Review of the Roll-Damping, Measurements in the T-38 Wind Tunnel

Transcription

1 Internatinal Jurnal f Scientific and Research Publicatins, Vlume 3, Issue 12, December Review f the Rll-Damping, Measurements in the T-38 Wind Tunnel Dušan Regdić *, Marija Samardžić **, Gjk Grubr ** * Ph.D. Singidunum University ** Ph.D. student *** Ph.D., Singidunum University Abstract- In this paper review f rll-damping measurements in the T-38 blw-dwn wind tunnel is presented. Fundamental elements f the mathematical mdel fr stability derivatives measurements are shwn. Measurements are based n rigidly frced scillatins methd. Apparatus fr stability derivatives measurements in rll scillatins tests and data reductin prcedures used in VTI are described. Rll apparatus is designed and prduced with regard t high requirements in stability derivatives measurements. Index Terms- wind tunnel, stability derivatives, experimental aerdynamics, frced scillatin V I. INTRODUCTION TI has great experience in wind tunnel stability derivatives measurement. Starting frm 1960 up t nw several generatins f apparatuses were designed and manufactured. Nwadays, the technique fr measurements f stability derivatives applied in the T-38 wind tunnel is frced scillatin technique [1, 2]. Mdel is frced t scillate at cnstant amplitude within a single degree f freedm, which implies that any aerdynamic reactin cherent with such mtin can nly be due t such mtin. Wind tunnel run includes the fllwing three stages: An amplifier calibratin runs, when knwn signals frm the signal generatr are an input t data acquisitin system. The subject measurement yields the gains and phase shift fr each channel with respect t the displacement channel; Wind-ff run when mdel is scillating but the wind tunnel is nt running. This measurement, using the data frm amplifier calibratin run, enables determinatin f the inertial frces; Wind-n run, when the mdel is scillating at the same frequency as during the wind-ff run but with the wind tunnel running. Used symbls p & sin - Dynamic direct damping derivative in rll sin Clp* - Rlling mment derivative due t sideslip - Nn-dimensinal dynamic direct derivative in rll f I x,y,z I xz - Mechanical damping - Inertia mments abut O x,y,z axes - Centrifugal inertia mment K - Mechanical stiffness, M, N - Ttal mments abut O x,y,z axes X,Y,Z - Aerdynamic frce cmpnents u,v,w - Velcity cmpnents in x, y and z directin aer. meh. T,,, p, q, r - External aerdynamic mment abut O x axis - External mechanical mment abut O x axis - Excitatin mment abut O x axis,,, - Partial derivative,, - Partial derivative p q r

2 Internatinal Jurnal f Scientific and Research Publicatins, Vlume 3, Issue 12, December p, q, r p, q, r, θ, ψ t - Time... - Amplitude - Rll, pitch and yaw rates - Time derivatives f rll, pitch and yaw rates - Angle f attack - Time derivative f angle f attack - Sideslip angle - Time derivative f sideslip angle - Angles f rlling, pitching and yawing mtin - Phase shift - Angular velcity II. DETERMINATION OF RO-DAMPING DERIVATIVES USING METHOD OF RIGIDY FORCED OSCIATION TECHNIQUE The equatins f mtin fr the angular degrees f freedm relative t a set f mving axes that are fixed in the mdel, Figure 1, can be written as [2-3]: p I M q N r I r x I xz I y p (2) z I xz (1) (3) Figure 1: Bdy axis system eft sides f abve equatins represent the sum f all the variatins in the external mments acting n the mdel in the particular degree-f-freedm due t a very small departure frm a steady-state mtin. Such external rlling mment include: aer. mech. T (4) Fr mdel at the equilibrium angle f attack perfrming small-amplitude lw-frequency angular scillatin, aerdynamic reactin can be expressed by linear superpsitin f cntributins caused by:,, derivative f and with respect t time, p, q and r. Relatins between thse parameters are:, sin cs p q r q,,,,, p sin r cs. Change in aerdynamic reactin due t the mdel scillatin can be expressed as fllws: p q r aer. p q r (5) A captive mdel perfrming scillatry mtin experiences mechanical reactins caused by its supprt:

3 Internatinal Jurnal f Scientific and Research Publicatins, Vlume 3, Issue 12, December mech. f p K (6) Cnsidering equatins (4-6) the equatin (3) becmes: x p & sin sin & cs cs & I p& f p K I r& r q xz r q T (7) Stability derivatives in rll are btained frm equatin (7) by equalizing left side f equatin with excitatin mment sin & I p& f p K x p T Excitatin mment T T T cs t is: (9) Rlling scillatry mdel mtin is: cs t (10) Time derivative f the equatin is: sin t, (11) (8) T : And time derivative f the equatin is: 2 cs t (12) sin t and cs t Taking equatins (9-12) in equatin (8) and separating values next t, tw equatins are btained: I 2 x cs f p sin & sin K sin cs T (13) I 2 x sin f p sin & cs K sin sin 0 (14) Slving the abve equatins simultaneusly direct dimensinal static and dynamic stability derivatives in rll are btained: K f where: p sin I x 2 sin T cs T sin K I 2 T x cs, (16) f (15) T sin Finally, expressins fr determinatin stability derivatives in rll are: 2 2 T T sin Ix cs cs (17) T sin T sin p & sin (18) Values with index in equatins (17-18) are measured in wind-ff run..

4 Internatinal Jurnal f Scientific and Research Publicatins, Vlume 3, Issue 12, December Rll apparatus The rll apparatus is shwn in the Figures 2-3. The suspensin system cnsists f tw rings jined by axially riented beams equal spaced arund the periphery f the rings. There are tw suspensin systems fr lw and high lads. Such cnfiguratin prvides the necessary cmpliance in the rll attitude while having a substantial stiffness in the ther degreesf-freedm. A five-cmpnent balance is munted n the frnt end f the drive shaft and n the frnt end f the suspensin system, prtruding frward thrugh the cavity surrunded by the suspensin beams, while the aft part f the suspensin system is firmly fixed t the end f the sting. A five-cmpnent internal balance is mn-blck type and semicnductr strain gages are used in rder t increase its sensitivity and, cnsequently, signal t nise rati as well. The scillatry rlling mtin is imparted by hydraulic driving mechanism lcated at the rear end f the sting via drive shaft whse frnt end is attached t the balance. Table 1: Perfrmance list f the rll apparatus Rll Apparatus Amplitude () Frequency (Hz) Sting Diameter (mm) Hydraulic Pressure (bar) Maximum nrmal frce: N Maximum angle f attack: up t 21 Maximum angle f side slip: Mach number: up t 2.0 Blwing pressure: up t 2.3 bar Driving mechanism: 0 Elastic suspensin with internal hydraulic drive Feedback psitin sensr Elastic cupling Primary mtin sensr Suspensin system Serv valve Actuatr Drive shaft Sting Excitatin mment Figure 2: CAD mdel f rll apparatus Balance Figure 3: Rll apparatus III. DATA REDUCTION Fr determinatin f direct stability derivatives in rll fllwing physical values must be measured: Amplitudes f primary mtin ( ) and excitatin mment ( T ); Frequency f primary mtin ( );

5 Clp* Internatinal Jurnal f Scientific and Research Publicatins, Vlume 3, Issue 12, December Phase shift between excitatin mment and primary mtin ( ). All f the abve data are btained by signals frm suitable lcated strain gages n the apparatus. A five-cmpnent internal mnblck balance measures the frces and mments that act n the mdel during the tests. The primary mtin is sensed by strain gages lcated at the suspensin system. Excitatin mment is estimated by strain gages lcated n the drive shaft r frm balance bridge fr rlling mment. During the measurements, all the sensr signals are amplified, filtered and then digitized by a 16-bit AD cnverter. The sampling recrd f data cvers apprximately 82 cycles with 8192 measuring pints f the primary scillatin. The data frm the test runs are prcessed in the fllwing steps: Data acquisitin system interfacing and signals nrmalizatin; Determinatin f flw parameters; Determinatin f mdel attitude; Determinatin f static aerdynamic cefficients f frces and mments; Determinatin f frequency, amplitude and phase shift f each channel with respect t the primary mtin channel; Determinatin f the direct damping derivatives; Calculatin f nn-dimensinal aerdynamic direct derivatives; Output f tabulated results and plts. Different sftware mdules perfrm each stage f the abve prcess. Tests results f the rll-damping measurements n Mdified Basic Finner Mdel are presented in the Figure 5. [4, 5]. Results btained in the T-38 wind tunnel are cmpared with published experimental data frm the AEDC wind tunnel [6] (Arnld Engineering Develpment Center-vn Karman - USA) and at = 0 with calculated rll-damping cefficient values btained by DMAC semi-empirical methd develped in the VTI [7]. 2V p & sin Clp* 2 q S d S - mdel reference area d - mdel diameter V - velcity q - dynamic pressure 0-3 T-38 wind tunnel AEDC wind tunnel M =1.75 DMAC [deg] Figure 4: Mdified Basic Finner Mdel Figure 5: Rll-damping derivative fr in the T-38 test sectin Mdified Basic Finner Mdel at the M=1.75 IV. CONCUSION Cmplexity f wind tunnel stability derivatives measurements is well knwn. The determinatin f rll-damping derivatives using methd f rigidly frced scillatin technique applied in T-38 wind tunnel is presented. Develped equipment, rll-apparatus and data reductin prcedures have reached a stage t be a very gd tl in design f missiles and aircrafts. [5] M. Samardžić, D. Marinkvski, Testing f MBFM calibratin mdel in the T-38 wind tunnel, Study number V I- 025, VTI Begrad, August [6] M. Samardžić, Z. Anastasijević, D. Marinkvski, Sme Experimental Results f Subsnic Derivative Obtained in T-38 Wind Tunnel by Frced Oscillatin, Scientific Technical Review, Vl.VII,N.3-4, Military Technical Institute, Begrad, 2007, pp [7]. Bb Useltn, M. ery Jenke; Experimental Missile Pitch and Rll- Damping Characteristics at arge Angles f Attack, ARO, Inc. Arnld Air Frce Statin, Tennessee, vl. 14, n.4, April REFERENCES [1] D. Regdić, Exterir Ballistics, MA, Begrad, [2] B. Medved, G. M. Elfstrm, The Yugslav 1.5 m Trisnic Bledwn wind tunnel; AIAA Paper CP, [3] K.J. Orlik-Rückemann, Techniques fr dynamic stability testing in wind tunnels, Agard cpp-235, May [4] Z. Anastasijević, M. Samardžić, D. Marinkvski, Applicatin f semicnductr strain gauges in measurements f dynamic stability derivatives in the T-38 wind tunnel, 26 th Cngress f Internatinal Cuncil f the Aernautical Scientists, September 2008, Anchrage, Alaska, sessins AUTHORS First Authr Prf. dr Dušan Regdić, Singidunum University, Belgrade, Serbia dregdic@singidunum.ac.rs Secnd Authr Marija Samardžić, Ph.D. student, Military Technical Institute (MTI), Belgrade, Serbia, majasam@ptt.rs Third Authr Prf. dr Gjk Grubr, Singidunum University, Belgrade, Serbia, ggrubr@singidunum.ac.rs Crrespndence Authr Prf. dr Gjk Grubr, Singidunum University, Belgrade, Serbia, ggrubr@singidunum.ac.rs

6 Internatinal Jurnal f Scientific and Research Publicatins, Vlume 3, Issue 12, December