# AUTO RESEARCH CENTER SCALE MODEL WIND TUNNEL

STUDY USING A SPECIFIC LONG HAUL SLEEPER TRUCK

WHICH WE WILL CALL MODEL “C” AND A 2008 WABASH

TRAILER

June 20/21 , 201 1

Conducted by:

Auto Research Center

On Behalf of

The Environmental Protection Agency

CON FIGURATION:

Truck Model “C” with a 2008 53’ Wabash Trailer

Report Release Signature 

# Mike Camosy CEO

Date of Report Release July 7, 20114012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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## TABLE OF CONTENTS

Section Title Page

Table of Contents 2

1.0 Objective , K ey Individuals, Distribution list 3

2.0 Approach 3

3.0 Model Configuration 4

4 .0 Test Matrix 5

5 .0 Summary of Results 6

6 .0 Descri ption of Test Vehicle 6

7 .0 Descrip tion of Test Facility 8

8 .0 Test Procedure 1 1

9

. 0 Data Reduction 1 1

10.0 What Are t he Differences Between On

- Road 1 2

And A Wind Tunnel?

11 .0 Conclusions 1 5

APPENDIX A 2 04012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### 1.0 OBJECTIVE

The EPA conducted a wind tunnel test at the Auto Research Center (ARC) in Indianapolis,

Indiana. The first objective was to determine the Cd value of the vehicle in different

configurations at the 9 S AE standard yaw points and calculate the wind averaged drag a s per

SAE standards for Class

- 8 trucks and t railer s . The second objective was to report the fuel

economy change of each change over a range of varying road spee ds. This test was a validation

tes t and thereby follow ed a standard EPA verification process for each change

.

Key individuals at ARC:

Mike Camosy

– CEO/Chief Aerodynamicist was present during the test, created the excel

spreadsheet for the raw data and wrote the report

Fritz Marinko

- Dir ector of Business Development coordinated the project and prepared the test

matrix

Paul Cavanagh

– Lead Technician operated the wind tunnel during the test

Winston Bush

– Chief Model Maker prepared the model for the test and made all changes to the

model d uring the test

Report Distribution List:

ARC

- Mike Camosy, Fritz Marinko

EPA

- Arvon Mitcham, Sam Waltzer

URS

– Tariq Hasan, Bob Specht

2.0 APPROACH

The EPA provided a detailed test matrix. All test items already existed and were manufactured

by ARC. All items tested were pre

- manufactured and pre

- fit on the model prior to the test date.

The truck model used was a highly detailed scale model of a specific class 8 long haul sleeper

tractor which we will call model “ C ” with a 2008 Wabash 53 foot Trailer . The models were

detailed 1/8 scale model of these configurations. Every detail of the full scale tractor/trailer that

touches the air was accurately modeled. This model had articulating suspension and rotating

wheels. Every part of this model was adju stable (ie trailer/tractor gap or bogey position). ARC

also provided the rolling road testing facility, model makers, technicians, aerodynamicists and

computer hardware and software for data reduction.4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### T h e te st consisted of two phases: 1) Setting the init ial base line; 2) Component testing of 1 2

changes to the tractor/trailer . To set the baseline, a reference tractor trailer gap was used with a

California trailer bogey position. All testing was completed at 50 m/s. All tests were conducted

with multiple yawing angles sweeping the model through the following yaw angles (0 deg; 1

deg; 3 deg; 6 deg; 9 deg; 0 deg;

- 1 deg;

- 3 deg;

- 6 deg;

- 9 deg ; 0 deg ). Preceding every

individual test run were two model tares. The first was a static weight tare, which remov ed the

static weight of the model. The second was a rolling tare without wind completed at 5 0 m/s

which removed any mechanical drag imparted on the balance through the rotating wheels. For

the second tare, multiple tares were recorded for each yaw angle listed in the sequence above for

EACH run.

All aerodynamic forces were measure using an AEROTECH 6 component load cell balance.

This balance provided three forces: Lift, Drag and Side force as well as three moments: Pitch,

Roll and Yaw moments. The repea tability recorded during our baseline setting was under 0.25%

for fuel economy

.

3.0 MODEL CONFIGURATION

Tractor: Model “C” tractor

Full Sleeper raised roof

Chassis Fairings

22. 5 Tires

Trailer: 2008 Wabash 53’ Dry Van

Bogey in California Position

King Pin at 36”

Width = 102”

Front Corner Radius = 5”

Landing Gear in Standard Position

Note: California bogey position is defined as 40’ from the center of the king pin to the center line

of the rear most bogey axle.4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### 4 .0 PROGRESSIVE TEST MATRIX

Run# Description

1 Baseline Configuration

2 Repeat

3 Baseline

– Static Floor

4 Closed Grill & Bumper Openings

– Rolling Road

5 Open Grill, Remove Chassis Fairings

– Ro lling Road

6 Close Grill Only, Fit Factory Extenders

– Rolling Road

7 Tractor/Trailer Gap to 50” and 3” Trailer Corner Radii

– Rolling Road

8 5” Trailer Corner Radii

– Rolling Road

9 5” Trailer Corner Radii

– Static Road

10 Closed Grill

– Rolling Road

11 Overnight Repeat to Run #10

12 Repeat

13 Static Road

14 Remove Fairings

15 Refit Factory Extenders, Tractor/Trailer Gap = 48”

– Rolling Road

16 Tractor/Trailer Gap = 42”

– Rolling Road

17 Remove Chassis Fairings

– Rolling Road



### Note: Pictu res and results for each run can be found in Appendix A.4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### 5 .0 SUMMARY OF RESULTS

The individual results for each yaw angle were measured and put through the SAE recommended

process for wind averaging. The wind averaged Cd values for the individu al speeds were then

cross referenced to a study completed by NASA that related the fuel economy savings for each

percentage change in drag at various speeds. A summa ry of the results are shown in table format

in the appendix which displays t he final fuel savings for each component at various speeds. A

negative value reflects an improvement over the baseline tractor/trailer combination. All values

are given in percent (%) improvement.

6 .0 DESCRIPTION OF TEST VEHICLE

The test vehicle used was a 1/8 s cale tractor and trailer. The tractor model “B” had a sleeper.

The trailer was a 2008 5 3 f oot Wabash trailer. The model had articulating suspension. It also

included pressure taps that were not used for this test. Any part of the tractor/trailer that touched

the air was accurately represented in this model. This model also included internal flow

modeling from the tractor grill into the radiator and then into the engine bay. The bogey was

adjustable for multiple positions. Pictures of the model used are below.

Rivets on Side of Wabash Trailer4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### Rear Door & Bumper of Wabash Trailer

Starting Bogey Position was California.4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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## 7 .0 DESCRIPTION OF TEST FACILITY

Wind Tunnel

Type Closed single return tunnel with 3/4 open

- jet working section and

moving groun d plane

Construction Tubular steel frame with birch plywood skin, 20mm thick, 9 ply,

controlled grain panel

Corner turning vanes Rolled steel vanes welded into assemblies

Air settling Two stainless steel settling screens 1800mm apart at the entrance to

the contraction

Mesh screen specification 57.4% open area, 1mm aperture size

Air straightening Honeycomb wall in settling chamber, 75mm thick x 10mm core size

Tunnel volume 1,111 m 3 (39,235 ft 3 )

Surface area 2,147 m2 (23,110 ft2)

Average duct area 13. 94 m2 (150 ft2)

Circuit length 75.84 m (249 ft)

Temperature control Water cooled to ± 1° C (1.8° F) by a cooling coil



## Working Section

Type 3/4 open jet contained in a plenum

Length Adjustable up to 5.75 m (18.9 ft)

Contraction ratio 4.46:1

Maximum a ir velocity 50.0 m/s (164.0 ft/s) CDP

Maximum dynamic pressure 1,513 Pa (31.60 lb/in. ) at standard conditions

Nozzle width 2.500 m (7.414 ft)

Nozzle height 2.060 m (6.824 ft)

Plenum dimensions 10.62 m (34.8 ft) W, 16.46 m (54.0 ft) L, 8.28 m (27.2 ft) H

Plenum NET volume 1,141 m 3 (40,294 ft 3 )

Maximum model scale 50% open wheel, 40% yawed +/

- 8° NASCAR

Maximum model height above

road 330 mm

Strut movement rate 8 mm/sec

Strut movement time from

10 mm to 330 mm 39.5 sec

Model support A vibration isol ated balance frame surrounds the working section and

supports the model strut. The strut position is fully adjustable to

accommodate model geometry.

Primary boundary

- layer slot 0.050 m (0.197 ft) high

Boundary

- layer elimination Three stage fully adjustab le system4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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## Fan Section

Fan description Fixed geometry single stage axial pusher fan with nine equally

spaced carbon fibre blades

Fan diameter 3.790 m (12.434 ft)

Fan power 373 kW (500 hp) variable speed DC motor

Maximum rotational speed 610 rpm

Maximum tip speed 121.1 m/s (397.2 ft/s)

Fan support Fourteen upstream stators with pre

- rotation shrouds, eleven

downstream stators with flow straightening shrouds

Fan mechanical drive Two

- piece drive shaft on axis of tunnel through turning vane

Fan section to tal weight 21,729 kg (48,000 lb.)



## Moving Ground Plane (Rolling Road)

Construction Tubular Steel Frame, concrete filled with Cast Iron Platen

Yaw table 5.18 m diameter

Yaw range +/

- 8.0o

Moving ground length 4.180 m (13.58 ft)

Moving ground width 1.66 m (5.44 ft)

Belt type Ammeraal Flexam with Sandblast Profile

Maximum belt speed 50.0 m/s (164.0 ft/s) CDP

Belt suction 33 individually controlled suction chambers

Platen instrumentation 33 pressure sensors and 71 K

- type thermocouples

Temperature cont rol Water cooled to +/

- 3.0° C (+/

- 5.4° F) with 110 cooling tubes

Steering Hydraulically actuated steering roller controlled using two optical belt

edge sensors and a roller tachometer



## Data Acquisition and Control

Data acquisition Pi Research Mistral sy stem

Motor control 6 Control Techniques ‘Mentor’ DC drives

Tunnel Control PLC direct to Control Techniques drives

Model balance Aerotech 6

- component internal balance

Model pressure measurement Two 32 port PSI pressure scanners

Wheel drag balances 4 x single component strain

- gauge load cells

Wing/body panel balances 2 x three component strain

- gauge load cells

Model exhaust simulation Maximum flow 2.1 m 3 /s (75 SCFM)4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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## Equipment Ratings

Main fan motor 373 kW (500 hp) variable speed air cooled DC moto r

Rolling

- road motor 186 kW (250 hp) variable speed air cooled DC motor

Primary boundary

- layer motor 93 kW (125 hp) variable speed air cooled DC motor

Top

- plate boundary

- layer motor 11 kW (15 hp) variable speed air cooled DC motor

Secondary boundary

- la yer motor 22 kW (30 hp) variable speed air cooled DC motor

Belt suction motor 11 kW (15 hp) variable speed air cooled DC motor

Hydraulic power pack 2.5 kW (3.4 hp) AC motor

Road chiller capacity 281 kW (80 Tons)

Air chiller capacity 440 kW (125 Tons)



### The tunnel is a scale model rolling road tunnel that tests models of vehicles. The model is

mounted to a balance cradle that houses a 6

- component load cell balance. The balance cradle is

attached to a sting that is attached to a steel beamed structur e that is mounted on vibration pads 8

feet underground. This mounting allows for the model to be completely isolated from any

building noise. The model’s wheels run on top of our rolling belt that has a surface roughness to

match the average surface roug hness of highways and roads. The belt speed matches the wind

speed to +/

- 0.01 m/s.

Within the balance cradle is mounted a vehicle model motion system. The VMMS allows the

vehicle to automatically yaw, pitch, roll, heave and front wheel steer during a test session. To

maintain the road flatness, a multi

- suction port system is used throughout the platen. To

eliminate any belt edge curl, a pneumatic tensioning system is used to apply constant tension to

the belt during a test session. To eliminate the static electricity build up before it gets to the

model and effects test repeatability, a static electricity discharge system is utilized.

To minimize the road boundary layer that builds up in wind tunnels, a four stage boundary layer

suction system is uti lized.4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### 8 .0 TEST PROCEDURE

8 .1 Pretest Inspection and Warm up

At the beginning of each testing session, the tunnel and its data acquisition systems are run for a

minimum of 30 minutes to warm up the facility. The balance and laser systems are warmed u p

for a minimum of four hours prior to use. The model was inspected for any wheel bearing issues

or suspect/damaged parts that could affect testing. The tunnel and road system were inspected.

The yaw position, heave position and roll position were all me asured and maintained.

8 .2 General

Each test series began with a static weight t are of the model. Following the static weight t are , a

rolling wheel tare was taken for each model position that data was to be recorded. The model

position remained the same for all of the runs. The positions were standard road height at yaw

equaling 0, 1

, 3

, 6

, 9, 0,

- 1,

- 3,

- 6,

- 9, 0 degrees. There were three 0 degree points to allow for a

“first to last” run match that is used to determine potential belt stretch, or in t est model issue.

Positive 9 degrees is yawing the truck 9 degrees to the driver’s left. All rolling wheel t are s were

c ompleted with the belt running 5 0 m/s without any air speed.

Following the rolling wheel tares, the data sampl ing process took place for all 11 yaw angles

listed above. After all model point’s data samples were measured, the tunnel was shut down and

a change was made to the model. Following a model change, the general process would repeat

itself.

9 .0 DATA REDUCTION

All force and moment data measured using an AEROTECH 6 component load cell balance, 124

static pressures and all associated tunnel parameters (ie DC motor information, belt temperature,

wind speeds etc .) were recorded using a PI Mistral system. The data was organized through a

program called PI AERO which utilizes an ACCESS database. PI AERO was used to display

the reduced and raw data into Excel. Using Excel, the data was then summarized for reporting

purposes.4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### 10.0 WHAT ARE THE DIFFERENCES BETWEEN ON

- ROAD AND A WIND T UNNEL ?

This is a question that is consistently asked by our new trucking industry partners before they utilize one

of our wind tunnel facilities. It is a fair question that deserves a detailed answer. Currently, the trucking

industry relies on real world testing where the standards for these tests were determined by SAE in the

early 1980s. The standards were developed in an attempt to improve the accuracy of a real world test

as much as possible. The SAE standards helped to focus the real world results, but still left large

variances in accuracy due to the impossibility of limiting at least 10 other test critical factors. In a wind

tunnel , we are able to eliminate these 10 variables and offer a more realistic and true aerodynamic

representation with reg ards to trucking development. The following top 10 variables of concern with

“real world” testing are as follows:

1) Constant Temperature: It is impossible to conduct “real world” testing at a constant

temperature. Because of the temperature varying throug hout this type of test, the

aerodynamic forces of the vehicle being tested will change. The only way to compensate for

variable temperature during real world testing is to actually measure and record the ambient

temperature throughout the entire test usin g an on board data logging system or a chase

vehicle with similar data logging. After the temperature is recorded, the varying temperature

would have to be taken into account throughout all the sections of the test through reduction

formulas which would i ntegrate the results (varying with temperature) throughout the whole

test. In the aerodynamic testing community it is common practice to reference all data to a

standard temperature such as “sea level” temperature.

2) Constant Density: Along with varying te mperature, varying density will occur throughout the

entire “real world” test. The variable density also has a direct effect on the aerodynamic forces

acting on a semi

- truck through the relationship of D = P d 

### *C d 

### *A where the aerodynamic drag, D,

on a vehic le is equal to the product of the dynamic pressure, P d 

### ; the drag coefficient, C d 

### and the

vehicle’s frontal area, A. The dynamic pressure is equal to one half the product of the density, d,

and the square of the velocity, V as seen in the following equatio n: P d 

### = 1⁄2*d*V 2 

### . It is obvious

because of this that with the density varying on the day or through a vehicle traveling across

state lines, the forces on the truck during a specific test will definitely change and be

inconsistent. The only way to eliminate this is to measure the density change locally (on the

truck during the test at every moment it is actually testing) and then to compensate through a

speed variation with the truck. This can only be done accurately through using a computer

system to vary the speed continuously throughout the entire test.

3) Driver Input: The driver input will vary dramatically depending on many different factors. The

only way to eliminate this variable is through elimination of the drive by using a computer

system to mainta in control of the truck.

4) Tire Grip/Degradation: Over a test, the tire will degrade due to wear and weight of the vehicle,

along with speeds run during the test. The tire pressures will also change throughout the test

which will have an effect on the side wall stiffness of the tire and ultimately the aerodynamic4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### shape of the tire and an associated ride height and roll attitude of the truck itself. In a “real

world” test, this is a variable that cannot be completely eliminated.

5) Engine: Selecting the size a nd type of engine will play a role of the fuel economy numbers

based upon the engine’s efficiency and specific fuel consumption. Does the system use a fuel

burn to clean the system? If so, what is the frequency and amount of fuel used? How accurate

is t he system? Does it dump the same amount of fuel exactly each time?

6) Cross Winds: Differential cross winds during “real world” testing are a fact of life. Even for

straight line testing this presents inaccuracies. One way to eliminate this inaccuracy is to mount

a 5 hole probe to the test vehicle. This probe will measure the wind direction at all times while

the vehicle is testing. However, the data must then be used to correct the results over the

whole test through integrating the change in cross wind in parallel with the measured fuel burn.

7) Proper Fuel Measurements: The accuracy of measuring the fuel put into the fuel tank versus

what is left in the tank allows for inaccuracy. Was the tank truly “dry” of fuel to begin with?

Was all the fuel removed from the tank in the end (ie fuel residue left in or on the tank due to

viscosity or gaseous build up) ? Were there any evaporation losses of the fuel?

8) Traffic: Traffic conditions will have an effect on the fuel burned during a test. Not only would

traf fic affect the driver’s input due to changes associated with the gas pedal; but, traffic can help

or hurt the drag another vehicle sees based upon its positioning around this vehicle. Traffic is a

random variable that can have a significant impact on fuel economy runs over the entire test.

9) Type of Fuel: The type of fuel used will also affect the fuel economy runs for “real world”

testing. Not all diesel mixtures are the same. Also if pumps are used for specific fuel/water

mixtures this will also offer v ariability. This can play a role throughout “real world” testing.

10) Static Weight Changes: Throughout a “real world” test, the static weight of a truck will change

as it burns fuel and looses rubber from its tires. This overall reduction in static weight will

reduce the amount of fuel required to move the truck over the road due to a reduction in

mechanical weight. This variability happens throughout the entire test, but also requires an

exact starting fuel amount for all the tests. However, all the othe r variables will play a role into

how much fuel is burned and during what part of a test this will happen. Therefore, it is feasible

that the static weight changes on the truck (even when one begins with the “exact” amount of

fuel in the beginning) variab ly throughout the truck’s “real world” testing cycle.

Testing in a scale model , rolling road wind tunnel eliminates all 10 of these “real world” issues. All of our

testing is temperature controlled to within 2 degrees Fa h r e nhei t . The testing is all comp leted at a

constant dynamic pressure. We use models and electronically control them so there is no driver input.

The tires we use do not degrade and do not affect the aerodynamic data we record. Although we model

an engine, the engine does not burn fuel so it does not influence the aerodynamic data we measure.4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### The wind generated in our tunnel is a very controlled wind and therefore has no cross wind. For specific

crosswind testing, we yaw our model and scientifically control the angle of cross wind. Since we are

measuring the raw aerodynamic forces acting on the test vehicle, there is no fuel involved in this type of

testing and therefore, no ability for fuel measurement errors or different types of fuel errors. Our

vehicles are tested individually which eliminates the variable of traffic influencing the aerodynamic

outcome. The static weight of our test vehicles is taken out of the equation through our ability to “tear”

out this weight before the test run.

Although ARC can eliminate all 10 of the m ain variables that directly influence the outcome of a “real

world” test, ARC is still utilizing a scale model rolling road tunnel. The two areas of question in this

arena are Reynolds and scaling effects. Reynolds number is a number that demonstrates th e viscous

effects on an object. For instance, if you take a truck running on the highway at 65 mph and scale it

down to 50%, you would need to test this scale model at a speed greater than 65 mph to maintain the

same kind of effects the air has on this ve hicle. The number used to coordinate just how fast you need

to be testing at is called the Reynolds number.

At ARC we test 1/8 scale models. Tests conducted by NASA on the Reynolds number necessary for an

1/8 scale semi

- truck being simulated as a full sc ale truck running at 65 mph shows that ARC’s tunnel

testing speed of 50 m/s (111.8 mph) is within the acceptable Reynolds number range require for

accurate comparisons to full scale trucks at 65 mph.

The scaling concern covers two main areas. The first a rea is accuracy and the second is choking or

separation. With regards to the accuracy of ARC’s modeling, our highly experienced staff grew from the

racing industry. This meant that if our model makers made mistakes on a scale model during a test,

their e rrors were magnified in the “real world” due to scaling. It also meant that the potential for these

mistakes could literally kill a driver. Therefore, ARC established a culture based around accuracy. This

culture is still driven with the view of accurac y means safety. Therefore, through our maintaining the

same principles we have operated with from our racing heritage, our accuracy is second to none.

With regards to choking or separation due to scaling effects, imagine a small tube that has its opening

directly facing the airflow. When scaling this tube down, the actual air molecules that would normally

flow through this tube remain the same size. Therefore, it is possible to scale something down too small

and not allow the air molecules (that are rema ining the same size) to flow through this tube (or “choke.”

Because of this, care must be taken in the areas where these types of flows are critical to scaling. Over

the years “rules of thumb” are established to eliminate these issues with regards to sca ling. ARC has the

capabilities to eliminate these types of choking or separating effects on its models due to ARC’s

collective experience of scale model testing.4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### 1 1 .0 CONCLUSIONS

For a final analysis, we will examine trends associated with the wind av eraged drag coefficient at

65mph. The various wind averaged drag coefficients for other speeds can be found in

APPENDIX A along with all individual run data.

Results Summary

Run

# Model Setup CDW

@65

mph %F to

baselines

1 Baseline

- open grill, Factory Extenders,45" gap, 5" trailer

corner radius 0.586

2 Baseline

- open grill, Factory Extenders,45" gap, 5" trailer

corner radius 0.585

3 Baseline static road

- open grill, Factory Extenders,45" gap, 5"

trailer corner radius 0.582

4 closed grill & b umper openings, Factory Extenders, 45" gap, 5"

trailer corner radius 0.575

- 0.95%

5 open grill, removed chassis fairings, 45" gap, 5" trailer corner

radius 0.594 0.78%

6 closed grill, Factory Extenders, 45" gap, 5" trailer corner radius 0.576

- 0.89%

7 o pen grill, Factory Extenders, 50" gap, 3" trailer corner radius 0.594 0.78%

8 open grill, Factory Extenders, 50" gap, 5" trailer corner radius 0.596 0.97%

9 Static road

- open grill, Factory Extenders, 50" gap, 5" trailer

corner radius 0.594 1.12%

10 cl osed grill, Factory Extenders, 50" gap, 5" trailer corner radius 0.589 0.29%

11 closed grill, Factory Extenders, 50" gap, 5" trailer corner radius 0.588 0.23%

13 closed grill, Factory Extenders, 50" gap, 5" trailer corner radius 0.589 0.30%

14 Static

- closed grill, Factory Extenders, 50" gap, 5" trailer corner

radius 0.589 0.64%

15 open grill, removed chassis fairings, 50" gap, 5" trailer corner

radius 0.613 2.54%

17 open grill, Factory Extenders, 48" gap, 5" trailer corner radius 0.590 0.39%

18 open grill, Factory Extenders, 42" gap, 5" trailer corner radius 0.580

- 0.56%

19 open grill, removed chassis fairings, 42" gap, 5" trailer corner

radius 0.589 0.30%



### Based on the summary table on th is page, there are only two direct comparisons betwe en static

floor and rolling road from this test due to a changed EPA test matrix compared to the other two

tests ( Model “A” and Model “B”) . However, in comparing the results in a bar chart (as seen4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### below) it is shown that for the simple tractor/trailer gap increase of 5” (45” to 50”) while having

an open grill we see similar results between both static and rolling floor results. However, when

comparing the baseline run which has an open grill and 45” tractor/trailer gap to the second

comparison of a ch ange to a tractor/trailer gap of 50” while closing off the grill, we see that the

static floor results only give 50% of the rolling road results. This difference offers another

alarming comparison between static and rolling road and is unfortunately not u ncommon. It

should be noted that the only two comparisons we have from this test were at least directionally

correct.

When examining static floor results compared to rolling road results across the three different

EPA tests, it becomes evident that ther e is no simple rule that would clearly establish a “delta”

difference that could be used to compare different tests conducted between rolling road versus

static road. Therefore, it only makes sense to eliminate this questionable variable when looking

to r egulate change within this industry. If not, then the results clearly show that one will be

comparing apples to oranges in the future. These findings back up that of Max Sardou who

measured similarly inconsistent data between rolling road and static road in France in the early

1980s. In fact, comparing the three tests would make for a very interesting EPA technical paper

that could be presented at the SAE Comvec Conference.4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### Another question raised by the EPA is if multiple yaw angles on both sides of zero yaw are really

necessary. To examine this question, it is important to look at comparison runs instead of just

individual runs. To keep things simple, we will limit our comparison runs to rolling road versus

static road for the two comparisons ab ove to maintain consistency for comparison between all

three reports.

Baseline Configuration: Trailer Gap = 45"; Trailer Corner Radii = 5"; Open Grill

Yaw AOA Rolling Static Delta Delta Refl % Diff Rolling Refl Diff Static Refl Diff

0.00 0 0.529 0.522 0.007 22.4%

- 0.001

- 0.003

1.000 0.535 0.529 0.005

- 12.0% 0.000 0.001

3.000 0.568 0.561 0.008 45.1% 0.006 0.003

6.000 0.638 0.636 0.002

- 184.6% 0.003 0.007

9.000 0.720 0.726

- 0.006 128.6% 0.000 0.008

0.000 0.529 0.523 0.006

- 1.000 0.535 0.529 0.006

- 3.000 0.562 0.558 0.004

- 6.000 0.635 0.630 0.005

- 9.000 0.720 0.718 0.002

0.000 0.530 0.525 0.005



### The chart above shows the initial baseline configuration chosen by the EPA and reflected in our

“model configuration” section. The first column is the yaw angle. A positive yaw angle is when

the driver’s side is moved to the driver’s left (rear of trailer moved to the right). The “Rolling”

column shows the measured Cd (not wind averaged CdW) with the rol ling road. The “Static”

column shows the measured Cd (not wind averaged CdW) with the static floor. The “Delta”

column represents the rolling road Cd subtracted by the static floor Cd. The “Delta Refl % Diff”

column represents the percentage difference of the “Delta” column in the reflective yaw angles.

For example, the “Delta” column’s 9.0 yaw result has the “Delta” column’s (

- 9.0) yaw result

subtracted and then this result is divided by the “Delta” column’s 9.0 yaw result. By finally

multiplying the answer by 100, we get the percentage difference between the two “Delta”

column’s results for positive and negative 9.0 degree yaw cases. In this case, the result is

128.6%. The “Rolling Refl Diff” column shows the rolling reflective difference for the Cd value

in the “Rolling” column. For positive and negative 9.0 yaw, we get a value of 0.000. The

“Static Relf Diff” column shows the static floor reflective difference for the Cd value in the

“Static” column. For positive and negative 9.0 degree yaw case s we see a value of 0.008.4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### Examining this first baseline case, we clearly see quite a difference for the 6 degree and 9

degree +/

- yaw angles. It is definitely not ok to simply use one angle, say +6.0 yaw and draw

the assumption that

- 6.0 yaw is a simil ar and representative number. Common CFD practices

noted in the industry are trying to get the EPA to accept only two yaw angles for representing

their products (0.0 yaw and +6.0 yaw). In this case, a completely misrepresented result would

occur potentia lly leading the EPA to draw incorrect conclusions.

Baseline Configuration: Trailer Gap = 50"; Trailer Corner Radii = 5"; Open Grill

Yaw AOA Rolling Static Delta Delta Refl % Diff Rolling Refl Diff Static Refl Diff

0.000 0.538 0.531 0.007 24.7%

- 0.004

- 0.004

1.000 0.545 0.538 0.007

- 11.6% 0.002 0.003

3.000 0.577 0.573 0.004 49.4% 0.004 0.003

6.000 0.650 0.651

- 0.001 415.1% 0.001 0.006

9.000 0.739 0.746

- 0.007 132.7%

- 0.004 0.005

0.000 0.539 0.534 0.005

- 1.000 0.543 0.535 0.008

- 3.000 0.573 0.571 0.002

- 6.000 0.649 0.645 0.004

- 9.000 0.743 0.741 0.002

0.000 0.542 0.535 0.0074012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### The next comparison is where the tractor/trailer gap is increased by 5.0 inches. This table

accentuates the conclusions described during the baseline run. In fact, the delta reflective

difference for a yaw angle of +/

- 6.0 degrees is over 400%! Another interesting point to note is

that the reflective differences are in opposite directions for the rolling v ersus the static floor

cases at a yaw angle of +/

- 9.0 degrees. Again, this example clearly identifies that it is NOT

accurate to only use only a positive or negative yaw angle to represent both cases.

Baseline Configuration: Trailer Gap = 50"; Trailer C orner Radii = 5"; Closed Grill

Yaw AOA Rolling Static Delta Delta Refl % Diff Rolling Refl Diff Static Refl Diff

0.000 0.527 0.525 0.002 163.3% 0.001

- 0.003

1.000 0.536 0.532 0.004 128.8% 0.010 0.005

3.000 0.572 0.568 0.004 90.0% 0.013 0.009

6.000 0.648 0.650

- 0.002 841.5%

- 0.006 0.007

9.000 0.742 0.744

- 0.003 395.7% 0.000 0.010

0.000 0.525 0.526

- 0.001

- 1.000 0.526 0.527

- 0.001

- 3.000 0.559 0.559 0.000

- 6.000 0.654 0.643 0.011

- 9.000 0.742 0.734 0.008

0.000 0.526 0.527

- 0.001



### The final comparison is with a 50” tractor/trailer gap and a closed off grill. This is the most

alarming comparison yet! The best delta reflective difference occurs at a +/

- 3 degrees of yaw

and is a startling 90%. L ooking at +/

- 6.0 degrees we see over 800% difference. In comparing

rolling versus static reflective differences we are seeing multiple cases of opposite trends. The

only conclusion that can reasonably be drawn with these three examples is that all angle s

MUST be run to get an accurate picture of what physical changes do to a ffect the vehicle

aerodynamics.4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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# APPENDIX A

Individual Run Pictures if Approved

&

Run Data4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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### FUEL ECONOMY DATA FOLLOWS

MPG = Miles Per Hour

CDW = Wind Average Drag

Del CDw = Difference to Comparison CDW

%CDw = Percentage Difference to Comparision CDW

%F = Percentage Fuel Economy4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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Run # Description MPH CDW Baseline for Rolling road

1 Morning Baseline 75 0.572

70 0.578

65 0.586

60 0.595

55 0.607

50 0.622

compared to baseline for rolling road

Run # Description MPH CDW del CDw % CDw %F

Run 2 Baseline Repeat 75 0.572 0.000

- 0.03%

- 0.02%

70 0.578 0.000

- 0.03%

- 0.02%

65 0.585 0 .000

- 0.04%

- 0.02%

60 0.595 0.000

- 0.04%

- 0.02%

55 0.606 0.000

- 0.05%

- 0.02%

50 0.622 0.000

- 0.06%

- 0.03%

Baseline for static

compared to baseline for rolling road

Run # Description MPH CDW del CDw % C Dw %F

Run 3 Static Road 75 0.568

- 0.004

- 0.69%

- 0.46%

70 0.575

- 0.004

- 0.64%

- 0.37%

65 0.582

- 0.003

- 0.58%

- 0.31%

60 0.592

- 0.003

- 0.51%

- 0.25%

55 0.604

- 0.003

- 0.42%

- 0.20%

50 0.620

- 0.002

- 0.31%

- 0.13%4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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Run # Description MPH CDW del CDw % CDw %F

Run 4 Closed Grill 75 0.561

- 0.011

- 1.94%

- 1.29%

70 0.568

- 0.011

- 1.85%

- 1.06%

65 0.575

- 0.010

- 1.75%

- 0.95%

60 0.585

- 0.010

- 1.63%

- 0.81%

55 0.598

- 0.009

- 1.48%

- 0.69%

50 0.614

- 0.008

- 1.28%

- 0.56%

compared to baseline for rolling road

Run # Description MPH CDW del CDw % CDw %F

Run 5 remove Chassis

Fairings, 75 0.579 0.007 1.20% 0.80%

open grill 70 0.586 0.008 1.31% 0.75%

6 5 0.594 0.008 1.43% 0.78%

60 0.604 0.009 1.59% 0.79%

55 0.618 0.011 1.78% 0.83%

50 0.635 0.013 2.01% 0.87%

compared to baseline for rolling road

Run # Description MPH CDW del CDw % CDw %F

Run 6 Closed Gril l Only, 75 0.562

- 0.010

- 1.82%

- 1.22%

back to factory extenders 70 0.568

- 0.010

- 1.74%

- 1.00%

65 0.576

- 0.010

- 1.64%

- 0.89%

60 0.586

- 0.009

- 1.52%

- 0.76%

55 0.598

- 0.008

- 1.38%

- 0.64%

50 0.615

- 0.007

- 1.19%

- 0.52%4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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Run # Description MPH CDW del CDw % CDw %F

Run 7 with 50" gap, 3" trailer 75 0.580 0.008 1.35% 0.90%

corner radius 70 0.586 0.008 1.39% 0.79%

65 0.594 0.008 1.43% 0.78%

60 0.604 0.009 1.50% 0.75%

55 0.616 0.010 1.57% 0. 73%

50 0.633 0.010 1.68% 0.73%

compared to baseline for rolling road

Run # Description MPH CDW del CDw % CDw %F

Run 8 5" trailer corner radius 75 0.582 0.010 1.73% 1.16%

70 0.588 0.010 1.76% 1.00%

65 0.596 0.010 1.79% 0.97%

60 0.606 0.011 1.83% 0.92%

55 0.618 0.011 1.88% 0.88%

50 0.634 0.012 1.95% 0.85%

compared to baseline for static

Run # Description MPH CDW del CDw % CDw %F

Run 9 Static Road 75 0.580 0.011 1.99 % 1.33%

70 0.586 0.012 2.02% 1.16%

65 0.594 0.012 2.06% 1.12%

60 0.604 0.013 2.11% 1.06%

55 0.617 0.013 2.18% 1.01%

50 0.634 0.014 2.26% 0.98%4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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Run # Description MPH CDW del CDw % CDw %F

Run 10 Close grill 75 0.574 0.002 0.30% 0.20%

70 0.581 0.002 0.41% 0.23%

65 0.589 0.003 0.54% 0.29%

60 0.599 0.004 0.70% 0.35%

55 0.612 0.005 0.89% 0.41%

50 0.629 0.007 1.14% 0.49%

compared to bas eline for rolling road

Run # Description MPH CDW del CDw % CDw %F

Run 11 overnight Repeat to run

10 75 0.573 0.001 0.19% 0.13%

70 0.580 0.002 0.30% 0.17%

65 0.588 0.003 0.43% 0.23%

60 0.598 0.004 0.59% 0.30%

55 0.612 0.005 0.79% 0.37 %

50 0.629 0.007 1.05% 0.46%

compared to baseline for rolling road

Run # Description MPH CDW del CDw % CDw %F

Run 13 Morning Repeat 75 0.574 0.002 0.32% 0.21%

70 0.581 0.002 0.42% 0.24%

65 0.589 0.003 0.55% 0 .30%

60 0.599 0.004 0.71% 0.36%

55 0.612 0.006 0.91% 0.42%

50 0.630 0.007 1.16% 0.51%4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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Run # Description MPH CDW del CDw % CDw %F

Run 14 Static Road 75 0.574 0.006 1.02% 0.68%

70 0.581 0.006 1.09% 0 .62%

65 0.589 0.007 1.18% 0.64%

60 0.599 0.008 1.28% 0.64%

55 0.613 0.009 1.41% 0.66%

50 0.630 0.010 1.58% 0.69%

compared to baseline for rolling road

Run # Description MPH CDW del CDw % CDw %F

Run 15 remove fairings 75 0.598 0.025 4.43% 2.95%

70 0.605 0.026 4.55% 2.60%

65 0.613 0.027 4.69% 2.54%

60 0.624 0.029 4.87% 2.43%

55 0.638 0.031 5.09% 2.37%

50 0.656 0.033 5.36% 2.33%

compared to baseline for rolli ng road

Run # Description MPH CDW del CDw % CDw %F

Run 17 back to factory

extenders, 75 0.576 0.004 0.70% 0.46%

48" Gap 70 0.582 0.004 0.71% 0.40%

65 0.590 0.004 0.72% 0.39%

60 0.599 0.004 0.74% 0.37%

55 0.611 0.005 0.76% 0.35%

50 0.627 0.005 0.80% 0.35%4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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Run # Description MPH CDW del CDw % CDw %F

Run 18 42" Gap 75 0.567

- 0.006

- 1.00%

- 0.67%

70 0.572

- 0.006

- 1.02%

- 0.58%

65 0.580

- 0.006

- 1.04%

- 0.56%

60 0.589

- 0.006

- 1.07%

- 0.54%

55 0.600

- 0.007

- 1.10%

- 0.51%

50 0.615

- 0.007

- 1.14%

- 0.49%

compared to baseline for rolling road

Run # Description MPH CDW del CDw % CDw %F

Run 19 remove chassis fairings 75 0.575 0.002 0.38% 0. 25%

70 0.581 0.003 0.46% 0.26%

65 0.589 0.003 0.56% 0.30%

60 0.599 0.004 0.68% 0.34%

55 0.612 0.005 0.83% 0.39%

50 0.629 0.006 1.02% 0.45%4012 Championship Drive, Indianapol is, Indiana 46268; Tel: 317

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