870001 Heavy!DutyTruckAerodynamics Richard A,Drollinger Kenworth TruckCo. ADivisionofPACCAR ABSTRACT Theappearance ofheavydutytrucks has beguntochangeduetomanufacturers' efforts to improve truckaerodynamics. Theneedtomake trucks moreaerodynamic hascomefromhigher fuelcostsandtheovmers' needtostaycost­ competitive. Improving theaerodynamics of Class8trucksisnotsimple. Itrequires an understanding oftheaerodynamics involved, the testsneeded toevaluate thevehicle shape changes, andvalidestimates ofthevehicle operational costsavings. Thispapersupplies thereaderwithanintroductory discussion in theseareas, coversthebasicsofheavyduty truckaerodynamics, andexplains someofthe current dataavailable forimproving truckaero­ dynamics. INTROOUCTI ON FORYEARSITSEEMEDtherewaslittlemotivation tohavegoodaerodynamics withheavy duty trucks. Today, however, goodaerodynamics is recognized tobeofgreatimportance toany highway truckoperation, primarily asasource ofreduced operating expense. Inthenottoo distant past,typical fueleconomy ofafully loaded Class8truckwasabout4milesper gallon, whereas todayitispossible toachieve over9mpgwithmodernaerodynamic shapes; high torque, lowRPMengines; lowprofiletiresand efficient drivetrains, combined withcareful drivinghabits. Theaerodynamic trucksoftodaydidnot comeaboutovernight. Somephotographic examples oftheevolution oftheClass8truckshapeare showninFigure1.Windtunnelworkonheavy dutyvehicles wasconducted asearl~as1953at theUniversity ofMaryland [IJ Another significant earlyheavytruckaerodynamic study wasconducted in1961bytheGeneral Motors *Numbers inbrackets, [J,indicate References. 1Corporation [2J.Therewere,however, onlyafew testpr09rams conducted bytheendofthe fifties andthrou9h thesixties. Forsometime,engineers haverealized a needforminimizing fuelconsumption, andthata substantial amountoffuelcouldbesavedwith improved aerodynamics. Intheearlysixties, it wasestimated thatrolling resistance andaero­ dynamic dragwereaboutequalat60mph,and thattheaerodynamic dragcouldbereduced by37 percent [2J.Interestin91y, thosesameestimates applytoday: although improvements havebeen made,thereispotential forfurther improvement basedoncurrent research. Also,therestofthe trucksystem--for example, thetirerolling resistance--has improved, soaerodynamic dragis stillabout50percent ofthetotaldragonthe truckatfreeway speeds. Fromtheearly1960suntilthemidseven­ tiestherewasrelatively littleaerodynamic research conducted onClass8trucks. In1973, however, theOPECoilembargo focussed thetruck industry's interest onsavin9fuel.Wholesale pricesofdieselfuelfrom1966to1986[3]are plotted inFigure2.Tothesewholesale costs, onemustaddthecostoftaxes, shipping and dealerprofit. From1972until1975thecostof dieselfuelmorethandoubled. Thenagainfrom 1978to1981thepriceofdiesel fuelrose sharply. Forthewhole1972to1981period, wholesale fuelcostsroseover850percent. Thetransportation industry isthemajor userofenergyintheUnitedStates. Sincethe 1950s, truckshaveusedabout30percent ofall theener9Yconsumed bytransportation needsin theUnitedStates[4].Asaresultofthisand theoilembar90, Congress considered abillin 1974torequire a20percent improvement inthe fueleconomy ofnewautomobiles bytheyear 1980.Congress laterconsidered thepossibility ofmandatory fueleconomy improvements for trucksandbuses. In1975,however, CongressDownloaded from SAE International by University of Michigan, Monday, September 17, 2018Figure1.Some vehicles from future.examples thepast 2ofHeavy Duty topossibly theDownloaded from SAE International by University of Michigan, Monday, September 17, 201866676869 70 7172 73 74 757677787980818283 84 85 86 Year Figure2.Wholesale priceofdiesel fuel from1966to1986. decided totrya"Voluntary Truckand8usFuel Economy Program'linlieuofmandatory require­ ments. Theriseinoilpricesintheseventies caused thefuelcostofheavydutytruck operation togofromabout10percent tonearly 50percent ofthetotalcostsinsomefleets [5J,takingitssharefromtheprofits. An improvement of15percent inaero