DRIVE AGAINST DRAG

Much of the ad­vanced world is seek­ing sav­ings by re­duc­ing trailer drag and an op­por­tu­nity to do more ex­ists here. Rob McKay writes

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Much of the ad­vanced world is seek­ing sav­ings by re­duc­ing trailer drag; the op­por­tu­nity to do more ex­ists here

AUS­TRALIA IS ONE OF THE WORLD’S great truck­ing suc­cess sto­ries, with trailer in­no­va­tions, par­tic­u­larly as re­lated to Per­for­mance-Based Stan­dards, one area the coun­try is recog­nised as a global leader. Road trains are also seen as a heavy-duty pro­duc­tiv­ity marvel that would be picked up else­where if na­tions that would gain from them could get past their own red tape and vested in­ter­est. Much of this progress has ar­rived through cre­ativ­ity driven by need and bright minds, and much more could still be done if our own in­er­tia and bu­reau­cracy could be shifted out of the way.

In­deed, and per­haps un­sur­pris­ingly, Aus­tralia is home to an in­ter­na­tional trailer aero­dy­nam­ics equip­ment man­u­fac­turer and in­no­va­tor in Aero­trans Aus­tralia, based in Rowville, Vic­to­ria.

Mostly the in­dus­try play­ers have been keen to take on ideas that al­low them to steal a march on com­peti­tors and make them at­trac­tive to ex­ist­ing and po­ten­tial cus­tomers, often brav­ing the some­times bizarre and sur­real world of ve­hi­cle and road com­pli­ance for years be­fore be­ing able to hit the road with new con­cepts. So it is some­thing of a co­nun­drum for some in­dus­try ob­servers that trailer aero­dy­nam­ics strug­gles as a pop­u­lar av­enue to run­ning ef­fi­ciency and cost sav­ings.

It’s not as if ex­ten­sive re­search on the sub­ject over decades has not been un­der­taken for trail­ers and even the most ca­sual ob­server of the truck man­u­fac­turer’s art will strug­gle hard to avoid de­scrip­tions of ta­per­ing and wind-re­sis­tance re­duc­tion strate­gies even for some­thing as blunt as a cab-over.

Nor is the north­ern hemi­sphere with­out sig­nif­i­cant in­ter­est and in­vest­ment among fleet own­ers in trail­ers de­signed to be as dra­g­less as pos­si­ble. The Air­Flow Star­ship shows the lat­est US think­ing on the con­cept.

Two years ago, Owner//Driver re­ported on Bri­tish su­per­mar­ket chain Waitrose, a fleet-owner in its own right, and its work on ef­fi­ciency per­for­mance of its trail­ing equip­ment. This had got to the point that it could jus­tify the cost of fit­ting less cargo into lower-roofed trail­ers with drag-low­er­ing de­sign as­pects, given on sav­ings en­joyed in the rest of the driv­ing and dis­tri­bu­tion task.

Re­search by the US En­vi­ron­men­tal Pro­tec­tion Agency (EPA)-

backed SmartWay part­ner­ship, with its list of ver­i­fied body tech­nol­ogy, in­cludes re­sults for skirts, tails, gap re­duc­ers, un­der trailer de­sign and splash guards.

This is not to say noth­ing has been done. Aero­trans Aus­tralia has seen progress its busi­ness through an on­go­ing fo­cus on in­no­va­tive aero­dy­namic so­lu­tions. Through its bran­d­line busi­ness, AerozProd­ucts, it of­fers Fuelscoop and NoseCone to all sec­tors of the mar­ket.

It has found that many fleets, which in the past spec­i­fied NoseCone, have de­vel­oped to now use roof­mounted Fuelscoop, and Full Aero­dy­namic Kits.

Fur­ther to stan­dard roof mounted Fuelscoop, the Aeroz-Prod­ucts range now in­cludes new roof mounted prod­ucts for rigid re­frig­er­ated trucks. Re­cent trials by PFD con­firmed a 12.2 per cent fuel sav­ing from Fridgescoop 4 Small Trucks, and they now have added this to their stan­dard truck spec­i­fi­ca­tion.

Fuel-Skirts have been avail­able within the AerozProd­ucts range since devel­op­ment for a suc­cess­ful trial with Toll and Wool­worths, where Fuel-Skirts were com­bined with our longer cab ex­ten­der kit for Mercedes Benz Ac­tros. Recorded re­sults of this trial were 7.8 per cent fuel sav­ings in ad­di­tion to the per­for­mance gained from the stan­dard Mercedes Benz OEM aero­dy­nam­ics that was re­placed with the Fuelscoop Full Aero Kit.

“The mar­ket seems to have de­vel­oped over our 29-year his­tory from noth­ing with NoseCone as an op­tion, to NoseCone be­ing the base re­quire­ment, with those more aware of aero­dy­nam­ics mov­ing to Fuelscoop,” Aero­trans Aus­tralia MD Nigel Fletcher tells Owner//Driver. “Be­yond this, in­creased aware­ness leads oper­a­tors to fit Full Aero­dy­namic Kits, in­clud­ing cab ex­ten­ders.

“Aero­trans Aus­tralia con­tin­ues to de­velop its stan­dard prod­ucts and is work­ing on a range of new ini­tia­tives to of­fer lo­cal and over­seas fleets with ad­di­tional ways to re­duce fuel con­sump­tion.

“In Aus­tralia, the ‘slip­pery’ na­ture chal­lenge for the trailer starts at the cab due to the size of gap be­tween truck and trailer [in cab-over ap­pli­ca­tions]. Trials of a com­bi­na­tion of prod­ucts have con­firmed fill­ing the gap goes ‘hand in hand’ with de­vel­op­ing the trailer aero­dy­nam­ics.

“We have con­cep­tual pro­pos­als based on our 29 years of IP that will pro­vide huge sav­ings by means of more ‘slip­pery’ trailer. To be­come a re­al­ity, it will re­quire for­ward think­ing within the in­dus­try and small changes in trailer de­sign.’’

But de­spite hav­ing what ap­pears a com­pelling story to tell the lo­cal in­dus­try, the com­pany is fac­ing a cer­tain in­er­tia, notwith­stand­ing hav­ing just com­pleted its best year fi­nan­cially. But Fletcher is not de­terred.

“We be­lieve in the prod­uct cat­e­gory and con­tinue to de­velop the prod­uct and are cur­rently de­vel­op­ing open­ings in ex­port markets,” he tells Owner//Driver.

“A cou­ple of trailer man­u­fac­tur­ers are work­ing on pre­par­ing trail­ers to more eas­ily of­fer the Fuel-Skirts op­tion for clients. Fur­ther to this, Aero­trans Aus­tralia has much broader trailer ini­tia­tives with po­ten­tial sav­ings well be­yond Fuel-Skirts alone.”

Wind tun­nels

Aus­tralian in­ter­est in trailer aero­dy­nam­ics has been around for decades but mostly in aca­demic cir­cles, and much re­search has cen­tred on Melbourne in­sti­tu­tions. It is pos­si­ble to go back to 1986 to find Royal Melbourne In­sti­tute of Tech­nol­ogy (RMIT) re­searchers tak­ing to wind tun­nels to prove points and dis­cuss the mer­its of the ap­proach as re­lated to on-road test­ing.

So, 30 years ago, RMIT re­searchers con­cluded that wind tun­nel test­ing often sig­nif­i­cantly over-pre­dicts the drag re­duc­tion of add-on aero­dy­namic de­vices on trucks and that over pre­dic­tion is a func­tion of the type of de­vice and the yaw an­gles in­volved.

Lack of tur­bu­lence sim­u­la­tion was sug­gested to be a sig­nif­i­cant fac­tor in the dis­crep­an­cies be­tween wind tun­nel and on-road re­sults and the for­mer should be a first-es­ti­mate de­sign tool only, with fi­nal con­clu­sions to be in real-world test­ing. That said, they also con­cluded that ba­sic tip­per truck con­fig­u­ra­tions are aero­dy­nam­i­cally very in­ef­fi­cient with a wind av­er­age drag co­ef­fi­cient of about 1.6, with sig­nif­i­cant sav­ings pos­si­ble with add-on de­vices.

For a rep­re­sen­ta­tive truck speed of 80km/h and a to­tal mass of 26 tonnes the fol­low­ing fuel sav­ing re­duc­tions to within 2 per cent ac­cu­racy were pre­dicted:

• Tarp over trailer 7.6 per cent

• Tarp with trailer far­ing 9.7 per cent

• Light por­ous rap with trailer far­ing 4.9 per cent

• Trailer fair­ing with tail­gate fair­ing 4.8 per cent.

Aero­dy­nam­ics

A few decades later, tech­nol­ogy ad­vances meant changed per­cep­tions. RMIT re­searchers found that even sim­ple mod­i­fi­ca­tions such as a fair­ing on the front of the truck are ca­pa­ble of re­duc­ing drag by as much as 20 per cent at a zero-de­gree yaw an­gle. Ad­di­tion­ally un­der small cross winds, as lit­tle as five-de­gree yaw an­gle, with the ad­di­tion of a full skirt­ing along the truck, aero­dy­namic drag can be re­duced by over 35 per cent.

“These find­ings in­di­cate that there is high po­ten­tial for aero­dy­namic drag re­duc­tions in ex­ist­ing heavy com­mer­cial ve­hi­cles,” they said in a 2012 re­port,

A Com­pu­ta­tional Sim­u­la­tion of Aero­dy­namic Drag Re­duc­tions for Heavy Com­mer­cial Ve­hi­cles.

“These drag re­duc­tions could be ca­pa­ble of lead­ing to siz­able re­duc­tions in fuel costs and CO2 emis­sions.

“With trucks be­ing the re­sult of around 20 per cent of global warming emis­sions, a re­duc­tion of even 20 per cent in aero­dy­namic drag is siz­able. There is clear po­ten­tial for drag re­duc­tions in heavy com­mer­cial ve­hi­cles.”

Fuel ef­fi­ciency

Like al­ter­na­tive fu­els, it seems few things fo­cus in­dus­try’s at­ten­tion on in­no­va­tion more than a rise in fuel prices. It should come as no sur­prise that the lat­est bout of ad­vice from in­dus­try ex­perts and or­gan­i­sa­tions should co­in­cide with the price spike in the first half of this decade.

The Vic­to­rian Trans­port Association (VTA), in its fuel ef­fi­ciency ad­vi­sory doc­u­ment of the time, made the case for aero­dy­nam­ics.

‘’At high­way speeds, over half the en­ergy used by your truck is re­quired to over­come aero­dy­namic drag,” its Trans­port Safety Pack Fuel Ef­fi­ciency Guide says. “You can re­duce your fuel bill by re­duc­ing aero­dy­namic drag and min­imis­ing me­chan­i­cal and rolling re­sis­tance. Choose to have a roof fair­ing with van trail­ers, chas­sis fair­ings, cab ex­ten­ders and aero­dy­namic mir­rors.

“Fit­ting aero­dy­namic cab de­flec­tors can im­prove fuel ef­fi­ciency by at least six per cent and in some cases more than 20 per cent (de­pend­ing on the body fit­ted and the load car­ried).

“Close cou­pling – min­imis­ing the gap be­tween the rear of the prime mover and trailer/body – also dra­mat­i­cally re­duces drag. A re­duc­tion of aero­dy­namic drag of 25 per cent will re­duce high­way fuel con­sump­tion by 10-15 per cent.”

In the vor­tex

Around the same time, the New South Wales Green Truck ini­tia­tive took time amongst other tech­nolo­gies to test vor­tex gen­er­a­tion in semi-trail­ers. Aero­dy­namic drag is cre­ated as air re­sists the move­ment of a ve­hi­cle. The ve­hi­cle en­gine must work harder to over­come this re­sis­tance and there­fore con­sumes more fuel.

At high speeds, up to half of the truck’s fuel burn can be for over­com­ing aero­dy­namic drag. “Aero­dy­namic de­vices re­di­rect air flow more ef­fi­ciently, re­duc­ing drag and im­prov­ing fuel ef­fi­ciency,” its case study states of the tech­nol­ogy that does have its crit­ics.

This trial in­volved a vor­tex gen­er­a­tor de­vice. The de­vice was fit­ted to the trail­ing edges of both the prime mover and trailer, to re­duce drag in ar­eas where it is most sig­nif­i­cant: usu­ally at the truck-trailer gap and at the rear of the ve­hi­cle.

These de­vices work by break­ing up the air flow into counter ro­tat­ing vor­tices, thereby dis­pers­ing the en­ergy more evenly. They are eas­ily at­tached – es­sen­tially glued to the ve­hi­cle in a strip along the trail­ing ver­ti­cal and hor­i­zon­tal edges of the truck cab and trailer. The lit­er­a­ture also sug­gests that var­i­ous kinds of aero­dy­namic de­vices can achieve fuel sav­ings of two to three per cent in­di­vid­u­ally and up to 15-20 per cent in com­bi­na­tion

The find­ings of this trial sug­gest that vor­tex gen­er­a­tors can pro­vide a mea­sur­able im­prove­ment in fuel ef­fi­ciency and green­house gas (GHG) ben­e­fit in a cur­tain-sided semi-trailer line­haul ap­pli­ca­tion. The truck in this trial showed a 2.7-4.1 per cent im­prove­ment af­ter the de­vices were fit­ted.

Though the im­prove­ment may seem small, it is a sta­tis­ti­cally sig­nif­i­cant im­prove­ment and highly un­likely to be a ran­dom re­sult.

Sim­i­larly, the vari­a­tion in im­prove­ment us­ing dif­fer­ent anal­y­sis tech­niques sim­ply shows dif­fer­ent an­a­lyt­i­cal view­points, none of which are nec­es­sar­ily more right than oth­ers. Fur­ther, the an­a­lyt­i­cal tech­niques were ap­plied to two dif­fer­ent sets of data log­ging sys­tems, and both data sets re­turned rel­a­tively con­sis­tent fig­ures of im­prove­ment.

In fi­nan­cial terms, this would rep­re­sent a $1.40 per 100 kilo­me­tres sav­ing (or 1.4 cents per kilo­me­tre) on the truck used in this trial (us­ing net diesel costs at the time of the trial of $1.20 per litre). Over an an­nual mileage of 150,000 kilo­me­tres in a re­gional line haul ap­pli­ca­tion, this could trans­late to a fuel sav­ing of over $2,100 per an­num.

Tak­ing into ac­count the pur­chase and in­stal­la­tion cost at the time of the trial, this would re­sult in a pay­back pe­riod of around one year (less with a higher diesel price). In ad­di­tion, the de­vice is low main­te­nance and rel­a­tively easy to in­stall.

Pre­vi­ous stud­ies on vor­tex gen­er­a­tors, along with pre­lim­i­nary anal­y­sis of un­pub­lished stud­ies, sug­gest that the ben­e­fit may be sen­si­tive to the con­fig­u­ra­tion of the truck and trailer. In other words, dif­fer­ent types of trail­ers may not achieve the same sav­ing. De­spite such find­ings, progress seems glacially slow in Aus­tralia, de­spite the mag­ni­tude of the task.

To some, the seem­ingly in­escapable equa­tion of greater dis­tance trav­elled lead­ing to greater sav­ings still awaits gen­eral in­dus­try ac­cep­tance.

“There is high po­ten­tial for aero­dy­namic drag re­duc­tions in ex­ist­ing heavy com­mer­cial ve­hi­cles.”

Be­low: The Air­Flow Star­ship has a slip­pery trailer pro­file

Above: One of Waitrose’s specif­i­cally de­signed trail­ersOp­po­site top: The cur­rent gen­er­a­tion of Aero­trans skirts as in­cor­po­rated on a Krueger TrailerOp­po­site mid­dle: Aero­trans skirts fit­ted to a Max­iTrans Freighter trailerOp­po­site be­low: Skirts on a Chee­tah trailer in the UK

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