[aerohead]

Hello all.Cd got a thread going about freight-train streamlining and I said I'd dig out what I had from Hoerner and post it.Since that thread got off on some tangents,I thought I'd begin a new thread.

The following material is from AERODYNAMIC DRAG,by Sighard F.Hoerner,1951.The material does not pertain specifically to freight trains and probably due to considerations already mentioned by BicycleBob,ConnClark,BigDave,MetroMpg,and others.We may derive some insight into the potential gains for freight trains,if only for academic reasons,as the practicality of ideally streamlined trains rubs up against some unique hurdles when considering the myriad forms of freight cars and there possible combinations within a "train."

It appears that the "state-of-the-art" for railroad train aerodynamics was basically in the bag by 1932.Researchers,Tietjens and Ripley had developed a self-powered railcar design with Cd 0.08 by modifying an inter-urban trolley with an inverted and reversed boat hull body,with full boat-tail.You can see this form operating today in Japan,between Sendai and Kitakami with East Japan Railway's Shinkansen 'bullet train'.This would compare to the trolley's original Cd 0.50,and Cd 0.80 for a San Fransisco Streetcar.

In 1939,when GM's Diesel/electric locomotive debuted,standard steam locomotives with tender demonstrated drag coefficients in the range of 0.98-0.37.A New York Central Railway train with single passenger "tail car" was Cd 0.97,with 2-cars Cd 1.17,and with 3-cars Cd 1.27.

A standard "Pullman" or "Harriman" passenger car (within the train ) had drag coefficients on the order of Cd 0.18 ( measured by actual draw-bar tests ).The Cd of additional cars was basically constant,all within a 3-car NASCAR draft,with exception of tail car,which saw the base-drag.

By streamlining to the "ideal" shape,the drag of the cars could be reduced to Cd 0.05.

At 100-mph,a 800,000-pound,100-square-foot frontal area,6-coach passenger train could be streamlined to reduce it's power load from 2,100 -horsepower,to 1,012 -horsepower,over 50 %.

At 60 mph,a typical standard train would see equal mechanical resistance and aerodynamic loading.

The "Total" aerodynamic load is a combination of locomotive frontal drag,skin-friction of all the cars,and base-drag of the tail car,and centrifugal pumping losses at each exposed wheel.

Flat-out,at 100-mph,the standard train would see 5,900-lbs of air resistance,where the ideal streamliner's would be cit to 1,300-lbs.

Since trains are "long" in comparison to automobiles,skin-friction plays a more significant role.Each car's wetted-area is approximately 15X it's frontal area.A 6-car train would have on the order of 100X it's frontal area in wetted surface.

Given that today's mile-long freight-trains could be configured with any mix of box-cars,flat-cars,auto-haulers,tank-cars,hopper-cars,double-stacked container-box cars,they pose a veritable torture-chamber to the air.In their defense however,consider the following from a CAR and DRIVER "road-test" of a GM Electro-Motive Division,SD-60 Locomotive,from September,1990.

The 195-ton locomotive pulls a 12,000-ton train,at 70-mph,consuming 187-gallons per hour.

12,195-tons,times 70 miles per hour,equals 853,650-ton-miles per hour,divided by 187-gallons of Diesel per hour,yields, 4,565-ton/miles/gallon.And that's with a hodge-podge of railcars behind it.

I compared this with a CAR and DRIVER "road test" of a 633-foot,roll-on/roll-off ( Ro-Ro ) ship.The 17,500-ton GVW ship,carrying 6,400 automobiles,at 20-mph,consumes 60-"TONS" of bunker fuel a day.

At 20 mph and 24-hours/day,the Ro-Ro covers 480 miles a day.At 60-tons a day,that's 120,000-lbs of fuel.Dividing by 24-hours,that's 5,000-lbs per hour.Dividing by 6-lbs/gallon,yields 833 gallons per hour.

So,17,500-tons,times 20 miles per hour equals 350,000-ton-miles/hour,divided by 833-gallons,yields 420-ton-miles per gallon.

These are only gross figures and without tares for the railroad and ship it's hard to make a comparison as to energy spent per net cargo mile.I'm hoping some of you will jump in and help fill in the blanks.

As I mentioned in the opening,while there may be significant theoretical room for aero improvement in freight-trains,the practical barriers to implementation may far over-shadow their implementation.A real can of worms!

One closing remark,and it has to do with the Ro-Ro ships.In the article,the Wallerius Line spokesperson mentioned that ocean-going shippers are actually looking into submarines for the future in shipping.Evidently,the rough seas and gale-force wind loading on hulls makes underwater "weather" look very attractive and potentially more profitable.