Technology & Public Policy (Volume 9, Issue 1)
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DOI
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10.11648/j.stpp.20250901.11
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Page(s)
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1-13 |
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Creative Commons
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This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.
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Copyright
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Copyright © The Author(s), 2025. Published by Science Publishing Group
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Keywords
Aeroelasticity, Finite Element Model (FEM), Empty Equipped Configuration, External Stores Configurations, Subsonic Flow, Flutter, MSC.PATRAN, MSC.NASTRAN
1. Introduction
Attached stores can be defined as any object, such as engines, cannon and/or additional fuel tank or other types of armament, that are attached either to the wing in various positions in the wingspan and to the chord and/or under the fuselage. This diversified typology for couplings makes us think first of all about military aviation, in commercial aviation we can consider a variant with couplings, attached engines and some variants with additional tanks at the top of the plane.
The analysis of the flutter with stores seen from the broader field of aeroelastic study, appeared after the Second World War in aicrafts, when on the one hand many of the questions asked during the war began to be re-posed and the designers' answers were expected and necessary
| [10] | E. I. Garrick, Wilmer H. Reed III Historical Development of Aircraft flutter/ J. of Aircraft Nov. 1981. |
[10]
. The problems resulting from the interaction of wing/stores in aviation, especially in military aviation, become under these conditions a subject of maximum interest in the aeroelastic community. The complexity of the interaction between aerodynamics and structure makes researchers continue to develop truly reliable concepts, which can often eliminate the dangerous effects of self-induced oscillations that occur in the different wing/store configurations.
It has been found that flutter usually occurs when the fundamental frequency of wing bending is coupled with any of the torsional frequencies of the wing or with oscillation frequencies occurring during typical movements of some hitches or on the occasion of their release. With the evolution at increased speeds, there will be increases in dynamic pressure and there will be pitch oscillations of the hooked body and changes in the bending frequencies of the wing. Under these conditions, they can coincide with either or both torsional frequencies of the wings or stores. At this critical velocity, if two natural frequencies coincide, the probability of flutter occurrence increases.
Mounted stores, which have the effect of reducing both the fundamental wing bending frequencies and the torsional frequencies at high speeds, can thus cause a critical speed resulting from the combination of the two frequencies, which is reached earlier, and the flutter can become a threat right inside the flight tire.
In the 1970s the wing/stores flutter became an interesting research topic and under these conditions many advances were made. Much of the research at the time was also carried out using the wind tunnel study on models and later the validation of the results obtained through flight tests.
In 1973 Triplett et al.
| [7] | W. E. Triplett, H.-P. F. Kappus and R. J. Landy Active flutter control—an adaptable application to wing/store flutter/Journal of Aircraft, 10(11): 669–678, 1973. |
[7]
of the McDonnell Aircraft Company investigated for the first time analytically the possibility of eliminating the appearance of the flutter on the wing/store assembly.
Today the topic of wing/stores flutter continues to be of great interest, but especially from an analytical point of view. Most of the published research concerns the improvement of existing concepts in terms of reliability and structural robustness. The increased performance of computers provides reasons for advanced analysis and finding new numerical methods for determining limits and ways to eliminate flutter,
| [16] | Earl H. Dowell A Modern Course in Aeroelasticity/Duke University Durham, NC USA Fifth Revised and Enlarged Edition / 2015. |
[16]
.
2. The Fem Model of the Iar-99, HAWK in Different Store Configurations
2.1. General Description of the IAR-99 HAWK, in Different Store Configurations
The IAR-99 aircraft had its first flight on December 21, 1985. The aircraft was designed in accordance with the requirements of the military regulation MIL 8870-ASG.
| [15] | Military Specification Airplane Strenght and Rigidity Vibration, Flutter and Divergence/MIL-A-8870 ASG/2015. |
[15]
. The flutter analysis was performed using a model in bar theory on which the free vibrations, the aerodynamic forces generalized by the DLM method were calculated, considering only the lifting surfaces and finally the V-g method was applied
| [4] | Colectiv INCREST Sinteza calculului aeroelastic al avionului prototip IAR-99, ŞOIM/ Raport INCREST RC-339, DEC. 1988, |
[4]
.
The IAR-99, HAWK aircraft is a single-engine, school-training and ground attack aircraft, with various stores configurations
| [1] | Colectiv INCREST Cartea I. Descrierea tehnica pentru structura IAR-99 PROTOTIP/Raport INCREST 1990. |
[1]
, designed for school and training units, for the training of pilots, in the transition phase from classic, low-speed aircraft, to high-speed jet aircraft, as well as for the advanced training of already trained pilots, in the second training group, with the possibility of performing specific missions of direct tactical air support,
Figure 1.
A military aircraft, by the nature of its evolutions and especially of the missions it has to fulfill, is characterized by the hooked stores it carries and the speed restrictions to which the structure is subjected in the various variants of hooks.
Figure 1. The IAR-99 HAWK aircraft, in configurations with hooked stores.
2.2. The New FEM Model of the IAR-99 HAWK Aircraft, in Different Store Configurations
Based on the methodology developed by MSC. NASTRAN,
| [2] | MSC Software Corporation/2004, MSC. Nastran 2003. Linear Static Analysis. User’s Guide. |
[2]
has developed a new Finite Elements Model (FEM), based on the refinements developed in
| [9] | MSC.Patran User’Guide/ MSC Software Corporation/2004. |
[9]
for modeling and in
| [14] | Louis Komzsik MSC. Nastran 2001 Numerical Methods User’s Guide/The MacNeal-Schwendler Corporation/1993. |
[14]
respectively, allows the visualization of the results and the study of the behavior of the structure at the local level (frames; lises; spars; frame-body, shell-body and longeron-body interaction) in the case of global dynamical phenomena.
In the description of the new FEM model of the aircraft, in this case in attachment configurations, we consider first of all the attachment pylons under the wing:
Under these conditions, the wing with the two pylons will have the following image for FEM modelling:
Based on the FEM models of the hitches together with the FEM model of the IAR-99 Hawk aircraft, in smooth configuration, we will have the following FEM models of the aircraft in the configurations of stores chosen for analysis:
Figures 4, 5, 6, 7, and
Tables 1, 2, 3, 4.
Figure 2. FEM model, wing detail with pylons.
While the FEM model for the entire aircraft is:
Figure 3. FEM model airplane with hooking pylons.
Table 1. FEM, A Configuration.
| No. of knots | No. elements | CTRIA3 | CQUAD4 |
SMOOTH CONFIGURATION | 565551 | 584794 | 26164 | 558630 |
2 * ADDITIONAL TANK | 528 | 504 | 4 | 500 |
2 * LAUNCHER 16*57 | 1456 | 1498 | 90 | 1408 |
TOTAL | 567535 | 586796 | 26258 | 560538 |
Table 2. FEM, B Configuration.
| No. of knots | No. elements | CTRIA3 | CQUAD4 |
SMOOTH CONFIGURATION | 565551 | 584794 | 26164 | 558630 |
4 * B-250 | 2888 | 2192 | 0 | 2192 |
TOTAL | 568439 | 586986 | 26164 | 560822 |
Figure 4. A Configuration.
Figure 5. B Configuration.
Table 3. FEM, C Configuration.
| No. of knots | No. elements | CTRIA3 | CQUAD4 |
SMOOTH CONFIGURATION | 565551 | 584794 | 26164 | 558630 |
2 * 2 * B-100 | 10868 | 10438 | 304 | 10132 |
TOTAL | 576419 | 595232 | 26468 | 568764 |
Figure 6. C Configuration.
Figure 7. D Configuration.
Table 4. FEM, D Configuration.
| No. of knots | No. elements | CTRIA3 | CQUAD4 |
SMOOTH CONFIGURATION | 565551 | 584794 | 26164 | 558630 |
2 * B-100 | 5434 | 5218 | 152 | 5066 |
2 * LANSATOR PR 32*42 | 2464 | 2408 | 0 | 2408 |
TOTAL | 573449 | 556420 | 26316 | 566104 |
3. Vibrations [3]
3.1. Vibration Characteristics, A Configuration
Figure 8. Rigid Mode – Roll: f = 0.000533691 Hz.
Figure 9. Symmetrical wing bending: f = 15.9148 Hz.
3.2. Vibration Characteristics, B Configuration
Figure 10. Rigid Mode – Vertical Displacement on OZ: f = 0.00190711 Hz.
Figure 11. Antisymmetrical Interior Bombs Gyration: f = 6.23348 Hz.
3.3. Vibration Characteristics, C Configuration
Figure 12. Rigid Mode – Roll: f = 0.000551875 Hz.
Figure 13. Antisymmetrical External Bomb Gyration: f = 11.7889 Hz.
3.4. Vibration Characteristics, D Configuration
Figure 14. Rigid Mode – Gyration: f = 0.0011725 Hz.
Figure 15. Roll Symmetrical Bombs: f = 16.6627 Hz.
4. Application of the DLM Method to the Calculation of Generalized Aerodynamic Forces, [3] in the Iar-99, Hawk Aircraft in Different Configurations of Stores, [12]
For all the load-bearing surfaces: wing, empennages and respectively the bodies considered, we will apply the methodology presented in
| [6] | Albano, E., and Rodden, W. P A Doublet-Lattice Method for Calculating Lift Distributions on Oscillating Surfaces in Subsonic Flows/AIAA J., Vol. 7, pp. 279-285, p. 2192/1969. |
[6]
and developed in
| [8] | Giesing, J. P., Kalman, T., and Rodden, W. P. Subsonic Unsteady Aerodynamics for General Configurations, Part II, Volume I - Application of the Doublet-Lattice-Method and the Method of Images to Lifting-Surface/Body Interference/Air Force Flight Dynamics Laboratory Report No. AFFDL-TR-71-5, Part II, Vol. I/1972. |
[8]
for the aircraft with stores. we will idealize the surfaces and bodies from an aerodynamic point of view, generating aerodynamic surfaces that will cover the geometric surfaces of the FEM model.
Figure 16. Aerodynamic idealization A configuration.
Figure 17. Aerodynamic idealization overlay with FEM, A configuration.
Figure 18. Aerodynamic idealization overlay with FEM, B configuration.
Figure 19. Aerodynamic idealization overlay with FEM, C configuration.
Figure 20. Aerodynamic idealization overlay with FEM, D configuration.
5. Results of the Analysis of the Iar-99 Hawk Aircraft, in Different Store Configurations, [12]
It can be noted that by any of the flutter analysis methods: K, KE or PK, V-g curves (velocity – structure damping) will result for each vibration mode in the respective flutter combination studied
| [13] | NX Nastran Basic Dynamic Analysis User’s Guide / MSC Software Corporation/2004. |
[13]
. The p-K method was used, described in detail in Chapter 2 of the paper
| [5] | Tudor Vladimirescu Contribuții asupra studiului de flutter al avionului echipat cu acroșaje/Teza de Doctorat - octombrie 2024. |
[5]
, in accordance with
| [3] | MSC Software Corporation/2004, MSC. Nastran Version 68. Aeroelastic Analysis. User’s Guide”. |
[3]
. The results of the flutter calculation are related to the maneuver diagrams presented in
| [11] | Colectiv INCREST Diagramele de manevra, de calcul si de exploatare ale avionului IAR-99 cu acrosaje/ Raport INCREST, AG-302/1987. |
[11]
. The design of the IAR-99, HAWK aircraft was made using
| [15] | Military Specification Airplane Strenght and Rigidity Vibration, Flutter and Divergence/MIL-A-8870 ASG/2015. |
[15]
, so the limitations of this regulation are the basis of the safety margin that the evolution of the aircraft must respect. The flutter combination must contain as many vibration modes as possible for a very complete analysis and then it can be established which are the two modes responsible for the appearance of the flutter phenomenon, namely the excited mode, which leads to g=0 and the exciting mode that induces the loss of damping on this excited mode.
Figure 21. Curves V-g, H=0 m, for the combination of vibration modes, A configuration.
For Hooking A Configuration, the following are identified:
- excited mode – Symmetrical rotation of the ailerons – f = 20.8283 Hz;
- excitatory mode – Vertical empennage bending – f = 18.9784 Hz;
for which at H = 0 m, the flutter velocity occurs at the value of Mach 1.2, a value in the supersonic flow regime, well outside the safety margin in the evolution of the IAR-99 aircraft with hooks.
Figure 22. Curves V-g, H= 0 m, for the combination of vibration modes, B configuration.
For Hooking B Configuration, the following shall be identified:
- excited mode – Symmetrical wing bending – f = 16.3096 Hz;
- excitatory mode – Symmetrical pitch of external bombs – f = 18.3253 Hz;
for which at H = 0 m, the flutter velocity occurs at the value of Mach 1.2, a value in the supersonic flow regime, well outside the safety margin in the evolution of the IAR-99 aircraft with hooks.
Figure 23. Curves V-g, H= 0 m, for the combination of vibration modes, C configuration.
For Hooking Configuration C, the following are identified:
- excited mode – Antisymmetrical vibration mode for hooks – f = 15.8692 Hz;
- excitatory mode – Symmetrical gyration of external bombs – f = 11.7572 Hz;
for which at H = 0 m, the flutter speed appears at the value of Mach 0.82, a value outside the safety margin in the evolution of the IAR-99 aircraft with hooks.
Figure 24. Curves V-g, H= 0 m, for the combination of vibration modes, D configuration.
For Hooking Configuration D, the following are identified:
- excited mode – Vertical empennage bending – f = 18.0631 Hz;
- excitatory mode – Symmetrical bomb roll – f = 16.6620 Hz;
for which at H = 0 m, the flutter speed appears at the value of Mach 0.82, a value outside the safety margin in the evolution of the IAR-99 aircraft with hooks.
6. Conclusions [5]
All research, papers, studies, reports and/or doctoral theses that touch, at least tangentially, the subject of fluttering with hooks propose a solution for eliminating this aeroelastic phenomenon in the event of its appearance in the flight envelope of the aircraft, in accordance with its design requirements.
Whatever path a researcher takes in the field of the study of flutter with hooks, he will permanently combine analytical methods with experimental methods. Going through some stages of numerical analysis: the mass model; the elastic model; the calculation of free vibrations; the calculation of the stationary aerodynamic forces; the flutter calculation; will be validated or updated by experimental methods: ground vibration tests; wind tunnel tests on scale models; in-flight flutter tests.
The new FEM finite element model presented in this thesis allows both the visualization of the results and an analysis of the behavior of the structure up to the local level (frames; lises; spars; frame-body, shell-body and longeron-body interaction) in the case of global dynamical phenomena. Thus, it is possible to use a single FEM model for the simulation of dynamic phenomena, in order to be able to draw conclusions on the behavior of the structure up to the local level in the case of studying a global aeroelastic phenomenon.
In the present case regarding the flutter analysis of the IAR-99 HAWK aircraft, smooth configuration and in different docking variants, we can exemplify on the symmetrical bending mode of the wing, the behavior of the wing – central caisson assembly, the displacement in different selected nodes can be easily read and the appearance of the behavior of the wing structure and/or the central fuselage at the wing bending frequency can be visualized:
Figure 25. Symmetrical wing vibration. Structure of the central fuselage – wing.
The portion of the central fuselage comprising the wing-fuselage junction is easily isolated from the overall model:
Figure 26. Symmetrical wing vibration. The structure of the central fiuselage – central caisson.
and later from this the central caisson is individualized.
Figure 27. Symmetrical wing vibration. The structure of the central caisson.
This advantage is given by the new FEM model, which allows this analysis on structural elements and nodes.
Under these conditions, the proposed flutter analysis methodology based on the new FEM model also has a very useful feedback, starting from the vibration mode(s) responsible for flutter, for the excited elastic and the exciting mode, respectively, the displacements that occur in different nodes or precisely individualized elements can be identified.
The use of analytical methods for the analysis of free vibrations, calculation of stationary aerodynamic forces and flutter calculation aims to reduce the high costs involved in ground vibration tests, tests on models in wind tunnels and last but not least in-flight flutter tests. These analytical methods are previously validated, as is the case with the MSC. Nastran program.
The results of the simulations presented show a vibration behavior as well as the forecasted limits of the flutter, sensitive to: the flight altitude; the mass variation of the hooked bodies; the position in the span and respectively chord, of the hooked bodies; the stiffness of the wing/pylon/hook joints;
The DLM method used for subsonic non-stationary aerodynamic idealization provides a very good approximation for obtaining results for load-bearing surface configurations and interference with thin bodies. Under these conditions, the DLM method is also used to introduce the hooks in the aerodynamic idealization presented for the smooth plane that is well structured, allowing a flutter analysis of the IAR-99 plane in the different docking variants, making possible a subsequent laborious analysis on the influences of the hooks on the flutter speed.
The flutter analysis performed on the new FEM model of the IAR-99 HAWK aircraft, in smooth configuration and in different variants of hitches, leads us to the conclusion that in any analyzed configuration the aircraft is free of flutter inside the maneuver diagram.
The V-g curves drawn highlight first of all the fact that in the smooth configuration, the IAR-99 aircraft is free of flutter, the speed of 1.2 MACH places us in the Maneuver Diagram well above the Safety Margin calculated. From the present flutter calculation, we get a flutter velocity in the supersonic area and a binary flutter analysis, considering the excited mode and the excitant mode respectively is not relevant in the subsonic regime.
The continued operation of the IAR-99 HAWK aircraft, used to train pilots even for the transition to the F-16, may be useful, after equipping with appropriate equipment and specific hooks, a professional aeroelastic analysis on the new IAR-99 aircraft. It is necessary to validate the results of the flutter analysis through flight tests on smooth configuration and various docking configurations and/or subsequent docking variants that have not been considered of interest so far.
It will be of further interest to analyze aeroelastic and other dynamic phenomena, dynamic response, order reversal speed, etc. using the present FEM model, the most complete and complex ever made.
Abbreviations
GVT | Ground Viration Test |
V-g | Velocity – Structural Damping |
DLM | Doublet Lattice Method |
FEM | Fnite Elements Model |
Conflicts of Interest
The authors declare that there are no conflicts of interest related to the publication of this paper. The research, analysis, and conclusions presented are conducted independently and without bias from any external influence or commercial interest.
References
| [1] |
Colectiv INCREST Cartea I. Descrierea tehnica pentru structura IAR-99 PROTOTIP/Raport INCREST 1990.
|
| [2] |
MSC Software Corporation/2004, MSC. Nastran 2003. Linear Static Analysis. User’s Guide.
|
| [3] |
MSC Software Corporation/2004, MSC. Nastran Version 68. Aeroelastic Analysis. User’s Guide”.
|
| [4] |
Colectiv INCREST Sinteza calculului aeroelastic al avionului prototip IAR-99, ŞOIM/ Raport INCREST RC-339, DEC. 1988,
|
| [5] |
Tudor Vladimirescu Contribuții asupra studiului de flutter al avionului echipat cu acroșaje/Teza de Doctorat - octombrie 2024.
|
| [6] |
Albano, E., and Rodden, W. P A Doublet-Lattice Method for Calculating Lift Distributions on Oscillating Surfaces in Subsonic Flows/AIAA J., Vol. 7, pp. 279-285, p. 2192/1969.
|
| [7] |
W. E. Triplett, H.-P. F. Kappus and R. J. Landy Active flutter control—an adaptable application to wing/store flutter/Journal of Aircraft, 10(11): 669–678, 1973.
|
| [8] |
Giesing, J. P., Kalman, T., and Rodden, W. P. Subsonic Unsteady Aerodynamics for General Configurations, Part II, Volume I - Application of the Doublet-Lattice-Method and the Method of Images to Lifting-Surface/Body Interference/Air Force Flight Dynamics Laboratory Report No. AFFDL-TR-71-5, Part II, Vol. I/1972.
|
| [9] |
MSC.Patran User’Guide/ MSC Software Corporation/2004.
|
| [10] |
E. I. Garrick, Wilmer H. Reed III Historical Development of Aircraft flutter/ J. of Aircraft Nov. 1981.
|
| [11] |
Colectiv INCREST Diagramele de manevra, de calcul si de exploatare ale avionului IAR-99 cu acrosaje/ Raport INCREST, AG-302/1987.
|
| [12] |
Colectiv INCREST Stabilirea configuratiilor critice de acrosare pentru calculul aeroelastic / Raport INCREST, RA-121/1983.
|
| [13] |
NX Nastran Basic Dynamic Analysis User’s Guide / MSC Software Corporation/2004.
|
| [14] |
Louis Komzsik MSC. Nastran 2001 Numerical Methods User’s Guide/The MacNeal-Schwendler Corporation/1993.
|
| [15] |
Military Specification Airplane Strenght and Rigidity Vibration, Flutter and Divergence/MIL-A-8870 ASG/2015.
|
| [16] |
Earl H. Dowell A Modern Course in Aeroelasticity/Duke University Durham, NC USA Fifth Revised and Enlarged Edition / 2015.
|
Cite This Article
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APA Style
Vladimirescu, T., Fuiorea, I., Vladimirescu-jr, T. (2025). IAR-99 HAWK Flutter Model Studies with External Stores. Science, Technology & Public Policy, 9(1), 1-13. https://doi.org/10.11648/j.stpp.20250901.11
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Vladimirescu, T.; Fuiorea, I.; Vladimirescu-jr, T. IAR-99 HAWK Flutter Model Studies with External Stores. Sci. Technol. Public Policy 2025, 9(1), 1-13. doi: 10.11648/j.stpp.20250901.11
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Vladimirescu T, Fuiorea I, Vladimirescu-jr T. IAR-99 HAWK Flutter Model Studies with External Stores. Sci Technol Public Policy. 2025;9(1):1-13. doi: 10.11648/j.stpp.20250901.11
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@article{10.11648/j.stpp.20250901.11,
author = {Tudor Vladimirescu and Ion Fuiorea and Tudor Vladimirescu-jr},
title = {IAR-99 HAWK Flutter Model Studies with External Stores},
journal = {Science, Technology & Public Policy},
volume = {9},
number = {1},
pages = {1-13},
doi = {10.11648/j.stpp.20250901.11},
url = {https://doi.org/10.11648/j.stpp.20250901.11},
eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.stpp.20250901.11},
abstract = {The new Finite Elements Model (FEM) allows the visualization of the results and the study of the behavior of the structure at the local level (frames; lises; spars; frame-body, shell-body and longeron-body interaction) in the case of global dynamical phenomena. After creating FEM of the aircraft IAR-99 HAWK in the empty equipped configuration using special elements, the team decided to extend the study of flutter to aircraft in different external stores configurations. The results of the theoretical free-free vibrations obtained for the IAR-99 HAWK in different external stores configurations are presented and compared to those obtained from ground tests, thus confirming the accuracy of the new Finite Element Model (FEM). The aerodynamic idealization of the IAR-99 HAWK in external stores configurations aircraft was made using the Doublet Lattice Method (DLM) for subsonic flow, also considering the load-bearing wing/fuselage/pylon/store interference and aims to determine the generalized aerodynamic forces. The flutter calculation for the IAR-99 HAWK in external stores configurations aircraft, was made using the p-K methodology presented in the MSC. Nastran program, using the vibration modes obtained on the basis of the new finite element model and the matrix of generalized aerodynamic forces in subsonic flow. The V-g curves drawn lead us to flutter speeds outside the safety margin related to the maneuvering diagram, according to the regulations in force, both in the case of the plane in smooth configuration and the plane in the selected external storers variants.},
year = {2025}
}
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TY - JOUR
T1 - IAR-99 HAWK Flutter Model Studies with External Stores
AU - Tudor Vladimirescu
AU - Ion Fuiorea
AU - Tudor Vladimirescu-jr
Y1 - 2025/01/22
PY - 2025
N1 - https://doi.org/10.11648/j.stpp.20250901.11
DO - 10.11648/j.stpp.20250901.11
T2 - Science, Technology & Public Policy
JF - Science, Technology & Public Policy
JO - Science, Technology & Public Policy
SP - 1
EP - 13
PB - Science Publishing Group
SN - 2640-4621
UR - https://doi.org/10.11648/j.stpp.20250901.11
AB - The new Finite Elements Model (FEM) allows the visualization of the results and the study of the behavior of the structure at the local level (frames; lises; spars; frame-body, shell-body and longeron-body interaction) in the case of global dynamical phenomena. After creating FEM of the aircraft IAR-99 HAWK in the empty equipped configuration using special elements, the team decided to extend the study of flutter to aircraft in different external stores configurations. The results of the theoretical free-free vibrations obtained for the IAR-99 HAWK in different external stores configurations are presented and compared to those obtained from ground tests, thus confirming the accuracy of the new Finite Element Model (FEM). The aerodynamic idealization of the IAR-99 HAWK in external stores configurations aircraft was made using the Doublet Lattice Method (DLM) for subsonic flow, also considering the load-bearing wing/fuselage/pylon/store interference and aims to determine the generalized aerodynamic forces. The flutter calculation for the IAR-99 HAWK in external stores configurations aircraft, was made using the p-K methodology presented in the MSC. Nastran program, using the vibration modes obtained on the basis of the new finite element model and the matrix of generalized aerodynamic forces in subsonic flow. The V-g curves drawn lead us to flutter speeds outside the safety margin related to the maneuvering diagram, according to the regulations in force, both in the case of the plane in smooth configuration and the plane in the selected external storers variants.
VL - 9
IS - 1
ER -
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