INTERNATIONAL CONFERENCE of SCIENTIFIC PAPER [609653]

“HENRI COANDA” GERMANY “GENERAL M.R. STEFANIK”
AIR FORCE ACADEMY ARMED FORCES ACADEMY
ROMANIA SLOVAK REPUBLIC

INTERNATIONAL CONFERENCE of SCIENTIFIC PAPER
AFASES 2011
Brasov, 26-28 May 2011

IAR-99 GROUND VIBRATIO N TESTS AND DYNAMICS
FINITE ELEMENT MODEL

Dorin LOZICI-BRINZEI*, Simi on TATARU**, Radu BISCA*

*National Institute for Aerospace Researc h “Elie Carafoli”, Bucharest, Romania
**Aerospace Consulting, Bucharest, Romania

Abstract:

In this presentation, we will concentrate on typica l Ground Vibration Test (GVT) and Finite Element
(FE) comparisons software. It is necessary to note, that standard GVT are obligatory for any new aircraft
configuration. We can mention here the investigati ons of the IAR-99, modern trainer and ground attack
aircraft, using PRODERA® GVT equipment. A Finite Element Model (FEM ) of the IAR-99 has been
developed in PATRAN/NASTRAN®, partly from a previous ANSYS® model. The results obtained with Finite
Element Analysis (FEA) are strongly depending on th e experience and judgment of the engineers involved
in the analysis. Highly representative FEM can be used to investigate potential structural modifications
or changes with realistic component corrections. Model validation should be part of every modern
engineering analysis and quality assurance procedure.

Key words: aircraft , ground, vibration, test, model

1. INTRODUCTION

This paper presents a study performed on the
IAR-99, advanced trainer and ground attack
aircraft (Fig. 1).

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Fig. 1 IAR-99 Advanced trainer

Fig. 2 IAR-99 Advanced trainer

The Romanian Air Force has 17 of the IAR-99
trainer aircraft in service with the 67th Fighter
Bomber Group based at Craiova (Fig. 3).

Fig. 3 Armament configuration example

2. LIBRARY OF CAD SUBSYSTEMS

A CATIA® library of CAD models of the IAR-
99 and external stores has been developed (Fig. 2).

Fig. 4 CAD Library – MK-82

Fig. 5 CAD Library – OPHER

Fig. 6 CAD Library- IAR-99

3. LIBRARY OF FEM SUBSYSTEMS

As an example, the FEM of the IAR-99 without
external stores, is represented in Fig. 3

Fig. 7 IAR-99 – FEM

Fig. 8 FEM Library – MK-82

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“HENRI COANDA” GERMANY “GENERAL M.R. STEFANIK”
AIR FORCE ACADEMY ARMED FORCES ACADEMY
ROMANIA SLOVAK REPUBLIC

INTERNATIONAL CONFERENCE of SCIENTIFIC PAPER
AFASES 2011
Brasov, 26-28 May 2011

Fig. 9 FEM Library – OPHER

4. AIRCRAFT FEM ASSEMBLY

A finite element model of the IAR-99 has been
developed, partly from pr evious model [3], using
PATRAN/NASTRAN software [1].

Fig. 10 IAR-99+4xOPHER configuration

Fig. 11 IAR-99+4xOPHER configuration

Fig. 12 MK-82 +OPHER configuration

The normal modes obtained from the FE
model, represent an accurate enough estimation of
the aircraft eigenfrequencies and mode shapes.

Fig. 13 Wing 1st vertical bending mode

Fig. 14 Wing 2nd vertical bending mode

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Fig. 15 Wing 1st in plane bending mode

Fig. 16 HT 1st vertical bending mode

Fig. 17 OPHER 1st gyration mode

Fig. 18 OPHER 1st gyration mode

Fig. 19 OPHER 2nd gyration mode

Fig. 20 Fig. 6 Wing 1st torsion mode

Fig. 21 MK-82 Lateral bending mode

5. GROUND VIBRATION TEST

The INCAS/STRAERO stress team completed
a successful GVT of the full IAR-99 aircraft, with
weapons, in December 1999. During the series of
tests, many different weapons configurations were loaded onto the test aircraft. After the first tests,
PRODERA equipment was widely used for the GVT of all classes of flying vehicles, military and civil.

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“HENRI COANDA” GERMANY “GENERAL M.R. STEFANIK”
AIR FORCE ACADEMY ARMED FORCES ACADEMY
ROMANIA SLOVAK REPUBLIC

INTERNATIONAL CONFERENCE of SCIENTIFIC PAPER
AFASES 2011
Brasov, 26-28 May 2011

Fig. 22 GVT configuration example, [2]

During the test, the airplane was standing on
under-inflated tyres of the main landing gear.

Fig. 23 GVT configuration example (detail)

For each test condition, external shakers
induced vibration of the aircraft’s wings, stabilizer
and stores to verify the stores’ effect. The
aircraft’s response was measured with more than
50 accelerometers and other external devices.

Fig. 24 Wing measuring point example

Table 1 Measuring points coordinates
CURVE NO.1 CURVE NO.2 Sec.
No. It.
No.X
(mm) Y
(mm) Itm
No X
(mm) Y
(mm)
1 1 827 920 13 1731 920
2 2 867 1305 14 1734 1305
3 3 902 1635 15 1736 1635
4 4 934 1950 16 1718 1950
5 5 969 2286 17 1741 2286
6 61004 2622 18 1743 2622
7 71034 2912 19 1745 2912
8 81071 3265 20 1748 3265
9 91104 3585 21 1750 3585
10 10 1145 3975 22 1753 3975
11 11 1191 4420 23 1756 4420
12 12 1240 4891 24 1760 4891

Fig. 25 GVT configuration

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The frequency and shapes of all four modes
was used to modify the model, and the results of
the updating has errors of less than 5% on each of the first three modes; and less than 10% for the fourth mode

Table 2 Test-FEA comparison
Mode
description FEM GVT FEM/GVT
1st Wing
Bending 7.301 7.29 0.15%
2nd Wing
Bending 36.05 34.32 5.04%
OPHER
Gyration 12.388 12.34 0.39%
MK-82
Lateral 15.88 15.18 4.61%
HT Sym.
Bending 24.83 27.58 -9.97%

At the conclusion, the ultimate goal of the
IAR-99 finite element analysis effort is to have a highly representative model, which has been validated by measured ground and flight test data.

Fig. 26 IAR-99 External Stores Dynamics FEM

Fig. 27 GVT-FEA comparison

Highly representative FEM can be used to
explore future structural modifications or changes with realistic component modifications.

Fig. 28 IAR-99 External Stores Dynamics FEM

REFERENCES

1. MSC – PATRAN, NASTRAN, 2010.
2. A.Ionita, D. Lozici-Brinzei, s.a., Ground
vibration experiments, IAR-99 STRAERO/
INCAS internal report N-9913/C-2340,
Nov. 1999.
3. P. Rosu, Teza de doctorat , Academia
Tehnica Militara, 2010.
4. MIL-A-8591H , Airborne stores suspension
equipment and aircraft -stores interface,
March 1990

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