# AUTO RESEARCH CENTER SCALE MODEL WIND TUNNEL

STUDY USING A SPECIFIC LONG HAUL SLEEPER TRUCK

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

TRAILER

Test conducted on:

M ay 26 , 201 1

Conducted by:

Auto Research Center

On Behalf of

The Environmental Protec tion Agency

CONFIGURATION:

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

Report Release Signature _____ 

# Mike Camosy CEO

Date of Report Release _____ June 7, 2011

Revision

- 54012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

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## TABLE OF CONTENTS

Section Title Page

Table of Contents 2

1.0 Objective , Key Individuals, Distribution list 3

2.0 Approach 3

3.0 Model Configuration 4

4 .0 Test Matrix 5

5 .0 Summary of Results 5

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 Wi nd Tunnel?

11 .0 Conclusions 1 5

APPENDIX A 2 24012 Championship Drive, Indianapolis, 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 v ehicle in different

configurations at the 9 SAE 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

test 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 d ata and wrote the report

Fritz Marinko

- Director 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 during 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 a lready existe d 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 “A” with a 2008 Wabash 53 foot Trailer

. The model s w ere

detailed 1/8 scale model of th ese configuration s . Every detail of the full scale tractor/trailer that

touches the air was accurately modeled. This mo del had articulating suspension and rotatin g

wheels . Every part of this model was adjustable (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, Indianapolis, Indiana 46268; Tel: 317

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### T h e te st consisted of two phases: 1) Setting the initial 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 removed 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, mult iple 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 mome nts: Pitch,

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

for fuel economy

.

3.0 MODEL CONFIGURATION

Tractor: Model “A” Truck

Wheel Base of 238”

Full Sleeper

Hood Mounted Mirror s

Cab Extenders

Chassis Fairings with out Extenders

275/60/ 22.5 Tires

Tractor

– Trailer Gap = 45”

Trailer: 2008 Wabash 53’ Dry Van

Bogey in California Position

King Pin at 36”

Width = 102”

Front Corner Radius = 5”

Landing Gear in Standar d 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, Indianapolis, Indiana 46268; Tel: 317

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### 4 .0 PROGRESSIVE TEST MATRIX

Run# Description



### 1 Baseline Configuration

2 Repeat

3 Repeat

4 Baseline

– Static Floor

5 Closed Grill

– Rolling Road

6 Closed Grill

– Static Floor

7 Trailer Gap = 50"; 3" Trailer Corner Radii; Open Grill

– Rolling

Road

8 Trailer Gap = 50"; 5" Trailer Corner Radii; Open Grill

– Rolling

Road

9 Trailer Gap = 50"; 5" Trailer Co rner Radii; Open Grill

– Static

Floor

10 Closed Grill

– Rolling Road

11 Closed Grill

– Static Floor

12 Remove Chassi s F airings; Open Grill

- Static Floor

13 Remove Chassi s F airings; Open Grill

- Rolling Road

14 Trailer Gap = 45"

- Rolling Road

15 Tra iler Gap = 45"

- Static Floor



### Note: Pictures and results for each run can be found in Appendix A.

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 individual 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 app endix 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.4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

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### 6 .0 DESCRIPTION OF TEST VEHICL E

The test vehicle used was a 1/8 scale tractor and trailer. The tractor was a model “A” sleeper.

The trailer was a 5 3 f

oot Wabash trailer. The model had articulating suspension. It also

included pressure taps that were not used for this test. Any par t 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, Indianapolis, Indiana 46268; Tel: 317

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### Rear Door & Bumper of Wabash Trailer

Starting Bogey Position was California.4012 Championship Drive, Indianapolis, 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 ground 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)

Con traction ratio 4.46:1

Maximum air 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 isolated 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 elimin ation Three stage fully adjustable system4012 Championship Drive, Indianapolis, 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 r otational 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 thro ugh turning vane

Fan section total 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 control 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 acq uisition Pi Research Mistral system

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 sc anners

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, Indianapolis, Indiana 46268; Tel: 317

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## Equipment Ratings

Main fan motor 373 kW (500 hp) var iable speed air cooled DC motor

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 D C motor

Secondary boundary

- layer 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 chille r 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 attac hed to a steel beamed structure 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 roughness 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 a nd 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 te st 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 bounda ry layer

suction system is utilized.4012 Championship Drive, Indianapolis, 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 up

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 measured and maintained.

8 .2 General

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

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

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 p otential belt stretch, or in test model issue.

Positive 9 degrees is yawing the truck 9 degrees to the driver’s left. All rolling wheel tears were

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

Following the rolling wheel tares, the data s ampl 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, Indianapolis, Indiana 46268; Tel: 317

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### 10.0 WHAT ARE THE DIFFERENC ES BETWEEN ON

- ROAD AND A WIND TUNNEL ?

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 truckin g

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 t o 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 aero dynamic

representation with regards 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 throughout 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 using 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 r eduction

formulas which would integrate 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 temperature, 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 vehicle 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 a s seen in the following equation: 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

inconsist ent. 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 u sing 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 us ing a computer

system to maintain 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 sidewall stiffness of the tire and ultimately the aerodynamic4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

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### 13

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 and 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 o f fuel used? How accurate

is the 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 t o 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 integ rating 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 duri ng a test. Not only would

traffic 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 ha ve 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 variability. 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 over all 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 th e tests. However, all the other 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 o f

fuel in the beginning) variably 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 completed 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, Indianapolis, 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 co ntrol 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

ve hicles 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 AR C can eliminate all 10 of the main 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 i s a number that demonstrates the 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 vehicle. 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

- tru ck being simulated as a full scale 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 cove rs two main areas. The first area 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 sca le model during a test,

their errors 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 accuracy 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 s mall 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 t he air molecules (that are remaining 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 t hese issues with regards to scaling. 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, Indianapolis, Indiana 46268; Tel: 317

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### 15



### 1 1 .0 CONCLUSIONS

For a final analysis, we will examine tren ds associated with the wind averaged 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# Description 

### Cdw @

65mph %F (to baselines)

1 Baseline Configuration 0.629

2 Repeat 0.629

3 Repeat 0.631

4 Baseline

– Static Floor 0.616

- 1.26%



### 5 Closed Grill

– Rolling Road 0.617

- 1.22%



### 6 Closed Grill

– Static Floor 0.605

- 1.03%



### 7 Trailer Gap = 50"; 3" Trailer Corner Radii; Open Grill

– Rolling Road 0.642 0.93%



### 8 Trailer Gap = 50"; 5" Trailer Corner Radii; Open Grill

– Rolling Road 0.640 0.72%



### 9 Trailer Gap = 50"; 5" Trailer Corner Radii; Open Grill

– Static Floor 0.628 1.01%



### 10 Closed Grill

– Rolling Road 0.628

- 0.25%



### 11 Closed Gr ill

– Static Floor 0.616

- 0.05%



### 12 Remove Chassi s Fairings; Open Grill

- Static Floor 0.633 1.44%



### 13 Remove Chassis Fairings; Open Grill

- Rolling Road 0.648 1.43%



### 14 Trailer Gap = 45"

- Rolling Road 0.642 0.92%



### 15 Trailer Gap = 45"

- Static Floor 0.63 0 1.15%4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

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### 16



### From the results listed above for 65 mph, all of the static floor versus rolling road changes are

directionally consistent with this vehicle configuration. This vehicle configuration is a high drag

level.

The above chart clearly shows no t only similar trends between rolling road and static floor , but

also close results. This is the opposite to the previous vehicle tested for the EPA. These results

show that sometimes both rolling road and static floor can be consistent and other times t hey

can’t be. It is results like this that cause people to take this consistency for granted and later run

into problems.

The cooling chart above shows that cooling changes are more sensitive in rolling road with the

45” trailer gap; however , with static floor , the cooling is more sensitive with the larger 50” trailer

gap. These differences are due to the flow development over the distance from the tractor to the

front of the trailer as well as the tire pumping effect caused by the rolling road. It seems that

with the 45” trailer gap, the front of the trailer is still with in the wake effect of the tire pumping

flow, but at 50” could be outside of this effect due to the similar differences at this trailer gap

measure with static floor

.4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

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### 17



### Comparing the ch assis fairings, one sees some interesting trends. Although both the rolling road

and static floor results are in the same direction, we see a much larger effect going to the trailer

gap of 45” with the static floor than the rolling road. In both cases th e 45” trailer gap produces

the bigger effect with chassis fairings. With the 45”trailer gap, the static floor over predicts this

change, while with the 50” trailer gap, the static floor under predicts this change compared to the

rolling road.

Looking at t he next chart showing the changes to their respective baselines, one can see a fair

amount of consistency between the rolling road and the static floor results. In two cases, the

static floor is under predicting the rolling road. In another two changes, the static floor is over

predicting the rolling road. In one case, the static floor is giving the same delta as the rolling

road. This shows the inconsistencies between rolling road and static floor . One cannot predict a

simple delta offset when testing in a static floor environment in an attempt to predict what

happens in a rolling road environment.4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

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### 18



### 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 t o look at comparison runs instead of just

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

static floor for a few isolated changes. In a previous report to the EPA we did the same analysis

on a different tr actor/trailer combination with the same results.

The chart below 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 s ide 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 rolling road. The “Static”

column shows the measured Cd (not wind averaged CdW) with the static floor. Th e “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 ha s 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 finally4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

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- 8600; Fax: 317

– 291

- 8700 Pg. 

### 19



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

column’s results for positive an d negative 9.0 degree yaw cases. In this case, the result is 83.5 %.

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 0.0 38 . 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 cases we see a value of 0 .0 23

.

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

Yaw

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

Diff

0.000 0.562 0.549 0.013 1.0% 0.002

- 0.001

1.000 0.572 0.558 0.014 6.7% 0.009 0.008

3.000 0.606 0.596 0.010

- 26.1% 0.011 0.014

6.000 0.688 0.673 0.015 4 6.1% 0.016 0.009

9.000 0.798 0.780 0.018 83.5% 0.038 0.023

0.000 0.564 0.551 0.013

- 1.000 0.563 0.550 0.013

- 3.000 0.595 0.582 0.013

- 6.000 0.672 0.664 0.008

- 9.000 0.760 0.757 0.003

0.000 0.561 0.550 0.010



### Taki ng a second example, in this case changing the trailer gap to 45” with a trailer radius of 5”

and closing the grill , w e find a large variance for 6.0 and 9.0 degree yaw cases when comparing

the positive and negative yaw results from the “Delta” column. It should also be noted that the

reflective differences in the respective rolling road and static floor runs shows a 13 count or

greater drag difference. Since the tunnel’s repeatability is well below this at around 2

– 3 counts,

these results are significa nt.

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

Yaw

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

Diff

0.000 0.550 0.538 0.012 15.3% 0.000

- 0.002

1.000 0.556 0.545 0.010

- 5 .0% 0.002 0.002

3.000 0.591 0.582 0.010 6.5% 0.010 0.010

6.000 0.678 0.663 0.014 72.3% 0.023 0.013

9.000 0.783 0.768 0.015 60.8% 0.027 0.018

0.000 0.550 0.540 0.010

- 1.000 0.554 0.543 0.011

- 3.000 0.581 0.572 0.009

- 6.000 0.654 0.6 50 0.004

- 9.000 0.756 0.750 0.006

0.000 0.549 0.540 0.0104012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

- 291

- 8600; Fax: 317

– 291

- 8700 Pg. 

### 20



### Examining a third case, where we have a 50”trailer gap with a 5” trailer corner radii and an open

grill , we still see a similar trend for 6.0 and 9.0 degree yaw cases. The dr ag count changes

between the respective yaw angles are, as large as 58 counts, which is very large. If one was

only using half of the acceptable yaw range, they would really misunderstand this change.

Trailer Gap = 50"; 5" Trailer Corner Radii; Open Gril l

Yaw

AOA Rolling Static Delta Delta Refl % Diff Rolling Refl

Diff Static Refl

Diff

0.000 0.561 0.549 0.012 29.9% 0.001

- 0.002

1.000 0.569 0.557 0.012

- 10.0% 0.004 0.005

3.000 0.610 0.601 0.009 2.8% 0.013 0.013

6.000 0.697 0.681 0.0 16 55.4% 0.027 0.018

9.000 0.841 0.831 0.010 23.3% 0.058 0.056

0.000 0.560 0.551 0.008

- 1.000 0.566 0.552 0.013

- 3.000 0.597 0.589 0.009

- 6.000 0.670 0.663 0.007

- 9.000 0.783 0.775 0.008

0.000 0.560 0.552 0.008



### A fourth case;

Trailer Gap = 50"; 5" Trailer Corner Radii; Closed Grill

Yaw

AOA Rolling Static Delta Delta Refl % Diff Rolling Refl

Diff Static Refl

Diff

0.000 0.552 0.538 0.014 15.9% 0.001

- 0.003

1.000 0.556 0.547 0.009

- 49.4% 0.00 0 0.004

3.000 0.596 0.586 0.011 55.6% 0.015 0.010

6.000 0.691 0.674 0.017 62.9% 0.038 0.027

9.000 0.831 0.815 0.016 31.2% 0.052 0.047

0.000 0.553 0.541 0.012

- 1.000 0.556 0.543 0.013

- 3.000 0.581 0.576 0.005

- 6.000 0.653 0.647 0.00 6

- 9.000 0.778 0.768 0.011

0.000 0.551 0.541 0.0104012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

- 291

- 8600; Fax: 317

– 291

- 8700 Pg. 

### 21



### A fifth case;

Remove Chassi Fairings; Open Grill

Yaw

AOA Rolling Static Delta Delta Refl % Diff Rolling Refl

Diff Static Refl

Diff

0.000 0.570 0.559 0.011 44.0% 0.003 0.001

1.000 0.577 0.566 0.011

- 5.6% 0.004 0.005

3.000 0.617 0.609 0.007

- 22.8% 0.004 0.005

6.000 0.715 0.699 0.016 25.8% 0.022 0.018

9.000 0.863 0.824 0.039 50.0% 0.024 0.005

0.000 0.565 0.559 0.006

- 1.000 0.572 0.561 0.011

- 3.000 0.613 0.604 0.009

- 6.000 0.692 0.680 0.012

- 9.000 0.839 0.819 0.019

0.000 0.567 0.558 0.009



### Looking at these five example s , we find similar trend s . These combined examples illustrate the

change in forces caused by the asymme try of a tractor/trailer. For each tractor/trailer these

asymmetries are different and therefore cause different variances on the measure force values at

the corresponding positive and negative yaw angles. This is the reasoning behind the SAE

standard re quiring the mapping of both yaw directions . There really is no short cut for tunnel

testing, track testing or CFD.4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

- 291

- 8600; Fax: 317

– 291

- 8700 Pg. 

### 22 

# APPENDIX A

Individual Run Pictures if Approved

&

Run Data4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

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- 8600; Fax: 317

– 291

- 8700 Pg. 

### 23 

### 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, Indianapolis, Indiana 46268; Tel: 317

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- 8600; Fax: 317

– 291

- 8700 Pg. 

### 24 Run # Description MPH CDW

Run 1 Baseline Configuration 75 0.614

70 0.621

65 0.629

60 0.640

55 0.654

50 0.671

Compared To Previous Run

Run # Description MPH CDW del

CDw % CDw %F

Run 2 Repeat 75 0.613

- 0.001

- 0.15%

- 0.10%

70 0.620

- 0.001

- 0.13%

- 0.07%

65 0.629

- 0.001

- 0.11%

- 0.06%

60 0.639

- 0.001

- 0.08%

- 0.04%

55 0.653 0.000

- 0.05%

- 0.02%

50 0.671 0.000 0.00% 0.00%

Compared To Previous Run

Run # Description MPH CDW del

CDw % CDw %F

Run 3 Repeat 75 0.615 0.002 0.37% 0.25%

70 0.622 0.002 0.39% 0.22%

65 0.631 0.00 2 0.40% 0.21%

60 0.642 0.003 0.41% 0.20%

55 0.656 0.003 0.43% 0.20%

50 0.674 0.003 0.44% 0.19%4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

- 291

- 8600; Fax: 317

– 291

- 8700 Pg. 

### 25 Compared To Previous Run

Run # Description MPH CDW del CDw % CDw %F

Run 4 Static Road 75 0.601

- 0.014

- 2.34%

- 1.56%

70 0.608

- 0.0 15

- 2.34%

- 1.34%

65 0.616

- 0.015

- 2.33%

- 1.26%

60 0.627

- 0.015

- 2.31%

- 1.16%

55 0.641

- 0.015

- 2.29%

- 1.07%

50 0.659

- 0.015

- 2.26%

- 0.98%

Compared To Run #3

- Baseline

Run # Description MPH CDW del CDw % CDw %F

Run 5 Cl osed Grill

- Road

Road 75 0.601

- 0.014

- 2.31%

- 1.54%

70 0.608

- 0.014

- 2.28%

- 1.31%

65 0.617

- 0.014

- 2.25%

- 1.22%

60 0.628

- 0.014

- 2.21%

- 1.10%

55 0.642

- 0.014

- 2.16%

- 1.00%

50 0.660

- 0.014

- 2.09%

- 0.91%

Compared To Run #4

- Base line

Run # Description MPH CDW del CDw % CDw %F

Run 6 Closed Grill

- Static

Road 75 0.589

- 0.012

- 1.94%

- 1.29%

70 0.596

- 0.012

- 1.92%

- 1.10%

65 0.605

- 0.012

- 1.90%

- 1.03%

60 0.615

- 0.012

- 1.88%

- 0.94%

55 0.629

- 0.012

- 1.85%

- 0.86%

50 0.647

- 0.012

- 1.80%

- 0.78%4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

- 291

- 8600; Fax: 317

– 291

- 8700 Pg. 

### 26 Compared To Run #3

- Baseline

Run # Description MPH CDW del CDw % CDw %F

Run 7 Open Grill; Trailer Gap =

50" 75 0.624 0.008 1.36% 0.91%

3" Trailer Corner Radii 70 0.632 0.009 1.52% 0.87%

65 0.642 0. 011 1.72% 0.93%

60 0.655 0.013 1.95% 0.97%

55 0.671 0.015 2.23% 1.04%

50 0.692 0.017 2.58% 1.12%

Compared To Run #3

- Baseline

Run # Description MPH CDW del CDw % CDw %F

Run 8 Trailer Corner Radii = 5" 75 0.621 0.006 0.98 % 0.65%

70 0.629 0.007 1.14% 0.65%

65 0.640 0.008 1.34% 0.72%

60 0.652 0.010 1.57% 0.79%

55 0.668 0.012 1.85% 0.86%

50 0.689 0.015 2.21% 0.96%

Compared To Run #4

- Baseline

Run # Description MPH CDW del CDw % CDw %F

Run 9 Static Road 75 0.610 0.009 1.50% 1.00%

70 0.618 0.010 1.67% 0.95%

65 0.628 0.012 1.87% 1.01%

60 0.640 0.013 2.11% 1.05%

55 0.656 0.015 2.40% 1.12%

50 0.677 0.018 2.76% 1.20%4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

- 291

- 8600; Fax: 317

– 291

- 8700 Pg. 

### 27 Compared To Run #3

- Baseline

Run # Descri ption MPH CDW del CDw % CDw %F

Run 10 Close Grill

- Rolling Road 75 0.610

- 0.006

- 0.91%

- 0.60%

70 0.618

- 0.004

- 0.71%

- 0.40%

65 0.628

- 0.003

- 0.47%

- 0.25%

60 0.641

- 0.001

- 0.18%

- 0.09%

55 0.657 0.001 0.18% 0.08%

50 0.679 0.004 0.61% 0.27%

Compared To Run #4

- Baseline

Run # Description MPH CDW del CDw % CDw %F

Run 11 Close Grill

- Static Road 75 0.598

- 0.003

- 0.51%

- 0.34%

70 0.606

- 0.002

- 0.32%

- 0.18%

65 0.616

- 0.001

- 0.10%

- 0.05%

60 0.628 0.001 0.16% 0.08%

55 0.644 0.003 0.49% 0.23%

50 0.665 0.006 0.88% 0.38%

Compared To Run #4

- Baseline

Run # Description MPH CDW del CDw % CDw %F

Run 12 Remove Chassis Fairings; 75 0.615 0.014 2.36% 1.57%

Open Grill

- Static Road 70 0.623 0.015 2.49% 1.42%

65 0.633 0.016 2.66% 1.44%

60 0.645 0.018 2.86% 1.43%

55 0.661 0.020 3.11% 1.45%

50 0.682 0.023 3.43% 1.49%4012 Championship Drive, Indianapolis, Indiana 46268; Tel: 317

- 291

- 8600; Fax: 317

– 291

- 8700 Pg. 

### 28 Compared To Run #3

- Baseline

Run # Description MPH CDW del CDw % CDw %F

Run 13 Remove Chassis F airings; 75 0.628 0.013 2.14% 1.43%

Open Grill

- Rolling Road 70 0.637 0.015 2.37% 1.35%

65 0.648 0.017 2.65% 1.43%

60 0.661 0.019 2.99% 1.50%

55 0.679 0.022 3.42% 1.59%

50 0.701 0.027 3.97% 1.73%

Compared To Run #3

- Baseline

Run # Description MPH CDW del CDw % CDw %F

Run 14 Trailer Gap = 45" 75 0.625 0.009 1.52% 1.01%

Rolling Road 70 0.632 0.010 1.60% 0.91%

65 0.642 0.011 1.70% 0.92%

60 0.654 0.012 1.82% 0.91%

55 0.669 0.013 1.99% 0.93%

50 0.689 0.015 2.21% 0.96%

Compared To Run #4

- Baseline

Run # Description MPH CDW del CDw % CDw %F

Run 15 Trailer Gap = 45" 75 0.613 0.012 1.96% 1.30%

Static Road 70 0.620 0.012 2.03% 1.16%

65 0.630 0.013 2.13% 1.15%

60 0.641 0.014 2.2 4% 1.12%

55 0.656 0.015 2.40% 1.11%

50 0.676 0.017 2.59% 1.13%