Winds of Change

July 1, 2001
BOB Englar is a 57-year-old aerodynamics expert. He speaks authoritatively, but his voice carries an unvarying tone. He is not a carnival barker or a

BOB Englar is a 57-year-old aerodynamics expert. He speaks authoritatively, but his voice carries an unvarying tone. He is not a carnival barker or a televangelist or a shill. If he tried to sell people on his ideas the way Don King promotes boxing matches, he might be famous.

He has no schtick. He just has encyclopedic knowledge of the principles of air flow, plus an undeterred desire to turn the principles into something tangible.

It would be easy to overlook Englar. Some very powerful people already have.

When he was an inventor, developer, aerospace engineer, and flight-test manager for the Navy in the late 1970s, he engineered some significant high-lift and drag-reduction studies and flight tests on the A-6 Intruder, but the results were never used on an operational airplane.

It was an era during which the Navy was requesting two monstrous nuclear carriers, and with Englar offering an aircraft that could land on something smaller than that, it was not politically popular.

Starting in 1998, he spent nearly two years in a wind tunnel at the Georgia Tech Research Institute (GTRI), applying those same principles to automobile and small-scale tractor-trailer models.

His tests showed that the car's drag coefficient can be reduced by at least 35% and possibly as much as 50%. He showed those numbers to the American Trucking Associations, which determined that a 35% reduction would translate into a 12% fuel savings for the US heavy-vehicle trucking fleet or about 1.2 billion gallons of diesel per year and a 50% reduction would save an additional half-billion gallons.

Vic Suski, senior automotive engineer for the ATA, says the industry average of 6.8 mpg could be boosted to as much as 12 mpg.

Those are some jaw-dropping numbers, particularly in light of spiraling fuel prices the average cost of a gallon of diesel nationwide in June was $1.49, almost 10 cents higher than a year ago that have dealt a devastating knockout punch to the industry, particularly to small trucking firms that can't offset the cost of the fuel and are being forced out of business.

Great Dane, Volvo Chip In

What does it all mean? We'll find out sometime in August, when the Department of Energy sponsors a series of road tests at the Department of Transportation track in East Liberty, Ohio, using a pair of tractors supplied by Volvo and a pair of trailers from Great Dane. One tractor-trailer combination will be standard. The other will be equipped with 90-degree arcs and blowing slots at the back of a trailer, plus a compressor to drive the air. DOE isn't releasing any other details about the road demonstrations, other than to say they will follow the standard Society of Automotive Engineers (SAE) Type II fuel economy test.

The results expected to be released in a DOE/GTRI by October could rock the industry.

“I'm very interested,” says Dan McCormack, director of design and analysis for Great Dane, which jumped at the chance to contribute two 53' reefers to what could be history-making road tests.

“A lot of people have tried a lot of different things over the years, and the bottom line is that the tractor-trailer combination is a pretty dirty aerodynamic thing. Now, if there are some savings to be made even if they are much more modest than what he (Englar) indicates, it could still have a significant impact in savings for the industry. Even a 10 to 15% reduction in fuel consumption is very significant.”

Since GTRI released the results of its wind-tunnel tests last October, Englar says he has received “hundreds of phone calls” by people who are intrigued by the possibilities.

A Florida man called and said he'd be delighted if Englar could reduce the drag on his RV by even 35%, since he gets a maximum of 6 mpg at 55 mph and 3 mpg at 75 mph. They talked for a few more minutes and he finally blurted, “Why don't I just bring my motor home up to Georgia and you guys can fix it for me?”

Replied Englar, “Wait a minute. We're not a motor home manufacturer. We're an aerodynamics research agency. I can tell you how to fix it, but I'm not going to start bending sheet metal.”

They apparently reached an understanding, but Englar probably wouldn't be surprised to walk into the GTRI parking lot and find his car blocked by an RV with Florida plates.

If that's the reaction from an RV owner, what will it be from the truck-trailer manufacturing industry and the fleet industry if Englar's numbers are supported by the road tests?

‘Can't Afford to Ignore It’

“I think if you're a truck operator and somebody tells you, ‘I can reduce your fuel consumption to overcome drag by one-third to one-half,’ you can't afford to ignore that, even if you don't have any idea what we're doing or how it works,” Englar says. “And then if somebody tells you, ‘It's a six-inch piece you add to the back of your trailer and the worst it's going to cost you is you have to come up with a small amount of compressed air from somewhere,’ I really don't see how you could afford to ignore it.”

Says Suski, “We were interested in the concept before we really knew Bob, because it's a well-known aerodynamic phenomenon. We're happy to see somebody doing something with it from the standpoint of ground vehicles. Obviously, we're very supportive of his effort, and we hope the road tests support the wind-tunnel predictions.”

Suski was instrumental in leading Englar to the truck-trailer industry. He had read one of Englar's SAE papers that applied the airplane aerodynamics concept to streamlined commercial cars something that Suski had never seen before. He called Englar and said, “You're applying this to the wrong thing. You should be applying it to tractor-trailers. They're the ones that need drag reduction not cars.”

Suski led Englar to the DOE, which set the process in motion.

Streamlined Trailers

Englar's research produced a paper, “Advanced Aerodynamic Devices to Improve the Performance, Economics, Handling and Safety of Heavy Vehicles,” in which he offers that despite significant reductions in drag coefficients in the latest generation of tractors, these Heavy Vehicles (HVs) remain “draggy” compared to much more streamlined automobiles. He says that's because there are practical limitations on: providing a long, smooth aft surface such as a boat tail to prevent flow separation and turbulence at the rear of the trailer; completely sealing the gap between the tractor and the trailer; and smoothing the underbody of the vehicle. The result? Typical drag coefficient values for a variety of HVs can range from 0.65 to 0.9.

He also believes current designs have ignored aerodynamic forces and moments other than drag, saying that the creation of lift on the vehicle (effective weight reduction) can unload the tires and reduce rolling resistance, while the creation of negative lift or downforce can increase “weight” on the wheels and traction, thus increasing braking and handling in wet and icy weather. He says the aerodynamic download can reduce hydroplaning.

“While it has been shown that drag increases greatly due to side wind or yaw angle, side-wind presence also implies increased side force and yawing moment on the trailer, thus reducing its directional stability and safety,” he says. “Safety, stability, and handling can be enhanced by blowing control of side loads and moments on these Heavy Vehicles if caused by side winds, gusts, or other vehicles passing. An aerodynamically controlled concept may also help to eliminate the jackknifing problem if resulting from extreme wind side loads on the trailer. Lastly, there are instances where additional drag increase is desirable, such as steep downhill operations in mountains, or sudden need for emergency braking from high speed.”

The wind-tunnel tests at GTRI's Aerospace, Transportation and Advanced Systems Lab near Marietta, Georgia, applied pneumatic (pressurized air blowing) concepts the tangential injection of pressurized air into the vehicle's aft region strongly modifying the aerodynamic flowfield around the vehicle. Another term for it is Circulation Control (CC) aerodynamics.

An airfoil's conventional mechanical trailing-edge device is replaced by a fixed curved surface and a tangential slot ejecting a jet sheet over that surface. That jet remains attached to the curved surface by a balance between sub-ambient static pressure on the surface and centrifugal force (the so-called Coanda Effect, named after the Romanian physicist who discovered it in the 1930s). Englar says this greatly influences the external flowfield to follow the jet, thus enhancing the circulation around the airfoil and the aerodynamic forces produced by it.

“The small, thin slots blow over a curved surface and the jet follows that curved surface, and dramatically changes the air flow around the vehicle,” he says. “On a tractor-trailer, it prevents all the separated flow that you normally have on the back end of this rectangular box, which is where most of the current drag is coming from. Most of the tractors are reasonably faired on the front end these days. So the drag is coming mostly from the trailer.”

Aircraft Principles Applied

Applying the governing parameter of the blowing momentum coefficient, Englar says an 8000% return in aerodynamic lift force has been calculated on the invested momentum. He says this is “quite extraordinary,” given that thrust-deflecting Vertical Takeoff and Landing (VTOL) aircraft are fortunate if they recover 100% of the engine thrust expended for vertical lift. Because of this high return, or conversely, because of very low blowing input and associated power required to achieve a desired lift, he believes Circulation Control airfoils are promising for a number of applications. The A-6CC Wing Short Takeoff and Landing (STOL) flight demonstrator aircraft, developed by Englar, suggested capabilities very useful to ground vehicles: During takeoff, it demonstrated very high lift and reduced drag, while in the approach/landing mode, high lift with high drag was shown.

When he applied that pneumatic concept to improve the aerodynamics of an already streamlined car, he discovered that the results varied greatly depending on which portion of the tangential slot was blown. Blowing the full slot produced large turning and drag increases of greater than 70%, showing potential for pneumatic aerodynamic braking. Blowing only the outside corner of the slot weakened the corner vortex rollup, lessened aft suction, and reduced drag by as much as 35%. Blowing the aft slot also yielded a lift increase of 170%. If this slot were on the bottom, that should yield a 170% downforce increase. This concept has been patented by GTRI and verified by installation on a model of a European Formula One race car. (Englar says the results are “significant” and expects that “you'll see that relatively soon on racing cars.”)

Based on those results, Englar initiated a research program at GTRI for DOE's Office of Heavy Vehicle Technologies in an attempt to develop an experimental proof-of-concept evaluation that would lead to a road demonstration on an operating blown Pneumatic Heavy Vehicle (PHV).

Englar and his team of researchers chose as their baseline model a faired cab-over-engine vehicle based on an earlier Penske racing team's car carrier. The test model was scaled to be compatible with the GTRI tunnel test section area of 1,290 sq in. The resulting .065-scale model produced a blockage of 5.1%.

The model was mounted on a single strut which was hollow and was later used as the blowing air supply duct into the model and attached to a six-component floor balance below the tunnel floor, which could be yawed and raised vertically to vary ground-clearance height. Particle-imaging laser velocimeter data were used to quantify the flowfield characteristics aft of the vehicle.

Pneumatic Configurations

Phase I was intended to determine the effects of various cab/trailer geometries prior to the initiation of the blowing tests. Phase II involved 99 wind-tunnel runs to evaluate a range of pneumatic configurations:

  • Blown trailer trailing-edge (TE) radius, jet turning angle, jet slot height, blown slot combinations, and TE geometry modifications.

  • Blown trailer leading-edge (LE) radius and blown slot combinations.

  • Blowing pressure, jet velocity, mass flow, and momentum coefficient.

  • Tunnel dynamic pressures from 5 to 40 psf, wind speeds from 45.9 to 129.8 mph and Reynolds number (based on tractor/trailer total length) from 1.61 million to 4.61 million.

  • Trailer-wheel configuration.

  • Gap between cab and trailer, plus gap side plates.

  • Yaw (side wind) angle.

The blowing variations were run at tunnel (vehicle) wind speeds of approximately 70-71 mph (dynamic pressure, q=11.86 psf) and blowing slot heights set at h=.01", if not closed.

The combination of all four slots blowing together at the same slot height produced the greatest drag reduction more effective than blowing individual slots. When only the top slot, the bottom slot, or both of these slots were blown in the absence of the side jets, drag initially reduced slightly, but then significantly increased with the addition of blowing which Englar says represents an excellent aerodynamic braking capability to supplement the hydraulic brakes.

If additional air is available from an onboard source such as an existing turbocharger or an electric blower, additional drag reduction is possible. Tests on a pneumatic heavy vehicle showed a drag coefficient of .13 which is less than half that of a 1999 Corvette coupe (.29). Englar concluded that even though it was not achieved in the most efficient blowing operation range, it represents an 84% drag reduction compared to the unblown baseline configuration.

In terms of life and downforce generation, blowing the trailer's upper slot alone can more than triple these values, which Englar says can be used to “lighten” the vehicle and thus reduce tire-rolling resistance. Conversely, blowing the bottom slot can generate a down-force increment 2½ times the unblown lift, which can increase traction and braking, and reduce hydroplaning.

“By blowing the bottom slot, you're making the trailer generate negative lift, which is downforce, which in essence is the same as more weight on the wheels,” Englar says. “And more weight on the wheels when you need it is the same as better traction and better braking. You can do that with no moving parts. You just need an internal valve that switches from equal blowing on all four sides to all the blowing on the bottom side. You can dramatically increase traction, which is great for icy-weather or wet-weather driving.”

Englar says when he initially explained to trucking agencies his concept of reducing aerodynamic drag by 50%, one operator said, “Well, I don't want 50% drag reduction all the time. When I'm running down a mountain, I depend heavily on aerodynamic drag to help the brakes. If you guys knocked out half of my drag, you just ruined my brakes. By the time I get to the bottom of the hill, my brakes will be worn out.”

A Different “Air” Brake

Englar's answer: Blow air through just one slot and you can increase drag by 25-30%, instead of reducing it by 50-84%. “That's an interesting possibility instantaneous braking when you need it, just by changing which slot is blown,” he says.

And then there's the force of a sidewind against a tractor-trailer. It creates a significant yawing moment and side force. Englar tested that in the wind tunnel and says that the answer is to blow just the slot on the side opposite of the one that is being hit by the wind, which generates side force and yawing moment to the opposite side.

“So it's like using the trailer as a vertical wing to generate aerodynamic side force back in the direction you want to go,” he says. “You can reduce its directional instability and make it directionally stable.”

Englar says there would be a system on board that could correct the trailer without driver input. A sensor would indicate which direction the wind is coming from, and then it would automatically blow on the opposite side. In jackknifing situations, the sensor would direct the system to blow on the opposite side.

Englar says a correctional system like this would increase fuel economy. He found that if he yawed a tractor-trailer to 6-7 degrees of the side wind, the drag coefficient doubled. So if the rig was going at 70 mph and experienced a 7-degree side wind, fuel economy would drop proportionate to the drag-coefficient increase.

McCormack appears to be much more enthralled by the fuel-economy aspect of Englar's research than the notion that the slots could make a tractor-trailer more stable.

“I think getting into stability and handling is a long way away,” he says. “I think the most straightforward thing would be aerodynamic drag, and therefore fuel consumption. The conclusions and data he's presented imply that you could do something to enhance the stability of the trailer. But that's way down the road, in my opinion.”

There's another issue: What about the power expended to compress (pump) the air for blowing? How will that affect fuel consumption? Even Englar doesn't know the answer.

“I'm guessing we'll get a 40-50% drag reduction,” Englar says. “The 84% we measured in the tunnel, we can duplicate that. But the blowing process that's required to get to 84% starts to eat into it. What you save in drag is a horsepower reduction to the engine. But the compressor runs off the engine or its own fuel, so you have to subtract the horsepower for the compressor from the horsepower you save from the truck. So 84% drag reduction will give you a huge aerodynamic horsepower reduction, but from that you have to subtract whatever power you employ to pump up the air. It's very nice to say we have a drag coefficient that's less than half of a Corvette, but it doesn't say how much power we had to put into that to pump it up to that.”

McCormack: “It looks like there might be something there on paper. But the proof is in the pudding.”

Suski: “Until we run the tests, nobody's going to believe what's being said.”

Tough Environment

And even beyond the road tests, Suski wonders how durable the slots would be when exposed to the harsh reality of nature and the abuse trailers take. “Will they get caked over with dirt, freezing rain, and snow?” he asks. “We don't know.”

Englar is accustomed to skepticism. His role as a Navy inventor, developer, and Lockheed senior aerospace engineer prepared him for anything he will encounter from the trucking industry. Although he developed a technique that increased lift by 140%, cut takeoff speed by 33%, and takeoff distance by 67%, the response was not always encouraging.

“New technology requires how can I say this nicely? visionary people to make it work,” he says. “Once you've proven it technologically, you have to have people in the industry who are eager for new technology on their vehicles.

“In the case of the A-6, after they had flown it, it never got put on Navy carriers because in the late '70s and early '80s, the Navy was putting in requests for two more big nuclear carriers and the last thing you want to have is somebody saying, ‘Oh, I have an airplane that doesn't need a big-deck carrier.’ So what we did then was politically at the wrong time. It wasn't something that the Navy wanted to hear.

“If you're in the technology field, you know that frequently you come up with a neat idea that obviously will work technologically. And then for some reason, some political issue prevents it from getting anywhere. I've been frustrated by that. But the tractor-trailers could be our first operational blown vehicle. I'm convinced of that. They should be our first production vehicle.”

Previous Add-Ons Were Unwieldy

Englar says heavy vehicle manufacturers previously have installed add-ons such as big inflatables or metal fairings in an attempt to keep a separated flow from occurring. Add-ons such as boat tails and long, streamlined fairings do reduce drag, but can violate federal regulations on length of overhang and also prevent the driver from making turns or backing into loading docks.

His solution is a patented curved surface 6-9" in radius that is attached by bolts, screws, or epoxy to the four corners at the back end of the trailer, running corner to corner. When he put them on the unblown test model in the wind tunnel, they reduced drag by 15%. Then when he applied blowing through the slots, drag was reduced by 84%. He says this is the generic version he has developed other shapes that are even more efficient and take less blowing to get the same amount of drag reduction. Englar says the proprietary nature of the actual patented devices that will be used in the road demonstrations prevents them from being described in greater depth.

Englar says the device also could be installed on the front of the trailer.

“The reason for that is that many of the trailers I've seen have square top corners,” he says. “I've never figured out why that is. The vertical corners on the fronts of trailers are rounded, but I've never seen one with a round top. We've found you can reduce drag on a trailer by as much as 8% just by rounding off the front top corner to match the side corners.

“I know the argument usually is, ‘We don't want to do anything to cost us internal volume, because the more cubic feet of stuff we can cram in there, the more each run is worth to us.’ But the front sides have already been rounded, and if you figured out what few cubic inches of space you'd lose by rounding the top in return for an 8% drag reduction, it's not clear to me why that's not done. But we found that if you round the front corner and put blowing on there, you can also reduce the drag.

“The other more beneficial thing is that in a tractor-trailer that has a refrigeration unit, that's where the heat exchanger is the gap between the tractor and the trailer. The more streamlined the tractor is, the less flow that you have going into the heat exchanger on the refrigeration unit. If you essentially put blowing on the top corner of the trailer, you can use the blowing not only to reduce the drag, but also to suck air up through the gap, which is now essentially a closed, heated area because there's no air flow going through it.

“So you can use the device to entrain air past the refrigeration unit on the front of the trailer and make it much more effective as a cooling device, because now you have cooling air flow going through it, instead of just a stagnated dead region between the tractor and trailer.”

Marketing the Device

Englar says he has discussed the drag-reduction arcs with a few small companies that have shown an interest in manufacturing them. He envisions an aftermarket parts company obtaining licensing rights from GTRI, which holds the patents, and then building the device and selling it to trailer manufacturers, who would install it on their new trailers. Compressed air for the system would come from the exhaust gases, the turbocharger on the truck engine, storage tanks, or an electrically powered compressor in the trailer. (Turn page)

“Trailer manufacturers that are far-sighted as soon as they see what this can bring them would immediately start putting them on their production trailers,” he says. “I can't imagine them being an expensive item. You're talking about four 90-degree arcs that you bolt to the back, and some way to pressurize them so they carry a bit of air flow, and some kind of air source.

“I don't know how they can refuse.”

Any way you look at it, Englar's research has gotten the attention of the industry. It is impossible to ignore.

“If there's something we can do to make our trailer better, we're going to pursue it,” McCormack says.

About the Author

Rick Weber | Associate Editor

Rick Weber has been an associate editor for Trailer/Body Builders since February 2000. A national award-winning sportswriter, he covered the Miami Dolphins for the Fort Myers News-Press following service with publications in California and Australia. He is a graduate of Penn State University.