Re: Arcane question of the week

Dave Nelson

Whoa, now that’s what I like… real data.

Thanks so much for posting it.

Dave Nelson

From: []
Sent: Sunday, March 20, 2016 6:01 PM
Subject: Re: [STMFC] Arcane question of the week

Taken from an NKP Center of Gravity Diagram book - date unknown - presume 1930 to 1935

Tank Car - 10,000 gallons - mty wgt 46,064 lbs - CoG = 48.25 inches

loaded with 10248 gallons of gasoline - actual wght 105,862 - CoG 72.187 inches

loaded with 10,248 gallons of mineral oil - actual wght 125.656 - CoG 75 inches

Coal Hopper - 50 ton - mty wght 39,600 - CoG = 39.0625 inches

loaded with a 10 inch heap - actual wght 140883 - CoG = 70.625 inches

loaded with a 30° heap - actual wght 151,632 - CoG = 63.125 inches

Gondola - 50 ton - mty wght 44,100 lbs - CoG = 33.125 inchesg

loaded with coal - 10 inch heap - act wght 143341 - CoG = 63.75 inches

Loaded with coal - 30° heap - actual wght 157445 - CoG = 68.5 inches

Boxcar - 40 ton - 3736 cuft - mty wght 46450 lbs - CoG = 56.0625 inches

loaded with oats - actual wght 136000 - CofG = 84.75 inches

Loaded with corn - acyual wght 136000 - CoG = 69.0625 inches

Reefer ARTCo blt 1926-1927 - 40 tons - mty wght 52362 - CoG = 61.5 inches

mty car with 9615 lbs of ice in bunkers - actual wght 61977 - CoG = 69.03 inches

Super elevation back prior to the FRA, and when cars were not as tall was 7 inches max where passenger trains were operated, and the speed & radius required it. For frght only lines the max was 4 to 5 inches max.

Generally 1.5 inches of underbalance was - and still is - a safe maximum for frgt cars. Passenger trains normally operated at 3 inches of underbalance. Underbalance is how many inches a pendulum deflects while going around a curve. Envision an equilateral triangle with 56.5 inch side set up inside a car. A pendulum attached to its upper junction point. On straight track the pendulum hangs straight down at the zero point on the scale. Then we head into curve with no superelevation, the pendulum deflects outward 1½ inches. If that same curve had 1½ inches of superelevation, and the train was moving at the same speed as above, the pendulum would stay at zero. Hint - the triangle uses legs that are the same length as track gauge.

Even today's taller hicube cars when stopped on a curve with 4 inches of SE, still need a good crosswind - say 60+ MPH - before there is a likelihood of an mty car blowing over. Loaded cars would take tornado like winds to blow them over. Today you would need about 20 inches of superelevation to reach where a car would tip over. The actual angle would be determined by a triangle formed with a base of 56.5 inches and the other two equal legs of the length from the gauge point to the CoG elevation on the centerline of the car. When the CoG point tips far enough so that it is outside to the gauge line, the car tips over.

Mark Landgraf

Albany NY

railroad office engineer


From: " [STMFC]" <>
Sent: Saturday, March 19, 2016 10:14 PM
Subject: RE: [STMFC] Arcane question of the week

Dave Nelson said:

… gets you thinking of how the weight difference between a flat car and boxcar of reasonably similar construction translates into a different center of gravity… I would not think that much given the sides and roof panels for a boxcar are so thin.

Consider that a box car underframe has a lot less steel than a flat car. It's not so much a matter of adding the weight of the boxcar superstructure as redistributing mass higher above the rail. I'm still going from memory here, so feel free to fact-check, but I think the USRA box cars were no more than a ton or so heavier than the composite gon, and likewise to the proposed USRA flat cars. For another example, C&NW had some 50' merchandise box cars built prewar that were under 50000# light weight, well within the range of 50 ft, 50T flat cars. Admittedly, that's a somewhat light 50' box, but by no means unique.

In turn, this leads on to the question of why do empty covered hoppers have such a high center of gravity? Those sides must be much more substantial than I thought.

I was thinking specifically of 4600 CF and larger grain cars, where much of the car structure has been reduced to what's basically a big rectangular steel tube. Again, not really a matter of how heavy the sides are, as how much of the total body is fairly high up.

Jack Mullen

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