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SAE TECHNICALPAPER SERIES 2001-01-2072

Advanced Aerodynamic Devices to Improvethe Performance, Economics, Handling and

Safety of Heavy Vehicles

Robert J. EnglarGeorgia Tech Research Institute Aerospace

Transportation & Advanced Systems Lab

Government/Industry MeetingWashington, D.C.

May 14-16, 2001

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1

2001-01-2072

Advanced Aerodynamic Devices to Improve thePerformance, Economics, Handling and

Safety of Heavy Vehicles

Robert J. Englar Georgia Tech Research Institute

Aerospace, Transportation & Advanced Systems Lab

Copyright © 2001 Society of Automotive Engineers, Inc.

ABSTRACT

Research is being conducted at the Georgia TechResearch Institute (GTRI) to develop advancedaerodynamic devices to improve the performance,economics, stability, handling and safety of operationof Heavy Vehicles by using previously-developed andflight-tested pneumatic (blown) aircraft technology.Recent wind-tunnel investigations of a generic HeavyVehicle model with blowing slots on both the leadingand trailing edges of the trailer have been conductedunder contract to the DOE Office of Heavy VehicleTechnologies. These experimental results show overallaerodynamic drag reductions on the Pneumatic HeavyVehicle of 50% using only 1 psig blowing pressure inthe plenums, and over 80% drag reductions ifadditional blowing air were available. Additionally, anincrease in drag force for braking was confirmed byblowing different slots. Lift coefficient was increasedfor rolling resistance reduction by blowing only thetop slot, while downforce was produced for tractionincrease by blowing only the bottom. Also, side forceand yawing moment were generated on either side ofthe vehicle, and directional stability was restored byblowing the appropriate side slot. These experimentalresults and the predicted full-scale payoffs arepresented in this paper, as is a discussion of additionalapplications to conventional commercial autos, buses,motor homes, and Sport Utility Vehicles.

INTRODUCTION

Users of heavy trucks such as tractor/trailercombination vehicles face a number of less thanoptimum operating conditions. Despite significantreductions in drag coefficients in the latest generationof tractors, these Heavy Vehicles (HVs) remain“draggy” compared to much more streamlinedautomobiles. This is due in part to practical limitationson: physically providing a long smooth aft surfacesuch as a boat tail to prevent flow separation andturbulence at the rear of the trailer; completely sealing

the gap between the tractor and the trailer; andsmoothing the underbody of the vehicle. In addition,front radiators have not been optimized from a drag-reduction standpoint. Typical drag coefficient valuesfor a variety of HVs can range from 0.65 to 0.9 (fromReference 1). Figure 1 shows the significant fuelsavings that can result if the drag coefficient can bereduced. It has been estimated by engineeringpersonnel of the American Trucking Associations(ATA) that, if applied to today’s US Heavy Vehiclefleet operating on level roads, these drag reductionsapproaching 35% could result in roughly 1.2 billiongallons of fuel saved per year. Extrapolated, a 50%drag reduction could save over 1.7 billion gallons ofdiesel each year. A further result of aerodynamically“dirty” vehicles is the production of splash and spray,a nuisance to motorists and truck drivers alike, as wellas turbulence in the vicinity of large vehicles, which isdisturbing to passenger car drivers. Theseshortcomings are explained further in the ATAStatement of Need for Improved Heavy TruckAerodynamics, Reference 2.

Figure 1 – Effect of Drag Coefficient Reductionon Fuel Consumption (from Ref. 1)

2

Considerable recent interest has arisen in technology toreduce Heavy Vehicle drag to improve highwayoperating efficiency, primarily because the drag forcerises with the square of the vehicle speed while therequired horsepower to overcome that drag increaseswith the cube of the velocity. With fuel prices risingdramatically recently, drag reduction is thus a vitalconcern to the trucking industry. However,appreciable additional gains can also be had by carefulcontrol of aerodynamic forces and moments other thandrag, which for the most part have been ignored incurrent truck design and operation. For instance, thecreation of lift on the vehicle (effective weightreduction) can unload the tires and reduce rollingresistance, while creation of negative lift or downforcecan increase “weight” on the wheels and traction, thusincreasing braking as well as handling in wet/icyweather. This aerodynamic download can alsoeliminate hydroplaning. While it has been shown thatdrag increases greatly due to side wind or yaw angle(Refs. 1 and 3), side wind presence also impliesincreased side force and yawing moment on the trailer,thus reducing its directional stability and safety.Safety, stability and handling can be enhanced byblowing control of side loads and moments on theseHeavy Vehicles if caused by side winds, gusts or othervehicles passing. An aerodynamically-controlledconcept may also help to eliminate the jack-knifingproblem if resulting from extreme wind side loads onthe trailer. Lastly, there are instances where additionaldrag increase is desirable, such as steep downhilloperations in mountains, or sudden need foremergency braking from high speed.

Based on the above considerations, it should be quitedesirable to develop aerodynamic devices that couldachieve at least two or more of these potential gainswhile requiring little mechanical restriction or impacton vehicle operation. Recent aerodynamic research(Reference 3) at GTRI’s Aerospace, Transportationand Advanced Systems Lab has identified significantreductions and/or augmentations of vehicle forces andmoments which can be achieved on automotivevehicles by the use of tangential injection ofpressurized air into the vehicle’s aft region, stronglymodifying the aerodynamic flowfield around thatvehicle. Since momentum injection can affect thevehicle’s lift, drag, and side force as well asaerodynamic moments, the impact of blowing on theperformance, safety, economics and stability appears tooffer significant improvements in Heavy Vehicleoperation. These potential gains have led to a currentresearch program being conducted at GTRI for theDOE Office of Heavy Vehicle Technologies(Reference 4). A description of this program and thenovel aerodynamic technology being employed isprovided in Reference 5. Since that paper waspresented in June, 2000, two series of wind-tunnelevaluations have been conducted at GTRI to confirmaerodynamic improvements yielded first by novelunblown geometry changes, and second by theaddition of blowing to various portions of a HeavyVehicle model. The objectives of these tests were toverify the blown concept’s capabilities to: reduce

aerodynamic drag for efficiency or increase drag forbraking; increase lift to reduce tire rolling resistance orreduce lift to increase traction and braking; andprovide increased lateral/directional stability and safety,all without use of external moving aerodynamiccomponents. The present paper first describes thebasis of pneumatic aerodynamics and its application toHeavy Vehicles, and then provides details of the twowind-tunnel programs, their results, and possible futureapplications.

PNEUMATIC AERODYNAMICS

GTRI researchers have been involved for a number ofyears in the development of pneumatic (pressurized airblowing) concepts to yield efficient yet mechanicallysimple means to control and augment or reduce theaerodynamic forces and moments acting on aircraft.This was detailed in References 5, 6, 7, and 8, but willbe summarized briefly here to familiarize the readerwith the technology. Figure 2 shows the basicpneumatic concept, which has become known asCirculation Control (CC) aerodynamics. Here, anairfoil’s conventional mechanical trailing edge devicehas been replaced with a fixed curved surface and atangential slot ejecting a jet sheet over that surface.That jet remains attached to the curved surface by abalance between sub-ambient static pressure on thesurface and centrifugal force (the so-called CoandaEffect, Reference 8). This greatly entrains the externalflowfield to follow the jet, and thus enhances thecirculation around the airfoil and the aerodynamicforces produced by it. The governing parameter is notangle of attack, but rather the blowing momentumcoefficient:

Cµ = m Vj / (q S)

where m is the jet mass flow, Vj the isentropic jetvelocity, S is a reference wing area (or frontal area Afor a vehicle configuration) and q is the freestreamdynamic pressure, 0.5 ρ V 2 , with ρ being the free-stream density, not the jet’s density. At lower blowingcoefficient (Cµ) values, augmentation of theaerodynamic lift by a factor of ∆Cl / Cµ = 80 has beenrecorded (Ref. 8), representing an 8000% return on theinvested momentum (which in a physical sense is alsoequal to the jet thrust). Familiarity with blown

Figure 2 – Basics of Circulation Control Aerodynamics on a Simple 2-D Airfoil

3

aerodynamic systems will remind the reader that this isquite extraordinary: thrust-deflecting Vertical Take-Off and Landing (VTOL) aircraft are fortunate if theyrecover anything near 100% of the engine thrustexpended for vertical lift. It is because of this highreturn, or conversely, because of very low requiredblowing input and associated power required to achievea desired lift, that Circulation Control airfoils appearvery promising for a number of applications. The A-6/CC Wing Short Take Off & Landing (STOL) flightdemonstrator aircraft (Figure 3 and Reference 6)showed the STOL performance listed, but alsosuggested capabilities very useful to ground vehicles:during short takeoff, it demonstrated very high lift andreduced drag, while in the approach/landing mode,high lift with high drag was shown.

These advantages led to the application of thispneumatic concept to improve the aerodynamics of analready streamlined car (Reference 3). The resultinglarge jet turning angle and the curved rear of thevehicle are shown in Figure 4. Significant butdistinctly different trends were observed dependingupon which portion of the tangential slot was blown.Blowing the full slot produced the large jet turning inFigure 4, and drag increases of greater than 70%,showing potential for pneumatic aerodynamic braking.Blowing only the outside corner of the slot weakenedthe corner vortex rollup, lessened aft suction, andreduced drag by as much as 35% (refer back to Figure1 for representative fuel savings). Blowing the aft slotalso yielded a lift increase of 170%. One can envisiona similar slot applied to the lower rear surface thatcould yield negative lift or positive down force instead.This concept has been patented by GTRI and verifiedby a similar installation on a model of a EuropeanFormula 1 race car (Reference 5).

Figure 3 – A-6/CCW STOL Flight Tests Confirming Pneumatic Devices for Aerodynamic Force Augmentation or Reduction

Figure 4 - Experimental Confirmation ofPneumatic Technology on a Streamlined Car; AftView showing Blown Jet Turning

DOE PNEUMATIC HEAVY VEHICLEPROGRAM TEST RESULTS

Based on the above results, a research program wasinitiated at GTRI for the Department of Energy’sOffice of Heavy Vehicle Technologies (Reference 4).The goal was to apply this pneumatic technology totractor-trailer configurations to develop anexperimental proof-of-concept evaluation that wouldhopefully lead to an on-the-road demonstration on anoperating blown Pneumatic Heavy Vehicle (PHV).Portions of that effort, including a preliminaryfeasibility study, Computational Fluid Dynamics(CFD) pneumatic analyses, and design of baselineand pneumatic wind-tunnel configurations, have beencompleted and were reported in Reference 5. Figure5 shows a possible schematic of a generic PneumaticHeavy Vehicle with tangential blowing slots on eachof the trailer’s aft edges as well as blowing on therounded upper leading edge of the trailer.

PHASE I WIND-TUNNEL EVALUATIONS OFBASELINE UNBLOWN HV-

To serve as a reference and to investigate initial non-blown aerodynamic improvements, a Phase I baselinewind-tunnel test was conducted. For this, a baselinemodel was needed to act as a standard prior to theplanned blowing tests, and as a basis upon which toinstall the pneumatic model configuration. A team ofcurrent researchers working for DOE on the HVaerodynamic drag problem had determined that anexisting generic Heavy Vehicle configuration, theGround Transportation Systems (GTS) vehicle ofReference 9, was quite appropriate. It is sketched inFigure 6, and is actually representative of a faired cab-over-engine vehicle based on the Penske racing team’scar carrier, before the blowing modifications shownwere installed. As such, it is relatively generic andindependent of the numerous and varying cab rooffairings employed on a number of current HeavyVehicles.

Flight Test Results:140% Increase in Usable Lift Coefficient, CL

30-35% Reduction in Takeoff & Approach Flight Speeds60-65% Reduction in Takeoff & Landing Ground Rolls75% Increase in Liftable Takeoff PayloadConfirmation of Full-Scale Blown CCW Operation

4

Figure 5 – Schematic of Application of GTRI Pneumatic Aerodynamic Technology toHeavy Vehicle Trailer, Showing 4 Aft Blowing Slots and Upper Leading-EdgeBlowing Slot

Full Scale Vehicle: W=8.5’, H=13.5’, LTRAILER=48’, LRIG=65’; at V=70 mph, ReTrailer =29.3x106

Model: Blockage W,in. H.in. Scale LTRAILER,in. LRIG,in. ReTrailer (V=70 mph) (q=50 psf) 0.051 6.63 10.53 .0650 37.44 50.70 1.90x106 3.90x106

Figure 6 - GTRI 0.065-scale Baseline GTS & PHV Wind-Tunnel Model and Variables

(a) Full-Height Tractor and Yawed Trailer with Rounded Leading Edge andSquare Trailing Edge

Figure 7 – Various Configurations of GTRI’s Baseline GTS Model, Full Open Gap

5

Before being fabricated as a valid wind-tunnel model,issues such as model size, wind tunnel blockage andtest Reynolds number were important. The test modelwas scaled to be compatible with the GTRI tunnel testsection area of 1290 in2. Based on Reference 10criteria, a physical blockage of 5 to 6 percent of tunnelarea was desired, as well as a reasonably high Reynoldsnumber. Figure 6 shows that a 0.065-scale modelproduces a blockage of 5.1% and Reynolds numberbased on trailer length of 1.90x106 at V=70 mph, or3.90x106 at maximum tunnel speed. These factorswere incorporated into the Figure 6 design, andfabricated into the model of Figure 7 by prototypeshop Novatek Inc. of Smyrna, GA. Here, a number ofparameters are variable, including cab/trailer gap, cabheight, a removable gap fairing, trailer leading-edgeand trailing-edge radii, wheels on/off, vehicle heightabove the road (floor) and yaw angle between thetractor and trailer. The model was mounted on a singlestrut, which was hollow and was later used as theblowing air supply duct into the model. This strut wasmounted on a six-component floor balance below thetunnel floor, which could be yawed and raisedvertically to vary ground clearance height. The testsetup will be very similar to that described inReference 3 for the blown streamlined car testprogram. Particle-imaging laser velocimeter data were

used to quantify the flowfield characteristics aft of thevehicle.

The Phase I unblown investigations were intended todetermine the effects of various cab/trailer geometriesprior to initiation of the blowing tests. Figures 8 and 9are plots of drag coefficient (based on a model truckprojected frontal area of A=0.4542 ft2, including thewheel projections) versus freestream dynamic pressure,q = 1/2 ρ V2.. Reynolds number (now based on vehicletotal length) and several wind speeds in mph are alsoshown. The uppermost curve of Figure 8 shows a cabheight lower than the trailer height, and a rather largegap (0.824 x width) between the cab and trailer. Theflow visualization tuft seen in the gap shows significantseparation and vorticity there, and the flowunsteadiness is also seen in the data-point scatter forthat run. Raising the cab height to a value level withthe trailer reduces the drag coefficient by 7% at 70mph because it shields the sharp square leading edgeof the trailer. Then, filling the gap entirely (“Hi Cab,No Gap”) reduces CD by another 20.1%, or 25.7%from the initial configuration. Whereas this solidconfiguration is not actually possible because of theneed for some clearance/movement between the caband trailer, it does represent an ideal, which mightnearly be achieved by flexible connections. Figure 8also notes the significant drag reduction if the wheelsare removed. This also is not a feasible configuration,but identifies the large drag increment which must beadded back to model test data or CFD predictions fornon-wheeled HV models. Notice in all of these runsthat as the regions of separated flow are reduced, soalso are the CD values and the CD variations withReynolds number, i.e., the CD versus q curves becomeflatter, and the percentage drag reductions becomegreater. For reference, the full-scale HV at 70 mphwould experience a Reynolds number of 40.0x106 atsea-level standard-day conditions.

Figure 9 shows additional drag reductions due tofurther geometry improvement. Run 19 is the “NoGap” configuration from Figure 8. The curveimmediately above it shows a drag increase if the no-gap cab is lowered slightly and exposes the squareleading (LE) edge of the trailer. This is an actualcondition seen on many current faired HVs, where thefairing frequently does not extend high enough tototally shield the trailer’s square top LE corner.However, for the same height difference, if the squaretop LE of the trailer is merely rounded (here a3/8”radius is sufficient), CD is reduced by 8.3%. Then,if a 90° arc with 3/4” radius is added to each of the aftedges of the trailer (this represents the unblownpneumatic trailing edge (TE), see Figure 21 ofReference 5), an additional 7.3% drag reduction occursdue to aft flow reattachment and reduced separation.Thus, adding unblown LE and TE rounded cornersreduces drag by 15% over the square LE/TEconfiguration. Significant improvement has beenachieved by the pneumatic LE and TE geometriesbefore blowing has even been applied. It should benoted that in both of these figures, and in all thefollowing data, the HV model was situated so that the

(b) Shorter-Height Tractor, Unyawed Trailer

(c) Front Wheels removed

Figure 7 (continued) – Various Configurationsof GTRI’s Baseline GTS Model, Full Open Gap

6

wheels were 0.06” above the tunnel floor, and thetunnel boundary layer was eliminated by tangentialfloor blowing (see Reference 3).

Phase I also investigated the effects of side winds (yawangle) on the forces, moments and stability of theunblown HV. Figure 10 shows drag variation withside-wind angles up to ±14°. Not only do the open-gap configurations have higher zero-yaw drag values,but they also show dramatic drag increases by a factorof 2 or more with side winds as low as only 5-7° due tohigher separation and greater yawed-flow over-

pressures on the trailer front face. The “no-gap”models show much lower zero-yaw drag as well aslesser drag increases with yaw because thesedetrimental gap effects don’t occur. Figure 11 showsresulting side force and yawing moment for these sameconfigurations. Whereas there is little difference inside force (CY) for those configurations, the modelswith a gap show much less yawing moment (CN) versusyaw angle and thus much less loss in directionalstability (CNψ = dCN/dψ) than the non-gapped models.Thus the lower-drag “No-Gap” HVs may encounter aproblem with directional stability, as implied here.

0.35

0.4

0.45

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0.65

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CD

0 5 10 15 20 25 30 35 40 45

q, psf

Run 26- Hi Cab, Full Open Gap, G=0.824W

Effect of Cab and Gap Geometry, Square Trailer LE & TE, Wheels On, α=0°, ψ=0°

Run 19- Hi Cab, No Gap

Run 41- Hi Cab, No Gap, Wheels Off

Run 36- Lo Cab, Full Open Gap, G=0.824W

V=70 mph 130 mph

Re/106

=1.5 2.0 3.0 4.0

∆CD=-7.0%

∆CD= -20.1%

= -25.7%from Blue

∆CD=-29.0%

Figure 8 - Phase I Test Results for Unblown Configurations, Showing Effectsof Cab Height, Cab/Trailer Gap, Reynolds Number and Wheels

0.5

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CD

0 5 10 15 20 25 30 35 40 45

Run 80,85- Lo Cab, No gap, Sq LE, Sq TE

R 19- Hi Cab, No gap, No LE, Sq TE

R 79- Lo Cab, No gap, Round LE, Sq TE

R 68- Lo Cab, No gap, Round LE, Round TE

Effect of Cab Ht, Gap & Trailer LE and TE on Drag, Wheels On, α=0°, ψ=0°

V=70 mph

∆CD=-2.3%

∆CD=-8.3%

from R80

∆CD=-7.3% =-15.0% from R80

Figure 9 - Phase I Test Results for Unblown Configurations with No Gap, Showing Effects ofCab Height and Trailer Leading– and Trailing- Edge Geometries

q, psf

7

PHASE II WIND-TUNNEL EVALUATIONS OFBLOWN HV CONFIGURATIONS-

Based on the lower-drag configurations of Phase I,Phase II was intended to evaluate the additionalaerodynamic improvements resulting from variousblown configurations. Phase II consisted of 99 windtunnel runs evaluating a range of pneumaticconfigurations and parameters, including:

• Blown trailer trailing-edge (TE) radius, jet turningangle, jet slot height, blown slot combinationsand TE geometry modifications

• Blown trailer leading-edge (LE) radius and blownslot combinations

• Blowing pressure, jet velocity, mass flow, andmomentum coefficient, Cµ

• Tunnel dynamic pressures from 5 to 40 psf, windspeeds from 45.9 to 129.8 mph and Reynoldsnumber (based on tractor/trailer total length)from 1.61x106 to 4.61x106

• Trailer wheel configuration

• Gap between cab and trailer, plus gap side plates

• Yaw (side wind) angle

Details of these investigations are presented in thefollowing sections and emphasize near-termaerodynamic improvements generated by thesepneumatic devices. Unless otherwise noted, theblowing variations were run at tunnel (vehicle) windspeeds of approximately 70-71 mph (q=11.86 psf)and blowing slot heights set at h= 0.01”, if not closed.

Drag Reductions (Fuel Economy) or Increases(Braking & Stability)- The slot heights at each aftedge of the trailer could be tested either unblown orblown in any combination of the 4, or later, with theleading edge slots on the trailer front face also blown.Flow visualization tufts in Figure 12 show jet turning of90° on all four sides, even the bottom slot blowingupwards. This is the 0.75” radius TE configuration.Figure 13 shows even greater turning for the smallerradius (0.375”R) TE surfaces. This smaller radius onthe 0.065-scale model represents a full-sized turningradius of only 5.77”. Figure 14 shows the results ofthis jet turning on reducing or increasing aerodynamicdrag by blowing various combinations of these aftslots. In order to represent meaningful values of the jetvelocity/free stream velocity ratio, these data were runat blockage-corrected tunnel speeds of approximately70-71 mph, dynamic pressure of 11.86 psf andRe=2.51x106 based on tractor/trailer length. Thecombination of all 4 slots at the same slot heightblowing together yielded the greatest drag reduction,more effective than blowing individual slots.Compared to the typical unblown baselineconfiguration from Phase I (full gap between cab and

(b.) Yawing Moment about Mid-Length

-4

-3

-2

-1

0

1

2

3

4

5

CN

-15 -10 -5 0 5 10 15Yaw Angle, , deg

Yawing Moment vs Yaw Angle ψ, α=0° Wheels ON, q=15 psf

Nose right

Moment center is mid-length

Hi Cab, No Gap, Square TE

Low Cab, No Gap, Rnd LE & TE

Hi Cab, Full Open Gap, Square LE & TE Low Cab, Full Open Gap,

G=0.842W, Square LE & TE

Figure 10 - Effects of Side Winds on Drag forVarious Unblown HV Model Configurations

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CD

-15 -10 -5 0 5 10 15Yaw Angle, , deg

Drag vs Yaw Angle, α=0°, Wheels On

Nose right

Run 39, Hi Cab, No Gap,Square TE

Run 38, Hi Cab,Full Open Gap,Square LE &TE

Run 35, Lo Cab, FullOpen Gap, G=0.824W,Square LE and TE

Run 69, Lo Cab, No Gap,Trailer Rnd LE, Rnd TE

(a.) Side Force

-4

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-1

0

1

2

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4

CY

-15 -10 -5 0 5 10 15Yaw Angle, , deg

Side Force vs Yaw Angle, ψ, α=0° Wheels ON, q=15 psf

Nose right

Hi Cab, No Gap, Square TE

Hi Cab, Full Open Gap,Square TE & LE

Low Cab, No Gap, Round LE & TE

Low Cab, Full Open Gap,G=0.824W, Square LE & TE

Figure 11 – Effects of Side Winds on Stability(Positive dCN/d is Directionally Unstable)

8

trailer, square trailer LE and TE, and cab fairingslightly lower than the trailer front) which produced aC

D =0.824 at this Reynolds number, the blown

configuration reduced drag coefficient to 0.459 at Cµ= 0.065. This is a 44% C

D reduction, and the internal

plenum blowing pressure required was only 0.5 psig.A second blown configuration (labeled 90°/30° TE)used less jet turning on the upper and lower surfaces togenerate even greater drag reduction: at 0.5 psig, C

D

was reduced by 47%, and at 1.0 psig (Cµ=0.13), CD was

reduced by 50%.

Figure 12–Jet Turning on all 4 Sides of Blown TE, 0 . 7 5 ” R

Figure 13 – Jet Turning on Smaller 0.375”R, 90°/30°Blown Trailer TE with 1/2“ plates

0.40

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CD

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

Momentum Coefficient, C

h=0.01", 0.375"R Circular Arc 90°TE, Wheels onq=11.86 psf, V=70 mph, ψ=0°, α=0°

CD=0.824

Top & Bottom Slots Only

Bottom Slot Only

All 4 Slots Blown

Run 36,Unblown Baseline,Unfaired, Full Gap

2 Side Slots Only

Blown Truck,Low Cab, No Gap,Round LE, 0.375"R, 90° TE, (Runs 147-171)

Top Slot Only

90°/30° 1/2"plte TE,0.375"Radius, All 4 Slots Blown

0.25 psig

0.5 psig0.75 psig

1.0 psig

Figure 14 - Drag Reduction or Augmentation onBlown Trailer with 0.375"R Turning Surfaces

When only the top slot, the bottom slot, or both ofthese slots were blown in the absence of the side jets,drag initially reduced slightly, but then significantlyincreased with the addition of blowing. This representsan excellent aerodynamic braking capability tosupplement the hydraulic brakes. Blowing efficiencyis plotted in Figure 15, where ∆CD is an incrementfrom the blowing-off value (negative ∆CD is reduceddrag). Absolute values of ∆CD/Cµ greater than 1.0represent greater than 100% return on the inputblowing Cµ = (total mass flow x jet velocity) / (tunneldynamic pressure x frontal area). It is seen that the 4-slotted configuration generates values as high as -5.50,representing 550% of the input blowing momentumrecovered as drag reduction. The figure also shows theopposite trend as well, with up to 200% of the blowingmomentum from top/bottom slots recovered asincreased drag for braking. When ∆CD/Cµ is less than±1.0, the blowing efficiency diminishes.

However, should additional air be available from anonboard source such as an existing turbocharger or anelectric blower, additional drag reduction is possible, asshown in Figure 16. The drag on the previous “worstunblown baseline configuration” with a large opencab/trailer gap is reduced 30% by the blownconfiguration. Drag coefficients of less than 0.30 areshown for faired blown HV configurations. This is inthe arena of streamlined sports cars. The dragcoefficient of a 1999 Corvette coupe is CD = 0.29.Figure 17 shows drag reductions as high as 590 to600% of the input blowing momentum for the Figure16 configurations, with the greatest reductionsoccurring on the previous “worst” unblownconfigurations due to their large regions of separatedflow. Figure 18, originally intended to show that the

Tufts

Slots

9

drag curves tend to converge onto one slopeindependent of Reynolds number, also shows ameasured drag coefficient of 0.13 for a PneumaticHeavy Vehicle. This is less than half the dragcoefficient value of the Corvette as well as the newHonda Insight (CD=0.25). Even though not achievedin the most efficient blowing operation range, this is an84% drag reduction compared to the unblown baselineconfiguration. Note that the tractor cab in Figure 18has “gap plates” (or fairing extensions) instead of thefull “No Gap” fairing, and is thus much closer toactual tractor/trailer configurations.

-5.5

-5.0

-4.5

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-3.5

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CD/C

-0.15-0.12-0.09-0.06-0.03-0.000.030.060.090.120.15CD = CD-CD0

Low Cab, No Gap, Round LE,0.375"R Circular Arc 90°TE, q=11.86psf, V=70mph, ψ=0°, Re=2.5 x 10**6

Note: CD0 = CD at C =0

All 4 SlotsBlown

Bottom Slot OnlyTop & Bottom Slots

Top Slot Only

2 Side Slots Only

90/30°,1/2"plate TE, All 4 Slots Blown

∆CD/Cµ = +/− 1.0,100% Momentum Recovery

Figure 15 - Blowing Efficiency & Drag Incrementsdue to Blowing Slot Configuration

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CD

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

Momentum Coefficient, C

h=0.01", 0.375"R Circular Arc 90°/30°,1/2" plates TE, Wheels onq=11.86 psf, V=70 mph, ψ=0°, α=0°, Re=2.5 x 10**6

CD=0.824Unblown Baseline,Unfaired, Full Gap,

Blown HV, Low Cab, No Gap, Round LE,0.375"R TE, 90 °sides,30° 1/2" plate Top & Bottom, 4 Blown Slots,

Worst Unblown Baseline ConfigurationRe-tested with Best Blown TE

Figure 16 - Additional Drag Reductions andComparative Configurations

-6.5

-6.0

-5.5

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CD/C

-0.30-0.28-0.26-0.24-0.22-0.20-0.18-0.16-0.14-0.12-0.10-0.08-0.06-0.04-0.02-0.00

CD = CD-CD0

Low Cab, No Gap, Round LE,0.375"R, 90° and 90°/30°TEs, q=11.86psf, V=70mph, ψ=0°, Re=2.5 x 10**6

Note: CD0 = CD at C =0

CD/C = -1 .0 ,

100% Momentum Recovery90° TE,4 Slots Blown

90°30° 1/2"plate TE,4 Slots Blown,Extended Cµ

Worst Unblown Baseline Configuration,Low Cab, Full Gap, Square LE,90°30°, 1/2" TE, 4 Slots Blown

Figure 17 - Blowing Efficiencies and DragIncrements at Increased Blowing Levels

0.10

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CD

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Momentum Coefficient, C

h=0.01", 0.375"R Circular Arc 90°/30°1/2"TE, LE & TE Blowing, Wheels on, Cab/Trailer Gap Plates E Installed, ψ=0°, α=0°

q=6.1 psf, V=51 mph, Re=1.76x10**6

q=11.9, V=70.9 mph, Re=2.51x10**6

q=25 psf, V=103.3 mph,Re=3.66x10**6

Figure 18 - Reynolds Number Effects and IncreasedBlowing Values, Plus Leading-Edge Blowing andCab Gap Plates

It should again be mentioned when comparing thesedata to other experiments on similar GTS models beingconducted by other researchers, that these GTRI dataabove and below include simulated wheels, which asFigure 8 shows, should add about ∆CD = 0.18 to thesenon-wheeled vehicles’ CD values, perhaps more,depending on how well the tunnel ground effects aretreated experimentally. GTRI measured data aregenerated using test section tangential floor blowing to

10

eliminate the floor boundary layer interference, asdiscussed in References 3 and 11.

Lift and Down Force Generation- Figure 19 shows liftand down force generated by various slot combinationsfor the blowing configurations of Figure 14. Thebaseline unblown configurations show slight positivelift due to underbody overpressures and cab uppersurface curvature. Blowing the trailer upper slot alonecan more than triple these values, which can be used to“lighten” the vehicle and thus reduce tire rollingresistance. Conversely, blowing the bottom slot cangenerate a down force increment 2.5 times theunblown lift, which can thus increase traction, increasebraking, and reduce hydroplaning.

Stability and Control-Strong directional instability canbe experienced by Heavy Vehicles at yaw angles (i.e.,experiencing a side wind) because of large side forceson the flat-sided trailers (see Figure 11). Figure 20shows the yawed model and the unblown aft pneumaticsurfaces. This yaw sensitivity is confirmed by theunblown (Cµ = 0) half-chord yawing moment CN

shown in Figure 21, where yaw angle as small as -8°produces a large unblown yawing moment coefficientof CN=-2.0 about the model mid-length.

-0.20

-0.15

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-0.05

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0.45

CL

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18

Momentum Coefficient, C

All 4 Slots Blown

Top & Bottom Slots Only

Top Slot Only

Bottom Slot Only

2 Side Slots Only

90°/30°1/2"TE, 0.375"R,All 4 Slots Blown

Blown HV Truck, Low Cab, No Gap,Round LE, 90°TE, 0.375"R, 4 Slots

Unblown Baseline,Unfaired, Full Gap,CL=0.157

Faired UnblownBaseline, No Gap,Square LE CL=0.092

MTF 053--Blown Heavy Vehicle Lift Modificationsh=0.01", 0.375"R Circular Arc 90° TE, Wheels ONq=11.86 psf, V=70 mph, ψ=0°, α=0°, Re=2.5 x 10**6

Figure 19 -Lift and Downforce Generation onBlown Trailer with 0.375"R Turning Surface

Figure 20 - Pneumatic Heavy Vehicle ModelInstalled Yawed (at Side-Wind Angle) in the GTRIModel Test Facility Subsonic Wind Tunnel

-2.5

-2.0

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CN

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

Momentum Coefficient, C

90°/30° 1/2" TE , 0.375"Rα=0°, Wheels ON, Left Slot Blowing Only

Nose Right

Nose Left

ψ=-8°, Nose Yawed Left

ψ=0°, Nose Straight Ahead

Yawing Moment Trimmedby Blowing

Blowing Produces ExcessYaw in Opposite Direction

CN = Half Chord Yawing Moment Coefficient

Figure 21 - Directional Control CapabilityProvided by Blown HV Configuration

Blowing only one side slot can easily correct this: withthe nose straight ahead, blowing the left slot at Cµ =0.06 yields the equivalent opposite yawing moment(CN=+2.0). With the nose yawed left (for example, ψ =-8°), slightly higher blowing (Cµ = 0.065) returns thisunstable yawing moment to CN=0.0. Then, increasingthe blowing a bit more causes the nose to yaw in theopposite direction, to the right. The opportunity for ano-moving-part quick-response aerodynamic controlsystem is apparent.

BLOWING EFFECT ON PERFORMANCE ANDBLOWING POWER REQUIRED

To evaluate the effects on performance which can beproduced by the above pneumatic changes inaerodynamic lift and drag, required power was

11

calculated for a range of highway speeds. Figure 22shows the results for a hypothetical 65,000 pound 18-wheel tractor-trailer rig with a frontal area of 107.5 sq.ft. traveling over flat highway at sea level. Three casesare considered: a conventional rig with CD = 0.80(from Reference 1, typical); a pneumatic rig showing a35% drag reduction (i.e., the Reference 3 pneumaticstreamlined car’s drag reduction levels); and apneumatic rig with a 50% drag reduction below theconventional rig (from Figure 14). This produces thethree “Aerodynamic” horsepower-required curves,where drag force D = CD q A = CD (0.5 ρ V 2) A, andHPreq’d = DV/ 550. Thus the required aerodynamichorsepower reduces in the same proportion as the dragcoefficient, i.e., 35 or 50% at any given speed. Alsoincluded here is horsepower required to overcomerolling resistance of the tires, which is directlyproportional to effective weight on the wheels times theeffective tire friction coefficient, taken here to be0.015. For the conventional rig, the HP to overcomerolling resistance varies linearly with velocity. For theblown configurations, lift varies with blowing availableand dynamic pressure, so the “effective weight” of thevehicle reduces as the lift increases proportional to V2.The upper curves are the total horsepower required atthe wheels (exclusive of gearing and internal enginelosses), so total engine horsepower required would begreater. For these cases, at a sample speed of 70 mph,the horsepower required for the conventional rig toovercome drag plus rolling resistance can be reduced24% by the lesser pneumatic configuration and 32%by the more effective one. If fuel consumption isreduced proportionally, these numbers indicateconsiderable increase in cruise efficiency for theseblown vehicles. Note also how blowing lessens thedominance of aerodynamic drag at higher speeds. Forthe conventional Heavy Vehicle, horsepower requiredto overcome drag is equal to horsepower to overcome

rolling resistance at about 66 mph, but that speedmoves to about 77 mph for the 35% CD reductioncurve, and to 86 mph for the 50% CD reduction.

To the discussion above must be added a considerationof any power expended to compress (pump) the air forblowing. Figure 23 makes this comparison, where theblowing performance is derived from the lowest CD vsCµ curves of Figures 14 and 16 (these are the sameconfigurations). In Figure 23, the CD is converted tohorsepower required at a typical speed of 70 mphusing the equations above with q=11.86 psf. Thisyields Curve A, HPaero required, which when subtractedfrom the HP value for the baseline unblown referenceconfiguration yields Curve B, showing HPaero saved. Atthis truck speed, the compressor HP required tocompress the air from ambient to the Cµ required isgiven by Curve C, HPpump = ∆P Q / 33000, where ∆P isthe pressure rise required in psf and Q is the volumeflow rate through the slots in ft3/min. Then the netHPsaved is Curve D, which is the difference HPaero saved -HPpump . A maximum HPsaved occurs between Cµ = 0.05and 0.06, and is 43% below the baseline vehicle,slightly less than the 50% HPsaved from CD reductionalone without compressor power removed. HPsaved

continues to be positive until about Cµ = 0.355, atwhich point HPaero saved = HPpump. Note, however, that ifthe blowing power were obtained totally from theoutput of a turbocharger waste gate at cruise speed(i.e., no extra compressor power required),

0

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HP

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45

Momentum Coefficient, C

Curve AHPaero required, Run 183

Curve BHPaero saved (= HPsaved

if Turbo, & HPpump=0)

Curve C HPpump, h=0.615" Full Scale

(from h=0.04" Model)

Curve D HPsaved = HPaero saved

- HPpump

HPaero saved

Unblown Baseline,Unfaired, Full Gap, Run 36,HPaero=198.5 at CD=0.824

∆CD=50%

h=0.615" Full Scale(from h=0.04" Model)

Full Scale at V=70 mph (q=11.86 psf) from 0.065-scale Model, (h=0.04", 0.375"R, 90°30°Arc, 1/2" TE)

then HPpump = 0 and HPsaved would convert to Curve B,which continues to increase until Cµ reaches the limitsof the turbo output. In reality, the saved-horsepowercurve would probably end up somewhere betweenCurves B and D depending on the turbocharger, but

0

100

200

300

400

500

600

700

800

900

BHP req'd

10 20 30 40 50 60 70 80 90 100 110 120

V, mph

Total BHP

Aerodyamic

RollingResistanceµF=0.015

ConventionalCD=0.80

Pneumatic HV,35% CD Reduction,Trailer Lift

Pneumatic HV,50% CD Reduction,Trailer Lift

Sea Level, Flat Ground, T=70° F GROSS WEIGHT = 65,000 lb

Figure 22 – Comparative Blowing-ProducedReductions in Power Required to OvercomeDrag and Rolling Resistance blown vehicles.

Figure 23 – Horsepower Required to OvercomeDrag at 70mph, plus Required Compressor Powerand Horsepower Saved

12

this still represents HPsaved of at least 43% of thebaseline vehicle’s aerodynamic horsepower required.

ADDITIONAL APPLICATIONS OF PNEUMATICAUTOMOTIVE AERODYNAMICS

In addition to Heavy Vehicle application, the aboveresults appear quite promising to other forms ofautomotive vehicles. Clearly, buses and Sports UtilityVehicles are also prone to large drag values anddirectional stability issues due to aft flow separationand large side panels exposed to side winds. Thesevehicles do offer the built-in advantage that rearcorners as well as front corners are usually already atleast partially rounded, and thus application of a blownsystem like that above would be easier than on square-edged HVs whose trailer designers don’t want to yieldinternal volume. Discussions between GTRI personneland representatives of these industries are alreadyunderway. The possible payoffs are implied in Figure24, which plots yearly fuel consumption in the US forvarious vehicle types (from References 12 and 13).Whereas automobile fuel usage is relatively level inrecent and projected years, values for HVs and busescontinue to rise with year, but light trucks and SUVscontinue to rise at a much greater rate and to a muchhigher yearly fuel consumption. Reduction in draglevels could help considerably here, especially relativeto fuel usage at highway “cruise” speeds.

GTRI personnel have also been contacted by motorhome users, as these vehicles are likely to have squaredand draggy front and rear corners causing high dragand fuel consumption. Another possible application isrelative to improving aerodynamic performance oftrains, not only high-speed bullet trains but also thevery boxy freight trains. For these boxy trains, the keyto large economic improvements depends on theaverage operating speed of these connected vehicles,and again, drag versus rolling resistance.

In a related application, GTRI is also currentlydeveloping a patented aerodynamic heat exchangerthat is based on these pneumatic principles . This canfurther reduce the drag associated with the verticalconventional radiator and related cooling system, whilealso adding favorable aerodynamic characteristics tothe vehicle. Of course, the application of improvedblown aerodynamics to increase the performance,traction, braking and handling of race cars is a veryrelated and promising subject.

0.0

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BGY

1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020Year

(Source: Refs. 12 and 13)

Total Fuel Consumed

Domestic Oil Production

Autos

Light Trucks, SUVs(Class 1&2a)

Heavy Trucks (Class 2b-8) & Buses (No Military Vehicles)Report Date

"Gap"

BGY=Billions of Gallons per Year

Figure 24 - Highway Energy Usage Comparisons(Billions of Gallons per Year) by Vehicle Type

CONCLUSIONS

Blown and unblown wind-tunnel evaluations have beencompleted at GTRI in a research program conductedfor the DOE Office of Heavy Vehicle Technologies todevelop, evaluate, and apply pneumatic aerodynamicdevices to improve the performance, economy, andsafety of operation of Heavy Vehicles. The datapresented above confirm the aerodynamic potential ofthese new Pneumatic Heavy Vehicle configurations.

Summarizing the above:

• Drag coefficient can be pneumatically increased ordecreased as desired in increments of as high as600% of the input blowing momentum coefficient,Cµ.

• Drag coefficient reductions of as much as 50%were produced by blowing with internal pressuresof only 1.0 psig; CD values as low as 0.13 (an 84%drag reduction from the baseline HV model) weremeasured at increased blowing rates.

• Variable slot combinations and blowing Cµvariations yielded drag decrease for fuel

efficiency, or drag increase for braking andstability.

• Variable slot combinations and blowing Cµvariations yielded lift increases for reduced rollingresistance, or down force increases for additionaltraction and/or greater braking.

• Blowing one side slot alone generated sufficientyawing moment to restore directional stability and

13

to offset side force due to gusts or side winds onlarge trailer side panels.

Thus all the original objectives for this PneumaticHeavy Vehicle program have been experimentallyconfirmed: drag, lift, down force, side force and allcorresponding moments can be significantlyaugmented (increased or decreased as needed) byblowing, and improved to the point where appreciableincreases in Heavy Vehicle performance, economy,stability and safety of operation should result.

Prediction of on-the-road performance of a pneumaticHeavy Vehicle using blown drag reduction coupledwith lift-enhanced reduced rolling resistance suggeststhat these aerodynamic improvements can result in24% to 32% reductions in horsepower required toovercome drag plus tire rolling resistance. Even whenthe compressor power for blowing is factored in,savings of up to 43% are calculated in horsepowerrequired to overcome the aerodynamic drag alone.Higher savings appear possible if turbochargerwastegate flow is used. The potential of pneumaticaerodynamic devices applied to Heavy Vehicles can besummarized as:

• Pneumatic devices on back of trailer, blowing slots onall sides and/or front top can yield dramaticimprovement in aerodynamic performance,efficiency, stability, control, and safety of largecommercial Heavy Vehicles

• Control of all aerodynamic forces and moments fromthe same pneumatic system using existing on-boardair sources, which can be driver or system controlled

• Separation control and base pressure recovery = dragreduction; or base suction = drag increase

• Leading-edge (LE) suction on trailer = dragreduction

• Additional lift for rolling resistance reduction (FRolling

= µN, where N = Weight - Lift), or reduced lift(increased download) for traction, braking andreduced hydroplaning

• Blowing slots and their corresponding effects can beinstantaneously interchanged

• Partial slot blowing or differential blowing can yieldroll control & lateral stability

• One-side blowing can yield yaw control & directionalstability

• Non-moving external components = all-pneumaticsystems and components with very small (if any)component drag

• Very small-size aft trailer extension = no lengthlimitations; minimal front or top add-ons

• Splash, spray & turbulence reduction accompaniesdrag reduction

• Use of existing on-board compressed air sources(exhaust, turbocharger, brake tank)

• Advanced pneumatic aerodynamic cooling systemscan further reduce drag by reducing radiator size

• Fast response and augmented forces = safety ofoperation

• For safety, stability and/or economy, positive use canbe made of aerodynamic forces/moments (lift,download, side force, yaw, roll) which are not

currently employed in Heavy Vehicle operation, anddrag control can be used for braking as well as fuelefficiency.

RECOMMENDATIONS

The above aerodynamic data confirm the PneumaticHeavy Vehicle as a viable concept for improving theaerodynamic performance, economy, stability,handling and safety of operation of large tractortrailers. Data presented has exceeded the 35% dragreductions (previously demonstrated on streamlinedcars) that the American Trucking Associations claimwill result in savings of more than 1.2 billion gallons ofdiesel fuel per year for the US heavy trucking industry,and as much as 1.7 billion gallons per year can besaved at the 50% drag reduction level. The followingrecommendations are made to suggest a meaningfulcontinuation of this program:

• Additional wind-tunnel evaluations should beconducted to even further reduce the requiredblowing momentum which needs to be acquiredfrom some air source on board the tractor-trailerrig. These tests might include slot height variation,improved blowing surface geometry, alternate jetturning characteristics, pulsed blowing, or otherinnovative means.

• Continued feasibility studies are needed, where theabove results are transferred to the HV industryand interactions occur with tractor and trailermanufacturers, as well as with enginemanufacturers, turbocharger builders, or otherpossible air-supply specialties.

• Preparation for a full-scale on-the-road demon-stration of this technology should be begun,including further study of available air suppliesand any associated penalties, plus design of a full-scale demonstrator configuration.

It is thus felt that the proof-of-concept has beensuccessfully completed in smaller model scale, and it isrecommended that a full-scale on-the-road demon-stration of the Pneumatic Heavy Vehicle soon beundertaken.

ACKNOWLEDGEMENTS

The author wishes to acknowledge and thankDr. Sidney Diamond, Dr. Jules Routbort and Mr.Richard Wares of DOE OHVT for their continuedsupport and encouragement of this work, as well as Mr.Victor Suski for the continued very valuableinvolvement of the ATA. The technical assistance ofMr. Ken Burdges of Novatek, Inc. in wind-tunnelmodel design and fabrication is also greatlyappreciated, as are experimental efforts of GTRI Co-opstudents Graham Blaylock, Warren Lee and ChrisRaabe of the GT School of Aerospace Engineering.

14

CONTACT

Robert J. Englar, Principal Research EngineerGeorgia Tech Research InstituteAerospace, Transportation & Advanced Systems LabAcoustics and Aerodynamics BranchAtlanta, GA 30332-0844

(770) 528-3222(770) 528-7586, Wind tunnel(770) 528-7077, Faxbob.englar@gtri.gatech.edu

REFERENCES

1. Hucho, Wolf-Heinrich, Editor, "Aerodynamics ofRoad Vehicles, from Fluid Mechanics to VehicleEngineering," Butterworth-Heinemann, London,1990.

2. Suski, Victor, “Improved Heavy TruckAerodynamics, Statement of Need,” AmericanTrucking Associations, Alexandria, VA, 1995.

3. Englar, R. J., M. J. Smith, C. S. Niebur and S. D.Gregory, "Development of PneumaticAerodynamic Concepts for Control of Lift, Drag,and Moments plus Lateral/Directional Stability ofAutomotive Vehicles," SAE Paper 960673, Feb.26-29, 1996. Also published in SAE SP-1145,"Vehicle Aerodynamics: Wind Tunnels, CFD,Aeroacoustics, and Ground TransportationSystems," pp. 27-38.

4. U. S. Department of Energy, Oak Ridge NationalLaboratory, “Development and Evaluation ofPneumatic Aerodynamic Devices to Improve thePerformance, Economics, Stability and Safety ofHeavy Vehicles”, Contract No. 450000555,December 1, 1998 – December, 31, 2001.

5. Englar, Robert J., “Development of PneumaticAerodynamic Devices to Improve the Performance,Economy and Safety of Heavy Vehicles,” SAEPaper 2000-01-2208, June 20, 2000.

6. Englar, Robert J., “Development of the A-6/Circulation Control Wing Flight DemonstratorAircraft,” DTNSRDC Report ASED-274, January1979; and Englar, R. J,. et al, “Design of theCirculation Control Wing STOL DemonstratorAircraft,” AIAA paper No. 79-1842, August 1979.

7. Englar, R. J. and C. A. Applegate, “CirculationControl-A Bibliography of DTNSRDC Researchand Selected Outside References (Jan 1969 to Dec1983),” David Taylor Naval Ship Research andDevelopment Center Report 84/052, Carderock,MD, Sept., 1984.

8. Englar, R. J., “Circulation Control Aerodynamics:Blown Force and Moment Augmentation andModification; Past, Present and Future,” AIAAPaper 2000-2541, June, 2000.

9. Gutierrez, W. T., B. Hassan, R.H. Croll, and W.H.Rutledge, “Aerodynamics Overview of the GroundTransportation Systems (GTS) Project for HeavyVehicle Drag Reduction,” SAE Paper 960906,February, 1996.

10. SAE Information Report J2085, “AerodynamicTesting of Road Vehicles; Closed-Test-SectionWind Tunnel Boundary Interference,” August1993. Also published as “Closed-Test-SectionWind Tunnel Blockage Corrections for RoadVehicles,” SP-1176, February, 1996.

11. Englar, Robert J., “Development of Pneumatic TestTechniques for Subsonic High-Lift and In-Ground-Effect Wind Tunnel Investigations,” Paper#18, presented at the AGARD 73rd FluidDynamics Symposium, Brussels, Belgium, October4-7, 1993.

12. “Transportation Energy Data Book: Edition 19,”DOE/ORNL-6958, September, 1999.

13. “EIA Annual Energy Outlook 2000,” DOE/EIA-0383(2000), December, 1999 and “AEO 2001”,Appendix A Table 11.