- https://ntrs.nasa.gov/search.jsp?R=19810011498 2020-03-21T13:44:30+00:00Z NASA TP 1837 NASA TechnicalPaper 1837 c. 1 . A Computer Technique for Detailed Analysis of MissionRadius and ManeuverabilityCharacteristics of Fighter Aircraft Willard E. FOSS, Jr. MARCH 198 1 TECH LIBRARY KAFB, NM 00b788Z NASA Technical Paper 1837 A ComputerTechnique for Detailed Analysis of Mission Radiusand ManeuverabilityCharacteristics of FighterAircraft Willard E. FOSS, Jr. La ugley Resea rcb Ceu ter Harnpton, Virginia National Aeronautics and Space Administration Scientific and Technical Information Branch 1981 SUMMARY A computer technique to determine the mission radius and maneuverability characteristics ofcombat aircraft has been developed. The technique has been used at the Langley ResearchCenter to determine critical operational require- ments and the areas in which research programs would be expected to yield the most beneficialresults. In turn,the results of researchefforts havebeen evaluated in terms of aircraft performance on selected mission segments and for complete mission profiles. The aircraftcharacteristics and flight constraints are represented in sufficient detail to permit realistic sensitivity studies in terms of either configuration modifications or changes in operational proce- dures. Sample calculationsare provided to illustrate the wide variety of mili- tary mission profiles that maybe represented.Extensive use of thetechnique in evaluationstudies indicates that the calculated performance is essentially the same as that obtained by the proprietary programs in use throughout the air- craft industry. INTRODUCTION A computer technique to determinethe mission radius and maneuverability characteristics ofcombat aircraft for a variety of military profiles hasbeen developed. The technique has beenused at the Langley Research Center todeter- mine critical operational requirements and the areas in which research programs wouldbe expected toyield the most beneficialresults. In turn, the results of research efforts havebeen evaluated in terms of aircraft performance on selected mission segments and for complete mission profiles. The aircraft char- acteristics and flight constraints are represented in sufficient detail to per- mit realistic sensitivity studies of configurationmodifications and changes in operational procedures. The technique has also been utilized in cooperative efforts with the Department of Defense to evaluate the performance capabilities of a proposed military aircraft andof configuration concepts developed at Langley Research Center. In a preliminary phase of the former effort, the per- formance for several mission profiles was determined by using thepresent tech- - " nique, and theresults werecompared with similarcalculations by thecontractor forthe purpose of calibrating any differences in calculation technique. The results were in excellent agreement both in terms of overall mission capability and detailed mission segment performance. Themain text of this paper is a description of the features andassump- tions of the technique andof theassociated numerical computerprogram. The mission profiles are described, and then the representation of each mission segment is discussed in detail. As each item is described, examples are included to illustrate aircraft performance. Appendix A contains a description of the input data required to define the aircraft as well as the input data concerned with profile selection and flight-pathcontrol. Appendix B contains descriptions of theoutput data. Options to control both the amountand form of theoutput resultsare described, and sample output listings are included to illustrate the effect of theseoptions. The outputparameters are also defined in appendix B. The program requires 105 0008 words of central core memory to run on the Control Data CYBER 175 computer system operating under NOS 1 .3 at the Langley computercomplex. The run time for a single mission profile is aboutfour sec- onds; about 12 seconds arerequired for a series of five different profiles. SYMBOLS The units used forthe physical quantities in thefigures and discussion in this paper are given in theInternational Systemof Units (SI) and parentheti- cally in the U.S. Customary Units. The tabulatedoutput data are in SI units. Calculations weremade in U.S. Customary Units. Conversion factorsrelating the two systems arepresented in reference 1. D aircraft drag Dr engine ram drag ESF engine s izing factor ES aircraft specific energy 9 gravitational acceleration h altitude L aircraft lift L/D aircraft lift-drag ratio M Machnumber n load factor OWE aircraft operating weight empty PS aircraft specific power R range SEC engine specific fuel consumption SLS sea-level-static conditions engine gross thrust T9 Tom aircraft take-offgross weight T/w aircraft thrust-weight ratio(thrust loading), installed SLS 2 V velocitytrue W we ight Wf engine-fuelweight w/s wing loading,gross weight over wing reference area X horizontaldistance c1 ofangle attack Y flight-pathangle 6 thrustinclination angle, positive nozzle down A dot over a symbol denotes its time derivative. RESULTS AND DISCUSSION GENERAL DESCRIPTION OF PROGRAM Inthe development of the program a modularconcept was selected as the most logicalapproach to a multimissionprogram. The presentprogram is a com- bination of five mission modules which represent mission profiles currently of interest. The missionmodules are listed by number identificationin table 1 withbrief descriptions to indicatethe profile variety that is available. Each mission module is designed to determinethe combat radius or rangecapability for a specific military mission with its associatedground rules and profile definitions.Several of these mission modules contain optional profile segments which may bedeleted to representalternate missions. The module conceptper- mits theaddition of new modules, or themodification of existing modules, to represent new or unusual mission profile specifications. Althoughthe mission modules havebeen used in vehicle sizing studies, the program is notdesigned to internallysynthesize configurations or to generate aerodynamic,propulsion, or structural characteristics. The characteristicsof thesevehicles are predetermined by specialists in each discipline, andthey are input to theprogram as a database for all calculations. The representa- tionof the aircraft data (appendix A) is extensive and includes realistic limits on engine and aircraft operational boundaries andon maximum attainable lift coefficients. Each missionmodule controls the calculation of themission-segment data (take-off, climb, cruise, combat, etc.) required by theprofile definition and utilizesappropriate segment modules. The profile logic withinthe mission module is thenused to calculate theoverall range or radiuscapability with balancedoutbound and inbound radii and with the required combat fuelallowance. If a low-levelpenetration, or dash, is includedin the profile definition, the outboundand inbound dash radii may also bebalanced. Performance for missions withalternate radii and combat fuelallowances are also calculatedfor use in 3 trade-offstudies. For each mission profile, an iterative procedure is used to balancethe radii.Initially, the outbound performance is calculatedto a desired mission radius. Then the fuel allowances at the combat stationare determined. Finally,the remaining fuel is consumed to determine the inbound (return)radius. Basedon thedifference in outbound and inbound radii, an estimate of the outbound radius is made,and thecalculations are repeated until the radiiare equal. During each iteration some outbound segments, and all inbound segments, must be recalculated because of the sensitivity of segment performance tovehicle weight. Although most mission profilesare bal- anced in several iterations, this processcould involve a large numberof cal- culations, particularly if the inbound profile includes a climb to a return cruisecondition. MISSION SEGMENT MODULES The present program was developed with the assumption that great emphasis wouldbe placed on balanced-radius profiles, and that alternate radius missions wouldbe of interestas trade-off information. A technique was therefore developed that would produce accurate performance results for all mission seg- ments andwould minimize the repetitive calculations normally required to bal- ance radii and develop radiustrades. When a segmentmodule is first utilized to compute performance for a particular modeof flight (for example, climb to cruise altitude) which is known to be sensitive to vehicle weight, the segment performance is automatically computed for a series of four initial weights. The results, in terms of quantitiesappropriate to the particular segment, are retained in dataarrays as functions of thefour initial weights. These data arraysare referred to as mission-segment data. The four initial weights are selected(internally) to cover the range of actual weights that wouldbe expected to occurthroughout the mission. Specificdetails of the segment data are presented as each segmentmodule is described in a subsequent section. Afterthe mission-segment data has been calculatedfor all segments in the mission definition, the mission-module logic can determinethe balanced radii and alternate radii missionsvery efficiently by interpolating the segment data forrequired parameters at theappropriate segment weight. I Afterthe performance hasbeen determined for a given aircraft take-off i gross weight (TOGW) and associatedoperating weight empty