Derivation of Flight Characteristics.pdf

7/29/2019 Derivation of Flight Characteristics.pdf

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D.-K. Baik (Ed.): AsiaSim 2004, LNAI 3398, pp. 450457, 2005. Springer-Verlag Berlin Heidelberg 2005

Derivation of Flight Characteristics Dataof Small Airplanes Using Design Softwareand Their Validation by Subjective Tests

Sugjoon Yoon 1, Ji-Young Kong 1, Kang-Su Kim 1,Suk-Kyung Lee 1, and Moon-Sang Kim 2

1 Department of Aerospace Engineering, Sejong University 98 Gunja-Dong,Gwangjin-Gu, Seoul, 143-747 Republic of Korea

2 School of Aerospace and Mechanical Engineering, Hankuk Aviation University200-1,Whajon-dong, Koyang-city, Kyungki-do, 412-791 Republic of Korea

Abstract. It is very difficult to acquire high-fidelity flight test data for smallairplanes such as typical unmanned aerial vehicles and RC airplanes becauseMEMS-type small sensors used in the tests do not present reliable data in gen-eral. Besides, it is not practical to conduct expensive flight tests for low-pricedsmall airplanes in order to simulate their flight characteristics. A practical ap-proach to obtain acceptable flight data, including stability and control deriva-tives and data of weights and balances, is proposed in this study. Aircraft de-sign software such as Darcorp's AAA is used to generate aerodynamic data forsmall airplanes, and moments of inertia are calculated from CATIA, structuraldesign software. These flight data from simulation software are evaluated sub-

jectively and tailored using simulation flight by experienced pilots, based onthe certified procedure in FAA AC 120-40B, which are prepared for mannedairplane simulators. Use of design S/W for generation of parameter values rep-resenting flight characteristics turns out valid. In this study a practical proce-dural standard is established for procuring reliable data replicating flight char-acteristics of an airplane.

1 IntroductionIn general, parameter values representing flight characteristics of an airplane are de-rived from either flight tests or dedicated design software such as DATCOM [1].However, it is practically very difficult to obtain reliable data from flight tests forsmall airplanes such as RC (Remote Control) airplanes and UAVs (Unmanned Ae-rial Vehicles), which have very limited payload capacities. High-fidelity sensors usedin typical flight tests of manned airplanes are relatively big in volume and weight forsmall airplanes, which causes change of original flight characteristics and results inthe measurement of data with significant errors. MEMS sensors may be considered to

be alternatives to conventional ones. But their fidelity and reliability are much lowerthan those of conventional sensors, and their test results are not accurate enough to beused in typical flight simulation.

The purpose of this study is to establish a practical procedural standard for procur-ing reliable data replicating flight characteristics of an airplane, which can be used in


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Derivation of Flight Characteristics Data of Small Airplanes Using Design Software 451

flight simulation and design of a flight control system of a small airplane. In thisstudy Darcorps AAA (Advanced Aircraft Analysis) software [2], which has beenwidely used in the conceptual design of an airplane, is adopted for derivation of aero-dynamic data and structural design software, Dassaults CATIA [3], for computation

of moments of inertia. Then the design data obtained from AAA and CATIA areimplemented in a proven flight simulation code and subjectively validated based onthe test procedure regulated in FAAs AC120-40B [4]. RC airplanes such as Extra300s and 40% scale Night Intruder UAV of Korea Aerospace Industry are used inthis paper as test beds for validation of the proposed procedure. The standardizedprocedure has been applied to derivation of flight characteristics data of several otherairplanes, and turns out to be satisfactory.

2 Derivation of Flight Characteristics Data

2.1 Derivation of Aerodynamic Data

In this study seven RC airplane models, including high-wing Trainer 40, UT-1, low-wing Extra 300s (Fig. 1), and 40% scale Night Intruder (Fig. 2) are selected and theiraerodynamic data are derived from Darcorps AAA design software. Among themonly Extra 300s and 40% scale Night Intruder are used as test beds in this paper.Aerodynamic data generally vary depending on the position in the flight envelop.However, a flight envelop of an RC airplane is usually very small, and its flight char-acteristics is about the same in the whole flight envelop. Thus steady state level flight

is assumed as a single reference flight condition in the derivation of aerodynamicparameters of an RC airplane. Geometric dimensions are obtained by either measur-ing real RC airplanes or reading manufacturers design drawings. Total mass and thecenter of gravity of an airplane are computed by measuring mass and position of eachcomponent such as fuselage, main wing, tail wing, fuel, landing gear, servo, and soon. Aerodynamics depends on the external shape of an airplane. Especially, airfoils of main and tail wings are critical in computation of aerodynamics. These features areused as important inputs to AAA. In computing thrust forces of engines manufac-turers data are essential.

Fig. 1. Extra 300s Fig. 2. 40% scale Night Intruder

While a typical AAA design process is illustrated in Fig. 3, the customized designprocess applied to this study is described in Table 1. Fig. 4 shows the result of the 9 th process in the table, and Table 2 summarizes major flight characteristics data ob-tained from AAA for Extra 300s and 40% scale Night Intruder.


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452 Sugjoon Yoon et al.

Table 1. Customized design process for derivation of stability and control derivatives

1. input present velocity, altitude, weight2. input engine type, configuration of main and tail wings, number of landing gears, etc3. measure and input sizes of fuselage, main wing, tail wing, etc

4. input derivative values related to airfoils of main and tail wings5. measure and input weights of fuselage, main and tail wings, fuel, landing gear, etc6. set and input required flight performance values such as stall velocity, landing distance,

maximum cruise speed, etc7. input propulsion performance values such as maximum thrust, fuel consumption rate, etc8. set other required values for stability and control derivatives9. AAA returns stability and control derivatives for a designed airplane

Fig. 3. Typical AAA design process

Fig. 4. AAA GUI showing stability and control derivatives of Extra300s


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Table 2. Flight characteristics data for RC airplanes (NI: Night Intruder)

Aero Coeff. Extra 300s 40%scale NI Aero Coeff. Extra 300s 40%scale NICL0 0.4119 0.6043 CMAdot -2.2830 -3.9936CLA 4.5802 5.0169 CMQ -4.0303 -12.3658CLQ 5.7712 5.5208 CLB -0.0027 -0.0769CD0 0.089 0.0434 CLP -0.6167 -0.6375CDA 0.9061 0.2117 CLR 0.3744 0.3692CYB -0.4035 -0.5463 CLDR -0.0102 -0.0243CYP -0.0337 -0.0435 CNB 0.123 0.1134CYR 0.3154 0.2839 CNP -0.0037 -0.0100CM0 -0.0553 0.0000 CNR -0.1469 -0.1326CMA -0.9076 -1.0026 CLDE 0.5216 0.1922

2.2 Computation of Weight and Balances

Principal moments of inertia of an airplane are computed by two different methods:one is to conduct experiments with a real RC airplane, and the other one is to useDassaults CATIA design software. However, product of inertia can be obtained onlyby CATIA design. Two different data sets of moments of inertia are examined byimplementing them in the in-house flight simulation software, which has been devel-oped and examined for simulation of several military UAV systems. Experiencedpilots fly the simulation models with different data sets, and validate the models sub-

jectively based on the test procedures regulated in FAA 120 40B.

2.2.1 Experimental Method

Moments of inertia of an RC airplane can be obtained by measuring weight, cablelength, distance between cables, and period of oscillation in the experiment illustratedin Fig. 6. The mathematical relation [5] between these parameters is as follows:

L D

T W I M 22

2

16 = (1)

where, I = moment of inertia ( kg/m 2)W M = weight of an airplane ( Kgm/sec

2)T = period of oscillation ( sec )

D = distance between cables ( m) L = cable length ( m)

The average period of oscillation is obtained by measuring five consecutive periodsafter the coupling effect between principal axes diminishes significantly. Fig. 5 showsthree experimental settings for three principal axes, while Table 3 contains experi-mental values for Extra 300s.

Table 3. Experimental values of 3 principal moments of inertia for Extra 300s

I xx I yy I zz 0.147 kg/m2 0.204 kg/m2 0.044 kg/m2

2.2.2 Computational Method Using CATIACATIA, 3D structural design software from Dassault, returns every moment of inertiaand center of gravity once 3D configuration design is completed and material density


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is input. The design process of Extra 300s is illustrated in Fig. 6, and resulting mo-ments of inertia are listed in Table 4. Moments of inertia for 40% scale Night Intruderis also included in the table. Use of CATIA requires more efforts and time in thelearning and design process than the experimental method, even though it can avoid

the structural damage in the cable connection part of an airplane, which may not beavoidable for preparation of the experiment.

Table 4. Computational values of moments of inertia for Extra 300s and 40% scale NI (unit:kg/m 2 )

Ixx Iyy Izz IxzExtra 300s 0.175 0.179 0.342 -0.000824840% scale NI 10.832 22.080 24.220 -4.902

Fig. 5. Experimental settings for measuring 3 principal moments of inertia ( I x , I y , I z)

Fig. 6. CATIA design process of Extra 300s

The values of moments of inertia in Table 3 and 4 are noticeably different. Twodifferent sets of parameter values are implemented in proven flight simulation soft-ware and subjectively validated based on the test procedures regulated in FAAsAC120-40B. Pilots turn out to prefer data values derived from CATIA because theflight characteristics with the computed data set resembles the real one better than theflight model with moments of inertia from experiments. In order to obtain a moreaccurate data set, the RC plane should be heavily damaged for cable connection.Because structural damage of an expensive airplane was not allowed in the experi-ment, the cable hook could not be located at the right position. This constraint causescouplings among oscillations with respect to three principal axes, and results inmeasurement errors in moments of inertia.


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3 Test and Evaluation of Design Parameters

3.1 Flight Simulation S/W (RC Virtual Flight)

The main purpose of derivation of valid aerodynamic data is to simulate the flightcharacteristics of an airplane without flight test data. On the contrary, the data setmostly from computer simulation software is validated subjectively by flying a simu-lated airplane in this study. Therefore, reliable flight simulation software is requiredfor the purpose. UAV-HILS laboratory at Sejong University has developed compre-hensive flight simulation software named RC Virtual Flight [6], [7] since 1998. RCVirtual Flight has been upgraded and applied to various research projects sponsoredby Korean government and industry. Table 5 summarizes its features, while Fig. 7captures some of its GUI windows.

Fig. 7. Snapshots of RC virtual flight simulation

Table 5. Features of RC virtual flight

Features Remarks

fixed-wing androtary-wing models

Pioneer, F16, ChangGong-91, Extra300s, UH60, S61, AH1, Yamaha Rmax, etc.full flight envelope6 DOF nonlinear math models

3D terrain librariesdomestic airports such as Kimpo, Incheon, Kimhae, Jeju, etc.domestic RC runways such as Amsadong, Yoido, Oedo, etc.military UAV runways

atmosphericenvironment turbulence, side wind, gust, wind shear, etc.

sound effectsengine, propeller noiseDoppler effects5.1 channel

lesson planRC flight training lessons edited by experience RC Flight Instructorsmilitary UAV training lessons

Maintenance andupgrade

off-the-shelf hardware productsobject oriented program based on C++, Matlab, and Simulinkopen architecture

remote controllerUSB interfaceRC trainer jack interfacecompatible with either simulated or real hardware

3.2 Subjective Tests in FAA AC120-40B

Validation procedure of the simulation data follows the subjective test rules in FAAAC 120-40B, which is prepared for manned airplane simulators. The test procedureand its applicability to RC airplanes are summarized in Table 6. Flight profiles of RCand manned airplanes are about the same. Thus typical flight profiles, such as taxing,taking-off, cruising, loitering, and landing, and their relevant tests have to be applica-ble to RC airplanes, too. Test items for the flight profiles and systems, which are


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neither comprised nor critical in RC flight, must be discarded. Besides, test proce-dures with respect to a visual system and a motion platform of a manned flight simu-lator do not have to be applied to the flight data validation process of an RC airplane.

Table 6. Subjective test items in FAA 120-40B and their applicability to RC airplanes Subjective Tests

Check Items DetailsApplicability

pre-flight check system equipments such as switches, indicators, etc. Oengine start Opre-takeoff

taxi Onormal takeoff Otakeoff

abnormal/emergency Takeoff Oclimb Ocruise OIn-flight

descent Onon-precision Xapproaches

precision Xnormal landing Olanding

abnormal/emergency landing Opost landing landing roll and taxi O

airplane and power plant systems operation Oflight management and guidance system X

airborne procedures Oflight phase

engine shutdown and parking O

visual system X

motion system Xspecial effect X

3.3 Subjective Test and Evaluation by Experienced RC Pilots

Following the procedure regulated in FAA AC 120-40B, the design parameter valuesobtained from AAA and CATIA are subjectively evaluated by experienced RC pilots.The design data such as moments of inertia, stability derivatives, etc are implementedin RC Virtual Flight and tuned based on the indications of experienced pilots. Table 7shows a part of pilots indications and corrected parameters with respect to Extra300s.

Table 7. Pilots indications and corrected parameters with respect to Extra 300s

Pilots Indications Corrected Parameters

Rudder effectiveness on roll is too large. CLB ( L

C )

Rudder effectiveness on yaw is too small. CNDR (r N

C

)

Airspeed is too sensitive to thrust. CDu (u DC )

Pitch angle becomes too large during the trimmed level flight as theairspeed increases.

CMu (u M

C )


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4 Conclusions

Darcorps AAA is used for aerodynamic design and Dassaults CATIA for derivationof weights and balances, while a subjective test procedure is extracted from FAA AC

120 40B. Seven RC airplanes, comprising Extra 300s and Night Intruder 40% scale,are selected as test beds. Use of design S/W for generation of parameter values repre-senting flight characteristics turns out valid. In this study a practical procedural stan-dard is established for procuring reliable data replicating flight characteristics of anairplane, which can be used in flight simulation and design of flight control systemsof small airplanes.

Acknowledgement

This research(paper) was performed for the Smart UAV Development Program, oneof the 21st Century Frontier R&D Programs funded by the Ministry of Science andTechnology of Korea.

References

1. USAF Stability and Control DATCOM, Flight Control Division, Air Force Flight DynamicsLaboratory, Write-Patterson Air Force Base, Fairborn, OH.

2. Jan Roskam,: Airplane Design, Roskam Aviation and Engineering Corporation (1986)3. CATIA Reference Manual.4. FAA AC120-40B.: Airplane Simulator Qualification (1991)5. R.C. Nelson.: Flight Stability and Automatic Control, McGraw-Hill (1998)6. Yoon S.: Development of a UAV Training Simulator Based on COTS Products and Object-

Oriented Programming Languages, Proceedings of AIAA Modeling & Simulation Confer-ence, Aug. 3-5 (2001)

7. Yoon S. and Nam K.: Development of a HLA-based Simulation Game for RC Airplanesand UAVs, Proceedings of AIAA Modeling and Simulation Conference, Aug. (2004)

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Derivation of Flight Characteristics.pdf