T/W vs. W/S Sizing PlotAE 3310 PerformanceLecture- Traditional Aircraft DesignAE 3310 PerformanceDr. Danielle SobanGeorgia Institute of TechnologyAircraft Design:a distinct discipline in aeronautical engineeringDesigner must be well versed in all disciplines“The intellectual engineering process of creating on paper a flying machine that either meets certain requirements and performance objectives, or explores new concepts, technologies and innovations”Three phases of design:Conceptual: First step in the design processIn response to a certain design goal (requirements or exploration)Overall (fuzzy) shape, size, weight, performance of airplane configurationBasic drivers are aerodynamics, propulsion, and performanceSome, but not much, consideration for stability/control, cost, no detail designAnderson’s 7 Intellectual Pivot PointsRequirementsWeight-first estimateCritical performance parameters:ClmaxL/DT/WW/SConfiguration LayoutBetter weight estimatePerformance analysisOptimizationRaymer’s Design WheelSizing Trade StudiesDesignConceptDesignAnalysisRequirementsAE 3310 PerformanceLecture- Traditional Aircraft DesignAE 3310 PerformanceDr. Danielle SobanGeorgia Institute of TechnologyNext 2 Phases of Aircraft Design Preliminary Design: major design features locked in, only minor changes allowed. Substantial analysis begins to take place, including CFD and wind tunnel tests. By the end of this phase, the manufacturer will decide if the program is a “go” or “no-go”.Detailed Design: Precise and detailed decisions are made. By this time, the aero, propulsion, structures, etc are locked in. Only very subtle details are left to make the design a realistic vehicle capable of being manufactured.AE 3310 PerformanceLecture- Traditional Aircraft DesignAE 3310 PerformanceDr. Danielle SobanGeorgia Institute of TechnologyRequirementsOften put forth in a document called an RFP (Request for Proposal)Outlines basic design requirements and goalsBasic mission or mission profileExamples:payload and type of payloadrange/loiter requirementscruise speed and altitudefield length for takeoff/landingfuel reservesclimb requirementsmaneuvering requirementsCertification base (experimental, FAR 23, FAR 25, military)Can be specific or vagueInitial Weight EstimationWTO= WOE+ Wf+ WPLWTO Takeoff Gross WeightWOE Operating Empty WeightWfMission Fuel WeightWPLPayload WeightFAR 23- normal, utility, aerobatic, commuterFAR 25- transportsAE 3310 PerformanceLecture- Traditional Aircraft DesignAE 3310 PerformanceDr. Danielle SobanGeorgia Institute of TechnologyWOE = WE+ Wtfo+ WcrewFurther,WcrewWeight of crewWtfoWeight of all trapped (unusable) fuel and oilWEEmpty Weight = manufacturer’s empty weight + fixed equipment weightFor initial weight estimation, we want to estimate WTO, WEand WfStep 1: Determine mission payload weight passengers and baggagecargomilitary loads (bombs, ammunition, etc)Rules of Thumb: passenger aircraft: 175 lbs per person30 lbs luggage per person, short to medium flights40 lbs luggage per person, long flightsAE 3310 PerformanceLecture- Traditional Aircraft DesignAE 3310 PerformanceDr. Danielle SobanGeorgia Institute of TechnologyCrew Weight:passenger: 175 lbs per crew member, 30 lbs baggagemilitary: 200 lbs per crew member, no baggageStep 2: Guess a likely value of take-off weight Base this guess on existing similar aircraftStep 3: Determine mission fuel weight, WfWf= WFused+ WFresWfresare the fuel reserves required for the mission. As a fraction of WFusedAs a requirement for additional range to an alternate airportAs a requirement for loiter timeAE 3310 PerformanceLecture- Traditional Aircraft DesignAE 3310 PerformanceDr. Danielle SobanGeorgia Institute of TechnologyTo find Wfused, use fuel fraction methodBreak down mission into a number of mission phases and calculate fuel used in each phase based on simple calculations or experience.Fuel Fraction: for each phase is defined as the ratio of end weight to begin weightPhase 1: Engine Start and Warm UpW1/WTOUse Handout Table 2.1Phase 2: TaxiW2/W1Use Handout Table 2.1Phase 3: TakeoffW3/W2Use Handout Table 2.1AE 3310 PerformanceLecture- Traditional Aircraft DesignAE 3310 PerformanceDr. Danielle SobanGeorgia Institute of TechnologyPhase 4: Climb to Cruise and Accelerate to Cruise SpeedW4/W3Use Handout Table 2.2andUse Breguet’s Endurance Equation(you will need to assume appropriate values for L/Dclimb, specific fuel consumption, time to climb [or rate of climb])Phase 5: CruiseW5/W4Use Handout Table 2.2 andUse Breuget’s Range EquationE = 550ηprcVE =1ctLDlnW0W1(prop)(jet)R =Vct(jet)R = 550ηprcLDlnW0W1(prop)LDlnW0W1LDW0W1lnBe careful using these equations. You must use consistent units!AE 3310 PerformanceLecture- Traditional Aircraft DesignAE 3310 PerformanceDr. Danielle SobanGeorgia Institute of TechnologyPhase 6: LoiterW6/W5Use Handout Table 2.2andBreguet’s Endurance EquationPhase 7: DescentW7/W6Use Handout Table 2.1Phase 8: Landing, Taxi, and ShutdownW7/W6Use Handout Table 2.1Now calculate the mission fuel fraction:Mff= multiply all phase fractions togetherWFused= (1 - Mff) WTOWF = (1 - Mff) WTO+ WFresAE 3310 PerformanceLecture- Traditional Aircraft DesignAE 3310 PerformanceDr. Danielle SobanGeorgia Institute of TechnologyStep 4: Calculate Tentative WOEWOEtent= WTOguess-WF-WPLWtfocan be as high as 0.5% for some airplanes, often neglected at this stageStep 5: Calculate Tentative Value for WEWEtent= WOEtent-Wtfo-WcrewStep 6: Find Allowable Value for WEFor most aircraft of a defined type, there exists a linear relationship between log10WEand log10WTO.Use existing graphs or use Handout Table 2.15.If you don’t have graphs or Handout Table 2.15, create your own by plotting WEand WTOof similar aircraft and regressing the curve yourself.For completely new aircraft, try and extrapolate existing data, or use non-traditional techniques (GT advanced design sequence in graduate program)AE 3310 PerformanceLecture- Traditional Aircraft DesignAE 3310 PerformanceDr. Danielle SobanGeorgia Institute of TechnologyThis linear relationship looks like this:Empty Weight, lbsGross Takeoff Weight, lbslog10 scale!!!Regression Curve: Assumes WE was designed to be lowest possible for best cost/performance, so each point represents “state of the art”.Regression Equation: inv log10{[log10WTO-A]/B}A and B are the regression constants (slope and intercept) of the line. Use Handout Table 2.15 for values for types of aircraft, or plot your own